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UMTS RADIO NETWORK PLANNING, OPTIMIZATION AND QOS MANAGEMENTFOR PRACTICAL ENGINEERING TASKS

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UMTS RADIONETWORK PLANNING, OPTIMIZATION ANDQOS MANAGEMENTFOR PRACTICAL ENGINEERING TASKS

Edited by

Jukka Lempiäinen

and

Matti ManninenEuropean Communications Engineering (ECE) Ltd.

KLUWER ACADEMIC PUBLISHERSNEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

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eBook ISBN: 1-4020-2599-8Print ISBN: 1-4020-7640-1

©2004 Springer Science + Business Media, Inc.

Print ©2003 Kluwer Academic Publishers

All rights reserved

No part of this eBook may be reproduced or transmitted in any form or by any means, electronic,mechanical, recording, or otherwise, without written consent from the Publisher

Created in the United States of America

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This book is dedicated to the

families of all authors.

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Contents

Dedication

Preface

Acknowledgments

PART I: UMTS CONFIGURATION PLANNING 15

INTRODUCTION TO UMTS NETWORK 17JUKKA LEMPIÄINEN

1. INTRODUCTION TO UMTS NETWORK 181.1 UNIVERSAL MOBILE TELECOMMUNICATION SYSTEM 191.2 UNIVERSAL TERRESTRIAL RADIO NETWORK 201.3 WCDMA CELLULAR CONCEPT AND PLANNING STRATEGY 221.4 UMTS RADIO INTERFACE 301.5 UMTS RADIO PLANNING PROCESS 361.6 RADIO NETWORK EVOLUTION 42

UMTS CONFIGURATION PLANNING 45JARKKO ITKONEN, RISTO JURVA

2. UMTS CONFIGURATION PLANNING 462.1 BASE STATION CONFIGURATION 462.2 MOBILE STATION 572.3 POWER BUDGET 59

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2.4 REPEATER CONFIGURATION 692.5 INDOOR CONFIGURATION 72

DIGITAL MAPS 79KIMMO KANTO

3. DIGITAL MAPS 803.1 MAPPING PURPOSE 803.2 MAPPING METHODS 843.3 COORDINATE SYSTEMS 913.4 DIGITAL MAP LAYERS 953.5 ADDITIONAL USE OF SOURCE MATERIALS 1093.6 QUALITY REQUIREMENTS 111

RADIO NETWORK PLANNING TOOLS 117HANS AHNLUND

4. RADIO NETWORK PLANNING TOOLS 1184.1 RADIO NETWORK PLANNING TOOL ENVIRONMENT 1184.2 DESIGN TOOL 1234.3 MEASUREMENT TOOLS 1344.4 ANALYSIS TOOLS 1384.5 MANAGEMENT AND INFORMATION PROCESSING TOOLS 143

PART II: UMTS TOPOLOGY PLANNING 147

UMTS TOPOLOGY PLANNING 149JARNO NIEMELÄ, JUKKA LEMPIÄINEN

5. UMTS TOPOLOGY PLANNING 1505.1 INTRODUCTION 1505.2 TOPOLOGY PLANNING 1515.3 UMTS SITE CONFIGURATION 1665.4 UMTS ANTENNA CONFIGURATION 186

PART III: UMTS NETWORK FUNCTIONALITY 205

WCDMA RADIO INTERFACE 207MATTI MANNINEN

6. WCDMA RADIO INTERFACE 2086.1 PHYSICAL LAYER 2096.2 SPREADING AND MODULATION 223

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6.3 PROCEDURE EXAMPLES 2276.4 RADIO RESOURCE MANAGEMENT IN

6.5 3GPP PARAMETERS FOR WCDMA RADIO ACCESS 243

UMTS RADIO INTERFACE FIELD MEASUREMENTS 259

7. UMTS RADIO INTERFACE FIELD MEASUREMENTS 2607.1 MEASUREMENT PROCESS 2607.2 FIELD MEASUREMENT EQUIPMENT 2667.3 MEASUREMENTS IN IDLE MODE 2677.4 MEASUREMENTS DURING CONNECTION ESTABLISHMENT 2767.5 MEASUREMENTS IN CONNECTED MODE 278

QUALITY-OF-SERVICE MEASUREMENTS 305

8. QUALITY-OF-SERVICE MEASUREMENTS 3068.1 QUALITY-OF-SERVICE FRAMEWORK 3068.2 UMTS MEASUREMENTS IN PRACTICE 321

Index 337

9

KAI OJALA, PASI NIEMI

MARKUS AHOKANGAS, TAPIO HEIKKILÄ, TAISTO NIIRANEN, TAPIO TAIPALE, JOUKO UIMONEN

WCDMA 237

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Preface

In cellular networks, a new generation of CDMA or WCDMA-based networks will start operations in most countries in the near future. The standardized WCDMA technology generates new challenges in radio network planning, optimization and QoS management because of the dynamic nature of its radio interface and various new services and different network operating modes. Moreover, new and modified radio planning phases as well as new field measurements and emphasized QoS management are needed when UMTS networks are designed and optimized. Hence, a practical UMTS planning process must be defined in detail, from dimensioning to optimization tasks.

This book follows the UMTS planning process. It is organized in three parts: Part I - UMTS configuration planning; Part II - UMTS topology planning; and Part III - UMTS network functionality. The first chapter in Part I introduces the UMTS and UTRAN systems and radio network planning strategy, and defines a planning process for UMTS. In Chapter 2, the UMTS planning process is covered, and a detailed description of the UMTS power budget is given, with planning threshold examples provided. Coverage predictions are next done in a traditional cellular planning by utilizing a planning tool together with digital maps. Therefore, digital maps and their production are introduced in Chapter 3, and the planning tool environment is covered in Chapter 4. Chapter 3 gives an overview of digital map production methods and their accuracies for different purposes. Chapter 4 defines the required UMTS planning environment: a dimensioning tool, a radio planning tool for coverage predictions and topology planning, a measurement tool for field tests, a protocol analyzing tool, and database tools. Hence, Chapters 1 through 4 explain UMTS network configuration-

related planning phases and the whole planning environment before actual coverage predictions in a radio network planning tool.

In Part II a new UMTS planning phase called topology planning is highlighted because UMTS network coverage and system capacity should be planned together. The first part of Chapter 5 introduces coverage and capacity-related network elements, site configurations, and initial and detailed topology planning. The second half of Chapter 5 includes the most relevant and critical site configuration simulation examples during detailed topology planning. These examples include variations of base station site location and antenna direction and antenna configurations as beam width, sectoring, antenna height and down tilting. Also, the most relevant UMTS network related parameters, such as coverage overlapping (site distance or site density) and load of the network, are taken into account. Chapter 5 covers the impact of major site configurations on network coverage and system capacity.

In Part III (Chapters 6 - 8), the functional properties of the UMTS radio network are explained to optimize the UMTS network and manage end-to-end QoS. Chapter 6 introduces the physical layer of the UMTS network and main processes in idle, connection establishment and connected mode, in order to understand how mobiles and base station communicate with each other. Next, the main Radio Resource Management (RRM) functionalities are defined, and finally the main 3GPP-related radio parameters are explained.

Chapter 7 introduces measurements related to radio interface communication (Layer 3 messages) and other relevant field measurements for idle, connection establishment, and connected modes. The measurement types defined in Chapter 7 are needed for testing, planning, and optimization purposes during different network evolution phases. Chapter 8 introduces the QoS architecture in UMTS and the most relevant QoS measurement types and systems. Together with QoS (Chapter 8) and field measurements (Chapter 7), the UMTS radio interface functionality (Chapter 6) can be optimized for different services.

Jukka Lempiäinen Matti Manninen

Helsinki, July 2003

12

Acknowledgments

The authors would like to thank European Communications Engineering Ltd, FM Kartta, Nemo Technologies, Nethawk and Tampere University of Technology for making this project possible.

Also warmest thanks have to be expressed to the families and colleagues of the authors for their support during the writing and editing process.

PART I: UMTS CONFIGURATION PLANNING

Chapter 1

INTRODUCTION TO UMTS NETWORK Overview of radio network fundamentals

JUKKA LEMPIÄINEN European Communications Engineering (ECE) Ltd Tampere University of Technology (TUT)

Abstract: In this chapter, the most relevant terms and technical aspects of the Universal Mobile Telecommunication System (UMTS) and Universal Terrestrial Radio Network (UTRAN) are introduced. A short overview of the whole UMTS system and more detailed overview of UTRAN are given, including essential network elements and the interfaces between them. Moreover, a Code Division Multiple Access (CDMA)-based cellular concept and different major planning strategies of the UTRAN are shortly presented. The technical details of the radio propagation channel are highlighted in order to point out the behavior of the Wideband Code Division Multiple Access (WCDMA) scheme in different radio propagation environments. Finally, a WCDMA-based planning process is defined and multi mode (GSM/UMTS) and multi band (GSM900/GSM1800/UMTS) network evolution challenges are described.

Key words: Cellular concept, planning process, radio propagation channel, UMTS, UTRAN, WCDMA

17

J. Lempiäinen and M. Manninen (eds.), UMTS Radio Network Planning, Optimization

© 2003 Kluwer Academic Publishers. Printed in the Netherlands. and QoS Management, 17-44.

18 UMTS RADIO NETWORK PLANNING,OPTIMIZATION AND QOS MANAGEMENT

1. INTRODUCTION TO UMTS NETWORK

Mobile networks, also called cellular networks, are based on different kinds of multiple access schemes in their radio interface (communication between mobile station and base station). Traditional multiple access schemes, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) are utilized in first-generation (1G) and second-generation (2G) systems.

Analog FDMA-based networks, such as Advanced Mobile Phone Service (AMPS), Nordic Mobile Telephone (NMT), and Personal Handy phone System (PHS), are called first-generation systems. The first digital mobile networks, such as North American TDMA (also known as D-AMPS because of the same frequency band used), and cdmaOne, European Global System for Mobile communications (GSM), and Japanese Personal Digital Cellular telecommunication system (PDC) are called second-generation (2G) systems. Enhancements of 2G systems, such as packet transmission - General Packet Radio System (GPRS) and Enhanced Data calls for GSM Evolution (EDGE) - are usually referred to as 2.5G.

In specification work, the International Telecommunication Union (ITU) defines the common name IMT-2000 for 3G systems, and the third-generation partnership project, 3GPP, takes care of standardization work for the entire mobile network family - GSM (2G), GPRS (2.5G), EDGE (2.5G) and UMTS (3G). See Figure 1-1 [1-4]. This book concentrates on analyzing how Frequency Division Duplex (FDD) WCDMA radio access technology should be designed for a third-generation UMTS system.

Figure 1-1. 3GPP mobile network family.

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INTRODUCTION TO UMTS NETWORK 19

1.1 Universal Mobile Telecommunication System

UMTS as a system is an evolutionary step for voice and data calls of different transmission rates measured in kbps or Mbps. The key idea of UMTS is to be as dynamic as possible and to use system resources for different purposes (for example FACH or RACH channels for both signaling and low data traffic needs). Voice calls range from low quality to high quality (6-12 kbps, for example), depending on the user profile. Data services also vary (from 0 kbps to 2 Mbps), depending on the application needs. Various data applications like video streaming and games are aggressively marketed, even though the applications most expected today are email and Multimedia Messaging Service (MMS) solutions, and the major goal of UMTS is the reduction of response time in these data transmission applications.

The UMTS network contains Radio Access Network (RAN), Core Network (CN), and Network Management System (NMS); the interfaces between them are depicted in Figure 1-2 [5].

Figure 1-2. UMTS network elements and interfaces.

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Radio access network is also called UMTS Terrestrial RAN (UTRAN), and radio access (radio interface) is also called UMTS Terrestrial Radio Access (UTRA). Figure 1-2 also shows that GSM is part of the UMTS network; thus the UMTS system has similar types of interfaces and network elements as in GSM. Table 1-1 gathers and compares UMTS and GSM radio network element and interface names.

Table 1-1. Radio network element names in UMTS and in GSM. UMTS GSM

(UT)RAN BSS RNC BSC NodeB BTS Cell Cell Site Site UE MS Iur - Iub Abis Uu Um

Due to similar architecture, the UMTS part of the specification is similar to the GSM part of the specification (for example, in the names and use of signaling channels or radio interface parameters); therefore, a good knowledge of the GSM is very helpful in understanding the UMTS system.

1.2 Universal terrestrial radio network

UTRAN contains Radio Network Controller (RNC) and NodeB elements and the interfaces between them. In UTRAN, two or more RNC elements can be connected to each other via Iur because of soft handovers; thus, traffic data can be utilized much better than in GSM (no connections between BSC elements). In UTRAN, Iub interface is also open to all manufacturers.

The functionality of a cellular radio network like UTRAN can generally be divided into three categories: the cellular concept layer, the radio interface management layer, and the radio interface technology layer. See Figure 1-3.

The main cellular concept functionalities are related to Radio Resource Management (RRM) and Mobility Management (MM). For example, location areas and paging or other signaling channel needs (such as radio access channel (RACH) in call establishment) or UE tasks in idle mode with no connection (such as measurements, system info, neighbor cells, or cell selection) are enhanced and utilized in UTRAN.


Radio interface management is also related to RRM that is moreover managed mainly by RNC. In practice, radio interface management happens by utilizing different signaling messages between RNC and UE. RRM and signaling needs can be divided into connection-based and cell-based needs. For each connection, fast power control (PC) and soft handovers (SHO) are required by a WCDMA radio access in order to maximize system capacity in a radio network. For RRM, in each cell, more advanced Admission Control (AC), Load Control (LC) and Resource Management (RM) are required due to different services (various bit rates from 6 kbps (voice) to 2 Mbps (data) transmission rates). Moreover, several packet transmission services (for example, MMS-over-packet transmission) set higher requirements for Packet Scheduling (PS) in order to optimize system performance. Hence, RNC design is much more complicated in UMTS than in GSM, and communication between RNC and NodeB, and between NodeB and UE, requires significantly more information and signaling.

Figure 1-3. Cellular radio network functionality layers.

WCDMA technology causes major changes also in NodeB receiver and transmission units because of wide bandwidth. In transmission direction (downlink), the linear amplifier of NodeB is critical because high transmit power over the whole carrier bandwidth is needed. At the receiving end, a new receiver called a RAKE receiver is needed in order to utilize multi path components in a multi path propagation environment. The performance of a RAKE receiver is essential in order to receive maximal signal power and thus to maximize the power budget and path loss. Finally, all frequency-dependent elements, such as antennas, cables, power amplifiers, low noise amplifiers, filters, etc., must be designed for the 2100 MHz frequency band; and therefore new equipment is needed in a UMTS implementation.

It can be concluded that WCDMA has a strong impact on radio interface management and technology layers, and thus UTRAN radio planning principles and planning and measurement tools must be updated for

Cellular concept (network elements and tasks, RRM, MM)

Radio interface management (Iub, Iur and Uu interfaces)

Radio interface technology requirements

Cellular concept (network elements and tasks, RRM, MM)

Radio interface management (Iub, Iur and Uu interfaces)

Radio interface technology requirements


WCDMA technology needs. Moreover, modifications are needed in the planning process and detailed planning parameters for different planning phases.

1.3 WCDMA cellular concept and planning strategy

Radio or mobile networks are more generally known as cellular networks when a cellular concept is used in the radio network infrastructure. In the cellular concept [6], depicted in Figure 1-4, a base station is transmitting and receiving a radio signal and providing service for a particular coverage area called a cell (in Europe) or sector (in the U.S.). Several cells are needed to cover a wide geographical area because transmit power is typically limited due to technical challenges. Moreover, several cells are needed for higher transmission capacity. When a cell structure is repeated, frequency channels can be re-used without experiencing co-channel interference, as occurs in FDMA and TDMA networks (for example, with GSM). The performance of FDMA/TDMA-based networks depends on the frequency reuse efficiency (average number of cells between co-channels), which typically varies from 10 to 20 as a function of propagation environment and software features [6-7].

Figure 1-4. FDMA/TDMA cellular concept.

In CDMA-based networks, the same frequency can be used in neighbor cells because cells and users are separated by using orthogonal codes, as shown in Figure 1-5. The transmitted data (voice or data transmission) is multiplied by a spreading code, and the received data is decoded by using the same code. The name WCDMA represents Wideband CDMA radio

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access. Wideband refers to a flat fading radio propagation channel, even if WCDMA is not flat fading in all propagation environments. (See Section 1.4.1.3.)

Figure 1-5. CDMA/WCDMA cellular concept.

The capacity of WCDMA radio access is typically interference-limited because all mobile phones and neighbor base stations interfere with each other in the uplink and downlink directions. In practice, non-orthogonal codes cause additional interference for mobile phones in the downlink direction due to multi path propagation. Figure 1-6 depicts all the different sources of co-channel interference in WCDMA radio access.

Figure 1-6. Uplink and downlink co-channel interference in WCDMA network.

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The sources of co-channel interference can be divided into two categories: intra-cell interference (also called “own-cell-interference”) and inter-cell interference (also called “other-cell-interference”), both of which strongly depend on the locations of the mobile station. Due to both interference sources, system level (“system” meaning a certain cluster of cells) calculations (also called simulations) are required in order to estimate the final performance of the WCDMA radio access network. This new calculation requirement has a strong impact on a UMTS radio network planning strategy and process.

1.3.1 Radio network planning strategies for UMTS

UMTS radio network planning strategy must be done before actual planning can be started. In this planning strategy work, the overall layout of the radio network and the evolution path are decided upon in order to reach the optimal network configuration for quality, capacity, and coverage. Strategy work starts by analyzing the existing radio network configuration and by defining the needs of a UMTS network for a certain planning area. (See Figure 1-7.) Next, the UMTS network major topology or layout (antenna heights and site density) must be decided upon in order to define the radio propagation environment and to fix planning principles. After defining the propagation environment, the major technical definitions of the radio network can be made. These include traditional (typical cellular concept) and new technologies such as adaptive antennas, Multiple Input Multiple Output (MIMO) or Opportunity Driven Multiple Access (ODMA) concepts in the future.

Figure 1-7. UMTS network over a GSM/GPRS/EDGE network.

UMTS?

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1.3.1.1 2G/3G interworking strategy and principle

The existing 2G networks (typically GSM/GPRS and/or EDGE combinations) were originally built for voice calls, and radio network coverage is now excessive due to several years of deployment. Typically, the lowest 2G frequency band (800-900 MHz, where outdoor propagation is better) is a coverage layer, used mainly when other network layers are not working. The next 2G layer in dual band networks operates on a higher frequency band (1800-1900 MHz). Compared to the lower frequency band, this layer has worse outdoor radio wave propagation and a reduced coverage. Therefore, this layer is mainly used for capacity extensions. When GPRS/EDGE services are added to the existing 2G radio network, the capacity layer should be utilized for its capacity, but then the coverage of data services would be limited. Thus, data services must be added to the coverage layer, and voice calls must be moved to the capacity layer along as well as some data calls.

The purpose of a UMTS system in a multi mode, multi band radio network is to extend radio access capacity (more frequency band together with GSM), to offer higher data rates and a larger variety of services, and to be a new step in technology evolution. Thus, UMTS coverage has to be almost equivalent to GSM/GPRS/EDGE coverage, and UMTS capacity is mostly reserved for new services and partly reserved as a capacity layer for old services. Moreover, UMTS coverage should be continuous wherever implemented in order to maintain a consistent service level.

1.3.1.2 2G/3G radio network layout

An existing coverage layer of 2G network (800-900 MHz layer in single and dual band networks, or 1800-1900 MHz in single band networks) must be a reference layer when a UMTS layer is designed. In multi band TDMA-based networks co-siting and co-sectoring (like overlay-underlay structure [7]) is preferred due to significantly easier handover planning between frequency layers, as shown in Figure 1-8. If new site locations are used for the 1800 MHz capacity layer, careful parameter planning is needed also for cell selection in call establishment in order to move traffic smoothly to the capacity layer. The same co-siting and co-sectoring approach is preferable also for a GSM/UMTS multi mode network layout.

Figure 1-9 shows different 2G/3G layouts when UMTS is added to a single or dual band 2G network. UMTS operates on the 2100 MHz frequency band. UMTS coverage planning is straightforward if the existing 2G radio network is a single band 1800-1900 MHz network, because the coverage areas are almost equivalent for both frequency bands. If UMTS is added to a single band 800-900 MHz network, new sites are needed to have continuous coverage for UMTS; and efficient co-siting is challenging due to


the optimization of new site locations. Moreover, in a multi band multi mode network, an equivalent coverage layer should be implemented for both 2G and 3G layers. Thus, UMTS coverage planning should follow as closely as possible the 2G coverage layer site locations in order to optimize handovers.

Figure 1-8. A 900/1800 MHz multi band radio network layout when co-siting and co-sectoring are utilized.

a) b)

Figure 1-9. 2G/3G radio network layouts: (a) based on 900 MHz GSM coverage layer,

(b) based on 1800 MHz GSM coverage layer.

In UMTS site selections, co-siting with a 2G network layout is preferred due to lower site rental costs. However, the final value of co-siting must be evaluated carefully because of inter-system interference related to technical limitations and because of traffic distribution in the radio network. Traffic

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distribution is not as important an item in TDMA-based networks as it is in CDMA-based networks, so 2G site locations are often selected with a lower traffic layer priority. Hence, co-siting is preferred only if 2G site locations are appropriately chosen for traffic demands.

Before the final site selection, different base station layer structures and radio propagation environments must be defined for the UMTS radio interface, as presented in Figure 1-10. The required size of the base station coverage area must be calculated. Furthermore, the average base station antenna height for the network must be decided. During the early phase of the radio network evolution, large coverage areas are needed, mainly to cover the area. This leads to a macrocellular type of network topology where base station antennas are above the average building heights in urban areas. If enormous capacity is needed for a dense urban area, several micro cells and a microcellular type of topology are required: base station antennas must be implemented below the rooftop levels in order to avoid interference. Also special indoor systems are needed for office blocks and shopping centers to provide enough capacity. In UMTS, as in all other radio networks, one main layer (macro or micro) should be used for coverage and other layers would only help the primary layer. UMTS networks are most probably implemented with the macrocellular approach due to practical considerations (number of sites, rental costs, etc.), theoretical considerations (propagation, breakpoint distance, antenna tilting, etc.), and because of an existing 2G network.

Figure 1-10. UMTS base station layers.

Finally, the applicability of the UMTS radio network topology must be evaluated for new software features and service concepts such as location technologies. If mobile terminal location information will have a high priority in the future, UMTS radio network topology should also be

Micro layer= capacity layer

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optimized, based on location information needs as accuracy and area to be served. Location technologies, like Observed Time Difference of Arrival (OTDOA), cause significant requirements on the radio network topology in UMTS in order to maximize accuracy and area of applicability [8-12]. Moreover, it must be analyzed whether repeaters [13], for example, can be used for improving coverage without reducing the accuracy of location information.

1.3.2 Advanced cellular concepts

Traditional radio network planning principles must be modified if new technologies like adaptive or smart antennas (also called Space Division Multiple Access, SDMA), Multiple Input Multiple Output (MIMO), or Opportunity Driven Multiple Access (ODMA) are utilized in UMTS networks in the future.

Adaptive antenna systems for cellular systems [14] have different levels of complexity in terms of software (digital signal processing, DSP) and hardware requirements. When complexity is increased, system intelligence and performance are also strongly increased. Figure 1-11 shows a fixed multi beam (Butler matrix) and dynamic beam forming adaptive antenna solutions for a radio network layout. The fixed multi beam is easier to implement, and it does not cause major changes to radio network planning, but the improvement in system performance is also limited. Dynamic beam forming needs strong changes in base station implementation and also lots of DSP capacity. But system performance is also significantly increased because antenna beams can be directed separately for each user. This also means strong changes in radio planning: for example, coverage areas as well as handover decisions are dynamic.

Figure 1-11. Fixed multi beam and beamforming SDMA system.

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The MIMO concept is based on the existence of multiple distinguishable radio channels between transmit and receive antenna arrays in the scattering propagation environment. When different data is transmitted through each of these channels, the capacity of the system increases significantly [15-16]. The impact of the MIMO concept on traditional radio network planning is still under research.

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Figure 1-12. MIMO system.

ODMA is being studied for CDMA-based systems and is proposed, for example, for WLAN (also called intelligent relaying, or ad hoc network) and UMTS systems [17-20]. In ODMA, the mobile station creates a radio link by transmitting and receiving data via other mobile stations that are closer to the base station, as shown in Figure 1-13. This helps with power consumption, and thus interference is reduced and capacity increased. If ODMA is adapted in UMTS, the power budget and cell ranges must be defined for chain structures [17-20].

Figure 1-13. ODMA system.

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1.4 UMTS radio interface

A WCDMA radio access is utilized in the UMTS radio interface (Uu). The characteristics of a WCDMA radio propagation channel have to be known well in different propagation environments because WCDMA radio network capacity depends heavily on interference and furthermore on the received signal level. Essential WCDMA parameters for UMTS system are presented in Table 1-2.

Table 1-2. WCDMA radio access parameters for UMTS. Parameter Value

Access technology DS-CDMA Chip rate 3.84 Mchip/s Channel bandwidth 5.0 MHz ± Nx200 kHz, N = 1, 2, 3 Duplex Frequency Division Duplex (FDD)

Time Division Duplex (TDD) Frequency band (FDD) 1920-1980 MHz (UL), 2110-2170 MHz (DL) Frequency band (TDD) 1900-1920, 2020-2025 MHz (UL/DL) Frame structure 10 ms, 15 time slots

WCDMA radio access is based on direct sequence code division multiple access (DS-CDMA) technology. This means that a user data sequence is multiplied by a spreading sequence that has a symbol (also called “chip”) rate much higher than the user data rate. This spreads the user data signal to a wider frequency band. The relation between the user data rate and chip rate is called the spreading factor ( bitchip RRSF = ). The chip rate in WCDMA is 3.84 Mchip/s; spreading factors are in the: range of 4 to 512; and the user net bit rates supported by one code channel are in the range of 1 to 936 kbps in the downlink direction. Up to three parallel codes can be used for one user, thus giving bit rates up to 2.3 Mbps. In the uplink direction, data rates are half of these figures due to modulation differences.

The nominal channel bandwidth of WCDMA signal is 5 MHz, as illustrated in Figure 1-14. The specification gives the flexibility to define the exact channel center frequency at 200 kHz raster, and thus the actual channel separation may be smaller than the nominal 5 MHz.

The WCDMA standard includes two modes of operation, WCDMA/FDD and WCDMA/TDD. WCDMA/FDD is a frequency duplex division mode, in which the uplink and downlink signals are at different frequency bands (1920-1980 MHz in uplink and 2110-2170 MHz in downlink). WCDMA/TDD is a time duplex division mode, where the uplink and downlink signals are at the same frequency (1900-1920, 2020-2025 MHz for both uplink and downlink) but separated into different time periods. In this


book, WCDMA or UMTS refers to WCDMA/FDD because this type of air interface is first deployed and utilized.

Figure 1-14. Theoretical spectrum of two WCDMA carriers with 5 MHz channel spacing.

The transmission in WCDMA is split into 10 ms radio frames that consist of 15 pieces of 666 and 2/3 µs (2560 chips) time slots. The bit rate and channel coding can be changed for every frame by offering a very flexible user data rate control. Every time slot has bits reserved for the pilot signal, power control (TPC bits), transport format indication (TFCI bits), and, if needed, for closed-loop transmit diversity (FBI bits). The exact signal format and multiplexing is quite different in uplink and downlink signaling, and the dedicated and shared channels have several differences in signal format [21-22].

1.4.1 Radio propagation channel

The UMTS radio interface has special characteristics for different propagation environments that can be classified into outdoor macrocellular, outdoor microcellular, and indoor propagation types. A macrocellular environment contains an urban, suburban and rural type of area, depending on the building or other obstacle density. Each propagation environment has its own propagation characteristics, which can be defined by the following parameters: – multi path propagation, – angular spread, – delay spread,

4 2 0 2 4 6 8 1040

30

20

10

0

Frequency / MHz

Pow

er /

dB

.


– fast fading and coherence bandwidth, – slow fading, and – propagation slope.

Each of the above parameters has a specific value for a different environment and an impact on planning principles. Multi path propagation causes non-idealities for orthogonal codes, which furthermore causes own-cell interference in the downlink direction. Angular spread and delay spread cause fast fading, which has a strong effect on the received signal levels. Slow fading causes a variation in signal levels as well, and the propagation slope illustrates a total attenuation between the base station and the mobile station antenna as a function of distance.

1.4.1.1 Multi path propagation in UMTS

Multi path propagation occurs due to reflections, diffractions, and scatterings from different obstacles such as buildings in the radio path. Figure 1-15 shows the different paths d1, d2, and d3 from the base station antenna to the mobile station antenna. In Figure 1-15, transmitted signals s1, s2, and s3 have a certain amplitude and phase, depending on the transmission direction. At reception, each signal component s1’, s2’, and s3’ (also called the multi path component) may have a different amplitude, phase, and path length because of reflections, diffractions, and scattering. These multi path components cause different incident angles (angular spread), propagation time (delay spread), and a constructive or destructive sum (fast fading) at reception.

Figure 1-15. Multi path propagation.

A

UE1

Reflection

Diffraction

d1’d1’’

d2’

d3’’ d3’’’d3’’’’

d3’

s1 = a+jbs2 = c+jds3 = e+jf

s2’ s1’s3’

d1’’’

t

P

s1’ = a’+jb’s2’ = c’+jd’s3’ = e’+jf’

A

UE1

Reflection

Diffraction

d1’d1’’

d2’

d3’’ d3’’’d3’’’’

d3’

s1 = a+jbs2 = c+jds3 = e+jf

s2’ s1’s3’

d1’’’

t

P

s1’ = a’+jb’s2’ = c’+jd’s3’ = e’+jf’


Thus, the transmitted signal is spread over time and in frequency domain, and the result at reception is the sum of different signal components. This spreading, especially in the time domain, causes interference in the downlink direction in WCDMA because spreading codes are not ideally orthogonal. Interference due to non-ideal orthogonal codes increases the load of the network, and this must be taken into account in power budget calculations. Non-ideality of orthogonal codes is measured by an orthogonal factor (OF) [23]. Orthogonal factors of 60% and 85% are typically used in a power budget for urban and rural, and for microcellular and indoor propagation channels, respectively.

1.4.1.2 Angular spread in UMTS

Angular spread describes the deviation of the signal incident angle. Angular spread can be calculated based on the incident angle of the received power in the horizontal and vertical planes [24-25],

ΦΦΦ−Φ=+Φ

−Φ ΦΦ d

)()(

180

180 _

2

totalP

PS (1-1)

where Φ is the mean angle, P(Φ) is the angular power distribution, and PΦ_total is the total power. Angular spread depends mainly on the environment type, and typical values are 5-10° for macrocellular environment and up to 360° in the indoor propagation channel.

1.4.1.3 Delay spread in UMTS

Delay spread S can be calculated from the power delay profile P ,

( ) ( )totP

dP

_

0S

τ

τ

τ

ττττ∞

−= , (1-2)

which describes the signal power as a function of delay. A power delay profile can also be presented as an impulse (power) response of the channel. Figure 1-16 presents an example of a power delay profile based on a WCDMA channel model for a typical macrocellular urban environment [26].

In Table 1-3, calculated delay spread values are presented for different propagation environments based on Equation 1-2 and a typical power delay profile of each environment.


Figure 1-16. Channel impulse response, typical urban channel [26].

Table 1-3. Delay spread, coherence bandwidth and type of propagation channel for different radio propagation environments. Delay spread [µs] fC [MHz] WCDMA

Bandwidth 3.84 MHz Macrocellular Urban 0.5 0.16 Wideband Suburban 0.1 1.6 Narrowband/Wideband Rural 3 0.053 Wideband Microcellular < 0.01 > 16 Wideband Indoor < 0.01 > 16 Narrowband

1.4.1.4 Fast fading and coherence bandwidth in UMTS

Power delay profile and delay spread are time domain properties of the radio channel. The effect of the multi path propagation to the radio channel can also be described by the frequency domain properties of the radio channel. In the frequency domain, multi path propagation causes frequency selective variation of signal levels called fading: signals at different frequencies have different amplitude and phase. The frequency response of the channel can be calculated as Fast Fourier Transformation (FFT) of the complex impulse response of the channel. Figure 1-17 presents the frequency response of the channel, whose power delay profile was presented in Figure 1-16.

0 0.5 1 1.5 2 2.50

0.1

0.2

0.3Power delay profile

Delay, ms

Pow

er

.


Figure 1-17. Frequency response of the multi path channel shown in Figure 1-16.

One frequency domain property of the channel is coherence bandwidth fc. It can be calculated from the time domain property delay spread.

τπSfc

2

1=∆ (1-3)

Coherence bandwidth is the minimum frequency separation of two carriers that have significantly uncorrelated fading. In Table 1-3, typical coherence bandwidths for different radio propagation environments were presented.

The system is called narrowband when the radio signal bandwidth is much narrower than the coherence bandwidth of the radio channel; it is called wideband when it is much wider. Narrowband means that the fast fading of a channel is not frequency selective and the channel can be called flat fading. In a wideband environment, the fast fading of the channel is frequency selective.

1.4.1.5 Slow fading in UMTS

Slow fading, or log-normal fading occurs because of obstacles such as buildings. The standard deviation of an outdoor signal is approximately 7-10 dB at 200-3000 MHz, depending on the environment [27]. At a UMTS frequency band of 1900-2125 MHz (TDD+FDD), the slow fading is on the level of 8-9 dB with reasonable accuracy. Based on the standard deviation,

0 2 4 6 8 1020

15

10

5

0

5

10Frequency responce of channel

Frequency / MHz

Pow

er /

dB

.


the slow fading margin can be defined for different location probabilities in the radio network [28].

1.4.1.6 Propagation slope in UMTS

UMTS utilizes the 1900-2125 MHz frequency band, which is close to the 1800 MHz band. Thus, the propagation slope in different propagation environments follows the 1800 MHz frequency band with reasonable accuracy.

1.5 UMTS radio planning process

UMTS radio interface is based on WCDMA technology, and thus the radio network planning process must be modified from the traditional GSM (TDMA-based) planning process. The major planning phases depicted in Figure 1-18 – pre-planning (dimensioning), detailed planning, and post-planning (optimization) – are still valid. But the detailed planning phases – configuration planning, coverage planning, capacity planning, frequency planning, and parameter planning – and their content must be modified.

Figure 1-18. WCDMA planning process.

1.5.1 Dimensioning

In the dimensioning phase, a rough estimate of the network layout and elements is needed, such as the number of base stations to cover a certain area and to serve a certain capacity. Moreover, one critical parameter for a detailed planning phase is the base station antenna height, which must be

PRE-PLANNING”DIMENSIONING”

”DETAILED”PLANNING

POST-PLANNING”OPTIMIZATION”

• Network layout• Network elements• Antenna heights

• Configuration• Coverage-Capacity• Code• Parameter

• Verification• Parameters• Monitoring

PRE-PLANNING”DIMENSIONING”

”DETAILED”PLANNING

POST-PLANNING”OPTIMIZATION”

• Network layout• Network elements• Antenna heights

• Configuration• Coverage-Capacity• Code• Parameter

• Verification• Parameters• Monitoring


defined in order to be able to define the characteristics of the radio propagation channel and optimized planning guidelines (such as antenna tilting) for that environment. Thus, the main result of dimensioning phase is a list of required network elements and the average antenna height.

Whereas dimensioning uses hypothetical data, the detailed planning phase (described next) uses the same procedures but actual data.

1.5.2 Configuration planning

In configuration planning, the base station and base station antenna line equipment is defined, and the maximum loss allowed between the base station antenna and mobile station antenna is calculated in the uplink and downlink directions. In UMTS power budget calculations, gains (antenna, amplifier, etc.), losses (cable, filters, etc.), and margins (slow fading, etc.) are added to transmit and receiving power levels, as in GSM. In UMTS, the transmission requirements of common control channels and the pilot channel must be included in the power budget. In addition, the impact of intra-cell and inter-cell interference (interference margin, IM) and new WCDMA margins (for example, fast fading margin also called power control headroom) must be added to the power budget, as presented in Table 2-6 and Table 2-7 in Section 2.3. It must be remembered that the UMTS power budget is uplink-limited when maximum coverage is targeted and the load of the network is low. Moreover, the UMTS power budget is downlink-limited when the load of the network is increased to the maximum. Finally, it must be noted that the base station antenna configuration has a strong impact on the interference level in the network and on radio network capacity, and thus antenna selection must be done carefully.

The power budget must be calculated for different service profiles, and cell-breathing phenomenon must be taken into account in coverage threshold settings and cell range calculations. The result of configuration planning is a detailed base station configuration and a list of antenna line elements for different network evolution phases and the maximum uplink and downlink path loss information for coverage predictions. More detailed explanations of power budget calculations are presented in Chapter 2.

1.5.3 Topology planning

UMTS coverage planning can be done as in GSM by using path loss information and prediction models such as Okumura-Hata if there is no other traffic (only one mobile terminal) and thus no interference in the radio network. When traffic is included, cell-breathing occurs and cell range, as well as coverage area, is dynamic, based on the load of the network. Thus,


coverage areas are linked to each other as a function of mobile terminal locations. Moreover, the maximum load or capacity of the UMTS radio network depends on the coverage areas (cell overlapping, depth of propagation slope, etc.), base station locations, and base station antenna line configurations (antenna height, direction, beam width, tilting, etc.). Hence, coverage calculations and capacity estimation must be done simultaneously. This planning phase can be called topology planning, because the final coverage and capacity of the network mainly depends mainly on the base station antenna line configuration and network layout.

Topology planning in UMTS begins with coverage predictions, as shown in Figure 1-19, in order to estimate coverage overlapping and dominance areas. Coverage thresholds are used at this point for estimating coverage and dominance areas, as in GSM planning.

Figure 1-19. WCDMA topology planning.

Next, system level simulations are needed to estimate maximum traffic or load of the network in different cells. These system level simulations must be done for a certain cluster of cells so that all uplink and downlink interference is included. System level simulations are based, for example, on Monte Carlo type of simulations, where a certain number of mobile terminals are located over a coverage area and distributed homogenously or non-homogenously (with greater weight for indoor locations, for example). The results of Monte Carlo simulation include coverage, capacity, and interference-related information such as transmit powers of base stations, maximum number of users in each cell, and own-cell-to-other-cell

COVERAGEPREDICTIONS

MONTE CARLOSIMULATIONS

NETWORK PERFORMANCE

ANALYSIS• Pilot coverage • Thresholds• Overlapping

• Traffic distribution• Services• Load • Interference

• Throughput (kbit/s) • Soft handover area• Service probability

COVERAGEPREDICTIONS

MONTE CARLOSIMULATIONS

NETWORK PERFORMANCE

ANALYSIS• Pilot coverage • Thresholds• Overlapping

• Traffic distribution• Services• Load • Interference

• Throughput (kbit/s) • Soft handover area• Service probability


interference. These results finally give an estimate on whether base station sites are located correctly (throughput, service probability) and the total capacity of the radio network for a particular area. If one or more cells or sites need to be reconfigured (new site location, new antennas, new tilting, etc.), new simulations are always needed in order to get a performance estimation for the whole cluster. The detailed impact of the base station configuration and network layout on the final capacity in the UMTS radio network are introduced in Chapter 5.

1.5.4 Code and parameter planning

After topology planning, only code planning and parameter planning are needed before the network can be launched because frequency planning is actually not needed in CDMA-based systems. In code planning, scrambling codes are allocated for different cells in order to separate cells in the downlink direction (Figure 1-20). Code planning is straightforward because there are enough codes in the 3GPP specification (altogether 512 primary codes); therefore, code limitations should not occur. See Chapter 6.

In parameter planning, the radio interface functionality is optimized; this mainly includes signaling and radio resource management tasks. Parameters can be divided into signaling, identifier, RRM, measurement, handover and power control groups, which are all related to idle, connection establishmentand connected modes. In the parameter planning phase, all parameters are grouped to these different categories, and default values are given when the network or a cell is launched. Later on, separate parameter values (such as active set parameters for handovers) can be changed, based on the needs of the radio propagation environment. The functionality of the radio interface and code and parameter planning are explained in more detail in Chapter 6.

Figure 1-20. Code and parameter planning.

Inter system handovers

A

C

B

Active sets for soft handovers

f1f7

A = 1011010010101...

B = 1110101010010...

Inter system handovers

A

C

B

Active sets for soft handovers

f1f7

A = 1011010010101...

B = 1110101010010...

www.itbookshub.com



1.5.5 Verification, monitoring and optimization

The UMTS radio network is designed after system level simulations in topology planning and code and parameter definitions. The next planning phase is verification, monitoring and optimization when the radio network is implemented. (See Figure 1-21.) In the verification phase, call establishments (idle mode) and soft and inter-system handovers (connected mode) are tested. Also, coverage and dominance areas must be verified and analyzed due to a strong impact on radio network capacity. Verification of the radio network is mainly carried out with the use of a radio interface field measurement tool that is explained in Chapter 7.

Figure 1-21. Verification, monitoring and optimization.

Monitoring contains Key Performance Indicator (KPI) values that are related to call success (or call establishment failures prevented by load or admission control) rates and drop call (soft, softer, or hard handover failures, cell-breathing and lack of coverage, overload, etc.) rates. More detailed monitoring is based on signaling messages between base station and mobile station measured by a radio interface field measurement tool or by a Quality-of-Service (QoS) analyzing tool, for example, from the Iub interface. The radio interface field measurement tool is based on information gathered by a UE and thus location information is also available. Accordingly, the Quality-of-Service analyzing tool measures or gathers detailed signaling and traffic information at the cell, site, and RNC levels. These QoS measurements are

PROBLEM INDICATION

• Verification measurements• KPI measurements • Field measurements

PROBLEM TYPE

• Coverage (no signal)• Capacity (low throughput)• Quality (bad voice quality)

RADIO PLAN VERIFICATION

• NodeB configurations• Antenna line configurations• Coverage measurements• System simulations• Code planning • Parameter values

• signaling• RRM (PC, HO)

PROBLEM SOLVING

• Configuration modifications• cell / site level• system level

• Parameter changes• signaling needs• PC improvements• SHO areas

PROBLEM INDICATION

• Verification measurements• KPI measurements • Field measurements

PROBLEM TYPE

• Coverage (no signal)• Capacity (low throughput)• Quality (bad voice quality)

RADIO PLAN VERIFICATION

• NodeB configurations• Antenna line configurations• Coverage measurements• System simulations• Code planning • Parameter values

• signaling• RRM (PC, HO)

PROBLEM SOLVING

• Configuration modifications• cell / site level• system level

• Parameter changes• signaling needs• PC improvements• SHO areas


especially needed for end-to-end QoS management and optimization purposes. QoS management is explained in more detail in Chapter 8.

Finally, optimization contains different kinds of planning-related actions to solve problems found in the verification and monitoring phases. Optimization entails continuous trouble solving; it could also be called re-planning because all planning phases and their results must be checked before any modifications can be done to the actual plan. The optimization process includes radio interface field measurements and QoS measurements to understand network bottlenecks at the cell, site, and RNC levels.

1.5.6 Radio planning environment

Radio network planning must be supported by different software and hardware tools in different planning phases. In the dimensioning phase, only MS Excel based calculations are needed, and different kinds of function libraries can be utilized when coverage areas or capacities in Erlangs are estimated. In detailed planning, a more advanced planning tool based on highly accurate digital maps is required to get reliable coverage predictions. Figure 1-22 shows that planning tool must have interfaces to measurement systems and the network in order to import and export data, for example, in model tuning (measurement import) and parameter planning (parameter value export).

Figure 1-22. Radio planning environment.


NodeB

RNC

3G MSC/VLR

NodeB

PSTN/ISDN3G GMSC

Field measurements

Planning tool

Protocol analyzerStatistical

performance indicators

Measurements

Network

Planning

Netw

ork

pla

n


NodeB

RNC

3G MSC/VLR

NodeB

PSTN/ISDN3G GMSC

Field measurements

Planning tool

Protocol analyzerStatistical

performance indicators

Measurements

Network

Planning

Netw

ork

pla

n


The graphical user interface (GUI) of a planning tool must follow the planning process phases exactly because man-made errors can be significantly reduced if all planning parameters are automatically set in a particular order. The planning tool also must have reasonable documentation tools in order to have essential radio network information in the same database. Digital maps and planning and measurement tool requirements are explained in more detail in Chapters 3, 4, 7, and 8.

1.5.7 Documentation

In UMTS, as in GSM, all data that is related to a UMTS site or UMTS cell must be documented. This data traditionally includes input data (NodeB and antenna line configuration data and parameters) and output data (measurement data as traffic - for example, kbps per busy hour, handover statistics, drop calls, etc.). In UMTS, some new items must be included in the documentation: – new power budget-related items as Eb/N0 in different environments (must

be measured in practice); – new hardware elements in NodeB as code channels (software and

hardware limitations); – new parameters for signaling (physical layer), load control, admission

control, packet control, power control, and handovers; and – more detailed traffic monitoring.

The quality of the NodeB and antenna line documentation must be strongly emphasized in UMTS. Because cells interfere with other, every mistake in documentation means changes in radio network coverage and capacity. Therefore, a reliable documentation tool that follows the planning process exactly is strongly recommended.

1.6 Radio network evolution

UMTS is in full operation when all radio planning phases and implementation have been executed. The same planning process and planning phases need to be repeated whenever there is a new coverage or capacity need in the radio network. This change in the radio network is called network evolution; it includes, for example, local traffic changes such as new residential or business areas. Network evolution should be predictable with some accuracy 3 to 5 years ahead, in order to take it into account in long-term network layout design.


1.6.1 UMTS site configuration and topology evolution path

Network evolution has a different impact on different planning phases. In configuration planning, it must be defined whether uplink or downlink is limiting the cell or site service area and which direction is used for actual planning. Traditionally, uplink and downlink directions have been balanced (equivalent path loss in both directions), and actual radio planning has been done in the downlink direction. In UMTS, uplink limits coverage when there is no traffic in the network, but downlink transmission power limits the service when the radio network is highly loaded. Thus, cell or site coverage or service areas (site locations) should be planned directly for a certain load and for both uplink and downlink directions.

Another critical topic is network topology (layout) and especially base station antenna configuration. In the first phase of UMTS, three-sectored sites are preferred in order to have reasonable antenna costs, but later on, six-sectored antenna configurations offer significantly higher capacity. It is essential to have a planning guideline (site locations and antenna configurations) for changing the network from a three-sectored to a six-sectored configuration with a minimum change in radio network functionality as in soft handover areas. At this point, inter-system operability must also be kept in mind.

Finally, new applications and features such as location techniques must be considered, and the radio network configuration must be adapted for different service needs during the network evolution.

REFERENCES

[1] S. Faruque, Cellular Mobile Systems Engineering, Artech House Publishers, 1996. [2] R. Steele, C. Lee, P. Gould, GSM, cdmaOne and 3G Systems, John Wiley & Sons Ltd,

2001. [3] H. Holma, A. Toskala, WCDMA for UMTS, John Wiley & Sons Ltd, 2001. [4] J. Laiho, A. Wacker, T. Novosad, Radio Network Planning and Optimisation for UMTS,

John Wiley & Sons Ltd, 2002.[5] Universal Mobile Telecommunications System (UMTS), UTRAN Overall Description,

3GPP TS 25.401. [6] W. Lee, Mobile Communications Design Fundamentals, John Wiley & Sons, 1993. [7] J. Lempiäinen, M. Manninen, Radio Interface System Planning for GSM/GPRS/UMTS,

Kluwer Academic Publishers, 2001. [8] M. Birchler, E911 Phase II Location Technologies, IEEE Vehicular Technology Society

News, November 2002. [9] J. Syrjärinne, Studies of Modern Techniques for Personal Positioning, Doctoral Thesis,

Tampere University of Technology, 2001.


[10] S. Ahonen, J. Lähteenmäki, H. Laitinen, S. Horsmanheimo, Usage of Mobile Location Techniques for UMTS Network Planning in Urban Environment, Proceedings of IST Mobile & Wireless Telecommunications Summit, 2002.

[11] K. Watanabe, M. Kuwahara, A. Ogino, K. Tsunehara, H. Suzuki, N. Doi, A Study on the Accuracy of a CDMA-Based Location Systems, IEEE 55th Vehicular Technology Conference, vol. 4, 2002.

[12] D. Porcino, Performance of a OTDOA-IPDL Positioning Receiver for 3G FDD Mode,Second International Conference on 3G Mobile Communication Technologies, Conf. Publication No. 477, 2001.

[13] Universal Mobile Telecommunications System (UMTS), UTRA Repeater: Planning Guidelines and System Analysis, 3GPP TR 25.956.

[14] A. Boukalov, S-G. Haggman, System Aspects of Smart-Antenna Technology in Cellular Wireless Communications – An Overview, IEEE Transactions on Microwave Theory and Techniques, vol. 48, Issue 6, June 2000.

[15] R. Janaswamy, Radiowave Propagation and Smart Antennas for Wireless Communications, Kluwer Academic Publishers, 2001.

[16] D. Gesbert, M. Shafi, D. Shiu, P. Smith, A. Naguib, From Theory to Practice: An Overview of MIMO Space-Time Coded Wireless Systems, IEEE Journal on Selected Areas in Communications, vol. 21, no 3, April 2003.

[17] T. Rouse, I. Band and S. McLaughlin, Capacity and Power Investigation of ODMA in TDD-CDMA based Systems, IEEE International Conference on Communications, vol. 5, 2002.

[18] T. Rouse, S. McLaughlin and H. Haas, Coverage-Capacity Analysis of Opportunity Driven Multiple Access (ODMA) in UTRA TDD, Second International Conference on 3G Mobile Communications Technologies, Conf. Publication No. 477, 2001.

[19] T. Harrold and A. Nix, Performance Analysis of Intelligent Relaying in UTRA TDD,IEEE 56th Vehicular Technology Conference, vol. 3, 2002.

[20] T. Harrold, A. Nix and M. Beach, Propagation Studies for Mobile-to-Mobile Communications, IEEE 54th Vehicular Technology Conference, vol. 3, 2001.

[21] Universal Mobile Telecommunications System (UMTS), Multiplexing and Channel Coding (FDD), 3GPP TS 25.212.

[22] Universal Mobile Telecommunications System (UMTS), Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD), 3GPP TS 25.211.

[23] K. Pedersen, P. Mogensen, The Downlink Orthogonality Factors Influence on WCDMA System Performance, IEEE 56th Vehicular Technology Conference, vol. 4, 2002.

[24] J. Laiho-Steffens, A. Wacker, Experimental Evaluation of the Two-Dimensional Mobile Propagation Environment at 2 GHz, IEEE 47th Vehicular Technology Conference, vol. 3, 1997.

[25] K. Kalliola, Experimental Analysis of Multidimensional Radio Channels, Doctoral Thesis, Helsinki University of Technology, 2002.

[26] Universal Mobile Telecommunications System (UMTS), Deployment Aspects, 3GPP TR 25.943.

[27] J. Parsons, Mobile Radio Propagation Channel (second edition), John Wiley & Sons Ltd, 2000.

[28] W. Jakes, Jr., (ed.), Microwave Mobile Communications, Wiley-Interscience, 1974.

Chapter 2

UMTS CONFIGURATION PLANNING Base station configuration and power budget

JARKKO ITKONEN, RISTO JURVA European Communications Engineering (ECE) Ltd

Abstract: In configuration planning, the radio network planner selects the optimum configuration of the base station for the planned cell or part of the planning area. The planner must figure out a configuration that meets the network quality targets, takes into account the physical limitations, and requirements of the base station site and meets the given investment and operating cost limits. The main base station configuration planning options are presented in this chapter together with power budget calculations, which connect the selected options to the radio link path loss and further to cell size. Special configurations of repeaters and indoor solutions are also presented.

Key words: Antenna, base station, cable, configuration planning, Eb/N0, Ec/N0, indoor planning, LNA, mobile station, noise figure, path loss, performance, power budget, repeater, sensitivity

45




2. UMTS CONFIGURATION PLANNING

The target of UMTS configuration planning is to find the optimum configuration of the base station for each base station site in the planning area or a nominal base station configuration for different parts of the planning area. In configuration planning, several factors must be considered: – propagation environment type (macro, micro, indoor cell); – site characteristics (indoor, outdoor, wall, mast); and – required capacity and coverage.

The planner must select the optimum combination among several options in order to fulfill the quality requirements.

The main tool used in configuration planning is the power budget, which links the selected base station configuration to the maximum allowed attenuation of the radio signal in the radio path, i.e., maximum path loss. The maximum cell size can be calculated from the maximum path loss with propagation prediction models.

The configuration planning of an indoor base station, a micro cell, and a repeater are special cases due to the special propagation environment type, site characteristics, or equipment configuration.

2.1 Base station configuration

In this chapter, the base station configuration options are categorized into two categories: base station configuration and base station antenna line configuration.

2.1.1 Base station architecture

The UMTS base station architecture is driven by the use of a single high-power linear power amplifier per cell and the high signal processing power requirement set by the WCDMA air interface. A typical high-level architecture for a UMTS base station with a 3-sector configuration is presented in Figure 2-1.

Antenna filter (AF) unit filters out-of-band noise and interference from the received power, e.g., from other WCDMA carriers or radio networks, and amplifies the signal in the reception path. The performance of the AF unit affects the base station noise figure, and thus the sensitivity of the base station. In the transmit path, the AF unit filters out-of-band noise and spurious signals from the transmitted power. The attenuation of the AF unit to the transmit signal has to be taken into account in the base station transmit power.

UMTS CONFIGURATION PLANNING 47

AF TRU

Base bandunit

Interfaceunit

PA

AF TRU

PA

AF TRU

PA

O&M

Antennaline 1 UMTS Base Station

Antennaline 2

Antennaline 3

Figure 2-1. Base station architecture.

Power amplifier (PA) amplifies the signal to the required power level. The power amplifier is characterized by amplifier linearity, output power, and bandwidth. The amplifier linearity requirement is set by the adjacent power leakage (APL) power and transmit modulation requirements, and given in the 3GPP specifications [1]. The output power depends on the product type (typically 5–40 W). The power amplifier bandwidth for a single carrier amplifier is about 5 MHz, and for a wideband amplifier, it is 15–20 MHz, which makes it possible to amplify several carriers with a single amplifier and usually cover the whole operator frequency band. Most commercial amplifiers are of the wideband type. With multiple carriers per amplifier, the output power of the amplifier is shared between the carriers.

Transceiver unit (TRU) is in the base station between analog radio frequency (RF) signal processing and digital signal processing. In the reception path, the signal is typically down-converted to the inter-frequency (IF) band, filtered, and then converted from analog to digital (A/D conversion). In the transmit path, the signal is converted from digital to analog (D/A conversion), filtered, and converted to the selected carrier frequency.

The Base Band Unit (BBU) simultaneously handles numerous tasks such as the following: – common signaling channel processing

– random access channel (RACH) detection – common pilot channel (CPICH) generation

– L1 signal processing for common and dedicated physical channels – error detection – channel coding/error correction


– interleaving – transport channel multiplexing – spreading/despreading – channel estimation for phase correction and RAKE receiver

configuration – RAKE receiver – modulation – filtering – fast closed-loop power control

– load estimation for all carriers. The processing power requirement of the BBU can be divided into static

processing (common signaling channels) and dynamic processing (common and dedicated data channels). The BBU processing capacity must be planned according to both of these.

Interface unit connects the base station to the Radio Network Controller (RNC).

Operation and maintenance (O&M) unit is the interface to the network management system for network supervising and configuration.

A combiner solution (not shown in Figure 2-1) must be selected if the configuration supports multiple carriers per sector. The combiner solutions are vendor-specific.

Base station performance is mainly related to the transmit power, processing capacity and sensitivity. Transmit power depends on the power amplifier performance, and processing capacity depends on BBU performance and the number of hardware units installed in the base station. Base station sensitivity depends on base station RF and base band performance. Sensitivity depends also on the service type, data rate and propagation environment, but these are not related to the performance of the base station itself. Section 2.3.3 presents the calculation of the base station sensitivity and Chapter 5 includes typical sensitivity values for different services.

3GPP specifications [1] set several requirements for the characteristics and performance of the base station transmitter and receiver. The main receiver performance requirements are given as Eb/N0 levels in different propagation conditions. The specification defines the Eb/N0 as

b

cc

frameb

frameccchipcb

R

R

N

E

TR

TR

N

E

L

L

N

E

N

E

00inf00

=== (2-1)

where


– Eb is the energy per information bit; – N0 is the total one-sided noise power spectral density due to all noise

sources; – Ec is the received total energy per PN chip per antenna from all paths; – Lchip is the number of chips per frame; – Linf is the number of information bits in dedicated traffic channel

(DTCH); excluding CRC bits per frame; – Rc is the chip rate (3.84 Mcps); – Rb is the information bit rate between Layer 1 and Layer 2; and – Tframe is the duration of the radio frame (10 ms).

In Table 2-1, an example from the specification for multi path Case 3 is shown to approve the performance of the base station in multi path conditions resembling a small macro cell with the mobile speed of 120 km/h. The test configuration is for a dual branch receiver (antenna diversity) and no power control.

Table 2-1. Base station performance requirement for multi path Case 3 channel [1]. Measurement channel Required received Eb/N0 BLER

12.2 kbps n.a. < 10-1 7.2 dB < 10-2 8.0 dB < 10-3 64 kbps 3.4 dB < 10-1 3.8 dB < 10-2 4.1 dB < 10-3 144 kbps 2.8 dB < 10-1 3.2 dB < 10-2 3.6 dB < 10-3 384 kbps 3.2 dB < 10-1 3.6 dB < 10-2 4.2 dB < 10-3

2.1.2 Base station antenna line configuration

A typical configuration of a UMTS base station antenna line is presented in Figure 2-2. The antenna line configuration directly affects the cell coverage area, cell capacity, and interference; thus it must be planned before the detailed coverage/capacity planning phase is started (see Chapter 1).

First, antenna line configuration planning must consider which systems and frequencies are supported and what are the main site characteristics, such as antenna height and base station location (roof, basement, etc.). After that comes the planning of the antenna line equipment configuration (antenna type selection, feeder cable type selection, use of LNA/MHA, selection of antenna diversity method, antenna tilting, and antenna installation equipment setup).

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BTS

Feedercable

LNAJumpers

Antenna

I

I

I

I

Base stationantenna line

Bias - T

Figure 2-2. Typical base station antenna line elements.

2.1.2.1 Base station antenna

The characteristics of the base station antenna have a direct effect on the shape and size of the cell coverage area and on the amount of interference radiated outside the cell coverage area. Hence, several requirements must be considered in the selection of the base station antenna. – Antenna physical size is limited by the base station site. Large antennas

can be installed on masts and rooftops, but usually smaller antennas are used in building wall installations, micro cells, etc.

– Antenna frequency band: The base station antenna can be designed for single or multiple frequency bands. A single band antenna can be a so-called broadband antenna with a wide frequency band covering multiple systems (e.g., 1710–2170 MHz covering GSM1800 and WCDMA). Multiple band antennas usually work in two or three distinct frequency bands (e.g., 880–960 MHz, 1710–1880 MHz, 1920–2170 MHz) serving different systems (GSM900, GSM1800, and UMTS).

– Vertical beam width is inversely proportional to the antenna vertical size. – Horizontal beam width is set mainly by the number of sectors selected

for the site.


– Antenna polarization is typically vertical in single polarization antennas. In polarization diversity antennas, two perpendicular polarizations are used, usually at ±45 degrees.

– Antenna down tilting method can be either mechanical or electrical. Mechanical tilting is implemented by the antenna installation. Electrical tilting is a feature of the antenna element. Electrical down tilt is usually in the range of 2–8 degrees, either fixed or tunable. The most important antenna specification values and typical

specifications of four different antennas designed for UMTS bands are presented in Table 2-2.

Table 2-2. Typical antenna specifications [2]. Ant 1 Ant 2 Ant 3 Ant 4 Unit

Site 3-sector, macro

3-sector, macro

6-sector, macro

Micro

Max. dimension 1.8 1.3 1.8 0.7 M Gain 18 17 20 15 dBi Beam width

Horizontal 65 65 30 65 degrees Vertical 4.5 5.5 4.5 13.5 degrees

Electrical tilting 5, fixed

2 – 7, variable

5,fixed

0 degrees

Polarization ± 45 ± 45 ± 45 ± 45 degrees Frequency range 1900 – 2179 1900 – 2179 1900 – 2179 1900 – 2179 MHz

2.1.2.2 Feeder cable, jumpers and connectors

Feeder cable is the other main part of the base station antenna line in addition to the antenna. Together with the jumpers and connectors, it connects the base station to the antenna. The main parameter of the cable is the signal attenuation or cable loss, which depends on the cable diameter and the signal frequency. Typical cable loss figures for different frequency bands and cable sizes are listed in Table 2-3.

Table 2-3. Typical cable attenuation (dB/100 m) with different signal frequencies [2]. Diameter 900 MHz 1800 MHz 2200 MHz

½" 7.1 10 12 7/8" 3.7 5.4 6.1 1 5/8” 2.0 2.7 3.0 Jumper 13 19 21

Jumper loss per 100 m is much higher than the cable loss because of the small diameter, but typically the jumpers are quite short (< 1 m) and the loss of one jumper is a fraction of a dB. Connector loss is also typically quite small, e.g., 0.02 dB/connector.


2.1.2.3 Low noise amplifier

The base station system noise figure can be improved by using a low noise amplifier (LNA, also called Mast Head Amplifier MHA) close to the antenna before connectors and antenna feeder losses. This is achieved by amplifying the received signal by an LNA before the receiver losses.

The improvement of the system noise figure of a base station will increase the uplink maximum path loss (Section 2.3), thus LNA is considered an effective method to improve cell coverage in UL.

The amount of improvement in system performance depends on: – LNA gain, GLNA;– LNA noise figure, FLNA;– total antenna line loss (cable, connectors, jumpers), LC; and – BS receiver noise figure, FBS.

The improvement to the system noise figure can be calculated as the ratio of the noise figure without LNA and with LNA, as presented in Equation 2-2.

( )11 −+

=∆CBS

LNALNA

CBS

LFG

F

LFF

(2-2)

The maximum improvement MAXF∆ can be solved from Equation 2-2 when the LNA gain approaches infinity.

LNA

CBSMAX F

LFF =∆ (2-3)

In the dB scale, the maximum improvement is

CLNABSMAX LFFF +−=∆ . (2-4)

The effect of the LNA gain to the noise figure improvement with two different cable loss figures is shown in Figure 2-3. The improvement exceeds the cable loss in both cases, with typical LNA gain values of 12–14 dB.


0 5 10 15 200

1

2

3

4

5

6

7

L_C = 3 dBL_C = 6 dB

LNA gain / dB

Sys

tem

noi

se f

igur

e im

prov

emen

t / d

B

3

6

.

Figure 2-3. System noise figure improvement, FLNA = 2 dB, FBS = 3 dB, LC = 3 dB or 6 dB.

The effect of the LNA to the uplink performance will be significant in UMTS networks as the feeder cable loss is high due to the high frequency band. The effect of the cable loss on the system noise figure and on the noise figure improvement with and without LNA is shown in Figure 2-4.

0 2 4 6 8 100

1

2

3

4

5

6

7

8

9

10

11

12

13

14

System noise figure, no LNASystem noise figure with LNA (gain 12 dB)System noise figure improvement

Cable loss / dB

dB

.

Figure 2-4. System noise figure and noise figure improvement vs. cable loss with and without LNA (FLNA = 2 dB, FBS = 3 dB).


The LNA causes a loss in the downlink signal path. This loss is equal to an LNA insertion loss that is typically about 0.5 dB. This should be taken into account in the downlink power budget antenna line loss (Section 2.3).

Bias-T is required to provide power to the LNA via the antenna cable. Also, an external power feed directly to the LNA can be used, or Bias-T can be included in the antenna filter unit. In both cases, Bias-T is not required.

2.1.2.4 Antenna diversity configurations

Base station antenna diversity is traditionally used in most configurations to enhance the uplink coverage and capacity. Space diversity and polarization diversity are the most common methods used for antenna diversity. The selection between these methods and the achievable gain to power budget depends on the propagation environment and the antenna installation.

Space diversity provides gain in all environments, but it requires two antennas with a minimum separation to achieve the optimum gain. The minimum separation depends on the environment; typically, it is 15-25 in rural environments, 10-15 in urban/suburban environments, and 1-2 in urban microcellular environments [3]. If the separation is less than that, the achieved gain is still at least 2.5–3 dB from the maximum ratio combining of two signals. A practical maximum gain of about 4-5 dB in receiver sensitivity has been measured in GSM with more than the minimum separation [3]. In WCDMA multi path diversity affects the achievable gain; i.e., in indoor and micro cells, the antenna diversity gain is higher than in large macro cells [4].

Polarization diversity has good performance in propagation environments with a large number of reflections and diffractions causing random polarization of the received signal. In GSM, the achievable gain in receiver sensitivity is 4-6 dB in urban, suburban, microcellular, and indoor environments. In rural environments, the gain is typically less than with space diversity [3, 5]. In WCDMA, the amount of multi path diversity also affects the achievable gain from polarization diversity. Polarization diversity is typically implemented with one polarization antenna, making it easier to install than space diversity.

Typical configurations of antenna lines for space diversity and polarization diversity are presented in Figure 2-5.

More complex antenna diversity methods are proposed to further improve the performance of uplink reception. For example, four branch diversity receivers with four space diversity or two polarization diversity antennas have been proposed. The additional gain compared to two branch diversity is about 1-2 dB [6].


I

I

I

I

I

I

I

I

X

X

X

X

X

X

X

X

RX/TX RX RX/TX RX

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

X

X

X

X

X

X

X

X

RX/TX RX RX/TX RX

I

I

I

I

I

I

I

I

Figure 2-5. RX diversity configurations for polarization and space diversity, with and without LNA.

In UMTS systems, downlink performance is often considered to be the most critical, especially in high capacity (capacity-limited) cells. In order to improve downlink performance, support for base station transmit diversitywas included in the WCDMA specification. The main principle of transmit diversity is to transmit the signal of one user via two different antennas. Two different methods to control the transmission of the signal are specified: so-called open-loop and closed-loop transmit diversity. Closed-loop transmit diversity has two different modes [7].

The achievable gain from transmit diversity depends strongly on channel conditions such as orthogonality and terminal speed. In the closed-loop method, the receiver performance in measuring the received signals and controlling the transmit antennas also affects the gain. Receiver Eb/N0 gains in the range of 0 to 3.5 dB has been reported have been reported for open-loop and closed-loop methods [7].

2.1.2.5 Multi system antenna configurations

The antenna line must be planned to support both GSM and WCMDA systems in many sites, because support for GSM interworking is essential for WCDMA networks and installing both systems at the same site (co-siting) is often the most cost-efficient solution. Several different antenna types, such as broadband antennas and multiple band antennas, have been developed to support co-siting. The selection of the antenna type will also influence the antenna line configuration.

The main selection related to the feeder configuration is whether to use separate or shared antenna lines. Figure 2-6 presents typical antenna line


configurations with separate polarization diversity antennas for GSM and WCDMA systems and with separate antenna lines. The same configuration with shared antenna lines is presented in Figure 2-7. Antenna line diplexer units are required to combine the signals in the same cable and to separate the signals at the antenna end when two different systems share the same antenna. Triplexers are used when there are three systems.

X

X

X

X

X

X

X

X

GSM base station

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

WCDMA base station GSM base station WCDMA base station

X

X

X

X

X

X

X

X

Figure 2-6. GSM and WCDMA co-siting with separate antennas and antenna lines.

X

X

X

X

X

X

X

X

GSM base station

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X


X

X

X

X

X

X

X

X

Diplexer

Diplexer

GSM antenna WCDMA antenna GSM antenna WCDMA antenna

Vendor specificDC feedto LNAs

Figure 2-7. GSM and WCDMA co-siting with separate antennas and shared antenna lines.


A diplexer or triplexer is also required when broadband antennas are used to combine the systems in the same antenna connectors. (See Figure 2-8.) From the antenna line point of view, multi band antenna configurations are similar to configurations with separate antennas because both use separate antenna connectors for the two systems.

GSM base station

X

X

X

X

X

X

X

X


Diplexer

WCDMA&GSMantenna

Diplexer

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

WCDMA&GSMantenna

Figure 2-8. GSM and WCDMA co-siting with broadband and multi band antennas with common antenna cables.

2.2 Mobile station

Transmit power and receiver sensitivity are the main mobile station parameters in the configuration planning. The 3GPP specification [8] sets requirements for the mobile station performance. These requirements can be used as the baseline for the configuration planning, although it must be considered that the performance requirements are given for different test cases that do not necessarily reflect realistic conditions in a radio network.

In UMTS, a mobile station can belong to one of the four different power classes presented in Table 2-4, depending on the maximum transmit power. Most of the handheld mobiles will belong to class 4 with +21 dBm maximum transmit power. It should be noticed in power budget calculations that the tolerance for the transmit power is large (±2 dB). Products during their first years tend to prioritize current consumption over transmit power; thus, their maximum transmit power is closer to the lower limit.


Table 2-4. Mobile station power classes in UMTS [8]. Power Class Nominal maximum output

power

Tolerance

1 +33 dBm +1/-3 dB 2 +27 dBm +1/-3 dB 3 +24 dBm +1/-3 dB 4 +21 dBm ± 2 dB

The specification sets requirements for the mobile station receiver performance for type approval purposes. Table 2-5 shows an example of a receiver performance requirement in the multi path propagation environment Case 1, which resembles an indoor or small micro cell environment with a small delay spread. No antenna diversity or downlink power control is used. The requirements are formulated for type approval and cannot be directly applied in network planning to power budget calculations.

Table 2-5. Receiver sensitivity (case 1) [8]. Test Number (bit rate)

or

c

I

EDPCH _ BLER

1 (12.2 kbps) -15.0 dB 10-2

2 (64 kbps) -13.9 dB -10.0 dB

10-1

10-2

3 (144 kbps) -10.6 dB -6.8 dB

10-1

10-2

4 (384 kbps) -6.3 dB -2.2 dB

10-1

10-2

The performance requirements are given as a ratio of the dedicated physical channel transmitted chip energy DPCH_Ec and the total transmit power spectral density Ior. This can be projected from the transmit end to the receiver antenna connection as:

RXor

c

TXor

c

I

E

I

EDPCH=

ˆ_

(2-5)

where Ec is the received chip energy at the receiver and orI is the power spectral density of the transmitted signal at the receiver.

The specified test conditions must be understood in order to use these requirements, e.g., in the power budget. The received total interference power density N0 has been derived in the following equation in order to figure out the relation of the total interference power density and the orI


used in the specification. N0 is the sum of the own-cell interference, other-cell interference and thermal noise spectral densities.

( ) ( ) 000ˆ1ˆ1ˆ NthiIINthIIN ororocor ++−=++−= αα (2-6)

where – Îor is the total own-cell received signal level; – is the orthogonality factor; – Ioc is the power spectral of a band-limited white noise source (simulating

interference from cells, which are not defined in a test procedure) as measured at the UE antenna connector [8];

– little i ( oroc IIi ˆ= ) is commonly used for describing the level of other-

cell interference; and – Nth0 is the receiver thermal noise power density. (In a real environment,

this also includes external interference from other carriers and systems.) The equation can be reformatted to a correction factor (CF), which can

be used to calculate the Ec/N0 or Eb/N0 requirement for the service. The last approximation can be done when Ioc >> N0.

iiI

Nthi

I

Nthi

I

NCF

ocoror

+−≈++−=++−== ααα 11ˆ

1ˆ

000(2-7)

The specification [8] defines that for Case 1, the external interference level Ioc is -60 dBm/3.84 MHz, and i is 9 dB. In that case, CF = -6.5 dB with an orthogonality of 0.9. The orthogonality depends on the channel’s multi path profile [9].

b

ccb

or

cc

R

R

N

E

N

E

CFI

E

N

E

000

,1

ˆ== (2-8), (2-9)

For example, a -15 dB requirement in Table 2-5 corresponds to Ec/N0

level of -8.5 dB and with Eb/N0 of 16.4 dB (Test 1, 12.2 kbps).

2.3 Power budget

The target of the power budget is to calculate the maximum uplink and downlink path loss and to verify that the uplink and downlink path losses are

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at an equal level, i.e., the link is balanced (see Chapter 1). In a UMTS system, the link balance is not constant, as it is affected by the system load. In the downlink, the effect of the load is bigger because the users in the cell share the same power amplifier. Because of that, in high traffic cells, the downlink is the limiting direction (see Chapter 5).

In the downlink, the maximum path loss is calculated from the base station transmit antenna to the cell edge, and in the uplink, from the mobile transmit antenna to the base station location. The transmit power at the transmit antenna (EIRP) and the minimum planned signal level on the cell edge (planning threshold) must be calculated in order to calculate the maximum path loss in the downlink, as shown in Figure 2-9.

BS

DL EIRP

DLPlanningthreshold

Maximum Path Loss

Cell range

Figure 2-9. Downlink power budget.

The same calculation is repeated in the uplink, and the direction with the smaller maximum path loss is selected as the limiting direction. The cell range is calculated from the maximum path loss of the limiting direction by using the selected propagation prediction model.

The calculations of the downlink and uplink path loss are shown in the following equations:

ThresholdPlanningDLEIRPDLpathlossDLMaximum −= (2-10)


ThresholdPlanningULEIRPULpathlossULMaximum −= (2-11)

The main principle of the planning threshold calculation is shown in Figure 2-10 and covered in more detail in the next sections. Figure 2-10 shows that the planning threshold is affected by equipment performance and configuration, cell interference level, and service quality requirements. It is also affected by propagation environment, terminal mobility, etc.

Thermal noise at receiver

Total interference

Amount of interference

Signal level at reveiverinput

C/I requirement

Antenna line parameters

Coverage quality, margins

Signal level at antenna

Average signal level at cell edge = Planning Threshold

Receiver noise figure

Background noise

Figure 2-10. Calculation of planning threshold.

The planning threshold (and maximum path loss) is service-specific and it depends on the service-quality targets, e.g., data rate, BER target, coverage probability, etc. As the UMTS system supports the implementation of a multiple service network offering a wide range of different services, the power budget has to be calculated separately for each service, with the selected Quality-of-Service level and the final cell range being limited by the service that allows the lowest maximum path loss in the radio link.

Typical power budget tables for a downlink and uplink power budget are presented in Tables 2-6 and 2-7. The power budget calculation phases have been described in more detail in Sections 2.3.1–2.3.7. The calculations have been presented with equations in linear scale and dB values have to be converted to linear values with conversion 1010dBlin = , and

( )lindB log10= .


Table 2-6. Downlink power budget. Receiver (MS)

Antenna noise temperature 290 KReceiver noise figure 8 dBReceiver noise temperature 1539.8 KSystem noise temperature 1829.8 KReceiver thermal noise density -166.0 dBm/HzNoise bandwidth 3.84 MHzThermal noise power -100.1 dBmCell interference margin 3 dBTotal interference level -97.1 dBm

User bit rate 12.2 kbpsRequired Eb/N0 7 dBAntenna diversity gain 0 dBSoft handover diversity gain 4 dBPower control gain in Eb/N0 3 dBRequired C/I -17.0 dB

Receiver sensitivity -114.1 dBm

Antenna line losses 0 dBRX/TX antenna gain 0 dBiRequired isotropic power -114.1 dBm

Planning threshold (DL)

SHO gain 3 dBBody loss 3 dBPropagation slope 35 dB/dec

Outdoor coverage probability 95 %Outdoor slow fading st. dev. 7 dBOutdoor slow fading margin 4.3 dBOutdoor planning threshold -106.8 dBm

Indoor coverage probability 90 %Indoor slow fading st. dev. 9 dBIndoor slow fading margin 3.5 dBBuilding penetration loss 15 dBIndoor planning threshold -92.6 dBm

Transmitter (BS)

Max. power per connection 29.5 dBmBS TX losses 0.5 dBBS Output power per connection 0.8 WAntenna line losses 4 dBRX/TX antenna gain 18 dBiEIRP 43.0 dBm

Maximum path loss

Indoor path loss 135.6 dBOutdoor path loss 149.8 dB

Total interference

C/I requirement

Receiver sensitivity

Isotopic received power

Outdoor planningthreshold

Indoor planningthreshold

Base stationEIRP


Table 2-7. Uplink power budget. Receiver (BS)

Antenna noise temperature 290 KReceiver noise figure 4 dBReceiver noise temperature 438.4 KSystem noise temperature 728.4 KReceiver thermal noise density -170.0 dBm/HzNoise bandwidth 3.84 MHzThermal noise power -104.1 dBmCell interference margin 3 dBTotal interference level -101.1 dBm

User bit rate 12.2 kbpsRequired Eb/N0 3 dBAntenna diversity gain 0 dBSoft handover diversity gain 2 dBPower control gain in Eb/N0 3 dBRequired C/I -23.0 dB

Receiver sensitivity -124.1 dBm

Antenna line losses 6 dBRX/TX antenna gain 18 dBiLNA gain 0 dBRequired isotropic power -136.1 dBm

Planning threshold (UL)

SHO gain 3 dBBody loss 3 dBPropagation slope 35 dB/dec

Outdoor coverage probability 95 %Outdoor slow fading st. dev. 7 dBOutdoor slow fading margin 4.3 dBOutdoor planning threshold -128.8 dBm

Indoor coverage probability 90 %Indoor slow fading st. dev. 9 dBIndoor slow fading margin 3.5 dBBuilding penetration loss 15 dBIndoor planning threshold -117.6 dBm

Transmitter (MS)

Max. power per connection 21.0 dBmRX/TX antenna gain 0 dBiEIRP 21.0 dBm

Maximum path loss

Indoor path loss 138.6 dBOutdoor path loss 149.8 dB

Total interference

C/I requirement

Receiver sensitivity

Isotopic received power

Outdoor planningthreshold

Indoor planningthreshold

Mobile stationEIRP


2.3.1 Total interference

The calculation of the power budget starts with the calculation of the total interference level at the receiver input.

Antenna noise temperature (Ta) is affected mainly by the surrounding environment and antenna radiation pattern. Under a clear sky, the antenna noise temperature can be about 60 K, but when surrounded by buildings, located indoors or inside a pocket, the antenna temperature is about the same as the ambient temperature, often approximated as 17 degrees Celsius (290 K).

Receiver noise figure (F) is the measure of receiver noise performance, i.e., how much thermal noise is added to the received signal in the receiver. In the base station, the reference point is usually the input of the base station. In the mobile station, the receiver noise figure is usually defined at the antenna connector, so it includes the antenna line losses, etc. Typically, the UMTS base station noise figure is around 2.5–5 dB, and the mobile station noise figure is typically about 8 dB.

The noise bandwidth (BN) is the bandwidth of the receiver filters before signal despreading. The chip-matched filter noise bandwidth is the same as the chip frequency 3.84 MHz.

Cell interference margin (IM) is one of the main parameters in the UMTS power budget. It is defined as the ratio of the total interference level to the thermal noise level N:

N

INIM

+= (2-12)

In most of the references interference margin IM takes into account only the intra system and intra frequency interference (own-cell + other-cell), but interference from other carriers, systems (e.g., GSM), and other external interference are either included in the noise floor level N or left out of the power budget calculation. The total interference level Itot is calculated with Equation 2-13, where k is the Boltzman constant (1.38E-23 J/K) and Tphys is the receiver physical temperature (usually 290 K) and Tsys is the system noise temperature.

( )( ) IMBkTIMBTFTkI NsysNphysatot =−+= 1 (2-13)


2.3.2 Required carrier-to-interference ratio

The required carrier-to-interference ratio (C/I) has to be calculated (see Table 2-6 and 2-7) in order to calculate the required signal level at the receiver when the receiver interference level is known. The service type, service quality requirements and also the propagation environment, base station configuration and terminal speed will have an effect on the C/Irequirement.

User bit rate (Rb) is the bit rate of the service for which the power budget is calculated. Usually the user bit rate is the bit rate between the Physical and MAC layer, i.e., it includes the L2/L3 headers but not the physical layer bits (CRC, error coding, rate matching, etc.). (See Section 2.1.1 and [10].) Also the bit rate at other protocol levels can be used, but the definition has to be the same that is used in the definition of the Eb/N0 value.

The Eb/N0 value is the energy per bit Eb divided by total interference power density requirement N0 (I0 also used) for the service for which the power budget is calculated. The relationship of Eb/N0 to signal quality C/I in the radio interface can be presented using chip rate Rc and user bit rate Rb or processing gain PG.

PGI

C

RI

RC

N

E

c

bb 1

0

== (2-14)

In practice, the required Eb/N0 depends on a large number of variables, such as: – service QoS profile (bit rate, BLER target, RLC mode, etc.), – Layer 1 channel configuration (CRC, error coding, rate matching, etc.), – receiver performance (channel estimation, etc.), – propagation conditions, – receiver speed, – effect of power control, – antenna diversity reception/transmission, and – SHO conditions (number of links, relative powers of the links).

Because of the complex nature of the Eb/N0 requirement, it is impossible to give one fixed value for different services, and reasonable estimates have to be used, e.g., in power budget calculations. Some compensation factors are usually take into account in order to compensate the difference between the conditions in which the Eb/N0 has been defined and the conditions in the power budget cell. Antenna diversity gain, soft handover diversity gain and power control gain in Eb/N0 are used in the presented power budget.


Antenna diversity gain (GAdiv) has to be included in the power budget calculation if diversity is used and if it is not included in the Eb/N0

requirement. Both receive and transmit diversity gains have to be considered when applicable (see Section 2.1.2.4).

Soft handover diversity gain (GSHOdiv) is defined as the macro diversity gain against fast (Rayleigh) fading caused by multi path propagation. The soft handover diversity gain is different in the UL and DL directions due to a different macro diversity combining method. In the downlink, the signals from different base stations are combined in the mobile station RAKE receiver, which equals to maximal ratio combining. In a soft handover situation in the UL, the signals are combined in the macro diversity combiner of the radio network controller (RNC). It typically uses frame or block selection combining based on quality information of the signals from the different base stations. In a softer handover situation, the UL signals from different sectors of the same base station are combined in the base station RAKE receiver.

Soft handover diversity gain depends also on the relative powers of the handover links and the level of diversity from other diversity types (RX antenna diversity, TX antenna diversity, multi path diversity and time diversity from interleaving). For the uplink, soft handover diversity gain figures of 0–1.6 dB have been simulated with two branch receive antenna diversity [11]. It was shown that the diversity gain depends on the receiver speed and relative powers of the soft handover links.

Power control gain in Eb/N0 (GPC,: also called power control headroom [4]) is taken into account in the uplink power budget when the Eb/N0 has been defined with power control. It is taken into account because at the cell edge, the mobile station transmitter is transmitting continuously at full power and thus cannot follow the fading according to the uplink power control commands. The power control gain in Eb/N0 depends especially on mobile speed and level of diversity. At low speeds and at a low level of diversity, it is highest (6-8 dB). At high speeds and a higher level of diversity, it decreases to close to 0 dB [4, 7].

The required C/I is calculated according to Equation 2-15.

PCSHOdivAdivc

bb GGGR

R

N

E

I

C 1

0

= (2-15)


2.3.3 Receiver sensitivity

Receiver sensitivity Cmin, i.e., the minimum received power per service in question, can be calculated when the total interference power and C/Irequirement are known.

totII

CC =min (2-16)

2.3.4 Isotropic received power

The calculation of the required isotropic power at the receiver antenna takes into account the effect of the antenna line on the receiver performance.

The mobile station antenna gain (Ga) depends on the terminal type and usage (in the hand, pocket, etc.), and often the antenna gain is approximated to be 0 dBi because it is not the same for all users. Typically, the mobile station antenna line losses (La) are included in the mobile station receiver noise figure. Equation 2-17 shows the calculation of the downlink isotropic

received power ( DLIP ).

a

aDLI L

GCP min= (2-17)

In the uplink, all the required figures (BS antenna gain and antenna line losses) are based on equipment manufacturer specifications (Section 2.1.2). If the LNA is used, the LNA gain GLNA is also taken into account in the calculation of the isotropic power (Section 2.1.2.3). Equation 2-18 shows the

calculation of the uplink isotropic received power ( ULIP ).

LNAa

aULI GG

LCP min= (2-18)

2.3.5 Planning threshold

The planning threshold calculation considers mainly the effect of slow (log-normal) fading caused by shadowing in the radio path. Shadowing is caused by terrain shape, foliage, buildings, and other obstacles. The effect of


the user’s body (Lbody) together with building penetration loss (LBP) for indoor coverage is also taken into account in the planning threshold calculation.

The calculation of slow fading margin (MSF) is presented in [12]. The slow fading margin is affected by the variation (standard deviation) of the slow fading, coverage probability requirement for the service in question (Pcov), and the propagation slope (slope) in the area.

( )slopePfM SFsingleSF ,, covσ= (2-19)

In UMTS, a soft handover also affects the slow fading statistics. In a soft handover, the user is connected to several base stations simultaneously and the statistics of the slow fading seen by the receiver is a composite of the slow fading of each link. In practice, the slow fading of the radio links in the soft handover are partly correlated. The soft handover gain can be defined as the difference of the slow fading margin with one link and the slow fading margin with multiple links with a certain level of correlation [7].

SHO

singleSF

SF G

MM = (2-20)

At least two planning thresholds are typically calculated for both uplink

and downlink, one for outdoor coverage ( DLULoutPth / ) and the other for indoor

coverage ( DLULinPth / ). The calculation of the indoor coverage planning

threshold takes into account the attenuation caused by the building structure to the signal coming from the outdoor base station, the indoor slow fading standard deviation and the indoor coverage probability target.

outSFbody

DLULI

DLULout MLPPth // = ,

BPinSFbody

DLULI

DLULin LMLPPth // =

(2-21)

(2-22)

where DLULIP / is the isotropic power for the uplink or downlink.


2.3.6 Equivalent isotropic radiated power

The uplink equivalent isotropic radiated power (EIRPUL) calculation considers the terminal antenna line and terminal transmit power. Usually antenna line losses are taken into account in the mobile station TX power ( MS

txP ). Mobile station antenna gain ( MSaG ) depends much on the terminal

and terminal antenna type and also the terminal position, typically an average value of 0 dBi is used in power budget calculations.

The downlink equivalent isotropic radiated power (EIRPDL) calculation takes into account the effect of the base station antenna line. The base station transmit power for each service connection ( BS

txP ) is limited by the total transmit power required for all users and services in the cell, and in low traffic cells more power can be allocated for each service. The downlink power budget can be used to find out the required downlink transmit power that gives equal path loss for the uplink and downlink by selecting the required base station transmit power.

MSa

MStxUL GPEIRP = ,

abs

BSa

BStx

DL LL

GPEIRP = (2-23), (2-24)

2.3.7 Maximum path loss

Finally, the maximum path loss can be calculated as

Pth

EIRPPL =max (2-25)

for the uplink, downlink, indoor, and outdoor cases.

2.4 Repeater configuration

In residential and rural areas or on highways, where there are large topographic or morphologic obstacles attenuating the signal, repeaters are commonly used as fast and cost-effective solutions to fill coverage holes and gaps. Another significant reason to introduce a repeater is when implementing an indoor coverage, e.g., in large shopping malls, office buildings, stations, or underground premises. In such a case, the repeater is typically connected to a distributed antenna system (DAS). A repeater amplifies the signal received from a base station and transmits it further

www.itbookshub.com



towards the coverage gap. Since a repeater is sharing the capacity of a donor base station, capacity planning must be considered especially in the case of hot spots. On the other hand, repeaters are used to save capacity. In a situation where there is a group of users having a weak downlink signal, the base station is continuously sending with high power, ‘wasting’ the available capacity. If there is a repeater taking care of this hot spot of users, it enables the base station to transmit with lower power, thus releasing the capacity for other users. This is emphasized in indoor locations, where a single user can reserve a lot of capacity due to large losses caused mainly by building penetration loss. In the uplink direction, the repeater may help to reduce the interference in the neighboring cells if the mobiles can use lower transmit power.

A repeater system consists of a donor antenna, amplifier, and serving antenna, as illustrated in Figure 2-11. The role of the donor antenna is to offer a link to a donor base station. Thus, a prompt alignment is critical, especially in cases where several base stations have equivalent link performance with the repeater. The strongest signal should be at least 8-10 dB better than the others to effectively avoid a continuous soft handover. Narrow beam (<30°) donor antennas would be optimal to achieve a sufficient margin, but typically 45° - 60° antennas are used due to size limitations. A line-of-sight condition is required between the base station and donor antennas.

UEREPEATERBS

COUPLING LOSS BS-RPT

ISOLATION

COUPLING LOSS RPT-UE

GAIN

Figure 2-11. An illustration of a repeater system.

Repeater parameters: – coupling loss BS-RPT = coupling loss between base station and repeater; – isolation = isolation between donor and serving antenna;


– coupling loss RPT-UE = coupling loss between repeater and terminal; and

– gain = repeater gain. The serving antenna is like any normal antenna used at the base station

for outdoor coverage and directed towards the coverage gap. Between the donor antenna and serving antenna, there must always be sufficient isolation, which is the most dominating parameter when defining suitable locations for the repeater antennas. The required isolation is at minimum 15 dB higher than the repeater gain (see Equation 2-26). In case there are problems achieving this, the coverage antenna also needs to be specially selected. Preferably both antennas should have high front-to-back ratios. Still, in outdoor repeater systems, achieving the required isolation can be a challenge and it requires an innovative utilization of buildings or towers. One solution is to utilize the nulls on the antenna pattern in the direction pointing towards the other antenna. The isolation also expects vertical separation and minimizing reflections. Additionally, installation of attenuating structures in between the antennas can be considered.

In the amplifier part of the repeater system, the signal can be given a gain typically up to 90 dB, and it can be set in the downlink and the uplink independently. Taking into account the isolation requirement, the gain (GRepA) should be set as follows [13]:

dBisolationRepeaterGRepA 15−≤ (2-26)

In case of a reduction in isolation, e.g., due to environmental changes, Automatic Gain Control (AGC) functionality is employed to prevent the amplifier self-oscillation. In normal use, the AGC is not active and the following gain (G) is given for the downlink:

BSARepABSARepA PmaxCLPmaxG −+≤ − (2-27)

where – PmaxRepA is the maximum gain of the repeater, – CLBSA-RepA is the effective coupling loss between the donor Base Station A

and the Repeater A, and – PmaxBSA is the maximum gain of the base station A.


The repeater gain, together with the coupling loss and base station sensitivity, also affects the repeater transferred sensitivity, which is defined as:

( )RepARepABSABSARepA GCLySensitivitySensitivit −−= − (2-28)

To minimize noise in the base station, the transferred sensitivity is preferred to be approximately 5-10 + repeater noise figure (typically ~5 dB) lower than the base station sensitivity. The margin between the base station sensitivity and the transferred repeater sensitivity is formulated as follows:

( )dBGCLM RepARepABSA −= − (2-29)

The maximum allowed delay of 20 µs between signal paths must be considered when planning the repeater site location. When the repeater entails an additional delay of 5-6 µs, it means that the repeater must be located between the base station and the repeater serving area [13].

The donor link can also be realized with an optical fiber system. In such a construction, the donor antenna is connected to an optical fiber through an electrical-to-optical converter for transforming the RF signal to light. Due to negligible losses of the optical fiber, the signal can be transferred long distances, up to few kilometers, to the serving antenna where the transformation back to the RF signal takes place. An optical link is suitable for locations where the distance between the base station and repeater is large.

2.5 Indoor configuration

With the enhanced high data rate services available by UMTS, the role of indoor systems will greatly increase. All the indoor planning strategies familiar from 2G networks will be applicable also in UMTS, i.e., indoor coverage can be realized with outdoor macro sites, dedicated indoor base stations or with repeaters. Due to the nature of UMTS networks, there will still be many new challenges when planning the indoor coverage and capacity with macro outdoor base stations in urban and suburban areas. If we examine an indoor traffic hot spot located right in the overlapping area of two or more outdoor cells, it will cause the mobiles to be in a continuous soft


handover, reducing the system capacity. These mobiles will also be increasing the interference levels of the closest cells when sending with high output power. Additionally, the signal level received by the indoor UE should support high user data rates and thus the allowed path loss between BS and UE tolerates no heavily attenuating material in the signal path. Some simulations show that when designing an indoor system for a five-storey building, the outdoor base station cannot be more than 100-200 meters away from the building. Due to these reasons, dedicated indoor base stations and repeater systems are mostly preferred in hot spots like offices, stations, shopping malls, and stadiums.

An UMTS indoor system typically includes a base station or repeater connected to an antenna system specially designed for the building. The base station configuration is planned mostly as in an outdoor base station (see Section 2.1.2), but the antenna system configuration deviates from outdoor sites. An example of this is presented later in this chapter. There are three main configurations used for indoor antenna systems:

1. Distributed Antenna System (DAS) 2. Radiating Cable System 3. Optical solutions

2.5.1 Distributed Antenna System (DAS)

The distributed antenna system consists of a trunk cable divided into branch cables connected to indoor antennas. The number of antennas can vary from a few up to 25-30 antennas depending on the requirements given for the system. The target is to achieve evenly distributed coverage with the EIRP values in the 5-8 dB range measured at the antenna where typical EIRP is 20-25 dBm. This can be reached by careful topology planning and optimizing the use of dividers, splitters and tappers. Also the cabling causes an additional loss that must be counted. In a large DAS system, there may be a need to use an amplifier in the downlink direction if the antenna line becomes very long. In the uplink direction, there is usually no need to use an LNA. Trials have been made to use antenna diversity and the results have shown up to a 6 dB reduction in average UE transmit power and a 1.5 dB reduction in standard deviation [14]. The increased implementation costs will still limit the use of diversity.

Finally the base station output power is adjusted to reach the planning thresholds (see Section 2.3.5). With too high antenna EIRP, the signal can easily leak outside the building causing interference to the macro cells and unnecessary handovers between outdoor and indoor cells. A typical construction of a DAS system is shown in Figure 2-12.


Special attention should be paid when planning the antenna locations to ensure the required QoS without disturbing the outdoor network. The distribution of the received signal level depends strongly on the antenna topology. Typically one antenna is located close to each main entrance to give a clear indoor dominance and controlled performance with the outdoor cells. A principal illustration of signal coverage based on the antenna construction described above is shown below in Figure 2-13.

UMTS BS

3. FLOOR

2. FLOOR

1. FLOOR

Figure 2-12. A schematic diagram of a distributed antenna system in UMTS indoor configuration.

Figure 2-13. An illustration of received signal level in DAS system.


2.5.2 Radiating cable system

The principle of a radiating cable system is to install special cabling throughout the whole building to be served by UMTS. The cable acts as an antenna by radiating the signal through small holes along the cable. The topology is typically like in DAS system, i.e., the cables need to be run everywhere where the service is needed. A benefit of the radiating cable system is that the transmitted signal is more evenly distributed because there are several radiating points. Figure 2-14 presents a radiating cable system. As is shown, the cable can also be connected to an antenna. Components like dividers, splitters and tappers can be used as in the DAS system.

UMTS BS

3. FLOOR

2. FLOOR

1. FLOOR

Figure 2-14. A schematic diagram of a radiating cable system in UMTS indoor configuration.

As mentioned, the coverage provided by radiating cable is even more than by DAS. Another benefit is that the planning of an indoor system is not so critical with distributed antennas because the cable can usually be run more flexibly due to system invisibility. Figure 2-15 below illustrates the received signal strength in a radiating cable implementation.

Sometimes the base station or repeater is not connected to any DAS or radiating cable system but just to a single antenna providing coverage to a very limited area of 1 to 3 floors. These applications are typically designed for a limited number of users requiring a lot of capacity. In case coverage or capacity expansion is needed, it is done by installing new base stations. It has to be noted that this requires careful planning of dominance areas whereas with DAS and radiating cable implementation the coverage can be done by one cell in the limits of the power budget. Additionally, in


distributed implementations, the whole system capacity with trunking efficiency is available wherever it is needed.

Figure 2-15. Illustration of received signal level in an indoor system with radiating cable.

2.5.3 Power budget

The power budget for indoor systems is calculated by defining the cable, divider, splitter, and tapper losses on the way to the antenna. The antenna gain needs to be added before subtracting the value from the BS output power. Some typical values are given in Table 2-8.

Table 2-8. Power budget for indoor system. Antenna line configuration DL UL

Branch A 2 –way tapper - 1.0 1.0 dB 2 –way splitter - 3.0 3.0 dB 3 –way splitter - 5.0 5.0 dB Cabling - 2.7 2.7 dB Connectors - 0.8 0.8 dB Antenna gain + 7.0 7.0 dBi Branch A total - 5.5 5.5 dB Branch B 2 –way tapper - 7.0 7.0 dB


Antenna line configuration DL UL

2 –way splitter - 3.0 3.0 dB 2 –way splitter - 3.0 3.0 dB Cabling - 2.0 2.0 dB Connectors - 0.6 0.6 dB Antenna gain + 7.0 7.0 dBi Branch B total - 8.6 8.6 dB Branch C Radiating cable - 7.5 7.5 dB Connectors - 0.2 0.2 dB Branch C total - 7.9 7.9 dB

2.5.4 Antennas

Some typical antenna patterns for indoor systems are presented below:

Figure 2-16. A presentation of indoor antenna patterns: (a) directional, (b) bi-directional, and (c) omni-directional.

Directional antennas with 65° - 90° beam width are mostly used in distributed antenna systems because of high gain typically in the range of 6…10 dBi. Another useful solution for long indoor corridors and tunnels is an antenna with bi-directional horizontal pattern. For open offices, an omni-directional antenna can be the most preferred solution.

2.5.5 Tools

There are few indoor planning tools available in the market. With these tools, the signal propagation can be modeled usually based on ray-tracing when the building layout is imported and all the parameters describing the materials and obstacles are given. From experience, the modeling is still

a) b) c)


known to be very challenging especially in complicated buildings. This is why the indoor planning is mostly done by experimental measurements using a test transmitter. See Chapter 4.

REFERENCES

[1] Universal Mobile Telecommunications System (UMTS), BS Radio Transmission and Reception (FDD), 3GPP TS 25.104.

[2] Several antenna and cable manufacturers´ product specifications. [3] J. Lempiäinen, Assessment of Diversity Techniques in a Microcellular Radio Propagation

Channel, Doctoral Thesis, Helsinki University of Technology, 1999. [4] H. Holma, D. Soldani, K. Sipila, Simulated and Measured WCDMA Uplink Performance,

IEEE 54th Vehicular Technology Conference, vol. 2, 2001. [5] J. Lempiäinen, J. Laiho-Steffens, The Performance of Polarization Diversity Schemes in

Small/Micro Cells at 1800 MHz, IEEE Transactions on Vehicular Technology, vol. 47, no. 3, August 1998.

[6] H. Holma, A. Tolli, Simulated and Measured Performance of 4-Branch Uplink Reception in WCDMA, IEEE 53rd Vehicular Technology Conference, vol. 4, 2001.

[7] J. Laiho, A. Wacker, T. Novosad, Radio Network Planning and Optimisation for UMTS,John Wiley & Sons Ltd, 2002.

[8] Universal Mobile Telecommunications System (UMTS), UE Radio Transmission and Reception (FDD), 3GPP TS 25.101.

[9] K. Pedersen, P. Mogensen, The Downlink Orthogonality Factors Influence on WCDMA System Performance, IEEE 56th Vehicular Technology Conference, vol. 4, 2002.

[10] A. Toskala, and H. Holma, WCDMA for the UMTS, John Wiley & Sons Ltd, 2000. [11] K. Sipila, M. Jasberg, J. Laiho-Steffens, A. Wacker, Soft Handover Gains in a Fast

Power Controlled WCDMA Uplink, IEEE 49th Vehicular Technology Conference, vol. 2, 1999.

[12] W. Jakes, Jr. (ed.), Microwave Mobile Communications, Wiley-Interscience, 1974. [13] Universal Mobile Telecommunications System (UMTS), UTRA Repeater; Planning

Guidelines and System Analysis, 3GPP TR 25.956. [14] S. Harju-Jeanty, Space Diversity in Indoor WCDMA System, Master’s Thesis, Tampere

University of Technology, 2002.

Chapter 3

DIGITAL MAPS A key feature for a successful radio network planning

KIMMO KANTO FM-Kartta Oy

Abstract: Up-to-date and precise geographical information, i.e., land-use information and an accurate elevation model of the planning area, is essential for successful radio network planning. This chapter presents the digital map production process, geographical information accuracy, and the applied use of digital maps in radio network planning. Different mapping methods and fundamental cartography principals are discussed. Telecom maps in selected resolutions are described with a few examples. The map ordering process, map quality, and copyright issues are also discussed.

Key words: Digital map, geographical information system, coordinate systems, projections, datum, topographic information, morphographic information, aerial photography, satellite image

79



80 UMTS RADIO NETWORK PLANNING, OPTIMIZATION AND QOS MANAGEMENT

3. DIGITAL MAPS

The telecommunication industry uses geographical information products in a variety of tasks, from business proposals through the dimensioning, coverage planning, network design, and implementation phases to the final site acquisition and in some cases a in line-of-sight analysis [1-2]. Digital maps are commonly utilized to predict radio wave propagations in natural and built-up environments [1]. To achieve reliable prediction results, and moreover to be able to plan a radio network successfully, up-to-date and accurate geographical information is needed. Digital maps play a key role in a radio network planning, since the use of high quality telecom maps helps in planning the network and considerably lowers the investments in planning [2].

3.1 Mapping purpose

The objective in digital map production is to simplify and model environmental properties that have an effect on radio wave propagation. Since electromagnetic radiation is affected by terrain height variations and surface properties [3], all natural elements, such as water surfaces, forests, canopies, and open grasslands, influence radio wave propagation [4]. The estimations of signal propagation loss or wave propagation prediction are calculated by using a specific terrain model and simplified morphographical information. A terrain model presents the surface topography, and a morphographic model presents variations in terrain type.

The criteria for a useful map are sufficient mapping resolution, mapping accuracy, and age of the source material used. A useful map is also compatible with other material about the planning area, available in a correct coordinate system, and in a proper data format.

Digital maps for the telecommunication industry are commonly provided as off-the-shelf products, or they are produced from scratch specially made for a certain operator or planner. Archived databases such as off-the-self products can be updated or modified as necessary for the planning application and when suitable source material for the map modification is available. Such digital maps are ready for use on short notice, but sometimes they may lack a needed information layer or they may be insufficient in their coverage area. Another alternative is customized products, which take more time to produce but are typically more suitable for an operator’s planning application. Digital map production methods are similar in both products, but they do vary because of the mapping resolution used and the source materials available.

DIGITAL MAPS 81

3.1.1 Map description

Digital raster maps or digital models are commonly characterized by their information content and mapping resolution used. Information content is typically either topographic or morphographical information. But in some specific cases, other information, such as traffic densities, can be included in geographical information layers. Different mapping resolutions are used to model different planning environments. Radio planning tools utilize coarser resolution maps in a macrocellular environment than in a microcellular environment, and thus a different mapping resolution is used, for instance, for countrywide areas than for municipality regions. The mapping resolution used defines the smallest picture element of the digital map and commonly the amount of detail in the digital map. Information content is thus related to the final resolution of the digital map. A higher resolution model introduces more detailed information about surface properties than medium or coarse resolution models. Even though a coarser digital map used for macrocellular planning can have tens of different land cover classes, detailed features such as single buildings or smaller rivers are presented only in the high resolution models. Digital maps can be produced with different mapping resolutions and mapping accuracy levels by using different source materials.

Digital maps used in a macrocellular environment have a typical resolution of 10 to 100 meters. Maps for microcellular planning areas are in the order of a few meters, from 1 to 10 meters. A comparison of map resolutions is illustrated in Figure 3-1. From this comparison, it is evident that by decreasing the pixel size, or by increasing the spatial mapping resolution from 10 to 1 meter, the number of pixels is multiplied by 100. This means that the lower the map resolution, the larger the digital map file size.

Figure 3-1. Raster data resolution comparison between 1 – 30 meters.

Even if the map resolution is increased a hundred times, it does not mean that the information content will increase by the same amount. Map


resolution is often considered to be the same as data accuracy. This is not always the case, as it is common that the smallest mapping unit differs from the digital map data resolution. Up to a certain threshold value, the resolution of the digital map improves the coverage prediction results. Beyond that value, a higher resolution means a larger amount of data, which can complicate and delay the calculation process. As mentioned earlier, the macrocellular and microcellular models utilize different mapping resolutions. The required information accuracy for macro- and microcellular prediction models is a function of radio wave frequency. Examples of the accuracy recommendations for macro- and microcellular models are presented in Table 3-1 [5]. The stated accuracy requirement for topographic information is better than 1/5 of the map resolution; that is less than a 2-meter vertical error in a 10-meter map [3, 6].

Table 3-1. Recommendations for macro- and microcellular model accuracy. Spatial (xy) accuracy threshold values are given for different propagation environments [5]. Model Frequency Dense Urban Urban Suburban Rural

Macrocellular 1800 MHz 10 – 20 m 25 – 50 m 25 – 50 m 50 – 100 m Microcellular 1800 MHz < 10 m < 10 m - -

The digital maps used in telecom applications are just one of the many applications of geographical information data. Since geographical information data can be produced with diverse methods using different source data, it is also possible to produce digital maps from various source data and still meet the accuracy limits given above. In this introduction to the digital map production process, different source data sets such as existing Geographical Information System (GIS) databases, printed topographical maps, aerial photographs, and optical satellite images are presented. The use of these source materials is described in detail with examples in the digital map layer sections. Selected source data attributes and digital map resolutions produced for different source data are shown in Table 3-2.

Table 3-2. Selected source data attributes. Satellite image resolutions are given for panchromatic and color channels separately. Type of information Source data Scale or Resolution Produced model

GIS data and maps: Printed maps 1:1000 – 1: 200 000 1 – 200 m Aerial images: BW, color, IR 1:1 000 – 1: 60 000 0.5 – 25 m Satellite images: Landsat ETM+ 15 / 30 m 20 – 200 m Spot 4 10 / 20 m 10 – 50 m Terra / Aster 15 m 15 – 50 m Spot 5 5 / 10 m 5 – 25 m Eros A1 1.8 m 2 – 10 m Ikonos 1 / 4 m 1 – 10 m

DIGITAL MAPS 83

Type of information Source data Scale or Resolution Produced model

Quickbird 0.61 / 2.44 m 1 – 10 m

From Table 3-2, it should be clear that several different source data variations are available for telecom applications. In Table 3-2, satellite images are defined with two different resolutions. This is due to two different imaging sensors.

3.1.2 Map production process

Source material selections define most of the processing methods used in digital map production. In Figure 3-2, the overview of the digital map production process is illustrated.

Figure 3-2. Universal production process scheme.

In this egg-shaped figure, the outer rim presents quality guidelines that should continuously improve the production process. All digital map production processes are included in this circle. The production process


starts and ends with interaction with the customer. The definition phase, i.e., the contract and project plan of the process, is used to specify the area of interest, choice of proper mapping resolutions, and source data types to be used.

It is usually recommended to start the map purchase process with a proper Request for Quotation (RfQ), which will be sent to potential map suppliers. Another strategy might be that the planner uses a trusted map consultant who acts as an advisor and searches for the best-suited existing digital map data sets and feasible source materials such as satellite and aerial images, etc., which could be used to fulfill the request, taking into account quality, accuracy and timetable requirements. The map consultant then integrates the available data and delivers it in the required map format of the planning tool to the client.

The RfQ should include at least the following requirements: – region of interest, – map resolution, – clutter classification, and – delivery schedule.

The number of processing phases and interim products during the production process are related to the selected source data and the produced information content. All individual production phases include a production fragment, a quality control, and results. Production processes and interim products are discussed in detail in the section on digital map layers.

3.2 Mapping methods

Mapping methods can be divided into primary and secondary methods according to the data acquisition method used [7]. Land surveying, photogrammetric mapping and remote sensing are primary data acquisition methods [7], since only direct imaging or actual measurements from the field are performed. Traditional land surveying using GPS measurements is a very accurate and precise mapping method but less cost-effective than two remote sensing methods. Whereas land surveying is practical for local mapping applications, aerial photogrammetry and spaceborne satellite imaging are more suitable for large area mapping [8].

Digital maps can also be produced by using so-called secondary data acquisition methods such as paper map scanning and manual digitization. These methods are called secondary since they utilize data that has already been manipulated in one way or another. Printed maps are commonly produced using photogrammetric methods and can be used for digital map production if they are proven to be current and spatially correct.

DIGITAL MAPS 85

3.2.1 Land surveying

Geodetic surveys are accurate but time-consuming mapping methods and are especially not used for large area coverage applications such as macrocellular telecom applications. Measurements are made in the field with electronic tachymeters, differential GPSs and Inertial Survey Systems [7]. Land survey methods are used in photogrammetry and satellite remote sensing mapping to gather geodetic control points for precise image orientation and image rectification.

3.2.2 Photogrammetric mapping

Photogrammetric mapping using vertical aerial images is an accurate and universally used mapping method, and it is especially suitable for topographic map production. Aerial images used in photogrammetric measurements are often acquired by local governmental or military authorities and in some cases by private companies. These aerial image acquisition campaigns are often controlled by local regulations. Regulations may cause limitations for any planned project time schedule and areal coverage.

The photogrammetric mapping process includes different phases starting from the project implementation defined in the flight plan. The flight plan includes information about areas to be photographed, used flight routes and flight altitude, photo scale and photo overlap percentages. A flight plan is needed for all flights, and special permission has to be requested for areas near national boarders or areas close to military bases. This means that all aerial imaging campaigns must be planned well in advance to meet all regulations and the most appropriate time window for image acquisition. Limitations are due to light and atmospheric conditions such as cloudiness and haze or pollution. These conditions reduce the amount of information available from the photographs. For example, the most convenient time for aerial image acquisition in the Nordic countries is after snow has melted and before trees have sprouted their leaves.

Before the aerial photography campaign, the ground control points are commonly marked with a white cross and the position is measured by GPS. This will help the control point locations to be shown in low-altitude photographs. In some cases, existing GPS-measured points, such as building corners that are identifiable on the image, can be used to replace these signalizing marks.

After successful image acquisition flights and the necessary photo processing phases, the films are scanned at the desired resolution. The


spatial resolution of the produced aerial photograph is a function of the scanning resolution and original photo scale.

Scanned images are imported to image-processing software for height measurement and triangulation. Stereophotogrammetry is a 3-dimensional method of measuring geographical objects from a pair of aerial photographs by using a stereo workstation called a digital plotter. Stereo models are used to measure terrain topography and other relevant information such as building outline vectors, forests, roads, and rivers.

Aerial triangulation is a triangular survey based on aerial photographs to minimize ground survey work. Images are adjusted and tied to the ground coordinates using accurately measured ground control points. Images are ortho-rectified by using ground control points and additional photo tie points derived by triangulation. An orthophotograph is a geometrically rectified aerial photograph at a fixed scale. In orthophotographs, projection and perspective distortions due to camera angle and difference in ground elevation have been eliminated. These orthorectified aerial photographs are signed into a known coordinate projection corresponding to a map, but the information has not been generalized or interpreted. Such orthophotographs can be utilized as source data for screen digitations or as backdrop images in a planning tool. Orthorectified aerial images are used to digitize on-screen geographical information in two dimensions. Adjacent orthophotographs can be fused together to produce a photo mosaic that covers a larger area.

Imaging scale is associated with the camera properties used and the flying altitude. The higher the plane flies, the bigger the image coverage and, the lower the image resolution. An aerial imaging system is depicted in Figure 3-3.

Figure 3-3. An aerial photography scale is defined by the camera focal length and flying altitude. For central projection camera systems like the above, distortion is introduced at the edges of the photograph due to the changing viewing angle compared to the vertical view.

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If using aerial photographs as source data for any map production, the photo scale and quality of the photographs, production technology, and year of exposure should be known. Archived aerial photographs can be used if they are suitable by their scale, image type, and imaging date. New images are needed if archived photographs do not exist, the area of interest has been changed, or the image scale is too small, i.e., the resolution is too coarse. Sometimes the scale is too large which means there will be too many photos to handle. This can be overcome by using a smaller image scale.

Aerial images can also be used in stereo workstations. Stereo imaging is used if there is a need for terrain elevation or object height measurements. Stereo image acquisition is conducted so that the overlap between images is normally 60% in the flight direction and 30% across the flight line, as illustrated in Figure 3-4.

Figure 3-4. Stereo image acquisition of 60% and 30% overlap between images.


3.2.3 Satellite remote sensing

Spaceborne remote sensing images have been used extensively for decades for earth observation applications such as weather monitoring and worldwide vegetation mapping. Through satellite technology development, sensor resolutions have been improved making it possible for the other more detailed earth observation applications to utilize remote sensing data.

Remote sensing methods are divided into two groups: active and passive methods. Active remote sensing methods, such as radar, use their own energy source to produce the necessary electromagnetic radiation and measure the amount of microwave energy returned from the target. The advantage of radar is its ability to collect data during the night and through cloud cover. The limitations of the radar imaging are complexity of the data interpretation and large energy consumption during imaging. Radar satellites currently in operation are the Canadian Radarsat, the European ERS, and Envisat. Correspondingly, passive remote sensing methods measure the radiation reflected and emitted from the earth in optical and infrared wavelengths. For optical satellite images, the following issues should be taken into account: satellite and sensor properties, image resolution, image channels, quality of the image, production technology, spatial accuracy, age of the image, and atmospheric conditions.

Satellite remote sensing has the advantage of producing timely geographical information over large planning areas. Different satellites acquire data using different resolutions and methods. Satellite images can be used to produce most of the topographic and morphographic models needed in network planning. Radar and optical stereo images can be used to produce topographic information or digital elevation models, and optical images can be used to produce morphological information. Radar processing methods for land-use classification are under development. Unfortunately, for the urban mapping applications, it has been shown that the spaceborne interferometric radar technique does not work properly in closely built-up areas due to radar shadows and multi path backscattering [6]. A detailed discussion about radar technology is outside the scope of this chapter and will not be addressed further.

3.2.3.1 Image interpretation

Morphological information is commonly produced using multi-spectral imagery. A multi-spectral image can be analyzed and classified by visual interpretation or by using pattern recognition algorithms. Optical satellite image interpretation can be difficult without accurate reference material of

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the object. This ground truth information can be acquired by field surveys, digitized from maps or from higher resolution aerial photography [8].

Visual interpretation of satellite imagery is conducted as on-screen digitizing after appropriate image restoration and enhancements. Image enhancement improves image the contrast and color information of the mapped features and objects. An example of extensively used Landsat 7 ETM+ satellite image channels is presented in Figure 3-5. This satellite captures an image in eight different bands from visual to thermal infrared wavelengths [9]. In Figure 3-5, bands 1-5, 7, and 8 are illustrated; color composites of bands (3, 2, 1) and (7, 5, 2) are presented. Channel 6 is a thermal infrared channel and is omitted since it has little use in telecom applications.

Statistical pattern recognition methods can be divided into unsupervised and supervised classification methods. In the unsupervised classification methods, image statistics are calculated and image data is categorized into statistically distinct classes. After an unsupervised classification run, an image analyst merges similar classes into meaningful classes and names them by using the ground truth information. In the supervised classification, the image analyst points out typical land cover classes from the image before running the classification. Statistics for each class are calculated and the rest of the image is classified based on these pre-selected values. The classification algorithm seeks all areas that have similar spectral properties as training areas and classifies pixels to this land cover type [8]. The final classification result can be a combination of the unsupervised, supervised, and visual methods. Field measurements and checks in the target area are mandatory if no up-to-date reference information about the land cover is available. The accuracy of the classification results can be calculated by using a standard error matrix. In the error matrix, the classified image is compared with reference data and the results are shown in percentages for each land-use type.


Figure 3-5. The Landsat 7 ETM+ spectral channels. Vegetation appears bright in near infrared channels and dark in shorter wavelengths. Urban area is partly in view on the right.

Water absorbs most of the radiation and appears dark in all channels.

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3.2.4 Maps and databases

The production process using printed maps is time-consuming. It includes scanning, vectorizing, digitizing, and additional data manipulations such as coordinate transformations, format conversions and corrections, classifications and integration of the data. Products derived from paper maps can be geographical information databases or value-added digital maps. With printed maps, the following issues should be taken into account: scale of the map, source material compilation, production year, content and quality of the information.

If existing digital geographic databases are used as source material for new digital map production, the following aspects of the database should be known: database source material, database contents, mapping scale and accuracy, database classification, format and coordinate system, production date, and all licensing issues. The availability of digital geographical information databases varies in different countries. The content and type of existing data varies a lot as well. In the optimal case, an up-to-date database is available in vector format thus saving production time and resources. Accurate vector map data is rare in most parts of the world, especially in developing countries.

3.3 Coordinate systems

This section introduces fundamentals of cartography by defining basic coordinate systems and different projection types. The coordinate systems are commonly divided into two categories: geographic and Cartesian coordinate systems.

The geographic coordinate system is defined by using a reference ellipsoid consisting of latitude (parallels – angle between the surface location and the equator measured from the earth’s center) and longitude (meridians – angle between the surface location and the Greenwich meridian). Coordinates are given in degrees. Locations below the equator or west of the prime meridian are designated as negative. Locations north of the equator and east of the prime meridian are designated as positive. This geographic coordinate system is called also the spherical coordinate system.

Maps are most commonly presented in the Cartesian coordinate system. In this system, locations from the earth’s surface are projected onto a two-dimensional plane. Coordinates are typically given in meters, i.e., east and north from the origin. This makes it much easier to work with a Cartesian coordinate system on a map, since distance and direction calculations are simpler than with a geographic coordinate system.


3.3.1 Map the projections

In surveying and cartography, the earth’s surface is replaced by an ellipsoid or sphere that approximates the natural surface of the earth in overall shape, especially the general curvature. In the computation of map projections, the earth ellipsoid or sphere is called the datum [10].

Transformations between the three-dimensional earth curvature and a two-dimensional map are called projections. The change in dimensions inevitably distorts at least one of the following properties: shape, area, distance, and direction. Different projection systems have evolved according to the scale and purpose of the map. There is no single ideal map projection for all mapping applications. In telecom applications, digital maps are used to derive site locations, so the shape, or horizontal angles, must be accurately preserved.

A certain projection for a local area is defined only together with associated projection parameters like the geodetic datum, i.e., the approximation of the earth’s shape [10]. A geodetic datum consists of two major components. First by ellipsoid and origin, and secondly by points and lines surveyed using the best methods and equipment [11]. An ellipsoid has a major axis and a minor axis. The major axis is longer than the minor axis. The earth’s ellipsoid is obtained as a curved surface in which a plane ellipse is rotated about its minor axis [10]. Mathematically, an ellipse is defined [11] by the length of its semi-major and semi-minor axis, a and b (Figure 3-6). The difference in polar and equatorial radii can be described by the flattening factor.

Figure 3-6. The semi-major axis and semi-minor axis of the ellipsoid [11].

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A commonly used geocentric datum is the World Geodetic System 1984 (WGS84). This datum serves as a framework for supporting location measurements worldwide. GPS measurements are also based upon the WGS84 datum.

The earth’s natural surface varies slightly from the mathematically smooth surface defined by an ellipsoid. Variations between the reference ellipsoid and true elevation are due to local variations in gravity, which are caused by the differences in the density and distribution of materials in the interior of the earth. This undulating shape is called a geoid. Over most of the earth, the geiod varies by less than 100 meters from the reference ellipsoid. Geoidal variation in the earth’s shape is the main cause for different ellipsoids being employed in different parts of the world. The geoid is used as a vertical reference. Heights are therefore typically defined relative to the geiod. The geiod is a measured and interpolated surface, not a mathematically defined surface. In Figure 3-7, different surfaces - the ellipsoid, the geiod, and the earth’s natural surface - are presented relative to each other.

Figure 3-7. Three different surfaces used to define a position on the earth [11].

Projections can be divided into three main categories: azimuthal, cylindrical and conical (Figure 3-8). For azimuthal projections, from a spherical coordinate system, circles of equal distance can be projected onto circles concentric around the center, and verticals can be projected onto straight lines passing through the center of these circles. The angle separating any two verticals is equal to the corresponding separation angle on the sphere [10, 12].

For cylindrical projection, parallels are projected into horizontal parallel lines and meridians are projected into vertical parallel lines, the interval between two meridians being in direct ratio to the corresponding difference in longitude [10].

For conical projections, geographical coordinate system parallels can be projected as concentric arcs, and meridians can be projected as a set of equally-spaced lines passing through the center of the circles. The angle of


separation of two meridians is in direct ratio to the corresponding difference in longitude [10].

Figure 3-8. Typical map projections. A tangent is used when a sphere contacts a single point or along a line. A secant is used when the surface is cutting or intersecting the sphere [13].

In Figure 3-8, the example cylindrical projection is also known as a Mercator projection. This projection is a conformal projection where local angles are maintained. The conformal projections listed in Table 3-3 are commonly used in general reference maps, since they do not distort local shapes or areas too much. An example of a conformal cylindrical projection is the Universal Transverse Mercator projection (UTM). A UTM projection is similar to a Mercator projection except that the cylinder is transverse. In a UTM projection, the central meridian is selected for the region to be mapped. The world is divided into 60 zones that are 6 degrees wide and have their own central meridian, like zone 35 with a central meridian at 27°E. Centering minimizes distortion of all properties in that region. A Transverse Mercator is often used in projection for countries that stretch north to south but are narrow from east to west. Commonly used projections and variations of the three main projections are summarized in Table 3-3.

Table 3-3. Summary of common map projections based on type of projection surface and geometric properties [13]. Surface Plane Cylinder Cone

Property Azimuthal - - Perspective Gnomonic - - - Stereographic - - - Orthographic Equivalent -

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Surface Plane Cylinder Cone

Equidistant Azimuthal Equidistant Equirectangular Simple Conic Conformal Stereographic Mercator Lambert Conformal Conic Equivalent Lambert Equivalent Orthographic Albers - - Sinusoidal Bonne’s - - Mollweide -

Combining data between two different datums can and will introduce error on spatial coordinates. Differences may be small (less than a meter for certain locations) but shift can sometimes be a few hundred meters. Thus, care should be taken not to merge spatial data across different datums unless the magnitude for the datum shift has been established for the area of interest, and this magnitude is considered small relative to overall data use and accuracy specifications. If maps have to be combined together, they must be converted or transformed before integration.

Transformation, also known as rectification, is a computational process of converting a raster image or map to the required coordinate system. Simple affine transformation is a combination of linear transformations and translation. Affine transformation involves rotation, translation, and scaling of grid cells, and thus requires resampling of original values. An affine transformation is a simple and often used transformation method between two Cartesian coordinate systems in areas where datum difference is small. It is especially useful in a basic image rectification process, since only a few known coordinate points in both systems are needed. The basic property of an affine transformation is that parallel lines remain parallel [14] and mapped objects maintain their mapped form. Detailed descriptions about the more complex coordinate transformations are presented with equations in the reference literature [10].

3.4 Digital map layers

Geographical information consists of spatial information and attribute information. Spatial information describes the location of the mapped object, and attribute information describes the properties of the mapped feature. Location is defined by the chosen coordinate system, and attribute information by numerical or alphanumerical data related to the associated data description. Attributes can be either information about physical properties of local features, i.e., land-use class or terrain height, or more abstract information about demography which could be used when estimating radio traffic density.

Geographical information in a network plan is normally presented as a raster data layer. Raster data is built by pixels sized at a given resolution.


Raster data is divided horizontally by columns and divided vertically by rows. In raster layers, locations are defined in a regular matrix structure and header information. Each pixel has only one value per layer that defines the property of the pixel. In a topographic layer, height information is presented; and in a morphographic layer, different land-use classes are presented according to the radio wave propagation environment. Morphographical information describes the environment with aspect to radio propagation [4], and therefore classification results differ from typical soil and vegetation classifications. High resolution models are normally produced with a more detailed building layer [2]. A building layer can be presented either in raster or vector format. A vector layer is also used for roads, coastlines, and other necessary linear features. In vector format spatial information is built with points, lines, polygons, circles, arcs, and so on.

Digital maps exist in many resolutions with a variable number of raster layers. The resolution requirements are connected to the planned frequency band and planning area environment [2]. Digital map suppliers classify maps by their resolution, from wide-area coverage to high-resolution city models. Countrywide maps are normally coarse, having 20–200 meter resolution with 4–15 land-use classes. Basic land-use classes include water, forest, agricultural, suburban, open land and urban (Figure 3-9). The number of classes can be increased but additional classes are case-dependent. Variable satellite images and printed paper maps at a scale of 1:25 000 – 1:200 000 can be used as source data.

Figure 3-9. Attenuation value estimates by land-use classes from left: water, forest, agricultural, buildings, open and tall buildings.

Medium resolution models are commonly produced at 10–20 meter resolution. Natural land-use classes are similar to low-resolution models, and built-up areas are defined by building blocks with an associated height class.

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Source data can be aerial images, variable satellite images, and printed paper maps at a scale of 1:10 000 – 1:25 000.

The resolution of high-resolution city models is typically better than 10 meters. The number of land-use classes can be higher than for a medium resolution model. Basic city model classes include information about different natural vegetation types with heights, street locations and widths, buildings with heights and even building material classes [3]. In addition, different rooftop properties can be shown. Source material can be aerial images, high-resolution satellite images, and printed paper maps at a scale of 1: 2 000 – 1:10 000.

3.4.1 Topographic layer

Topographic information is used to define terrain and surface elevations. The digital elevation model, also known as DEM, DTM (digital terrain model) and terrain height, is used to calculate propagation loss due to natural terrain variations. The quality of topographic information, or DEM, is an essential factor for its successful use. The production method and source material selection are key features when producing high quality elevation models. The quality of a good DEM consists of integrity, accuracy and authenticity. Figure 3-10 shows an example of a 5-meter resolution digital elevation model. In Figure 3-10, height information is presented by two different methods: on the left, heights are presented as 16-bit grayscale values, and on the right the same data is presented with a sunshade effect.

Figure 3-10. A digital elevation model of 5-meter resolution in two different presentations. The area presented is around the city of Helsinki. (FM-Kartta)


3.4.1.1 Use of a terrain model in radio planning

Topographic information is used in radio planning to predict coverage area [2]. A topographic layer is utilized together with a morphographical layer in coverage planning to optimize the number and locations of the sites. This is done with the propagation models included in the planning software. Calculated propagation results are used as input parameters for later planning phases such as the capacity planning phase. According to geographical information usage, coverage planning is the most important planning phase.

Topographic information is typically presented in raster format with variable resolutions. Produced raster resolutions vary from 1 meter to 200 meters. The resolution used depends on the frequency band and planning area environment. The most accurate data, a data resolution of 1 meter to 5 meters, is used in microcellular planning for dense urban areas. Terrain models can be visualized as intensity values or sun-shaded relief.

3.4.1.2 Topographic information production process

The digital elevation production process is illustrated in Table 3-4. Production methods are related to the source data, which can be stereo images or topographic maps. Images are processed by stereophotogrammetry methods, and topographic maps are processed through elevation contours digitization.

Table 3-4. Topographic information production process. Production phase Information

Source data selection Stereo aerial images, stereo satellite images, topographic maps, contour lines, spot heights, break lines, existing databases

Production system selection Stereophotogrammetry, GIS-software Contour and point measurements Data compilation

Stereo models, manual or automatic methods Measured and existing data

Coordinate system transformations From one system to another if necessary Triangulation Contours, heights, obscure areas and break

line calculations to produce a TIN-model TIN-to-Grid conversion Vector-to-raster conversion Digital elevation model for planning software Additional information

3.4.1.2.1 Source data selection

Topographic information is usually produced by using geodetic surveys, topographic maps, stereo aerial photographs, and stereo satellite images. Newer methods such as radar interferometry and laser scanning are also used. Topographic information databases can be used as well. The DEM production process by using such a database is discussed below.

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A database can include contour lines and point measurements. A contour is a line that connects points of the same height. A spot height point is a local point of elevation; it is used to improve DEM accuracy. Such a database is originally produced by using geodetic survey or stereophotogrammetry, or contours have been vectorized from printed maps. The source data used for DEM generation should be agreed on, based on the application and usability, and topographic maps of a scale smaller than 1:50 000 should be examined before production. As mentioned earlier, the accuracy of topographic information depends on map scale and image data resolution, and in some cases, contour printed in smaller-scale maps are not adequate for detailed DEM production.

3.4.1.2.2 Data processing

Data compilation and coordinate transformations are done using geographical information processing software. The available contour lines and spot height measurements are combined together with breaklines and shorelines to produce an interim dataset for triangulation. A breakline is a linear feature, such as river, that defines and controls the surface behavior of a TIN in terms of smoothness and continuity [14]. An example of a dataset with contour lines and spot heights is shown in the upper left of Figure 3-11.

Figure 3-11. Digital elevation model is produced from contour lines and point measurements (upper left). Triangulated Irregular Network with node points is shown in upper right. TIN-to-

Grid conversion (bottom) interpolates raster values from vector information.

A triangular irregular network is a terrain model based on triangles. The vertices of the triangles form irregularly spaced nodes [14]. Since most


planning tools utilize topographic information in raster mode, the TIN model is converted to the Grid model. Conversion interpolates elevation values for each discrete unit, i.e., pixel. Once converted to raster format, all topological relations of vector data are lost. An example of a raster grid without null values is shown in the lower right of Figure 3-11.

3.4.2 Morphographic layer

Geographical information gives a more accurate input of the planning area in the dimensioning phase. Normally detailed morphographic information is acquired before the “coverage planning” phase. Geographical information is used to calculate the coverage value for each pixel in the planning area. Coverage prediction results can be presented as raster images on the screen. A detailed description of a high-resolution morphographical layer, i.e., clutter, land-use, terrain type or earth coverage, is presented in the following sections. In Figure 3-12, an example of a produced clutter model is presented. A five-meter-resolution model from the city of Helsinki, Finland, is shown in color. Different land-use classes are water, trees, open, road, railways, and building with heights.

Figure 3-12. The city of Helsinki. Raster resolution is 5 meters and classes illustrate water, trees, open, roads/railways, and buildings with heights (FM-Kartta).

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3.4.2.1 Use of morphographic layer in radio planning

In coverage planning, the morphographic layer is considered the most important type of information; it is used together with propagation models and field strength measurements. Field strength prediction and measurements are needed to find out proper morphographic correction factors for the different area types to tune the propagation model. Morphographical information used in radio network planning includes fewer classes than typical land-use maps. From these land-use maps, appropriate classes can be combined and used in the digital morphographical information layer. In some cases, only typical classes are produced, but more commonly, classes are divided into main classes and their subclasses. In countrywide maps, information on water, open, vegetation, forest, and urban is presented. These classes are often divided into sub-classes such as rivers and lakes, open natural or man-made areas, different vegetation and forest types, and urban classes from residential to dense urban or high-rise buildings.

3.4.2.2 Morphographic information production process

Morphographic information can be produced by using a variety of source materials, from field surveys to remotely sensed imagery. In the following example, optical satellite images are used as source data. The production method used, satellites, and area coverage are defined for each project in the project planning phase.

Digital image processing can be divided into two phases: pre-processing and interpretation. In pre-processing, image restoration and enhancement are performed to improve image interpretability. Interpretation, i.e., information extraction, is conducted manually or semi-automatically. After the processing phases, data is handled as with any other geographical information. Table 3-5 shows these steps in the morphological information production process.

Table 3-5. Morphological information production process by using optical satellite images. Production phase Information

Source data selection Sensor properties: bands, resolution (< 1 m – 30 m) and area coverage

Image restoration Geometric distortions, noise patterns, solar angle variations and atmospheric corrections

Image enhancement Color and contrast improvements, image sharpening and fusions

Image interpretation Visual interpretation, automatic land-use classifications, vector extraction

Data management Filtering, merging and resampling Format conversion Conversion to planning tool format


3.4.2.2.1 Optical satellite image

Satellite images used are selected based on their resolution and areal coverage. The more precise the satellite image resolution is, the smaller the single image coverage area and thus the number of images needed increases. Satellite imaging has limitations because of its path, i.e., its orbit. Orbit parameters define the satellite flying altitude and location in space. Sensor parameters define the used viewing angle and used frequency bands. Image acquisition by satellite can be made depending on the area of interest. Near the poles, orbits overlap more than they do close to the equator. In all locations, image frames are identified with a path and row index. A path is a location in the longitude direction. A row is a path in the latitude direction. An example of Landsat 7 ETM+ satellite acquisition coverage is shown in Figure 3-13.

Figure 3-13. Example of Landsat 7 ETM+ scene capture schedule for one day [9].

The common optical satellite images used as source material for radio network planning applications are Landsat, Spot, Aster, IRS, Resurs, Eros, Ikonos, and Quickbird. Satellites acquire images in optical and infrared bands depending on sensor properties. Different satellite sensor resolutions are compared in Table 3-6. Single scene area coverage and ground sampling distance vary due to sensor viewing angle and orbit altitude. Satellite images can be ordered from the satellite image resellers. Suitable and cloud-free images are commonly available from archives, but if not, satellites are programmed to collect new images from the area of interest.

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Table 3-6. Sensor parameters for selected optical satellites. (*) Aster has 6 additional 30 m SWIR and 5 additional 90 m TIR channels. (**) Spot 5 panchromatic images can be processed to produce 2.5 m resolution images. Spatial resolutions are given for multi-spectral (ms) and panchromatic (pan) separately.

Satellite

sensor

Spatial

resolution,

ms and pan,

m

Swath

width,

km

Number of

ms + pan

bands

Vis

ua

l

Nea

r IR

SW

IR

Th

erm

al

IR

Ra

dio

met

ry, b

its

Rep

eat

per

iod

, d

Landsat 7 30 15 185 7 + 1 x x x x 8 16 IRS 23 5.8 142 / 70 4 + 1 x x x - 6 24 Spot 4 20 10 60 4 + 1 x x x - 8 26 Aster * 15 - 60 3 x x - - 8 16 Spot 5 ** 10 5 60 4 + 1 x x x - 8 26 Eros A1 - 1.8 13.5 0 + 1 x - - - 11 7 Ikonos 4 1 11 4 + 1 x x - - 11 3 Quickbird 2.4 0.6 11 4 + 1 x x - - 11 3

3.4.2.2.2 Image restoration

Image restoration is done to correct errors and distracting effects in digital images. Errors and distortions are commenced during image acquisition due to the moving sensor and target, atmosphere and sensor properties. Types of errors and distracting effects are geometric distortions, noise patterns, variations in solar illumination angle, and atmospheric haze. Geometric correction is performed to eliminate systematic and random distortions. These errors are normally corrected by the satellite image operator. An image analyst performs radiometric corrections, which include corrections of the solar illumination angle, radiant variations due to changes in the distance between sun and earth, and errors due to the atmosphere.

3.4.2.2.3 Image enhancement

Image enhancements manipulate image contrast and color information, thus improving visual interpretation. Enhancements are done using pixel operations that alter gray tone values. Different band combinations can be used to improve extraction from a satellite image. Landsat 7 ETM+ sensor, for example, has eight different wavelength channels or bands (Table 3-6). The sensor operates in optical, near infrared, short-wave infrared and thermal infrared wavelengths. Every channel presents a target in a different manner and thus the combination of three channels can be used to construct a red-green-blue image. For example, combining a near-infrared channel with visual channels is used to differentiate vegetation types. In Figure 3-5, two different color combinations are presented. All introduced multi-spectral satellite sensors utilize both optical and near-infrared wavelengths.


Image fusion methods can be used to combine different sensor images into one image. Fusing higher resolution panchromatic images together with multi-spectral channels can sharpen low-resolution multi-spectral images and increase information content.

3.4.2.2.4 Image interpretation

Satellite image interpretation is done both manually and semi-automatically. Manual interpretation is similar as with aerial photographs where feature extraction is done according to the shape and color of the object. In the case of low-resolution satellite images, the single object shape is distorted and a project-related classification key is used to guide the image analyst to a correct interpretation. The classification key describes different land-use classes, and each class is presented with examples. Manual interpretation is limited to linear features such as roads and narrow rivers and classes that can be automatically classified without ambiguity. Built-up areas, for example, are difficult to classify accurately using only statistical methods since their spectral signature resembles certain open-area types such as sand pits.

Automatic or semi-automatic classification methods consist of different pattern recognition algorithms. Maximum likelihood classifier is typically used in satellite image interpretation. Classification can be done using statistical class range information from reference data, or statistics can be calculated from the processed image. Classification based on pixel values is used, for example, with different vegetation types due to their typical radiance in different wavelengths.

3.4.2.2.5 Format conversion

The format of the resulting classification is related to the image-processing software. Most of the raster formats used are easy to convert to any other image format. The final map format is defined in the project plan phase.

3.4.3 Building layer

Building information is stored in either raster or vector format. In raster format, building height information is included in the pixel values. In vector format, height information is attached to vector points, lines, and polygons. Building vectors are manually interpreted from the source material used. Source material for stereophotogrammetry measurements can be stereo aerial images and very high-resolution stereo satellite images. The derived building outlines are normally simplified to optimize the building data for

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microcellular coverage prediction. This procedure can be treated as the first filtering in the production process. The building information production process using aerial photographs is shown in Table 3-7. Aerial images are chosen because they are the most useful source data for detailed building layer production.

Table 3-7. Building information production process. Production phase Information

Source data selection Stereo aerial photographs, VHR satellite images Scanning Digital copy of the aerial film Orientation Interior, exterior, and absolute orientations Stereophotogrammetric measurements Building outlines and heights in vector format Post processing Data generalization and grouping Format conversion Conversion to the utilized planning tool format

3.4.3.1 Use of the building layer in radio planning

Building information is utilized especially in microcellular planning. For example, for ray-tracing applications, accurate vectorized building information is needed.

3.4.3.2 Building information production process

The stereophotogrammetry method is used to derive three-dimensional information from aerial photography or from very high-resolution satellite images, such as Ikonos or Quickbird. Prior stereo measurements aerial photographs are scanned into digital format. Scanning is done with high-resolution scanners that convert films to digital raster images. Scanning was described previously in Section 3.2.2.

3.4.3.2.1 Aerial photograph orientation

Before stereo model measurements are done, certain photogrammetric values must be known, and therefore image interior, relative and absolute orientations are performed. Interior image orientation defines the coordinate system of the photograph with respect to the coordinate system of the camera [15]. Fiducial point locations at the corners and edges of the photo are measured and compared with related camera information, such as camera focal length and principal point location.

The relative orientation of two overlapping photographs is defined to view images in stereo mode. Before measuring the point locations and heights, it is necessary to establish the true position, scale, and tilts of the stereo model with respect to the desired terrain or object-space datum. This so-called absolute orientation is computed by using ground control points in 3D space.


3.4.3.2.2 Stereophotogrammetric measurements

Measurements for the stereo pair are done with the photogrammetric workstation, i.e., the stereo plotter. This work is mainly visual interpretation and manual digitations where the image analyst measures the building corners and additional rooftop features in the virtual three-dimensional model. In Figure 3-14, an example of an acquired stereo pair around Helsinki city center is presented. And in Figure 3-15, the derived building outline vectors from this stereo pair are presented.

Figure 3-14. Stereo pair after necessary orientations are ready for 3D building measurements. The area is around Helsinki city center and image resolution is 0.5 m (FM-Kartta).

Figure 3-15. Stereophotogrammetrically derived building vectors (FM-Kartta).

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3.4.3.2.3 Post-processing

Classification into discrete height classes is done when height information is presented in 8-bit raster format. The desired building height classes should be described in the project plan. The building classification can also be done according to building wall type, e.g., glass, concrete, and wood, or according to building usage, e.g., commercial, educational, or residential. These attribute classes are not so evident on aerial images and need some additional information from other sources and are normally done during post-processing.

3.4.4 Vector layer

Linear features such as roads and railways are presented in vector format. National and county borders and other additional information can be visualized as well. Vectors are (or should be) corrected for topological errors and categorized into correct attribute classes.

3.4.4.1 Use of the vector layer in radio planning

Vector information is used to display linear features like roads and railways. Road information is used to locate a certain planning area, tune the model, and is used in simulations of the planned network. Roads are typically classified by their type, such as highways, main roads, connecting roads, and city streets.

3.4.4.2 Vector information production process

Vector information can be extracted from variable source material. Aerial photography can be used to produce accurate three-dimensional building and other linear feature vectors. The satellite images can be used in land-use classification and map revision, and for updating coastlines, rivers, and road information. Printed maps in variable scales and coordinate systems are extensively used to extract vector information. Printed maps can be used on digitizing table for manual a digitizing or they can be scanned for digital processing. The vector information production process using printed paper maps is presented in Table 3-8.

Table 3-8. Vector information production process. Production phase Information

Source data selection Printed maps, aerial and satellite images Scanning Printed map to digital raster image conversionCoordinate system transformations Map-to-map transformations Information extraction Digitization and vectorizing Post processing Classification and topological corrections Format conversion From working format to planning tool format


3.4.4.2.1 Pre-processing

Vector information is extracted, for example, from scanned paper maps after appropriate coordinate transformations are done. In the case of printed maps, a coordinate system transformation, such as an affine transformation, is used to warp geographical data to the desired Cartesian coordinate system.

3.4.4.2.2 Information extraction

Vector information can be extracted either automatically or manually. If raster data is converted to vector format automatically by computer, the process is called vectorization. If the work is done by hand, it is called manual digitizing. Automatic vectorization is used to convert a simple, area type of raster to outline vectors. It can be used, for example, to automatically convert classified land-use classes to vector mode. Semi-automatic digitizing is a method in which the majority of the line followings are controlled by a computer and complicated places are guided by the software user. Semi-automatic vectorizing can be used, for example, to extract contour lines from a map. Automatic vectorizing can be difficult if the quality of the contour layer is not good enough or the area is a complex mountainous area. Manual digitizing is usually performed by using on-screen digitizing rather than with a traditional digitizing table.

3.4.4.2.3 Post-processing

Post-processing of derived vector information is necessary. Post-processing includes attribute categorizing, such as road type classification, and topological correction, such as road line intersections. Topological errors are common especially in manual digitizing, as seen in Figure 3-16. Inconsistencies in the vector geometry are, for example: dangle (over- and undershoot), leaking polygons, and multiple centroid.

Figure 3-16. Topological errors in vector data for dangles (left) and polygons (right). Errors indicated by arrows from left: overshoot, undershoot, leaking polygon, and multiple centroid.

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3.4.5 Additional layers

A traffic density layer is a dynamic temporal map [2]. A traffic layer showing real traffic density is seldom available for planning purposes. Traffic density varies with time, and the planning is commonly done mainly according to the busy hours in the network. If the existing network is planned further, measured mobile traffic data can be used to produce traffic density maps. For a completely new network, data from other sources can be used to produce traffic density estimates. One way is to use morphological information and road classes together to calculate subscriber distribution during the day. The land-use classes such as industrial areas and office buildings can be converted to the traffic density classes if appropriate estimates of class relations are available.

Indoor planning is commonly done by using measurements and not predictions. If using indoor propagation predictions, indoor databases are produced from architect files or from building blue prints. The production process is similar to vector information extraction from maps, discussed in Section 3.4.4. Wall vectors can be classified by type of material used: concrete, brick, plaster, wood, etc. The floor and ceiling materials are also classified.

3.5 Additional use of source materials

Geographical information layers can be overlaid with source images and information content used in planning can be improved. The morphological classes produced can be visually checked when overlaid with map or source images. Building vectors can be overlaid with an orthorectified aerial image to see how precise the outline vectors are. Since image data contains much more detail than the produced models, they can be used to adjust predictions locally. High-resolution images can be used to replace some of the field visits and the entire planning process can be done from the office. Typically, backdrop images are used for navigation

3.5.1 Backdrop images

Backdrop images can be digital maps or orthorectified image data. Backdrop images are commonly used to view prediction results on top of them. In Figure 3-17, stereo-measured building vectors, tree and water classes are overlaid with an orthorectified aerial photograph.


Figure 3-17. Derived vectors overlaid onto an orthorectified aerial image. (FM-Kartta Oy).

3.5.2 Visualizations

Data visualization can be used to study the planning area from different altitudes and directions. Visualization can help the planner see the planning area as it is and possibly provide some additional information to assist in the planning process. In Figure 3-18, an example of terrain elevation visualization is presented. Visualizations are done combining different data layers in image processing software. The second example, in Figure 3-19, shows building vectors with heights overlaid with an Ikonos satellite image.

Figure 3-18. Terrain visualizations can be produced by using DEMs and image data. In this example, optical images of SPOT 4 and Ikonos have been fused and rendered over the

produced elevation model. (FM-Kartta Oy), (Ikonos Space Imaging), (Spot CNES)

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Figure 3-19. 3D building vectors overlaid with orthorectified Ikonos satellite image. (FM-Kartta), (Ikonos Space Imaging)

3.6 Quality requirements

Geographical information can be defined as information about features and phenomena located on or near the surface of the earth. Advances in geographical information technologies, such as remote sensing and GIS, have revolutionized the way geographical information is gathered and processed. Since information is acquired remotely, it is very important to validate the methods used and accuracy of the databases produced.

Geographical data is essential for the radio network planning process. It is needed especially in coverage predictions. Raster data is used in topographic, morphologic, and traffic density information. Vector data is used to present roads, rivers, buildings, and texts. Undoubtedly, the quality of this geographical information is crucial for network planning. The digital map data on which calculations are based must be correct when predicting the propagation of radio waves with the planning tool. Better data quality enhances the ability to have a better network plan and therefore even better network quality.

The key to successful use of geographical information is knowledge of the data quality. Errors in digital maps are made during the production of the geographical information, hence these processes should be known well.

3.6.1 Geographical information accuracy and uncertainty

The geographical information quality requirements for each entity are described with positional accuracy, attribute information exactness,


completeness, and data origin. Geographical information quality elements and accuracy assessments are discussed in the following paragraphs.

Lineage [16], or data history, relates to source data acquisition and processing methods as well to conducted coordinate transformations. The age of source material is important for all geographical information, but in case of topographic information, the content does not change rapidly. How old data can be used as source material depends on the particular case. Source data should be as new as possible. In some cases, 5 years is considered maximum. Old but otherwise accurate geographical information can be very valuable if used in the map revision process. Of course, topographic information is valuable even if older than 5 years, since it does not change so much.

Positional accuracy is very important for all geographical information. It defines spatial location exactness in all directions. Positional accuracy is related to source data accuracy and map production methods [17]. In telecom applications, the need for horizontal positional (i.e., planimetric) accuracy is less than in conventional surveying applications [2]. Several steps in the map production process include positional error sources. Positional location errors in the final digital map product may cause major problems for network quality [5]. Planimetric errors may cause inappropriate base station locations, and errors in height information may cause overly pessimistic or optimistic coverage predictions. Positional accuracy should be inspected using known point locations or available field measurement data. Note that it is often necessary to convert GPS measurements or other ground truth information to the appropriate coordinate system before making an error estimate, i.e., a mean square error calculation. If such field measurements are available during the map production process, they may be used to correct positional errors and thus improve data compatibility.

Attribute accuracy [18] describes the certainty of the geographical data properties, such as the exactness of the land-use classes derived from optical satellite images. An attribute check can be done by using an error matrix. In an error matrix, accurate reference data is compared with classified digital map information. This method describes how accurately image classification is done in reference data areas, but not how good it is elsewhere in the scene. Classification accuracy has a significant influence on macrocellular coverage prediction. Classification errors may arise, for example, from using old source material in areas where new residential areas have been built. This has a direct effect on coverage prediction and the result is too optimistic if changes are not taken into account.

Completeness of the data [19] delineates the perfection of the data contents. This is an important factor when producing building and road

DIGITAL MAPS 113

vectors. Completeness is related to mapping resolution, i.e., the smallest mapping unit. This means that objects smaller than a certain threshold value defined in the project plan will not be assigned.

Logical consistency [20] compares the number of the correct attributes, objects, and their relationships to the data specifications. Topological consistency is important for the vector information. In building vectors, for example, two single buildings can be close to each other but cannot overlap. Road information should be a continuous road network without topological errors, as illustrated in Figure 3-16. All road lines or edges should meet at exactly the same coordinates in the intersections or nodes, and all road lines should intersect only at node points [5].

Semantic accuracy [17] outlines how well the data describes the reality. Semantic accuracy refers to the characteristics of the geographical objects.

3.6.2 Map production quality and licensing

For a geographical information producer, the overall producing quality consists of the quality of the final product, the production personnel involved, production methods, and production tools and software. Quality control during map production includes, e.g., source material verification, production phase control, final product verification, process documentation, production method validation, production tools testing, training, research, and development.

The quality of the source material must be verified, and possible risks of utilizing the material should be listed. The main criteria for usable source material are its accuracy and age. Important factors for each source data are presented in Section 3.4.

Intermediate quality checks are to be performed during the production process. These are conducted for each interim product generated during the project. The production process is documented in detail by internal quality control.

Delivery is the last process in the production chain and therefore one of the most important. The final product must fulfill the customer’s needs in quality, delivery time, and price. A detailed product description and production documentation should be delivered to the customer as well. Before delivery, the product should be checked with a system or planning tool similar to one that the customer uses. In a project that includes thousands of files, this is very important since importing digital map data to the customer’s system can be time-consuming and should be done only once for each data set.

The production methods should be efficient and based on exact, scientifically-tested methods. The production methods used and instructions


should be defined in the project plan. Sometimes tight schedules require a very fast production process, which requires optimal methods to be selected, and quality must be sacrificed in order to meet deadlines. It should be noted that the professional staff plays a key role in a successful geographical information production.

Usually the copyright for a digital map remains the property of the map creator, who only sells a license to use the map, just as most computer software products are sold. This means the purchaser is only allowed to use the map data for internal purposes and is not allowed to pass the data to third parties without the specific consent of the copyright owner. The terms of the license agreement or Non-Disclosure Agreement (NDA) varies among suppliers, but the main objective is to protect the rights of the copyright owner against illegal use of the data.

REFERENCES

[1] J. Lempiäinen, M. Manninen, Radio Interface System Planning for GSM/GPRS/UMTS,Kluwer Academic Publisher, 2001.

[2] M. Metsälä, Geospatial Raster Analyses in Mobile Phone Network Planning, Licentiate’s Thesis, Helsinki University of Technology, 2001.

[3] ITU-R Recommendations, Propagation Data and Prediction Methods for the Planning of Short-range Outdoor Radio Communication System and Radio Local Area Networks in the Frequency Range 300 MHz to 100 GHz, ITU-R P.1411-1, 1999.

[4] V. Garg, Wireless Network Evolution: 2G to 3G, Prentice Hall, 2002. [5] E. Tiihonen, Geographical Information and Its Quality in Radio Network Planning,

Master’s thesis, Helsinki University of Technology, 1997. [6] T. Turkka, Radioverkkosuunnittelussa Käytettävän Paikkatietoaineiston Tuottaminen

Kaukokartoitusmenetelmin, Master’s Thesis, Helsinki University of Technology, 2002. [7] K. Thapa, R. Burtch, Issues of Data Collection in GIS/LIS, Technical Papers, ACSM-

ASPRS Annual Convention, Vol. 3, 1990. [8] T. Lillesand, R. Kiefer, Remote Sensing and Image Interpretation, 4th ed., John Wiley &

Sons Ltd, 2000. [9] USGS, Landsat 7 Science Data Users Handbook, 2002. http://landsat7.usgs.gov/ [10] Q. Yang, J. Snyder, W. Tobler, Map Projection Transformation: Principles and

Applications, Taylor & Francis, 2000. [11] P. Bolstad, GIS Fundamentals: A First Text on Geographical Information Systems, Eider

Press, 1997. [12] J. Snyder, Flattening the Earth: Two Thousand Years of Map Projections, The

University of Chicago Press, 1993. [13] C. Jones, Geographical Information System and Computer Cartography, Longman,

1997. [14] Association for Geographical Information, GIS Dictionary, 1999. [15] C. Slama (ed.), Manual of Photogrammetry, 4th ed., American Society of

Photogrammetry, 1980.

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[16] D. G. Clarke, D. M. Clark, Lineage in S. Guptill, J. Morrison (eds.), Elements of Spatial Data Quality, 1995.

[17] S. Guptill, J. Morrison (eds.), Elements of Spatial Data Quality, Pergamon press, 1995. [18] J. Zhang, M. Goodchild, Uncertainty in Geographical Information, Taylor & Francis,

2002. [19] K. Brassel, F. Bucher, E-M Stephan, A. Vckovski, Completeness in S. Guptill, J.

Morrison (eds.), Elements of Spatial Data Quality, 1995. [20] W. Kainz, Logical Consistency in S. Guptill, J. Morrison (eds.), Elements of Spatial Data

Quality, 1995.

Chapter 4

RADIO NETWORK PLANNING TOOLS Tool environment requirements

HANS AHNLUND European Communications Engineering (ECE) Ltd

Abstract: The radio planning tool environment is an important factor in planning, optimizing and managing a UMTS network successfully. Tools that support the overall radio interface planning process are needed. This implies that the tools must address a variety of functional high-level key areas like design, analysis, measurement collection, and data management. This chapter addresses the key requirements of a UMTS planning tool environment for these high-level areas, and it also addresses particular requirements to support the radio interface planning process in a UMTS network.

Key words: Bit rate definition, Ec/I0, multi system radio network planning, multi vendor, pilot pollution, scanner measurements, service, static simulation, terminal, traffic layer generation, user equipment measurements

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4. RADIO NETWORK PLANNING TOOLS

In this chapter, the tool environment used for radio interface planning of UMTS networks is introduced. A variety of tools can be found on the market. The intention here is to explore the main features needed to expect from these tools in order to successfully accomplish the task of planning/optimizing and managing QoS in a UMTS network.

Subsequent sections present particular requirements in each key area of the radio network planning tool environment.

4.1 Radio network planning tool environment

A radio network planning tool environment consists of one or more integrated hardware and software systems whose primary function is to support the overall network planning process. For readability, integrated hardware and software systems are simply referred as tools. Furthermore, these tools run in standard operating system and hardware environments. The network planning tool environment can be divided into four high-level key areas. These areas are network design, measurement, analysis, and data management. A radio network planning tool environment will require tools from all these key areas to support the overall network planning process. (See Chapter 1.) These key areas are listed below: – radio network planning design – radio network planning measurement – radio network planning analysis – radio network planning management

In design, typically such as network dimensioning and configuration tools, network design, and implementation tools are used. Dimensioning and configuration is covered earlier in Chapter 2. A network design tool aids, for example, in NodeB footprint prediction. Requirements for a design tool are presented in Section 4.2.

In measurement, tools for drive test data collection and network performance statistics data collection are needed. Requirements for a measurement tool are presented in Section 4.3. UMTS radio interface measurements are further described in Chapter 7.

In analysis, there are tools for measurement analysis and network design analysis, e.g., service and capacity criteria evaluation. Requirements for analysis tools are presented in Section 4.4. A protocol analyzer is important for complete management of QoS in a UMTS network and is further elaborated in Chapter 8.

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In management, tools for tool system management (e.g., tool administration), tools for information and data management (e.g., report tools), and tools to manage seamless data compatibility and the inter-working between tools in the radio network tool environment (e.g., interface functions like data import and export) are required. Requirements for management tools are presented in Section 4.5.

In the past, there were generally separate tools dedicated to accomplish requirements in each high-level area mentioned above. The trend in software development today is module integration of tool functionalities needed for a virtually seamless environment for the end user.

For example, besides being a network design tool, an integrated design tool can have measurement capabilities in terms of the import and visualization of measurement data; analysis capability in terms of design analysis, i.e., network coverage and capacity analysis; and measurement analysis like soft handover verification for measured drive test routes. In addition, it can also have management capability, such as producing reports of the network configuration and parameter settings.

For the end user, the functionalities of different key areas are not separate software tools, but software modules integrated in a unified end user environment.

This implies that the end user is not aware if the tool comprises one or more integrated hardware or software modules or systems, but perceives the implementation as a single user interface. With this kind modular approach, an environment, where there is limited need for several separate physical software tools to accomplish our planning goals, is benefited. This is beneficial from the system administration point of view as it gives: – fewer tools to administer, and – usually one single logical storage point, a database to administer.

This improves the data consistency throughout the planning tool environment. End users benefit from a similar user interface, which shortens the process of adopting the tool. The relation between the key areas is illustrated in Figure 4-1.


Figure 4-1. High-level key areas of a radio network tool environment.

4.1.1 Planning process support

In addition to supporting functions related to the key areas mentioned above, a modern tool environment provides genuine support for the planning process as a whole. This includes not only technical engineering, e.g., design or optimization of a network, but also the ability to support inter-related functions such as project management and logistic functions within an organizational unit. Although not a primary goal, effective data sharing within organizations is increasing in importance, and a network planning tools environment is not an exception. In this context, it is worth pointing out that planning data is generally regarded as sensitive and strategic data, so available organizational security measures need to be considered when sharing such data.

A typical planning process consists of dimensioning, detailed radio planning, verification, optimization, and monitoring. These are fully described in Chapter 1 and in [1].

As depicted above, this process not only involves direct radio technical issues but it spans a much larger context, involving resources across companies’ internal and external organizational structures.

For example, a project manager might need to know who is responsible for a certain NodeB in order to solve whether the current cooling solution is


sufficient for a cabinet extension. A logistics person might be interested in how many NodeBs with LNAs there are, and how many LNAs for each NodeB. This kind of data is collected throughout the initial planning.

Thus an important requirement of a planning tool environment is: A planning tool environment should support the collection, storage, and

retrieval of planning data, regardless of organizational structure.

4.1.2 Planning tool setup

After acquiring any tool environment, somebody (the administrator or a planner, for example) eventually faces the task of setting up the tool environment and getting the planning data into the tool environment.

The first step involves dealing with the following: – tool environment configuration; – hardware configuration; – software installation, e.g., planning software and database system

software for data storage; and – user environment setup.

Today’s tools support a variety of software and hardware configuration possibilities. A suitable setup must be chosen to accomplish planning, and taking data sharing into account.

An important requirement of a tool is offering and supporting good administrative tools and procedures for backing up data. Hence, the strategic value of planning data.

A tool environment is, with few exceptions, a multiple user environment. This requires that the visualization of planning data is similar for all users. An example is using the same colors for coverage thresholds for all users in a planning organization. This is a very important requirement for avoiding misunderstandings and making the environment as unified as possible. From a high-level requirement, this is a tool management functionality.

The second step is to get planning data into the environment. Having the key areas in mind, this typically involves data such as:

Design tool

– digital maps – dimensioning data or radio network design – service definitions – terminal definitions Measurement tool

– digital map – survey area definitions – radio network design


Analysis tool

– digital map – radio network design – network statistics – network measurements.

4.1.2.1 Digital map

Digital maps are a fundamental part of any tool in a radio network planning tool environment. To project a point on the earth’s surface to a digital representation (or a paper map), a set of mathematical rules called projections and mathematical representations of the earth called ellipsoids are needed. Together these define a coordinate system. Digital maps also models real attributes, for example, terrain height, land-usage types, buildings, foliage, building heights, building structures, roads, railways and tunnels into a combination of raster and vector data (see Chapter 3, for details on digital maps). To provide flexibility for the end user, it is of vital importance that a tool provides support for various sets of digital map representations, that is, different combinations of coordinate systems, raster and vector data. Furthermore, from the above it is clear that there is a benefit if the same map representation can be used in all tools in the radio network tool environment. This provides cost efficiency and minimizes the need for digital map data conversions.

4.1.2.2 Import and export of dimensioning or radio network design

In the setup of a design tool, a representation of the network design must be created - a network plan. This is data from the dimensioning phase or perhaps an existing design from another tool. Various methods can be used to do this and a tool that supports them is required. Data could be entered one by one by the user through the user interface, e.g., create a NodeB with a certain configuration defined by a template or by copying and pasting. In practice, this would not be feasible if the design consists of a large number of network elements.

This requires the tool to be able to handle the import of whole network designs. The support for a large number of different import data formats is beneficial. As well as getting data into a tool, it is equal important to have the capability to export network design data for compatibility and working together with other tools in the tool environment. In the event that importing is not successful or partly successful for some reason, the tool should provide adequate functionality to manage the incomplete data, e.g., large-scale deletion of data or functionality to overwrite existing data.


Similarly, it is valuable if definitions like services and terminals can be imported/exported, minimizing the time consumed to redefine data in case of transferring data from one design tool to another, for example.

4.1.2.3 User interface

User interface design is a big topic and outside the scope of this chapter. However, it is worth mentioning some minimum requirements in terms of users orientating themselves while working with a tool. A tool should provide adequate information to the user about what object he is currently working with. This means, for example, providing an upper-level view (e.g., a network browser) of the object being worked on: showing the object, a graphical pointer visualizing the object on the digital map, and an object window visualizing the attributes of the object. This should also be applicable for multiple objects.

4.1.2.4 Multi network planning

Service providers operating multiple cellular networks are not uncommon. Thus an extremely important requirement of a tool, in terms of network design, is to handle planning and optimization of both a GSM and UMTS network with the same tool. In this respect, the main requirement for a planning tool is a structured, user-friendly user interface that simultaneously gives intuitive support for different planning processes between technologies. Consideration is further needed in terms of support for cross-organizational requirements, e.g., sharing of data within an organization.

4.2 Design tool

The main purpose of the design tool is to support the detailed planning. That is to evaluate and secure the service coverage and capacity of the network design. The first step is to predict the initial service coverage of the design, i.e., calculate coverage footprints for each sector in the network design. After that, the capacity and coverage relationship can be iterated with a Monte Carlo simulation. This iterative process typically involves changes of attributes in the initial network design. This means a design tool has to provide functionality to add, delete, copy and modify various object attributes in a network design.

Prior to doing any coverage and capacity evaluations, it is necessary to input the results from the network dimensioning, that is, the initial network design, including NodeB transmitting power, NodeB equipment and antenna line configurations, service thresholds and adequate propagation models into


the design tool. The main tool requirements for coverage and capacity planning are explained in the following paragraphs.

4.2.1 Coverage planning tool

Before doing coverage planning, attributes, as a result of pre-planning, are required to input in the design tool. These inputs include: propagation models and corresponding correction parameters based on the outcome of propagation model tuning; equipment definitions like feeder length and attenuation; and antenna equipment parameters in terms of electrical properties like gain and radiation patterns. Furthermore, amplifier equipment properties must be definable in terms of gain and noise figures. Finally, NodeB and NodeB sector equipment properties must be defined. Typically, these involve transmitting power parameters (from the power budget), antenna line configuration (i.e., feeder and antenna type, antenna diversity, amplifiers), number of hardware channels, noise rise limitations and noise figures.

A summary of parameters that are required input in a design tool to perform initial coverage planning is presented in Table 4-1.

Table 4-1. Definitions needed for coverage planning. Entity Parameters Remark

Propagation model Prediction frequency Correction parameters Model

Clutter Line-of-sight Diffraction Topography Building properties

Antenna Gain Radiation pattern Beam width Vertical, horizontal Feeder Attenuation Feeder loss, connector losses

and jumper losses Length Amplifier Gain Noise figure Losses Insertion losses NodeB Location Geographical location Number of hardware

channels Maximum number of soft

handover connections Number of sectors Sector configuration Single transmit single receive


Entity Parameters Remark

Omni transmit single receive Transmit powers NodeB transmit power

Pilot channel power Maximum power of data connection Common channel powers

Antenna diversity Transmit / Receive Amplifier Feeder Antenna Type

Tilt Direction Height

Coverage calculation area Service Coverage thresholds

In the coverage planning process, the goal is to meet the setup coverage criteria for different services. As coverage is closely related to capacity, a set of minimum attribute changes that the coverage tool should support can be identified. These are listed below: – change location of cell sites – tune antenna line properties, including

– antenna height – antenna direction – antenna tilt – antenna type

– change antenna line equipment – low noise amplifiers – feeder type – booster – power dividers

– change cell site configuration – base station combiners – receive diversity – transmit diversity – power amplifiers It is important that the tool supports changes in these attributes in a user-

friendly manner. This implies that it should be as easy to make a single attribute change as making multiple changes, and possible to change numerous attributes for the whole network design.

Initially, the most important coverage to be planned is service and pilot coverage. A coverage prediction tool must be able to provide the user with the necessary functionality to address this.


At this stage, before load simulations are done with Monte Carlo simulations, the required functionality includes: – identification of insufficient coverage for services and pilot; and – identification of excessive coverage overlapping for services and pilot.

From a practical planning point of view, it is important to capture the identification of both insufficient and excessive coverage in an early stage in planning. The reasons for early identification are: – the process of acquiring cell sites is generally tedious and involves a lot

of manpower resources; it is therefore crucial to capture indications for site changes in the early stage of planning;

– provide a good initial input for capacity simulations, minimizing the time for capacity simulations;

– secure sufficient pilot coverage throughout the service area; and – address identification of probable pilot pollution areas.

Examples of a display showing insufficient service coverage is shown in Figure 4-2.

Figure 4-2. Insufficient service coverage.


4.2.2 Capacity planning tool

A capacity planning tool is necessary to perform capacity planning for a given network design. Here, interference estimations are of vital importance. This is generally accomplished with static simulations of the network design. Typically, Monte Carlo simulations are used to aid in providing a foundation for capacity simulations of the network design.

Monte Carlo simulations simulate the outcome of a service establishment for a number of users randomly distributed in the network design. The resulting outcome is collected in what is commonly called a “snapshot”. The simulation process is repeated until a satisfactory number of snapshots are generated to give a statistically significant output.

The underlaying theory of the Monte Carlo simulation technique, “The Central Limit Theorem”, described in [2], say in brief:

The sum of a large number of independent, identically distributed random variables is approximately a normal distribution. This is regardless of what kind of distribution the identical random variables have from which the sum is calculated. This makes the Monte Carlo simulation a convenient approach to simulate users in a network design, providing a fair amount reliability and performance, versus making dynamic simulations that model users as moving around in the network design. Dynamic simulations are still regarded as too time-consuming for practical use.

The required definitions a tool must have for a Monte Carlo simulation are: – bit rates; – services; – terminal types; and – signal fading.

4.2.2.1 Bit rate definition

For bit rates, the necessary definitions, apart from the service bit rate (kbps) with corresponding bit rate Eb/N0 requirements [3] and bit rate noise model, are mainly related to corrections of Eb/N0 requirement values accounting for user equipment speed and gain from soft or softer handover connections.

The corrections that should be possible to define are: – Mobile transmitting power corrections; – Average power rise gain corrections; – Power control headroom gain corrections; and – DL Eb/N0 target reductions.


In Chapter 2, Eb/N0 requirements and their derivation from [3-4] is described. In practice, Eb/N0 values must be simulated or measured for different environments [5].

Examples of definitions are depicted in Figures 4-3 to 4-6:

Figure 4-3. Mobile transmitting power corrections.

Figure 4-4. Average power rise gain correction parameters.


Figure 4-5. Power control headroom gain correction parameters.

Figure 4-6. Downlink target reduction correction parameters, power control headroom values, and average power rise.


These parameters are link level performance table examples from accompanying material [5] for the pedestrian A channel of the ITU recommendations.

4.2.2.2 Service definition

The service definition requirement is to be able to define the service type, which typically is a packet switched or circuit switched service. The necessary bit rate associated with each service is derived from defined bit rates. Furthermore, it should be possible to account asymmetric activity of the service. A packet model is specified in [6].

An example service definition is found in Figure 4-7, and a packet service definition in Figure 4-8.

Figure 4-7. Example of general parameters for service definition.


Figure 4-8. Example of packet service definition parameters [6].

4.2.2.3 Terminal type definition

The terminal type definition requirement is to have service-dependent terminal parameter definitions available, e.g., UE dynamic range, UE transmitting power, body loss, antenna gain, and noise figure of UE [4-5].

Apart from necessary terminal or UE parameters, the terminal definitions need parameters to define the terminal properties in terms of amount and terminal density in relation to the digital map used. The service that the terminal is using must also be definable. Also needed are definitions to model the terminal velocity. This can be done with a mapping of terminal speed to the different terrain types present in the digital map used.

As an additional definition possibility, it is usually good from the usability point of view to be able to assign terminals to a user-defined area on the map, e.g., a polygon.

The following Figures 4-9 to 4-11 show user interface examples with parameters used for the purpose of defining a terminal.


Figure 4-9. User equipment-specific parameters [4-5].

Figure 4-10. Clutter-specific parameters.


Figure 4-11. User equipment mobility parameters.

4.2.2.4 Signal fading

To account for radio channel fading in capacity simulation, the capability to define a fading model for the radio channel is required. This can, for example, be via statistical definitions like outdoor standard deviation values for different clutter types in the digital map. This information can be used to apply fading to link loss estimations, which in turn is part of the calculations of transmitting power in the uplink and downlink [5].

4.2.3 Neighbor cell generation

A functionality to generate and manage neighbor cells is required. The main target of this is to provide an easy way for the user to automatically generate neighbor lists for each cell in the network design, also accounting for the multi network scenario; that is, the capability not only to generate neighbors on the same or adjacent carriers of UMTS, but also to generate and manage neighbor relations between the UMTS and GSM networks. The minimum requirements to perform neighbor generation (which can be found in [5]), are: – radio access system; – target cells for creation;


– maximum number of neighbors per cell; and – field strength threshold for the generation procedure.

The management of a neighbor list requires at least the capability to edit the generated lists. Beneficial to support the planning process is the capability to import/export the neighbor data to/from the network management system.

4.2.4 Scrambling code planning tool

In the planning of a UMTS network, it is recognized that the scrambling code planning will be of less importance. (See Chapter 1.) From a practical planning point of view, however, it is no drawback if the design tool is capable of performing scrambling code planning. The minimum requirements for scrambling code planning functionality are to provide the following in the assignment of scrambling codes to the sectors of NodeBs: – capability to take into account neighboring cells; – capability to take into account adjacent cells; – capability to take into account a minimum re-use distance of codes; and – capability to divide scrambling codes into customizable scrambling code

groups.

4.3 Measurement tools

4.3.1 Radio interface measurement

The radio interface measurement tools are of vital importance for successfully planning, optimizing and maintaining a third-generation mobile network. Tools are required for collecting field measurements from a selected test route (a drive or field test tool). A tool is also needed to collect signaling flow between the RNC and the NodeB for in-depth optimization. The latter is also referred to as a protocol analyzer.

4.3.1.1 Field test tool

This is a drive test tool with the capability to measure the radio interface through a user terminal and with scanner receiver functionality to be able to scan the radio frequency environment. Both these functions are not contradictory, but complement each other to provide the necessary information to capture a third-generation network.

A further vital part, as in any mobile network measurement system, is the presence of a GPS receiver. This ensures that measurements have a


geographical location attribute. Furthermore, it is advantageous if the tool can utilize digital map to display positions. For cost reasons, preferably the portfolio of planning tools should be able to utilize the digital map of the same format.

The mentioned items constituting the measurement tool collection is listed below and can be seen visualized in Chapter 7, Figure 7-4. – laptop equipped with software for data collection; – UMTS user equipment; – receiver scanner; – GPS receiver; and – digital map.

It is clear that the concept of a measurement tool for UMTS consist of two measurement units, the user terminal and the scanner. The advantage of such a tool is the ability to provide information gathered from multiple sources, increasing the overall flexibility of the system.

Notice that the user-terminal measurements indicate how the end users perceive the network performance. This makes the measurements dependent on the network where measurements take place. The scanner on the other hand, gives a pure view of the radio environment, independent of any particular network and/or user terminal. These two differences combined provide the greater flexibility and usability of the measurement tool. It can be concluded that the user terminal handles subscriber-call quality-related encounters, and the scanner helps explain why the subscriber encounters problems. However, one can manage with only the user terminal measurement functionality and without digital maps. Especially because digital maps are expensive, this could be a cost-effective configuration initially.

Hence, measurement tools need to be versatile to align with the different measurement needs throughout the life span of a network. Viewing the need from the radio network evolution, different steps for measurement tool needs can be identified. These are listed below: – propagation model tuning; – site evaluation; – NodeB integration; – acceptance test; and – optimization.

Propagation model tuning

The accuracy of the propagation model for predictions in a planning tool is crucial for the end result. This is a necessary task when acquiring a new or updated digital map, and when changing properties related to the propagation environment, e.g., a major carrier frequency change. This is


preferably performed with a CW transmitter and receiver system with an omni antenna where the transmission line of the system is well-known. This means attenuations and gains of all parts in the transmitter system setup.

Site evaluation

During the site acquisition process or before installing a NodeB, it is generally necessary to do a site evaluation, that is, to verify the site location in terms of suitability from the radio propagation point of view. This is done with a test transmitter at the site location. The transmitter generates a continuous wave (CW) signal that is received and measured by the measurement tool.

NodeB integration

When a NodeB is turned on and integrated in the network, it is important to verify the RF footprint of the NodeB, as well as HO functionality verification. This is typically done measuring pilot signal power of the serving and neighboring NodeBs.

Acceptance test

The result of an acceptance test generally consists of a set of documents proving that the NodeB is commissioned and integrated in the network, complying with the defined acceptance test definitions. For example, if a third party is responsible for network implementation, a successful compliance with the acceptance test criteria implies that the NodeB responsibility is handed to the service provider from the third party. Generally, this handoff of responsibility is effective on a larger entity than a single NodeB, typically a geographical area, e.g., a city.

Optimization

Optimization is a continuous process throughout the life span of a network. A network “lives”, i.e., new NodeBs are integrated or relocated as a result of changes in subscriber growth or due to environmental effects, e.g., trees growing, urban development such as new buildings, and degradation of equipment. This makes continuous measurements to give the latest radio environment information to the optimization team important. The gathered data is post-processed and analyzed where problems are identified. The outcome of the analysis provides solutions to the identified problems and the implementation of the solutions. After implementation, measurements are again gathered and the process starts all over.


Measurements

A high-level minimum required measurement capability of a measurement tool is listed in Table 4-2. The list is divided into the different phases mentioned in the previous paragraph.

Table 4-2. Minimum measurement capability of a measurement tool. Phase Measurement type Extent

Propagation model tuning CW (un-modulated carrier) Serving Site evaluation CW (un-modulated carrier) Serving NodeB integration Received Signal Strength Indicator

(RSSI)Serving, neighbors

Received Code Power (RSCP) Serving, neighbors Ec/I0 Serving, neighbors Soft handover Serving, neighbors Power control

Open-loop Serving

Optimization Call success Serving, neighbors Power control

Closed-loop Serving, neighbors

Call control messages Serving, neighbors Frequency scanning Serving, neighbors,

adjacent Delay spread Serving, neighbors Synchronization channels Serving, neighbors Signal time of arrival Serving, neighbors

Optimization, in addition to listed items also should include same requirements as NodeB integration. More detailed information is presented in Chapter 7. Acceptance test is deliberately left out due to its varying nature.

4.3.2 Interfaces

Interfaces within the tool and to other tools are important for user friendliness and flexibility.

The interface within the tool typically consists of a set of user interface windows, which are able to present measurement data to the user both on-line and from stored data extracted from a storage device. Examples of such interfaces are found in Chapter 7.

The interface to other tools is usually implemented by means of a file export/import utility. The file formats supported by today’s tool vendors are extensive and covers the needs well. An added requirement to file import/export is the ability to manage the data. That could, for example, be


automatic labeling and archiving of imported data in the storage hierarchy of the tool.

4.4 Analysis tools

The tools used for analysis are important and should support the user in making the right conclusions from the analyzed data.

Generally, graphical results or the interface provides the end user with an intuitive and fast path to making conclusions.

4.4.1 Design tool coverage and capacity analysis

For coverage analysis, it is important to be able to perform both standard path loss predictions and interference analysis. This can be useful to gain an initial perception of coverage overlapping and cell-boundary coverage. This is seen in Section 4.2. Also, since coverage and capacity is closely related to each other in a UMTS system, coverage analysis should be linked to analysis of the simulated uplink and downlink performance. Hence, this simulation is performed with a Monte Carlo simulation. A good tool inherently provides concurrently the analysis in conjunction with the simulation. The method behind iterations in the uplink and downlink is elaborated in [5, 7].

The Monte Carlo simulation relies on information about the distribution of user equipment within the network design. The result of the Monte Carlo simulation is connected to how well this distribution is made. The generation of such distribution, commonly known as building a traffic layer, i.e., a raster data representation of user-equipment distribution, is very important. Not only is it required by the tool to be able to generate a traffic layer by the land-usage types in the digital map, it is also of crucial importance that the tool can handle generation based on existing traffic data, e.g., from a GSM network and additionally have functionalities to restrict traffic distribution, for example, where the coverage exceeds a certain threshold.

Important graphical displays from coverage and capacity analysis are shown in Figures 4-12 to 4-16.

The displays are: – Pilot Ec/I0 (carrier); – SHO types (service); – number of cells in active set (service); – user equipment transmitting power (service); and – load in the uplink direction (carrier).

Note that the capability to analyze both service and carrier level performance is important. This is indicated in the above list in parenthesis.


Figure 4-12. Example of pilot Ec/I0 display.

Figure 4-13. Example of SHO type display.


Figure 4-14. Example of number of cells in active set.

Figure 4-15. Example of user equipment transmitting power display.


Figure 4-16. Example of load display for the uplink direction.

4.4.1.1 Pilot pollution

For pilot pollution to occur, the following criteria are fulfilled. – There are more pilot signals received at the user equipment than the

correlation receiver is capable of processing. – None of the pilot signals is dominant in signal power level.

The number of signals a user equipment receiver can handle is vendor-specific. In a planning tool environment, a way to identify possible areas with pilot pollution is to define it as areas where the relative carrier over interference level is poor and at the same time the received signal code power level is sufficient. One definition is:

Ec/I0 < -14 dB and CPICH RSCP > -95 dBm [8]

where Ec/I0 is the received chip energy relative to the total power spectral density, and CPICH RSCP is the received signal code power for the common pilot channel [5].


4.4.1.2 Hardware channels

In addition, one very important requirement of an analysis tool is to be able to present the number of hardware channels used by the design. This is important to be able to plan for hardware unit extensions. Hardware channels are sometimes also referred to as channel elements, and a hardware unit as a channel element kit.

This is important in any evaluation of a UMTS planning tool environment since the hardware channel utilization in the network differs from vendor to vendor.

4.4.2 Drive test analysis

An analysis tool for drive test data analysis can, as mentioned earlier, be a separate tool or an integrated part of a family of tools. Regardless of the implementation, a mandatory requirement of an analysis or post-processing software tool is to pinpoint pilot pollution areas. This is a major contributor to poor Quality-of-Service and as a possible result, a dropped call. As pilot pollution is related to the design of the user equipment, i.e., the number of fingers in the RAKE receiver implementation in the user equipment, settings to define this are also needed.

Ultimately, it is the design engineer who decides to make design changes based on the analysis results. The design engineer’s goal is to optimize the network so that the number of pilots in any given location does not exceed the design goal. A good analysis tool provides the design engineer with support in the decision process. Not only can it determine the number of pilots in a given location, but also their origin. To do this, the analysis tool must be able to combine and analyze both data captured with user equipment and data captured with scanner equipment.

A further ability is to analyze soft handover functionality in relation to the corresponding threshold parameters for the active and monitored set and also the number of cells in the active and monitored set. Too many or too few cells is not good, and the tool should help in the analysis to ultimately provide the best settings for optimized soft handover performance.

Also important is the ability to provide signal delay information from cells in the network. When a NodeB timing is not aligned, it causes problems to the area affected by the footprint of this unaligned cell.

Quality-related analysis support is important in terms of key quality indicators like BER and FER.

Drive test analysis is further described in Chapter 7.


4.5 Management and information processing tools

The information or amount of data stored on different devices in a planning tool environment can be numerous. There is planning design data, measurements and analysis results. Furthermore, the data stored within a tool is organized in a structured manner. However, the relation between data from different sources is far from always corresponding to each other in a one-to-one relation. That is, the task of combining data, and sometimes visualizing the combined data, from one tool with another is not always trivial.

This either requires that the information processing can be handled through a central data storage implementation or through a set of independent data sources. The latter will generally have a higher grade of flexibility, at the expense of increased development and maintenance efforts. This is mainly due to data compatibility issues between independent data sources.

4.5.1 Network design and implementation management

A powerful report tool is mandatory. It should be able to produce reports of network design, analysis, and simulations. Furthermore, in order to simplify any post-processing of the generated information, the capability to output reports in a variety of common file formats is beneficial.

The most important information that should be producible is: – throughput statistics on a service basis; – service success and failure statistics with related causes for failures; – power statistics (pilot, common, synchronization, user, and total

transmitting power); – handover statistics; and – carrier level (load, noise rise, hardware channel usage, etc.).

Not mandatory, but extremely useful for documentation purposes, is the capability of the tool to generate output in specifically adopted portable document format (for example, coverage plots).

During the initial rollout of a radio network and throughout the evolution of the radio network, the importance of information for groups of people indirectly dependent on planning decisions is of crucial importance. Typically, this involves, for example, project management teams, construction teams, and logistics team. This requirement is important as the outcome of overall planning will always have a direct impact on the work for these organizational units. This means that the planning tool environment not only requires handling planning-specific parameters, but also parameters related to these organizational units.


For example, in project management, this typically includes data such as: – status of a site; e.g., has the technical team assessed the site?; – responisble persons, e.g., for planning of a site; and – contact information, e.g., to access a site.

For logistics, data related to products used in the network, e.g., – manufacturer; – pricing; – product number; and – number of units.

And for constructions, data related to implementation – equipment configuration, e.g.,

– type of equipment; – amount of equipment; and – location of equipment;

– address; – contact persons; and – blue prints, floor layouts of a NodeB equipment room.

This data is gathered throughout the planning process and input in the planning system. It is important that the tool also provides the possibility to make this information available for these dependent groups of people.

4.5.2 Network Management System (NMS)

For continuous tuning and optimization of a radio network, it is required to have the statistical information on network performance, gathered in a NMS system, available also in the planning environment. The regular transfer and management of the huge amount of existing statistical data is commonly done via propriety solutions that vary from vendor to vendor. In multi vendor networks, it is of key importance that the tool, either via an separate information processing tool or integrated in the design tool is able to flawlessly handle and match data structures of different vendors.

REFERENCES

[1] J. Lempiäinen, M. Manninen, Radio Interface System Planning for GSM/GPRS/UMTS,Kluwer Academic Publishers, 2001.

[2] A. Papoulis, S. Unnikrishna Pillai, Probability, Random Variables and Stochastic Processes, Fourth Edition, International Edition, McGraw Hill, 2002.

[3] Universal Mobile Telecommunications System (UMTS), UTRA (BS) FDD; Radio Transmission and Reception, 3GPP TS 25.104.


[4] Universal Mobile Telecommunications System (UMTS), UE Radio Transmission and Reception (FDD), 3GPP TS 25.101.

[5] J. Laiho, A. Wacker, T. Novosad, Radio Network Planning and Optimisation for UMTS,John Wiley & Sons, Ltd, 2002.

[6] ETSI, Selection Procedures for the Choice of Radio Transmission Technologies of the UMTS, TR 101 112.

[7] A. Toskala, H. Holma, WCDMA for the UMTS, John Wiley & Sons Ltd, 2000. [8] WCDMA Training, E6474A, Agilent Technologies 2002.

PART II: UMTS TOPOLOGY PLANNING

Chapter 5

UMTS TOPOLOGY PLANNING Coverage and capacity

JARNO NIEMELÄ, JUKKA LEMPIÄINEN Tampere University of Technology (TUT)

Abstract: Coverage and capacity planning of WCDMA-based UMTS cellular networks are strongly tied together. This chapter introduces the principles of the UMTS topology planning, which means combined coverage and capacity planning. The topology planning phase contains definitions of site locations and configurations together with the base station antenna configuration. These technical elements influence the network coverage and system capacity of a UMTS network. Critical coverage and capacity topics such as signaling channel power needs, multiple services, Erlang-B capacity, and load equations are first introduced separately as they relate to the initial topology planning phase. Finally, radio network system simulations of actual topology planning are described and the impact of different base station site configurations on system coverage and capacity are presented with examples.

Key words: Antenna tilting, base station antenna configuration, capacity planning, cell range, coverage overlapping, coverage planning, sectoring, sector orientation, site locations, topology planning, traffic distribution

149




5. UMTS TOPOLOGY PLANNING

5.1 Introduction

Required network coverage and system capacity together with sufficient Quality-of-Service (QoS) and implementation costs are the most essential elements that define an operator’s site density and site configuration for a planning area. Furthermore, traffic distribution has a great impact on the site density and configuration. In urban environments, traffic requirements are much higher than in rural areas, and thus the site density and configuration is different for these environments. Moreover, the utilized implementation strategy for the site configuration defines the overall coverage and capacity of each particular site. Site locations, number of sectors and sector directions together with antenna configuration have to be considered altogether in order to provide sufficient network coverage, system capacity, service quality, and low implementation costs.

In WCDMA-based UMTS networks, network coverage and system capacity are linked because the same carrier frequency is used over the radio network and other users’ signals are seen as additional interference. Thus, attention should be paid to coverage and capacity planning phases simultaneously when planning a UMTS network – hence the name topology planning. Due to the dynamic nature of a UMTS network, the overall performance cannot be determined with analytical formulas, and system or link-level simulations are typically used for defining the network performance of different scenarios. Furthermore, the uplink and downlink directions have to be considered separately due to different traffic requirements for each direction.

The main goal of this chapter is to understand the link between coverage and capacity and all the technical elements that have influence on the coverage and capacity (i.e., on the topology) of WCDMA-based UMTS networks. First, theoretical coverage and capacity are explained for a UMTS network. Next, the impact of site locations and configurations (sectoring, sector direction, and sector extension) on network coverage and system capacity are presented with system level simulation examples with the help of a sophisticated radio network planning tool to support theoretical and practical considerations. Finally, the impact of the most important base station antenna configurations (height and tilting) is shown with system level simulation examples.

UMTS TOPOLOGY PLANNING 151

5.2 Topology planning

The topology planning phase combines coverage and capacity planning for UMTS networks. Figure 5-1 describes the relation between coverage and capacity of UMTS networks and shows the effect of site and antenna configurations. In the topology planning phase, the site location and configuration are determined, together with the base station antenna configuration.

Cell loadInterference

margin

User bit rates- 12.2 kbit/s- 64 kbit/s

Number ofusers

Service types - circuit switched - packet switched

Link bugdet

Maximumpath loss

Cell range

Site / antennaconfiguration

Figure 5-1. The link between coverage and capacity of a UMTS network.

The load of a cell depends on the number of users together with service types offered and their bit rates – the more users in a cell, the more the load is increased. On the contrary, the load affects the required interference margin in the power budget. With a smaller maximum allowable path loss, the cell range is also smaller. Moreover, the sensitivity of the base station and mobile station depends on the interference level in the cell and the services provided. Because site and antenna configuration affects propagation and thus interference in the network, they link coverage and capacity together. In this section the most important aspects of network coverage and system capacity are discussed separately before initial topology planning is explained.

The topology planning phase can be divided into initial and detailed topology planning. Initial topology planning can be considered a dimensioning phase where an approximation of the network configuration is calculated. Due to the dynamic nature of the UMTS network, radio network system simulations are needed to verify the network performance; these simulations are done in detailed topology planning. Thus, the result of the detailed topology planning phase is the final site and antenna configuration


of the network. Also, the results are detailed coverage and capacity analysis of the corresponding network configuration.

5.2.1 Coverage of a UMTS network

A mobile radio network should provide sufficient coverage for its service area in order to satisfy customers’ requirements. Due to mobility requirements, a cellular system has to provide coverage both for traffic channels and for signaling channels. This coverage depends on several network elements, which are mainly defined in the configuration planning phase.

In the existing 2G cellular systems, such as GSM, the coverage planning phase is straightforward due to the constant signal transmit power and receiver sensitivity. With UMTS, transmit power is shared with mobiles in the downlink direction, and the required signal level for reception depends on the interference level. Thus, in UMTS networks the coverage thresholds in a cell depend on the number of users and their bit rates, i.e., on the load of the cell. Therefore, the coverage thresholds have to be determined for each cell and service separately. What makes this more complicated is that each service can have different bit rates and different QoS targets that must be met. In practice, the service with the tightest QoS target determines the cell range and, moreover, the overall site density for the planning area.

5.2.1.1 Signaling and traffic channel coverage

A cellular network requires coverage for traffic and for signaling purposes. Traffic channel coverage ensures that services can be used in the coverage area and the user is able to receive or send information. The purpose of signaling is to transmit controlling messages between the network and the terminals [1]. Because the maximum transmit power of a UMTS cell is limited, signaling channels consume the power of traffic channels – the more signaling, the less traffic capacity. Hence, UMTS network coverage can roughly be divided into two parts: common pilot channel (CPICH) coverage and dedicated channel (DCH) coverage [2]. CPICH is used for channel estimation, handover measurements and cell selection/reselection procedures. Also the other signaling channels need a certain amount of transmit power.

From the point of view of UMTS radio network planning, CPICH power must be minimized to leave as much power as possible for DCHs, in order to be able to serve as many customers as possible. However, enough power must be allocated to CPICH in order to ensure the required measurements and synchronization for a cell. If the transmit power of CPICH is too low,


the terminals in the border areas of that cell are more likely to select the neighbor cell, i.e., the cell dominance area is decreased. In the opposite situation, if the CPICH power is increased, the cell dominance area increases. Typically, 5–10% of the total base station power is reserved for CPICH [3].

The DCH coverage depends on the user data rate, on the location of the users, and thus also on the path loss between mobile and base station receiver. In the uplink (UL), the DCH coverage is limited by the transmit power of the mobile station, and in the downlink (DL), either by the maximum power allocated for one radio link or the maximum power. Both UL and DL DCH coverage depend on the load of the cell, i.e., on the interference level of the cell. In practical terms, this means that the effective range of a base station or the cell size varies depending on the number of active users within a cell and on the other-to-own-cell interference [4]. This variation in a cell size is known as cell-breathing.

5.2.1.2 Power budget analysis

The coverage of a UMTS cell depends more or less on the same network elements as the coverage of a 2G cell. Base station and antenna line equipment, such as antennas, LNAs and cables, plays an important role in network coverage. Moreover, the coverage depends on the propagation environment and location probability targets set for indoor and outdoor planning as well as for different services. One common aspect for 2G and UMTS coverage planning is that both directions must be analyzed separately, and the main objective is to balance the power budget in order to achieve balanced communication in both directions.

In Table 5-1, an example of a UMTS power budget is presented for symmetric speech service and for asymmetric data service. The power budget takes into account the base station equipment and the base station antenna line configuration. In this example, the maximum allowable propagation loss is calculated for speech service of 50% load in both directions, and separately for data services when a 64 kbps bit rate of 30% load is used in UL, and a 384 kbps bit rate of 75% load is used in DL. Allowed propagation loss is higher in the DL direction for speech service and for data service. Thus, in both cases, the UL direction would limit the coverage. In a hybrid traffic scenario, speech and data services must be handled together in order to find the maximum allowable path loss for both directions separately.

The cell range deviation of the previous example can be determined, for example, by using the Okumura-Hata [5] propagation model with typical urban values. Base station and mobile station antennas are set to 25 m and 1.5 m, respectively. With an area correction factor of -3 dB for an urban area


and a slow fading margin of 10 dB, the cell range of speech service is 1.84 km in the DL direction and 0.97 km in the UL direction. The corresponding cell ranges in DL and UL for data service are 1.07 km and 0.79 km.

Table 5-1: Example of UMTS power budget for speech and data services. Parameter Speech Data

Downlink Uplink Downlink Uplink Units

Bit rate 12.2 12.2 384 64 kbps Load 50 50 75 30 %

Thermal noise density -173.93 -173.93 -173.93 -173.93 dBm Receiver noise figure 8 4 8 4 dB Noise power at receiver -100.13 -104.13 -100.13 -104.13 dBm Interference margin 3.01 3.01 6.02 1.55 dB Total noise power at receiver -97.12 -101.12 -94.11 -102.58 dBm Processing gain 24.98 24.98 10 17.78 dB Required Eb/N0 7 5 1.5 2.5 dB Receiver sensitivity -115.10 -121.10 -102.61 -117.86 dBm

RX antenna gain 0 18 0 18 dBi Cable loss / body loss 2 5 2 5 dB Soft handover diversity gain 3 2 3 2 dB Power control headroom 0 3 0 3 dB Required signal level -116.10 -133.10 -103.61 -129.86 dBm TX power per connection 33 21 37 21 dBm Cable loss / body loss 5 2 5 2 dB TX antenna gain 18 0 18 0 dBi Peak EIRP 46 19 50 19 dBm Allowed propagation loss 162.1 152.10 153.61 148.86 dBm

The previous example illustrates how different services and their quality targets, together with different load targets, affect the cell range. For detailed analysis of coverage and coverage probabilities, a more exact analysis of service location probabilities is needed. In practical UMTS network planning, high indoor coverage probabilities are required; hence cell outdoor coverage areas overlap excessively. Moreover, a mobile station is able to connect to more than one serving cell due to the nature of WCDMA.

5.2.2 Capacity of a UMTS network

In TDMA/FDMA networks, the Erlang traffic model has been used for capacity dimensioning. The Erlang model is based on Erlang formulas that


include the average duration of a call and the average time of arrival of a call. The introduction of completely different air interface access methods and packet switched services has changed the principles of capacity planning in UMTS networks. Traffic channels that exist in TDMA/FDMA networks have been changed into codes that separate different users in the network. The concept of channel has thus changed. Packet switched services with variable bit rates make capacity analysis even more complex. Because UMTS networks include dynamically variable circuit and packet switched data connections, Erlang formulas cannot be used as such for capacity dimensioning needs in UMTS networks.

5.2.2.1 UMTS network capacity in Erlangs

The capacity of the radio network can be blocking limited or interference limited [7]. In the TDMA/FDMA networks, the capacity of a cell is determined according to a number of transceivers utilized in the base station site. With a known number of transceivers, the channel structure (traffic and signaling) can be determined and, moreover, the amount of traffic served by the base station can be determined using the Erlang-B formula. Therefore, the capacity of a TDMA/FDMA network is blocking-limited, which indicates that available traffic channels are running out, rather than the interference situation being the cause of blocking. In contrast to TDMA/FDMA networks, the capacity of a UMTS network is interference-limited (soft blocked). In soft blocked networks, a rise in interference in a cell causes the blocked calls rather than a lack of available traffic channels. The term “outage” is used to indicate blocking in UMTS networks.

The capacity of a UMTS network is known to be interference-limited [6], i.e., any reduction in interference can directly and linearly be converted into an increase in capacity. If the maximum capacity is limited by the amount of interference in the air interface, it is by definition a soft capacity, since there is no single fixed value for maximum capacity [1]. For a soft capacity-limited system, the traffic in Erlangs cannot be directly calculated from the Erlang-B formula, because it would give too pessimistic results. It overestimates the capacity need, because each service is handled separately in the system calculations. On the other hand, if the system is code-limited, the capacity can be estimated by using the Erlang-B model [8]. In a code-limited situation, the noise rise in the network does not cause outage, or blocking, because the communication between links is limited by the number of codes. Hence, in a code-limited situation, the behavior of a UMTS network is like that of TDMA/FDMA networks, and therefore Erlang-B formulas can be utilized.

In [9], a method has been presented for evaluating the number of traffic channels needed to handle traffic with respect to the blocking rate in a multi


service context in UMTS networks. Verification of the capacity need of a cell was implemented using the Erlang-B or Erlang-C model, which combines joint blocking probability calculations of different services. The results show that the multi service method avoids over-dimensioning the radio resources of the network and yields a more accurate business plan.

5.2.2.2 Load equation approach

The load equation is commonly used to make a semi-analytical prediction of the average capacity of a WCDMA cell, without going into system level capacity simulations [1]. There are a number of elements that influence the load on a UMTS network, which on the contrary defines the maximum number of users per cell. Moreover, the number of users and their bit rates influence the total throughput of a cell. Also, the activity factor in speech and data services affects the load and throughput. However, probably the most important contributor to the load is the required Eb/N0 value, which depends at least on service type, data rate of the service, propagation conditions, and receiver performance. If a very good quality (i.e., high Eb/N0

requirement) connection is desired, more bits are needed for the error correction in order to guarantee the quality of the connection. Thus, when more bits are used for error correction, the air interface load is increased and capacity for the traffic channels is decreased.

The own-cell and other-cell interference influences the load of a cell. If the total received noise is high, high powers are needed for the transmission in order to guarantee the communication. If high transmit powers are needed, transmit power may run out, with the result that Eb/N0 requirements for the services are not met and mobiles are out of service. The noise received from other cells also depends on the environment. In urban areas, the cells are isolated better than cells in rural areas. However, the radio network plan probably has the most significant influence on interference. An accurate radio network plan guarantees low interference levels and thus enables good quality and appropriate capacity.

5.2.2.3 Uplink load equation

Depending on the maximum allowed load in a cell, the number of users can be calculated by using the load equation and assuming that the load of each individual user can be estimated. In the UL direction, the load can be expressed by Equation 5-1 [10]:


( )( )

=

+

⋅⋅+

=N

ij

jjjob

UL i

RNE

W1

1

1

υ

η .(5-1)

In Equation 5-1, N is the number of active users in the cell and W is the system bit rate (chip rate), which in UMTS equals 3.84 Mcps. Rj is a bit rate of the jth user, and (Eb/N0)j is energy per bit over the noise spectral density requirement for the jth user. The activity factor j of the jth user indicates the activity of speech when discontinuous transmission (DTX) is used. For speech service, DTX is typically assumed to be from 0.4 to 0.7 and 1.0 for data services. Other-to-own-cell interference i informs the noise power received from the neighbor cells. The pole capacity is achieved when UL

approaches 1, but in practice the maximum allowed load must be kept clearly below 1 to ensure stability of the network [11].

The uplink load factor defines the required interference margin (IM) (Equation 5-2) in a power budget in order to take into account the effect of cell-breathing:

( )ULULIM η−−= 1log10 10 . (5-2)

The interference margin (also called noise rise) informs how much noise has to be added to the noise floor of the receiver to facilitate the exact amount of interference. The interference margin takes into account noise from own cell as well as noise from other cells. The more users there are in the network, the more interference there will be, both for own cell and from surrounding (other) cells. When the load factor approaches unity (i.e., 100% load), the interference margin approaches infinity, as seen in Figure 5-2.

By assuming only voice users of a 12.2 kbps bit rate, Eb/N0 requirement 5 dB, and voice activity factor 0.6, the resulting interference margin is plotted as a function of cell throughput values using the three different other-to-own-cell interference ratios 1.1, 0.9, and 0.7.

In this particular case, an uplink load of 50% (interference margin of 3 dB) equals cell throughput values of 495 kbps, 550 kbps, and 610 kbps, and an uplink load of 75% (interference margin 6 dB) to 738 kbps, 815 kbps, and 910 kbps, corresponding to interference values 1.1, 0.9, and 0.7, respectively. Figure 5-3 clearly indicates the importance of controlling the interference from other cells as well as in own cell.


0 10 20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

14

16

18

20

Load [%]

Inte

rfer

ence

mar

gin

[dB

]

Figure 5-2. Interference margin as a function of load.

0 100 200 300 400 500 600 700 800 900 10000

2

4

6

8

10

12

14

16

UL throughput [kbit/s]

Inte

rfer

ence

mar

gin

[dB

]

i=1.1i=0.9i=0.7

Figure 5-3. Uplink interference margin as a function of cell throughput.


5.2.2.4 Downlink load equation

In UMTS networks, downlink behaves a bit differently from uplink because multiple connections share the same base station transmit power. Moreover, each mobile at a different location experiences different interference levels (a different i for mobiles at different locations). In the downlink direction, the load equation can be presented by Equation 5-3 [1]:

( ) ( )[ ]jj

N

j j

jbjDL i

RW

NE+−=

=

αυη 11

0. (5-3)

The downlink load equation is similar to the uplink load equation, except it includes the orthogonality factor j ( j = 0…1). The value of the orthogonality factor depends on the orthogonality of the codes used in the network. Without multi path propagation, codes would be fully orthogonal ( j = 1), but multi path propagation destroys orthogonality, causes interference, and finally increases the load, as seen from Equation 5-3.

The downlink load factor also defines the base station transmit power, as shown in Equation 5-4 [12]:

( )

DL

N

j j

jb

jrf

BS

RW

NELN

Pη

υ

−= =

1

1

0

(5-4)

where L is the average path loss between the base station and mobile station, and Nrf is the noise spectral density. When the downlink load factor saturates, the system approaches its pole capacity and the required transmit power approaches infinity. In practice, the base station transmit power is limited by the specifications and thus the base station transmit power may limit the downlink capacity and coverage in highly loaded networks.

From Equations 5-1 and 5-3, it can be observed that by decreasing the other-to-own-cell interference, the load of the network can be significantly decreased. A lower load in the uplink direction affects the uplink noise rise and a lower load in the downlink direction reduces the average required base station transmit power.

5.2.3 Coverage and capacity enhancements in the topology planning

In order to improve network coverage and system capacity, equipment in the power budget and network topology should be enhanced or optimized. Power budget related enhancements are presented in Chapter 2. In this


section, network topology related coverage and capacity enhancements are introduced.

5.2.3.1 Coverage improvements

Coverage of a UMTS network should be enhanced when the network is coverage-limited in the uplink or downlink direction. First, the use of power budget related equipment such as a low noise amplifier [13-15], power amplifier, and diversity have to be optimized. After power budget enhancements, the network topology can be changed by sectoring the base station site.

Sectoring improves the base station coverage due to directional high gain antennas. When increasing the number of sectors from omnidirectional to 3-sectored, the sector antenna configuration has more gain than the omnidirectional configuration. Typically in 3-sectored sites, a 65° horizontal beam width antenna is utilized for best performance – both from the capacity and coverage point of view [16]. The effect of sectoring is further discussed in Section 5.3.3.

Repeaters can also be classified as network topology related equipment. Repeaters provide a solution to extend the coverage of an existing base station [13]. Moreover, the operational costs of repeaters are much lower than conventional sites [17]. In a UMTS, network repeaters cause additional interference for own and surrounding cells [18], so they should be included in system simulations. Repeater planning in UMTS is explained in more detail in Chapter 2.

5.2.3.2 Capacity improvements

This section gives a short introduction to some network topology related capacity enhancement methods. The capacity of a UMTS network must be increased if system capacity is lacking in some locations of the network or if growing traffic demands it. The methods for network topology related system capacity improvements are the following: – additional carriers – sectoring – micro cell deployment – base station antenna configuration.

The simplest and most effective way to increase system capacity is to add one or more carriers. Most UMTS operators have more than one carrier. If an operator’s frequency allocation allows, an additional carrier can be taken into use in order to increase the capacity of the network. Using macro cell and micro cell carriers efficiently can provide the highest overall system capacity and spectrum efficiency. This requires very careful radio network


planning to ensure adequate isolation between macro and micro layers if the same carrier frequencies are used [15].

Sectoring in cellular CDMA systems increases the capacity in proportion to the number of sectors per cell [19]. Because of sector overlapping, additional interference is generated in the uplink and downlink direction. Hence, antenna beam width plays an important role in sectoring when an increase in capacity is desired.

Micro cells provide a high capacity solution that is particularly suitable for urban and dense urban environments where high site densities are required and macro cell site acquisition becomes difficult [15].

Base station antenna configuration affects the capacity of the base station. By optimizing the base station antenna configuration, interference can be controlled thereby enhancing capacity.

5.2.4 Initial topology planning

By using power budget analysis and load equation approaches, estimations of site densities and configurations for a planning area can be determined. In the initial topology planning phase, the main goal is to use the information provided by power budget calculations for different services and the information provided by load equations in order to determine the average site density in the planning area. First, the maximum cell range of the limiting service is identified. Next, the load equations are used to verify whether or not the given load limits are exceeded when using the limiting cell range. If the load of a cell does not exceed the given threshold, the cell is dimensioned to be coverage-limited. On the other hand, if the load exceeds the given threshold and if the cell range defined by the capacity evaluations is smaller than the cell range defined by the coverage evaluations, the cell is capacity-limited. The initial topology planning can also be considered as system dimensioning.

5.2.4.1 Traffic distribution

Traffic in a cellular network is not distributed uniformly over a planning area. It is mainly concentrated in urban areas, which are more populated than rural areas. Thus cell ranges are smaller in urban areas. In addition to that, users are mainly located in indoor locations where propagation loss and slow fading standard deviation are higher. In order to provide indoor coverage, the coverage thresholds should be set to a sufficient level.

Figure 5-4 shows an example where indoor and outdoor users are served by the same sector. The required signal power level for a sufficient communication link is higher for an indoor user than for an outdoor user. Thus, the required transmit power for an indoor user is higher. Due to


additional transmit power, more interference is radiated in the direction of an outdoor mobile. Moreover, this causes an increased need for transmit power for an outdoor mobile.

In a TDMA/FDMA network, the situation depicted in Figure 5-4 does not cause any harm, since mobiles share either a different time slot or a different frequency. However, in UMTS networks, increased interference limits capacity.

Figure 5-4. Indoor and outdoor users.

Figure 5-5 presents coverage probabilities in three different traffic scenarios. In the upper-left corner, the simulation area is depicted. Two 3-sectored sites cover this example area. The light gray area is forest/park, white is open area, and dark gray/black blocks are buildings of different heights. Buildings cover a total of 8.7% of the simulation area.

In the upper-right corner a homogenous traffic distribution is used (traffic scenario 1). The yellow color indicates that the coverage probability in that area is 100%, and the blue dots mean that the coverage probability is less than 100%. As seen from Figure 5-5, outage connections occur randomly over the area where there is a homogenous traffic distribution, but are concentrated in the middle of the cells where the interference level is higher. In the lower-left picture, indoor users are included in the simulations (traffic scenario 2). An additional indoor loss of 15 dB is added in the power budget if users are located indoors. Furthermore, the standard deviation of slow fading is increased from 10 dB to 15 dB in indoor locations. Now, call


failures occur more frequently in indoor locations, but there are still outage connections in outdoor locations. The lower-right corner depicts a traffic situation (traffic scenario 3) where the number of indoor users is 70% of all users. In this case, nearly all failed connections occur in indoor locations, and only a few failed connections occur in outdoor locations.

Figure 5-5. Coverage of three different traffic scenarios.

In Table 5-2, the coverage probabilities of traffic scenarios 1, 2, and 3 are presented. The overall coverage and indoor coverage probabilities mean that the coverage probability for the service has exceeded the 90% threshold. Indoor coverage values are weighted average values, and for traffic scenario 1, the indoor coverage probability is calculated for building locations without indoor loss. As expected, the overall coverage probability decreases when adding indoor loss and weighting the indoor users. The indoor coverage probability for traffic scenario 3 is a few percent higher than for traffic scenario 2. This could be caused by the favorable locations of the buildings in the simulation area with respect to the base station locations.


Table 5-2. Overall and indoor coverage probabilities for speech users. Overall coverage Indoor coverage

Traffic scenario 1 92.78 90.83 Traffic scenario 2 91.62 62.57 Traffic scenario 3 89.95 64.55

In general, non-uniform traffic degrades overall performance of the system because it creates traffic hot spots where connection failures are more likely to occur. Also, dominance areas of the sectors are not evident due to the fact that the site density grows and the cells overlap more – this happens especially in urban areas. Hence, traffic distribution and especially indoor users have to be considered in UMTS network planning.

5.2.4.2 Coverage - Capacity

Identifying the limiting direction, uplink or downlink, is vital in order to balance the power budget. The network performance can be either coverage or capacity-limited in the uplink or downlink direction. Typically, uplink is limiting when the network has a low load. When the load increases, downlink starts to limit more and more due to the fact that the base station transmit power is divided among multiple users. Figure 5-6 depicts a typical coverage-capacity scenario.

[dB

]

Capacity

Pat

h lo

ss

DownlinkUplink

[kbit/s]

Figure 5-6. Uplink and downlink path losses as a function of capacity.

The coverage is uplink-limited due to the smaller transmit power of the mobile. The coverage is a limiting factor when the load of the network


remains lower than expected in cell range calculations in the dimensioning phase. Uplink coverage-limited situation is likely to occur in rural areas where users are spread out in a very large geographical area and the cells are planned with relatively a low load. Correspondingly, a downlink coverage-limited situation could occur in an urban area with asymmetric data traffic when high indoor coverage probabilities are required. In order to improve uplink and downlink coverage, diversity reception and diversity transmission, a low noise amplifier (LNA) and power amplifiers (PA) could be utilized.

A capacity-limited situation can also occur in both directions. An uplink capacity-limited situation occurs when the system load exceeds the given load threshold. The downlink capacity-limited scenario occurs when the base station’s transmit power is running out. Capacity-limited scenarios are likely to occur when the network is planned for too low load scenarios. Hence, sudden traffic congestion in a low loaded cell could easily create a capacity-limited situation. Moreover, capacity could be limited in the downlink direction in dense urban areas, where there is highly asymmetric traffic demand and more uplink load is allowed. An understanding of which direction is limiting in certain situations and a deep knowledge of power budgets and load equations are required for successful UMTS network planning.

5.2.5 Detailed topology planning

In the detailed topology planning phase, the network parameters and configurations of the initial topology planning phase are moved into a radio network planning tool or simulator. The most important requirements for a radio network planning tool are defined in Chapter 4. The planning tool is mainly used for coverage predictions and capacity simulations of the planning area. The power budget is also inserted in the planning tool together with base station site configurations.

Since traffic distribution is very important and has a strong effect on topology planning, the importance of traffic models also must be emphasized. The more accurate the traffic models are, the more precisely the load of the network can be modeled.

Finally, coverage predictions and capacity simulations are performed by utilizing a planning tool. The simulation results include a coverage and capacity analysis of a planning area when certain base station site configurations are used. If coverage or capacity is not good enough, base station site configurations have to be modified in order to achieve better coverage or capacity. New simulations are required when any coverage or capacity related network element is modified because interference levels


between neighbor cells have to be recalculated. Also a new coverage and capacity analysis has to be provided. In order to achieve the maximum coverage and capacity, base station site configurations (number of sectors, sector orientations, site distance) have to be optimized for different site locations and antenna configurations (antenna height, beam width, and tilting).

5.3 UMTS site configuration

Network coverage and system capacity are mainly determined by the site densities, locations, and configurations. In UMTS, the radio planning site location has to be first selected with an appropriate number of sectors that must be directed in optimal directions. Each of these three selections has a certain influence on radio network system capacity, and they have a certain influence on each other.

5.3.1 UMTS site locations

In UMTS network planning, the site density for a planning area is defined by the amount of traffic together with traffic requirements and distribution. When the maximum cell range for the most sensitive service is known (usually a high speed data service), the search for the candidate site location can be started.

A hexagonal grid planning would be the most efficient strategy to deploy a macrocellular network if the traffic distribution and environment were homogeneous. Unfortunately, traffic congestion is created both by the environment and building distributions, and moreover the environment is not typically favorable for hexagonal grid planning strategy. Typically, topography or morphology of the terrain creates restrictions for the ideal site locations. In urban environments where base stations are often located on top of buildings, the physical space required for the hardware of the planned site solution may not be enough. In some places, authority constraint or government regulations may prevent an operator from deploying a base station to an optimal place from their network performance point of view. Also economic reasons could persuade an operator to select another place for the site. Hence, a maximum deviation in site locations should be defined that avoids a significant reduction in network coverage and system capacity.

Figure 5-7 illustrates the impact of non-hexagonal base station locations. As a consequence of new base station locations, the interference level between BS2 and BS3 is rising and thus capacity is decreasing. On the other hand, the distance between base stations BS1 and BS2 is increasing and


reducing interference in that direction. Also, mobiles located in the area between BS1 and BS2 may have coverage problems. Hence, the effect of deviation of the site locations is mainly related to the average distance between base stations. This analysis was made by assuming a homogenous traffic distribution. In a non-homogenous traffic distribution, if the new (randomized) base station location would be farther away from a traffic hot spot such as a business building, network performance would deteriorate.

BS3

BS2

BS1

Figure 5-7. Impact of non-hexagonal site locations.

The displacement of base station locations from the ideal hexagonal grid has been found to have negligible impact on C/I values in cellular systems in a homogenous environment and traffic distribution [20–23]. These references cover the system performance for narrowband as well as wideband cellular systems. The results have great importance due to the fact that small deviations do not affect cellular system performance. On the contrary, in [24], which concentrated on a UMTS system, the base station location was concluded to have a notable impact on downlink and uplink performance with a relatively large cell range.

5.3.1.1 BTS location deviation simulation setup in topology planning

The impact of UMTS base station location deviation must be simulated in the topology planning phase (site selection) by using a radio network planning tool and moreover by utilizing a high-resolution digital map. A planning example of the impact of this planning phase is given by using a


reference macrocellular hexagonal grid layout, depicted in Figure 5-8. The hexagonal structure is not the optimum planning in the chosen simulation environment because the terrain has variations and the dominance areas of the base stations are not equal. However, the hexagonal grid represents an independently defined reference network that is used for comparison.

Figure 5-8. Ideal hexagonal grid of 17 base stations.

The simulation area must be defined by a digital map using very small pixels (e.g., 5m x 5m) and including topography and morphological data and building rasters. The area of the digital map represents a typical suburban or light urban environment. The performance of the radio network in different scenarios is calculated with a radio network planning tool that includes a static simulator for UMTS network system simulations.

In the system simulations, a cluster of cells is needed to calculate interference. In this example, 17 base stations are arranged in a hexagonal grid with sites separated by 1.5 km (the distance between sites). Base stations are configured with three sectors each having a 65° horizontal beam width antenna. Base station and mobile station antenna heights are 25 m and 1.5 m, respectively. Antenna directions are 0°, 120°, and 240°; and those are


kept fixed after moving the base station to its new location. The Okumura-Hata propagation model is utilized at a carrier frequency of 2140 MHz. The propagation model is adjusted with average -6.7 dB area correction factors and some topographical corrections. Propagation slope is also adjusted to 35 dB/dec. Only voice users (12.2 kbps) load the network, and the traffic distribution (homogenous or non-homogenous, indoor or outdoor users) must be accurately defined. The most relevant simulation parameters are gathered in Table 5-3, and the power budget for the simulations is presented in Table 5-4.

Table 5-3. General simulation parameters. Parameter Value

BS maximum power [dBm] 43 CPICH [dBm] 33 CCCHs [dBm] 33 SCH [dBm] 33 MS dynamic range [dB] 70 Required Ec/N0 [dB] -18 Standard deviation of slow fading [dB] 10 DL orthogonality 0.6 HO window [dB] 4

Table 5-4. Power budget for the simulations. Parameter Voice

Uplink Downlink Units

RX noise figure 5 9 dB Thermal noise -108.15 -108.15 dBm Noise power at receiver -104.15 -99.15 dBm Interference margin 6.02 6.02 dB Total noise power at receiver -98.13 -93.13 dBm Processing gain 24.08 24.08 dB Required Eb/N0 5 8 dB Receiver sensitivity -117.21 -109.21 dBm

RX antenna gain 18 0 dBi Cable loss / body loss 2.5 3 dB LNA gain 4 0 dB SHO diversity gain 1.5 3 dB Power control headroom 2 2 dB Required signal level -136.21 -107.21 dBm TX power per connection 21 33 dBm Cable loss / body loss 3 2.5 dB TX antenna gain 0 18 dBi Peak EIRP 18 48.5 dBm Allowed propagation loss 154.21 155.71 dBm


5.3.1.2 BTS location deviation simulations

An error is given for each base station location by vector, thus describing its new location in an irregular grid. In practice, the maximum deviation should not exceed one-quarter of the site separation in urban areas. Two different typical urban site separations of 1.5 km and 3.0 km are used in this example. After giving the error for the site locations, the average departure is 180 m and 356 m from the hexagonal locations, corresponding to 1.5 km and 3.0 km site separations. Altogether five different base station displacement cases are simulated to show the impact of site selection. A part of the reference (hexagonal) network and irregular grid base station locations are illustrated in Figure 5-9.

Figure 5-9. Hexagonal grid locations and other base station locations.

The network performance has to be evaluated by measuring service probability, soft handover (SHO) and softer handover (SfHO) probabilities, and averaged values of sector throughput (the same in the downlink and uplink direction), uplink noise rise and load, together with downlink average transmit power. The simulation results of 1.5 km site separation without indoor users are presented in Table 5-5. Three columns of the reference and base station irregular grid (displacement cases) represent homogenous traffic amounts of 1000, 2000, and 3000 voice users, i.e., a different network load. Irregular grid results are averaged values of five different network layouts.

According to the simulation results, a small deviation in hexagonal structure does not affect the overall performance of the network in a


practical urban network layout when indoor coverage is required (overlapping coverage). SHO and SfHO probabilities remain practically the same as in the reference case. Moreover, the difference between other parameters is very small. This simulation example shows that the hexagonal structure is not necessarily the optimal solution for the network when terrain topography and morphological information have been taken into account. In addition, only a small increase in network performance parameters (DL average transmit power and UL load) can be observed.

Table 5-5. Simulation results of irregular grid, outdoor users only and 1.5 km site separation. Parameter Reference grid Irregular grid (average)

Number of users 1000 2000 3000 1000 2000 3000 Service probability [%] 99.6 98.1 72.5 99.5 98.2 72.9 SHO probability [%] 24.1 24.9 31.3 24.4 25.0 31.4 SfHO probability [%] 3.7 3.9 5.5 3.8 3.9 5.5 Throughput [kbps/sector] 159 315 381 160 318 383 UL noise rise [dB] 1.09 2.53 2.89 1.09 2.55 2.94 UL load [%] 21.9 43.2 48.1 21.9 43.4 48.6 DL power [dBm] 32.7 37.2 40.1 32.8 37.3 40.2

In practice, system simulations have to be done with indoor users. For indoor users, a standard deviation of slow fading is 15 dB and an additional 15 dB indoor loss is added in the power budget. These simulation results are shown in Table 5-6. The difference between the reference network and displacement networks is still marginal, as seen from the results.

Table 5-6. Simulation results of irregular grid, indoor users and 1.5 km site separation. Parameter Reference grid Irregular grid (average)


In order to simulate practical non-homogenous traffic, indoor users are weighted 70% and outdoor users 30%. The simulation results of this non-homogenous traffic are only slightly changing, as shown in Table 5-7. However, the network is already uplink coverage-limited because of indoor users (hot spots), and the service probability remains less than 95% although only 1000 users are included.


Table 5-7. Simulation results of irregular grid, non-homogenous traffic distribution and 1.5 km site separation. Parameter Reference grid Irregular grid (average)

Number of users 1000 1000 Service probability [%] 94.0 94.1 Soft HO probability [%] 23.7 23.9 Softer HO probability [%] 3.4 3.5 Throughput [kbps/sector] 149 149 UL noise rise [dB] 0.99 0.98 UL load [%] 19.2 19.9 DL power [dBm] 32.6 32.6

The relation between site location and site distance can be analyzed by increasing the site separation by 3.0 km. The randomness in site locations has an affect as seen in Table 5-8. The service probability is now 2% lower than in the reference network, and the average sector throughput has slightly dropped. The uplink load has remained lower due to the decreased service probability in irregular grid networks, as in previous simulations. In the downlink direction, the averaged transmit power is approximately the same.

Table 5-8. Simulation results of irregular grid, outdoor users only and 3.0 km site separation. Parameter Reference grid Irregular grid (average)

Number of users 2000 2000 Service probability [%] 96.2 94.0 SHO probability [%] 17.2 18.0 SfHO probability [%] 4.6 4.9 Throughput [kbps/sector] 289 285 UL noise rise [dB] 2.10 2.07 UL load [%] 37.6 37.1 DL power [dBm] 36.3 36.3

Pilot coverage analysis is also important in topology planning for ensuring the proper functioning of soft handovers. In Table 5-9, indoor and outdoor pilot coverage probabilities of base station displacements of 1.5 km and 3.0 km site separations are compared.

Table 5-9. Indoor and outdoor coverage probabilities of 1.5 km and 3.0 km site separations. Site separation 1.5 km 3.0 km

Indoor Outdoor Indoor Outdoor

Reference grid 87.9 99.9 54.9 96.6 Displacement 1 90.2 99.9 50.6 96.6 Displacement 2 86.4 99.6 51.6 95.5 Displacement 3 87.9 99.6 52.7 96.9 Displacement 4 84.0 98.9 53.6 95.9 Displacement 5 87.5 99.9 52.5 95.9


In a 1.5 km site separation, indoor coverage probability is nearly 90% in all cases and outdoor coverage probably close to 100%. Correspondingly, the indoor service probability is closer to 50% in the case of a 3.0 km site separation.

5.3.1.3 UMTS site selection

The UMTS base station location and thus the site selection is robust for small deviations when traffic hot spots (shopping malls, mobile offices) are not included and when coverage overlapping is significant, as is typical in urban areas. Hence, an optimal site configuration is often a more critical task in the topology planning phase than the definition of the site location [25].

5.3.2 UMTS sector orientation

Sector orientation (also called antenna direction) is one of the key elements that define the coverage of a UMTS network, and thus it also affects the system performance. Base station antenna directions have to be defined in the detailed topology planning phase when defining the final network configuration for coverage and capacity simulations. Sometimes base station antennas are directed by having equal spacing. In urban areas, the base station antennas are typically installed on top of buildings. However, due to obstacles close to the base station site location or due to errors, e.g., in the base station antenna implementation, antenna directions may change and affect the UMTS system performance.

Figure 5-10 illustrates the effect of the base station antenna direction deviation on the handover areas.

BS2

BS1 Increased number ofSfHO connections

Increased number ofSHO connections

Figure 5-10. Impact of base station antenna direction deviation.


If the directions of the antennas belonging to the same site are changed like in BS1, the result is that the number of softer handover (SfHO) connections rises due to increased sector overlapping. The number of additional SfHO connections depends strongly on the horizontal beam width of the base station antennas. On the other hand, if antennas of different base stations are directed more towards each other, additional SHO connections could occur in that area.

5.3.2.1 UMTS sector orientation simulations in topology planning

An example of sector orientation is given in order to show the impact of this topology planning phase when a radio network planning tool is utilized. The same reference network (hexagonal base station locations, antenna directions and simulation parameters) are used as in Section 5.3.1.1. The indoor user characteristics are also the same. The simulation results of antenna direction deviation cases of 9.1° and 18.2° average deviation from original direction under different traffic scenarios are presented. The base station antenna directions with 18.2° average deviation are depicted in Figure 5-11.

Figure 5-11. Base station antenna direction with average 18.2° deviation.

The simulation results in Table 5-10 show that a small, random deviation in base station antenna direction does not greatly affect UMTS system


performance if overlapping is sufficient (as in urban areas in practice) and if traffic distribution is homogenous. However, the effect of antenna direction deviation seems to be more significant than the base station location deviation. The service probability is nearly the same with different network loads. Also the SfHO probability has increased by a small amount. Altogether, when taking into account only outdoor users, the impact of antenna direction deviation is quite small.

Table 5-11 introduces the results from the same simulation when the impact of indoor users is included. The service probability has deteriorated a bit, but adding indoor users in the system does not affect the differences between reference network and antenna direction deviation networks.

Table 5-10. Results of 9.1° antenna direction deviation without indoor users. Parameter Reference grid Random antenna

directions (average)


Table 5-11. Results of 9.1° antenna direction deviation with indoor users. Parameter Reference grid Random antenna



In Table 5-12 the impact of non-homogenous traffic distribution between indoor and outdoor users is presented. The simulation results in Table 5-10, Table 5-11, and Table 5-12 show that a small antenna deviation has no significant effect on the UMTS system performance. Furthermore, traffic distribution and indoor users must be highlighted in topology planning because they have a strong influence on the UMTS system performance.


Table 5-12. Results of 9.1° antenna direction deviation with non-homogenous traffic distribution and 70% weight for indoor and 30% weight for outdoor users. Parameter Reference grid Random antenna


Number of users 1000 2000 3000 1000 2000 3000 Service probability [%] 94.0 91.2 71.4 93.8 91.0 71.1 SHO connections [%] 23.7 24.6 29.2 23.9 24.6 29.3 SfHO connections [%] 3.4 3.6 4.8 3.6 3.8 5.1 Throughput [kbps/sector] 149 292 363 149 292 363 UL noise rise [dB] 0.99 2.23 2.71 0.99 2.23 2.70 UL load [%] 19.2 38.8 45.5 19.9 38.8 45.4 DL power [dBm] 32.6 36.7 39.3 32.6 36.7 39.3

Another example of sector orientation is presented in Table 5-13, and 5-14 by having 18.2° deviation with and without indoor users. Even if the deviation of 18.2° is significant compared to the 65° horizontal beam width of the base station antenna used in the simulations, the system performance still remains almost constant.

The results in Tables 5-10 – 5-14 give an idea about expected UMTS system performance deviations when sector orientations are designed in the topology planning phase using a radio planning tool.

Table 5-13. Results of 18.2° antenna direction deviation without indoor users. Parameter Reference grid Random antenna



Table 5-14. Results of 18.2° antenna direction deviation with indoor users. Parameter Reference grid Random antenna




5.3.2.2 Selection of UMTS sector orientation

In UMTS networks, as in other cellular networks, sector orientations are selected first by using common sense: UMTS networks are started with 3-sectored sites by having an approximately 120° separation in antenna directions. In practice, sector directions have to be changed and reasonable changes do not cause any major reductions in UMTS network performance in urban areas where cell overlapping is significant. However, traffic distribution and indoor users as well as rural areas have to be especially concerned in sector selections. Moreover, sector orientations can be mainly selected based on dominance area needs.

5.3.3 Base station sectoring and antenna beam width in UMTS

Sectoring is used to increase the system capacity as well as coverage in UMTS networks. Along with sectoring, the importance of the antenna horizontal beam width increases because sector overlapping becomes increasingly crucial. In topology planning, the number of sectors as well as antenna beam widths must be finally selected in order to optimize the network performance.

5.3.3.1 Sectoring

Sectoring means an increase in the number of sectors belonging to a site in order to increase the capacity of the cellular system [26]. Directional antennas transmit only to those directions where the signal is really intended, thus cutting down co-channel interference [27] and allowing a network to serve more mobiles. Hence, sectoring offers more capacity to the network. In order to achieve this extra capacity, antenna selection is crucial to effectively control interference and soft handover overhead [28].

In existing cellular networks, 3-sectored sites are commonly used, and 1-sectored base station antennas are used only in small micro cells or in indoor cells. 2-sectored base stations are used mainly in sectored micro cells or to provide roadside coverage. A standard macrocellular solution for low or average loaded networks is utilization of 3-sectored sites, and for high capacity needs in a macrocellular environment, 6-sectored sites are required to provide better system performance. A 4- or 5-sectored site is not commonly used but may be chosen to support a specific traffic scenario [15].

In Figure 5-12, two 6-sectored sites are depicted by having fixed antenna directions of 0°, 60°, 120°, 180°, 240°, and 300°. An arbitrary, narrow beam antenna radiation pattern is drawn to illustrate the main and side lobes of narrow beam sector antennas. Although the antenna radiation pattern is not real, it depicts quite accurately how a directional antenna radiates. The main beam direction of coverage is good and all the mobiles located in that


particular direction have good field strength. Furthermore, mobiles in adjacent sectors are not interfered with as much as with wider antenna beam widths (MS at light gray area). But in contrast, if the mobile is not in a handover with a sector belonging to cell site 2, the directional narrow beam antenna raises the interference level of the cell. The increased interference level forces mobiles to use higher transmit powers for the communication.

Cell site 1

Cell site 2

MS

Figure 5-12. 6-sectored base stations using narrow beam antennas.

On the other hand, sectoring increases the number of softer handover connections in the network if wide beam width antennas are used, thus decreasing the capacity of the network. The handover connections and interference can be controlled with proper antenna beam width selection.

5.3.3.2 Antenna beam width

Base station antenna beam width plays an important role in UMTS network performance, especially in higher-order sectoring. In order to provide sufficiently high capacity in both 3-sectored and 6-sectored sites, the other-cell interference has to be low. This can be achieved by narrowing the radiation patterns of the base station antennas [28].

In Figure 5-13, a 3-sectored base station with imaginary antenna radiation patterns is depicted. The darker areas between the sectors are sector overlapping areas and hence possible SfHO areas. SfHO areas are needed in a UMTS network in order to maintain the interference level as low as possible during the sector handover procedure, but too large SfHO areas


consume limited radio resources of the base station. A wider base station antenna beam width also increases the interference level of the neighboring sector, thus reducing the capacity. The importance of the base station antenna beam width is emphasized in higher-order sectoring. The sectoring efficiency is highly dependent on the base station antenna beam width.

Figure 5-13. A 3-sectored base station and illustration of sector overlapping.

5.3.3.3 Sectoring and beam width simulations in topology planning

A simulation example is given in order to show the impact of sectoring and antenna beam width selection on system capacity in topology planning when a radio planning tool is utilized. In the simulations, 10 base stations are placed in a typical macrocellular environment in a hexagonal grid by having a distance of 2.0 km. In the 3-sectored sites, the antenna directions are 0°, 120°, and 240°. In the 6-sectored sites, the antenna directions are 0°, 60°, 120°, 180°, 240°, and 300°. The antenna directions are kept fixed during the simulations. A homogenous traffic distribution of outdoor voice (8 kbps) users is used. The standard deviation of slow fading is 8 dB. The maximum power per connection is 40 dBm and the handover window is 3 dB. The rest of the simulation parameters are the same as in Table 5-3 (Section 5.3.1.1). The horizontal radiation patterns of the 33°, 65°, and 90° antennas used in the simulations are depicted in Figure 5-14.

First, 3-sectored sites of 90° antennas and 6-sectored sites of 90° antennas are simulated. The results are shown in Table 5-15. Two columns


of the same sectoring correspond to lower and higher traffic scenarios, i.e., different load simulations.

Figure 5-14. Horizontal radiation patterns of antennas (33°, 65°, 90°) used in simulations.

In Table 5-15, the service probability is observed to be quite low for both sectoring examples. This is caused by the power control error introduced in the simulation parameters of the radio planning tool.

Table 5-15. Results of sectoring of 90° antennas. Parameter 3-sector 90° 6-sector 90°

Service probability [%] 83.1 76.3 84.5 84.4 SHO probability [%] 13.9 9.1 11.9 11.9 SfHO probability [%] 7.7 6.3 19.3 19.6 Throughput [kbps/site] 823 1006 901 1261 UL noise rise [dB] 3.25 4.68 1.48 2.27 UL load [%] 52.0 65.6 28.6 40.3 DL power [dBm] 39.3 41.5 34.5 37.7

In the lower load simulation, the service probability of the 3-sectored network is lower than in the 6-sectored network. After increasing the load of the network, the performance of the 3-sectored network begins to deteriorate but the increased load has no influence on the service probability of the 6-sectored network. The total number of HO connections in the lower load situation is 21.60% and 31.20%, corresponding to the 3-sectored and 6-sectored networks, respectively. As the results show, sectoring increases the total number of HO connections. Especially in the 6-sectored network, due to the huge sector overlapping, the number of SfHO connections is higher than the number of SHO connections. When increasing the load of the network, the number of HO connections in the 3-sectored network decreases. This is caused by the deteriorated Ec/I0 relation due to the raised interference level. In the higher load network, the 3-sectored configuration becomes very


highly loaded in DL because its average transmit power is almost hitting the maximum.

Secondly, antennas with 65° horizontal beam width are used and the results are presented in Table 5-16. Also in this configuration, the service probability is enhanced due to sectoring. The number of SHO connections drops a little bit from 14.20% to 12.90%, but the number of SfHO connections increases from 6.20% to 16.60%. The average site throughput is increased from 815 kbps to 889 kbps due to additional SfHO connections. The performance in both downlink and uplink directions is improved after increasing the number of sectors, because less DL transmit power is used to serve the same number of users.

Table 5-16. Results of sectoring of 65° antennas. Parameter 3-sector 65° 6-sector 65°

Service probability [%] 83.1 76.7 84.4 84.3 SHO probability [%] 14.2 9.7 12.9 13.0 SfHO probability [%] 6.2 5.3 16.6 16.8 Throughput [kbps/site] 815 1010 889 1245 UL noise rise [dB] 3.18 4.60 1.45 2.22 UL load [%] 51.1 65.6 28.2 39.7 DL power [dBm] 38.9 41.2 34.2 37.3

The corresponding results of 33° antennas in the 6-sectored network are shown in Table 5-17. The service probability is marginally decreased due to lack of coverage but the overall performance is better compared to networks of 65°/90° antennas in a 6-sectored network.

Table 5-17. Results of sectoring of 33° antennas. Parameter 6-sector 33°

Service probability [%] 84.2 84.1 SHO probability [%] 15.4 15.6 SfHO probability [%] 4.8 4.9 Throughput [kbps/site] 823 1153 UL noise rise [dB] 1.28 1.97 UL load [%] 25.2 35.5 DL power [dBm] 32.5 35.2

In Figure 5-15, DL throughputs of different antenna horizontal beam widths of 3- and 6-sectored sites are plotted as a function of DL average transmit power. The lowest curves represent 65° and 90° antennas in 3-sectored configurations. The capacity performance seems to be better when using 65° antennas. The upper curves represent 6-sectored configurations of 33°, 65°, and 90° beam widths. The capacity performance of 65° and 90° antennas is equal but 33° antenna beam width gives better capacity. The


sectoring efficiency can be nearly 70% when using 65°/90° antennas. However, almost 100% sectoring efficiency can be achieved by using 33° antennas in 6-sectored sites.

800

1000

1200

1400

1600

1800

2000

32 33 34 35 36 37 38 39 40 41 42

DL average transmit power [dBm]

DL

thro

ughp

ut [

kbit/

s/si

te]

3-sector /90

3-sector /65

6-sector /90

6-sector /65

6-sector /33

Figure 5-15. Capacity curves of 3- and 6-sectored sites of different beam widths.

5.3.3.4 Sectoring and antenna beam width selection in UMTS

Sectoring is an important element of topology planning because it has a strong impact on system capacity. A proper number of sectors have to be selected for different network evolution phases (see Section 5.3.5), and base station antenna beam widths have to be selected based on the number of sectors. The selection of antenna beam width becomes crucial in higher-order sectoring. The consequence of too wide beam antenna is increased SfHO connections but on the contrary, with a too narrow beam antenna, coverage is easily reduced and hence the performance of the network is deteriorated.

5.3.4 Coverage overlapping in UMTS

In urban areas, the coverage requirements for indoor users determine the site density of a planning area. If high indoor coverage probabilities (80 – 90%) are required, the average site density grows, automatically resulting in large coverage overlapping areas. These overlapping areas cause cell-breathing, which reduces capacity because of an increased number of soft


handovers and increased other-to-own-cell interference. On the other hand, placing the base stations far apart is not a solution either. Too large of a site separation yields high transmit powers for the mobiles located near the cell edges. Thus, coverage overlapping is always needed, and the impact of coverage overlapping on system capacity must be understood when site selections are done in the topology planning phase.

5.3.4.1 Coverage overlapping in system simulations

The effect of coverage overlapping in topology planning is presented by an example of 3-sectored sites of 65° antennas and 6-sectored sites of 33° antennas. The distance between sites (site separation) is 1.5, 2.0, and 2.5 km in a typical light urban area. These distances of 1.5–2.5 km represent the typical site separation in this type of environment when indoor coverage is required. In both configurations, a regular hexagonal grid is used with 19 base stations. The simulation parameters are the same as in Table 5-3 in Section 5.3.1.1. Antenna tilting is not utilized (more interference in the network, see Section 5.4.3). The simulation results of a 3-sectored case of 65° antennas are shown in Table 5-18.

When the load is low (2000 users), the highest service probability can be achieved by a site separation of 1.5 km. When the load is increased, a site separation of 2.0 km seems to be optimum in this reference network. A smaller base station separation increases the other-cell interference and a larger separation requires higher transmit power for base stations. However, Table 5-18 shows that the deviation between different site separations is negligible.

Table 5-18. Simulation results of coverage overlapping of 3-sectored sites of 65° antennas, base station antenna height is 25 m. Parameter 1.5 km 2.0 km 2.5 km

Number of users 2000 4000 2000 4000 2000 4000 Service probability [%] 100.0 86.1 99.6 87.8 99.1 86.1 SHO probability [%] 18.9 19.1 16.5 16.2 17.1 17.5 SfHO probability [%] 4.8 5.0 5.1 5.2 5.0 5.3 Throughput [kbps/sector]

272 471 267 470 266 465

UL noise rise [dB] 2.14 4.81 2.00 4.52 1.98 4.43 UL load [%] 38.6 66.4 36.3 63.8 35.9 62.8 DL power [dBm] 34.6 39.7 34.3 39.2 34.2 39.2

The simulation results of the 6-sectored network are shown in Table 5-19. The performance of the 6-sectored network is similar to the 3-sectored network. With a lower load network of 1.5 km, the site separation is able to serve all mobiles because of good coverage. By increasing the load,


interference is also increased and thus the service probability begins to decrease. Also in this reference network, a 2.0 km site separation seems to be optimum from a service probability point of view.

Table 5-19. Simulation results of coverage overlapping in 6-sectored sites of 33° antennas, base station antenna height is 25 m. Parameter 1.5 km 2.0 km 2.5 km

Number of users 4000 6000 4000 6000 4000 6000 Service probability [%] 100.0 96.8 99.7 97.5 99.2 96.3 SHO probability [%] 23.2 23.0 19.8 19.5 17.2 17.2 SfHO probability [%] 4.0 3.9 4.6 4.5 4.7 4.6 Throughput [kbps/sector]

282 409 274 401 265 386

UL noise rise [dB] 2.27 3.89 2.08 3.57 2.00 3.40 UL load [%] 40.1 58.1 37.4 54.8 36.1 52.7 DL power [dBm] 34.9 38.2 34.5 37.6 34.0 37.0

5.3.4.2 Importance of coverage overlapping

The behavior of coverage overlapping towards interference and system capacity depends on the environment and planning thresholds. In an urban environment, where large overlapping is required due to indoor coverage, other-cell-to-own-cell interference seems to be constant if the antenna configuration is not changed. Thus, overlapping in urban areas is no more sensitive than other parameters in the topology planning phase. Correspondingly, in rural areas where the network is typically coverage-limited, small overlapping areas and cell-breathing may cause more problems if there are unexpected capacity needs in the radio network.

5.3.5 UMTS site evolution: from 3-sectored to 6-sectored

In 2G networks, as in GSM, mainly 3-sectored site configurations are used and thus 3-sectored sites are the typical choice in the early days of UMTS. Three-sectored sites are also cost-efficient solutions compared to 6-sectored sites because significantly more hardware is needed in 6-sectored sites.

However, capacity requirements will be increased in the future and the site evolution path has to be defined. Different site evolution strategies can be utilized as cell splitting (small macro cells and micro cells when needed). Sectoring is also an efficient application of cell splitting because base station antenna heights in the network are not changed. However, the change from a 3-sectored to a 6-sectored configuration has an impact on network coverage and system capacity.


5.3.5.1 Coverage analysis

A simulation example of site evolution from 3-sectored to 6-sectored is presented in order to show the impact of site configurations on long-term topology planning. The same environment and the same parameters are used as in Section 5.3.1.1. Altogether four different 6-sectored site solutions are compared to each other and to the original 3-sectored site of 65° antennas. The first two 6-sectored configurations are traditional site solutions of 65°and 33° antennas with fixed antenna direction. The third 6-sectored configuration is a 33° antenna with a 30° shift in antenna directions in the first tier of the base stations. This solution was done in order to fill the coverage holes caused by the narrow beam antennas. The fourth configuration is a hybrid: the original 65° three-sectored site configurations are maintained and 33° antennas are added between them. The results of pilot coverage probabilities of different site configurations are presented in Table 5-20.

Table 5-20. Pilot coverage probabilities of 3- and 6-sectored sites at different thresholds. Threshold [dBm]

Site type -75 -84 -104

3-sec/65 46.1 87.9 99.8 6-sec/65 61.9 91.5 99.9 6-sec/33 64.9 90.7 99.9 6-sec/33 (1st tier antennas) 67.8 91.0 99.9 6-sec/65&33 65.7 91.6 99.9

The thresholds in Table 5-20 correspond to urban in-building (-75 dBm), suburban in-building (-84 dBm), and outdoor coverage (-104 dBm). The results show that the coverage performance of the 33° antennas in 6-sectored sites is generally better than the performance of 65° antennas. On the other hand, the best suburban in-building coverage is achieved with a combined usage of 65° and 33° antennas since the coverage of 65° antennas is smoother and hence only a few coverage holes are observed. Due to the high requirement of the indoor planning threshold, the site separation was only 1.5 km and thus nearly full outdoor coverage probability was achieved in all cases.

5.3.5.2 Capacity and performance analysis

The results in Table 5-21 show the performance and capacity analysis of 3- and 6-sectored sites. The number of mobiles is selected based on the approximately 95% service probability in the network of 3-sectored sites. As expected, the service probability of 6-sectored sites is nearly 100%. Moreover, the mean number of mobiles in SHO is equal in all 6-sectored configurations and a couple of percent less than in a 3-sectored network. The


other-to-own-cell interference is increased due to 65° antennas in 6-sectored sites because of strong sector overlapping. Hence, also the number of SfHO connections is quite high. The number of SfHO connections can easily be controlled by using narrower antennas or a combined antenna solution (65°and 33°).

Table 5-21. Results of performance and capacity analysis with 2300 users in the network. Parameter 3-sec 6-sec 6-sec 6-sec 6-sec

Antenna [°] 65 65 33 33* 65&33 Service probability [%] 94.9 99.7 99.8 99.8 99.7 SHO probability [%] 26.7 23.0 23.8 23.8 23.5 SfHO probability [%] 4.2 22.5 3.8 3.7 10.6 Throughput [kbps/site] 1082 1252 1099 1099 1154 UL noise rise [dB] 2.53 1.73 1.45 1.45 1.57 UL load [%] 48.0 29.7 25.6 25.5 27.3 DL power [dBm] 38.4 34.5 33.4 33.4 33.8

5.3.5.3 UMTS site evolution path

An optimum UMTS network or site evolution path has to be selected based first on the original configuration in the UMTS network in order to minimize network element changes. Next, coverage and capacity analysis must be done as in the previous example in Sections 5.3.5.1 and 5.3.5.2. Even if separate sectoring and beam width calculations in Section 5.3.3.3 show that the maximum capacity is achieved using 6-sectored 33° antennas, an almost equivalent result could be obtained when a hybrid 33°/65° solution is used. Thus, a hybrid 33°/65° site configuration could be more favorable because significant cost savings can be achieved in implementation.

5.4 UMTS antenna configuration

Base station antenna height, beam width, and tilting properties have a strong impact on network coverage and system capacity and thus these antenna parameters are typically modified by changing antenna types in the topology planning phase.

5.4.1 Antenna height

Antenna height has an enormous effect on UMTS radio network performance. A network of too low antenna positions has poor coverage probabilities and hence site density must be increased. On the contrary, higher antenna positions create additional interference and hence reduce the capacity of the network. An average antenna height in different areas in the


radio network must already be defined in the dimensioning phase in order to define average cell ranges. In the topology planning phase, antenna heights can be modified but the impact of these changes on propagation and on breakpoint distance must be understood. Moreover, the effect of antenna height and antenna tilting must be known exactly.

5.4.1.1 Breakpoint distance

Base station antenna height affects radio propagation near the base station antenna. Until a certain distance, the propagation near the base station antenna follows a propagation slope of 20 dB/dec. The distance where the propagation slope changes is called breakpoint distance [31]:

λMSBTS hh

B 4= (5-5)

where hBTS and hMS are the antenna heights of the base station and mobile station and is the wavelength. After the breakpoint distance, the propagation slope is defined by the environment. Higher antenna positions yield longer breakpoint distances and therefore larger coverage areas, but on the other hand they yield higher interference levels in surrounding cells.

In a macrocellular environment, propagation occurs mainly above the average rooftop level. In Figure 5-16, two different antenna positions for macrocellular propagation are depicted: the lower antenna height is close to the average rooftop level.

Figure 5-16. Macrocellular coverage of two different antenna heights.

Figure 5-16 indicates that a radio signal will experience a harsher environment when a low antenna position is used [32]. The signal is


propagating above the rooftops, but after the breakpoint distance, which is closer to the base station than when the antenna position is used, the propagation slope changes to correspond to the environment. Thus, in this particular example, the coverage area is not entirely exceeded. With a higher antenna position, the required coverage is achieved, but also the interference level beyond the cell coverage area is higher.

5.4.1.2 Antenna height simulations in topology planning

A simulation example related to the topology planning phase shows the effect of base station antenna height on the UMTS network system performance of 3- and 6-sectored sites of 65° and 33° antennas. In addition, the function of different antenna heights and site separations must be known. The simulation area consists of 19 base stations in a hexagonal grid. The simulation parameters are the same as in Table 5-3 in Section 5.3.1.1.

In Table 5-22, the simulation results of 3-sectored sites with 65° antennas are shown. These results correspond to the base station antenna heights of 25 m and 45 m. When the base station site separation is 1.5 km, the service probability of a 45 m antenna height is only 86.7%. This is caused by the raised interference level. With a 25 m antenna height, the service probability is sufficiently good with a 1.5 km site separation. Moreover, the difference in SHO connections is also quite high. In this example, a network with lower antenna positions should be used when the site separation is 1.5 km and when tilting is not utilized.

The service probability of site separations of 2.0 km and 2.5 km is sufficient with lower and higher antenna positions. Moreover, the number of SHO connections is almost constant. Other-cell-to-own-cell interference is reduced when site separation is increased and thus performance of higher antenna positions is improved.

Table 5-22. Base station antenna heights of 25 m and 45 m, different site separations and 3-sectored sites of 65° antennas. Parameter 1.5 km 2.0 km 2.5 km

Number of users 3000 3000 3000 Service probability [%] 98.7 / 86.7 98.5 / 97.1 97.1 / 96.6 SHO probability [%] 18.5 / 34.9 16.0 / 25.2 16.8 / 22.2 SfHO probability [%] 4.7 / 4.0 5.0 / 4.3 5.0 / 4.5 Throughput [kbps/sector]

401 / 413 394 / 421 390 / 408

UL noise rise [dB] 3.77 / 4.39 3.47 / 4.22 3.41 / 3.89 UL load [%] 57.3 / 62.8 53.9 / 61.4 53.2 / 58.4 DL power [dBm] 37.8 / 39.6 37.4 / 38.8 37.2 / 38.2


The results of the consequent simulations of 6-sectored sites and 33° antennas are given in Table 5-23. The number of mobiles is increased in order to increase the load in the network. The performance of a 6-sectored network compared to a 3-sectored network is quite similar. A smaller site separation and higher antenna position causes a higher interference level and hence decreases service probability.

Table 5-23. Base station antenna heights of 25 m and 45 m, different site separations and 6-sectored 33° sites. Parameter 1.5 km 2.0 km 2.5 km

Number of users 6000 6000 6000 Service probability [%] 96.8 / 85.1 97.5 / 95.1 96.3 / 96.1 SHO probability [%] 23.0 / 41.9 19.5 / 29.9 17.2 / 23.8 SfHO probability [%] 3.9 / 2.3 4.5 / 3.3 4.6 / 3.7 Throughput [kbps/sector]

409 / 428 401 / 431 386 / 409

UL noise rise [dB] 3.89 / 4.26 3.57 / 4.2 3.4 / 3.88 UL load [%] 58.1 / 61.4 54.8 / 61.1 52.7 / 58.0 DL power [dBm] 38.2 / 39.7 37.6 / 39.0 37.0 / 38.1

5.4.1.3 Antenna height selection in UMTS

Base station antenna height has a significant impact on the performance of a UMTS network, as can be seen in Tables 5-22 and 5-23. Especially other-cell-to-own-cell interference is heavily increased if the antenna position is too high, cells are strongly overlapping, and antenna tilting is not utilized. Therefore selecting an average antenna height should be done carefully in the dimensioning phase, and modifications in the topology planning phase should be avoided. If antenna heights are still changed, antenna tilting should be utilized (see Section 5.4.3).

5.4.2 Antenna beam width in UMTS

The impact of base station antenna beam width on UMTS network coverage and system capacity in topology planning phase is explained in detail in Section 5.3.3.

5.4.3 Antenna down tilt in UMTS

Base station antenna mechanical down tilt has been traditionally used in TDMA/FDMA networks (e.g., in GSM) to decrease other-cell interference in order to minimize the frequency reuse factor and moreover to increase the capacity of the network. In UMTS networks, cell-breathing affects the cell range and no fixed coverage area exists. Thus the effect of antenna down tilt


is not as straightforward as in TDMA/FDMA networks. By using down tilting at the base station antenna, interference leakage to other cells can be reduced and thus the capacity of a UMTS network increased.

The difference between mechanical and electrical antenna down tilt has been studied in a WCDMA network in the uplink direction by using a 3-sectored site scenario [33]. The results of this study show that electrical down tilt provides slightly better capacity enhancements than mechanical tilt. Correspondingly, the results in [28] indicate that electrical down tilt should be used in urban environments as a pre-optimization method.

5.4.3.1 Mechanical down tilt

In Figure 5-17, the principle of antenna mechanical tilt is illustrated. When an antenna element is physically down tilted, only the main lobe is down tilted and the back lobe is up tilted. The side lobes are only partly tilted and coverage (or on the contrary, interference) is almost attained in the side lobe direction. As a consequence of a large mechanical down tilt angle, a notch can be observed in the radiation pattern. The notch becomes larger when the tilt angle increases [34]. Thus, only interference and coverage towards the main lobe are changed.

Figure 5-17. Illustration of base station antenna mechanical down tilt.

In Figure 5-18, the effect of base station antenna mechanical down tilt on signal propagation is represented in a real propagation environment defined by a digital map. A macrocellular propagation model is used to predict the coverage. The picture on the left represents coverage without down tilt and the picture on the right represents 6° mechanical down tilt. Blue color in Figure 5-18 refers a very good signal strength and light brown the weakest signal strength. The vertical beam width of the base station antenna is 6°.


Figure 5-18. Effect of antenna mechanical down tilt in a real propagation environment.

Figure 5-18 shows that the signal strength in the direction of back and side lobes remains approximately the same when the antenna is down tilted. Correspondingly, the coverage in the main beam direction starts to shrink, thus also decreasing the interference leakage.

5.4.3.2 Electrical down tilt

Figure 5-19 represents how the main, side, and back lobes of electrically down tilted antennas behave. In electrical down tilt, the side and back lobes of the antenna radiation pattern are also tilted. Because of side and back lobe down tilting, coverage as well as interference conditions are totally different in electrical down tilting than in mechanical down tilting. Thus, interference radiation is smaller compared to a similar mechanical down tilt situation but also the coverage area becomes smaller as the electrical down tilt angle is increased. The electrical down tilt is carried out by adjusting the antenna elements and hence it only slightly changes the antenna radiation characteristics.

Figure 5-19. Illustration of base station antenna electrical down tilt.


In Figure 5-20, an example of base station antenna electrical down tilt is depicted. The picture on the left represents coverage without down tilt and the picture on the right represents 6° antenna down tilt. The vertical beam width of the base station antenna is 6°. Figure 5-20 shows that the coverage towards the side and back lobe directions, as well as towards the main lobe direction, is smaller.

Figure 5-20. Effect of antenna electrical down tilt in a real propagation environment.

5.4.3.3 Optimum down tilt angle

Base station down tilt angle depends strongly on the site configuration and location. Base station antenna height and vertical beam width are critical parameters when an optimal down tilt angle is defined. A large cell range (as in a rural area) indicates that a smaller tilt should be utilized in order to maintain coverage. Correspondingly, in larger overlapping areas as in urban environments, the down tilt angle for interference leakage reduction can be bigger because of good coverage.

The required down tilt angle also depends on the load of the network. In a highly loaded cell, the cell range is effectively smaller than in a low loaded cell and thus the required tilt angle would be smaller. Furthermore, the type of tilting is an issue when selecting the base station antenna down tilting scheme. In a coverage-limited environment, the coverage is important and mechanical down tilt could be more useful. Correspondingly, in a capacity-limited environment, minimization of the interference is more vital and hence electrical down tilt could provide better performance.

5.4.3.4 Antenna down tilt simulations in topology planning

Examples of different antenna down tilting schemes are simulated in order to show the effect of tilting in different network scenarios. The


simulation area consists of 19 six-sectored sites, each having 33° horizontal beam width antennas with the base stations arranged in a regular hexagonal grid. All the other simulation parameters are taken from Table 5-3 in Section 5.3.1.1, except that the HO window is 3 dB, and the Eb/N0 requirements are 6 dB for downlink and 4 dB for uplink. A homogenous traffic distribution of voice users (12.2 kbps) is used.

The impact of site separation, antenna height, base station antenna vertical beam width, network load, and tilting scheme (electrical / mechanical) must be defined. The effect of site separation (coverage overlapping) is simulated by using site distance of 1.5 km and 2.2 km. In order to define the effect of base station antenna height, 25 m and 40 m base station antenna heights are chosen. In mechanical down tilt simulations, two different antennas are used – one antenna with a 6° vertical beam width and a gain of 20.7 dBi and another antenna with a 12° vertical beam width and a gain of 17.9 dBi. The vertical radiation patterns of antennas used in mechanical down tilt simulations are shown in Figure 5-21.

Figure 5-21. Vertical radiation patterns of 6° and 12° antennas used in the mechanical down tilt simulations.

In Figure 5-22, the vertical radiation patterns of an electrically down tilted antenna are presented. The gain of this antenna is 19.7 dBi. The horizontal beam width of each antenna is 33°.


Figure 5-22. Vertical radiation patterns of 0°, 2°, 4°, and 6° electrically down tilted antenna.

First, the site separation is set at 2.2 km, the base station antenna at 25 m, and an antenna with a 6° vertical beam width is utilized. Table 5-24 represents the simulation results based on the mechanical down tilt.

Table 5-24. Results of antenna mechanical down tilt, 2.2 km site separation, low load. Parameter 0° 2° 4° 6°

Service probability [%] 100.0 100.0 100.0 99.9 SHO probability [%] 16.4 15.0 13.5 12.1 SfHO probability [%] 4.3 4.2 4.9 6.6 UL load [%] 36.0 35.3 35.0 35.2 Throughput [kbps/sector] 427 421 418 420 DL power [dBm] 35.8 35.4 35.1 35.3

The results in Table 5-24 are based on the same number of users in the simulation area. The performance of the network is better when using down tilt. Due to a relatively low load, the service probability is nearly 100% in all configurations. The number of SHO connections is decreased when the down tilt angle is increased. In contrast, the number of mobile phones in SfHO is increased steadily when the down tilt angle is increased. This is due to the fact that the antenna radiation pattern is getting wider because only the main lobe is down tilted.


In Figure 5-23, DL throughput per sector is plotted as a function of the down tilt angle. The solid line represents capacity values of 33 dBm average base station transmit power (low load). The dashed line represents capacity values of 39 dBm average base station transmit power (high load). An optimum down tilt angle can be seen in Figure 5-23.

300

350

400

450

500

550

600

0 1 2 3 4 5 6

Tilt angle [degree]

DL

thro

ughp

ut [

kbit/

s/se

ctor

]

33 dBm39 dBm

Figure 5-23. DL sector throughput as a function of antenna mechanical down tilt angle, 2.2 km site separation, 25 m antenna height and 6° antenna vertical beam width.

In the simulations, the site separation is decreased to 1.5 km in order to have larger coverage overlapping. The results in Table 5-25 correspond to the same amount of traffic as in the 2.2 km site separation. An impact similar to the 2.2 km site separation can be observed. The number of SHO connections is decreased and the number of SfHO connections is increased as a function of the down tilt angle. The increase of SfHO probability is higher than in a 2.2 km site separation.

Table 5-25. Results of antenna down tilt, 1.5 km site separation, low load. Parameter 0° 2° 4° 6° 8°

Service probability [%] 100.0 100.0 100.0 100.0 100.0 SHO probability [%] 16.8 16.5 13.9 11.8 10.1 SfHO probability [%] 3.9 4.0 4.5 6.0 9.2 UL load [%] 35.8 35.7 35.0 34.8 35.6 Throughput [kbps/sector] 425 426 419 417 422 DL power [dBm] 35.6 35.5 35.0 34.8 35.2


In Figure 5-24, sector throughputs are depicted as a function of antenna down tilt angle. By comparing the results of 2.2 km and 1.5 km site separations in Figures 5-23 and 5-24, it can be noted that an optimum down tilt angle is larger when coverage overlapping is larger. Moreover, the down tilting becomes more significant because of the higher capacity enhancement.

300

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0 2 4 6 8

Tilt angle [degree]

DL

thro

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ctor

]

33 dBm39 dBm

Figure 5-24. DL sector throughput as a function of antenna mechanical down tilt angle, 1.5 km site separation, 25 m antenna height and 6° antenna vertical beam width.

In order to see the effect of a higher antenna position, all the base station antennas are raised to 40 m. Table 5-26 represents the corresponding simulation results.

In Table 5-26, the service probability is decreased with higher down tilt angles. The curves in Figure 5-25 show that the capacity of the network is lower than with lower antenna heights when the antennas are not tilted. (See Figures 5-23 and 5-24.) With a 25 m antenna height, the capacity is nearly 550 kbps/sector (see Figures 5-23 and 5-24), and in Figure 5-25 the capacity is decreased to 490 kbps/sector. This is caused by higher antenna positions and a raised interference level. However, after down tilting the antennas, the capacity of the network is raised more steeply than with the lower antenna positions and capacity is enhanced 25% when comparing 0° and optimal


tilting. In addition, the capacity curves also show that too much down tilt quickly reduces the coverage and hence also the capacity of the network.

Table 5-26. Results of antenna mechanical down tilt, 1.5 km site separation, 40 m antenna height, low load. Parameter 0° 2° 4° 6° 8° 10°

Service probability [%] 100.0 100.0 100.0 100.0 99.8 99.6 SHO probability [%] 23.5 20.5 16.5 12.6 12.0 10.2 SfHO probability [%] 3.4 3.3 3.9 4.9 5.6 9.7 UL load [%] 38.6 37.1 35.6 34.5 34.3 35.3 Throughput [kbps/sector] 445 438 426 416 410 423 DL power [dBm] 37.5 36.5 35.5 34.7 33.5 34.0

250

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650

0 2 4 6 8 10

Tilt angle [degree]

DL

thro

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33 dBm39 dBm

Figure 5-25. DL capacity as a function of antenna mechanical down tilt angle, 1.5 km site separation, 40 m antenna height and 6° antenna vertical beam width.

Finally, antennas with a 12° vertical beam width are used with mechanical down tilting. In Table 5-27, the results of this wider beam width down tilting are presented. The optimum down tilt angle is increased up to approximately 14° because of wider vertical beam width. Also the performance of the network begins to drop steeper after too strong down tilting (see Figure 5-26).


Table 5-27. Results of antenna mechanical down tilting, 1.5 km site separation, 40 m antenna height and 12° antenna vertical beam width. Parameter 0° 2° 4° 6° 8°

Service probability [%] 100.0 100.0 100.0 100.0 100.0 SHO probability [%] 19.1 17.8 16.7 15.5 14.3 SfHO probability [%] 2.8 2.7 2.8 3.0 3.3 UL load [%] 36.1 35.6 35.2 34.8 34.5 Throughput [kbps/sector] 431 427 432 420 417 DL power [dBm] 35.9 35.5 35.3 35.0 34.7

Parameter 10° 12° 14° 16°


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0 2 4 6 8 10 12 14 16

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DL

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33 dBm

39 dBm

Figure 5-26. DL capacity as a function of antenna mechanical down tilt angle, 1.5 km site separation, 40 m antenna height and 12° antenna vertical beam width.

A network equipped with electrically down tilted antennas behaves differently due to different behavior of antenna radiation pattern. In next simulations, a network with electrically down tilted antennas is studied by using 2.2 km site separation and 25 m antenna height.


In Table 5-28 and Figure 5-27, the performance of electrically down tilted network is presented. The capacity is rising quickly due to decreased interference but it also drops very rapidly. This is caused by the degradation in coverage due to the properties of the electrical down tilt. The deteriorated coverage conditions can be seen as decreased service probability and also as decreased sector throughput. Moreover, the changes in SHO probabilities are not as dramatic as in mechanical down tilt and also the number of SfHO is nearly constant.

Table 5-28. Results of the simulations of electrically down tilted antennas, 2.2 km site separation, 25 m antenna height and 6° antenna vertical beam width. Parameter 0° 2° 4° 6°


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0 1 2 3 4 5 6

Tit angle [degree]

DL

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33 dBm39 dBm

Figure 5-27. DL capacity as a function of antenna electrical down tilt angle, 2.2 km site separation, 25 m antenna height and 6° antenna beam width.

In the last simulation the site separation is decreased to 1.5 km. Table 5-29 shows that the coverage performance of down tilted antennas is improved


and thus the service probability is nearly 100%. The difference in SHO probabilities is also more obvious than with larger site separation.

Table 5-29. Results of the simulations of electrically down tilted antennas, 1.5 km site separation, 25 m antenna height and 6° antenna vertical beam width. Parameter 0° 2° 4° 6°

Service probability [%] 99.9 99.9 100.0 99.8 SHO probability [%] 24.1 19.4 17.3 15.0 SfHO probability [%] 4.3 3.8 3.9 4.0 UL load [%] 45.0 41.1 40.5 38.2 Throughput [kbps/sector]

368 350 343 338

DL power [dBm] 34.1 33.5 33.2 32.9

Figure 5-28 shows that the sector throughput is improved as a function of electrical down tilt angle because of coverage overlapping. Also the achieved capacity is a bit better than with mechanical down tilt antennas.

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0 1 2 3 4 5 6

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DL

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33 dBm

39 dBm

Figure 5-28. DL capacity as a function of antenna electrical down tilt angle, 1.5 km site separation, 25 m antenna height and 6° antenna vertical beam width.


5.4.3.5 Antenna down tilt selection in UMTS

Base station antenna down tilting is an efficient way to decrease interference and hence to increase the capacity in a UMTS network. An optimum down tilt angle always exists. It is a function of the site and antenna configuration: coverage overlapping (cell range), base station antenna height, and antenna vertical beam width. Sectoring and antenna horizontal beam width also have an impact on network performance due to side lobes. Moreover, electrical down tilt gives bit better throughput values compared to mechanical down tilt because of reduced interference. However, a network of electrically down tilted antennas requires more cautious planning due to the radiation properties of electrical down tilt antennas. Hence, antenna down tilting is a key planning element in the topology planning phase for ensuring optimal network performance in UMTS.

REFERENCES

[1] H. Holma, A. Toskala, WCDMA for UMTS, John Wiley & Sons Ltd, 2001. [2] T. Neubauer, E. Bonek, Impact of the Variation in the Background Noise Floor on

UMTS System Capacity, IEEE 53rd Vehicular Technology Conference, vol. 4, 2001. [3] J. Laiho, A. Wacker, Radio Network Planning Process and Methods for WCDMA,

Annals of Telecommunications, vol. 56, no. 5-6, Mai/Juin 2001. [4] P. Gould, Radio Planning of Third Generation Networks in Urban Areas, Third

International Conference on 3G Mobile Communication Technologies, 2002. [5] M. Hata, Empirical Formula for Propagation Loss in Land Mobile Radio Services, IEEE

Transactions on Vehicular Technology, vol. 29, no. 3, 1980. [6] K. Gilhousen, I. Jacobs, R. Padovani, A. Viterbi, L. Weaver Jr., C. Wheatley, On the

Capacity of a Cellular CDMA System, IEEE Transactions on Vehicular Technology, vol. 40, no. 2, 1991.

[7] K. Ruttik, Capacity Calculation for CDMA Network Planning, Licentiate’s Thesis, Helsinki University of Technology, 1999.

[8] K. Hiltunen, R. De Bernardi, WCDMA Downlink Capacity Estimation, IEEE 51st

Vehicular Technology Conference, vol. 2, 2000. [9] D. Adiego, C. Cordier, Multi-Service Radio Dimensioning for UMTS Circuit Switched

Services, IEEE 54th Vehicular Technology Conference, vol. 4, 2001. [10] J. Laiho, Radio Network Planning and Optimisation for WCDMA, Doctoral Thesis,

Helsinki University of Technology, 2002. [11] K. Sipilä, Z. Honkasalo, J. Laiho-Steffens, A. Wacker, Estimation of Capacity and

Required Transmission Power of WCDMA Downlink Based on a Downlink Pole Equation, IEEE 51st Vehicular Technology Conference, vol. 2, 2000.

[12] S. Malik, D. Zeghlache, Downlink Capacity and Performance Issues in Mixed Services UMTS WCDMA Networks, IEEE 55th Vehicular Technology Conference, vol. 4, 2002.

[13] J. Lempiäinen, M. Manninen, Radio Interface System Planning for GSM/GPRS/UMTS,Kluwer Academic Publishers, 2001.


[14] J. Laiho-Steffens, A. Wacker, P. Aikio, The Impact of the Radio Network Planning and Site Configuration on the WCDMA Network Capacity and Quality-of-Service, IEEE 51st

Vehicular Technology Conference, vol. 2, 2000. [15] J. Laiho, A. Wacker, T. Novosad, Radio Network Planning and Optimisation for UMTS,

John Wiley & Sons Ltd, 2002. [16] J. Niemelä, J. Lempiäinen, Impact of the Base Station Antenna Beam Width on Capacity

in WCDMA Cellular Networks, IEEE 57th Vehicular Technology Conference, vol. 1, 2003.

[17] M. Bavafa, H. Xia, Repeaters for CDMA Systems, IEEE 48th Vehicular Technology Conference, vol. 2, 1998.

[18] S-J Park, W. Woo Kim, B. Kwon, An Analysis of Effect of Wireless Network by a Repeater in CDMA System, IEEE 53rd Vehicular Technology Conference, vol. 4, 2001.

[19] R. Steele, C-C Lee, P. Gould, GSM, cdmaOne and 3G Systems, John Wiley & Sons Ltd, 2001.

[20] L-C Wang, K. Chawla, L. Greenstein, Performance Studies of Narrow-Beam Trisector Cellular Systems, IEEE 48th Vehicular Technology Conference, vol. 2, 1998.

[21] A. Spilling and A. Nix, Aspects of Self-Organisation in Cellular Networks, The Ninth International Symposium on Personal, Indoor and Mobile Radio Communications, 1998.

[22] V. Jovanovi , J. Gazzola, Capacity of Present Narrowband Cellular Systems: Interference-Limited or Blocking-Limited, IEEE Transactions on Personal Communications, vol. 4, issue 6, 1997.

[23] T. Brown, Cellular Performance Bounds via Shotgun Cellular Systems, IEEE Journal on Selected Areas in Communications, vol. 18, no. 11, 2000.

[24] M. Nawrocki, T. Wieckowski, Optimal Site and Antenna Location for UMTS – Output Results of 3G Network Simulation Software, 14th International Conference on Microwaves, Radar and Wireless Communications, 2002.

[25] E. Amaldi, A. Capone, F. Malucelli, F. Signori, UMTS Radio Planning: Optimizing Base Station Configuration, IEEE 56th Vehicular Technology Conference, vol. 2, 2002.

[26] T. Ojanperä, R. Prasad, Wideband CDMA for Third Generation Mobile Communications,Artech House, 1998.

[27] T. Wong, V. Prabhu, Optimum Sectorization for CDMA 1900 Base StationsIEEE 47th Vehicular Technology Conference, vol. 2, 1997.

[28] A. Wacker, J. Laiho-Steffens, K. Sipilä, K. Heiska, The Impact of the Base Station Sectorisation on WCDMA Radio Network Performance, IEEE 50th Vehicular Technology Conference, vol. 5, 1999.

[29] B. Christer V. Johansson, S. Stefansson, Optimizing Antenna Parameters for Sectorized W-CDMA Networks, IEEE 52nd Vehicular Technology Conference, vol. 4, 2000.

[30] S. Asari, A. Jalan, N. Velayudhan, Performance Analysis of the Forward Link in a Power Controlled CDMA Network, IEEE 47th Vehicular Technology Conference, vol. 3, 1997.

[31] W.C.Y Lee, Mobile Communications Design Fundamentals, John Wiley & Sons Ltd, 1993.

[32] E. Benner, A. Sesay, Effects of Antenna Height, Antenna Gain, and Pattern Down Tilting for Cellular Mobile Radio, IEEE Transactions on Vehicular Technology, vol. 45, no. 2, 1996.

[33] I. Forkel, A. Kemper, R. Pabst, R. Hermans, The Effect of Electrical and Mechanical Antenna Down-Tilting in UMTS Networks, IEE Proceedings of 3G Mobile Communication Technologies, 2002.


[34] D. J. Y. Lee, C. Xu, Mechanical Antenna Down Tilt and its Impact on System Design,IEEE 47th Vehicular Technology Conference, vol. 2, 1997.

PART III: UMTS NETWORK FUNCTIONALITY

Chapter 6

WCDMA RADIO INTERFACE Radio Resource Management and 3GPP Radio Parameters

MATTI MANNINEN European Communications Engineering (ECE) Ltd

Abstract: Understanding the WCDMA radio interface is essential for engineers dealing with UMTS radio networks. A knowledge of the structure and usage of the physical channels in the downlink and uplink directions, together with a knowledge of spreading and modulation, provides a good background for understanding how the WCDMA radio network works. Various kinds of services with different quality-of-service requirements and bit rates can be transmitted through the radio interface with the help of an effective and versatile radio resource management (RRM). The RRM consists of the handover control, power control, admission and load control, as well as resource management. In WCDMA networks, power control has an especially important role. The behavior of the RRM is controlled with a set of radio parameters. Most of these radio parameters are defined by 3GPP specifications. With these parameters and good network planning practice, the behavior of a WCDMA network can be optimized to meet coverage, capacity, and quality requirements. However, in the RRM, there can be vendor-specific implementations that may provide benefits in utilizing the radio resources.

Key words: Radio interface, radio parameters, radio resource management

207




6. WCDMA RADIO INTERFACE

This chapter describes the basics of the radio interface of UTRAN FDD, radio resource management, and the key parameters defined in the 3GPP specifications for the radio interface. The TDD radio interface is not covered in this chapter because large-scale implementation of TDD may come after a few years. However, the basics of TDD radio interface are covered in [1]. In this chapter, first the structure of the radio frame is described as well as the physical and transport channels of UTRAN FDD. Second, the basics of spreading and modulation in WCDMA are given and some of the physical layer procedures related to idle mode, call establishment and connected mode are described. Third, the key functionalities of radio resource management are explained. Finally, the key 3GPP radio parameters are explained at the end of the chapter.

The WCDMA radio interface is based on direct sequence code division multiple access (DS-CDMA). In DS-CDMA, the low bit rate data signal is spread by a spreading code. The benefits in spreading the signal over a wider bandwidth are, for example, tolerance to narrowband interference, better tolerance to fast fading, and flexibility in combining different data services in the radio channel. The use of CDMA in radio interface requires special arrangements at the mobile station, base station and radio network controller. The main issues are handovers and power control. When CDMA is used, it is possible to maintain connections to two or more cells at the same time. This improves the performance of the connection but at the same time it makes the equipment more complex. Typically, CDMA networks are interference-limited and the network must be able to scope the so-called near-far effect. This means that there can be users close to the center of the cell at the same time that there are users close to the cell edge. To minimize interference in the network and to be able to handle the near-far effect, fast and accurate power control is needed. This means that both mobile station and base station tune the transmit power in such a manner that the received power is high enough for decoding the transmitted data but at the same time is as low as possible. Handovers, power control, data transmission, and utilization of resources are managed with parameters used in mobile stations, NodeBs, and RNCs. The optimization of the parameters may result in valuable improvements in coverage, capacity, and quality.

In this chapter, it is assumed that the reader knows the basics of CDMA technology. The fundamentals of CDMA are described in many references. One such reference is cited below [2].

WCDMA RADIO INTERFACE 209

6.1 Physical layer

In this section, the physical layer of UTRAN FDD is explained. First, the radio frame structure is covered. This is essential for knowing how different physical channels are configured in the physical layer. Next, the physical and transport layer channels are introduced and their main characteristics are described. Finally, examples of the procedures provided by the physical layer in idle mode, call establishment, and connected mode are explained.

When a network communicates with a mobile station, there are different steps that have to be taken before the actual communication can take place. There are also requirements that must be fulfilled during the communication.

All communication between the network and mobile station takes place in different channels. In WCDMA, the channels are divided into three layers. Logical channels provide data transfer within the MAC layer and each logical channel defines a type of information that is transferred [3]. Transport channels carry data from the upper layer over the air interface. Furthermore, the transport channels are mapped to the physical channels.

6.1.1 Radio frame structure

In FDD, information is spread approximately over the 5 MHz bandwidth. There are separate 5 MHz radio channels for the uplink and the downlink. Also, the structures of these channels are different.

One radio frame consists of 38,400 chips and 15 slots. The duration of the radio frame is 10 ms, which results in a chip rate of 3.84 Mcps. Every slot in a radio frame consists of 2,560 chips, which corresponds to one power control period. The radio frame structure is illustrated in Figure 6-1.

Figure 6-1. Radio frame structure.


In the uplink and the downlink directions, each slot in a radio frame carries a set of common channels and dedicated channels. Each physical channel is defined with a code or a set of codes. The information rate of the channel varies from 7,500 symbols per-second to 960,000 symbols per-second in the downlink direction, and from 15,000 symbols to 960,000 symbols in the uplink direction. The difference between the uplink and the downlink symbol rates comes from the available spreading factors. In the uplink, the spreading factors are from 256 to 4, and in the downlink, from 512 to 4 [4].

6.1.2 Physical layer channels in the uplink

In the uplink direction, there are both dedicated and common physical channels. Dedicated physical channels are the uplink Dedicated Physical Data Channel (uplink DPDCH) and the uplink Dedicated Physical Control Channel (uplink DPCCH). Common channels in the uplink direction are the Physical Random Access Channel (PRACH) and the Physical Common Packet Channel (PCPCH).

The DPDCH and the DPCCH are I/Q code-multiplexed within each radio frame. Also, in the PRACH and the PCPCH, control and data parts are code-multiplexed.

6.1.2.1 DPDCH and DPCCH

For each radio link, there is only one DPCCH. It carries control information, such as pilot bits, transmit power control (TPC) commands, feedback information (FBI), and an optional transport format combination indicator (TFCI). Pilot bits are used to support channel estimation at the RAKE receiver. TPCs are used in power control. And FBI is needed with transmit diversity.

Each radio link may have no DPDCHs or several DPDCHs. The DPDCH carries the Data Channel (DCH) transport channel.

The structure of the frame for the DPCCH and the DPDCH is illustrated in Figure 6-2.

The spreading factor for the DPDCH can be between 256 and 4. The spreading factor of the DPCCH is always 256. In each DPCCH slot, there are always 10 bits that correspond to a bit rate of 15 kbps. In a DPDCH slot, there can be from 10 to 640 bits, depending on the spreading factor, which corresponds to channel bit rates from 15 kbps to 960 kbps.

FBI bits are needed in cases when the UTRAN access point (e.g., NodeB) needs feedback from the mobile station. The FBI bits are needed in


the closed-loop mode of transmit diversity and site selection diversity transmission (SSDT) .

Figure 6-2. The frame structure of the DPDCH/DPCCH in the uplink.

There are dedicated physical channels that include TFCI and dedicated physical channels that do not include TFCI. The usage of TFCI depends on the services carried by the physical channel. UTRAN determines whether TFCI is sent, but all the mobile stations should support the usage of TFCI in the uplink.

The mobile station uses TPC bits for the downlink fast power control. (See 6.4.1.3 for details.) The mobile station sends one or two TPC bits, depending on the slot format. If the mobile station sends two TPC bits, the allowed combinations are ‘00’ (TPC command ‘0’) and ‘11’ (TPC command ‘1’). If only one TPC bit is sent, then the TPC bit directly corresponds to the TPC command.

6.1.2.2 PRACH

The Physical Random Access Channel carries Random Access Channel (RACH). The channel is used by the mobile station when the physical random access procedure is initiated. The random access procedure is explained in physical layer procedures (see Section 6.3.1).

The random access transmission consists of one or several preambles and the message part. The length of the preamble is 4,096 chips. The preamble can be repeated several times if needed. The length of the message part is either 10 ms or 20 ms. The structure of the physical random access transmission is illustrated in Figure 6-3.

Figure 6-3. The structure of random access transmission.


The message part is sent with spreading factors of 256, 128, 64, or 32. Thus, the number of bits in the message part is 10, 20, 40, or 80 bits, which corresponds to channel bit rates of 15 kbps, 30 kbps, 60 kbps, or 120 kbps. For the control part, the spreading factor is always 256. The frame structure of the PRACH message part is illustrated in Figure 6-4.

Figure 6-4. The frame structure of the PRACH.

If the length of the message part is 20 ms, then data is sent with two consecutive 10 ms radio frames, and the TFCI is repeated in the second 10 ms radio frame.

6.1.2.3 PCPCH

The Physical Common Packet Channel carries the Common Packet Channel (CPCH). The CPCH transmission uses the Digital Sense Multiple Access - Collision Detection (DSMA-CD) approach with fast acquisition indication. The PCPCH access transmission consists of Access Preambles (AP), one Collision Detection Preamble (CDP), a DPCCH Power Control Preamble (PCP), and a message. The PCPCH access transmission structure is shown in Figure 6-5.

Figure 6-5. PCPCH access transmission structure.

In the PCPCH access procedure, the mobile sends access preambles with low power. If the preamble is not detected, the mobile station increases the


power and sends a new preamble. When the preamble is detected, the mobile station sends a collision-detection preamble. If there is no collision, the mobile station may send a power control preamble if configured by the higher layers. The inner-loop power control takes place in both the uplink and the downlink directions during the CPCH Packet Data transmission.

The frame structure of the PCPCH is very similar to the frame structure of the dedicated channels, as shown in Figure 6-6.

Figure 6-6. The frame structure of the PCPCH.

The spreading factor for the data part can be between 256 and 4. The spreading factor for the control part is always 256. In a slot of the control part, there are always 10 bits. In the data part, there can be from 10 to 640 bits per-slot, depending on the spreading factor, which corresponds to channel bit rates from 15 kbps to 960 kbps.

6.1.3 Physical layer channels in the downlink

The Downlink Dedicated Physical Channel (the downlink DPCH) is the only dedicated channel in the downlink direction. The control data and user data are time-multiplexed within one DPCH, contrary to the uplink direction where the dedicated control and user data were code-multiplexed. The common channels in the downlink are the Common Pilot Channel (CPICH), the Primary Common Control Physical Channel (P-CCPCH), the Secondary Common Control Physical Channel (S-CCPCH), the Synchronization Channel (SCH), the Physical Downlink Shared Channel (PDSCH), the Acquisition Indicator Channel (AICH), the CPCH Access Preamble Acquisition Indicator Channel (AP-AICH), the CPCH Collision Detection/Channel Assignment Indicator Channel (CD/CA-ICH), the Paging Indicator Channel (PICH), and the CPCH Status Indicator Channel (CSICH). The CPICH is further divided into the Primary Common Pilot Channel (P-CPICH) and the Secondary Common Pilot Channel (S-CPICH).


6.1.3.1 DPCH

The Downlink Dedicated Physical Channel carries both user data and control data. As in the uplink, the length of the radio frame is 10 ms and the frame is divided into 15 slots. The frame structure is shown in Figure 6-7.

Figure 6-7. The frame structure of the DPCH.

Even if the DPCH is the only dedicated physical channel, it can be seen as a combination of the downlink DPDCH and the DPCCH, which are time multiplexed onto the DPCH. The number of bits in the data part of the DPCH depends on the spreading factor. The spreading factor can vary between 512 and 4, which corresponds to 10 to 1,280 bits per a slot, or the channel bit rates of 15 kbps to 1,920 kbps. TFCI bits are optional in the DPCH. TFCI bits are used, for example, to indicate the bit rate of the channel and interleaving. There are some special cases in the configuration of the DPCH such as the downlink diversity and the DPCCH for the CPCH. These cases are explained in [5].

6.1.3.2 CPICH

On the Common Pilot Channel, a pre-defined bit sequence is transmitted with a bit rate of 30 kbps. The frame structure of the CPICH is illustrated in Figure 6-8.

Figure 6-8. The frame structure of the CPICH.


The CPICH is divided into two pilot channels. The Primary Common Pilot Channel (P-CPICH) is a phase reference for the SCH, Primary CCPCH, AICH, PICH AP-AICH, CD/CA-ICH, CSICH, and S-CCPCH. The P-CPICH can also be a phase reference for the DPCH. Because the P-CPICH is a phase reference, it must be transmitted over the entire cell. In all cells, the same channelization code is used for the P-CPICH, but the primary scrambling code is different between neighbor cells. The Secondary Common Pilot Channel (S-CPICH) can be scrambled with a primary or-secondary scrambling code. It may be also transmitted over the entire cell or only part of it. The S-CPICH can be the phase reference for the downlink DPCH.

6.1.3.3 P-CCPCH

The Primary Common Control Physical Channel carries the BCH transport channel. The P-CCPCH uses a fixed bit rate of 30 kbps with a spreading factor of 256. The frame structure of the P-CCPCH is shown in Figure 6-9.

Figure 6-9. The frame structure of the P-CCPCH.

In the P-CCPCH, there are no TPC, pilot bits, or TFCI bits. Moreover, the first 256 chips of the slot are used for the Primary and Secondary Synchronization Channels.

6.1.3.4 S-CCPCH

The Secondary Common Control Physical Channel is used to carry the FACH and the PCH. In the S-CCPCH, there are data bits, pilot bits, and optional TFCI bits. The bit rate of the S-CCPCH is from 30 kbps to 1,920 kbps. The S-CCPCH can be transmitted only to a smaller area of a cell. The frame structure of the S-CCPCH is illustrated in Figure 6-10.

It is important to notice that the S-CCPCH does not have the inner-loop power control.


Figure 6-10. The frame structure of the S-CCPCH.

6.1.3.5 SCH

The Synchronization Channel (SCH) is used in the cell search procedure. (See Section 6.3.1.) The SCH is divided into the Primary Synchronization Channel and the Secondary Synchronization Channel. Both the Primary and Secondary SCH consist of 15 slots with a length of 2,560 chips, as illustrated in Figure 6-11.

10 ms10 ms

Figure 6-11. The frame structure of the SCH.

The Primary Synchronization Channel carries the Primary Synchronization Code (PSC) that is transmitted in each slot of a radio frame. The code is 256 chips long. The PSC is the same for all cells in the network.

The Secondary Synchronization Channel consists of the Secondary Synchronization Codes (SSC) that are transmitted at the same time as the PSC. The system selects the SSC to be transmitted in a slot, based on the scrambling code group and the slot number; i.e., the SSC indicates to which scrambling code group the scrambling code used in a cell belongs to.


6.1.3.6 PDSCH

The Physical Downlink Shared Channel (PDSCH) is used for data transmission by one or-several simultaneous users in the downlink direction. It is allocated for a mobile station on a radio frame basis. One mobile station can have one or several PDSCHs. If multiple PDSCHs are allocated for a mobile station in the same radio frame, the spreading factor of each PDSCH must be the same. If the multiple PDSCHs are allocated from different radio frames, the spreading factors can also be different. The system can allocate several PDSCHs for different mobile stations by using code multiplexing.

For the PDSCH, there is always an associated the downlink PDCH. The PDCCH part of the PDCH carries the control information. The structure of the PDSCH is shown in Figure 6-12.

Figure 6-12. The frame structure of the PDSCH.

6.1.3.7 AICH

The Acquisition Indicator Channel (AICH) is used in a random access procedure by the network to indicate that the RACH preamble was detected. It consists of 15 consecutive access slots. The length of the access slot is 5,120 chips. Each access slot is further divided into 32 Acquisition Indicators and one part that has no transmission. The frame structure of the AICH is shown in Figure 6-13.

Figure 6-13. The frame structure of the AICH.


6.1.3.8 AP-AICH

The usage and structure of the CPCH Access Preamble Acquisition Indicator Channel are very similar to the AICH. The acquisition indicators of the AP-AICH are called AP acquisition indicators (API).

Figure 6-14. The frame structure of the AP-AICH.

6.1.3.9 CD/CA-ICH

The Collision Detection Channel Assignment Indicator Channel (CD/CA-ICH) is used in the CPCH Access Procedure as well as the AP-AICH. The frame structure of the CD/CA-ICH is similar to the AP-AICH. The acquisition indicators of the CD/CA-ICH are called CD Indicators (CDI). The frame structure of the CD/CA-ICH is shown in Figure 6-15.

Figure 6-15. The frame structure of the CD/CA-ICH.

6.1.3.10 PICH

The Paging Indicator Channel (PICH) carries Paging Indictors (PI). The paging radio frame consists of 300 bits. 288 bits are used for the paging indicators and the remaining 12 bits are reserved for future use. The length of the paging radio frame is 10 ms. The frame structure of the PICH is illustrated in Figure 6-16.


Figure 6-16. The frame structure of the PICH.

In each paging radio frame, there can be 18, 36, 72, or 144 paging indicators. Paging indicators are used to indicate to the mobile stations that they should decode the paging channel. Otherwise, the mobile stations are not listening to the paging channel. This reduces the tasks of the mobile stations and saves the battery.

6.1.3.11 CSICH

The CPCH Status Indicator Channel (CSICH) is associated with a CPCH AP-AICH. The duration of a CSICH radio frame is 20 ms. Each frame consists of 15 access slots (AS). The length of a slot is 40 bits. Each access slot has a part that is not transmitted and a status indicator part that includes 8 status indicator bits. The part that is not transmitted is used by the AICH, AP-AICH, or CD/CA-ICH. The frame structure of the CSICH is illustrated in Figure 6-17.

Figure 6-17. The frame structure of the CSICH.

6.1.4 Logical channels

In UMTS, the logical channels are categorized into control channels and traffic channels. The control channels carry the control plane information, and the traffic channels carry the user plane information.

The control and traffic channels are briefly described below.


– Broadcast Control Channel (BCCH) broadcasts system control information for all mobiles in a cell. The BCCH is used only in the downlink direction.

– Paging Control Channel (PCCH) transfers paging information in the downlink direction. This channel is used when the network does not know the location of the mobile, or the mobile is in the cell-connected state.

– Common Control Channel (CCCH) is used in both the uplink and the downlink directions. This channel is used to transfer control information between the network and mobiles, especially when there is no RRC connection between the network and the mobile. The CCCH is also used when the mobile is accessing a new cell after cell reselection.

– Dedicated Control Channel (DCCH) is used when there is an RRC connection between the network and the mobile. In the DCCH, dedicated control information is transferred between the mobile and the network. This channel is bi-directional.

– Dedicated Traffic Channel (DTCH) is used to transfer user data between the network and the mobile in both the uplink and downlink directions.

– Common Traffic Channel (CTCH) is used to transfer data from one point to all mobiles or a specified group of mobiles. Logical channels are mapped to the transport channels, and the transport

channels are mapped to the physical channels. This channel mapping is described in Section 6.1.6.

6.1.5 Transport channels

In the 3GPP specification [3], the transport channels describe how data is transferred over the air interface while the logical channels describe what is transferred. There are both common transport channels and dedicated transport channels. In common transport channels, mobile stations use inband signaling when using the channel for data transfer. In the dedicated channels, the mobile stations are identified by the physical channels. This means that each mobile has its own frequency and code. Here is a brief description of the transport channels: – Random Access Channel (RACH) is used to send a small amount of data

in the uplink direction. One of the main purposes of the RACH is for initial access. The channel is also used to send control and user data.

– Common Packet Channel (CPCH) is an uplink channel used for packet data. CPCH is a shared channel, i.e., several mobile stations may use the same channel for data transfer.


– Forward Access Channel (FACH) is a downlink common channel used to send small amounts of control and user data.

– Downlink Shared Channel (DSCH) is a common channel used to send dedicated control and user data.

– Broadcast Channel (BCH) broadcasts system information in the downlink direction for all the mobile stations in a cell.

– Paging Channel (PCH) is a downlink common channel used to send paging notification messages.

– Dedicated Channel (DCH) is a channel that is used to send dedicated control and user data between the mobile station and the network in the uplink and downlink directions. Transport channels allow user data to be sent on common channels or on

dedicated channels. Also, the mobile station can have one or several transport channels to be used in the downlink and at the same time one or more transport channels in the uplink. The mapping of the transport channels to the physical channels is described next.

6.1.6 Channel mapping

In WCDMA, there are several options for transferring data over the air interface. The differentiation is achieved by using different transport and physical channels for each logical channel. This means that data can be sent through the logical layer via different channels in the transport layer. Also, one transport channel can be sent via different physical channels. The selection of the channels in the transport and physical layer depends on the data itself and the radio resource management and its parameters.

Figure 6-18 illustrates the mapping of the logical channels to the transport channels in the uplink direction.


Logical Channels

Transport Channels

DCCH

DCH

CCCH

RACH

DTCH

CPCH

Logical Channels

Transport Channels

DCCH

DCH

CCCH

RACH

DTCH

CPCH

Figure 6-18. Logical channel mapping to transport channels in the uplink.

The mapping of the logical channels to the transport channels in the downlink direction is illustrated in Figure 6-19.

Logical Channels

Transport Channels

DCCH DTCHCCCHBCCH PCCHCTCH

PCHFACH DSCHDCHBCH

Logical Channels

Transport Channels

DCCH DTCHCCCHBCCH PCCHCTCH

PCHFACH DSCHDCHBCH

DCCH DTCHCCCHBCCH PCCHCTCHDCCH DTCHCCCHBCCH PCCHCTCH

PCHFACH DSCHDCHBCH PCHFACH DSCHDCHBCH

Figure 6-19. Logical channel mapping to the transport channels in the downlink.


As can be seen in Figure 6-19, the FACH in the transport layer can be used by many logical channels. The usage depends on the configuration of the channels and the parameters used in the radio resource management. Also, the DCH and the DSCH do not have a one-to-one mapping with the logical channels, but they are carrying data of two logical channels.

6.2 Spreading and modulation

In this chapter, the principles of spreading and modulation used for the uplink and the downlink are introduced. A more detailed description can be found in [6].

Spreading has two phases when applied to the physical channels. First, the channelization is achieved by multiplying the data by the channelization code. The selection of the channelization code depends on the data to be sent. After channelization, the data is spread in a way that the bandwidth of the signal equals 3.84 Mcps. Because the channelization code spreads the signal over a wider bandwidth, the channelization code is sometimes called the spreading code. After channelization, the scrambling of the data is done by multiplying the data by the scrambling code.

6.2.1 Spreading

Data that should be sent through the physical layer is spread by a channelization code. The spreading changes the bandwidth of the data stream. Because the chip rate after the spreading is always 3.84 Mcps, the length of the channelization code must be changed to achieve the constant chip rate. By definition, the spreading factor (SF) shows how many chips are used to present one symbol, i.e., how much wider the bandwidth grows in spreading. In WCDMA, the spreading factor varies between 4 and 256 in the uplink, and 4 to 512 in the downlink. Figure 6-20 illustrates the principle of spreading and despreading.

In Figure 6-20, data stream ‘1000’ is sent over the air interface. First, the spreading is done with a spreading code of ‘1010’. In this example, the spreading factor is 4 because four chips are used for each symbol. The TX data row shows the data stream that is modulated and sent over air interface. The RX data row shows the received data stream after demodulation. The despreading is done with the same spreading code (or channelization code) that was used in the spreading. The Data row at the bottom of Figure 6-20 shows the received data. Every four consecutive chips present one symbol. In the sixth chip sent over air interface, there was an error (indicated with a rectangle) because ‘0’ was sent over the air interface but it was received as ‘1’. However, the second symbol can be decoded


correctly because there are three ‘0’s and only one ‘1’, and thus the error in the air interface did not distort the data transmission.

Figure 6-20. Principle of spreading and despreading.

6.2.2 Channelization codes

As described earlier, the channelization codes are used to spread a data stream over a wider bandwidth. At the same time, the codes separate the channels from each other. This is achieved because the codes used for the spreading are Orthogonal Variable Spreading Factor (OVSF) codes. The length of the codes can be changed in order to have different bit rates at the same time through the same radio channel. The channelization codes are normally presented as a tree of codes, as shown in Figure 6-21.

When the system is allocating codes, each code reserves all the codes above and below the same branch. For example, if the code C8,3 is used (middle of Figure 6-21), the codes above it (C4,1, C2,0, and C1) and the codes below it (C16,6, C16,7, C32,12, C32,13, etc.) cannot be used. In WCDMA, the RNC allocates the channelization codes and tries to optimize the usage of the codes.


C1

C2,0

C4,0

C8,1

C8,0

C4,1

C8,3

C8,2

C2,1

C4,2

C8,5

C8,4

C4,3

C8,7

C8,6

C16,6

C32,13

C32,12

C16,7

C32,15

C32,14

[1]

[11]

[10]

[11111111]

[1100]

[1010]

[1001]

[11110000]

[1111]

[11001100]

[11000011]

[10101010]

[10100101]

[10011001]

[10010110]

SF=1 SF=2 SF=4 SF=8 SF=16 SF=32

C1

C2,0

C4,0

C8,1

C8,0

C4,1

C8,3

C8,2

C2,1

C4,2

C8,5

C8,4

C4,3

C8,7

C8,6

C16,6

C32,13

C32,12

C16,7

C32,15

C32,14

[1]

[11]

[10]

[11111111]

[1100]

[1010]

[1001]

[11110000]

[1111]

[11001100]

[11000011]

[10101010]

[10100101]

[10011001]

[10010110]

C1

C2,0

C4,0

C8,1

C8,0

C4,0

C8,1

C8,0

C4,1

C8,3

C8,2

C2,1

C4,2

C8,5

C8,4

C4,3

C8,7

C8,6

C2,1

C4,2

C8,5

C8,4

C4,3

C8,7

C8,6

C4,2

C8,5

C8,4

C4,2

C8,5

C8,4

C4,3

C8,7

C8,6

C4,3

C8,7

C8,6

C16,6

C32,13

C32,12

C16,7

C32,15

C32,14

C16,6

C32,13

C32,12

C16,6

C32,13

C32,12

C16,7

C32,15

C32,14

C16,7

C32,15

C32,14

[1]

[11]

[10]

[11111111]

[1100]

[1010]

[1001]

[11110000]

[1111]

[11001100]

[11000011]

[10101010]

[10100101]

[10011001]

[10010110]

SF=1 SF=2 SF=4 SF=8 SF=16 SF=32

Figure 6-21. Channelization code tree.

6.2.3 Uplink spreading and modulation

In the uplink, one DPCCH and up to six DPDCHs can be spread and transmitted simultaneously. Figure 6-22 illustrates the principle of the spreading of one DPCCH and one DPDCH.

The DPCCH is always spread by using the same channelization code that is 256 bits in length. The DPDCH is spread with the channelization code selected by the system. The length of the code depends on the bit rate of the channel. The amplitudes of the DPDCH and DPCCH are weighted with the gain factors, and the real value bit streams are treated as a complex valued chip stream. Finally, the proper scrambling code is applied to the chip stream. In the uplink, the system selects a unique scrambling code for a


mobile station which separates the mobile station from other mobile stations. In UMTS, there are over 16 million scrambling codes available in the uplink.

Scrambling codej

DPDCH

DPCCH

Channelizationcode

Channelizationcode

Gain factor

d

Gain factor

c

Control

Data

Scrambling codej

DPDCH

DPCCH

Channelizationcode

Channelizationcode

Gain factor

d

Gain factor

c

Control

Data

Figure 6-22. Spreading of one DPDCH and DPCCH.

6.2.4 Downlink spreading and modulation

The principle of spreading in the downlink direction is illustrated in Figure 6-23. The method presented applies to all the downlink physical channels except the SCH.

j

Scrambling code

1 0Serial to paraller

converterChannelization

code

0

1

I+jQ

Q

I

j

Scrambling code

1 0Serial to paraller

converterChannelization

code

0

1

I+jQ

Q

I

Figure 6-23. Spreading in the downlink.


In the downlink, two consecutive symbols are converted from serial to parallel and then mapped to the I and Q branches. The first symbol (‘0’ in Figure 6-23) is mapped to the I branch, and the second symbol (‘1’) is mapped to the Q branch. The result is treated as a complex valued sequence of chips. Finally, the scrambling code is applied to the sequence. The channelization codes used in the downlink are the same codes described in Section 6.2.2.

The scrambling codes in the uplink direction separate individual mobile stations from each other. In the downlink, the scrambling codes are used to separate cells from each other in the same frequency. There are altogether 8,192 scrambling codes used in UMTS. These 8,192 scrambling codes are divided into 512 groups of one primary scrambling code and 15 secondary scrambling codes. The primary scrambling code should be received over an entire cell. If the system is running out of channelization codes, i.e., the code tree is fully utilized, it is possible to allocate a secondary scrambling code and reuse the channelization codes. 512 primary scrambling codes are further divided into 64 primary scrambling code groups. The use of scrambling codes in a specific scrambling code group can be important, for example, close to the national frontier.

6.3 Procedure examples

In this section, some of the procedures needed in RAN are described. These procedures are involved in idle mode, call establishment, and the connected mode.

The states of the mobile station can be divided into idle mode and connected mode states. The connected mode state can be divided further into CELL_DCH, CELL_FACH, CELL_PCH, and URA_PCH states. The mobile station can change its state according to well-defined rules. The connection establishment, i.e., the change of state from idle mode to connected mode, is especially important from the service accessibility point of view. Some transitions are not possible between the different states in WCDMA. Also, the mobile station can alternate its state between WCDMA and GSM. The different states of the mobile station in WCDMA and the transitions are shown in Figure 6-24 [7-8].

In idle mode, the mobile station should perform the following tasks: – PLMN selection and reselection; – cell selection and reselection; and – location registration.


Connected Mode

Idle Mode

GSM

Connected Mode

GSM Idle Mode

URA PCH CELL PCH

CELL DCH CELL FACH

Establish/Release

RRC Connection

Establish/Release

RRC Connection

Connected Mode

Idle Mode

GSM

Connected Mode

GSM Idle Mode

URA PCH CELL PCHURA PCH CELL PCH

CELL DCH CELL FACHCELL DCH CELL FACH

Establish/Release

RRC Connection

Establish/Release

RRC Connection

Figure 6-24. State machine.

The prerequisites for the listed tasks are, for example, that the mobile station is synchronized with the network and the synchronization is achieved by the synchronization procedures provided by the physical layer.

If the mobile station has selected a cell belonging to an allowed PLMN, it can receive the system information of the PLMN and thus perform different kinds of tasks. For example, the mobile station can establish an RRC connection by using the control channels, receive paging messages from the network, and receive broadcast services [7, 9].

In connected mode, the mobile station does various tasks. Radio bearer establishment, data transmission, measurement reporting, cell update, URA update, radio link addition and remove, handovers and paging in connected mode (e.g., receiving a voice call during data transmission) are examples of tasks in connected mode [10].

The following chapters describe some of the main procedures performed by a mobile station in idle mode, connection establishment, and connected mode. Some tasks are also explained with the help of the measurement samples in Chapter 7.

6.3.1 Cell search

The mobile station performs a cell search procedure to get the initial access to the network. The mobile station tries to find a cell and determine the cell’s downlink scrambling code. The scrambling code information is needed to be able to receive system information sent on the BCCH.


The cell search procedure can be divided into three phases. These phases are:

1. Slot synchronization. 2. Frame synchronization and scrambling code group identification. 3. Scrambling code identification.

In the slot synchronization phase, the mobile uses the synchronization code of the primary SCH. (See Section 6.1.3.5.) The synchronization code is the same for all cells in the network. If the mobile station tries to decode the primary SCH by using the synchronization code and detects a peek in the RAKE receiver, the slot timing is obtained.

In the frame synchronization phase, the mobile station uses the secondary SCH to find the frame synchronization and scrambling code group. The mobile station correlates all possible secondary synchronization code sequences with the received signal and tries to find the maximum value. Due to the structure of the allocation of the secondary synchronization codes to the slots, the mobile station can detect the frame synchronization and the scrambling code group.

The mobile station finds the scrambling code used in a cell by correlating all the scrambling codes belonging to the scrambling code group identified in the previous step. After the scrambling code is determined, the mobile station can decode the CCPCH and start to receive the system information.

If the mobile station has prior information about the scrambling code used in a cell, phases two and three can be simplified. For example, if a neighbor cell has the scrambling code belonging to the same scrambling code group as the scrambling code of the serving cell, the cell search procedure can be quicker.

6.3.2 Cell selection and reselection

When the mobile station has found a suitable PLMN, it should try to find a suitable cell to camp on. It is possible that the mobile has no prior information about a cell to camp on. Then the mobile uses the Initial Cell Selection procedure. Otherwise, the mobile can use the information of the carrier frequencies, scrambling codes, etc. [11].

The criteria for cell selection for an FDD cell are given in Equation 6-1.

onCompensatirxlevminrxlevmeasrxlev

qualminqualmeasqual

PQSS

QSS

−−=−=

(6-1)


The mobile station should select the first cell that fulfills both Squal > 0 and Srxlev > 0.

According to the criteria, the selected cell should have good enough coverage (Srxlev) and also good enough quality (Squal). Quality in this context is defined by Ec/N0. In Equation 6-1, the following definitions are used.

Table 6-1. Notations used in Equation 6-1. Parameter Explanation

Squal Quality value for cell selection (dB). Srxlev RX level value for cell selection (dB). Squalmeas Measured Ec/N0, presents quality (dB). Srxlevmeas Measured RX level (dB). Squalmin Minimum accepted signal quality. Srxlevmin Minimum accepted signal level. PCompensation Power compensation, MS maximum power on RACH – MS

maximum power, non-negative (dB).

Cell reselection takes place when the mobile station detects a potentially better cell. In this cell reselection process, the mobile station can evaluate candidates on the same frequency or on different frequencies, in same layer or in different layers, or candidates using different radio access technology. If a candidate cell belongs to a different layer, a hierarchical cell structure (HCS) is used. This means, for example, that the mobile station is camped on a macro cell and the candidate cell is a micro cell. Before the mobile station can make any decisions, it must have measurement results from the cell reselection candidates. The measurements are started if the following rules are fulfilled (assuming HCS is not used).

Table 6-2. Measurement rules. Criterion Explanation

Intra-frequency measurementSqual > Sintrasearch No need to start intra-frequency measurements. Squal Sintrasearch Perform intra-frequency measurements. Sintrasearch not sent Perform intra-frequency measurements.

Inter-frequency measurementSqual > Sintersearch No need to start inter-frequency measurements. Squal Sintersearch Perform inter-frequency measurements. Sintersearch not sent Perform inter-frequency measurements.

Measurement on different RATSqual > SsearchRAT-m No need to start to start measuring cells of RAT m. Squal SsearchRAT-m Measure cells of RAT m. SsearchRAT not sent Measure cells of RAT m.


If HCS is used, a new threshold is introduced. SsearchHCS defines the minimum signal level when HCS is used. If the signal level of the serving cell is below the threshold, all intra-frequency and inter-frequency cells should be measured. If the signal level is above the threshold, HCS priorities are used in the cell selection procedure. When HCS is used, the behavior of the mobile station depends whether or not the mobile station is a fast moving mobile. The mobile station is considered a fast moving mobile if in the time period of TCRmax the number of cell selections exceeds NCR. When the number of cell selections decreases to under NCR, the mobile station is still considered a fast moving mobile for the time period of TCRmaxHyst; and after TCRmaxHyst has elapsed, the mobile station is treated as a normal mobile station.

If the signal level exceeds the SsearchHCS and the mobile station is not considered a fast moving mobile, the cell selection is performed as follows. – If Squal > Sintersearch, all the intra-frequency and inter-frequency cells

having that have higher HCS priority than the serving cell are measured. – If Squal Sintersearch, all the intra-frequency and inter-frequency cells that

have equal or higher HCS priority than the serving cell are measured. If the signal level exceeds SsearchHCS and the mobile station is a fast

moving mobile, the mobile station should measure intra-frequency and inter-frequency cells that have lower or equal HCS priority than the serving cell. Also, the mobile station should prioritize the cell reselection to the cells having lower HCS priority than the serving cell. The behavior of the mobile station in the case of HCS and high mobility is needed, for example, if the mobile station is moving fast through an area that has a lot of micro cells. It may be beneficial if the slow-moving mobiles are kept in the micro cell layer, and the fast moving mobiles are directed into the macro cell layer.

If the serving cell belongs to the hierarchical cell structure, a new threshold for the inter-system measurements is also specified. SHCS,RATm

shows the minimum signal level of the serving cell when HCS measurement rules are applied. If the signal level of the serving cell is below SHCS,RATm, the mobile should measure all inter-RATm cells. If the signal level is above the threshold and the mobile station is not a fast moving mobile, the following rules are applied. – If Squal > Slimit,SearchRATm, the mobile station does not have to measure the

cells belonging to RATm. – If Squal Slimit,SearchRATm, the mobile station should measure all neighbor

cells belonging to RATm that have equal or higher HCS priority than the serving cell. If the mobile station is a fast-moving mobile, it should measure the

neighbor cells in RATm that have equal or lower HCS priority than the


serving cell and prioritize the neighbor cells by the lower HCS priority in the cell reselection.

Based on the neighbor cell measurements, the mobile station ranks the measured cells. There are several steps in ranking. If HCS is used, the quality level threshold criterion H is calculated with the formulas in Equation 6-2.

nnnnLEVmeasn

ssLEVmeass

LTOQhcsQH

QhcsQH

×−−=−=

,_

,_(6-2)

If HCS is not used the H criterion can not be used. The cell-ranking criterion R is defined in Equation 6-3.

)L(TOQoffsetQR

QhystQR

nns,nmap,nn

ssmaps

−×−−=+=

1,

(6-3)

In Equation 6-2 and Equation 6-3 TOn and Ln are defined in Equation 6-4.

snn

snn

nnnn

PRIOHCSPRIOHCSifL

PRIOHCSPRIOHCSifL

xifxW

xifxW

TePenaltyTimWTempOffsetTO

__,1

__,0

01)(

00)(

)(

≠===

≥=<=

−×=

(6-4)

A temporary offset (TempOffset) in H and R criteria is applied for the period of PenaltyTime. However, the offset is applied only if the usage of HCS is indicated in the system information. The timer Tn is started: – when the HCS priority levels of the serving cell and the neighbor cell are

different and Qmeas_LEV,n > Qhcsn;– for FDD cells, when the HCS priority levels of the serving cell and the

neighbor cell are equal and Qmap,n > Qmap,s + Qoffset1s,n (quality measure is CPICH RSCP);

– for FDD cells, when the HCS priority levels of the serving cell and the neighbor cell are equal and Qmeas_LEV,n > Qmeas_LEV,s + Qoffset2s,n (quality measure is CPICH Ec/N0); and


– for all other cells, when the HCS priority levels of the serving cell and the neighbor cell are equal and Qmap,n > Qmap,s + Qoffset1s,n.The definitions used above are given in Table 6-3.

Table 6-3. Definitions of the parameters. Parameter Definition

Qmap,n Quality of the neighbor cell after the mapping function is applied. The parameters of the mapping function are sent in the system information. For FDD cells, CPICH RSCP or Ec/N0 is used. For GSM RXLev is used.

Qmap,s Quality of the serving cell after the mapping function is applied. For FDD cells, CPICH RSCP or Ec/N0 is used. For GSM, RXLev is used.

Qmeas_LEV The quality value of the received signal expressed in CPICH_Ec/N0 or CPICH RSCP level. RXLev is used for GSM.

Qoffset1s,n Quality offset between the serving cell (s) and neighbor (n) cell, quality measure is CPICH RSCP.

Qoffset2s,n Quality offset between the serving cell (s) and neighbor (n) cell, quality measure is Ec/N0.

The mobile station ranks only the cells fulfilling the S criterion among the cells that fulfill criterion H = 0 and have the highest priority in HCS. If there are no cells fulfilling criterion H = 0, the ranking should be done among all cells without considering HCS priority levels. The ranking is done according to R criterion and the mobile station reselects the best cell if the reselection criteria are fulfilled during the time interval indicated by the parameter Treselection [9].

6.3.3 Paging

The paging procedure is used to send paging information to mobile stations in idle mode, CELL_PCH and URA_PCH states. The core network may request paging to establish the signaling connection between the mobile station and the network. UTRAN can use paging to trigger a cell update procedure for the mobile stations in the CELL_PCH and URA_PCH states. Moreover, UTRAN can page mobile stations in idle mode, CELL_PCH or URA_PCH states and trigger them to read the updated system information.

UTRAN initiates paging by sending a PAGING TYPE 1 message to the mobile station(s). This message is normally repeated several times to improve the probability of receiving the message correctly. When the mobile station receives a page, it will indicate the reception of the page; and if the mobile station is in connected mode, it will perform a cell update procedure. If the information element, BCCH modification info, is included in the page, the mobile stations in idle mode or in CELL_PCH or URA_PCH states should read the new system information.

The paging procedure is shown in Figure 6-25.


Mobile Network

Paging Type 1

MobileMobile NetworkNetwork

Paging Type 1

Figure 6-25. Paging message.

6.3.4 RRC connection establishment

The RRC states were illustrated in Figure 6-24. When there is a need to create a connection between the mobile station and the network, a radio resource control connection (RRC connection) should be established. RRC connection is created, for example, if there is a mobile originating or terminating a voice or data call, signaling or emergency call. The RRC connection is always requested by the mobile station by sending an RRC CONNECTION REQUEST message on the uplink CCCH, as illustrated in Figure 6-26.

Mobile RNC

RRC Connection Request (CCCH)

RRC Connection Setup Complete (CCCH)

RRC Connection Setup (CCCH)

Mobile RNC

RRC Connection Request (CCCH)RRC Connection Request (CCCH)

RRC Connection Setup Complete (CCCH)RRC Connection Setup Complete (CCCH)

RRC Connection Setup (CCCH)RRC Connection Setup (CCCH)

Figure 6-26. RRC connection establishment.


The connection request message includes information about the reason for the request, the identifier of the mobile station, the protocol used, and measurement reports. The serving RNC replies to the request by sending a RRC CONNECTION SETUP message on the downlink CCCH. If the RNC has to reject the request, it may direct the mobile station to another carrier or another system. The RRC CONNECTION SETUP message informs the mobile station about transport channels in both uplink and downlink directions, radio resource parameters, and optionally frequencies to be used. The mobile station replies to the message with an RRC CONNECTION SETUP COMPLETE message and enters the CELL_DCH state. The RRC connection is always released by the RNC.

6.3.5 Location update

The location update procedure is used for several purposes in WCDMA by changing the content of the information element in the location update message. In the location updating procedure, first the RRC connection is established as described in Section 6.3.4. After the RRC connection is established, the mobile station sends the request to update the location that may be used, for example, to attach IMSI, attach GPRS, or update the location. After the request, the identification process, authentication process, and security mode control processes are carried out. Finally, the RNC sends the acceptance to the mobile station. The flow of the location update procedure is shown in Figure 6-27.

Mobile RNCBTSRRC Connection Request

RRC Connection Setup

RRC Connection Setup Completed

Identification Process

Authentication Process

Security Mode Control Process

Location Update Request

TMSI Reallocation Complete

Radio Link Setup

Radio Link Response

L1 SynchonizationSync Indication

Location Update Accept

Release RRC Connection

Mobile RNCBTSRRC Connection Request

RRC Connection Setup

RRC Connection Setup Completed

Identification Process

Authentication Process

Security Mode Control Process

Location Update Request

TMSI Reallocation Complete

Radio Link Setup

Radio Link Response

L1 SynchonizationSync Indication

Location Update Accept

Release RRC Connection

Figure 6-27. Location update procedure.


6.3.6 Radio bearer establishment

When the user data is sent between the mobile station and core network (either the PS or CS core network), there should be a Radio Access Bearer between the RNC and the core network, and a Radio Bearer between the mobile station and the RNC.

For the circuit switched data, the DIRECT TRANSFER message carries a CALL CONTROL SETUP message, which specifies the connection type. The RNC forwards this message to the CS core network. For the packet switched traffic, the DIRECT TRANSFER message carries a SESSION MANAGEMENT ACTIVATE PDP CONTEXT REQUEST. This message also specifies the connection parameters but the actual connection parameters are different. The RNC forwards this message from the mobile station to the SGSN. Next, the RNC sends the RADIO BEARER SETUP command to the mobile station, and the radio bearer is established. The mobile station replies to the message by sending a RADIO BEARER SETUP COMPLETE message. After this message, it is possible to start the call or to transfer data. The radio bearer establishment process is shown in Figure 6-28.

Figure 6-28. Radio bearer establishment.


6.4 Radio resource management in WCDMA

Radio resource management (RRM) controls the utilization of the air interface resources. RRM can be divided into power control (PC), handover control (HC), admission control (AC), load control (LC), and dynamic resource allocation. The aim of power control is to minimize the interference in the WCDMA radio network. This is achieved by using as low power levels as possible to maintain the requested performance. Handover control enables the mobility in WCDMA networks. HC is also used to optimize the performance of the network by enabling the use of different layers in the network, different frequencies, and different radio access techniques. Admission controls ensure that new radio bearers will not cause the existing connections to deteriorate. Load control ensures that the system does not become unstable due to changes in the air interface. Dynamic resource allocation ensures that the physical and logical resources, such as scrambling and spreading codes, are used effectively.

6.4.1 Power control

In WCDMA, many users share the same frequency at the same time. This means that users will interfere with each other and thus deteriorate the performance of the system. To achieve the best possible performance in the air interface, both the mobile stations and base stations should use as low power levels as possible. This means that power should be tuned based on the services, radio channel characteristics and fading conditions.

The power control is divided into open-loop, inner-loop and outer-loop power control.

6.4.1.1 Open-loop power control

The open-loop power control function is located both in the mobile station and in the network. In the uplink direction, it handles the initial power for the first preamble of PRACH and for the uplink DPCCH. In the downlink, the open-loop power control sets the power for the downlink channels. The power levels are based on the mobile station measurements. Actual algorithms are vendor-specific.

In the uplink direction, the power of the first preamble of PRACH is calculated as shown in Equation 6-5 [8].

Preamble_Initial_Power = Primary CPICH TX power – CPICH_RSCP + UL interference + Constant Value

(6-5)


In Equation 6-5, Constant Value is the required C/I in the uplink direction. The UL interference and required C/I are sent by the base station to the mobile station on BCH. The initial power for uplink DPCCH is calculated in a similar manner as the power of the first preamble, as indicated in Equation 6-6 [8].

DPCCH_Initial_power = DPCCH_Power_offset – CPICH_RSCP

(6-6)

DPCCH_Power_offset is transmitted to the mobile station in The uplink DPCH Power Control Info by the system. CPICH_RSCP is measured by the mobile station.

6.4.1.2 Downlink common channel power levels

The power levels of the common channels are usually considered as constant, even if the specifications do not prevent changing the power dynamically. This way, the power levels of the common channels are not part of the power control. However, the power levels should be set in a way that mobile stations can receive the channels well enough while power levels are as low as possible. In Table 6-4, power levels for the downlink common channels are suggested.

Table 6-4. The power levels of the downlink common channels [1]. Downlink common channels Power (dBm)

P-CPICH 33 P-SCH 30 S-SCH 30 P-CCPCH 28 S-CCPCH (assumed SF=256) 28 PICH (assumed 72 paging indicator per frame) 25 AICH 25

6.4.1.3 Inner-loop power control

The inner-loop power control adjusts the output power of the mobile station and base station 1500 times per second. Due to the high frequency of the power control the effect of fast fading in the radio channel can be compensated for almost all mobile stations. The inner-loop power control is based on feedback information from the receiving part. Both the base station and the mobile station have a target signal-to-interference ratio (SIR). If the received SIR is less than the SIR target, the receiving end asks the transmitting end to use higher output power. If the received SIR is higher


than the target SIR, the receiving end asks the transmitting end to reduce the power.

In the uplink, when the base station measures the SIR and compares it to the SIR target, it will generate a power control command based on either algorithm 1 or algorithm 2. In algorithm 1, power control commands are generated for each slot. The power step can be 1 dB or 2 dB. In algorithm 2, the power step is always 1 dB, and the power is increased only if five consecutive power commands are ‘UP’. Power is reduced only if five consecutive power commands are ‘DOWN’. Otherwise, the power is left unchanged. In a soft handover, the mobile station receives power commands from several cells. If algorithm 1 is used, the mobile station combines the power commands based on soft symbol decisions and adjusts the output power according to the combined power command. If algorithm 2 is used for each radio link set, a temporary power command is calculated. The temporary power command gets the value ‘UP’ if five consecutive TPC commands are ‘UP’. The temporary power command gets the value ‘DOWN’ if five consecutive TPC commands are ‘DOWN’. Otherwise the temporary power command gets the value zero. The actual power command is calculated as an average of the temporary power commands. If the DOWN command is represented by ‘-1’, and the UP command by ‘+1’, the combined power command get the value UP if the average of the temporary power commands is greater than +0.5, and it gets the value DOWN if the average is smaller than -0.5. Otherwise the power is not changed. If algorithm 2 is used, note that: – the power can be changed only with the frequency of 300 Hz because for

each decision, TPC commands from five consecutive slots are needed; and

– the power step is always 1 dB. In the downlink, there are two modes for inner-loop power control. In

mode 0, the power of the downlink DPCH is changed in each slot. In mode 1, the mobile station repeats the same power control command three times, and the system updates the output power in every three slots. The mobile station estimates the receiver SIR based on the pilot bits. If the estimated SIR is better than the target SIR, the mobile station sends a DOWN command. Otherwise, the mobile station sends an UP command.

6.4.1.4 Outer-loop power control

The RNC monitors the received quality at the mobile station and the base station. If there is a difference in the received quality and the target quality, the RNC changes the SIR target for the mobile station or for the base station. Even if the inner-loop power control can keep SIR in the SIR target, it is possible that the quality of the connections is too good or too bad. This can


happen because the achieved quality (i.e., BER or BLER) varies depending on the mobile speed and/or a multi path propagation environment. If the quality of any connection is too good, the SIR target for that specific connection is reduced by the RNC. If the quality is not fulfilling the requested targets, the SIR target is increased. The actual algorithms used to adjust the SIR targets for the uplink and downlink are vendor-specific [7].

6.4.2 Handover control

The most common handovers in WCDMA are softer handover, soft handover, inter-frequency handover, and inter-system handover. Handovers are needed when the mobile station moves from the coverage area of an old cell to the coverage area of a new cell. Moreover, handovers are needed to support multilayer networks as well as multi mode operations, e.g., using WCDMA and GSM networks together [11-12].

6.4.2.1 Soft and softer handover

Soft handover may be the most important handover in WCDMA because it is almost always needed when the neighbor cells are using the same frequency.

When the mobile station is in connected mode, it measures the serving cell as well as all neighbor cells indicated by the RNC. The RNC sends a list of cells that the mobile station should measure. Moreover, the RNC sends a set of thresholds that are used when the mobile station measures the neighbor cells and decides whether the measurements should be reported to the RNC. When the RNC receives the measurement results, it decides whether the active set, i.e., the set of cells that are serving the mobile station, should be updated. This update can include: – adding a new cell to the active set, – removing a cell from the active set, or – removing a cell and adding a new cell to the active set.

With a soft handover, the following benefits can be gained: – reduced interference because the mobile station is always connected to

the best server, – reliable handover without any interruptions for both RT and NRT

services, and – improved radio performance due to macro diversity.

Softer handover is similar to soft handover. In a softer handover, the mobile station is connected to the cells that are in the same base station, while in a soft handover, the cells belong to different base stations. In a softer handover, the combination of received uplink signals is done in the


base station, while in a soft handover, it is done in the RNC. In the downlink, the combination is done in the mobile station in both cases.

6.4.2.2 Intra-frequency handover

In some cases, it may be possible that the mobile station cannot make a soft handover between cells using the same frequency. This can happen, for example, if the source cell and the target cells are controlled by different RNCs and the inter-RNC handover is not possible, for example, because the IUr is not implemented. A typical example of an intra-frequency handover is a handover in a multi-vendor network when the handover is performed across the border of two vendors.

6.4.2.3 Inter-frequency handover

The inter-frequency handover is a hard handover, i.e., transmission to the old cell is stopped before transmission begins to the new cell. For RT services, this means a short interruption to the transmission, but in NRT services, the handover is lossless. Inter-frequency handover is needed if the network is using two or more frequencies. If the mobile station is in a location where the inter-frequency handover is possible, the RNC can request the mobile station to start inter-frequency measurements and report the results periodically to the RNC. The decision to make an inter-frequency handover is done by the RNC.

6.4.2.4 Inter-system handover

Inter-system handover in this content covers the handovers between FDD and GSM. In the WCDMA specifications, inter-system handover has had an important role because a large number of existing GSM operators are considering implementing a WCDMA network. In order to operate these two radio network layers as one network, fast and effective handovers between the layers are needed.

The mobile station has to be able to measure neighbor cells of the other system before making the handover. In GSM, the mobile station uses the idle time slots to measure the WCDMA neighbors. In WCDMA, the mobile station uses compressed mode to be able to measure the GSM neighbors. In compressed mode, the RAN creates gaps in the transmission and reception of a mobile station. These gaps can be created by splitting the spreading factor, reducing the bit rate used by the higher layers, or reducing the bit rate in the physical layer. Also, it is possible that the mobile station has two receiver chains, in which case compressed mode is not needed.

Typically, an inter-system handover is used to balance traffic in the GSM and WCDMA networks. It is also used to enable new services in the areas


where the GSM and WCDMA layers overlap. The inter-system handover can be divided into two different cases: – inter-system handover between GSM and WCDMA for CS connections,

or– cell reselection between GSM and WCDMA for PS connection.

The reason for an inter-system handover can be coverage (e.g., WCDMA coverage ends), capacity (e.g., capacity in GSM is running out, but in the WCDMA layer, there is unused capacity available), or services (e.g., high bit rates are supported only in the WCDMA layer). The steps in an inter-system handover can be described as: – parameter setting: the proper inter-system parameters are set in the BSS

and in the WCDMA; – measurement triggering: a measurement event is triggered (see Section

6.5.2.3 for the events); – inter-system measurements and analysis; and – a handover command is sent by the RNC or BSC.

The availability and support of the inter-system handover is vendor-specific. It should be noted that the support must be in both layers, i.e., in BSS and in WCDMA.

6.4.3 Admission control and load control

Admission and load control optimize the quality and capacity of the WCDMA network. Admission control and load control work in parallel. The main difference is that the admission control decides whether new connections can be established while the load control tries to maintain all the existing connections at the requested quality level.

The admission control handles the new connections in the RNC level. It ensures that the new connections will not deteriorate the quality of the existing connections. However, the quality classes can be taken into account when evaluating the impact of the new connection to the existing connections. The following assumptions are usually valid: – CS connections have higher priority than PS connections (note RT PS

connections); – RT connections have higher priority than NRT connections; – new NRT connections (e.g., background class) can be added even if the

load in the network is high, by taking into account only the impact of the signaling;

– the bit rates of NRT connections can be reduced to allow new RT connections.


The load in the WCDMA network varies depending on the location, time and services provided. The load control measures the load in the uplink and the downlink and tries to maximize the throughput of the network without jeopardizing the quality or coverage of the network. This means that the network tries to provide as many resources as are defined by the operator. However, it may happen that the network cannot provide the requested amount of resources for all connections. Then the load control decides how the situation is handled. Usually the throughput of the low priority connections, such as background traffic, is reduced or even stopped to ensure that the high priority connections have gotten the resources needed to maintain the required quality. When the low priority traffic is stopped, it is possible to reduce the throughput of the high priority traffic, and in an extreme case. Some of the connections may need to be dropped to ensure that the network will not become unstable. When the load decreases in the network, the load control starts to allocate the free resources once again for the low priority connections.

The algorithms of the admission control and the load control are proprietary for the vendors, so there can be different approaches for dealing with an overload situation.

6.4.4 Dynamic resource allocation

In WCDMA, physical and logical resources should be allocated effectively. Particularly the channelization codes should be used in a such way that the code tree is optimally utilized (see Section 6.2.2). When the amount of active connections changes in the network, there can be a need for optimizing the code tree. The dynamic resource allocation function in RNC takes care of the allocation of channelization codes and various other tasks. However, the implementation of dynamic resource allocation is vendor-specific.

6.5 3GPP parameters for WCDMA radio access

In this chapter, some of the parameters related to the WCDMA radio access are described. The tuning of the parameters of the radio network is one of the key tasks in optimizing the WCDMA radio network. Thus, it is important for the persons involved in optimization to know at least the basics of the parameters. The 3GPP specification leaves many issues open from the network side, and the actual implementation is vendor-specific. This means that the parameters used in the RAN can also be partly vendor-specific. This chapter focuses on the parameters defined by 3GPP.


6.5.1 Identities

In WCDMA, different entities must be identified. In this chapter, some of the most relevant identities for the radio network planning are covered. There are identifiers that are used only within UTRAN, between UTRAN and the core networks, and between UTRAN and GSM [13-14].

6.5.1.1 IMSI

The International Mobile Subscriber Identity (IMSI) is a unique identifier for a mobile subscriber in the GSM/UMTS system.

Figure 6-29. The structure of IMSI.

The IMSI consists of the Mobile Country Code (MCC), the Mobile Network Code (MNC), and the Mobile Subscriber Identification Number (MSIN). The MCC identifies the mobile subscriber’s country of domicile. The MNC identifies the PLMN of the subscriber, and the MSIN identifies the subscriber within the PLMN. Also, the National Mobile Subscriber Identity (NMSI) is defined as a combination of the MNC and MSIN [13].

IMSI = MCC + MNC + MSIN

6.5.1.2 LAI

The Location Area Identity (LAI) consists of the MCC, the MNC, and the Location Area Code (LAC). The LAC can have any value between 1 and 65535, except 0 (0000) and 65534 (FFFE) [13].

LAI = MCC + MNC + LAC

6.5.1.3 RAI

The Routing Area Identity (RAI) consists of the LAI and the Routing Area Code (RAC). The RAC can have any value between 1 and 255. As can be seen, the routing area’s maximum size is the location area. However, within one location area there can be several routing areas [13].


RAI = LAI + RAC = MCC + MNC + LAC + RAC

6.5.1.4 CGI and CI

The Cell Global Identification (CGI) consists of the MCC, the MNC, and the Cell Identity (CI). The CI can have values from 1 to 65535 [13].

CGI = MCC + MNC + CI

6.5.1.5 BSIC

The Base Station Identity Code (BSIC) consists of the Network Color Code (NCC) and the Base station Color Code (BCC). Both codes have fixed length of 3 bits, i.e., the BSIC can have values from 1 to 63. However, the usage of the NCC may be limited due to regulatory issues. The BSIC is used in GSM cells [13].

BSIC = NCC + BCC

6.5.1.6 PLMN Identifier

The PLMN Identifier (PLMN-Id) consists of the MCC and the MNC. The PLMN-Id specifies the PLMN globally [13].

PLMN-Id = MCC + MNC

6.5.1.7 CN Domain Identifier

The Core Network Domain Identifier specifies the CN Domain Edge Node. There are identifiers for both circuit switched and packet switched core networks. The CS core network’s CN domain identifier is called CN CS Domain-Id and consists of PLMN-Id and LAC. CN PS Domain-ID is defined for the PS core network and consists of PLMN-Id, LAC, and RAC [13].

CN CS Domain-Id = PLMN-Id + LAC CN PS Domain-Id = PLMN-Id + LAC + RAC

6.5.1.8 Global RNC-Id

Each RNC is identified within UTRAN with a unique RNC identifier (RNC-Id). The global RNC identifier consists of the PLMN-Id and RNC-Id. The identifier of the serving RNC (S-RNC), controlling RNC (C-RNC), and drift RNC (D-RNC) are built in the same way [13].

Global RNC-Id = PLMN-Id + RNC-Id


6.5.1.9 SAI

The Service Area Identity (SAI) is used, for example, in location-based services. The SAI consists of PLMN-Id, LAC, and the service area code (SAC) [13].

SAI = PLMN-Id + LAC + SAC

6.5.1.10 Cell Identifier and Local Cell Identifier

In Section 6.5.1.4, the CI was defined from the core network point of view. Within UTRAN, there is a Cell Identifier (C-Id) and a Local Cell Identifier. The C-Id is unique for a cell within the radio network subsystem (RNS). The C-Id combined with the identifier of the controlling RNC results in the UTRAN Cell Identity (UC-Id). The C-Id and UC-Id are used to identify the cells in the Iub and Iur interfaces.

In addition to C-Id in WCDMA, a Local Cell Identifier is also defined. The Local Cell Identifier is used to identify a set of resources in a NodeB. It is used before the C-Id is defined. The Local Cell Identifier must be unique within a NodeB but it can be used, e.g., for O&M purposes if it is unique within the UTRAN.

UC-Id = C-RNC-Id + C-Id

6.5.1.11 RNTI

The Radio Network Temporary Identities (RNTI) are used to identify the mobile station within UTRAN. Moreover, the RNTIs are used identify the mobile station when sending signaling messages between the mobile stations and UTRAN. There are a set of different RNTIs. – s-RNTI (serving RNC RNTI) is unique within the serving RNC. It is

used to identify the mobile station under the serving RNC, the drift RNC, and the mobile station.

– d-RNTI (drift RNC RNTI) is allocated by the drift RNC and used by the serving RNC to identify the mobile station for the drift RNC.

– c-RNTI (cell RNTI) is used by the mobile station and the controlling RNC to identify the mobile station.

– u-RNTI is allocated for the mobile station. It consists of SRNC-Id and s-RNTI.

6.5.1.12 URA Identity

The URA Identity specifies a URA. The URA Identity can be used to specify the URA to be used for the mobile station and the serving RNC in cases where there is more than one URA defined for a cell.


6.5.2 Measurement reporting parameters

In WCDMA, there are several triggers for the mobile station to start various kinds of measurements. The 3GPP specifications do not give actual parameters for the thresholds, but it is very likely that equipment vendors will implement the thresholds as parameters in UTRAN.

6.5.2.1 Intra-frequency measurements events

Six different events may trigger intra-frequency measurements. However, the measurements can be done periodically if the network has not been able to add a cell into the active set. Based on measurement results, the network can request the mobile station to perform a handover. The events that may trigger the measurements are: – Event 1a: a primary CPICH enters the reporting range; – Event 1b: a primary CPICH leaves the reporting range; – Event 1c: a non-active primary CPICH becomes better than an active

primary CPICH; – Event 1d: change of the best cell; – Event 1e: a primary CPICH becomes better than an absolute threshold;

and– Event 1f: a primary CPICH becomes worse than an absolute threshold.

The cells that are involved in a soft handover with the mobile station comprise the ‘active set’. The size of the active set can be three, for example, which means that the mobile station can communicate with a maximum of three cells simultaneously. A cell can be added if the primary CPICH is within the reporting range, which means that Ec/I0 (or RSCP) of the new cell must be within the reporting range.

In Figure 6-30, the reporting range is at all times 3 dB below the Ec/I0 of the best server. First, when Cell 2 enters the reporting range, Event 1a is triggered. When Cell 2 becomes better than Cell 1, Event 1d is triggered. Because Cell 1 drops below the reporting range, Event 1b is triggered. And finally, when Cell 1 goes below the absolute threshold, Event 1f is triggered.

An example of the parameters for intra-frequency measurements are presented in Table 6-5.

The intra-frequency measurement reporting can be modified by introducing hysteresis, cell-specific offsets, time-to-trigger, and forbidden primary CPICHs. Hysteresis can be used, for example, to avoid unnecessary events, as shown in Figure 6-31. Cell 1 is always better than Cell 2 in Figure 6-31. Cell 2 enters the reporting range but will not trigger Event 1a until the quality of Cell 2 exceeds the reporting range by ‘Hysteresis Event 1a’. Moreover, Event 1b is not triggered even if the quality of Cell 2 gets worse than the reporting range because ‘Hysteresis Event 1b’ is applied.


Ec/

N0

Reporting range

P-CPICH #1

P-CPICH #2

Absolute thresholdReporting range

Event 1a

Event 1d

Event 1b

Event 1f

Ec/

N0

Reporting range

P-CPICH #1

P-CPICH #2

Absolute thresholdReporting range

Event 1a

Event 1d

Event 1b

Event 1f

Figure 6-30. Intra-frequency measurement events.

Table 6-5. An example of the parameters for the intra-frequency measurements. Parameters Explanation

Active set size The maximum number of cells participating the soft handover.

For each event Reporting range The measurement of a new cell must be within the reporting

range before the cell can be added to the active cell; relative to the best server.

Absolute threshold Guarantees the minimum quality for a cell . Hysteresis A hysteresis for the reporting range of a cell. Time to trigger The cell has to fulfill the criteria for the time period of “Time

to trigger” before the event is triggered. W A weighting factor to weight the importance of the best server

and all cells in the active set. Offset Cell specific offset.

The parameter Time-to-trigger is also used to avoid unnecessary reporting events. When Time-to-trigger is applied, the criterion for the event must be fulfilled during the time period indicated by Time-to-trigger.

In Figure 6-32, Cell 1 is always better than Cell 2. When Cell 2 reaches the reporting range, Event 1a is not triggered until Cell 2 has been better than the reporting range during the time period indicated by ‘time-to-trigger’. In Figure 6-32, Event 1b is not triggered until the ‘time-to-trigger’ for Event 1b has elapsed, even if Cell 2 is clearly below the reporting range.

In some cases, it may be beneficial to apply cell-specific offsets for certain cells. These offsets can be applied separately for each cell, which


means, for example, that the behavior of the mobile station can be optimized based on knowledge of the environment.

Ec /

N0

Reporting range

Cell #1

Cell #2

Hysteresis event 1a

Event 1a

Hysteresis event 1bEc /

N0

Reporting range

Cell #1

Cell #2

Hysteresis event 1a

Event 1a

Hysteresis event 1b

Figure 6-31. The usage of the hysteresis.

Time

Ec/

N0

Reporting range

Cell #1

Cell #2

Time-to-trigger

event 1a

Event 1a

Time-to-trigger

event 1b

Event 1b

Time

Ec/

N0

Reporting range

Cell #1

Cell #2

Time-to-trigger

event 1a

Event 1a

Time-to-trigger

event 1b

Event 1b

Figure 6-32. The usage of Time-to-trigger mechanism.

In Figure 6-33, cell-specific offsets are applied for Cell 2. For Event 1a, a positive offset means that the event is triggered earlier, before the cell reaches the reporting range. This can be useful if an operator knows that Cell 2 can rapidly become stronger, as it does in Figure 6-33. The cell-specific offset is also applied to Event 1b in Figure 6-33. The positive offset causes


Event 1b to be triggered later than it would without the offset, as shown in Figure 6-33.

Time

Ec/

N0

Reporting range

Cell #1

Cell #2

Cell #2 + offset

Offset for cell #2

Event 1a

Event 1b

Time

Ec/

N0

Reporting range

Cell #1

Cell #2

Cell #2 + offset

Offset for cell #2

Event 1a

Event 1b

Figure 6-33. The usage of the cell-specific offset.

It is possible to forbid a cell in the active set to affect the reporting range. This can be useful when an operator knows that the quality of the forbidden cell is unstable and could cause unexpected behavior in the network. In Figure 6-34, Cell 2 is added to the active set, but it does not affect the reporting range; the reporting range is defined by Cell 1. This way, other potential and stable cells can be monitored more easily.

Time

Ec/N

0

Reporting range

Cell #1

Cell #2

Time

Ec/N

0

Reporting range

Cell #1

Cell #2

Figure 6-34. The usage of the forbidden cell mechanism.


If the RNC is not able to add a cell to the active set when the cell has entered the reporting range, the mobile station will continue to send the measurement reports to the RNC, based on the parameters set by the operator. There are parameters for the reporting interval and maximum number of reports sent. Normally the mobile station will periodically send the intra-frequency measurements until the number of measurement reports indicated by ‘Amount of reporting’ are sent to the RNC.

6.5.2.2 Inter-frequency measurement events

There are six different events defined for the inter-frequency measurements. These events are: – Event 2a: change of the best frequency; – Event 2b: estimated quality of the currently used frequency is below a

threshold, and the estimated quality of a non-used frequency is above a threshold;

– Event 2c: the estimated quality of a non-used frequency is above a threshold;

– Event 2d: the estimated quality of the currently-used frequency is below a threshold;

– Event 2e: the estimated quality of a non-used frequency is below a threshold; and

– Event 2f: the estimated quality of the currently-used frequency is above a threshold. These events are illustrated in Figure 6-35. Cell 1 is using Frequency 1

and Cell 2 is using Frequency 1 in Figure 6-35. It is assumed that Cell 1 is the serving cell. There are thresholds for both cells that are used for the measurement events. When Cell 1 exceeds the threshold defined for the cell, Event 2f is triggered. When Cell 1 falls below the threshold, Event 2d is triggered. In Figure 6-35, Event 2b is also triggered because Cell 2 is above its own threshold. For Cell 2, similar events are Event 2c and Event 2e (Event 2e is not shown in Figure 6-35). Event 2a is triggered when Cell 2 becomes better than Cell 1.

For Events 2a – 2f (as with Events 1a – 1f), there are parameters (Table 6-6) that are used with the inter-frequency measurements. In the Figure 6-35, the hysteresis parameters and Time-to-trigger parameters are not applied.

Table 6-6. Parameters for the inter-frequency measurements. Parameter Explanation

Threshold #1 The threshold for the serving cell. Threshold #2 The threshold for the neighbor cell on the other frequency. Hysteresis A hysteresis for an event. Time to trigger The cell must fulfill the criteria for the time period of “Time to

trigger” before the event is triggered.


Ec /

N0

Cell #1 on freq 1

Cell #2 on freq 2

Threshold for cell #1


Event 2a

Event 2c

Event 2b+2d

Event 2f

Ec /

N0

Cell #1 on freq 1

Cell #2 on freq 2



Event 2a

Event 2c

Event 2b+2d

Event 2f

Figure 6-35. Events for inter-frequency measurements.

6.5.2.3 Inter-system measurements events

In the inter-system measurements, both the WCDMA cells and GSM cells should be measured. In WCDMA, the measurement quantity can be either the downlink Ec/N0 or the downlink RSCP. In GSM, the RSSI of the carrier is measured.

For the inter-system measurements, there are four measurement events defined. These events are: – Event 3a: the estimated quality of the currently used UTRAN frequency

is below a certain threshold, and the estimated quality of the GSM is above a certain threshold;

– Event 3b: the estimated quality of GSM is below a certain threshold; – Event 3c: the estimated quality of GSM is above a certain threshold; and – Event 3d: change of the best cell in GSM.

The hysteresis and Time-to-trigger parameters can be used for Events 3a-3d. Using these parameters, it is possible to avoid unnecessary inter-system measurement events and to ensure that the measurements are done when they are really needed.

6.5.2.4 Traffic volume measurements

Traffic volume measurements are used to help the control of the radio bearers. The mobile station can report the buffer occupancy, the average buffer occupancy, and the variance of the buffer occupancy. The buffer occupancy indicates the amount of data for each logical channel to be read for transmission or retransmission. The average buffer occupancy and the


variance of the buffer occupancy are calculated from the amount of data in the buffer [15].

For traffic measurement reporting, two events are defined: – Event 4a: traffic volume exceeds an absolute threshold; and – Event 4b: traffic volume falls below an absolute threshold.

Traffic volumes are calculated for the transport channels. There are also two timers that can be used to limit the number of measurement events. Time-to-trigger indicates a time period during which the criterion of the traffic volume must be fulfilled before the actual event is triggered. The parameter Pending time after trigger indicates a time period when no new measurement reports are sent to the RNC, even if the criterion of the specific event is fulfilled. This parameter limits the number of measurement reports sent to the RNC.

6.5.2.5 Quality measurements

A mobile station measures the downlink transport channel BLER. If the mobile station detects more bad Cyclic Redundancy Checks (CRC) than defined by the parameter ‘BAD CRC’, the mobile station will trigger Event 5a. The number of bad CRCs is calculated as a sliding average of bad CRCs within a number of total CRCs indicated by the parameter ‘Total CRC’. The amount of reports sent to the RNC is limited by introducing the parameter ‘Pending time after trigger’. During the time period indicated by ‘Pending time after trigger’, the mobile station is not allowed to send new reports to the RNC.

6.5.2.6 Mobile station internal measurements

In FDD, the mobile station should measure the transmit power, the received signal strength, and the mobile station’s Rx-Tx time difference. The following six events are defined for these measurements: – Event 6a: the mobile station Tx power exceeds becomes an absolute

threshold; – Event 6b: the mobile station Tx power falls below an absolute threshold; – Event 6c: the mobile station Tx power reaches its minimum value; – Event 6d: the mobile station Tx power reaches its maximum value; – Event 6e: the mobile station RSSI reaches the mobile station’s dynamic

receiver range; – Event 6f: The mobile station Rx-Tx time difference for a radio link

included in the active set exceeds an absolute threshold; and – Event 6g: The mobile station Rx-Tx time difference for a radio link

included in the active set falls below an absolute threshold. The power measurements (Events 6a – 6e) can be used, for example, by

the handover control to ensure that calls can be maintained. Events 6f and 6g


are used by the network to adjust the timing of the downlink transmission [8, 16]

6.5.3 Cell selection and reselection parameters

Cell selection and reselection was described in Section 6.3.2. The parameters related to cell selection and reselection are summarized in the following table.

Table 6-7. Parameters for cell selection and reselection. Parameter Explanation

Sintrasearch Threshold for starting intra-frequency measurements. Sintersearch Threshold for starting inter-frequency measurements. SsearchRAT m Threshold for starting inter-system measurement for the

RATm. SsearchHCS Threshold to apply HCS. If the signal strength is below this

threshold, HCS rules are not applied, but intra-frequency and inter-frequency cells are measured.

TCRmax Time period used to determine whether the mobile station is in high-mobility state.

NCR Threshold for the number of cell reselections in high-mobility state.

TCrmaxHyst Time hysteresis for high-mobility state. Treselection Cell reselection timer. SHCS,RATm Threshold for applying HCS for inter-system measurements. Slimit,SearchRATm Upper threshold for inter-system measurements for RATm. If

the signal quality is above this threshold, the mobile station does not have to perform inter-system measurements.

TEMP_OFFSET1 Temporary offset for a neighbor cell. The offset is applied in the cell reselection during the time period PENALTY_TIME. Applied when CPICH RSCP is used as a signal quality measure.

TEMP_OFFSET2 Temporary offset for a neighbor cell. The offset is applied in the cell reselection during the time period PENALTY_TIME. Applied when CPICH Ec/N0 is used as a signal quality measure.

PENALTY_TIME Time period during the TEMP_OFFSET is applied in the cell reselection.

HCS_PRIO Priority for hierarchical cell structure. Qoffset1 An offset applied for a neighbor cell when ranking the cells.

Applied when CPICH RSCP is used as a signal quality measure.

Qoffset2 An offset applied for a neighbor cell when ranking the cells. Applied when CPICH Ec/N0 is used as a signal quality measure.

Qhyst1 Hysteresis value applied for FDD cells if the quality measure is CPICH RSCP.


Parameter Explanation

Qhyst2 Hysteresis value applied for FDD cells if the quality measure is CPICH Ec/N0.

Qhcs Quality level when applying HCS. Qqualmin Minimum required quality level in a cell. Qrxlevmin Minimum required RX level in a cell. UE_TXPWR_MAX_RACH Maximum UE TX power level when accessing the cell on the

RACH. P_MAX Maximum RF output power of a UE.

Many of the parameters listed in Table 6-7 are cell-specific. This means that for each cell, all the parameters in Table 6-7 have to be set. Also, a cell may have several neighbor cells that require the corresponding parameters.

6.5.4 Cell information

The identifiers related to a cell were described in Section 6.5.1. In addition to these identifiers, there are other parameters that describe the configuration or performance of the cell.

Table 6-8. Cell information parameters. Parameter Explanation

TX Diversity Indicator Indicates whether TX diversity is used in a cell. UARFCN The frequency of the cell. Calculated by using the formula

UARFCN = 5 x frequency in MHz. Primary Scrambling Code

Identifies the downlink scrambling code for the primary CPICH.

Tcell The offset for the start of the SCH. Tcell is used to avoid overlapping between SCHs under the same NodeB.

With the parameter TX Diversity Indicator, the use of diversity is indicated. TX diversity affects how data is sent to the mobile station. Thus the mobile has to know whether TX diversity is used in a cell.

The frequency and the primary scrambling codes are basic parameters that must be correctly set but otherwise do not require much work.

The Tcell parameter is used to have an offset for the SCHs of the cells under the same base station. Without correct values for this parameter, the SCHs of different cells under the same NodeB would overlap in the time domain and the synchronization of a mobile station would be more difficult.

6.5.5 Power control parameters

The power control was described in Section 6.4.1. There are several parameters that are used for the power control. Table 6-9 lists the most essential ones.


Table 6-9. Power control parameters. Parameter Explanation

DL_Power_Averaging_Window_Size

The length of the downlink power averaging window in number of slots. If the power raise is limited in the downlink the power raise calculated over the averaging window will be smaller than the limit indicated by ‘Power_Raise_Limit’.

Power_Raise_Limit Defines a limit for the downlink power raise during the downlink power averaging period.

Gain factor c Gain factor for the control part. See also Figure 6-22. Gain factor d Gain factor for the control data part. See also Figure 6-22. PowerControlAlgorithm Power control algorithm for combining the downlink power

commands. Algorithm 1 works well in most of the cases. Algorithm 2 would be used if the mobile speed is above 80 km/h or below 3 km/h [1].

TPC-StepSize The power-step in the mobile station. For the Algorithm 1, the possible values are 1 dB and 2 dB. For the Algorithm 2, the only possible value is 1 dB.

PO1 Power offset for the TFCI bits relative to the power of the secondary CCPCH.

PO2 Power offset for the TPC bits relative to the power of the secondary CCPCH.

PO3 Power offset for the pilot bits relative to the power of the secondary CCPCH.

Power Ramp Step The step of the power increase in the RACH procedure. Preamble Retrans Max The maximum number of retransmissions in the RACH

procedure. Power offset P p-m Power offset between the power of the last transmitted preamble

and the control part of the random-access message. Preamble_Initial_Power The initial power of the preamble in the RACH procedure. Constant Value The required C/I in the uplink. Used in the RACH procedure.

Even if there are several parameters listed in Table 6-9, there can be several other parameters related to the power control, depending on the implementation. Also, the equipment manufacturers may use different names than the ones used in Table 6-9.

REFERENCE


[2] R. Peterson, R. Ziemer and D. Borth, Introduction to Spread Spectrum Communications.Prentice-Hall, 1995.

[3] Universal Mobile Telecommunications System (UMTS), Radio Interface Protocol Architecture, 3GPP TS 25.301.


[4] Universal Mobile Telecommunications System (UMTS), Physical Layer - General Description, 3GPP TS 25.201.

[5] Universal Mobile Telecommunications System (UMTS), Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD), 3GPP TS 25.211.

[6] Universal Mobile Telecommunications System (UMTS), Spreading and Modulation (FDD), 3GPP TS 25.213.

[7] Universal Mobile Telecommunications System (UMTS), Physical Layer Procedures (FDD), 3GPP TS 25.214.

[8] Universal Mobile Telecommunications System (UMTS), RRC Protocol Specification,3GPP TS 25.331.

[9] Universal Mobile Telecommunications System (UMTS), UE Procedures in Idle Mode and Procedures for Cell Reselection in Connected Mode, 3GPP TS 25.304.

[10] Universal Mobile Telecommunications System (UMTS), Interlayer Procedures in Connected Mode, 3GPP TS 25.303.

[11] Universal Mobile Telecommunications System (UMTS), Requirements for Support of Radio Resource Management (FDD), 3GPP TS 25.133.

[12] Universal Mobile Telecommunications System (UMTS), Radio Resource Management Strategies, 3GPP TS 25.922.

[13] Universal Mobile Telecommunications System (UMTS), Numbering, Addressing and Identification, 3GPP TS 23.003.

[14] Universal Mobile Telecommunications System (UMTS), UTRAN Overall Description,3GPP TS 25.401.

[15] Universal Mobile Telecommunications System (UMTS), Medium Access Control (MAC) Protocol Specification, 3GPP TS 25.321.

[16] Universal Mobile Telecommunications System (UMTS), Services Provided by the Physical Layer, 3GPP TS 25.302.

Chapter 7

UMTS RADIO INTERFACE FIELD

MEASUREMENTS Key WCDMA measurements and parameters

KAI OJALA, PASI NIEMI Nemo Technologies

Abstract: In this chapter, the main WCDMA field measurements are described. Measurements are divided into three categories: measurements in idle mode, in connection establishment, and in connected mode. Measured parameters in these modes are explained with examples. Once WCDMA is new technology, new features and functionalities will have to be verified. In the beginning, coverage, power control, and soft handovers are the key issues as well as verification of different connection types provided by a WCDMA system. At the start of the 3G era, WCDMA coverage is not continuous, so inter-working with GSM/GPRS has to work as well, so that customers can access cellular services continuously. WCDMA is intended for various applications besides voice services: the testing of circuit switched and packet switched data in the field is described as well as the testing of applications that run on top of the packet switched or circuit switched connection.

Key words: Analysis of WCDMA field measurement results, data measurements, field testing, WCDMA field measurement tool

259




7. UMTS RADIO INTERFACE FIELD MEASUREMENTS

This chapter provides an overview of radio interface field measurements in the downlink direction, measurement equipment, and measured parameters.

7.1 Measurement process

When a technology is evolving, there are different phases and time frames for different kind of tests. Figure 7-1 illustrates the different phases.

Figure 7-1. Measurement needs in an evolving technology.

Measurements are conducted to a different extent during different phases. However, during every phase, measurements regarding idle mode, connection establishment and connected mode need to be conducted.

7.1.1 Planning phase

First, in the planning phase, there is a time frame for conducting initial tests before actual verification tests are started. This period can be used for building up expertise and putting theory into practice. Observing the radio interface process during measurements and analyzing L1 parameters and L3 signaling after field measurement tours provides useful insight on how the radio interface works.

EmpiricalMeasurements

PredictedData

Licence &

Planning

Phase

Propagation Model

Verification

Penetration

Loss Testing

NetworkImplementation

NetworkExtension

Operation & Maintenance

Propagationmeasurements

Coverage

Verification

(indoor/outdoor)

Analysis

Autonomous measurements

Benchmarking measurements

Indoor verification


7.1.2 Implementation phase

At the beginning of the implementation phase, different radio access network functions and their operations should be verified at the same time as coverage verifications are performed for the planned service offerings. In the radio interface, this means testing different connection types and data rates that will be used to carry the services. Once the new radio access network solution is delivered by the network infrastructure vendor, verification of the functionality of various UTRAN features has to be conducted. The most important functions to be tested are [1-2]: 1. cell selection and reselections in idle mode, 2. setting up connections, which in 3G means the setups of different

connection types with different data rates, 3. power control (open loop, closed-loop, and outer-loop), 4. soft and softer handover, 5. hard handover (mainly inter-frequency handovers in the first phase), 6. GSM/GPRS-WCDMA inter-working, 7. verification of vendor-specific traffic control algorithms

– admission control, – packet scheduling, – load control, and – resource management.

In general, initial tests should be performed in a laboratory. After the basic functioning has been approved there, it is time to apply the new functions to a network and conduct field measurements. This phase includes testing the functionalities in real radio environments since they should work there as well. Good preparations are needed during the field tests. These include planning the test routes, cross-checking the status of the network elements, and monitoring the state of the different elements.

There are a number of different connection types that have to be tested. The variety of connection types naturally depends on network functionalities and terminal capabilities, but at least voice, circuit switched, and packet switched connections with various possible data rates should be tested. For example, voice call setups or packet switched connections can be made (radio bearer setups, attaches, PDP context activations), running tests with scripts enabling the testing of multiple setups can be conducted. Furthermore, the reliability of different setups can be verified to test network accessibility. Figure 7-2 presents an example of the call setup success ratio from one test drive.

In addition, parameters controlling the way the traffic is directed on certain channels and the way this works should be verified (e.g., directing the traffic to DCH/FACH in the downlink (DL) direction, or RACH usage


and reliability in the uplink (UL) direction). This requires modifying the settings of certain network parameters. Testing can be conducted by sending packets of different sizes and monitoring which channels are used.

Figure 7-2. Example of voice call statistics.

Radio resource management (RRM) functions are a critical part of the radio network. These algorithms can be seen as the brains in the radio network. They affect the capacity of the network and control the way new service access requests are admitted, denied and handled in the radio network. First of all, if power control is not functioning correctly, the capacity of the radio network will be degraded. Uplink and downlink power control should be tested in different environments and with different mobile speeds because the radio environment affects the way the power control (PC) performs. Parameters from UL and DL should be traced simultaneously to enable analysis in both directions. Tests should be performed in all the different cell types that are deployed, for example, urban environments (micro and macro cells), suburban cells (macro cells, base stations on rooftops, poles, masts, etc.) and rural environments. This is important because a WCDMA receiver performs differently in different radio propagation environments. These tests will give parameters for more accurate coverage estimations and also rules of thumb for evaluating the coverage compared, for example, with previous technologies (GSM900/GSM1800). Having the actual measured parameters for planning will reduce the selection of unsuitable base station (BS) sites in the future and optimize network performance. The functionality of the power control with multiple users using different data rates would also be important to test. However, it is very difficult to create an actual test case for simulating real-life situations in the network. That’s because it requires moving users located with different path losses from the base station and using the available services randomly. It is difficult to create this scenario but it would reveal if power control will handle realistic situations correctly. Evaluations with multiple users in a cell could be performed when the first friendly users are allowed to use the network. At the same time, measurements can be conducted to observe how the PC performs. Another way to gain insight on

Voice Call Event Information Call Disconnect Information

Type Value Description

Total 27

Successful Release 24

Dropped 3 (i.e., network release)

Percentage of Successfull Calls 88,889 %

Percentage of Dropped Calls 11,111 %


PC performance could be to use multiple mobiles in one place. However, in real networks, users are scattered, which is more challenging for power control.

The next step in testing is RRM functions. Soft/softer handovers (SHO) and their parameter settings should be verified. First, an operator has to decide whether periodical reporting is used or whether soft handover is based on event-triggered reporting. Testing of the latter case includes parameters affecting add/drop/replacement windows and timers defining how long a certain condition should be valid before a measurement report and its triggering event is sent to the network, which could initiate an active set update [3]. Based on field measurements, the correctness of the first “default” values should be verified.

Handovers between radio network controllers (RNCs) are required in larger cities, where one RNC cannot handle all the deployed base stations (This depends on the number of BSs and the selected configuration of the RNC.) In these cases, intra-frequency hard handovers should be verified unless the network implementation uses the Iur interface, enabling soft handovers between RNCs. The operator also has to evaluate inter-frequency handovers (IF HO) at an early stage in order to be prepared for growing capacity needs. Therefore, measurements evaluating IF HO settings (in other words, thresholds for initiating inter-frequency measurements and compressed mode parameters: transmission gaps, pattern lengths, etc.) have to be conducted [1, 4].

The functioning of the GSM/GPRS-UMTS inter-working (inter-system cell reselections and inter-system handovers) will be crucial for having continuous coverage for services in the first phase of the 3G network launch. There are a number of parameters for these functions that can be altered and should be verified in field measurements.

The functionality of other critical RRM functions, such as admission control, packet scheduling, load control and resource management, should also be verified to make sure that the network really functions as a cellular network. These functions either allow or deny new connections. The basis for the algorithms is usually the interference level or throughput in the network in the UL direction and the use of the base station power resources or throughput in the DL direction [1]. Basic functionality tests should include laboratory tests and field tests during unloaded and loaded networks.

Before tests can be started, planning and defining the tests of the different WCDMA functions must be done. Depending on the chosen strategy, the infrastructure vendor can conduct these tests and report the test results of the different features to the operator. This, however, requires that the operator still agrees with the vendor on the acceptance criteria, and that requires expertise in WCDMA and GSM/GPRS. Another possibility for the operator


is to plan and define tests by themselves, but this demands more expertise. Planning and defining the tests has to be started well in advance since the task is not trivial due to new WCDMA radio interface features and functionality. Reserving time for that phase is valuable because the issues to look for during measurements have to be clear before starting the tests. In planning the verifications, one should take into account what interfaces have to be traced at the same time as field tests are driven; how to collect, store, and name measurement files, and what will be included in certain test cases? In other words, define in advance the key parameters for the analysis of test cases. Also, the human resources needed for different tasks should be planned, and training should be conducted to insure adequate expertise to conduct the tasks.

7.1.3 Operational phase

When the network is up and running, it is time to move to the optimization phase. There will be a number of parameters that can be tuned, and their effect should be verified with field measurements. In addition, at this phase, regular network surveys are conducted to see how well the network is performing in changing conditions. Behavior of the UE in idle mode, during connection establishments, and during connected mode is tested all together while test drives are conducted.

Situations in the network change due to traffic injected by real customers and the results vary depending on the traffic in the network. For example, special events that gather a lot of people in one place have an effect on the measurement results. There is also a need to verify the concepts and configurations used in the network, such as different antenna types, tilting, and the use of masthead amplifiers. Furthermore, new parameter settings and possible new features should be verified. Survey tests give a picture of how network upgrades or configuration changes affect the network performance.

Survey tests have to be well-planned in order to get comparable results, even if an operator uses automatic field measurement tools to measure network performance or if the operator uses more traditional methods for measurements, such as field measurement tools in a van operated by a network system engineer. The measurement routes have to be defined as well as the time of day for conducting the measurements. Also, the operator must decide what connection types are used in testing and what kinds of scripts are run to conduct automated tests. Below is an example of a list of details that need to be defined before measurements: – define the test routes that will be used in repetitive tests, – define the time of day for testing in order to achieve comparable results,


– define the connection type and its settings for testing, – define the key performance parameters for analysis, for example:

– CPICH Ec/N0,– received signal level (RSSI), – quality or block error rate, – TX power, – percentage of successful/dropped calls, – percentage of successful attaches and PDP context activations, – average data throughput during UL/DL downloading.

On the basis of the measurement results, it is easy to point out areas where, for example, call setups have not been functioning correctly. The following example in Figure 7-3 depicts possible problem areas for setting up calls.

Figure 7-3. Example of possible problem areas in the network.

The red phone symbols on the map point out problem areas in the network. One way to examine the problem is to first check if the pilot Ec/N0

is at the required level. In the picture above, there has not been an adequate CPICH level available, which has caused call failures during the test drive. If there is a good CPICH level available and the calls are not succeeding, it is necessary to analyze what has happened during the setups: has the RACH procedure succeeded, and what has happened in L3 signaling? Troubleshooting call setup problems usually requires analyzers connected to other network interfaces (Iub and Iu).


7.2 Field measurement equipment

The field measurement equipment usually consists of a laptop PC, which should optimally be dedicated for measurements, just to avoid other software interfering with the measurement configurations. The PC stores the measurement data and runs the software during the measurements. The exact location of the measured parameters has to be recorded as well, and for that purpose, a GPS receiver is connected to the PC. It is possible to use a scanner, or a mobile, or both as measurement devices.

Figure 7-4. Measurement equipment.

Using both a scanner and a mobile simultaneously in WCDMA measurements enables the measuring of all pilots available in the area and the comparison of the results to the view seen by the user equipment (UE). The UE reports values based on a neighbor list received through signaling and makes cell reselections and handovers based on the planned neighbor list. However, there can be pilots available that are not defined in the neighbor lists and these can be spotted with a scanner. In other words, measurements together with a scanner and a mobile would also identify missing or interfering pilots.

7.2.1 Equipment installation

The placement of the test mobile and the use of external antennas affect the results. The UE placement should be defined and the same placement should be used in repetitive tests. Today, mobile phone users mainly use

Fast Scanner (option)


mobiles inside cars without external antennas, or mobiles are used indoors. In other words, it might be a valuable strategy to perform measurements using the UE inside a car. The mounting of the UE should be fixed so that different measurement tours are comparable. The difference in using external/internal antennas is around 4-10 dB, depending on the placement of the mobile and the structure of the car. If external antennas are used, losses or gains produced by additional hardware should be taken into account in the results. In other words, the person performing the measurements should find out the performance figures given by the manufacturer for the following: – connectors; – cables; and – antennas.

Afterwards, when analyzing the results, the effect of the items above should be noted.

7.3 Measurements in idle mode

In this section, three different types of measurements are introduced. First, noise floor measurements are described. Secondly, measurements that can be done using WCDMA scanner are introduced. Thirdly, UE measurements during idle mode are presented.

Because WCDMA is an interference-limited network and power needs always affect the capacity that can be achieved, it is beneficial to conduct spectrum clearance measurements in the allocated UMTS bandwidth before anything is in the air. It is better to perform these measurements with a sensitive spectrum analyzer because the sensitivity of commercial scanners is not high enough. A band-pass filter should be connected in front of the spectrum analyzer to filter out other interfering signals.

In the uplink direction, the pure noise floor can be calculated by assuming a 4-6 dB noise figure in the base station [5]:

Noise floor UL = kTFB = kT [mW/Hz] + NF [dB] + B [dBHz]

= -174 dB(mW/Hz) + 4…6 dB + 67 dBHz =

= -104…-102 dBm. (7-1)

where k is Boltzman’s factor, T is temperature, F is the noise factor, B is bandwidth, and NF is the noise figure.

In the same way, the pure noise floor for the downlink can be calculated by assuming a 7-10 dB noise figure in the user equipment:


Noise floor DL = -174 dB(mW/Hz) + 7…10 dB + 67 dBHz =

= -97…100 dBm. (7-2)

In these measurements, the planning areas should be measured by selecting the planned places where the spectrum clearance measurements are conducted, and if the levels exceed the calculated noise floors, there is interference on the frequency band that should be cleaned away. High sensitivity is needed to point out interference, because load/admission control and packet scheduling strategies can be based on the interference level [1]. If there is wideband interference in the allocated frequency band, it will be added on top of the "clear noise floor". This will waste the capacity due to higher power needs for the radio links, and it will have a negative effect on the performance of the network. If, for example, admission control is based on measuring uplink interference, the existing wideband interference seen by admission control as artificial traffic could prohibit users from getting any service.

7.3.1 Scanner measurements

A scanner gets an overall image of the available pilots in the air and it can be used as an instrument that reflects the situation for a UE that is in idle mode. The difference between a UE and a scanner is that a UE measures a situation according to the network’s commands in signaling while a scanner measures all the pilots in the air. Coverage verification can be performed in the first phase using a WCDMA scanner. The main interest at the very beginning is coverage, and CPICH Ec/N0 measurements can be used to verify the coverage of selected BS sites. CPICH Ec/N0 values give a picture of how good coverage is provided from the BS sites and how large interference tails are produced. If large interference areas are generated, the problem could be minimized later by adjusting the antenna direction or height (unfortunately, this requires a new installation), or by down tilting the antenna or by slightly tuning the pilot power levels.

Operators can define their own thresholds for depicting good coverage areas, but empirically, Ec/N0 values down to -10 − -12 dB should be adequate once all sites are in operation. However, there are no requirements in the specifications for the required levels, and thus the operator has to verify good values. Ec/N0 values have to be defined with some margin for fading and other cell interference. On the other hand, Ec/No values smaller than -15 dB could be interpreted as “interference tail”. Because a scanner does not decode any real user data, measurements with commercial mobiles


are required for finding out the acceptable Ec/N0 level where UE still performs satisfactorily.

Figure 7-5. Scanner measurements of the CPICH Ec/N0 levels.

Another important use for a scanner is setting the neighbor lists in order and, once new cells are introduced, maintaining neighbor lists and pointing out possible interferers. See Section 7.3.3 for an example of the use of scanner results for neighbor list definitions.

7.3.2 Scanner parameters

After camping on a cell, a mobile station (MS) measures only cells defined by the network; in other words, cells that are shown in the neighbor list. With a pilot scanner, a wider picture of the pilot situation in the network can be obtained. In the following sections, parameters that typically can be measured with a scanner are explained.

CPICH Ec/N0

CPICH Ec/N0 is the received energy per chip divided by the power density in the band. The Ec/N0 is RSCP/RSSI. Measurement is performed on the Primary CPICH. The reference point for the CPICH Ec/N0 is the antenna connector of the UE [6].

CPICH RSCP

Based on the Received Signal Code Power of a CPICH (RSCP), measurements can be used to calculate coupling loss to the NodeB (CPICH power - RSCP = coupling loss, that is, loss to the BS antenna connector).


Coupling loss does not take into account feeder loss and antenna gain. RSCP measurements can also be used to check where other operators have their sites. Rough propagation model tuning is also possible by measuring CPICH RSCP values or by scanning continuous wave (CW) from the BS site.

Figure 7-6. RSCP measurement using a scanner.

P-SCH Ec/N0

The TX power value is set by the radio network planning engineer and it is set on a fixed offset level compared to the pilot [1]. The measurement values should show a difference between the pilot Ec/N0 and the primary synchronization channel Ec/N0. The difference should be around -3 - -6 dB according to the first settings (an operator decides on these values). For example, if the primary synchronization channel is set at 6 dB lower than CPICH, CPICH Ec/N0 -3 dB and P-SCH Ec/No -9 dB should be observed. An example is shown in Figure 7-7. The power levels of synchronization channels should be set correctly in order to be able to perform the cell search procedure by a mobile. A terminal gets the slot timing from the primary synchronization channel.


Figure 7-7. Example of P-SCH versus CPICH Ec/N0.

S-SCH Ec/N0

A terminal makes frame synchronization based on the secondary synchronization channel and, based on this, it knows what group of primary scrambling codes is in use; (there are 64 code groups). Secondary and primary synchronization levels should be equivalent compared to the pilot power (typically a -3 - -6 dB difference in the pilot power) [1].

P-SCH Ec/N0 measurements over time slot

The timing of primary synchronization channels can be shown as vertical lines; an example is shown in Figure 7-8. They should not overlap, and thus SCH bursts should not interfere with each other in the different cells of the NodeB in question.

In Figure 7-8, a unit of the x-axis is a half chip, and the y-axis shows the proportional difference in dB. Figure 7-8 shows that P-SCH bursts from the three available cells are not overlapping. This enables the synchronizing of the UE into the network. The time difference of P-SCH bursts is an RNP parameter [1].


Figure 7-8. Timing of the different sectors transmitting from the same site.

CPICH time of arrival

This parameter tells the timing of the different scrambling codes transmitted from different base stations.

Delay profile of CPICH and delay spread

The delay profile reveals the delay spread of the CPICH and together these parameters define the characteristics of the radio propagation environment in the measurement area. Both delay profile and delay spread can be measured. The first planning parameters are based on simulation values where certain radio channel models are used. By studying the delay spread, correct planning values for different areas can be chosen by comparing the delay spread shapes to the channel models that are used in the simulations.

In Figure 7-9, the y-axis is presented in dB and a unit of the x-axis is a half chip. It can be seen from the figures that propagation in the micro cell is close to the pedestrian A model [7, 8], and the suburban macro cell resembles the ITU vehicular model. The delay spread size is approximately 0.5 µs in Figure 7-9 (a), and approximately 1.5 µs in Figure 7-9 (b). By conducting these measurements, the planning parameters per site can be selected more realistically.


a) b)

Figure 7-9. Examples of delay profiles in (a) urban micro cell and (b) suburban macro cell.

7.3.3 Mobile measurements in idle mode

Cell selection and reselection are performed based on UE measurements, threshold values and hysteresis timers signaled by the network.

7.3.3.1 Initial cell selection

In an initial cell selection procedure, no prior knowledge of which RF channels are UTRA carriers is required [4]. UE scans all RF channels in its own UTRA frequency band to find a suitable cell in the selected public land mobile network (PLMN). On each carrier, the UE needs only to search for the strongest cell, and for that purpose the UE uses CPICH RSCP values. Once a suitable cell is found, it will be selected. If the cell selection is performed according to stored cell selection information, the UE will use the stored information of the carrier frequencies. Furthermore, the UE can optionally use information on cell parameters, for instance, scrambling codes from previously received measurement control information elements.

7.3.3.2 Cell reselection

In UTRA FDD mode, the UE uses CPICH Ec/N0 or the RSCP value to define which cell the UE is connected to during idle mode. Cell selection criteria in FDD is fulfilled if Srxlev and Squal are both greater than 0. (Squal is the measured quality value [Qqualmeas] minus the minimum quality threshold [Qqualmin], and Srxlev is the measured RX level [Qrxlevmeas ] minus the minimum RX level threshold [Qrxlevmin].) The pre-selection timer defines the hysteresis


time. When camped on a cell, the UE will regularly search for a better cell according to the cell reselection criteria. If a better cell is found, that cell will be selected. A change of the cell may also cause a change of radio access technology (RAT) [2-4, 8].

Furthermore, 3GPP specifications define the formulas for S, H, and R criteria, which are used in cell reselection. For details, see Section 6.3.2. This chapter will concentrate only on the S criterion. In other words, the criteria used in hierarchical cell structures (HCS) will not be discussed.

First, when the UE is switched on, it tries to camp on a cell via the cell search procedure. At the beginning, the UE tries to camp on the strongest cell. After camping on a cell, the UE conducts measurements controlled by the network and measures scrambling codes sent by RRC messages. System information block 3 (SIB3) includes parameters for cell selection and reselection, and these values are used in idle mode, CELL_FACH, CELL_PCH, and URA_PCH states. SIB4 contains the same parameters and it is used during connected mode. If SIB4 is not broadcast, SIB3 is also used in connected mode [3]. A neighbor list is sent on SIB11, and it also contains handover parameters. SIB11 is used in idle mode, CELL_FACH, CELL_PCH, and URA_PCH states. SIB12 contains the same parameters, and it is used in connected mode. If SIB12 is not sent, SIB11 is also used in connected mode. Figure 7-10 illustrates cell reselection.

Figure 7-10. Cell reselection in idle mode.


In Figure 7-10, the Ec/N0 level of scrambling code 285 (dark green) goes down and the Ec/N0 level of scrambling code 282 goes up, and thus the UE makes cell reselection at the point of the green star.

In Figure 7-11, the pilots detected by a scanner are plotted: 285, 286 and 282. The lower part of Figure 7-11 displays the views produced by the mobile: pilots 285 and 286 are measured.

Figure 7-11. Pilots measured by the scanner and terminal in idle mode.

The reason behind being able to detect different results may be the fact that pilot 282 is not defined as a neighbor for pilot 285. In addition, the measurement speed of the UE in different modes affects the results [2]. The


UE measures an active cell and neighbor cells with different rates. The measurement speed depends on many factors, such as the size of the neighbor list. However, the scanner measures every selected pilot with the same speed. Therefore, the scanner measures a given frequency band and its pilots objectively. Note also that receiver structures are not the same. Therefore, there might be differences in values obtained by the scanner or the UE.

Finally, in idle mode, the scanner can point out pilots that are available in the area. Thus, neighbor lists can be defined more accurately with scanner measurements than based on predictions made by a radio network planning tool, because propagation models and data of a planned environment always produce some inaccuracies.

7.4 Measurements during connection establishment

In connection establishment, the UE starts the random access procedure. When the UE leaves the idle mode in order to enter the connected mode, the UE will first attempt to access a current serving cell. If the access attempt to the serving cell fails, the UE will use the cell reselection evaluation procedure. The information needed for the random access procedure, that is, available signatures, sub-channels, and the spreading factor, are given in SIB5 to the mobile [3].

Based on the parameters signaled from the network and the measured values, the UE calculates the initial transmit power, which will be used by the first preamble. The power of the first preamble is calculated based on the RSCP of the CPICH and used CPICH TX power, the UL interference level, and the constant value given by the radio network planning. These values are also given in SIB5. This functionality is named “open-loop power control”. If the first preamble is not detected by the base station, the mobile sends a new preamble with higher power. The preamble step size is determined by an operator. The UE continues sending preambles for as long as it receives an acquisition indicator from the network and then proceeds to transmit the RACH message. The maximum number of preambles allowed is an RNP parameter along with the power offset between the last preamble and the RACH message. On the other hand, the network measures the UL interference level (the value signaled to UE in SIB7), and the UE measures the RSCP of a CPICH.

There are a couple of issues that should be monitored from the RACH process. First, if preambles go through with the first attempts and RACH messages are sent immediately, it is likely that the UE is using more transmit power than needed and thus extra UL interference is generated. On the other


hand, if too conservative RACH parameters are used, it can cause the UE to fail on RACH even though the maximum number of preambles is sent. This will result in access failures and additional RACH procedures and, moreover, additional UL interference to the network.

Figures 7-12 and 7-13 show an example of a RACH process. The blue dots represent the power level of the first preamble and the red dots represent the total power of the RACH message. Furthermore, on the right-hand side, there is a list of the sent preamble numbers, the preamble step size [dB], and the maximum number of allowed preambles.

Figure 7-12. Initial preamble powers vs. RACH message powers.

Figure 7-13. Example of successful RACH processes.


From Figure 7-12, it becomes apparent that the first UE has sent preambles but has not proceeded to send a RACH message. Therefore, it has not received the acquisition indicator or the base station has not received the preambles. Later in Figure 7-13, the RACH message has been sent and afterwards the connection has been established.

A script that enables several establishments of short calls could test connection establishments of voice calls or circuit switched data calls. Based on repetitions, the success rate of setups can be calculated and problem areas of call establishments can be pointed out. In addition, the uplink interference level can be monitored by making short calls while measuring, if necessary.

The same RACH process is performed in L1 when setting up packet data calls. The difference is that a connection is established to the packet data core. Therefore, success of attaches and PDP context activations should also be monitored.

Call setups should be verified over the entire planned service area. The connection establishments should be verified in cell edges and also in an indoor environment. In addition, the time of day affects the results because the system will work differently in loaded and unloaded situations. When evaluating the performance success rate of the connection establishment, there are several factors that should be kept in mind when analyzing the results:

- admission control (which monitors traffic status in the network), - resource manager (which monitors use of channelization codes), - packet scheduling (which monitors space for packet traffic that is

available on top of circuit switched traffic), - priorities (i.e., what has been requested vs. the network situation),

and- SGSN and GGSN status.

7.5 Measurements in connected mode

The main things to be considered during the connected mode are the verification of available coverage, the handover success rates of different handover types, and the behavior of the network and terminal during soft, inter-system, and inter-frequency handovers. These measurements are valid, regardless of the type of service used during measurements. During data transfer, there are specific key performance parameters that should be monitored. Data measurements are further discussed in Section 7.5.5.


7.5.1 Coverage

In the first phase, coverage verification should be performed and the coverage differences for different services should be of interest. The parameters indicating the coverage level are: – in the downlink: Ec/N0, because pure RSSI does not take into account

interference in the network. The required Ec/N0 level could be evaluated by determining a level where a receiver starts to perform poorly. (An example is given in Figure 7-14.)

– in the uplink: UE TX power, because a UE tries to maintain a defined quality level by adjusting the transmit power. Because of this, when the UE is in the cell edge area in the UL direction, it uses close to the maximum TX power. An estimate of the UL indoor coverage can be analyzed by subtracting the indoor loss used in the power budget from the measured TX power.

Figure 7-14. Ec/N0 and raw BER and BLER.

In Figure 7-14, the average of BLER (red curve) is at an adequate level until the raw BER (blue line) starts to rise. At that point, the CPICH Ec/N0

goes below -14 dB. Note that these values may differ in different radio environments, and different UE types may perform differently.


Figure 7-15 displays the coverage obtained in a DL data transfer. Ec/N0

values are shown on a map and the graph displays UE TX power. Figure 7-15 indicates that the downlink direction limits the coverage.

Data transfer has stopped at location X even if the Ec/N0 values are still adequate. Therefore, the reason for the lack of DL data coverage might be the DL resource allocation for the used data channel.

Figure 7-15. DL/UL coverage verification based on CPICH Ec/N0 and UE TX power.

When considering the evaluation of the coverage of different services, such a base station site should be selected so that a test route moves away from the site over the predicted coverage area. The test route should be measured 2 to 3 times per connection type, and the results should be averaged to draw conclusions. An example of voice coverage versus data coverage is shown in Figure 7-16.

In Figure 7-16, the end of voice coverage is represented by a yellow phone label, while the end of packet data coverage is point X. (The measurement results are shown in Figure 7-15.)

In survey tests, the same route will be driven at selected intervals (for example, every month). The analysis of these measurements includes some additional remarks. The key indicators are: – average Ec/N0 values to indicate CPICH coverage in the area; – map plots of the areas where Ec/N0 has been below the set threshold;


– average TX power values to point out how good the available UL coverage has been;

– areas where TX power has been over the set threshold to pinpoint bad UL coverage areas;

– areas where BLER has been over the set threshold which reveals the selected Quality-of-Service during the test drive; and

– map plots of dropped/failed call situations for indicating possible problem areas. An example of UE TX power distribution is given in Figure 7-17.

Figure 7-16. Coverage comparison of voice and packet data.

Figure 7-17. UL coverage verification based on UE TX power.

voice coverage

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Figure 7-17 shows that the UL power has been 90% under 10 dBm during the test drive. This indicates that in the close vicinity of the test route, the UL coverage for voice should be adequate, when the test van penetration loss around 8 dB is taken into account. For voice quality approximations, available BLER values could be monitored, and places where BLER goes over 5% (for example) could be sought in order to point out possible problem areas.

7.5.2 Power control

Power control is one of the most critical functions in WCDMA. It is therefore one of the key issues in testing. Power control includes UL and DL power control. In UL power control, a UE modifies TX power according to network commands. The UE’s TX power can be logged during field measurements, and also UL parameters should simultaneously be recorded with a time stamp to find out the functionality of the UL power control. In the DL, the UE handles the outer-loop power control. The UE compares the SIR to the SIRtarget and, based on that, sends power-up or power-down requests to a base station. If the used SIRtarget doesn’t provide sufficient quality (BLER), the UE raises the SIRtarget [1].

RAKE receivers are used in WCDMA; the performance then varies on different environments. In addition, the power control functions slightly differently in different circumstances. Because of this, the power control needs to be verified in different radio areas; therefore, the test routes should be planned for urban, suburban, and rural environments.

Figure 7-9 illustrated examples of delay profiles in different real radio environments. Even if delay profiles and RAKE finger allocations have an effect on the receiver performance, following the individual RAKE finger allocations during measurements does not reveal the whole picture for operator needs. In addition, other critical parts in the receiver, such as power control, channel coding, and interleaving, as well as mobile-specific implementations, affect the overall performance. Therefore, it is more beneficial to look at the final result of the receiver performance, which is shown in BLER values. Furthermore, trying to plot real-time finger allocations would require a very fast interface from the UE. Normally, the interfaces that are used cannot produce data fast enough to give a realistic picture of finger allocations. Moreover, the speed of the UE has an effect on the performance of power control. Thus, the drive tests should be made with different speeds. This also applies to soft handovers because the operations of SHO and power control are tied together.


Figure 7-18 displays a SIR target distribution in an urban micro cell and a suburban macro cell. The figures are examples of single field test drives. The average SIR target in the urban area was 6.1 dB and in the suburban area 6.3 dB. In other words, the difference was not significant. However, during the test drive in close vicinity of the micro cell antenna, the SIR target was approximately 5.5 dB. The difference in the SIR target was not remarkable and the values were close to the same level in different areas. The whole power control success during the test drive can be analyzed by plotting the overall cumulative distribution of BLER, which is shown in Figure 7-19.

a) b)

Figure 7-18. SIR target in (a) an urban micro cell and (b) a suburban macro cell environment.

Figure 7-19. Cumulative BLER distribution in a test drive in a micro cell.

The required quality depends on the application, and an operator can define the quality target. For example, for voice, an acceptable value could

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be BLER < 5%. This is by no means the exact truth – an operator can define its own acceptance levels for different application types. Examining the BLER values in Figure 7-19, it is apparent that 99% of the BLER values are under 5%, which is acceptable. Similarly, acceptable BLER values can be set for different service types and the operator can define what is cumulative level of BLER value that will fulfill the requirement.

Figure 7-20 shows the effects of UE speed on the SIR target value. In the upper left corner, there is a graph showing the SIR target while driving 50 km/h, on the upper-right corner 100 km/h, on the lower-left corner 20 km/h, and on the lower-right corner the test routes are displayed. Each graph is taken from the same location of different test drives.

Figure 7-20. Measured SIR target when driving on different speeds.

In the graphs above, the SIR targets are 7.5 dB at 20 km/h, 6.5 dB at 50 km/h, and 7.3 dB at 100 km/h. In other words, there seems to be no significant variation in the SIR targets at different speeds.

Figures 7-18, 7-19, and 7-20 show examples of different kinds of measurements that can be performed in different areas. In addition, it is important to remember that PC algorithms are vendor-specific and thus different terminals may behave differently.

7.5.3 Soft and softer handover

Intra frequency handovers, meaning soft/softer handovers, are typically made based on Ec/N0 values measured by the mobile. The mobile measures


cells in a certain area according to a neighbor list. Measurements are controlled by the network that is broadcasting on BCCH a list of cells that should be measured. For this purpose, SIB11 or SIB12 is used. Measurement control messages modify the neighbor list being used. The network also commands a UE to use a certain reporting type, which can be periodical or event-triggered. During a soft handover measurement, the control messages tell the UE which cells it should measure. The UE reports results back to the network, which decides whether the active set (AS) should be updated. Usually, the network allows new cells into the active set because the mobile should be connected to the best servers in order to maximize the overall capacity. The reason for denying an active set update, which would add a new scrambling code into the AS, might be the non-availability of resources in the new cell. This resource management is taken care of by the admission control during soft handovers.

Figure 7-21 shows the measured Ec/N0 values of the pilots according to the neighbor lists given in SIB12 and the measurement control messages [3].

Figure 7-21. Measured CPICH Ec/N0 values of active set and neighbor set.

The blue bars represent the serving cell or cells in an active set and their scrambling code number and frequency. The measurement of Ec/N0 values is defined in [9], and the reference point for the measurement is in the antenna connector of the UE. The red bars represent neighbor cells and their


parameters. In addition, drop and replacement window values are given in dB and calculated according to the 3GPP specification based on signaled values in SIB11, SIB12 and measurement control messages. Trigger 1A, trigger 1B, and trigger 1C give hysteresis time values. During these timers, the measurement results must fulfill add, drop or replacement window, before the UE reports results in measurement reports to the network. If periodical reporting is used, the network commands active set updates based on measurement reports. Furthermore, during a soft or softer handover, the link quality has to remain at an acceptable level. This can be observed from BLER values, which should remain at the same level as in a single-link case.

The behavior of the power control together with the soft handover functionality can be tested by driving first through individual cells. Collecting BLER and TX power values requires the barring or preferably the shutting down of the surrounding cells. Next, the same area should be tested when all cells are transmitting, and the TX power values should be compared to the first measurements when there were no SHOs. TX powers should remain at the same level, or preferably at a slightly lower level, if the SHO works acceptably. The analyzer should also check whether the UL and the DL quality values (BLER) have remained at an acceptable level. Furthermore, it is worthwhile to compare the SIR and SIR target values.

The main parameters to optimize for soft handover will be add, drop, and replacement windows, and the timers related to them [1-2]. Different environments may need different hysteresis timers. The sizes of the add and drop windows will affect the soft handover probability. Examples of soft handover areas are shown in Figure 7-22.

Figure 7-22. Soft handover locations and the number of pilots in the active set over the measurement area.

The simultaneous use of a scanner and a UE will point out the pilots that are not included in the active or monitored sets but that are relatively strong when compared to the active or neighbor cells. These pilots cause


interference that will affect the quality of the connection. In order to improve the performance level in the network, these interfering pilots should be added onto the neighbor lists. Figure 7-23 depicts the strongest pilot and all possible neighbors based on scanner measurements.

Figure 7-23. Distribution of CPICH Ec/N0 values compared to strongest CPICH (14).

Based on the example in Figure 7-23, an operator could define the neighbor list to contain the strongest pilots in the area.

7.5.4 Other handover cases

There are a few examples when WCDMA handovers can be classified as hard handovers. The first type of hard handover will occur if the intra-frequency cells are under different RNCs and a soft handover cannot be made. In this case, the measurement results look like those in Figure 7-21, which displays the cells in the active set and the monitored set. The difference is that the serving cell or the cells in the active set are replaced by one pilot scrambling code that is controlled by another RNC.

A second example is an inter-frequency (IF) handover, for which the UE conducts measurements only when the network commands [1]. The network commands the UE into the compressed mode for IF measurements after the defined condition has been fulfilled. The UE sends measurement reports periodically or when triggered by an event, and the RNC decides IF HO executions based on the measurement reports and the parameter settings. In

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an inter-frequency handover, the radio interface measurement tool can be used to measure periods in the compressed mode, IF HO executions versus compressed mode, SIR target and BLER behavior during the compressed mode, and signaling during an IF HO attempt or execution.

One of the most critical features in the first 3G network deployments is inter-system functionality between cellular systems meaning, for instance, cell reselections and handovers between WCDMA and GSM/GPRS. In order to be able to make measurements between systems and, especially, measurements needed for cell reselection or handovers from the WCDMA side, the UE has to be commanded into compressed mode. Another option for the UE vendors is to use a second receiver.

If the UE uses compressed mode for inter-system measurements, the network will control the compressed mode gap lengths and patterns. During the compressed mode, the same WCDMA parameters should be monitored and measured by the field measurement tool as in the case with IF HO. If the UE executes a cell reselection or a handover to GSM, the parameters measured from the 2G network are the well-known GSM/GPRS parameters. The most critical items in the inter-system operations or IF HO testing will be the settings for triggers and thresholds for compressed mode in vendor-specific algorithms. Examples of these can be found in [1].

7.5.5 Data measurements and application testing

Data measurements in WCDMA can be divided into two main categories: Circuit Switched Data (CS Data) and Packet Switched Data (PS Data). Due to the nature of these different types of data connections that are implemented in the network, the measurement configuration is also different.

7.5.5.1 Circuit switched data measurements

Circuit switched data have two different modes: transparent and non-transparent. The transparent data mode does not implement any error correction and thus does not guarantee data integrity for the application. The non-transparent mode has an error correction and a resending protocol.

7.5.5.1.1 Circuit switched data test setup and connection model

A circuit switched data connection also has additional elements of analog or digital modems that are used to make the connection to the target modem.

Figure 7-24 illustrates the data connection model that is used when a circuit switched data call takes place. In the connection model, it can be seen that with circuit switched data, the number of layers is relatively small. This


means, on the other hand, that there is not a great deal of overhead on the user data, and thus circuit switched data provides efficient data transfers.

Layer1 Layer1

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Figure 7-24. CS data connection model.

Circuit switched data testing is performed by dialing with a mobile to the modem pool of the server. When the data connection is enabled, the data is transferred between these two points.

Figure 7-25 illustrates that circuit switched data is routed from BTS to RNC and MSC where it connects through a public landline network to the server that is used as a terminating point of the tests.

Figure 7-25. CS data measurement setup.

Furthermore, it is possible to test circuit switched data by making a dialup to the modem pool of an Internet service provider and then negotiating a TCP/IP connection over PPP. After a successful connection, it is possible to measure the performance of the TCP connection. However,


although this is easy, it only adds protocols to the user data. This is especially deceptive if transparent data is measured, since a TCP brings an error correction to the data flow that does not normally have it.

Between Layer 1 and the user data, only the RLC and MAC layers are present. They both add headers to the user data so the actual amount of data that is transmitted over Layer 1 is somewhat more than the user data. See Figure 7-26.

Layer1

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MAC Header

Figure 7-26. Additional header data due to RLC and MAC layers.

By looking at the different protocol layers and the additional overhead that they introduce, it becomes apparent that the overhead in circuit switched data is marginal and it is also quite predictable. Due to the rather thin protocol layers on circuit switched data, the user data rate is comparable to the actual L1 data rate.

RLC Header

According to the 3GPP 25.322 specification, the RLC can either be in acknowledged mode or in unacknowledged mode (Figure 7-27). The headers added to the RLC depend on the mode that is used.


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Figure 7-27. RLC in (a) acknowledged mode or in (b) unacknowledged mode.

MAC Header

According to the 3GPP 25.321 specification, the header used in MAC depends on the subchannel used and the data mapping used.

Case (a) DTCH or DCCH mapped to DCH, no multiplexing of dedicated channels on MAC: Case (b) DTCH or DCCH mapped to DCH, with multiplexing of dedicated channels on MAC:


Case (c) DTCH or DCCH mapped to RACH/FACH: Case (d) DTCH or DCCH mapped to DSCH or USCH: Case (e) DTCH or DCCH mapped to DSCH or USCH where DTCH or DCCH are the only logical channels: Case (f) DTCH or DCCH mapped to CPCH:

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Figure 7-28. Headers used in the MAC layer.

7.5.5.1.2 Circuit switched data performance metrics

CS data performance measurements have many similarities with voice call measurements. In fact, the call setup is so similar that all the same metrics used for analyzing voice call performance can be used in analyzing circuit switched data call access performance.

However, it should be noted that when a CS data connection is made, it also requires that inter-working functions (IWF) successfully connect to the target modem via either an analog or an ISDN modem. This additional step can cause a situation where, although there is no problem with accessing the radio bearer, the connection to the target modem can fail due to a handshaking failure between modems.

Circuit switched data, once initialized, provides a constant radio bearer for the user data regardless of whether there is data being transmitted through this link. However, this radio bearer can be renegotiated with a different speed during the data call.

When measuring in transparent mode, the actual L1 data throughput and user data throughput are not affected by the radio link quality, but the data error rate increases instead. Thus, the key metrics for transparent mode


circuit switched data measurements, in addition to RF parameters, are data error rate and user data throughput.

In non-transparent mode, the data throughput is affected by the radio link quality, but due to an error correction, the data errors do not exist. See Figure 7-29 for an illustration of user data throughput when BLER is present. It can be noted from Figure 7-29 that data throughput is slower when high BLER is present; and when BLER is either low or nonexistent, data throughput is at a more constant level. Thus, the key metric for non-transparent mode circuit switched data measurements is user data throughput.

Figure 7-29. Non-transparent data throughput measurements when BLER is present.

7.5.5.2 Packet switched data measurements

Packet data testing differs significantly from circuit switched data testing. First, there are more network elements and protocols involved. Second, the radio bearer is not initialized as a call, but the mobile activates a connection to the network and gets an IP address that allows a connection to the Internet.

7.5.5.2.1 Packet switched data test setup and connection model

Figure 7-30 illustrates the data connection model that is used when a packet switched data connection is used. Figure 7-30 shows that in packet switched data, the number of layers in the connection model is considerably higher than in circuit switched data. Consequently, there is more overhead in


the user data when compared to a circuit switched data connection. Thus, the data transfer rates for the user data are going to be lower than in circuit switched data when the same data transfer rate in Layer 1 is used.

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Figure 7-30. PS data connection model.

Packet switched data testing is performed by initiating an attach and a PDP context activation in the 3G network. When this is performed, an IP connection is present and the data is being transferred between the server and the mobile unit using a TCP/IP protocol.

One additional consideration when doing packet data testing is the location of the server used as a test target. For instance, if the server is connected directly to a GGSN, this ensures that the internal latency and throughput of the network are measured. On the other hand, placing the server on the public Internet by using a T1, cable, or DSL connection would allow more realistic end-to-end measurements. Having the server on the public Internet would enable verification of the end-to-end connection by making sure that packets are able to pass through the firewall to the GGSN. This would also enable measurement of the latency and throughput to a public Internet server.

Figure 7-31 illustrates that in a packet switched data test setup, data is routed from BTS via RNC to SGSN and to GGSN. The test server used as a target for data testing is connected to GGSN via the Internet.


Figure 7-31. Packet switched data measurement setup.

In addition to the protocols in a 3G network, additional packet data protocols are needed before a user application can access the Internet with the packet data connection provided by a mobile terminal. Figure 7-32 shows the additional protocols that are introduced in the PC on top of the 3GPP network protocols before the application can access the packet network.

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Figure 7-32. Additional layers when MT is used with PC for packet data.

There are several different protocols present (MAC, RLC, PDCP, PPP, IP, and TCP or UDP) between Layer 1 and the user data. They all add headers to the user data; thus the actual amount of data that is transmitted over Layer1 is more than the actual user data sent by the application.

After a closer look at these protocols and the overhead generated by each protocol layer, it becomes clear that in order to be able to analyze the


expected user data throughput, one must know how the network is configured and which protocol stacks are utilized.

Next, the different kinds of headers that can be present in a PS data connection are introduced:

TCP Header without compression*:

Byte 1 Byte 2 Byte 3 Byte 4

Source port Destination port Sequence number Acknowledgment number Offs Flags Window Checksum Urgent Pointer Options Padding Source address Destination address PTCL TCP Length

*) TCP Header Compression is a method for compressing the headers of TCP/IP datagrams to improve performance. A typical 40-byte TCP/IP header can be compressed to 3 - 16 bytes.

UDP Header:


Source port Destination port Length Checksum

IP Header:


Ver IHL TOS Total length Identification 0 DF MF Frag

offset TTL Protocol Header checksum Source address Destination Address

PPP Frame:

Flag PPP header

Data CRC Flag


A PPP header can be 1 − 4 bytes, and it is negotiated by the protocol. CRC is 16 bits.

PDCP Header:

According to the 3GPP 25.323 specification, a PDCP can either have no header/data PDU or a sequence number and a PDU header.

PDCP Data PDU

PDU Type PID

PDCP SqNum PDU

PDU Type PID Sequence number Sequence number

RLC Header:

According to the 3GPP 25.322 specification, the RLC can either be in acknowledge mode or in unacknowledged mode. The headers added to the RLC depend on the mode used.

Acknowledge mode:

Sequence Number

Sequence Number

D/C

ELength Indicator

Data

PAD or a piggybacked STATUS PDU

Oct1

Oct2

OctN

P HEELength Indicator

.

.

.

(Optional) (1)Oct3


Unacknowledge mode:

Oct1

ELength Indicator

Data

PAD Last Octet

ELength Indicator (Optional) (1)

.

.

.

ESequence Number

(Optional)

(Optional)

MAC Header:

According to the 3GPP 25.321 specification, the header used in the MAC depends on which subchannel is being used and how the data has been mapped.

Case (a) DTCH or DCCH mapped to DCH, no multiplexing of dedicated channels on MAC: Case (b) DTCH or DCCH mapped to DCH, with multiplexing of dedicated channels on MAC: Case (c) DTCH or DCCH mapped to RACH/FACH: Case (d) DTCH or DCCH mapped to DSCH or USCH: Case (e) DTCH or DCCH mapped to DSCH or USCH where DTCH or DCCH are the only logical channels: Case (f) DTCH or DCCH mapped to CPCH:

UE-Id

UE-Id

Case b):

MAC SDUCase a):

MAC SDUTCTFCase d):

MAC SDUCase e) and f): UE-Idtype

UE-Id MAC SDUTCTFCase c): UE-Idtype

UE-Idtype

C/T

C/T

C/T

MAC SDUC/T

Figure 7-33. Headers used in MAC layer.


7.5.5.2.2 Packet switched data performance metrics

When measuring PS data performance, there are three key metrics: accessibility, retainability, and actual data performance.

Accessibility can be analyzed from the attach success rate and the PDP context activation success rate.

Retainability can be analyzed from the data connection success rate, where the data connection is the actual point-to-point TCP/IP data transfer session. Furthermore, the PDP context drop counts and the attach drop counts can be used when analyzing retainability.

Figure 7-34 shows an example of a quality survey analysis that can be done with a modern analyzing tool for attach events. A similar analysis can be also done for PDP context activations and data connect attempts.

Attach Event Info (PD)


Attach Attempts 22

Attach Attempt Failures 1

Attach Connections 21

Total Detaches 21

Attach Event Info (PD) Attach Connection Information


Total Attach Connections 21

Percentage of Attach Connections 95 %

Attach Event Info (PD) Attach Failure Information


Total 1

Timeout 1

Percentage of Attach Failures 5 %

Attach Event Info (PD)

Detach

Information


Total 21

User Detach 21

Percentage of User Detaches 100 %

Percentage of Dropped Transfers 0 %

Figure 7-34. Example of quality survey report on attach events.


Data performance consists of three different metrics: throughput, delay, and jitter.

When analyzing throughput, it has to be understood that the user data throughput and the actual L1 throughput are two different things. As can be seen in Figure 7-35, although there is a downlink data session in process and no user data is being transmitted in the uplink, there is however uplink data being sent on Layer 1. It is important to understand that if there are problems with the uplink data transmission, it will also affect the downlink even though user data is transmitted only in the downlink direction. However, user data throughput is the only thing that matters for the data performance experienced by the end user.

Figure 7-35: Example of how on a DL data transfer, UL data is transmitted on a physical layer although it is not being transmitted on a user data layer.


The delay can be analyzed by making ping measurements that give a round-trip delay for data packets. Although, the delay can be measured at the same time as the user data throughput measurements, it is not advisable since the user data transfer will affect the ping times.

The jitter (i.e., delay variation) can be analyzed from the variation on ping measurement results. When there is a lot of variation on the round-trip delay, it can cause problems for certain applications.

In Figure 7-36, it can bee seen that although most of the time ping times are at an acceptable level (<250ms), occasionally a significantly bigger ping result is received and the frequency and distribution of these occasions can be used to analyze the jitter present in the data connection.

Figure 7-36. Ping graph that shows also variation on delay values.

7.5.5.3 Application testing

Once data services are implemented in the network, it becomes important for operators to ensure that applications that are using data services are working properly in the network. The important thing to remember is that if a data connection does not work, none of the applications will work either.

The most important parameter when analyzing application performance is data accessibility. Data accessibility can be analyzed by making a statistical analysis on attach and PDP activation success rates.


After an application has been able to obtain access to the data connection, it has to be able to maintain the connection. In other words, it must have retainability to a data service. This can be analyzed from the statistics of the PDP context drop ratio.

If a data service can be accessed and the access can be maintained, the application performance can be analyzed.

Since all applications use either a circuit data or a packet data connection, there is no reason to test with a specific application. Instead, it can be estimated how a certain application will work on a known data performance. Table 7-1 lists example applications and their requirements on network performance.

Table 7-1. Applications and their requirements on network performance. Application Protocol Throughput

Need

Delay

Sensitivity

Jitter

Diversity

Email TCP low Low low MMS TCP low Low low Web browsing TCP med Med low Streaming video TCP or

UDP high Low med

Video conferencing TCP or UDP

high High high

Furthermore, all these different application uses can be well-simulated by using scripting in a measurement tool. In fact, this is even better than actually using the application because of its repeatability.

Email Testing

When a person uses email, either the POP3 or IMAP4 protocol runs on top of TCP/IP. Whichever email protocol is used, the actual data profile still remains the same. When email is used, typically a small amount of data is first uploaded to the server in order to request email retrieval. Afterwards, a larger amount of data (the email) is retrieved.

MMS Testing

The MMS data profile is very similar to the Email data profile, the only difference being that it does not incorporate POP3 or IMAP protocols. However, when testing for MMS by simulating its data profiles, it needs to be understood that when a real MMS is used, it also includes additional network elements that are not tested when testing is done by simulating data profiles.


Web Browsing Testing

Web browsing uses the HTTP protocol on top of TCP/IP. In a typical data profile for web browsing, a small amount of data is uploaded followed by a larger amount of data downloaded. This is then repeated until the page is loaded.

Streaming Video Testing

Streaming video uses, for example, the H.232 protocol to stream video and audio. It is irrelevant which streaming video protocol is used: the data profile is the same. In streaming video, the typical data profile is that a very small amount of data is uploaded as control data, while a considerably larger amount of data is being downloaded.

Video Conferencing Testing

Video conferencing is a two-way audio/video stream that can use, for example, the H.232 protocol. In two-way streaming video, the typical data profile is that a large amount of data is uploaded and downloaded at the same time.

REFERENCES


[2] J. Korhonen, Introduction to 3G Mobile Communications, Artech House, 2001. [3] Universal Mobile Telecommunications System (UMTS), Radio Resource Control (RRC),

Protocol Specification, 3GPP TS 25.331. [4] Universal Mobile Telecommunications System (UMTS), UE Procedures in Idle Mode

and Procedures for Cell Reselection in Connected Mode, 3GPP TS 25.304. [5] J. Lee, L. Miller, CDMA Systems Engineering Handbook, Artech House 1998. [6] Universal Mobile Telecommunications System (UMTS), Physical Layer - Measurements

(FDD), 3GPP TS 3G 25.215. [7] Universal Mobile Telecommunications System (UMTS), UE Radio Transmission and

Reception (FDD), 3GPP TS 25.101. [8] Recommendation ITU-R M. 1225, Guidelines for Evaluation of Radio Transmission

Technologies for IMT-2000, 1997. [9] Universal Mobile Telecommunications System (UMTS), Physical Layer Measurements,

3GPP TS 25.133. [10] Transmission Control Protocol, RFC-793. [11] User Datagram Protocol, RFC-768. [12] Compressing TCP/IP Headers, RFC-1144, Jacobson 1990. [13] Internet Protocol, RFC-791, Postel 1981. [14] The Point-to-Point Protocol (PPP), RFC-1661, Simpson 1994. [15] Universal Mobile Telecommunications System (UMTS), Packet Data Convergence

Protocol (PDCP) Specification, 3GPP TS 25.323.


[16] Universal Mobile Telecommunications System (UMTS), Radio Link Control (RLC) Protocol Specification, 3GPP TS 25.322.

[17] Universal Mobile Telecommunications System (UMTS), Medium Access Control (MAC) Protocol Specification, 3GPP TS 25.321.

Chapter 8

QUALITY-OF-SERVICE MEASUREMENTS For end-to-end testing

MARKUS AHOKANGAS, TAPIO HEIKKILÄ, TAISTO NIIRANEN, TAPIO TAIPALE, JOUKO UIMONEN NetHawk

Abstract: In the UMTS network, UTRAN, PS core, CS core, and UMTS QoS architecture form a framework for QoS measurements, which have to be performed to ensure that a UMTS subscriber is served properly. The true picture of QoS is perceived by acquisition signaling and user-plane data from the network interfaces, and performing analysis for those. From an operator’s perspective, the QoS consists of several factors, each of which brings different kinds of measuring requirements for the operator when developing and operating the UMTS network. Protocol decoding, signaling procedure analysis, and tracing of the subscriber dedicated protocol messages are needed for testing, verifying, and troubleshooting the UMTS network in live or laboratory environments. The traffic and capacity- measurement challenges rely on the interfaces where the user data is transferred over a packet or a circuit switched domain where the most important key performance indicators (KPI) are related to delay and throughput. KPI values, generated by statistical measurements, may be used to express the service availability or the behavior of the radio access or core network domain. Moreover, sophisticated protocol analyzers and network probes are the basic tools for acquisition, decoding, and analyzing the protocol layers, and they form the base for more intelligent post-processing or real-time applications.

Key words: CS core, delay, KPI, protocol analysis, PS core, QoS, throughput, trace, UTRAN

305




8. QUALITY-OF-SERVICE MEASUREMENTS

8.1 Quality-of-Service framework

The Quality-of-Service (QoS) provided to a subscriber in UMTS networks is a factor that will differentiate operators from each other. QoS in operative networks will determine which operators succeed against the competition when UMTS networks have been launched. However, before UMTS networks are in operation, several phases must be completed by manufacturers and operators when developing and deploying the networks. In each phase, including the operations phase, certain measurements must be performed to ensure that, in the end, the subscriber is served with a proper QoS. These are referred to here as Quality-of-Service measurements.

8.1.1 UMTS network services

Figure 8-1 illustrates a 3G UMTS network at a very high level, where mobile subscribers are served with circuit switch (CS) and (PS) packet switch services. At this level, the UMTS network can be seen as consisting of the UTRAN radio access network, the PS core, and the CS core network.

Figure 8-1. UMTS network.

Through the UTRAN, the subscriber is provided with a wide bandwidth radio connection to the CS and PS core networks. Via the CS core, the traditional voice call service to PSTN (Public Switched Telephone Network), ISDN (Integrated Services Digital Network) or to another PLMN (Public Land Mobile Network) is reachable as in second-generation PLMNs,

PS CN

CS CN

UTRAN

PDN

PSTN


but new voice codec options are available. Traditional short message service (SMS) is also available. CS data services utilize UTRAN’s ability to handle higher data rates than GERAN/BSS (GPRS EDGE RAN/Base Station Subsystem) has been providing so far. Via the PS core, the subscriber is able to access packet data networks (PDN) such as the Internet and use new kinds of services (such as streaming, MMS, etc.). Compared to the CS data services, the PS connection can be considered “always on”, where the bandwidth is consumed only when data is sent or received by the subscriber.

8.1.2 QoS in UMTS

From the subscriber’s perspective, the overall Quality-of-Service in a UMTS network is experienced in its entirety as being poor or excellent or somewhere in between. However, from the operator’s perspective, the final QoS experience consists of several factors, each of which brings different kinds of measuring requirements for the operator when developing and operating the UMTS network. If the operator’s network fails to fulfill some requirements, the subscriber’s experience is diminished. The UTRAN, PS, and CS core have their own tasks, so they are considered as different factors, and they are expected to fulfill different requirements.

Generally, the first step for an operator to guarantee the QoS in a UMTS network is to provide proper radio service and coverage via UTRAN. Subscribers expect to find radio coverage wherever they are, the radio connection should be quickly established and it should be stable while the services are needed. As the UTRAN is based on totally new WCDMA air interface technology, the QoS challenges rely strongly on the radio access network.

Regarding traditional CS services in a UMTS network, the subscriber expects to have the same level of QoS as in existing mobile networks. Fast setup times, reliable connections, and good quality voice and data, and reliable SMS services are minimum requirements.

With PS services, setup times and reliability are relevant as well, but there is still more to be examined. A subscriber’s PS connection can be considered as a source for valuable new services (for example, MMS, streaming and messaging) or just as a bit pipe to the Internet. Therefore, the experience of acceptable QoS is based on the service’s usability as well as on a proper connection. With the PS services, the attributes related to available bandwidth, such as delay, delay variance, and gained bit rates per second, will determine whether the service is usable and fulfills the subscriber’s QoS expectations. QoS classes, negotiated by the mobile station and network during a connection establishment, determine the limits for some QoS attributes. The operator and the subscriber may have signed a


Service Level Agreement (SLA), where the QoS class for the subscriber is defined.

The focus of the UMTS QoS measurements should be on the behavior and characteristics of the UTRAN and the PS core. The UTRAN and the PS core bring totally new challenges regarding radio environment and packet data transmissions. Another focus area for operators is the behavior of the service itself, but that is out of the scope of this discussion.

8.1.3 UTRAN interfaces and protocol layers in UMTS system

UMTS Terrestrial Radio Access Network (UTRAN) is the part of the network infrastructure that gives the user equipment (Ue) a way to access network services via the air interface (Uu interface) [1]. The UTRAN consists of a set of Radio Network Subsystems (RNS) that are connected to the core network through the Iu interface. Each RNS consists of one or several NodeBs and a Radio Network Controller (RNC). The UTRAN network elements and interfaces, which it provides for the Ue and core network as well as the internal interfaces, are presented in Figure 8-2.

Figure 8-2. UTRAN.

NodeB

NodeB

NodeB

NodeB

RNC

RNC

CS

core

PS

coreIub

Iub

Iub

Iub

IuPS

IuCS

IuPS

Iur

RNS

Uu

Uu

UTRAN CN

Uu

Uu IuCS


NodeB is a WCDMA transceiver for receiving from and transmitting to the Uu interface. As an essential part of that process, the NodeB manages tasks like channel coding, interleaving, spreading, scrambling, modulation, and error handling, as well as fast load control. One very important function that is performed between the NodeB and Ue is a closed-loop power control. With this functionality, the transmit power tries to adapt as fast as possible to the changing air interface fading conditions to maintain the target signal-to-interference ratio given by the RNC. The other function that the NodeB performs with Ue somewhat autonomously is the macro diversity achieved by means of a softer handover. In a softer handover, the NodeB, including several cells, has an existing radio link connection to a single Ue via two or more of its cells. It transmits the data related to the Ue redundantly via all these radio links. It combines the received signal from all these radio links and sends the data via the RNC to the core network.

The higher layer control plane data and user plane data are carried over the Uu interface between the NodeB and the Ue using transport channels which in turn are mapped to physical channels. The transport channels are divided into dedicated channels and common channels. There are also pure physical channels that do not have a transport channel mapped to them.

Considering Quality-of Service, the Uu interface between the NodeB and the Ue is a key object of interest. It is obvious that most of the delays in the data transmission in the UTRAN are generated in this interface because of its limited bandwidth compared to the terrestrial connections. Also, temporary failures in synchronization of the data transmission from the Iub interface to the Uu interface may cause an unexpected decrease in performance.

The NodeB is connected to the RNC through the Iub interface. There are several optional transport media specified for this interface, but currently the most typical ones are ATM over STM-1 (155 Mbps), or ATM over E1 (2 Mbps).

The RNC has a very significant role, considering the overall performance of the UMTS network and especially the radio resource utilization. The algorithms defined in the RNC try to find the optimal balance between the transmission power and radio-link quality and channel allocation within the defined QoS attributes. The power control, handover control, admission control, load control, and packet scheduling, together with the resource management, form the radio resource management function mainly located in the RNC [2].

Regarding power control methods, the RNC executes the outer-loop power control algorithm, which is used for setting up an adequate SIR target for inner-loop power control between the NodeB and the Ue. By adjusting the SIR target dynamically, the effect of the Ue speed and multi path fading


is tried to compensate and at the same time keep the power as low as possible in order to not disturb the other Ue connections with interference.

In handover control, the RNC makes the decision on the basis of the measurements received from the Ue, when the Ue should add a cell to its active set to activate a soft or softer handover. In a soft handover situation, the mobile has radio links via two or more NodeBs, which can reside under the same or different RNCs. The RNC combines the data received from macro diversity paths before passing the data to the core network. In addition to the soft/softer handover, the RNC also decides about hard handovers and inter-system handovers. One part of the handover management is control of the serving RNC’s relocation.

Admission control is a function by which the RNC decides whether a request for a new radio access bearer can be acknowledged or whether the situation could be handled by modifying existing RABs.

Packet scheduling is closely related to admission control. With the packet scheduling algorithm, the RNC can choose the optimal transport channel for transferring packet data.

The RNC is connected to the core network (CN) through the Iu interface. Because the core network divides into a circuit switched core and a packet switched core, there are separate interfaces for both domains: IuCS and IuPS.

In the UTRAN, the RNCs can also communicate with each other. The Iur interface between RNCs enables the collection of signaling and user data from several NodeBs before passing it to the core network. The macro diversity also utilizes this interface. The RNC, which acts as an interconnection point between the serving RNC and the NodeB, is called drift RNC. A slight drawback of this architecture is that the connection between drift RNC and serving RNC, and the serving RNC relocation procedures related to them, may cause variable delays during a call [3].

8.1.4 PS core interfaces and protocol layers in UMTS system

The purpose of the PS core is to provide a subscriber with access to the packet data networks (PDN) for enabling new services (email, MMS, etc.), a connection to the Internet, and the possibility to have the radio connection always on.

Figures 8-3 and 8-4 illustrate the PS core network domain with the most important network elements and protocol layers regarding QoS measurements. SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node) are the key elements of the PS core; through them, the


mobile station is connected to external packet data networks or PS domains in other PLMNs (Public Land Mobile Network) [4-5].

The SGSN can be considered as a packet traffic switching center. It switches uplink packet traffic from the RNC to the GGSN and switches downlink traffic from the GGSN to the RNC. When a subscriber registers on the network, the SGSN performs security and access control. It also stores subscription information and location information for each subscriber for which it has at least one PDP (Packet Data Protocol) context active. The location information defines, for example, which cell or routing area (depending on the mobile station’s operating mode) the subscriber is registered under and the selected GGSN on the path towards PDN. The GGSN is the PS core’s gateway to external PDNs. It saves location information and keeps the activated PDP context as well. The SGSN and the GGSN are connected via an IP-based PLMN backbone network. In order to access PS services, the mobile station has to make its presence known to the UMTS network by performing a GPRS attach, and in order to send and receive data with external PDN, the mobile station has to activate PDP context to the GGSN.

L1 L1 L1 L1 L1 L1

RLC

MAC

RLC

MAC AAL5 AAL5 L2 L2

PDCP PDCP GTP-U GTP-U GTP-U GTP-U

UDP/IP UDP/IP UDP/IP UDP/IP

E.g. IP, PPP

E.g. IP, PPP

MS UTRAN 3G-SGSN 3G-GGSN

Application

Iu-PS Uu Gn

Relay Relay

Gi

Figure 8-3. User plane from mobile station to GGSN.

Figure 8-3 shows that the RNC is connected over an IuPS reference interface to the SGSN and, furthermore, the SGSN to the GGSN over the Gn interface. From the RNC to the GGSN, the user plane data is carried by GPRS Tunneling Protocol for the user plane (GTP-U) that encapsulates all PDP PDUs (Packet Data Unit), for instance, a subscriber’s IP packet stream. UDP/IP is a backbone network protocol for routing user and control plane data. In the IuPS interface, UDP/IP is carried over ATM (Asynchronous Transfer Mode) and AAL5 (ATM adaptation layer 5) providing a variable bit rate connection-oriented or connectionless data service.


L1 L1 AMT ATM

RLC

MAC

RLC

MAC AAL5 AAL%

RRC RRC RANAP RANAP

SignalingBearer

SignalingBearer

GMM / SM / SMS

GMM / SM / SMS

MS RNS

Iu-PS Uu

Relay

3G-SGSN

Figure 8-4. Control plane from mobile station to SGSN.

On the control plane (Figure 8-4), the SGSN and the mobile station perform mobility management (GMM) and session management (SM) functions. GMM supports such functions as attach, detach, security and routing area update. SM supports PDP context activation, modification, deactivation and preservation functions. SMS (Short Message Service) is also supported.

Radio Access Network Application Protocol (RANAP) encapsulates and carries higher-layer signaling, handles signaling between the SGSN and the UTRAN, and manages the GTP connections on the IuPS interface.

8.1.5 CS core interfaces and protocol layer in UMTS system

The purpose of the CS core, shown in Figure 8-5, is to provide traditional CS voice and data services to the subscriber. The main elements in the CS core are MSC (mobile switching center) and GMSC (Gateway MSC) [4]. The MSC performs all necessary functions in order to switch the circuit switched services to and from the mobile stations. It is an exchange, which performs the switching and signaling functions for mobile stations located in a certain geographical area designated as an MSC area. The MSC terminates the user-to-network signaling and translates it into the relevant network-to-network signaling. The GMSC at the end of the CS core acts as a switching center towards external CS networks such as another PLMN, PSTN or ISDN. It terminates call control to the external networks.

Beginning from 3GPP Rel4, the MSC and the GMSC can be implemented, if needed, in two different entities: a (G)MSC Server handling only signaling, and a CS-MGW handling users’ data [6]. The MSC Server


and the CS-MGW creates the full functionality of an MSC. The new architecture enables support of different transports (for example, ATM or IP) in a bearer-independent way. In the case of ATM or IP transport, the passage of compressed speech at variable bit rates is possible through the CS core network. The users connected to the CS core network will not be aware whether an MSC server/media gateway combination or a monolithic MSC is being used.

MGW UTRAN

HLR

Nb

A

GERAN

MGW

MSC server MSC server

PSTN/ Legacy/External

Applications & Services

Iu

Iu

A NcMc Mc

Signaling Interface

Signaling and Data Transfer Interface

CAP

CAP

DC

Figure 8-5. CS core network.

The MSC server terminates the user-to-network signaling from the UE and translates it into a call control signaling over the Nc interface. Any suitable call control protocol may be used over the Nc interface (e.g., BICC). The MSC also terminates the signaling over the Mc interface with the CS-MGW and controls the parts of the call state model that relates to connection control of media channels in the CS-MGW. Over the Mc interface, the H.248 protocol, defined in ITU-T, together with 3GPP-specific extensions will be used. H.248 supports a separation of call control entities (like MSC server) from bearer control entities, and a separation of bearer control entities from transport entities (like CS-MGW).

The CS-MGW terminates the signaling over the Mc interface. The CS-MGW contains bearer terminations and media manipulation equipment (e.g., transcoders, echo cancelers, or tone senders). It may perform a media conversion and a framing protocol conversion for the user plane traffic. The CS-MGWs on the user plane are connected with the Nb reference point. The bearer control signaling and transport are carried over the Nb interface.

The GMSC server terminates the signaling over the Nc interface, and it also terminates the signaling over the Mc interface towards the CS-MGW. The GMSC server controls the parts of the call state model that relates to


connection control of media channels in the CS-MGW. It also contains the call control function in the BICC model.

8.1.6 UMTS QoS architecture

The expected services based on UMTS radio networks are much more numerous than with earlier radio network technologies. In 1G, there was only speech; and in 2G, there is a limited set of additional services providing content. In 3G, the situation is more complicated. It is said that the real reason for high investments in UMTS is the QoS. The system needs to handle end-to-end service requirements at all levels (physical transmission, network element, service creation, and content provider) [7]. Therefore, QoS management in a UMTS network requires an architectural framework that defines how QoS issues and requirements are solved within the UMTS network considering the network structure and characteristics.

8.1.6.1 UMTS QoS requirements

There is a variety of requirements concerning the QoS within UMTS networks. The most important ones are the following [8].

1) End user requirements

Basically, only the QoS perceived by the end user matters, and the number of defined/controlled attributes should be as small as possible and derivation/definition of QoS attributes from the application requirements must be simple. The QoS attributes should be able to support all applications that are used, considering that a certain number of applications have an asymmetric nature between the two directions (uplink and downlink). QoS has to be provided in end-to-end.

2) General and technical requirements

The QoS attributes should not be restricted to just one or a few control mechanisms. The QoS concept should be capable of providing different levels of QoS by using UMTS-specific control mechanisms. The UMTS QoS control mechanisms should provide QoS attribute control on a peer-to-peer basis between the UE and the 3G gateway node. In addition, the UMTS QoS mechanism should provide a mapping from application requirements to UMTS services. The QoS attributes are needed to support asymmetric bearers, and applications should be able to indicate the required QoS values. Finally, the QoS behavior should be dynamic, i.e., it should be possible to


change it during an active session. From the service point of view, the UMTS network should provide bit rates in three classes in its coverage area: 144 kbps, 384 kbps, and 2Mbps (peak values for PS connections).

8.1.6.2 Different levels of QoS

From the end user’s point of view, the UMTS network consists of services and the QoS relates to these end-to-end services. From this point of view, the QoS within UMTS has been described with different service bearers following the UMTS network structure (Figure 8-6) [8].

Figure 8-6. UMTS QoS architecture.

The end-to-end service seen by the end user, i.e., the TE-to-TE traffic has to pass different bearer services of the network. A TE is connected to the UMTS network by an MT (Mobile Terminal). The end-to-end service of an application uses the bearer service of the UMTS network, realized by a TE/MT Local Bearer Service, a UMTS Bearer Service, and an External Bearer Service. The UMTS operator offers various services by the UMTS Bearer Service, which also provides UMTS QoS.

The UMTS Bearer Service is composed of the Radio Access Bearer Service and the Core Network Bearer Service. Both these services reflect the optimized way to realize the UMTS Bearer Service over the respective cellular network topology by taking into account such aspects as the

MTTE UTRAN CN IuEDGEnode

CN Gateway

TE

End-to-End Service

UMTS Bearer Service

Radio Access Bearer Service

Radio Bearer Service

UTRA FDD/TDD

Service

External Bearer Service

TE/MT Local Bearer Service

CN Bearer Service

Iu Bearer Service

BackboneBearer Service

Physical Bearer Service


mobility and mobile subscriber profiles. The Radio Access Bearer Service provides confidential transport of signaling and user data between the MT and CN Iu EDGE node. The QoS adequate for the negotiated UMTS Bearer service, or with the default QoS for signaling, is based on the characteristics of the radio interface. If unequal error protection shall be supported, it is provided by the underlying Radio Bearer Services.

The Core Network Bearer Service of the UMTS core network connects the UMTS CN Iu EDGE node with the CN Gateway to the external network. The role of this service is to efficiently control and utilize the backbone network in order to provide the contracted UMTS Bearer Service.

The Radio Access Bearer Service is composed of the Radio Bearer Service and the Iu Bearer Service. The role of the Radio Bearer Service is to cover all the aspects of the radio interface transport. This bearer service uses the UTRA FDD/TDD Service. The Iu Bearer Service, together with the Physical Bearer Service, provides the transport between the UTRAN and the CN. The Iu Bearer Services for packet traffic provides different bearer services for a variety of QoS.

The Backbone Bearer Service covers the Layer 1 and Layer 2 functionality and is selected according to the operator’s choice in order to fulfill the QoS requirements of the Core Network Bearer Service.

8.1.6.3 UMTS QoS classes

There are four principal UMTS QoS classes to which the UMTS Bearer Services should be obtained correspondingly. The classes and their fundamental characteristics are as follows:

- Conversational class: preserve time relation (variation) between information entities in the stream; conversational pattern (stringent and low delay);

- Streaming class: preserve time relation (variation) between information entities in the stream;

- Interactive class: preserve payload content; request response pattern; - Background: destination is not expecting the data within a certain

time; preserve payload content. A set of attributes and their values define the characteristics of the UMTS

QoS classes [8].

8.1.6.4 UMTS QoS attributes

There are 13 UMTS QoS attributes to define the characteristics of the UMTS Bearer Services for the UMTS QoS classes. The attributes are:


- Traffic class (“conversational”, “streaming”, “interactive”, “background”): type of application for which the UMTS Bearer Service is optimized; the “class” is an attribute itself.

- Maximum bit rate (kbps): maximum number of bits delivered by UMTS and to UMTS at a SAP (Service Access Point) within a certain period of time. The maximum bit rate is the upper limit a user or application can accept or provide.

- Guaranteed bit rate (kbps): guaranteed number of bits delivered by UMTS and to UMTS at a SAP within a period of time. UMTS Bearer Service attributes, e.g., delay and reliability attributes, are guaranteed for traffic up to the guaranteed bit rate.

- Delivery order (y/n): indicates whether the UMTS Bearer Service shall provide SDU (Service Data Unit) delivery or not.

- Maximum SDU size (octets): the maximum allowed SDU size. - SDU format information (bits): list of possible exact sizes of SDUs. - SDU error ratio: the fraction of SDUs lost or detected erroneously;

defined only for conforming traffic. - Residual bit error ratio: undetected bit error ratio in the delivered

SDUs. If no error detection is requested, the residual bit error ratio indicates the bit error ratio in the delivered SDUs.

- Delivery of erroneous SDUs (y/n/-): whether the SDUs detected erroneously shall be delivered (y) or discarded (n). The value “y” implies that error detection is applied and erroneous SDUs are delivered together with an error indication. The value “n” implies that error detection is applied and erroneous SDUs are discarded. The value “-“ implies that SDUs are delivered without considering error detection.

- Transfer delay (ms): a maximum delay for 95 percentage of the distribution of delay for all delivered SDUs during the lifetime of a bearer service. Delay of SDU is defined as time from a request to transfer SDU at one SAP to its delivery to another SAP.

- Traffic handling priority: specifies the relative importance for handling of all SDUs belonging to the UMTS bearer compared to the SDUs of other bearers.

- Allocation/Retention priority: the relative importance for allocation and retention of the UMTS bearer compared to other UMTS bearers.

- Source statistics descriptor (speech/unknown): specifies characteristics of the source of submitted SDUs.

These attributes are used to define the level of quality of the UMTS Bearer Service, but all parameters are not used for all quality classes. Attributes discussed per quality class for UMTS Bearer attributes are used as illustrated in Table 8-1 for each quality class.


Table 8-1. UMTS QoS attributes per quality class.

Traffic Class Conversational Streaming Interactive Background

Maximum bit rate + + + +

Guaranteed bit rate + + - -

Delivery order + + + +

Maximum SDU size + + + +

SDU format information + + - -

SDU error ratio + + + +

Residual bit error ratio + + + +

Delivery of erroneous

SDUs

+ + + +

Transfer delay + + - -

Traffic handling priority - - + -

Allocation/retention

priority

+ + + +

Source statistics

descriptor

+ + - -

8.1.6.5 Mapping QoS attributes to radio access bearer service level

To fulfill service requests, the UMTS Bearer Service needs corresponding QoS from the underlying Radio Access Bearer Service. However, UMTS-level attribute values do not necessarily map directly to the Radio Access Bearer level, because the Core Network creates its share to the attribute values appearing at the UMTS level.

The following attribute values at the UMTS level will normally be at the Radio Access Bearer level:

- maximum bit rate; - delivery order; - maximum SDU size; - SDU format information; - delivery of erroneous Service Data Units (SDU); - guaranteed bit rate; - traffic-handling priority; and - allocation/retention priority. The following attribute values at the UMTS level will normally not be

the same at the Radio Access Bearer level, but this depends on implementation aspects like network dimensioning:

- SDU error ratio; - residual Bit Error Rate (BER); and - transfer delay.


For all these attributes, the Core Network creates a corresponding share included in the UMTS-level attribute values.

In addition, the following parameters are relevant only at the Radio Access Bearer level:

- SDU format information; and - source statistics descriptor. Mapping the application requirements to UMTS Bearer Service attributes

and mapping the UMTS Bearer Service attributes to Core Network Bearer Service attributes are implementation-dependent and done by the operator’s choice.

8.1.6.6 Attribute value ranges

For UMTS Bearer Services and Radio Access Bearer Services, there are definitions for the allowed value ranges of attributes. It is finally the set of these attribute values which concretely defines the level of quality. Some value ranges of the QoS attributes are still being studied.

For UMTS Bearer Services, the attribute values are given in Table 8-2. The values not shown in Table 8-2 are those currently being studied. The value ranges reflect the capability of the UMTS network.

Table 8-2. UMTS QoS attribute values per quality class.


Maximum bit rate

(kbps)

<= 20481 <= 20481 <= 20481-

overhead/

Layer 2

<= 20481-

overhead/

Layer 2

Delivery order Yes/No Yes/No Yes/No Yes/No

Maximum SDU size

(octets)

1500 or 15022 1500 or 15022 1500 or

15022

1500 or 15022

SDU format

information

3 3

SDU error ratio 10-2,7*10-3, 10-3,

10-4,10-5

10-1, 10-2, 7*10-

3, 10-3, 10-4, 10-

5

10-3, 10-4,

10-5

10-3, 10-4, 10-5

Residual bit error

ratio

5*10-2, 10-2,

5*10-3, 10-3, 10-

4, 10-5, 10-6

5*10-2, 10-2,

5*10-3, 10-3, 10-

4, 10-5, 10-6

4*10-3, 10-4,

6*10-8

4*10-3, 10-4,

6*10-8


SDUs

Yes/No Yes/No Yes/No Yes/No

Transfer delay (ms) 100–max value 280–max value

Guaranteed bit rate <= 20481 <= 20481

Source statistics

descriptor

Speech/

unknown

Speech/

unknown


1 Bit rate 2048 implies transparent RLC protocol mode, in which Layer 2 overhead is negligible.

2 PDP=PPP. 3 Exact sizes for transparent RLC protocol mode to be defined by RAN

WG3.

Some value ranges for Radio Access Bearer Service attributes are given in Table 8-3. The attribute values not shown in Table 8-3 are currently being studied. The value ranges reflect the capability of the UTRAN.

Table 8-3. Radio Access Bearer QoS attribute values per quality class.


Maximum bit rate (kbps) <= 20481 <= 20481 <= 20481-

overhead/

Layer 2

<= 20481-

overhead/

Layer 2

Delivery order Yes/No Yes/No Yes/No Yes/No

Maximum SDU size

(octets)

1500 or 15022 1500 or

15022

1500 or

15022

1500 or 15022

SDU format information 3 3

SDU error ratio 10-2,7*10-3, 10-3,

10-4,10-5

10-1, 10-2,

7*10-3, 10-

3, 10-4, 10-5

10-3, 10-4,

10-5

10-3, 10-4, 10-5

Residual bit error ratio 5*10-2, 10-2,

5*10-3, 10-3, 10-

4, 10-5, 10-6

5*10-2, 10-2,

5*10-3, 10-3,

10-4, 10-5,

10-6

4*10-3, 10-4,

6*10-8

4*10-3, 10-4,

6*10-8


SDUs

Yes/No Yes/No Yes/No Yes/No

Transfer delay (ms) 80 – max value 250 – max

value

Guaranteed bit rate <= 20481 <= 20481

Source statistics

descriptor

Speech/

unknown

Speech/

unknown

1 Bit rate 2048 implies transparent RLC protocol mode, in which Layer 2 overhead is negligible.

2 PDP=PPP. 3 Exact sizes for transparent RLC protocol mode to be defined by RAN

WG3.


8.1.6.7 QoS management functions

There is a set of QoS management functions defined how to establish, modify and maintain a UMTS Bearer Service with a specific QoS. The relations between the internal functions of the nodes are implementation-specific, and interfaces between nodes are protocol interfaces. There is a separate allocation of QoS management functions in the control plane and in the user plane.

The QoS management functions in the control plane are composed of four activities: service manager, translation function, admission/capability control, and subscription control. The service manager coordinates the functions of the control plane for establishing, modifying and maintaining the service it is responsible for. It also provides the user plane with QoS management functions with relevant attributes and may perform attribute translation to requested lower-layer services. The translation function converts between the internal service primitives of UMTS Bearer Service control and the various protocols for service control of interfacing external networks. The admission/capability control maintains information about all available resources of a network entity and about all resources allocated to the UMTS Bearer Service. The subscription control checks the administrative rights of the UMTS Bearer Service user to use the requested service with the specified QoS attributes.

The QoS management functions in the user plane are composed of four activities: mapping function, classification function, resource manager and traffic conditioner. The mapping function marks each data unit with the specific QoS indication related to the bearer service transferring the data unit. The classification function in the Gateway and in the MT assigns user data from the external bearer service or the local bearer service to the appropriate UMTS Bearer Service according to the QoS requirements of each data unit. The resource manager of each network entity distributes its resources between the bearer services requesting transfer of data units, and thus attempts to provide the QoS attributes required for each individual bearer service. The traffic conditioner in the MT provides conformance of the uplink user data traffic with the QoS attributes of the relevant UMTS Bearer Service. In the Gateway, the traffic conditioner may provide conformance in the downlink user data traffic with the QoS attributes of the relevant UMTS bearer service, i.e., per PDP context.

8.2 UMTS measurements in practice

Data that is exchanged between network elements in the UMTS network consists of control plane data and user plane data. The former is called signaling and the latter carries the payload that can be either normal speech


or any other data used between applications communicating over mobile networks. The true picture of QoS is perceived by acquisition of both signaling and user plane data from interfaces and performing analysis for those. In this chapter, the basic principles and methods for arrangements of QoS measurements are explained: accessing the protocol layers carrying control and user plane data across interfaces.

8.2.1 General about measurements

Testing and monitoring QoS in the UMTS network requires several kinds of analysis actions and network monitoring through the whole life cycle of the UMTS network, starting from the network element development and ending with the operation of the network. The protocol layers carrying signaling and user plane data have to be accessed and verified to ensure proper network performance. Protocol analysis and tracing of protocol messages are required for troubleshooting purposes and for finding the origins of any misbehavior. For long term or 24-hour monitoring, the signaling and user plane traffic on the protocol layers must be recorded and analyzed with post-processing tools as well as with applications capable of visualizing real-time metrics and following certain key performance indicators (KPI). The measurements take place during the idle mode, connection establishment, and connected mode of the network and the UE. By catching signaling transactions and giving them timestamps, it can be found out whether the network is performing correctly with acceptable response times. Validating correct performance is important in testing new network elements in laboratory environments or during the network configuration phase, but it is also relevant when operating and maintaining the network in the field. Analyzing the number of requests and their responses will reveal the rates for successful service provisions or mobility management transactions. In addition, in some circumstances (for example, when the load is changing or the network configuration or software releases in network elements are changed), the generally acceptable signaling sequence may cause trouble and misbehavior. If response times for the requests are increasing, decreased QoS can be expected.

Measuring and monitoring user plane data is important because it gives a true picture of the quality experienced by the end user when services are being used. It is especially important in packet switched networks where quality depends on many factors that can be tuned and modified according to available capacity, service level agreements, etc.

Sophisticated tools are needed by a UMTS operator for analyzing QoS. The protocol analyzer is the basic tool for decoding and analyzing the


protocol layers in laboratory tests, commissioning, and field testing. In the case of real-time monitoring of UMTS network performance, the network probes are required. The analyzers or probes can be provided with more intelligent applications; tracing of calls through the network, counting network-level statistics, or locating the sources of delay can be achieved by constructing networks of probes for data acquisition and by running a centralized application for monitoring the network behavior.

8.2.2 QoS measurement methods

QoS measurements can be made in different ways regarding time and scope of measurements. Time relates in this context to offline and online measurements, which do not necessarily make a great difference from the end-user’s point of view but greatly affects the implementation of the measurement system. Scope relates here to a measurement target (or granularity): does the measurement focus on a single call/session of a subscriber, a single subscriber, group of subscribers, a single network element, group of network elements, or a certain type of network element.

8.2.2.1 Offline vs. online measurements

Offline measurements mean that data is captured from the mobile network with an appropriate measurement probe and is analyzed afterwards. This allows more complex and time-consuming analyses since computation does not need to be made as fast as data is received. In 3G networks, this might be the only feasible method for time-consuming analyses because of the huge amount of data (up to 1 Gbps on Ethernet). Offline measurement also means that only a snapshot of the traffic can be analyzed since any recording device has a certain maximum capacity. (For example, at 50 Mbps, recording for one day would require 540 Gbytes of disk space.)

With online measurement, data is processed and analyzed live. This requires processing that is fast enough to process all incoming data without losing it. The best way to achieve this is to apply efficient filtering as early as possible on captured data so that only the useful part of the data is forwarded to a higher-level calculation. If possible, filtering should be made at the hardware level.

Offline measurement is useful for troubleshooting where indications of erroneous behavior have been received through other means (such as customer reclamation or online monitoring) and the actual cause of the problem is not known.

Online measurement is typically used for monitoring systems where the overall network status is followed using an appropriate set of indicators whose values are based on ongoing online measurements.


Offline processing can be done automatically so that data is captured periodically, processed later, and the results are then delivered to the end-users. From the end-user’s point of view, this is similar to online measurements with a delay.

8.2.2.2 Session vs. continuous measurement

Session and continuous measurements in network monitoring can be compared with process monitoring in the traditional industries where both production equipment (network elements) and end products (calls in a mobile network) must be monitored in order to guarantee optimal operation and adequate quality. Session-based measurement is related to end-product quality. Continuous measurement is related to process monitoring.

Session-based measurement means that measurement is calculated over a time window that is determined by start and stop events and that is related to a context. The most typical example of this is CDR (Call Data Record), which contains information on a single call, and TDR (Transaction Data Record), which contains data about one data session.

Continuous measurement means that measurement is not related to asynchronous events but to periodic intervals. Continuous measurements are used for monitoring network equipment. In the long term, session-based measurement results (CDRs, TDRs) can also be used as input for the continuous measurement.

8.2.2.3 Scope of measurements

Scope of measurements – one subscriber vs. a group of subscribers, or one network element vs. a group of elements – is more related to the presentation of measurement results than the actual measurements. The only requirement is that the captured data can be labeled with the related subscriber and/or originating network element. If stamping is possible, then scoping can be handled using filtering and grouping techniques provided by the reporting or visualization system.

Stamping captured data with the originating network element is easy (at least identifying the network interface is easy), because it should be known where the probes capturing the measurements are located. Of course, there can be data from several network elements on the same interface. Signaling must then be analyzed in order to be able to recognize the originating network element.

Subscriber identification is more difficult because static identifiers are not frequently used. Instead of static identifiers (IMSI, for example), temporary identifiers such as TMSI or P-TMSI are used. In order to recognize a certain subscriber (e.g., while troubleshooting user


reclamations), mapping between these static and temporary identifiers must be performed. This, on the other hand, requires access to the operator’s registers (HLR, VLR), which is not always possible or may be restricted by the authorities. However, for measurement purposes, it is not always necessary to recognize the individual subscriber but only make distinctions between different subscribers.

8.2.3 Protocol analysis

Protocol and signaling-procedure analysis is needed for testing, verifying and troubleshooting of the UMTS network, and it is utilized in all modes.

In the first testing phase, the network is usually still under development, and protocol analysis is studied in a certain interface or in a few interfaces consisting of a certain network entity, e.g., a UMTS radio access network (RAN). Testing is focused on checking certain protocols for ensuring correct behavior of a certain functional part of the network element, e.g., transmission control, radio resource control, O&M part control, etc.

The verification phase involves verifying the behavior of a certain entity of the network (e.g., RAN) as a part of the complete network or the behavior of the complete network. In this phase, protocol analysis is needed simultaneously in multiple interfaces and protocol events of different interfaces need to be correlated.

When networks are in the roll-out or maintenance phase, occasionally there are situations where studying the behavior of a complete system is needed. Typically, multiple interfaces need to be traced simultaneously. When a problem occurs randomly or only after a certain period, tracing is needed to be done over a longer period, and advanced triggering capabilities are useful when investigating the problem.

8.2.4 Traffic and capacity measurements

Considering the traffic and capacity measurements in UMTS networks during active connection, the biggest challenges rely on the interfaces where the user data is transferred towards or over a packet switched domain. In these interfaces, the most important key performance indicators are related to delay and throughput. In most cases, they directly show how an end user experiences the Quality-of-Service. For example, if a user is having a VoIP call over PS domain, the absolute delay should not exceed a critical threshold value, but throughput is less significant because speech does not carry so much information. On the other hand, if the user is watching a video stream throughput directly indicates the quality of the video presentation on


the user terminal, but absolute delay is not important (at least from end user’s point of view; it might be critical for an operator because long delays usually require buffering capacity from network equipment).

There are also other key performance indicators that are important. Jitter, (variations in the average delay between subsequent data packets) is an annoying feature in stream-oriented applications such as multimedia or VoIP. In addition, it could be troublesome for the UMTS network operator because large jitter requires large buffering capacity in the network equipment.

8.2.4.1 Delay measurements

A simple delay measurement called ‘ping’ is available using almost any computer. Pinging is an easy and straightforward method for measuring end-to-end round trip delay between the end-user terminal and the server. It requires that the user has access to a server that runs a ping daemon that replies to ping requests. Usually ping does not require logging in, so pinging can be made anonymously. The problem with pinging is that it only measures the total round-trip delay. That is enough for a normal user, but it is too general for a network operator. It does not indicate where in the network the total delay is generated.

In order to discover problematic network elements, delay must be measured across the network elements. That can be accomplished by capturing the same packet from two interfaces from both sides of a network element and then calculating the difference between the data packets’ timestamps. This requires equipment that can monitor and capture user-plane data and can mark packets with sufficiently accurate timestamps. The correlation of packets from different interfaces can be done on the IP layer by using sender and receiver addresses and a sequence number that appears in the same way in different interfaces in the UMTS network. The delay of the selected packet switched session can be filtered from the total IP packet stream according to the destination and source IP addresses. By using the destination address as a filter, the group of subscribers can be filtered out from the total stream. The port number may also be given to make more specific filtering.

Because end-to-end delay is divided into pieces that can be observed independently, the bottlenecks in the UMTS network can be reliably found. The measurements should be organized into Iub, IuPS, Gn, and Gi interfaces for both uplink and downlink directions. If IP packets are captured from several points in-between certain network elements, the delay generated by routers and switches located between those network elements can be estimated as well.


Delay measurements can be based on the traffic of all subscribers or of a dedicated subscriber. For the traffic of all subscribers, monitoring can be considered more or less as monitoring the load, as the delay increases with an increased load. When the distribution of delays of dedicated sessions are put into different categories, a more sophisticated view of network performance can be achieved. When a single subscriber requests a certain delay class when establishing a connection, it can be seen whether the UMTS network is capable of providing that by comparing the provided delay class to the defined delay categories. The reference for the thresholds of delay categories or classes can be found in the 3GPP specifications.

For a dedicated IP stream, an operator should also be able to see the jitter (delay variation). Jitter can be calculated on the basis of an IP packet captured from one interface by making a comparison between sequential IP packets. On the other hand, jitter may be seen when following the delay of IP packets captured from two different measurement points by concentrating on the visible variation in the delay curve.

8.2.4.2 Throughput measurements

End-to-end throughput can be measured with simple tools. Ping for measuring throughput can be used, and most data-transfer applications – such as ftp - are usually able to indicate average throughput during a user session. However, more detailed troubleshooting requires access to network interfaces where bottlenecks can be located by tracking both downlink and uplink IP packets and summing the payload size from the IP header. In some cases the application layer (FTP, HTTP, etc.) throughput may also be required. Usually throughput is measured for a specific subscriber, in which case IP packets should be filtered according to the sender’s or receiver’s IP address and port number. The resending ratio of TCP packets tells an operator how efficiently network capacity is utilized: the higher the resending ratio, the lower the efficiency. It is also important to measure the resending ratio in addition to throughput because high throughput with a high resending ratio will be seen as a poor throughput value by the end user.

A need of throughput measurements relies on Iub, IuPS, Gn and Gi interfaces (see the example in Figure 8-7). When the throughput perceived by a single subscriber is compared to the requested throughput or the average throughput received per subscriber, the comparable QoS level received in particular circumstances can be estimated. The biggest questions regarding capacity planning in the PS core and UTRAN relies on estimating how much throughput subscribers really need. As there are only a few subscribers and services in UMTS, subscribers’ behavior is not known yet (for instance, whether there are only a couple of registered subscribers under one network element having high throughput requirements, or vice versa).


Figure 8-7. Throughput measurement.

8.2.5 Tracing protocol messages

Tracing protocol messages is a powerful method for troubleshooting and error hunting in UMTS live networks or in laboratory environments. The function of tracing is to visualize dedicated signaling sequences, protocol messages, and information elements (IE) within messages. Tracing utilizes a QoS measurement system’s ability for space- and state-dimensioned measurements. A user of a trace tool is able to use sophisticated filters that identify the signaling required to be viewed.

The need for starting a tracing session may come from a user complaint or from the output of another tool monitoring network characteristics. The UMTS operator may desire to trace signaling of a predefined subscriber, a group of subscribers, equipment, or the signaling from a certain interface or network area. If a subscriber has complained about bad QoS, or test calls are performed in the field or laboratory, the subscriber may be traced. IMSI, IMEI, (P-)TMSI, MSISDN, or even the mobile station’s IP address can be given for a tracing tool to filter out the signaling of the particular subscriber. When IMEI is used as a filter, the issue is more about tracing malfunctioning terminals, whereas the mobile’s IP address can identify the traced PS session.

A trace tool should be able to coordinate the signaling of a selected subscriber or equipment performing a CS call or PS session. By coordinating the signaling, the signaling of the traced subscriber from more than one


network interface can be viewed concurrently. Following the horizontal signaling sequence through the network is helpful in locating the source of the problems.

Trace will also be used for error hunting in a certain area of the UMTS network. For example, notification of unacceptable high rates of dropped calls in a cell may be given, which leads to the need for filtering the signaling traffic under that cell. There are several levels that could be used for filtering in a cell, NodeB, RNC, SGSN, or MSC level. An operator should be able to define from which level and from which protocol layer the messages are collected. When the filters are set properly, the IEs carrying the reasons for the problems can be found. When hunting for errors, the identification of subscribers helps if, for instance, one specific subscriber causes the problems with a malfunctioning terminal.

A trace session (Figure 8-8) should be able to be performed in real-time mode as well as in the so-called history mode. In real-time mode, a subscriber is put under a trace in order to capture, filter and view the signaling instantaneously during the call or session. Collecting more signaling is continued during analyzing and filtering. In history mode, the subscriber is not put under a trace, but raw signaling must be recorded and available from the network interfaces. The time window for the selected time period is defined and the trace tool analyzes the signaling of that period.

Figure 8-8. Example of trace view.

8.2.6 Statistical measurements

Statistical measurements (Figure 8-9) play an important and more traditional role in the operative networks when QoS is controlled. Moreover, statistical measurements can be utilized right after rollouts to validate the UMTS network’s ability to provide a satisfactory QoS level.

Session Management and Data Transfer

1a2233a3 4B0

1a2233a3

33ae2211

33ae2211

1a2233a3

4B0

4B0

4B0

UL:Act PDPContext ReqDL:Act PDPContext AcceptUL:Act PDPContext ReqDL:Act PDPContext Reject

UL:IP Frame

091202100222.345091202100222.400091202100223.345091202100223.546091202100253.145

TimeEventCell ID

460007579032221

640007579031113

640007579031113

460007579032221

460007579032221

IMSI TLLI

4B0


Figure 8-9. Example of statistic measurement view.

Key performance indicators (KPI) are examined by the statistical measurements. With an adequate set of KPIs to be followed, a UMTS operator can form an overall picture of the UMTS network’s QoS behavior.

KPI calculations are based on the incrementing counters that are based on the defined protocol messages in the Iu, Iub, and Iur interfaces. The different counters are compared and the rates for successful or unsuccessful transactions can be found. Regarding 24-hour statistics for network monitoring purposes, the IuCS and IuPS are mainly used as a source of information, because the monitoring system is easier and cheaper to deploy in the core network side where Iu interfaces are reachable. However, during the roll-out phase of the UMTS network, or for ad hoc measurements, Iub is also used as a source of protocol data. In ad hoc sessions, which may last several days, the measurements are organized for finding the most important indicators expressing QoS of radio interface. During the measurement session, the scope may be on a cell, one or a cluster of NodeBs, or an RNC


area. The Iub interface provides valuable information when factors related to radio coverage, power control, and signal levels are optimized.

It is up to the operator to understand which thresholds for each KPI are acceptable and which should generate alarms for the QoS monitoring personnel. The chosen intervals depend on the type of KPI value and, for instance, the UMTS network area. In rural areas, a lower service level can be acceptable, whereas in urban areas with a greater number of subscribers, QoS is more critical.

The key issue for useful measurements is to define a wide set of KPIs. Statistics should be counted during idle mode, connection establishment and connected mode between the UMTS network and the mobile station. All the major transactions should be considered. In idle mode, the KPIs are related to mobility management and may be utilized to ensure that a mobile is reachable while its location changes every now and then. During connection establishment, KPI values may be used to express the availability of a service requested by a subscriber. During connected mode, KPI values express the behavior of the radio access or the core network domain and whether the service can be maintained or not.

8.2.6.1 Statistics in idle state

In the idle state, location and routing area updates are followed and statistics are gathered for success rates and number of total transactions. Moreover, the cause values of the transaction should be easily seen, as well as the distribution of unsuccessful transactions according to different possible reasons. Also the rate of successful radio resource connections should be visible.

8.2.6.2 Statistics in connection establishment

The method for showing the UMTS network’s capability of establishing connections is to monitor Layer 3 signaling between the mobile station and core network domains; both the CS and PS domain. At the beginning of the connection establishment, an increased number of paging messages in the network may express decreased QoS. In the IuCS interface, the mobile-originated (MO) and mobile-terminated (MT) circuit switched calls are monitored by keeping voice and data calls as separate items. In the IuPS interface, the success rate of GPRS attachments is an important indicator as well as identifications and authentication transactions. In chronological order, PDP context activations and possible modifications will take place after an attachment and should be recognized by the system as well. The reason for unsuccessful transactions should be visible.

Both PS services and CS services need to follow the average time of connection establishments. For example, increased average setup time or


PDP context activation time may indicate a shortage of service resources before the resources run out. That type of indication may force a UMTS operator to have more equipment in the network, but in some cases, a new configuration might be enough if there are free resources at another network location. Another important indicator of decreased QoS in the network is an increased load of signaling traffic, as it may indicate decreased availability of the requested service; the mobile station is forced to request the service repeatedly without acknowledgment.

Even though Layer 3 signaling expresses how successful a connection establishment is, it does not always indicate in detail the cause for an unsuccessful transaction. In most cases, the cause rests on the lower layer, and therefore the minimum requirement for covering statistical measurements is to have ability to follow establishments of radio access bearers (RAB) in RANAP protocol. The cause values of the failed RAB assignments will lead one step further in QoS management actions.

8.2.6.3 Statistics in connected mode

During the connection between the mobile station and the UMTS network, the main interest relies on the transactions managing the mobility and therefore the handovers (HO) and relocations. The handover success rates shall be counted for all handovers and for each handover type (soft, softer, and hard) as separate items. The distribution of each handover type expresses the radio network’s behavior and capability to maintain several active radio links for a single mobile station. One way to monitor a handover situation in the UMTS network is to have a diagram showing the distribution of a single active link, two (soft or softer) active links, or three (softer-softer, soft-soft, or soft-softer) active links in the active set of mobiles. Depending on the type of handover, the relocations may or may not take place; they are within the scope of statistical measurements. Relocation of the serving RNC is the most important one, but SGSN relocations and the HO seen by the CS core network domain should be followed as well.

Unfortunately, the CS call or PS session is often dropped during the connection. Therefore it is not enough to follow only the successful connection establishment; the rate of calls dropped during service should be followed. Most often the cause is an unsuccessful HO, but the cause may also lie elsewhere.

8.2.7 QoS measurement tools

For performing QoS measurements, a monitoring tool is needed by a UMTS operator and manufacturer. A QoS monitor explores characteristics


of a UMTS network in the field or in the laboratory by analyzing and monitoring both signaling and user-plane traffic captured with probes from the network interfaces. Different kinds of monitoring systems are available in the market. A general picture of the structure of such a system is given here. The QoS monitoring system consists of network probes and sophisticated software for analyzing the captured traffic.

QoS monitoring software (Figure 8-10) consists of two main software components: the GUI (graphical user interface) for operating the QoS monitoring system and showing the results of the QoS measurements, and the QoS server software for processing the gathered information. The QoS server software performs all the analysis of the information captured from the UMTS interfaces.

QoS

monitor

sw

QoS

DB

QoS

GUI

Capacity

Measurement

Call Trace Statistics

Measurement

Interface between

QoS monitor

and

data capture equipment

Probe Probe Probe

Figure 8-10. QoS monitor structure.

Through the GUI, the QoS server software can be set to gather data from probes and to analyze the information particular to the desired measurement or tracing. The server software delivers analyzed data to the GUI to be shown to the QoS monitor user. The database of the QoS monitor is a logical part of the QoS server software, which can be located within the QoS server or in a separate database server. The database saves the results of the measurements and tracing sessions. The QoS monitoring system requires data capture equipment as probes to collect appropriate information from the UMTS signaling and user-plane interfaces. The responsibility of the QoS


monitor software component is to analyze, store, and show the information collected by the capturing equipment.

The basic features of the QoS monitoring system are for statistic measurements, capacity measurements, and call tracing. With statistic measurements, the QoS monitor filters and counts protocol messages carried through UMTS interfaces and then defines, for example, the rate of the successful PS sessions or the rate of the successful handovers in the UTRAN radio network. With capacity measurements, the delay (generated for subscribers’ IP data by the network equipment) between two points in the UMTS can be calculated. With capacity measurements, the amount of PS data through an interface in the UMTS can be examined. Tracing is used for analyzing signaling traffic, captured from one or several interfaces within the UMTS, on the basis of filters like IMSI.

As the QoS monitor consists of software blocks, which can be located in the same or separate computer units, it is a scaleable system. There are several factors explaining the physical scale of the QoS monitoring system: the amount of the capturing equipment, the number of monitor components used (for GUI users), and the number of computer units where the monitor components are located. A small-scale QoS monitor system is illustrated in Figure 8-11. Data is captured by a single laptop PC with a probe that is connected to at least one network interface. The QoS server software and GUI reside in the same PC.

A small-scale QoS monitoring system can be used by manufacturers when testing basic functionality of network elements in the laboratory. In this case, the question is more about examining the characteristics of a single network element, or an area under that element, than about examining an entire network. Operators may also perform monitoring and testing of basic functionalities of network elements in laboratories before the rollout. If the small-scale QoS monitoring system is used in live networks, the usage may happen on an ad hoc basis when special problems are searched for. Moreover, the small-scale QoS monitoring system provides flexible measurement methods for the UMTS operator, because few measurement points can easily be moved from one interface to another.

Figure 8-12 illustrates a large-scale QoS monitoring system. The probes are connected to several interfaces (and points in a certain interface) in the UMTS network, and they provide data to the QoS server software running in a dedicated computer unit (QoS Server). GUIs for managing the QoS monitoring system and monitoring the measurements are located in separate PCs, which are connected over a LAN to a QoS server. As there are several points where data is captured, bottlenecks in the network can be quickly found, and the general behavior of the UTRAN can be fully followed.


Figure 8-11. Small-scale QoS monitoring system.

Figure 8-12. Large-scale QoS monitoring system.


Large-scale QoS monitoring systems, which are mainly used by UMTS operators, will be used in a live network during the optimizing phase or while operating the network. When the network is rolled out, it must be determined whether it is capable of serving users (subscribers and third-party service providers) with the desired QoS level. Moreover, while operating the UMTS network, an operator must be sure that the provided service level does not decrease when the traffic load and number of subscribers are changing.

REFERENCES

[1] Universal Mobile Telecommunications System (UMTS), UTRAN Overall Description,3GPP TS 25.401.

[2] Universal Mobile Telecommunications System (UMTS), UE Radio Transmission and Reception, 3GPP TS 25.101.

[3] J. Laiho, T. Novosad, A. Wacker, Radio Network Planning and Optimisation for UMTS,John Wiley & Sons Ltd.

[4] Universal Mobile Telecommunications System (UMTS), Network Architecture, 3GPP TS 23.002.

[5] Universal Mobile Telecommunications System (UMTS), General Packet Radio Service (GPRS), 3GPP TS 23.060.

[6] Universal Mobile Telecommunications System (UMTS), Bearer-Independent Circuit Switched Core Network, 3GPP TS 23.205.

[7] H. Kaaranen, A. Ahtiainen, L. Laitinen, S. Naghian, V. Niemi, UMTS Networks, Architecture, Mobility and Services, John Wiley & Sons Ltd, 2001.

[8] Universal Mobile Telecommunications System (UMTS), QoS Concept and Architecture,3GPP TS 23.107.

Index

3GPP 18, 208, 312 3GPP specifications 47, 48, 57, 208, 220,

243, 273

AC 21, 237, 242, 263 Acquisition Indicator 217 Active set 240, 250, 285 Adjacent power leakage See APL Admission Control See AC AGC 71 AICH 213, 217 Angular spread 33 Antenna

Adaptive antenna 28 Antenna line configuration 49 Beam width 161, 177, 178, 189 Configuration 37, 38, 150, 160, 186 Direction 173 Down tilt 189, 201 Electrical antenna down tilt 190 Electrical down tilt 191 Height 186, 188 Height selection 189 Mechanical down tilt 189 Optimum down tilt angle 192 Specification 51

Antenna filter 46 Antenna line configuration 153 AP acquisition indicators 218 AP-AICH 213, 218

API 218 APL 47 Application testing 301 Automatic Gain Control See AGC

Bandwidth 30, 209, 267 Base band unit 47 Base station configuration 46 Base station location 170 BCCH 220, 228, 233, 285 BCH 215, 221 Breakpoint distance 187 BSIC 245

C/I 65, 167, 238, 256 Capacity 154

Capacity-limited 161, 165 Improvements 160

Carrier to interference ratio See C/I CCCH 169, 220, 234 CD/CA-ICH 213, 218 CDMA 18, 208 CDP 212 Cell-breathing 182 Cell reselection 152, 220, 227, 229, 242,

253, 261, 263, 266, 273, 274, 288 Cell search 228 Cell selection 152, 227, 229, 253, 261,

273, 274 CELL_FACH 227, 274 CELL_PCH 227, 233, 274

338

Cellular concept 22 CGI 245 Channel mapping 221 Channelization code 224 Chip rate 30 CI 245 C-Id 246 Circuit switched data measurements 288,

293Co-channel interference 22, 177 Code planning 39, 134 Code tree 243 Coherence bandwidth 32, 34 Collision Detection Preamble 212 Combiner solution 48 Common channel power levels 238 Configuration planning 46 Connection establishment 227, 234, 260,

276, 307, 322 Connectors 51 Coordinate systems 91 Core Network Domain Identifier 245 Co-siting 27, 55 Coupling loss 70, 72 Coverage

Coverage-limited 161 Improvements 160 Overlapping 182 Pilot coverage 172 Signaling channel 152 Thresholds 152

Coverage planning 124 Coverage: 152 CPCH 220 CPICH 47, 152, 213, 214, 247, 276 CPICH Ec/N0 268 CPICH RSCP 269 CPICH time of arrival 272 C-RNTI 246 CSICH 213, 219 CTCH 220

DAS 69, 73 DCCH 220 DCH 152, 210, 221, 262 Delay measurement 326 Delay profile 272 Delay spread 33 Digital map 80, 121, 122, 135

Accuracy 80, 82, 89, 111 DEM 97 DTM 97 Map layers 95 Spatial accuracy 88

Dimensioning 118 Diplexer 57 Distributed antenna system See DAS Diversity 54, 165

Antenna diversity gain 66 Polarization diversity 54 Space diversity 54 SSDT 211 TX Diversity Indicator 255

Documentation 42 Downlink spreading 226 DPCCH 210 DPCCH Power Control Preamble 212 DPCH 213, 214 DPDCH 210 D-RNTI 246 DS-CDMA 30, 208 DSCH 221 DSMA-CD 212 DTCH 220 Dynamic resource allocation 243

Eb/N0 48, 65, 127 Ec/N0 268 EDGE 18 EIRP 60, 69 Enhanced Data calls for GSM Evolution

See EDGE Equivalent isotropic radiated power See

EIRP European Global System for Mobile

communications See GSM

FACH 221, 262 Fading

Fast fading 32, 34 Flat fading 22 Slow fading 35

Fast moving mobile 231 FBI 210 FDD 30, 208 FDMA 18 Feeder cable 51 Frequency reuse 22

339

General Packet Radio System See GPRS Geoid 93 GGSN 310 Global RNC-Id 245 GPRS 18 GSM 18

Handover 42, 143 Handover control 240, 310 Hard handover 261 HCS 230

HCS priority 231, 232, 233 Hexagonal grid 166, 170 Hierarchical cell structure See HCS Hysteresis 252

Identities 244 IM 64, 157 IMSI 244 Indoor 46, 72, 161 Inner-loop power control 238 Interface unit 48 Interference

Co-channel interference 23, 24 Interference limited 155 Intra-cell interference 24 Other-cell interference 24, 59, 156 Other-cell-to-own-cell 189 Own-cell interference 24, 59, 156

Interference margin See IM Inter-frequency handover 241, 261, 287 Inter-system handover 241 Interworking 263

2G/3G interworking strategy 25 GSM interworking 55 Multi network planning 123

Intra-frequency handover 241 IP Header 296 Isolation 70, 71 Isotropic received power 67

Jumpers 51

KPI 40, 322, 330

LAI 244 Laser scanning 98

LC 21, 237, 242, 263 LNA 49, 52, 67, 73, 121, 153, 165

Noise figure 52 Load 151, 156, 161

Downlink load 159 Load equation 156 Uplink load 156

Load Control See LC Local Cell Identifier 246 Location registration 227 Location update 235 Logical channels 219 Low noise amplifier See LNA

MAC Header 291, 298 Macro cell 230 Macrocellular 27, 177 Map layers

Backdrop images 109 Building layer 104 Morphographic layer 96, 100 Topographic layer 97 Vector layer 107

Map production process 83 Map projections 92 Mapping methods

Land surveying 85 Satellite Remote Sensing 88

Mapping methods 84 Mapping methods

Photogrammetric mapping 85 Mapping methods

Maps and databases 91 Mast Head Amplifier See LNA Measurement equipment 266 Measurement events

Event 1a-1f 247 Event 2a-2f 250 Event 3a-3d 252 Event 4a-4b 252 Event 5a 253 Event 6a-6g 253

Measurement process 260 Measurements in connected mode 278 Measurements in idle mode 267 Micro cell 230 Microcellular 27, 54, 81, 98 MIMO 24, 29 MM 20

340

Mobile station 57 Model tuning

Continuous measurements 324 Multi path 32 Multiple Input Multiple Output See

MIMO

Network evolution 42 Network topology 27 Noise bandwidth 64 Noise bandwidth 208 Noise figure 267 Noise figure improvement 52 Noise floor 267 Non-hexagonal grid 166

ODMA 24, 29 Offline measurements 323 Offsets 250 Online measurement 323 Open-loop power control 237 Operation and maintenance (O&M) unit

48Opportunity Driven Multiple Access See

ODMA, See ODMA, See ODMA Orthogonal Variable Spreading Factor

224Orthogonality 159 Outdoor 46 Outer-loop power control 239 OVSF 224

PA 165 Packet scheduling 21, 263, 310 Packet switched data measurements 293 Paging 233 Parameters 143, 243, 256 Path loss 60, 153, 159 PCCH 220 P-CCPCH 213, 215 PCH 220, 221 PCP 212 PCPCH 210, 212 P-CPICH 213, 215 PDCP Header 297 PDP (Packet Data Protocol) context 311 PDSCH 213, 217 Pending time after trigger 252, 253 Physical layer 209

PICH 213, 218 Pilot pollution 126, 141 Planning phase 260

Configuration planning 37 Dimensioning 36 Implementation phase 261 Monitoring 40 Operational phase 264 Optimization 40 Parameter planning 39 Planning tool support 118 Topology planning 37 Verification 40

Planning process See Planning phase Planning threshold 61, 67 Planning tool 41, 118

Analysis tool 122, 138 Capacity analysis 138 Capacity planning 127 Coverage analysis 138 Coverage planning 124 Design tool 121, 123 Management and information

processing tool 143 Measurement tool 121, 134 Neighbor cell generation 133 Network management system 144 Planning process support 120 Scrambling code planning 134

PLMN 306 PLMN selection 227 PLMN-Id 245 Power amplifier (see also PA) 47 Power budget 42, 59, 153

Indoor system 76 Power Budget 153 Power control 20, 237, 261, 262, 282

Headroom 66 Power control gain in Eb/N0 66

PPP Frame 296 PRACH 210, 211 Primary Synchronization Code See PSC Processing gain 65 Projection 91, 94 Propagation

Channel 31 Environment 22, 46 Model tuning 135 Slope 36

341

Protocol analysis 325 PSC 216 P-SCH Ec/N0 270, 271

QoS 306 Architecture 314 Attribute mapping 318 Attribute value ranges 319 Attributes 314, 316 Classes 316 Management functions 321 Measurement methods 323 Measurement tools 333 QoS in UMTS 307

RACH 47, 220, 276 Radar interferometry 98 Radiating cable 73, 75 Radio bearer establishment 228, 236 Radio frame 209, 218 Radio interface 30, 36, 208 Radio network planning strategy 24 Radio Resource Management See RRM RAI 244 RANAP 312 Receiver noise figure 64 Receiver sensitivity 67 Remote sensing 88 Repeater 69, 160 Resolution 81 Resource management 263 RLC Header 290, 297 RM 21 RNTI 246 RRC connection establishment 234 RRM 20, 237, 262

SAI 246 Scanner 135, 267 Scanner measurements 268 S-CCPCH 213, 215 SCH 213, 216, 217 S-CPICH 214 Scrambling code 227, 255

Group 216 Group identification 229 Identification 229

SDMA 28

Secondary Synchronization Code See SSC

Sector orientation 173 Sectoring efficiency 179 Session based measurement 324 SGSN 311 Simulation

Antenna height 188 Beam width 179 Coverage overlapping 183 Down tilt 192 Monte Carlo 127 Sectoring 179 Site evolution 184

SIR 239 SIR target 239, 282, 309 Site

Configuration 166 Evolution 184 Location 166, 172 Location deviation 167 Sector orientation 173 Sectoring 177 Selection 167, 173

Soft blocked 155 Soft handover 20, 171, 240, 261, 263,

285Diversity gain 66

Softer handover 66, 127, 170, 178, 240, 261, 263, 285, 309

Space Division Multiple Access See SDMA

Spreading Spreading code 223 Spreading factor 30, 223

Spreading 223 S-RNTI 246 SSC 216, 229 S-SCH Ec/N0 271 Synchronization

Frame synchronization 229 Slot synchronization 229

Tcell 255 TCP Header 296 TDD 30, 208 TDMA 18 TFCI 210, 211 Thermal noise 59

342

Third generation partnership project See 3GPP

Throughput Throughput measurements 327

Throughput 143 Time-to-trigger 249, 251, 252 Topology planning 150 TPC 210, 239 Trace 328 Traffic and capacity measurements 325 Traffic distribution 27, 161 Transceiver unit 47 Transport channels 220 Triplexer 56

UC-Id 246

UDP Header 296 UE TX power 279, 281 UMTS 19 Uplink spreading 225 URA Identity 246 URA_PCH 227, 233, 274 U-RNTI 246 UTRAN 20

WCDMA radio interface 208WGS84 93 World Geodetic System 1984 See

WGS84

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