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WCDMA Radio Functionalities

Chapter 11

OBJECTIVES:Upon completion of this chapter the student will be able to:

List the UTRAN functions

Describe soft and softer handover

Describe handover to and from GSM (inter-system handover)

Describe admission and congestion control

Describe channel rate switching

Describe (intra-system) inter-frequency handover

WCDMA Radio Network Design

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EN/LZT 123 6039 P1E

11 WCDMA Radio Functionalities


Table of Contents

Topic Page

INTRODUCTION......................................................................193

RADIO ACCESS BEARERS (RABS) AND SERVICES................................193

RADIO NETWORK FUNCTIONALITIES......................................................194

TRANSPORT NETWORK FUNCTIONALITY...............................................195

OTHER SERVICES......................................................................................196

FUNCTIONALITY STILL UNDER STANDARDIZATION..............................196

RADIO NETWORK FUNCTIONALITY....................................198

ADMISSION CONTROL...............................................................................198

BLOSSOMING AND WILTING.....................................................................198

CHANNEL SWITCHING...............................................................................199

CONGESTION CONTROL...........................................................................199

DOWNLINK POWER ALLOCATION...........................................................200

DOWNLINK POWER DRIFT PREVENTION................................................200

POWER CONTROL.....................................................................................201

RADIO CONNECTION SUPERVISION........................................................201

SOFT/SOFTER HANDOVER.......................................................................202

SYNCHRONISATION FUNCTIONS........................................203

FRAME AND NODE SYNCHRONISATION.................................................203

NETWORK SYNCHRONISATION...............................................................203

OTHER SERVICES/FUNCTIONALITY STILL UNDER STANDARDIZATION...............................................................204

GSM INTEROPERABILITY..........................................................................204

GSM HANDOVER........................................................................................204

CAPACITY IMPROVING FEATURES..........................................................205

TRANSMIT DIVERSITY...............................................................................206

IMPROVED POSITIONING..........................................................................207

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INTRODUCTION

The functions/functionalities of UTRAN can roughly be divided into

Radio Access Bearers (RABs) and services

Radio network functionalities

Transport network functionalities

Synchronization functions

RAN management functions

Other services

Functionality still under standardization

This chapter concentrates on the radio network functionalities but some information about other functions are given.

RADIO ACCESS BEARERS (RABS) AND SERVICES

Conversational RAB for AMR speechThis RAB supports AMR speech, 12.2 kbps (full rate). Support for voice activity detection and silence descriptor is provided by utilizing DTX. DTX is used independently in the uplink and the downlink.

Interactive RAB. This RAB supports packet switched best effort services up to 384 kbps (384 kbps in downlink and 64 kbps in uplink) with and without prioritization. Transport formats for lower rates than 384 kbps are supported as well. The channel rate switching functionality decides which transport format to use.

Conversational RAB for UDI 64 kbps service (circuit data)RAB to support UDI guaranteed 64 kbps circuit switched service. This RAB can be used for circuit switched based multimedia applications using e.g. H.324M.

Streaming RAB for NT CS data. RAB used e.g. to support fax and V.90 modem service.

Multiple simultaneous RABs2 simultaneous RABs per UE is supported. The multiple RABs can be a mix of RABs for circuit and packet switched services.

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Emergency call This function provides support for Emergency Calls. The support includes prioritization of the call.

PositioningA Cell based positioning method, i.e.; the position is determined with granularity of cell. Positioning with a better accuracy e. g. based on Round Trip Time measurements is also provided.To exploit GPS capability UTRAN can also offer the possibility to send the GPS parameters transparently between the CN and the UE.

Transparent Message TransferTransfer of control plane messages e. g. connection management, mobility management and Short Message Services (SMS), transparently through the UTRAN between core network and UE is supported.

Cell Broadcast Possibility to broadcast localized information, e.g. SMS cell broadcast

RADIO NETWORK FUNCTIONALITIES

These are treated in more detailed in a section that follows but the more important functionalities are

Soft and softer Handover A UE in soft handover mode is communicating with two or more RBSs, while a UE in softer handover communicates with multiple sectors at the same RBS. The soft/softer handover functionality includes decision on how many cell carriers to connect in soft/softer handover and functionality for setting up and releasing connections between the RBS and the UE. Soft/softer handover is supported for dedicated channels. During soft handover the macro diversity combining is conducted in the RNC. For softer handover, maximum ratio combining is conducted in the RBS.

Handover to and from GSM. The feature (inter system handover) planned for the first releases is based on congestion and on loss of coverage.

Admission and Congestion Control Admission control blocks new incoming calls as well as handover attempts when the load in the system is high. The admission functionality is also capable of including priority, for instance emergency calls, in the admission decision.Congestion control is used to resolve overload in both the uplink and the downlink. In case of overload, congestion

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control reduces bit rates of delay tolerant existing connections or as a second option, removes existing connections.

Channel switchingChannel switching includes channel type and rate switching. Channel type switching is used to switch between common and dedicated channels both in the uplink and downlink. The activation of the switching is based on data activity in order to assure an efficient usage of the dedicated channel resources. The channel rate switching functions allows for changes of transport format on the air interface, e.g. to increase/decrease the bit rate. The activation of the switching is based on changes in a user’s bit rate demand, due to addition or removals of RABs.

Inter-frequency handoverThe system supports inter-frequency HO between cellcarriers on different frequencies. The handover could be initiated both for capacity reasons, e.g. load sharing, and for mobility reasons.

TRANSPORT NETWORK FUNCTIONALITY

ATM interfacesThere are a number of different ATM interfaces available for both RNC and RBS:E1: 2MbpsJ1: 1.5Mbps, T1: 1.5Mbps, E3: 34Mbps, T3: 45Mbps, STM-1: 155Mbps

ATM PVC and PVP including VC cross connectAll logical ATM links for Iu and Iub are set up as permanent virtual ATM connections. These are then used either for user plane with AAL2 or AAL5, control plane with AAL5 or O&M with IP over AAL5.The PVCs and PVPs can be set up either directly between two nodes or via a third (or more) node(s), i.e. includes cross connect functionality.PVPs are used when handling a set of PVC as a single entity e.g. for cross connect and VP shaping. PVPs are normally used for connection of UTRAN nodes to ATM backbone networks.

Switched AAL2 connections AAL2 switched connections are used on Iu for circuit and

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speech connections and on Iub for all connections RBS-RNC.

ATM on fractional transmission over E1/T1.This is mainly used at smaller installations in the initial phase of UTRAN introduction, when capacity requirements are low. The function “ATM on fractional” on E1/T1 interfaces allows for using parts of STM transmission connections (e.g. E1, T1 etc) for ATM traffic.

Link redundancyFor control plane and O&M signaling the 1+1link redundancy is achieved by a loss less switch over. For user plane the data is distributed over both (all) links (1+1 or n+1). User plane links can hence be configured for optimal cost with some service degradation at loss of a link, or for maximal availability with over provisioning of link capacity.

Circuit emulation for transmission sharing (for E1/T1/J1)The Circuit emulation function allows STM connections terminated on E1/T1/J1 port (or a fractional of it) to be carried over ATM using ATM AAL1.

OTHER SERVICES

These services include

SMS cell broadcast

GSM interoperability

GSM handover

Inter-frequency handover

Packet data scheduling

Transmit diversity

Improved positioning

FUNCTIONALITY STILL UNDER STANDARDIZATION

Packet data up to 2 Mbps

Support for TDD

Other Radio Network capabilities

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Adaptive antennas

Interference Cancellation

Hierachichal Cell Structure (HCS)HCS is used to achieve high capacity at a low cost in high traffic density areas by introducing different cell layers in the system, i.e. macro layer, micro layer and perhaps also a pico layer.

Access to multiple MSC/SGSN from one RNC. (Virtual RNC)The system allows for one physical RNC node to be connected to several MSCs and SGSNs.

IP transport network

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RADIO NETWORK FUNCTIONALITY

The radio network functions provide a means for a fully mobile WCDMA network with high quality. Further, as power is the common shared resource in WCDMA. A large effort is put on different power management schemes in order to assure good performance. Some of the radio network functions are described below.

ADMISSION CONTROL

Guarantees the overall Quality of Service bycontrolling the number of users

New users blocked above this point

interference

Capacity / LoadPlanned load

Planned coverageCoverage

User added

Admission threshold

Figure 11-1 Admission control

Admission control blocks new incoming calls as well as handover attempts when the load in the system is high (Figure 11-1). By doing that, the call dropping probability is reduced. Admission control is used in both the uplink and the downlink. The admission decision is based on air interface load, by using measurements of uplink interference, downlink output power as well as the actual number of users. The admission functionality is also capable of including priority, for instance emergency calls, in the admission decision.

BLOSSOMING AND WILTING

Blossoming and wilting enables to gradually increase the output power at start up (or gradually power decrease at shut down) instead of initially letting the RBS transmit with maximum output power. This ensures graceful start up/shut down, to retain existing calls. This functionality has been proven to be very usefull in Ericsson’s commercial IS-95 networks.

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CHANNEL SWITCHING

Channel switching includes channel type and rate switching. Channel type switching (Figure 11-2) is used to switch between common and dedicated channels both in the uplink and downlink. The activation of the switching is based on data activity in order to assure an efficient usage of the dedicated channel resources.

Release dedicated channel

Random-AccessRequest

Random-Access Channel

Packet Packet Packet

Dedicated Channel

TTime-out

Switch to common

Switch todedicated

Random-AccessRequest

User 1 User 2

Figure 11-2 Channel type switching

The channel rate switching functions allows for changes of transport format on the air interface, e.g. to increase/decrease the bit rate. The activation of the switching is based on changes in a user’s bit rate demand, due to addition or removals of RABs.

CONGESTION CONTROL

Figure 11-3 Congestion control

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Congestion control is used to resolve overload in both the uplink and the downlink (Figure 11-3). It uses the same measurements as the admission control. In case of overload, congestion control reduces bit rates of delay tolerant existing connections or as a second option, removes existing connections.

DOWNLINK POWER ALLOCATION

This functionality allows for the possibility to set the output power of the common control channels as well as the possibility to set different maximum output powers of the downlink channels traffic channels (depending on the RAB). Since the downlink output power defines the coverage for individual channels, it is possible to design the system in such a way that the downlink data rate can be higher than the uplink data rate for users on cell border.

DOWNLINK POWER DRIFT PREVENTION

During period of soft handover, the output power from the different RBSs may drift apart. This feature offers a modified type of power control during the soft handover periods in order to prevent the drift (Figure 11-4).

UP / DOWN(closed loop)

RBS1 RBS2

FER/BERDataComb.

MRC

Mitigation of power drift

Figure 11-4 Power control during soft handover

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POWER CONTROL

F a s t q u a l i t y b a s e d p o w e r c o n t r o l- Im p r o v e s c a p a c i t y .

O u t e r lo o p p o w e r c o n t r o l

O p e n lo o p p o w e r c o n t r o l

F le x ib lep o w e r a l lo c a t io n

B lo s s o m&

w i l t

Figure 11-5 Power control

The power control is one of the most important functions in a WCDMA network (Figure 11-5). Ericsson’s products support three different types power control, namely inner loop power control, outer loop power control and open loop power control.

The inner loop power control is C/I based and consists of two parts. In the uplink, the quality of the received signal is compared to an Eb/Io target. Based on the comparison a power control command is transmitted to the UE. In the downlink, the output power per TCH is adjusted according to the power control command from the UE.

The purpose of the outer loop power control is to adjust the Eb/Io so that the quality of a connection meets the set FER/BER target. The uplink outer loop is conducted after diversity combining.

The open loop power control is used when transmitting on common channels.

RADIO CONNECTION SUPERVISION

The purpose of this function is to detect lost radio connections. The lost connections are released to free up the resources.

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SOFT/SOFTER HANDOVER

A lg o r ith m- R e la t iv e th re s h o ld s

m in im iz e s th e n u m b e r o fm o b ile s in s o ft h a n d o v e r

T im e

C /I

A d d B D e le te A

A d dm a rg in

D ro pm a rg in

B A

Figure 11-6 Soft/softer handover

A UE in soft handover mode is communicating with two or more RBSs (Figure 11-6), while a UE in softer handover communicates with multiple sectors at the same RBS. The soft/softer handover functionality includes decision on how many cell carriers to connect in soft/softer handover and functionality for setting up and releasing connections between the RBS and the UE. Soft/softer handover is supported for dedicated channels. Any combination of soft and softer handover is possible up to four handover legs in the active set.

During soft handover, the macro diversity combining, namely selection diversity, is conducted in the RNC. For softer handover , maximum ratio combining is conducted in the RBS. The soft handover functionality is also supported when a UE moves from one RNS to another.

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SYNCHRONISATION FUNCTIONS

FRAME AND NODE SYNCHRONISATION

Node synchronisation aligns the TX/RX parts of the RBSs with the RNC and is necessary for soft handover. Frame synchronisation guarantees that the same frame (sent from the RNC in UTRAN) is transmitted over the air interface at the same time from RBSs in macro diversity operation. Another objective is to select/combine correct UE frames (from different RBSs) in the RNC.

NETWORK SYNCHRONISATION

Synchronises the UTRAN nodes to the transport network node(s) with respect to clock references in order to regain and distribute synchronisation references in a master-slave approach within UTRAN (primarily RNC-RBS). The transport network can either be built with external ATM/PDH/SDH equipment or with direct connections, i.e. own fibre/copper lines or microwave systems.

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OTHER SERVICES/FUNCTIONALITY STILL UNDER STANDARDIZATION

GSM INTEROPERABILITY

Handover from WCDMA to GSM means that WCDMA can be deployed in islands overlaying GSM. As the demand for WCDMA increases, those islands can be expanded. To be able to limit the initial deployment to large cities, the initial investment in WCDMA can be kept low. Handover from GSM to WCDMA allows access to WCDMA services. Further, if RANOS is used, the management functions for intersystem support can be added in order to make the operation and maintenance efficient and easy.

GSM HANDOVER

Inter frequency measurements are needed tosupport inter system handover

Compressed mode supports these measurements

Inter system

WCDMAGSM

time for measurementsTf = 10 ms

SF=SF0

SF=SF0/2SF=SF0

Compressed mode

Figure 11-7 Inter system handover

This function provides the means for intersystem handover from UTRAN to GSM and from GSM to UTRAN. Handover to GSM is triggered due to loss of WCDMA coverage. Handover from GSM may be triggered in order to access UMTS services1. To conduct intersystem handover, measurements are needed on the GSM system. Compressed mode is supported in order to conduct such measurements (Figure 11-7).

1 The availability of handover from GSM to UTRAN is dependent of the GSM standardisation.

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CAPACITY IMPROVING FEATURES

Inter-frequency Handover

MicroMacro

• Support of multiple carriers in high capacity regions• Load sharing to increase performance

Load distributed between carriers

Figure 11-8 Inter frequency handover

This function supports handover between cell-carriers belonging to different WCDMA frequency layers (Figure 11-8). To be able to measure the quality on other frequencies prior to inter- frequency handover compressed mode is utilised.

Packet Data Scheduling

extra capacitycan be givento packet datausers

load

time

max planned load

• Load sharing in time results in a high capacity• Smooth interference levels in the system

Figure 11-9 Packet scheduling

Packet data scheduling of interactive RABs is used to assure that the planned spectrum is used efficiently (Figure 11-9). This is achieved by continuously update the transport format for the interactive RABs. The aim is to maximize the bit rate for the packet data users, without exceeding the capacity that the system is planned to handle. This functionality relies on the

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same measurements that are used for admission and congestion control.

TRANSMIT DIVERSITY

As transmit diversity improves the downlink capacity, it can be viewed as one expansion possibility. In areas with high capacity demand, it is of course also possible to use it at initial deployment.

Open Loop Transmit Diversity

On

Off 15 dB

10 dB

Figure 11-10 Transmit diversity (STTD)

To enjoy the benefits of transmit diversity, the RBS must have the proper installed hardware. The usage of Space Time Transmit Diversity (STTD) improves downlink capacity (Figure 11-10). The largest gain is expected in environments where the users are moving slowly. STTD transmits nearly the same information from two antennas at nearly the same time. The two antennas experience different fading patterns, which results in a diversity gain since the fast fading is combated. It is possible to switch on/off the TX diversity.

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IMPROVED POSITIONING

The positioning function provides different alternatives with different accuracy as well as different costs. The most basic one, is when UTRAN provides the position using the stored cell information.

Positioning

For a higher accuracy, positioning based on Round Trip Time (RTT) measurements can be used. In order to further improve the accuracy achieved by RTT measurements, RBSs outside the current active set can also be used.

In order to exploit GPS capability, UTRAN can also offer the possibility to send the GPS parameters transparently from the CN to the UE and from the UE to the CN.

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1236039_11_p1e

Documents

services conversational

streaming rab

interactive rab

services functionality

multiple rabs

amr speechthis rab

management functions

mix of rabs