cell planning for lte networks - lt2901 - v2

Cell Planning for LTE NetworksCourse Code: LT2901 Duration: 2 days Technical Level: 3

LTE courses include:n LTE/SAE Engineering Overview

n LTE Air Interface

n LTE Radio Access Network

n Cell Planning for LTE Networks

n LTE Evolved Packet Core Network

n 4G Air Interface Technologies

n LTE Technologies, Services and Markets

...delivering knowledge,maximizing performance...

www.wraycastle.comWray Castle – leading the way in LTE training

CELL PLANNING FORLTE NETWORKS

First published 2009Last updated May 2011

WRAY CASTLE LIMITEDBRIDGE MILLS

STRAMONGATE KENDALLA9 4UB UK

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Apart from fair dealing for the purposes of research or private study, as permitted under the Copyright, Designs andPatents Act 1988, this manual may only be reproduced or transmitted in any form or by any means with the prior

permission in writing of Wray Castle Limited.

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© Wray Castle Limited

Cell Planning for LTE Networks

II © Wray Castle Limited

Section 1 LTE Planning Considerations

Section 2 Coverage Planning and Link Budgets

Section 3 Traffic Characterization

Section 4 LTE Cell Parameters

Section 5 Frequency Planning

Section 6 LTE Performance Simulations

Section 7 The LTE Planning Process

CELL PLANNING FOR LTE NETWORKS

CONTENTS

III© Wray Castle Limited


IV © Wray Castle Limited

SECTION 1

LTE PLANNING CONSIDERATIONS


I© Wray Castle Limited

Cell Planning Work Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.1

Requirements and Targets for the Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.2

Coverage Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3

Traffic Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.4

Cost Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.5

Planning Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.6

CONTENTS

LTE Planning Considerations


At the end of this section you will be able to:

describe how conventional planning philosophy can be applied for the rollout and

subsequent expansion of LTE networks

describe how planning constraints such as capacity, coverage and quality are interrelated

for LTE

justify the use of an iterative approach in the planning process for LTE

OBJECTIVES


V© Wray Castle Limited


VI © Wray Castle Limited

Analyze the requirements for the network plan

Produce an initial plan

Define planning constraints and radio configurations

Use simulation to test against requirements

Produce a working plan

Commence network build

Perform testing, monitoring and analysis on live network

Revise planning constraints and radio configurations if required

Revise planning constraints and radio configurations if required

LT2901/v2 1.1© Wray Castle Limited

Cell Planning Work Flow

The term cell planning refers to a collective series of processes designed to produce a network plan thatwill meet a predefined set of cost and performance targets. It would, however, be wrong to think ofplanning as a finite process which ends at some point when a particular target is met. It should beiterative, and each additional step may result in a re-evaluation of the existing plan.

The planning process is probably best considered as a loop. The loop involves target setting, initialplanning, assessment and re-evaluation at all stages. This is an important concept, which can be appliedboth to individual planning processes and to the system plan as a whole.

Like the 3G system UMTS, LTE is potentially very sensitive to variations between initial planningassumptions and real network characteristics after build; this makes subsequent optimization moredifficult. This means that there is a long term cost saving dividend to be gained from careful andconsistent reassessment of planning assumptions as network build progresses.


Essential DesirableXXXXXXXX XXXXXXXXXXXXXXX XXXX XXXXXXXXX

XXX XXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXX XXXX

Coverage

Timescale

Cost

QoS

Capacity

Plan Requirements

LT2901/v21.2 © Wray Castle Limited

Requirements and Targets for the Plan

Before any plan can be started, a set of design criteria must be set out. These will define where and howthe completed system should operate. In general, the criteria will describe five key factors:

coverage capacity QoS (Quality of Service) timescale cost

Each of these factors will consist of a series of individual requirements, some of which may be essentialand some simply desirable. The requirements for each factor almost always need to be balanced againstthose for the others.

LTE coverage and capacity need to be defined in terms of differentiated service requirements since thesystem capabilities will differ in different radio conditions. One approach for initial rollout is to plan allareas for a minimum acceptable level of performance (in terms of bit rate and delay) and then addresshigher capability requirements on a hot-spot basis only. These high-capacity high-bit rate hotspots maybe provided initially through careful location of rollout sites and then expanded later through the use ofmicrocells, picocells and femtocells as well as the introduction of optimal features such as MIMO(Multiple Input Multiple Output) antenna systems.

Where a network plan is being produced in a system based on infrastructure and spectrum sharing all ofthe planning constraints must be considered for the potentially slightly different requirements of morethan one operator.


Digi-wide

XXX XXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXX XXXX

Power budget

Service differentiation

Railways, roads, motorways

Frequency band constraints

% Population% Geographical

Coverage Requirements

Licence conditions

In-building

Special events


Coverage Requirements

The initial driving force for coverage will usually be competitive advantage, but in many cases the licenceagreement will itself stipulate a coverage requirement within a given timeframe. It is important that anycoverage requirements set should be realistic, i.e. acknowledgement that 100% coverage is impossible.

Percentage population coverage is probably the most important driver and it is likely to be one of theterms of the licence. There is perhaps little point striving for complete geographical coverage since mostoperators already have very effective 2G or 3G coverage for basic services.

The power budget will impact on coverage and this will need to be carefully planned taking into accountthat signal strength requirements will vary a great deal for different throughput requirements. The effectof cell loading will also impact coverage, but in a way that is dependent on the system engineeringstrategy adopted.

Voice and message traffic is often dominant along roads and motorways, with high-bit-rate data servicesbecoming more significant on railway or bus routes, in residential areas, in transit points such as airportsand at special events such as sports fixtures or concerts.


Digi-wide

?

QoS requirements

Service differentiation

Features and configuration

Customer profiles and demographics

Sales strategies

Capacity Requirements

Spectrum

CS voice handling

Backhaul

EPCUMTS/GSMLTE


Traffic Factors

The specification of traffic capacity requirements for the network cannot be exact at the planning stage.Initially an estimate must be used, which will not accurately reflect the traffic that occurs on the builtnetwork. This should be taken into account when setting realistic targets within the planning criteria. Anylarge variations from this which show up once the network begins operation should result in re-evaluationand adjustment of planning targets.

To plan a multimedia network it is important to know the total volume of traffic expected. This can then bebroken down into the different traffic types. These types will include voice traffic, which has been themost dominant traffic type in 2G networks. This could be handled by an existing 2G or 3G infrastructure,leaving the LTE network to support the high-bit-rate data services.

Many of the new services are based on lifestyle, so it is important to define user profiles, detailing thebehaviour of subscribers and incorporating demographic information.

The available spectrum has an impact upon capacity. LTE spectrum may be either FDD (FrequencyDivision Duplex) or TDD (Time Division Duplex) and, since the system is ‘bandwidth agnostic’, importantdecisions need to be made at the pre-planning stage about how any licensed spectrum is divided andallocated to cells.

Finally, LTE is a wholly packet-based system but it still needs to support real time services requiringguaranteed QoS. This is an important consideration for all aspects involving capacity dimensioning.


Man hours

Optimal feature upgrades

Mast and antenna systems

Radio access hardware

Licence fee

Costs

Network infrastructure and

switching

Ground rent

$£

¥

Transmission


Cost Considerations

Almost every aspect of the planning process will have an impact upon cost. In most cases, cost will bethe main constraint in the design process. The aim will always be to provide the best overall performanceat the least cost. Careful planning, particularly at the roll-out stage of a network, can make a bigdifference in this respect.


Cost

LicenceService

Requirements

Coverage/Capacity

QoS


Planning Constraints

It is impossible to produce a plan that will fully satisfy all requirements all of the time; there has to be acompromise between conflicting requirements. A decision will need to be made about how best tobalance these conflicting requirements and which, if any, are higher priorities.

For example, almost all requirements will need to be balanced against the initial cost of the rollout.However, if strict adherence to budget results in poor coverage or capacity, then there will be a long-termreduction in revenue from the network. This relates back to the concept of the planning loop. Any majorand irresolvable conflicts between requirements should result in re-evaluation before planning evenbegins. The overall aim should be to make targets ambitious, but realistic.


SECTION 2

COVERAGE PLANNING AND LINKBUDGETS



The Link Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.1

Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.2

Channel Bandwidths and Subcarriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.3

Radio Channel Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.4

Band Setting in a Planning Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.5

Receiver Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.6

Signal to Noise Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.7

Considerations for Spectrum Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.8

Example SFN Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.9

Modulation and Error Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.10

CQI Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.11

LTE SINR and Sensitivity Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.12

LTE Receiver Sensitivity Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.13

LTE UE Reference Sensitivity Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.14

Example DL LTE Link Budgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.15

Example UL LTE Link Budgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.16

Example Range Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.17

LTE Link Budget Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.18

Example Urban Plan – Brussels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.19

Basic Coverage by Signal Level Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.20

Best Server Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.21

Determining Effective Downlink Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.22

Propagation Modelling Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.23

Deterministic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.24

CONTENTS



Allowance for Building Clutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.25

Best Server with Building Clutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.26

Service Coverage with Building Clutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.27

Model Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.28

Example ‘k’ Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.29

CONTENTS

Coverage Planning and Link Budgets



discuss the key parameters that must be included in LTE link budgets

identify the spectrum bands and blocks that are defined for LTE operation

state the bandwidth and subcarrier options available for LTE systems

explain how subcarriers are grouped into resource blocks and how channel centre

frequencies are identified

calculate LTE receiver sensitivity for any given physical layer configuration option

describe the key options open to an operator when dividing licensed spectrum for use on

LTE cells

discuss the impact in the chosen spectrum division policy on the inter-cell interference level

and explain how this can be included in the link budget

compile realistic link budgets for typical LTE coverage scenarios

interpret, evaluate and compare coverage predictions from an example LTE planning tool

explain the importance of effective propagation model tuning for reliable multi-service

coverage prediction

explain the principles of propagation model tuning

OBJECTIVES



Maximum acceptable path loss

TX PowerRX sensitivity

Interference margin

Fade margins

Antenna configuration and

performance

RF equipment losses

TX Power

RX sensitivity


The Link Budget

The starting point for coverage assessment in any radio system is the link budget. A link budget must beperformed in both the uplink and downlink directions. The chief inputs to a link budget are radio factorssuch as transmit power, receiver sensitivity, feeder losses and antenna gains. The overall aim is to find amaximum path loss that is acceptable in both the uplink and the downlink directions.

However, for LTE the link budget is not static because it is affected by varying operating conditions andby varying service requirements. This means that other margins need to be included that reflect thesevarying possibilities. Usually, multiple link budgets will be required to give a full picture of likely systemperformance.

In high capacity cellular systems there is an assumption that the system will be required to operate underhigh interference conditions. One way to account for this is to include an additional interference margin inthe link budget. The interference margin reflects the interference that will occur between users with thesame frequency resource. The magnitude of the margin depends on the implementation options selectedby the operator, for example, the spectrum division and frequency planning strategy, or the use of MIMOoptions.

As for any other terrestrial radio system margins must also be included that reflect the behaviour of theradio channel, predominantly this means slow and fast fade margins, but could also include factors suchas building penetration loss or body loss.


FDDBand UL Range (MHz) DL Range (MHz)

1 1920 – 1980 2110 – 2170 2 1850 – 1910 1930 – 1990 3 1710 – 1785 1805 – 1880

7 2500 – 2570 2620 – 2690 8 880 – 915 925 – 960

13 777 – 787 746 – 756 ... ... ... 20 832 – 862 791 – 821

24 1626.5 – 1660.5 1525 – 1559

... ... ...

... ... ...

... ... ...

TDDBand UL/DL Range (MHz)

33 1900 – 1920 34 2010 – 2025 35 1850 – 1910 36 1930 – 1990 37 1910 – 1930 38 2570 – 2620 39 1880 – 1920 40 2300 – 2400


Frequency Bands

There is considerable regional variation in the availability of spectrum for LTE operation and this isreflected in the standards. Along with flexibility in bandwidth there is considerable flexibility for spectrumallocation. There are no requirements for minimum band support nor for band combinations. It isassumed that this is determined by regional requirements.

The standards currently identify 15 bands for FDD operation, ranging from frequencies of approximately700 MHz through to frequencies in the range 2.7 GHz. There also eight bands identified for TDDoperation ranging from approximately 1900 MHz to 2.6 GHz. Considerable scope has been left in thestandards to add more frequency bands as global requirements evolve. Additionally, the use of differentuplink and downlink bandwidths is not precluded and is expected to be specified in future releases.

Further Reading: 3GPP TS 36.101:5.5, 36.104:5.5


Channel bandwidths (bandwidth/subcarriers)

1.4 MHz/72

3 MHz/180

5 MHz/300

10 MHz/600

15 MHz/900

20 MHz/1200


Channel Bandwidths and Subcarriers

E-UTRA (Evolved Universal Terrestrial Radio Access) /LTE is designed to work in a variety ofbandwidths ranging initially from 1.4 MHz to 20 MHz. As E-UTRA is described as being ‘bandwidthagnostic’, other bandwidths, ones that allow E-UTRA to be backwards compatible with channelallocations from legacy network types, for example, could be incorporated in the future.

The version of OFDMA (Orthogonal Frequency Division Multiple Access) employed by E-UTRA is similarto the versions employed by WiMAX (Worldwide Interoperability for Microwave Access) or DVB, but witha few key differences.

In systems such as WiMAX, OFDMA schemes occupying different channel bandwidths employ differentsubcarrier spacing, meaning that there is a different set of physical layer parameters for each version ofthe system. The E-UTRA scheme allows for two fixed subcarrier spacing options; 15 kHz in most cases,with an optional 7.5 kHz spacing scheme, only applicable for TDD operation and intended for very largecells in an SFN (Single Frequency Network). Fixing the subcarrier spacing reduces the complexity of asystem that can support multiple channel bandwidths.

Further Reading: 3GPP TS 36.211, 36.101:5.5, 36.104:5.5


Channel bandwidth (MHz)

Transmission bandwidth configuration (n x RB)

Transmission bandwidth (n x RB)

12 subcarriers

EARFCN(100 kHz raster)


Radio Channel Organization

For both uplink and downlink operation subcarriers are bundled together into groups of 12. This groupingis referred to as an RB (Resource Block). The RB also has a dimension in time and when this iscombined with the frequency definition it forms the basic unit of resource allocation.

The number of resource blocks available in the system is dependent on channel bandwidth, varyingbetween 100 for 20 MHz bandwidth to just six for 1.4 MHz channel bandwidth. The nominal spectralbandwidth of an RB is 180 kHz for the standard 15 kHz subcarrier spacing. Note that this means there isa difference between the stated channel bandwidth and the transmission bandwidth, which is expressedas n x RB. For example in a 5 MHz channel bandwidth the transmission bandwidth would beapproximately 4.5 MHz. This difference acts as a guard band.

OFDMA channels are allocated within an operator’s licensed spectrum allocation. The centre frequencyis identified by an EARFCN (E-UTRA Absolute Radio Frequency Channel Number). The precise locationof the EARFCN is an operator decision, but they must be placed on a 100 kHz raster and thetransmission bandwidth must not exceed the operator’s licensed spectrum.

Further Reading: 3GPP TS 36.101:5.6, 5.7; 36.104:5.6, 5.7



Band Setting in a Planning Tool

The diagram shows a screen shot from the Atoll Planning tool. It can be seen that in this tool the bandused and the selected channel bandwidth are defined as a single entity simply referred to as ‘FrequencyBand’. Thus each band is independently defined for each bandwidth option and for operation in eitherTDD or FDD mode.


Receiver sensitivity

Maximum Range

EIRP

Receiver sensitivity = Thermal noise + Required SNR + Receiver noise figure + Implementation loss

– 174 + 10Log10BW Dependent on modulation scheme, FEC and channel performance requirements

Dependent on equipment hardware and firmware design

and build


Receiver Sensitivity

Ultimately the operating range for a radio link is determined by receiver sensitivity. In effect, thisrepresents the minimum receive signal level for the radio to meet the performance requirements for achannel. In digital systems the performance requirement will typically be expressed as a bit or a blockerror rate. In analogue systems it may be expressed as a SNR (Signal to Noise Ratio) or SINAD (Signalto Interference Noise And Distortion).

In general the receiver sensitivity is derived from the thermal noise in the channel, the required SNR, thereceiver noise figure and any implementation losses. Thermal noise is usually calculated as a multiple ofthe bandwidth assuming –174 dBm/Hz. Note that in extreme climates it may be necessary to adjust thisfigure for ambient temperature. The required SNR will depend on many factors including modulationscheme, FEC (Forward Error Correction) and channel performance requirements. The receiver noisefigure accounts for the noise generated through a variety of characteristics of the analogue RFcomponents used in the receive chain. It is quantified as the total increase in noise level between theinput and the output of the receiver chain. The implementation loss accounts for sub-optimalperformance in the digital signal processing algorithms used in the receiver.


Noise floor–174 dBm/Hz

Good SNR

Noise floor–174 dBm/Hz

Degraded SNR

Noise rise


Signal to Noise Ratio

In addition to absolute signal level, it is important to consider the relative noise level. This is important inall radio systems, but it is particularly important in cellular, broadband access and wireless LAN systems,which typically operate with very high levels of interference between users and between cells. Thisinterference often results in a very significant rise in the receiver noise floor, and this should be taken intoaccount if a realistic system performance prediction is to be made.

For example, cellular systems are planned such that the interference level is as close to the systemtolerable limit as possible. This ensures maximum spectral efficiency and hence maximum system trafficcapacity. In cellular systems therefore, it may be necessary to include an estimated figure for noise risedue to neighbour-cell interference. In CDMA (Code Division Multiple Access) based systems this is evenmore extreme such that the interference contribution includes other users in the same cell and the signalto noise ratio will be negative.


15 MHz

?C0

High interference at cell edge

High capacity in cell core

C0

C0

C0

C0 C0

C0

C0C0

C0

C0 C1 C2

Good performance at cell edge

Lower total capacity in whole cell

C0

C1

C2

C0

C1

C2

C0

C1

C2


Considerations for Spectrum Usage

One of the key decisions that an operator approaching the build of a new LTE network has to make is theway they will use their licensed spectrum in terms of allocation to cells. The flexibility of LTE forbandwidth options means that most operators have a number of potential spectrum division strategiesfrom which they can choose. Ultimately however, the decision becomes one of balancing capacityagainst quality and reliability.

Because of the dynamic resource allocation mechanisms used on the LTE air interface and the ability ofneighbouring eNBs (Evolved Node B) to negotiate and cooperate in resource allocation, it is possible touse a variety of frequency planning strategies, including 1:1:3.

The simple example shows an operator with 15 MHz of radio spectrum available. Two simple optionsthey may consider are to use the spectrum as a single channel of 15 MHz bandwidth and allocate this toall cells in a 1:1:3 frequency plan of the type usually associated with CDMA systems. This will result inconsiderable interference and therefore loss of capacity at the edges of cells, but the potential for veryhigh capacity within the cell area. Alternatively, the operator may choose to split the spectrum into threechannels of 5 MHz bandwidth and allocate them in a 1:3:3 pattern. This provides a degree of frequencyplanning such that at least adjacent cells will not be using the same frequency allocation. The result willbe reduced total throughput in each cell, but a much more consistent and reliable service capabilityacross the coverage area as a whole.


1:3:3 Frequency Reuse1:1:3 Frequency Reuse (SFN)


Example SFN Approach

The diagram shows two screen shots taken from a simulation performed with the Atoll planning tool withboth a 1:3:3 reuse pattern and 1:1:3 SFN approach with the same network architecture. In both cases 15MHz is available to the operator. In the first case (left) it is used as a single channel and in the secondcase (right) it is split into three 5 MHz-channels.

The colouring in the coverage patterns indicates potential bit rate. In the 1:1:3 case the highest bit rate isin the order of 18 Mbit/s, but it is available only over a very limited coverage area with the potential bitrate falling sharply at the cell edges. In the 1:3:3 case the highest bit rate is lower at around 7 Mbit/s, butit is available over a much wider area.


Modulation Schemes

Error Coding Schemes

CRC

BPSK

QPSK

16QAM

64QAM

Signalling functions only

Optional on uplink

1/3 Turbo Coding Traffic and most control channels

1/3 CC BCH only

Transport Block 24 bit CRC


Modulation and Error Protection

The range of modulation schemes used in E-UTRA comprises BPSK (Binary Phase Shift Keying), QPSK(Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation) and 64QAM. BPSK is onlyemployed for a limited set of signalling and reference functions, while 64QAM is optional on the uplink.

The range of error coding options used in E-UTRA devices is far more limited than those available to, forexample, an UMTS device. For most channels the only option is one third rate turbo coding based onconvolutional coding.

Broadcast traffic channels are only permitted to use 1/3 Tail Biting convolutional coding. Various controlchannels have been assigned either convolutional coding, block coding or simple repetition as their errorcoding options.

In addition to error coding, transport blocks containing user and control traffic may also optionally have aCRC (Cyclic Redundancy Check) block attached. Transport blocks on connections that have CRCselected have a 24-bit CRC block appended to the end of the data container.

The familiar UMTS error monitoring levels of BER (Bit Error Rate) derived from the error coding service,and BLER (Block Error Rate), derived from CRC, continue to be available in E-UTRA.

Further Reading: 3GPP TS 36.211, 36.212, 36.300


Downlink channel adaptation based on

UE CQI reporting

Uplink channel adaptation based on eNB measurements of UL data

transmissions and SRS if requested


CQI Reporting

Link adaptation is a crucial part of the LTE air interface and involves the variation of modulation andcoding schemes to maximize throughput on the air interface.

Link adaptation for scheduled uplink resources can be calculated by the eNB from a number of differentinputs based on measurements of the UE’s uplink transmissions. Additionally the eNB may request thatUEs transmit sounding reference signals, the measurements results of which can also be used for linkadaptation.

For downlink transmissions the eNB needs information about the success or otherwise of the UE inreceiving its downlink transmissions. The UE assesses the quality of the downlink signal throughmeasurements of the received signal and consideration of the error correction scheme. It then calculatesthe maximum modulation and coding scheme that it estimates will maintain an error rate better than 10%.This is indicated to the eNB as a CQI (Channel Quality Indicator) value.

Further Reading: 3GPP TS 36.213:7.2


Modulation Scheme

Code Rate SINR (dB) IM (dB)

1/8 –5.1 1/5 –2.9 1/4 –1.7 1/3 –1 1/2 2 2/3 4.3 3/4 5.5 4/5 6.2 1/2 7.9 2/3 11.3 3/4 12.2 4/5 12.8 2/3 15.3 3/4 17.5 4/5 18.6

QPSK 2.5

16QAM 3

64QAM 4

Receiver sensitivity = kTB + 10Log10(NRB) + SINR + IM + NF – 3 (dBm)

From table Assumed to be 9 dB(real may be 5-6 dB)

NRB is the number of allocated

resource blocks

T is defined as 15° C and B is defined as 180 kHz (1 RB) therefore:

kTB = –121.5 dBm


LTE SINR and Sensitivity Requirements

The receiver reference sensitivity level for LTE can be approximated from the table and formula in thediagram.

In this formula kTB is calculated assuming that T is 15°C (288 K) and B is the bandwidth of one RB (180kHz). NRB is the number of allocated RBs, SINR (Signal to Interference and Noise Ratio) is the requiredSINR for each modulation and coding configuration as indicated in the table, IM is the ImplementationMargin (loss) with assumed values indicated in the table and NF is the receiver noise figure, assumed tobe 9 dB, although practical implementations may achieve values in the region 5–6 dB.


5 MHz 10 MHz

QPSK 1/3

16QAM 3/4

64QAM 4/5

Sensitivity values in dBm

Modulation scheme

Required SINR IM

Receiver sensitivity

Receiver sensitivity = -121.5 + 10Log10(NRB) + SINR + IM + NF – 3 (dBm)


LTE Receiver Sensitivity Exercise

Calculate and fill in the receiver sensitivity values for the table in the diagram for a link using all availableRBs for 5 MHz and 10 MHz bandwidths.

Note that for 5 MHz bandwidth there are 300 subcarriers and 25 RBs, for the 10 MHz bandwidth thereare 600 subcarriers and 50 RBs.


-115.0

-110.0

-105.0

-100.0

-95.0

-90.0

-85.0

-80.0

-75.0

-70.0

1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

QPSK 1/8QPSK 1/5QPSK 1/4QPSK 1/3QPSK 1/2QPSK 2/3QPSK 3/4QPSK 4/516QAM 1/216QAM 2/316QAM 3/416QAM 4/564QAM 2/364QAM 3/464QAM 4/5

UE Power Class

1 ...

2 ...

3 23 dBm

4 ...


LTE UE Reference Sensitivity Summary

The curves on the graph are calculated from the general formula for LTE UE sensitivity and all assumethe maximum number of RBs is allocated at each bandwidth.

The diagram also shows the current definition for LTE UE power classes.


QPSK 1/3High

Mobility_Outdoor

16QAM 3/4Low

Mobility_Outdoor

64QAM 4/5Low

Mobility_Indoor eNB

TX power 43 dBm (20 W) 43 dBm (20 W) 43 dBm (20 W) a RF equipment loss –4 dB –4 dB –4 dB b

RS power boost correction –0.7 dB –0.7 dB –0.7 dB c TX antenna gain 18 dBi 18 dBi 18 dBi d

EIRP 56.3 dBm 56.3 dBm 56.3 dBm e = a+b+c+d Link margins

Log normal fade margin 8 dB 5 dB 0 dB f Fast fade margin 0 dB 4 dB 0 dB g

Building penetration loss 0 dB 0 dB 10 dB h Interference margin

(noise rise) Body loss 3 dB 0 dB 0 dB j

Total margins 13 dB 11 dB 12 dB k = f+g+h+i+j UE

RX antenna gain 0 dBi 0 dBi 0 dBi l RF equipment losses 0 dB 0 dB 0 dB m

RX sensitivity –97 dBm –83.3 dBm –75.9 dBm n Budget totals

RX level at UE antenna –84 dBm –72.3 dBm –63.9 dBm o = n–m–l+k Max acceptable DL path

loss 140.3 dB 128.6 dB 120.2 dB p = e–o

i

Derivation

2 dB 2 dB 2 dB

Downlink 10 MHz Bandwidth


Example DL LTE Link Budgets

The link budgets shown are based on a bandwidth of 10 MHz, frequency reuse in a 1:1:3 pattern andallocation of the maximum 50 RBs available to a single connection. This last point means a theoreticaldata rate from about 5 Mbit/s for QPSK 1/2 to about 33 Mbit/s for 64QAM 4/5.


QPSK 1/3High

Mobility_Outdoor

16QAM 3/4Low

Mobility_Outdoor

64QAM 4/5Low

Mobility_Indoor UE

TX power 23 dBm (0.2 W) 23 dBm (0.2 W) 23 dBm (0.2 W) a RF equipment loss 0 dB 0 dB 0 dB b

c TX antenna gain 0 dBi 0 dBi 0 dBi EIRP 23 dBm 23 dBm 23 dBm d = a+b+c

Link margins Log normal fade margin 8 dB 5 dB 0 dB

f Fast fade margin 0 dB 4 dB 0 dB g Building penetration loss 0 dB 0 dB 10 dB

h Interference margin(noise rise) Body loss 3 dB 0 dB 0 dB

e

Total margins 13 dB 11 dB 12 dB j = e+f+g+h+ieNB

RX antenna gain 18 dBi 18 dBi 18 dBi l RF equipment losses –2.8 dB –2.8 dB –2.8 dB

m RX sensitivity –108 dBm –94.3 dBm –86.9 dBm

k

Budget totals RX level at eNB antenna –110.2 dBm –98.5 dBm –90.1 dBm n = m–l–k+j Max acceptable UL path

loss 133.2 dB 121.5 dB 113.1 dB o = d–n

i

Derivation

2 dB 2 dB 2 dB

Uplink 10 MHz Bandwidth (10 RBs allocated out of 50)


Example UL LTE Link Budgets

The link budgets shown are based on a bandwidth of 10 MHz, frequency reuse in a 1:1:3 pattern, anassumed 4 dB improvement in receiver noise figure and implementation loss compared to the UE andthe use of 10 allocated RBs for a single connection out of the total of 50 RBs available. This last pointmeans a theoretical data rate from about 1.4 Mbit/s for QPSK 1/3 to about 7 Mbit/s for 64QAM 4/5.


60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

220.0

Metro Urban Sub-Urban Quasi-Open Open

Distance /km

DL path loss /dB

QPSK 1/3

c.360 m(Metro)

c.3.7 km(Open)


Example Range Determination

The curves in the graph represent plots of path loss against distance calculated using the COST 231Hata model, an assumed frequency of 2.1 GHz and an eNB antenna height of 25 m.

Based on the estimation of minimum acceptable path loss made in the example link budgets for QPSK1/3 of 133.2 dB it can be seen that the operating range in a metropolitan (dense urban) environmentcould be expected to be below 400 m. At the other extreme, in an open area (rural area) the rangeincreases to almost 4 km. Note that this channel configuration represents that used for the definition ofthe reference sensitivity level and consequently is an important benchmark for conformance testing.

Increasing the channel throughput results in a degradation of sensitivity level. From the example linkbudgets the maximum acceptable path loss for 16QAM 3/4 was 121.5 dB. The corresponding ranges formetropolitan and open are approximately 220 m and 2.3 km respectively. For 64QAM 4/5 themetropolitan range would be below 100 m and a little over 700 m in an open environment.


16QAM 1/2Low Mobility_Indoor

eNB TX power 43 dBm (20 W)

RF equipment loss –4 dB RS power boost correction –0.7 dB

TX antenna gain 18 dBi EIRP

Link margins Log normal fade margin

Fast fade margin Building penetration loss

Interference margin(noise rise) Body loss

Total margins UE

RX antenna gain 0 dBi RF equipment losses 0 dB

RX sensitivity Budget totals

RX level at UE antenna Max acceptable DL path

loss

Power available in used RBs

Downlink

UE TX power

RF equipment loss 0 dB TX antenna gain 0 dBi

EIRP Link margins

Log normal fade margin Fast fade margin

Building penetration loss Interference margin

(noise rise) Body loss

Total margins eNB

RX antenna gain 18 dBi

RF equipment losses 3 dB

RX sensitivity –2.8 dB

Budget totals RX level at eNB antenna Max acceptable DL path

loss

Uplink

RX diversity gain

16QAM 1/2Low Mobility_Indoor


LTE Link Budget Exercise

Use the table above to complete downlink and uplink link budgets for the following criteria:

1. 5 MHz channel bandwidth

2. Base station transmit power 20 W

3. Mobile station transmit power 0.2 W

4. 12 DL used RBs

5. 5 UL used RBs

6. 2.1 GHz frequency band

All other parameters are as previously assumed for a low mobility in-building user. Note that you willneed to calculate the receiver sensitivity values.

Determine whether the link is uplink or downlink limited and then use the limiting figure with the path losscharts provided to estimate cell-edge range.



Example Urban Plan – Brussels

This example network is based on an area in the centre of Brussels. A focus zone has been definedaround an area measuring approximately 3 km by 2 km. There are 16 three-sector sites within thedefined focus zone with a resulting cell density of approximately eight cells per square kilometre. Another20 similar sites have been placed within a much larger computation zone, which has been definedbeyond the focus zone. The sites outside the focus zone will enable more realistic simulation ofinterference effects between cells within the focus zone.

All the sites in the focus zone are defined with:

one cell in each sector 15 MHz bandwidth 35 m antenna height 43 dBm transmit power capability receive diversity (3 dB gain) 18 dBi antenna gain (65° beam width, 2° electrical downlink, 4° mechanical downtilt) 4 dB transmit RF equipment loss 2.8 dB receive RF equipment loss 5 dB eNB receiver noise figure



Basic Coverage by Signal Level Plot

The plot shown was produced in the Atoll planning tool using the same site configurations as in theexample link budgets. Propagation modelling was based on Cost 231 plus allowance for diffraction lossresulting from terrain variations. Resolution for the plot is 20 m.



Best Server Plot

The plot shown indicates the best server demarcation for cells based only upon signal strength. In thisplot the tool has not taken into account the potential effects of cell reselection or handover parameters.



Determining Effective Downlink Coverage

It should be noted that indication of a measurable signal in any given location by the tool is notnecessarily an indication of acceptable coverage for any given service. This plot has been modified suchthat only signal levels higher than –75 dBm are shown. This means this now provides an approximationof effective coverage for 16QAM operation with low error protection overhead.


Variablesfrequencyantenna heightregion type

Signal level

DistanceBest-fit curve

COST231-Hata

Lp (urban) = 46.3 + 33.9Logf – 13.82Logh b – a(hm) + (44.9 – 6.55Loghb)Logd + Cm

Where

hb and hm are in meters, d is in kilometers and f is in MHz.

and a(hm) = 3.2(Log(11.75h m))2 – 4.97 for a large cityor a(hm) =(1.1Logf – 0.7)h m – (1.56Logf – 0.8) for a small to medium city

and Cm is 3 dB for metropolitan centres and 0 dB for medium sized cities or suburban areas.


Propagation Modelling Accuracy

There are many widely accepted propagation models that have been used in the planning andoptimization of 2G and 3G systems. In most cases similar methods are being used for LTE planning,however, careful consideration should be given to the approach used to ensure accuracy in the results.There are two main categories of propagation model, empirical models and deterministic models.

Empirical models are based on a power law modified to align with best-fit curves derived from real-worldmeasurements. Perhaps the best known of these is the Okumura-Hata model. The COST231-Hatamodel is an adaptation of this model based on measurements taken in several modern European cities. Itis widely used and generally considered to be suitable for initial coverage estimation of LTE macro cells.The urban variant of COST231-Hata is shown; modifications for suburban, quasi-open and open areasare also available.

A number of comparisons have been made between the performance of empirical models and that ofdeterministic models. In general, empirical models work well in open areas but with degradedperformance in urban areas. Even when well tuned, the effects of street canyons and building lossmeans they can exhibit considerable localized errors. These errors are tolerable in a single-servicesystem such as GSM (Global System for Mobile Communications), but much less so in multi-servicesystems such as UMTS and LTE.



Deterministic Models

These are physical models based on knowledge of wave theory and on detailed knowledge of themorphological and electrical characteristics of the local environment. The most widely used deterministictechnique is ray tracing.

Ray tracing models calculate specific reflections and diffractions for rays launched into the modelledenvironment. The aim is to reproduce as closely as possible real-world propagation. The most accurateprediction comes with three-dimensional environmental data, but two-dimensional predictions can alsobe effective in some environments.

For ray tracing to be effective it is necessary to have accurate data about the environment to bemodelled. This kind of data is now more widely available, which makes ray tracing more viable. Anotherlimiting factor for ray tracing in the past has been the lack of sufficient processing power for it to beperformed on a large scale. In recent years this too has become a much less significant problem. Anumber of trials have shown that ray tracing is significantly more effective for predicting signal level inurban and in indoor areas than empirical techniques.



Allowance for Building Clutter

Although COST 231 is a widely used model for range estimation, it does not allow for many of thevariables that will be present in the real network once it is built. Therefore it would always be preferableto use a more comprehensive model in the planning tool itself. The Atoll tool also includes severalmodels, each suited to slightly different applications.

For the area within the defined focus zone there is building height data available. The example shownhere involves the use of a more sophisticated propagation model that is able to allow for the buildingheight information. As can be seen it produces a significantly different plot from the one produced usingCOST 231. However, it is extremely important that the building height data is accurate and up to date.One problem with this approach, particularly in metropolitan areas, is that building structures can changevery rapidly.

Although the height of the building is now included, there is still no allowance for the materials used inconstruction. This model assumes that that all building structures are solid. No account is being made forreflections or penetration of the building structures themselves. Therefore this model is very likely to beoverly pessimistic whereas the basic COST 231 model is likely to be overly optimistic.

In both cases prediction accuracy can be significantly improved with careful attention to area-specificmodel tuning prior to planning the built network.



Best Server with Building Clutter

This plot shows best server coverage based on predicted signal strength when accounting for buildingheights.



Service Coverage with Building Clutter

This plot shows those areas with predicted signal strength better than –75 dBm when accounting forbuilding heights.


Test site

UE or scannerGPS


Model Tuning

Almost all propagation modelling done for network planning is based on empirical models. In most casesthe basis will be a standard model such as COST 231, often with additional features to incorporate asmuch information as is possible from that which is available as background information in the tool itself.However, by definition an empirical model is set up only to copy a set of measurements taken in a limitedvariety of environmental conditions. In a different environment, particularly a built environment, wherebuilding styles and materials will differ significantly, the parameters (‘k’ values) in the model will beinappropriate. It is therefore necessary to tune the model to fit the environment in which it is to be used.

Tuning is performed by making direct comparisons between predicted signal levels and realmeasurements, typically carrier wave measurements of a test site. The measured values are thenimported into the planning tool and adjustments made to the model ‘k’ values of the chosen propagationmodel.



Example ‘k’ Values

The screen shot shows an example of the set of ‘k’ values available for model tuning in one of thepropagation models that form the core of the Atoll planning tool. These values are changed carefully toachieve the closest match possible between predicted values and measured values. Note that in thiscase other factors can also be adjusted such as the diffraction modelling approach and factors forconsideration of clutter characteristics.

Ideally model tuning should be performed using measurements and predictions in several different but‘typical’ environments in the planned area. It is possible to save multiple versions of the tuned model tobe used by planners in different environments. A basic example of this would be to have independentlytuned rural, suburban and dense urban versions of the model. However, different cities and differentregions of a country will exhibit different building styles and materials and consideration should be givento the possibility of independent tuning in different network areas.


SECTION 3

TRAFFIC CHARACTERIZATION



PDN Connectivity Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1

Traffic Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.2

EPS Bearer QoS Class Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.3

CQI Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.4

Example Atoll Tool – Factoring CQI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.5

Example Atoll Tool – Relating CQI to Radio Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.6

Device Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.7

Subscriber Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.8

Relating Services, Devices and Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.9

Area Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.10

Example Atoll Tool – Service Definition (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.11

Example Atoll Tool – Service Definition (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.12

Example Atoll Tool – Mobility Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.13

Example Atoll Tool – Terminal Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.14

Example Atoll Tool – User Profile Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.15

Example Atoll Tool – Environment Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.16

Example Atoll Tool – Traffic Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.17

CONTENTS

Traffic Characterization



outline the concept of the allocated resource in LTE as the PDN (Packet Data Network)

connectivity service

discuss different traffic types that may be carried over an LTE system and consider their

differing requirements

describe how QoS is defined for LTE service provision

explain how channel adaptation can be factored into traffic modelling for LTE systems

describe the impact of system design on the different possibilities for user access device

define potential classifications for varied user profiles that could be used for traffic modelling

in an LTE network

explain how service types, device types and user profiles can be related to offered traffic

distribution on the ground

describe how a traffic map can be created that reflects varied combinations of service,

device and user profiles

OBJECTIVES



PDN-GW

PDN Connectivity

Service

Evolved Packet System

EPS Bearer

Packet Data Network


PDN Connectivity Services

The EPS is designed to provide IP connectivity between a UE and a PDN (Packet Data Network). Theconnection provided to a UE (User Equipment) is referred to as a PCS (PDN Connectivity Service). Thisconsists of an EPS (Evolved Packet System) bearer that connects the UE to an Access Point in a PDN-GW (PDN Gateway) and traverses both the E-UTRAN (Evolved UMTS Terrestrial Radio AccessNetwork) and the EPC (Evolved Packet Core). The PDN-GW routes traffic between the EPS bearer andthe external PDN.

The EPS bearer, in turn, carries one or more SDF (Service Data Flow) between the UE and external dataservices.

If a UE requires additional connectivity that is only available via a different PDN-GW Access Point, thenadditional PDN Connectivity Services may be established in parallel.

Further Reading: 3GPP TS 23.401:4.7.1


LTE Traffic

Real time Non real time

VoiceVideo telephonyVideo conference

Content downloadVideo on demandBroadcast videoVPN accessMessagingFTPInternet access

Web pagesFlickrYoutubeBBC iPlayerFacebookTwitteriTunesRSS FeedsNews/online magazinesOnline bankingE-mailSkypeSecond LifeGoogle EarthRetailOnline backupCloud computing

Fixed Mobile


Traffic Types

2G cellular systems were planned to work with a very clearly defined and relatively simple service profile.Essentially, they had to be planned for acceptable voice operation across the complete coverage area.The development of 2.5G and 3G systems facilitated the provision of packet data services, but largelythese are provided as ‘best effort’ only with voice and simple messaging remaining the dominant capacitydemand.

The advent of HSPA (High Speed Packet Access) combined with all-inclusive data tariffs makes asignificant difference in the voice-data capacity balance. Once these things are in place the cellularnetwork begins to take on new roles. In particular it can be seen as a viable IP-CAN (IP ConnectivityAccess Network) and thus under the right conditions can become a competitor for Wi-Fi access pointsand even fixed broadband. Additionally, whilst there remains a need to support real time voice services inLTE, there is no longer a dedicated resource on the air interface. This means that all traffic is now carriedas packet data and operators are forced to confront the issue of differentiated QoS in an All-IP network.

At the same time the concept of simple Internet access has also changed. Formerly this could have beenconsidered as a single service that enabled basic web browsing. However, the Internet has now evolvedinto a very complex array of sophisticated service delivery platforms with widely diverse QoSrequirements. The diagram includes just a few examples of the kinds of service delivery Web 2.0functionality that users may expect to access via LTE.

An operator must identify, plan coverage and dimension sites in order that all these services are cateredfor in a way that they consider appropriate for their target subscriber base.


QCI Resource Type Priority

Packet Delay

Budget

Packet Error Loss

Rate Example Services

1 2 100 ms 10-2 Conversational voice

2 4 150 ms 10-3 Conversational voice (live streaming)

3 3 50 ms 10-3 Real time gaming

4 5 300 ms 10-6 Non-conversational voice (buffered streaming)

5 1 100 ms 10-6 IMS signalling

Video (buffered streaming)TCP-based (e.g. www, e-mail, chat, ftp, p2p,

file sharing, progressive video)

7 7 100 ms 10-3 Voice, video (live streaming), interactive gaming

8 8 Video (buffered streaming)TCP-based (e.g. www, e-mail, chat, ftp,

p2p,file sharing, progressive video) 9 9

GBR

Non-GBR

6 6 300 ms 10-6

300ms 10-6


EPS Bearer QoS Class Identifiers

In order that common levels of QoS can be provided in different operators’ networks the 3GPP havedefined a limited set of QoS levels that are therefore standardized for all operators. Each QoS level isidentified with a QCI (QoS Class Identifier) value. The QoS targets for each QCI value are shown in thetable in the diagram. It can be seen that there is a broad division between GBR (Guaranteed Bit Rate)and non-GBR services. There are also targets for the delay budget and packet loss rate. Additionally,each QCI is allocated a priority level. This is used for prioritizing resource allocations at the eNB.

Collectively, the parameters associated with each QCI determine the layer 2 and physical layerconfigurations that are used on the air interface. For example, a GBR service with low delayrequirements would make use of the unacknowledged mode of RLC, while a non-GBR service with morerelaxed delay requirement but low packet loss tolerance would use the acknowledged mode of RLC.

The 3GPP have also provided guidance on the kind of services applicable to each QCI. It can be seenthat in several cases the same or similar services are associated with more than one QCI. This is to allowfor the possible differentiation of services as ‘standard’ and ‘premium’.

While the radio network planning tool will not emulate the effects of the complete LTE system someconsideration must be given to the prioritization of different traffic types. The table in this diagram, whichis taken from the 3GPP standards, provides some guidance as to how to prioritize service types forsimulations in the planning tool.

Further Reading: 3GPP TS 23.203


Efficiency(bits/symbol)

0 No TX ... ... 1 QPSK 0.076 0.15232 QPSK 0.12 0.23443 QPSK 0.19 0.3774 QPSK 0.3 0.60165 QPSK 0.44 0.8776 QPSK 0.59 1.17587 16QAM 0.37 1.47668 16QAM 0.48 1.91419 16QAM 0.6 2.4063

10 64QAM 0.45 2.730511 64QAM 0.55 3.322312 64QAM 0.65 3.902313 64QAM 0.75 4.523414 64QAM 0.85 5.115215 64QAM 0.93 5.5547

CQI Index Modulation Approx. code

rate

Downlink channel adaptation based on

UE CQI reporting

Uplink channel adaptation based on eNB measurements of UL data

transmissions and SRS if requested


CQI Reporting

The table in the diagram (taken from the 3GPP standards), shows how the CQI values are interpreted asmodulation and coding schemes. The table is also useful for estimating the likely physical layerthroughput in a given radio configuration.

The action of link adaptation must therefore be reflected in the planning tool if it is to be able to indicatecapacity and reliability in the network plan.




Example Atoll Tool – Factoring CQI

This diagram shows how the CQI values used for LTE link adaptation are integrated into the Atoll tool. Ascan be seen, the values used are referred to as radio bearers and the values are based on those definedby the 3GPP standards; although they can be modified.

These values are used by the tool for estimation of link performance in terms of throughput once it hascalculated the specific channel conditions. Modification of this set would be required if either theequipment vendor or the operator chose to implement only a subset of these configurations in the builtnetwork.



Example Atoll Tool – Relating CQI to Radio Conditions

Once the CQI (radio bearers in Atoll) options are defined the tool needs to understand how they areapplied in any given calculated channel condition. For Atoll this relationship is defined as part of the LTEequipment description. The diagram shows how this is defined for both mobility states and for the radiobearer options. As can be seen, the table enables the tool to estimate which radio bearer would beselected in given variations of mobility and signal quality. The table also enables the estimation ofBER/BLER performance given channel quality and mobility.


Home E-mail Web

Meet me there at 5:00

LTE Device Types

Embedded laptops

Embedded netbooks

Fixed Internet access

Data dongles

PDAs

Mobile phones

Navigation/traffic avoidance

devices

Multimedia phones

Mobility


Device Types

The multimedia-multiservice nature of LTE means that there is considerable variation in device types thatmay be used to access the network. The diagram shows some examples, but the important considerationfor the network planner is how the radio capabilities of device types affect the performance of the radiolink. For example, many subscribers use data dongles to adapt their laptops or netbooks for dataconnectivity via LTE. However, when such devices contain embedded LTE equipment they may havemore transmit power capability, higher antenna gain, improved sensitivity or MIMO capability.

A more extreme example would be a fixed access terminal which will have a high gain antenna and islikely to be installed in a position providing line of sight or near line of sight for the transmission path tothe eNB. This makes a very significant difference to the performance of the radio link and hence to theservices available.

The device type may also affect the amount or nature of data transfer activity. Again the fixed terminal isa good example where, unlike mobile devices, it is likely to remain connected all the time and subscribersare more likely to make use of data-hungry services such as video on demand or online backup.

A final consideration that may be related to device type, and that will have a significant effect on radio linkperformance, is mobility. Ideally some kind of categorization should be included for this in the planningprocess.


GeographicCountry Region Urbanization Climate

DemographicAge Gender Family Family life cycle

Education Income OccupationSocioeconomic Religion Nationality Race

PsychographicPersonality Lifestyle Attitude Values

TechnographicMotivation Attitude Usage pattern Lifestyle


Subscriber Profiles

In addition to service types, an operator must also consider subscriber profiles. It is very clear thatdifferent subscriber profiles will focus on different service mixes. Once again, it is important that as muchinformation as possible in this regard is considered for both the general identification of service provisionrequirements and prioritization of specific service planning goals.

As a minimum, an estimation of the relative proportions of each user type within the complete subscriberbase should be factored into the generation of traffic maps. Ideally, the proportions should be adjustedfor different regions or even for different clutter types. This will be of great help in the planning stage toensure approximate load balancing between cells and sites, thus reducing the optimization effort requiredat a later date. In an extreme case the physical network architecture could be impacted by the expectedservice profiles of users in a particular area.


Service A

Service B

Service C

Service n

Service typeMin bit rateMax delay(mapped QCI)

Device type A

Device type B

Device type C

Device type n

Supported configsTX powerAntenna gainRX sensitivityMIMO support

User type A

User type B

User type C

User type n

GeographicDemographicPsychographicTechnographic


Relating Services, Devices and Users

In a multiservice-multimedia system offered traffic can be classified by service type, device type and usertype. Each of these factors has an impact of the provision of the service and its potential performanceonce a resource is allocated. Thus when traffic is modelled in the planning tool some indication must begiven about the mix of potential service, device and user types.

Ideally, the planner would try to model as accurately as possible all possible combinations, but clearlythis could be very time consuming and, unless the market intelligence was very accurate, could givemisleading results. Therefore, the number of types in each category and the number of potentialcombinations is generally limited to a relatively small number, but with the aim that it is representative ofa balance between the most common and the most demanding possibilities.



Area Classification

Once service applicability has been determined in terms of user profiles and terminal types it is thennecessary to build a traffic map relating these factors to geographical areas within the network coverage.In most cases this will be based on clutter categories. Ultimately this will enable the planning tool todetermine the offered traffic density in each cell coverage area. Once this is done a number of networksimulation options may be available to the cell planner or optimizer. This will range from simple loaddetermination for coverage adjustment and load balancing to a more time consuming static simulationapproach.

Ideally, special traffic cases should also be factored into the overall traffic map. Common examples ofthis will be sports arenas, railway stations, airports and shopping centres.



Example Atoll Tool – Service Definition (1)

The diagram shows examples of how services are defined in the Atoll planning tool. In this case an FTP(File Transfer Protocol) download service and a Web browsing service are defined. However, the cellplanner must recognize that these are only intended to be representative of very wide range of servicepossibilities that users may access via an LTE-based bearer. Thus while the web browsing service isintended to represent more conventional page downloading and reading activities, the FTP service isintended to cover a large number of widely differentiated services that may be more bandwidth hungry.



Example Atoll Tool – Service Definition (2)

This diagram shows how real time services are defined in the Atoll planning tool. In this case both videoconferencing and VoIP have been defined. Note that they are given prioritization for schedulingsimulation.



Example Atoll Tool – Mobility Definition

The Atoll tool also allows different mobility characteristics to be applied to service/UE/user combinations.In this example four mobility states are defined: pedestrian (3 kph), 50 kph and 90 kph to be used for LTEmobiles and fixed (0 kph) to be used for fixed radio access terminals.



Example Atoll Tool – Terminal Definition

It may be important to define a number of different terminal types. Even if at rollout it is envisaged thatmost users will be equipped with either mobiles or data cards/dongles with similar capabilities, anoperator may wish to plan for other terminal capabilities so that they can be integrated into the builtnetwork when required without the requirement for extensive optimization work.

In this example case a standard mobile terminal has been defined, which is assumed to cover both datacard/dongles and mobile devices, as well as a 2x2 MIMO equipped device allowing the operator toevaluate the benefits of this feature for future implementation.

Note that in the Atoll tool this window provides only basic radio capability definition. More detaileddefinition is defined in the specification of the selected ‘LTE Equipment’ value, in this case ‘Default LTEEquipment’.



Example Atoll Tool – User Profile Definition

The diagram shows an example of user profile definition. This definition creates the association betweena service and a UE terminal type. In addition, the usage profile is then added for each user type. In thiscase only two user types are defined, a business user and a standard user.



Example Atoll Tool – Environment Definition

Once services, mobility options, terminal types and user profiles are defined they must be mapped to theground as a traffic map. There are a number of options in the Atoll planning tool for doing this. Theexample shown involves the definition of ‘Environment’ types. An environment in this context means adescription of a particular proportion of user/terminal/service combinations in each clutter category. Thisinformation can then be used to define the user distribution in a traffic map.



Example Atoll Tool – Traffic Map

There are many ways that a traffic map can be generated. These include the import of live traffic datafrom a network, the conversion of a traffic map already defined for 2G or 3G network planning (whichmay be based on network statistics) or the manual definition of different service/user/terminal/mobilitydensities for each clutter category. However, the example shows projected LTE traffic generated from thedefinition of environments within a polygon drawn on the map.


SECTION 4

LTE CELL PARAMETERS



Basic Radio Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1

LTE Specific Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.2

Physical Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.3

Type 1 Frame Structure (FDD Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.4

Type 2 Frame Structure (TDD Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.5

Resource Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.6

Downlink Reference Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.7

Uplink Demodulation Reference Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.8

Summary of the Downlink Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.9

Downlink Structure with MIMO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.10

MIMO Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.11

Example Atoll Tool – MIMO Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.12

MIMO Options for LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.13

Summary of the Uplink Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.14

Other LTE Planned Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.15

Example Atoll Tool – Transmitter Templates (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.16



CONTENTS

LTE Cell Parameters



identify the standard radio parameters that need to be defined for an LTE site in a typical

planning tool

list the key physical channels on the LTE air interface and outline their functions

describe the frame structures used for LTE FDD mode and for LTE TDD mode

identify those features of the frame structure that need to be defined for LTE cells in a

typical planning tool

describe the key control channel structures used for the LTE air interface

identify those features of the control channel structures that need to be defined for LTE cells

in a typical planning tool

describe how receive diversity, transmit diversity and MIMO capabilities can be defined for

LTE cells in a typical planning tool

identify the requirements and options for physical layer cell ID, frequency allocation and

neighbour cell lists that need to be applied to LTE cells in a typical planning tool

OBJECTIVES

LTE Cell Parameters



Basic Radio Parameters

For an LTE plan the setting of basic site and cell parameters is similar to any other cellular technology. Atthe start of the planning process some form of standardized site template is defined in the tool. This willbe used as the standard site build in terms of the eNB equipment type, the standard RF componentdesign and the standard antenna configuration. The cell planner may have rights to change some or allof these factors on a specific planned site.

It is normal practice to define a range of standard site templates to increase efficiency in the planningprocess and to reduce site variability within the final plan. Thus there are likely to be standard buildsdefined for urban, suburban and rural areas; possibly also differentiating between macro and micro sitetypes. Additionally, many sites will need to be configured for inter-technology or inter-operator sitesharing. In some cases this will impact the design of the RF components, for example the need to includemultiport duplexers, filters or isolators. Site sharing may also restrict antenna options.

LTE Cell Parameters

FDD/TDD

Frequency band

Channel bandwidth

Frequency allocation

Cyclic prefix

UL/DL switching point (TDD only)

Control channel configuration

Channel Power offsets

Cell ID

LTE-Specific ParameterseNB


LTE Specific Parameters

In addition to the standard cell parameters that are common with any other cellular technology there area number of LTE-specific parameters that will be required if full simulation of an LTE system is to beperformed.

However, it should be noted that simple coverage planning could be achieved without resort to theseparameters. If such a strategy was adopted it would be necessary first to calculate representative linkbudgets for planned services. Link balancing would then need to be performed to arrive at one or moreminimum downlink receive signal strength requirements. Coverage planning on this basis would thenprovide some indication of where each service would or would not be available. Nevertheless, such anapproach would not give any indication about how interference levels, traffic distribution or optimalfeatures such as MIMO would affect the overall system performance.


Physical signalsPSS/SSS

Reference signals

Physical layer

MACBCCH PCCH CCCH DCCH DTCH

BCH PCH RACH DL-SCH UL-SCH

PBCH PDCCH PHICH PCFICH PRACHPUCCH PDSCH PUSCH

MAC Control


Physical Channels

The physical layer involves the transmission and reception of a series of physical channels and physicalsignals. The physical signals relate to the transmission of reference signals, the PSS (PrimarySynchronization Signal) and the SSS (Secondary Synchronization Signal).

The PBCH (Physical Broadcast Channel) carries the periodic downlink broadcast of the RRC (RadioResource Control) MasterInformationBlock message. Note that system information from BCCH(Broadcast Control Channel) is scheduled for transmission in the PDSCH (Physical Downlink SharedChannel).

The PDCCH (Physical Downlink Control Channel) carries no higher layer information and is used forscheduling uplink and downlink resources. Scheduling decisions, however, are the responsibility of theMAC (Medium Access Control) layer; therefore the scheduling information carried in the PDCCH isprovided by MAC. Similarly the PUCCH (Physical Uplink Control Channel) is used to carry resourcerequests from UEs that will need to be processed by MAC.

The PHICH (Physical Hybrid ARQ Indicator Channel) is used for downlink ACK/NACK of uplinktransmissions from UEs in the PUSCH (Physical Uplink Shared Channel). It is a shared channel anduses a form of code multiplexing to provide multiple ACK/NACK responses.

The PCFICH (Physical Control Format Indicator Channel) is used to indicate how much resource in asubframe is reserved for the downlink control channels. It may be either one, two or three of the firstsymbols in the first slot in the subframe.

The PRACH (Physical Random Access Channel) is used for the uplink transmission of preambles as partof the random access procedure.

The PDSCH and the PUSCH are the main scheduled resources on the cell. They are used for thetransport of all higher layer information including RRC signalling, service related signalling and usertraffic. The only exception is the system information in PBCH.

Further Reading: 3GPP TS 36.213, 36.211, 36.300

LTE Cell Parameters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190

Frame – 10 ms

Slot – 0.5 ms

0 1 2 3 4 5 6

Subframe – 1 ms

Normal cyclic prefix(c. 5 μs)

0 1 2 3 4 5 6

OFDM SymbolCP

CP

00 1 2 3 4 5 0 1 2 3 4 5

Extended cyclic prefix(c. 17 μs)

OFDM SymbolCP

CP


Type 1 Frame Structure (FDD Mode)

There are two basic frame types employed in E-UTRA, which are common to both uplink and downlink.Type 1 frames are employed for FDD full- and half-duplex systems, while Type 2 frames are reserved forTDD operation only. Frame type will need to be configured for each cell in the planning tool, however thiswill be implicit when either TDD or FDD mode is set.

The Type 1 frame duration is 10 ms and it is divided into 20 slots, each of 0.5 ms duration. Moresignificantly however, for most information transmission, two slots are combined to form a subframe.Thus subframe duration is 1 ms, which corresponds to the TTI (Transmission Time Interval) for LTE.

Type 1 slots contain either seven or six symbols, depending upon which cyclic prefix length is in use. Ingeneral, the longer cyclic prefix will be used on cells likely to show more extreme time dispersion. Thecyclic prefix length will need to be set for each cell in the planning tool.

Scheduling occurs across a subframe period. Up to the first three symbols in the first slot of eachsubframe can be defined as a ‘control region’ carrying control and scheduling messages. The remainingsymbols of the first and all symbols in the second slot within the subframe are then available for usertraffic.

Further Reading: 3GPP TS 36.211


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190

Frame – 10 ms

Slot – 0.5 msHalf-frame – 5 ms

2 3 4 5 7 8 90

Subframe DL/UL switch point

(optional)DL/UL switch point

(mandatory)

0 1 2 3 4 5 6

Subframe – 1 ms

0 1 2 3 4 5 6

or

00 1 2 3 4 5 0 1 2 3 4 5

UL/DLConfig.

5 ms (half-frame) switching

0 D U1 D U2 D U6 D U

10 ms (full-frame) switching3 U4 D U5 D U

UL/DL Switching Options

D

DDDD

DD

D

DDD

DD

D

D

DD

DDD

DDD

D

DD

DD

UD

UD

U

U

U

U

U

U

UUUU

UU

U

U


Type 2 Frame Structure (TDD Mode)

Type 2 frames are used in TDD configured systems. They share the 10 ms frame structure and 1 mssubframe of type 1 frames but an additional demarcation known as a half-frame is also defined.

Each half-frame carries five subframes, the second of which is used for the TDD downlink to uplinkswitching point. The switching point in the first half-frame is mandatory, but the second is optional. Thusselection of either half-frame switching or full-frame switching will be a planning tool configurationparameter.

The diagram also shows the options for allocation of slots for either uplink or downlink use. This is usedto adjust the relative uplink/downlink capacity and will also be a planning tool configuration parameter.

Further Reading: 3GPP TS 36.211:4

LTE Cell Parameters

Subcarrier 1

Subcarrier 12

Resource block

1 ms subframe (2 slots)

Resource element

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6


Resource Blocks

A resource block consists of 12 subcarriers for one slot period. In both the uplink and downlink directions,12 subcarriers correspond to 180 kHz of bandwidth. The minimum possible capacity allocation period isthe TTI of 1 ms. This equates to the allocation of two consecutive resource blocks. Additionally, the sumof all the resource blocks in a single slot period is known as the resource grid.

The minimum definable capacity unit is the resource element, which is one subcarrier during one symbolperiod. Within each resource grid the resource elements that will be carrying reference signals areassigned first; the remaining elements are then available to have user data or control mapped to them.

In data transfer terms, one resource element is the equivalent of one modulation symbol on a subcarrier,so if QPSK modulation was being employed, one resource element would be equal to two bits, with16QAM four bits and with 64QAM six bits of transferred data.

If MIMO is employed on the downlink then separate resource grids are created for each antenna port –each port maps to a different MIMO stream.



0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2R0 5 6 1 2 5 6

R0

R0

R0

R0

R0

R0

R0

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

0

0

4

4

0

0

4

4

SISO (Normal CP)

Cell-specific downlink reference signals

2x2 MIMO (Normal CP)

Antennaport 0

Antennaport 1

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2R0 5 6 1 2 5 6

R0

R0

R0

R0

R0

R0

R0

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

0 1 2 4 5 6 0 1 2 4 5 6

0 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3

3 3R1

R1

R1

R1

R1

R1

R1

R1


Downlink Reference Signals

In any mobile radio system it is necessary to provide mobile devices with a means of measuring andmonitoring the strength and quality of the signal they receive and of calibrating their own output to ensurethat the correct frequencies are being employed.

LTE employs a physical reference signal, embedded in the main body of the transmitted signal to providean opportunity for channel estimation and frequency calibration on the downlink. On the downlink, threetypes of downlink reference signals are currently defined: cell-specific reference signals, MBSFN(Multicast/Broadcast Single Frequency Network) reference signals, associated with MBSFNtransmission, and UE-specific reference signals. In most circumstances only the first of these referencesignal types will be used. The reference signal takes the form of a modulated time and frequency shift ofsymbols, generated from a Gold code of length 231–1.

Reference signal symbols are inserted into the transmitted resource grid following a predeterminedsequence as shown in the diagram for cell-specific SISO (Single Input Single Output) and 2x2 MIMO(Multiple Input Multiple Output) antenna arrangements and the normal CP. Modifications of this patternare also defined for 4x4 MIMO operation, for use of the extended CP and for MBSFN operation.

Cell-specific reference signals, as well as providing a ‘known signal’ upon which to base channelestimations, are modulated to identify the cell to which they belong. The sequence is related to the cell’sphysical layer identity in the set of 504 options.

Reference signals may have an applied power-boost over data symbols of up to 6 dB.

The cell’s physical layer identity and any power offset associated with the reference signal will beconfiguration parameters in a cell planning tool.

Further Reading: 3GPP TS 36.211:6.10, 36.300

LTE Cell Parameters

0 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 6

0 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 60 1 2 DRS 4 5 6


Uplink Demodulation Reference Signals

There are two types of reference signal used in the uplink, known as DRS (Demodulation ReferenceSignals) and SRS (Sounding Reference Signals). DRS symbols are multiplexed with user data andcontrol transmissions. DRSs provide the receiving eNB with a ‘known signal’ element upon which toperform channel estimations and from which it can calculate timing adjustments.

For the PUSCH one DRS symbol is transmitted per slot in the 4th symbol position (symbol numberthree). In the PUCCH there may be either two or three DRS symbols per slot dependent on configuration(not shown).

Because DRS symbols are multiplexed with user data they will always occupy the same allocatedbandwidth as the user data. This means that the length of the reference symbol sequence needs to bethe same as the number of allocated subcarriers in the transmission bandwidth (and always a multiple of12). For each possible bandwidth allocation a number of base DRS sequences are defined. This isorganised such that there are 30 base sequences for one, two and three resource block allocations andmore than 30, dependent on specific bandwidth, for allocations of more than three resource blocks. Thusthere are multiple DRS sequences in many different lengths. They are organised into 30 ‘sequencegroups’. Each sequence group contains one base DRS sequence of each length up to that suitable forbandwidth allocations up to five resource blocks, and two base DRS sequences for bandwidth allocationsabove five resource blocks.

Each cell is allocated one sequence group. In addition, multiple orthogonal DRS sequences are thencreated from a single base sequence using cyclic shifts; 12 are available for each base sequence. Theseorthogonal sequences are used to multiplex signals from different UEs in the same cell.

It is unlikely that specific configuration of parameters relating to DRS will need to be set in a planningtool.



FrameSubframeSlot

0 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2R0 5 6 1 2 5 6

R0

R0

R0

R0

R0

R0

R0

3 33 33 33 33 33 33 33 33 33 33 33 3

0 0

4 4

0 0

4 4

Downlink control channels configured for one, two or three

slots(PDCCH + PHICH + PCFICH)

PSS/SSS Primary and Secondary Synchronization Signals

PBCH Physical Broadcast Control Channel

PDSCH Physical Downlink Shared Channel


Summary of the Downlink Structure

The diagram shows an example of a populated downlink FDD frame using the normal CP andimplemented in a 5 MHz bandwidth channel.

The PBCH is transmitted during subframe 0 of each 10 ms frame and occupies the centremost sixresource blocks. Alongside this and also in the sixth subframe in the frame are the primary andsecondary synchronization signals. Reference signal positions for two resource blocks within a singlesubframe are shown. All these resource allocations are fixed and therefore need no special attention in aplanning tool. However, the PSS and SSS are related to the cell’s physical layer ID, which is configuredin the tool. Additionally, it is possible that power offsets could be included for these channels.

The diagram also shows the space allocated for downlink control channels, which includes PDCCH,PCFICH and PHICH resources. A UE will be required to monitor some proportion of this dependent onthe connectivity state and the cell configuration. Crucially, this is a variable resource that may occupyone, two or three symbol periods at the start of each subframe. The setting will affect available capacityand therefore it will be a parameter that needs setting in the planning tool.

The remainder of the allocation space will be used for scheduled downlink transmission in the PDSCH.This includes common control signalling (system information and paging), dedicated control signallingand traffic packets.

Further Reading: 3GPP TS 36.211, 36.300

LTE Cell Parameters

0 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 6

R1

R1

R1

R1

3 33 33 33 33 33 33 33 33 33 33 33 3

Antenna port 1 Antenna port 1R1

R1

R1

R1

FrameSubframeSlot

0 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2 5 6 1 2 5 60 1 2 4 5 6 0 1 2 4 5 60 1 2 4 5 6 0 1 2 4 5 6

1 2R0 5 6 1 2 5 6

R0

R0

R0

R0

R0

R0

R0

3 33 33 33 33 33 33 33 33 33 33 33 3

Antenna port 0

Antenna port 0


Downlink Structure with MIMO

The diagram shows an example of a downlink FDD frame using the normal CP with 2x2 MIMOconfigured. Again it is based on a 5 MHz bandwidth channel.

Reference signal position for two resource blocks within a single subframe are shown for both antennaports in the 2x2 MIMO system. Note that control allocation on the second antenna port is the same asthat on the first port. This means that for MIMO implementations planning tool parameter setting is littledifferent than for non-MIMO configurations. However, LTE does offer a number of different MIMOconfigurations and the selected configuration will need to be set. The planning tool will also requireinformation about how MIMO will impact channel performance.



Data stream

mapping

Pre-coding matrix

Signal generation

MIMO decoding

and channel estimation

Stream 1

Stream 2

Layer 1

Layer 2

Power weightings and beamforming

Feedback

2x2 MIMO or Rank 2 4x4 MIMO or Rank 4


MIMO Concept

MIMO antenna arrays offer significant performance improvements over conventional single antennaconfigurations.

The technique involves placing several uncorrelated antennas at both the receiving and transmitting endsof the communication link. If there are four uncorrelated antennas at the transmitter and a further fouruncorrelated antennas at the receiver, then there will be 16 possible direct radio paths between thetransmitter and the receiver. Each of these is open to multipath effects creating even more radio pathsbetween the transmitter and the receiver. These radio paths can then be constructively combined, thusproducing micro diversity gain at the receiver.

Since the receiver can distinguish between the various uncorrelated antennas, it is possible to transmitdifferent data streams in different paths. The stream applied to each antenna can be referred to as alayer and the number of antennas available at the transmitter and receiver can be referred to as rank. Forexample a system operating with a 4x4 MIMO antenna array can be described as having four layers andbeing of rank four. The way in which data streams are mapped to layers will change the specific benefitsoffered by a particular MIMO implementation, and the specification of this is an important part of systemdesign. Pre-coding may also be used to improve the MIMO system performance. Pre-coding may beadaptive and as such would be based on some source of channel estimation. This could be derived atthe transmission or the reception end of the link.

It is relatively easy to mount antennas on the base station in an uncorrelated manner. For a 2x2 MIMOarray a single cross-polar panel could be used. A 4x4 MIMO array would require two cross-polar panelswith suitable special separation. This is harder to achieve in a mobile. However, as for the base station2x2 MIMO could be achieved with cross polarization, but this could result in some undesirable directivityin the antenna.

LTE Cell Parameters


Example Atoll Tool – MIMO Performance

The diagram shows an example of how the gain from MIMO options can be reflected in LTE systemperformance simulations. In this case the planning tool applies gains as defined for differing channelconditions, radio bearers (CQI indications) and mobility states as determined appropriate by the planner.


Transmit Diversity BeamformingClosed loop with PMI feedback

SU-MIMO (ranks up to 4) MU-MIMO (virtual MIMO)


MIMO Options for LTE

In its first release LTE is specified with several options for SU-MIMO (Single User MIMO) implementationand a more limited option for MU-MIMO (Multi User MIMO) operation. The specifications includedescriptions of operation up to 4x4 MIMO.

The simplest option is not MIMO as such but uses the multi antenna array at an eNB to provide transmitdiversity. The standards allow configuration with up to four antennas at the base station. It is likely thatcross-polar antennas would be used as part of the antenna array so a two-antenna array could beimplemented using a single cross-polar panel, with a four-antenna array requiring two cross-polar panels.Transmit diversity involves the transmission of a single data stream to a single UE, but makes use of thespatial diversity offered by the antenna array. This can increase channel throughput or increase cellrange.

There are also two beamforming options available. The two options for this are a closed loop mode,which involves feedback of PMI (Pre-coding Matrix Indicators) from the UE, and an open loop mode,which involves the transmission of UE-specific reference signals and the eNB basing the pre-coding forbeamforming on uplink measurements.

Full SU-MIMO configurations are available in LTE in the downlink direction up to 4x4. However, amaximum of two data streams is used, even when four antenna ports are available. In SU-MIMO the UEcan also be configured to provide feedback indicating the configuration that the UE calculates will givethe best performance.

In the first release of the LTE specification there is only a limited implementation of MU-MIMO specified.It is applicable in the uplink direction and allows two UEs to use the same time-frequency resource withinone cell.

Further Reading: 3GPP TS 36.211:6.3.3, 6.3.4, 36.213:7.1

LTE Cell Parameters

Frame

SubframeSlot

0 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 60 1 2 DRS 4 5 6 0 1 2 DRS 4 5 6

Configured for one, two or three RBs at the edges of the channel

PUSCH Physical Uplink Shared Channel

PUCCH Physical Uplink Control Channel


Summary of the Uplink Structure

The diagram shows an example of a populated uplink FDD frame using the normal CP and implementedin a 5 MHz bandwidth channel. The overall uplink frame structure is simpler than that employed by thedownlink.

Symbol three in each slot carries the uplink demodulation reference signal, leaving the other six symbolsavailable to carry traffic.

A configurable number of outer resource blocks can be set aside to carry PUCCH messages. Thenumber of resource blocks used for PUCCH in this way will therefore need to be set in the cellconfiguration for the planning tool.

PRACH resources are included in some of the remaining resource blocks as indicated to the UE insystem information. Since the tool will be limited to static simulation it is unlikely that any settings forPRACH operation need to be configured in the planning tool.



Neighbour List(LTE intra-freq, LTE inter-freq, UMTS, other technologies?)Cell 1: N-cells = (N1, N2, ... Nn)Cell 2: N-cells = (N1, N2, ... Nn)Cell 3: N-cells = (N1, N2, ... Nn)

Physical Layer ID(one of 504 in 168 groups of 3)Cell 1: CID = ?Cell 2: CID = ?Cell 3: CID = ?

Frequency AssignmentCell 1: EARFCN = ?Cell 2: EARFCN = ?Cell 3: EARFCN = ?

Cell 1

Cell 2

Cell 3


Other LTE Planned Parameters

The frequency allocation will be a very important planned parameter. However, whether there is afrequency plan or not depends on the strategy adopted by the particular licensed operator. Some LTEsystems may be operated as SFNs (Single Frequency Network). In such cases there is no frequencyplanning to be performed, but the frequency will still need allocating within the tool for interferenceestimation and network simulations. Even where a frequency planned multi-frequency strategy isadopted the number of planned frequencies is typically very small; often only three. Again for a basicplan there may be little frequency planning to do since all three frequencies can be simply added one toeach of the cells on each site. However, in a real non-ideal plan it is likely that some benefit may begained by applying an automatic frequency planning function after first generating an interference matrix.

A physical layer cell ID must be allocated to each cell. Although not specifically required for planning orsimulation they do need planning to avoid potential ambiguity of cell identity in the built network. Theplanning tool will offer a mechanism for applying cell IDs either manually or automatically. Since the3GPP standards define 504 cell IDs, organized into 168 groups of three, it is logical to apply one group toeach site.

Most tools also offer sophisticated mechanisms for both neighbour list creation and analysis. Typically,automatic neighbour cell creation is performed as a starting point and then fine tuned. Sanity checking isapplied manually. LTE cells will have intra-frequency neighbours, inter-frequency neighbours (except inSFNs) and UMTS neighbours. It may also be the case that neighbours are required for othertechnologies which could include GSM, WiMAX, CDMA2000 or Wi-Fi.

LTE Cell Parameters


Example Atoll Tool – Transmitter Templates (1)

The Atoll tool uses the term ‘transmitter’ to represent a cell and the term ‘station’ to represent a site or aneNB. The station template predefines the key characteristics of a typical site so that they can be addedquickly to a new plan. Once added however, any of the variables can be adjusted on a site-by-site or cell-by-cell basis.

Note that in this version of the tool uplink and downlink control channel capacity, and for TDD cells, thefull-frame/half-frame switching options are treated as global parameters. Thus they will be considered asset for a network and not adjustable on a site or cell basis.




The diagram shows an example of a station template for parameters that are predominantly standardRF-related settings. However, note that the number of available antenna ports is specified here, which isrelated to the receiver diversity, transmit diversity and MIMO capabilities of the cells.

LTE Cell Parameters

Provides for the inclusion of control channel power offsets

Indication of centre frequency (represents the EUARFCN)

One of 504, can be allocated manually or planned automatically

Selection defines both the band to be used and the channel bandwidth

Defines performance relationship and selection thresholds for radio bearers (CQI values)

Defines scheduling emulation for simulations

Sets UL/DL structure for TDD cells

Represents hardware and backhaul limits for the eNB equipment

Acceptability threshold for reference signals

Used to set receive diversity, transmit diversity and MIMO capabilities for the cell

Load constraints to be used for simulations

Provides default noise rise values for coverage estimation, but specific values for each cell can be calculated through simulation

Defines limits for automatic neighbour cell allocation



The diagram shows the LTE parameter options for the an example station template. Some explanation isgiven of the key LTE settings in the diagram.


SECTION 5

FREQUENCY PLANNING



Spectrum Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.1

Example – PCS1900 Operator LTE Spectrum Refarming . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.2

Example – US Operator with 700 MHz New Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.3

Example – IMT-2000 Operator LTE Spectrum Refarming . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.4

Example – GSM900/1800 Operator LTE Spectrum Refarming . . . . . . . . . . . . . . . . . . . . . . . .5.5

Example – European LTE New Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.6

Example – New European Spectrum at 800 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.7

Considerations for an SFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.8

Partial Frequency Reuse in an SFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.9

Limitations of Partial Frequency Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.10

Multi-frequency Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.11

Example Frequency Plan with Three Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.12

Example Frequency Plan with Six Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.13

SINR for a Three-Frequency Planned Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.14

SINR for a Six-Frequency Planned Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.15

SINR for an SFN Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.16

Downlink Throughput for a Three-Frequency Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.17

Downlink Throughput for a Six-Frequency Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.18

Downlink Throughput for an SFN (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.19

Downlink Throughput for an SFN (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.20

Histograms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.21

Downlink Throughput for Fixed Users in a 3FN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.22

Downlink Throughput for Fixed Users in an SFN (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.23

Downlink Throughput for Fixed Users in an SFN (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.24

Downlink Throughput for MIMO Users in a 3FN (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.25

Downlink Throughput for MIMO Users in a 3FN (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.26

Downlink Throughput for MIMO Users in an SFN (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.27

Downlink Throughput for MIMO Users in an SFN (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.28

CONTENTS

Frequency Planning



identify factors that are affected by the frequency allocation strategy for LTE cells

describe potential reframing options for existing GSM, UMTS and CDMA2000 spectrum

describe potential licence options for LTE operation in new spectrum

characterize network LTE network behaviour for single- and multi-frequency allocation

strategies

discuss the appropriateness of single- and multi-frequency allocation strategies for different

LTE network scenarios

interpret example planning tool studies of network performance for a range of frequency

allocation and frequency planning scenarios

OBJECTIVES

Frequency Planning


Which frequency band?

How much spectrum?

Build a single-frequency or multi-frequency

network?

What kind of services are required?

Mobile?Fixed?

Broadband access?Broadcast?

What coverage is needed?

Urban?Rural?Both?

Refarm existing spectrum?

Unused spectrum already available?

FDD or TDD?

Compatibility with legacy spectrum/technologies?

Consideration for compatibility for

roaming?

?


Spectrum Considerations

Unlike the 2G and 3G technologies that have preceded it, where spectrum usage is fairly constrained, forLTE there are many options for spectrum bands and spectrum division within a band that an operatormay have access to. The specific spectrum availability will depend on the country and region in which thenetwork will operate. Spectrum options will also be impacted by legacy technology choices. For example,an operator may already have licensed spectrum available in which LTE could be rolled out. This maybecause an older legacy technology can be progressively switched off, or because they have spectrumthat is currently unused.

In most cases however, an operator will need to consider purchasing new spectrum in which to operateLTE. Even when new spectrum is available, an operator will need to consider a number of operationoptions. For example, the spectrum block will be either FDD or TDD, there may be a number ofbandwidth options, they may want to provide for a mixture of fixed and mobile access and there may bespecific interference issues to think about resulting from other technologies in use or from geographicalfactors.

Frequency Planning

Reverse Forward

1850 1910 1930 1990Frequency MHz (E-UTRA Band 2)

A(15 MHz)

D(5 MHz)

B(15 MHz)

E(5 MHz)

F(5 MHz)

C(15 MHz)

GSM/GPRS/EDGE(5 MHz)

UMTS/HSPA(5 MHz)

LTE(5 MHz)

GSM/GPRS/EDGE(10 MHz)

LTE(5 MHz)

CDMA2000 1x/1xEV-DO(10 MHz)

LTE(5 MHz)

8 CDMA radio carriers

1 x 5 MHz (FDD)3 x 1.4 MHz (FDD)1 x 1.4 MHz plus 1 x 3 MHz (FDD)

50 GSM radio carriersGSM/UMTS

(5 MHz)LTE

(10 MHz)

CDMA2000 1x/1xEV-DO

LTE(10 MHz)

4 CDMA radio carriers

1 x 10 MHz (FDD)2 x 5 MHz (FDD)3 x 3 MHz (FDD)3 x 1.4 MHz plus 1 x 5 MHz (FDD)

25 GSM radiocarriers(viable?)

1 UMTS radiocarrier

1 UMTS radio carrier

25 GSM radiocarriers(viable?)


Example – PCS1900 Operator LTE Spectrum Refarming

The diagram shows some of the options open to an operator with one of the A,B or C blocks of PCS1900spectrum. This spectrum is used for both CDMA2000 operation and GSM/UMTS operation. Differentoperators will demarcate their spectrum in different ways but some possibilities are shown here.

A CDMA2000 operator could fairly comfortably refarm a 5 MHz frequency block to be made available forLTE. This would leave them with enough spectrum to continue operation of eight CDMA2000 radiocarriers, probably used with a mixture of 1x and 1xEV-DO configurations. The 5 MHz of LTE spectrumcould be used in a number of ways. For example the operator could build an SFN based on a 5 MHzbandwidth channel. Alternatively, the operator could chose to implement the spectrum as a three-frequency network based on 1.4 MHz channel bandwidth.

Another theoretical possibility is for the LTE frequency block to be utilized as two 5 MHz TDD channels,one in the reverse spectrum and one in the forward spectrum. However, this would probably result inunacceptable inter-technology or inter-operator interference, and in any case, would most likely be abreach of the licence conditions and is not specified in the LTE standards.

If a GSM operator were to refarm 5 MHz for LTE operation they would be left with sufficient spectrum tooperate 50 GSM radio carriers, which could offer a mixture of GSM and GPRS/EDGE connectivity. Theywould have the same options for LTE spectrum division. If, however, the operator has already refarmedspectrum for UMTS operation, which would demand at least one 5 MHz block, then the amount ofspectrum remaining for GSM operation would be sufficient for only 25 radio carriers. It is doubtfulwhether this amount of spectrum would be viable.

In both cases, as time passes more spectrum can be refarmed for legacy 2G and 3G for LTE operation.


Former analogueTV channels

Ch. 52

Ch. 53

Ch. 54

Ch. 55

Ch. 56

Ch. 57

Ch. 58

Ch. 59

Ch. 60

Ch. 61

Ch. 62

Ch. 63

Ch. 64

Ch. 65

Ch. 66

Ch. 67

Ch. 68

Ch. 69

Lower 700 MHz Band

(698 MHz-746 MHz)

Upper 700 MHz Band

(746 MHz-806 MHz)

A B E A B

C(11 MHz)

D Public safety C(11 MHz)

D Public safety

Divisionsfor FCCAuction 73


10 MHz(DL)

10 MHz(UL)

LTE Band 13


Example – US Operator with 700 MHz New Spectrum

Following TV digital switchover in the US the FCC (Federal Communication Commission) has made anumber of licences available in the 700 MHz band for use as broadband digital access. The diagramshows an example of use based on an operator with a licence to use the ‘C’ block of the Upper 700 MHzband.

As can be seen the C-block licence corresponds approximately with LTE Band 13. Thus the operator hasthe potential to use 10 MHz for LTE FDD operation. The bandwidth agnostic nature of LTE means thatthe operator has a number of frequency division and reuse options to consider. However, the chiefadvantage is the relatively low frequency, which significantly improves the achievable coverage from asingle site. This means the operator can take advantage of substantial infrastructure savings and at thesame time provide more reliable coverage, particularly in terms of in-building coverage.

Frequency Planning

TDD FDD SAT TDD FDD SATIMT-2000Spectrum

1885 1920 1980 2010 2025 2110 2170 2200

TDD FDD FDDTypicalEuropeanallocation

DECT

1900

5 MHz 15 MHzTypicalEuropeanlicence

15MHz

UMTS(10 MHz)

LTE(5 MHz)

UMTS(5 MHz)

LTE(10 MHz)

1 x 5 MHz (TDD)3 x 1.4 MHz (TDD)1 x 1.4 MHz plus 1 x 3 MHz (TDD)

1 x 5 MHz (FDD)3 x 1.4 MHz (FDD)1 x 1.4 MHz plus 1 x 3 MHz (FDD)

2 UMTS radio carriers

LTE(5 MHz)



Example – IMT-2000 Operator LTE Spectrum Refarming

The diagram shows some of the options open to an operator with a typical licence for Europeanoperation of UMTS in the IMT-2000 spectrum corresponding to LTE band 1. Such an operator couldrefarm a 5 MHz frequency block to be made available for LTE. This would leave them with enoughspectrum to continue operation of two UMTS FDD radio carrier pairs (including HSPA capability). The 5MHz of LTE spectrum could be used in a number of ways. For example the operator could build an SFNbased on a 5 MHz bandwidth channel. Alternatively, the operator could choose to implement thespectrum as a three-frequency network based on 1.4 MHz channel bandwidth.

There are many cases where European operators already hold licences for 5 MHz of TDD spectrum butare not currently making use of it. For operators in this position this spectrum could be made availableimmediately for LTE TDD operation. The only restriction may be limitation in the original licenceconditions.

Another important consideration is that most European UMTS operators will also have some GSM900and/or GSM1800 spectrum. Again, dependent on licence conditions, it may make more sense to try andrefarm GSM spectrum for LTE operation rather than UMTS spectrum.


E-GSM(10 MHz)

P-GSM(25 MHz)

E-GSM(10 MHz)

P-GSM(25 MHz)

E-GSM(5 MHz)

P-GSM(12.5 MHz)

LTE(5 MHz)

P-GSM(12.5 MHz)

E-GSM(5 MHz)

P-GSM(2.5 MHz)

LTE(10 MHz)

880 890 915 925 935 960

GSM1800(75 MHz)

GSM1800(75 MHz)

GSM1800(18 MHz)

GSM1800(8 MHz)

LTE(10 MHz)

1710 1785 1805 1880

GSM1800(3 MHz)

LTE(15 MHz)

TypicalEuropeanlicence

TypicalEuropeanlicence


Example – GSM900/1800 Operator LTE Spectrum Refarming

There are two chief advantages in a operator with both GSM and UMTS spectrum choosing to refarmGSM spectrum before they refarm UMTS spectrum. The first is that upgrading UMTS HSPA to HSPA+provides an economic way of achieving very similar performance to LTE, at least in the more restrictedbandwidths. Thus it may be difficult to make a business case for replacing UMTS with LTE in the shortterm. Secondly, the lower frequencies in the GSM spectrum, particularly GSM900, mean that LTEimplemented in these bands would require less capital expenditure and could provide more reliablecoverage.

Licences for GSM900/1800 vary very widely, but the diagram provides examples of some possibilities.These blocks of spectrum are completely covered by LTE bands eight and three.

Frequency Planning

Additional spectrumallocated as TDD from here

Additional spectrumallocated as TDD from here

2500 2570 2620 2690Nominally paired (FDD) Nominally paired (FDD)Nominally unpaired (TDD)

Potential organization for UK 2.6 GHz licences (blocks of 5 MHz)

FDD TDD FDD TDD

Operator 1 FDD + TDD

Operator 2 FDD + TDD

Operator 3 FDD

Operator 4 TDD

Operator 5 TDD

Guard

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38


Example – European LTE New Spectrum

In many countries new spectrum is becoming available in which LTE could be implemented. The largenumber of defined LTE bands and the fact that it is ‘bandwidth agnostic’ means that most new spectrumcan be considered for LTE operation.

The example shown in the diagram is for 190 MHz of spectrum that is likely to be offered in the UK. Theaim is to offer the spectrum in a very flexible way. It is divided into 5 MHz blocks that can be licensedindividually or in groups. There is also a nominal division between that which is offered for FDD use andthat which is offered for TDD use. The split shown at the top of the diagram is the minimum configurationfor TDD spectrum and corresponds exactly to LTE FDD band 7 and LTE TDD band 38. However, asshown in the diagram, it is envisaged that some of the FDD spectrum could be assigned for TDDoperation. This would be outside the scope of the current LTE specification, but this spectrum is likely tobe offered as being independent of technology choice.


61 2 3 4 561 2 3 4 5

791 796 801 806 811 816 821 832 837 842 847 852 857 862

UplinkDownlink1 MHz Guard

band

11 MHz Duplex gap

41 MHz Duplex distance

MHz


Example – New European Spectrum at 800 MHz

A total of 60 MHz will become available in the 800 MHz spectrum as a result of the ‘digital dividend’. It isanticipated that 6 x 5 MHz channels between 791 MHz – 821 MHz will be paired with 6 x 5 MHz channelsbetween 832 MHz – 862 MHz. There is a 1 MHz guard band starting at 790 MHz to control interferencewith neighbouring DTV. The duplex distance will be 41 MHz.

Frequency Planning

Best performance when both cells transmit at highest power

C1 I1I2C2

C1

I1

I2

C2

Best performance when one cell transmits at highest power and the other cell transmits nothing


Considerations for an SFN

For most cellular technologies single frequency reuse is not considered an option unless CDMA is in use.The reason for this is the high level of mutual interference that is assumed to result. However, it is not thecase that there will always be an unacceptably high level of interference between two adjacent cellsusing the same frequency allocation.

Consider two mobiles in two adjacent cells using the same frequency allocation. Both mobiles will bereceiving a wanted signal ‘C’ and a co-channel interfering signal ‘I’. When the mobiles are close to theirrespective serving cells there will be a large difference in the two signals that results in a strongly positivesignal to noise ratio. It can be shown that the best signal quality results from both cells transmitting higherdownlink powers. In this scenario good performance is achievable for both mobiles whilst maintaining avery spectrally efficient single-frequency reuse pattern.

As the mobiles move further from their respective serving cells and closer to the edge-of-cell area, thesignal to noise ratio degrades. Once they reach edge-of-cell there will be little difference between thewanted signal ‘C’ and the interfering signal ‘I’; i.e. the SNR will approach 0 dB. The result will be verypoor performance or loss of connection. However, it can be shown that the signal to noise ratio can beimproved with increasing difference between the respective cell transmit powers. The ideal situationwould be to switch one cell off while the other was transmitting maximum power. Such a workingcondition is not normally considered viable since one or other mobile would be denied service. However,an OFDMA based system can offer a compromise in terms of spectrum sharing.


C1

C2

X2 Interface(resource negotiation)

Full cell capacity

Full cell capacity

frequency

frequency frequency

Same frequency allocation to both cells


Partial Frequency Reuse in an SFN

When adjacent LTE eNBs are allocated the same frequency resource the scheduling can be coordinatedbetween them. This is organized such that for UEs on the edge of cell the selection of allocated RBs(Resource Block) will be selected from different parts of the available channel bandwidth. The exampleshown is based on 5 MHz bandwidth with 25 available RBs. Each eNB has the same channel frequencyand each has allocated five RBs to a UE on the edge of cell, however, the five allocated RBs are in adifferent part of the 5 MHz bandwidth. The remainder of each of the eNBs resource can be allocated toin-cell UEs in the normal way. Thus the full capacity is potentially available to each eNB with therestriction that only partial capacity is available to UEs in edge of cell areas.

This coordination can occur in two different ways. Firstly, the protocol used on the X2 interface, whichlinks eNBs, includes a facility for direct resource negotiation between the eNBs. However, it is optionalfor this functionality to be used. Even in the case where direct negotiation is not performed the selectionof allocated resource is dynamic, very frequent and based on channel quality assessment. Thus theeNBs will tend to schedule resources that show the lowest value of interference.

Coordination of resource allocation in this way at the edge-of-cell while allowing full resource allocationwithin the cell can be described as partial frequency reuse.

Frequency Planning


Limitations of Partial Frequency Reuse

In typical physical cell architecture involving three-cell sites it is important to remember that the termedge-of-cell is not only at the most distant points for the eNB. Edge-of-cell includes the areas of overlapbetween cells (or sectors) on the same eNB. These regions run from the edge of coverage back and upto the eNB site. When an SFN frequency allocation is used these intra-site overlap areas are potentiallysubject to very high levels of interference. In particular, because of the close proximity of UEs to the eNB,uplink interference from UEs served by adjacent cells may be even higher.

As seen in the diagram, the area within the nominal cell coverage in which un-negotiated full cell capacityis available for allocation to UEs is relatively small. It can also be seen that even in a regular andidealized coverage plan there is a need to coordinate resource allocation between up to three differentcells on three different eNBs. This means that while the peak bit rates achievable in the in-cell area maybe very high, the average throughput may be lower than for a frequency planned system using a lowerradio bandwidth.

Nevertheless, there are exceptions where the SFN partial frequency reuse strategy becomes veryattractive. The first is where LTE is being used to provide fixed wireless broadband access. In this casethe UEs can be assumed to have high gain directional antennas. The antenna gain provides significantisolation from adjacent cell interference and in some cases removes the need for resource negotiation.Thus cell-edge throughput can remain very high. The second exception is for the use of the moreadvanced forms of MIMO operation, particularly the options for beamforming and MU-MIMO.



Multi-frequency Networks

In an idealized three-frequency reuse pattern the complete resource bandwidth should be available in allareas of the cell without the need for resource negotiation between eNBs. However, for any given licencespectrum this will require subdivision to create the three different channels. The result will be reducedmaximum throughput, but more consistent performance across the cell area. In general the averagethroughput for the system will be higher than for an equivalent SFN approach.

Nevertheless, non-idealized plans may show different characteristics. There is still a strong likelihood thatadjacent reuse sectors will suffer from some interference.

Frequency Planning


Example Frequency Plan with Three Channels

The diagram shows a screenshot indicating the layout of a simple three-frequency plan. The plan isbased on LTE FDD band 1 with an assumed licence for 15 MHz of spectrum. The hypothetical operatorhas subdivided the band to create three 5 MHz bandwidth allocations. The channels have been addedmanually one to each sector in a geometrically repeating pattern on each eNB.

The same licence for 15 MHz of spectrum will also be studied when allocated as an SFN using a single15 MHz channel.



Example Frequency Plan with Six Channels

Further studies have been performed assuming a licence for 20 MHz of radio spectrum with which thehypothetical operator has created six channels each with 3 MHz bandwidth. The screen shot shows thefrequency plan.

Frequency Planning


SINR for a Three-Frequency Planned Network

The Atoll planning tool has been used to calculate the downlink SINR for the network when configured forthree frequencies of 5 MHz bandwidth. Note that over most of the ground within the focus zone the SINRis above 12 dB with some areas exceeding 25 dB.



SINR for a Six-Frequency Planned Network

The Atoll planning tool has been used to calculate the downlink SINR for the network when configured forsix frequencies of 3 MHz bandwidth. Note that over most of the ground within the focus zone the SINR isabove 20 dB.

Frequency Planning


SINR for an SFN Configuration

The Atoll planning tool has been used to calculate the downlink SINR for the network when configured fora single frequency of 15 MHz bandwidth. Note that the SINR is generally much lower than for frequencyplanned network configurations over almost all of the ground area.



Downlink Throughput for a Three-Frequency Network

This screen shot shows a study of DL (Downlink) RLC (Radio Link Control) throughput when the networkis configured with three frequencies. It can be seen that a rate in the region of 17 Mbit/s is achievedacross a significant proportion of the ground area within the focus zone.

Frequency Planning


Downlink Throughput for a Six-Frequency Network

This screen shot shows a study of DL RLC throughput when the network is configured with sixfrequencies. It can be seen that a rate in the region of 11 Mbit/s is achieved across most of the groundarea within the focus zone. This is lower that the peak bit rate achieved in the three frequencyconfiguration because the channel bandwidth is lower. However, this rate is achieved over a larger areabecause the SINR performance was better.



Downlink Throughput for an SFN (1)

This screen shot shows a study of DL RLC throughput when the network is configured as an SFN with achannel bandwidth of 15 MHz. It can be seen that rates achievable over ground area within the focuszone are very variable, but the highest rate is in excess of 20 Mbit/s. This is higher than the peak bit rateachieved in the three frequency configuration because the channel bandwidth is higher. However, thisrate is achieved over a smaller area because the SINR performance was poorer.

Frequency Planning


Downlink Throughput for an SFN (2)

In order to study in more detail the effect of using an SFN strategy the display scale has been modifiedfor this study. Now the variation on performance across the cell area can be more clearly seen as can theincrease in peak performance, which in some places reaches rates in excess of 50 Mbit/s.


3FN – 5 6FN – 3

SFN – 15


Histograms

Histograms provide a very effective way of contrasting the performance variations between a frequencyplanned segmented approach and a single frequency network approach. This example shows theconsistency of service provision for the three-frequency network configuration where 18–19 Mbit/s isbeing achieved across 60% of the ground area. The consistency of service provision is lifted to morethan 80% for a six-frequency plan but at the expense of ultimate performance, since the rate achievedfalls to 11–12 Mbit/s.

The distribution is very different for the SNF configuration. Peak rate is significantly improved reaching54–55 Mbit/s but over only 4% of the ground area.

Frequency Planning


Downlink Throughput for Fixed Users in a 3FN

The Atoll Tool is also able to model the effects of providing fixed radio access. In this case the users areassumed to have high gain antennas directed at the intended serving cell. As can be seen, the effect ofthe antenna on coverage is considerable. The peak bit rate is still limited to 18–19 Mbit/s by the channelbandwidth of 5 MHZ, but this capability is now available across almost all of the ground area in the focuszone.



Downlink Throughput for Fixed Users in an SFN (1)

When the three-frequency configuration for fixed users is replaced by an SFN configuration the rate risesas would be expected. However, unlike the mobile case where more extreme service variation was seen,the directivity in the high gain antennas used by subscribers provides isolation from neighbour-cellinterference and thus improves performance over a larger ground area.

Frequency Planning


Downlink Throughput for Fixed Users in an SFN (2)

The effect of the SFN configuration in a fixed radio access system is more clearly seen with scaleadjustment and the histogram. This indicates the highest bit rate (more than 50 Mbit/s) may be availableover more than 80% of the ground area.



Downlink Throughput for MIMO Users in a 3FN (1)

The Atoll tool is able to perform studies on the effects of using a variety of MIMO configurations. In thiscase a 2x2 MIMO configuration for mobile users is being studied in the three-frequency network set up. Itis clear that the study suggests an improvement both in terms of throughput and in terms of coveragearea.

Frequency Planning


Downlink Throughput for MIMO Users in a 3FN (2)

The effects of the MIMO configuration in the 3FN system can be more clearly seen with scale adjustmentand the histogram. It can be seen that the peak rate has increased to more than 30 Mbit/s and that thisrate is available over approximately 75% of the ground area within the focus zone.



Downlink Throughput for MIMO Users in an SFN (1)

In this study a 2x2 MIMO configuration is being used along with an SFN arrangement using 15 MHzchannel bandwidth. The use of MIMO has a marked effect on the performance of the network when anSFN configuration is used. Bit rate is increased as would be expected, but most significantly MIMO alsoappears to be compensating for the poor SINR at edge-of-cell and high bit rates are still being achievedover a significant ground area.

Frequency Planning


Downlink Throughput for MIMO Users in an SFN (2)

The real effects of the MIMO configuration in the SFN system can be more clearly seen with scaleadjustment and the histogram. It can be seen that the peak rate has increased to more than 90 Mbit/s.However, this rate is available in only about 3% of the ground area. Nevertheless, very good rates arestill achieved over a wide area. Overall users could expect access to rates more than 17 Mbit/s in about95% of the ground area.


SECTION 6

LTE PERFORMANCE SIMULATIONS



The Need for Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.1

Monte Carlo Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.2

Simulation Preparation – Traffic Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.3

Radio and Feature Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.4

Starting a Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.5

Snapshot Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.6

Multiple Snapshots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.7

Simulation Detailed Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.8

Merged Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.9

Difference – Simulation and Direct Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.10

CONTENTS

LTE Performance Simulations



discuss the advantages and disadvantages of using a Monte Carlo analysis for coverage

prediction

describe the general process used in a Monte Carlo analysis

identify configuration parameters that will be required when performing a Monte Carlo

analysis

interpret snapshot results from a Monte Carlo analysis

explain how snapshot results can be merged to provide network performance information

identify when it would be appropriate to use a performance simulation approach in the

planning workflow

OBJECTIVES



time consumingcomplex set updifficult to interpret resultsneeds good understanding of simulation process and inputsgood representation of multi-service operationgood representation of uplink performanceGood for look-ahead planning strategy assessment

fastsimpleclear resultswell understood processpoor representation of multi-service operationpoor representation of uplink performance

Detailed performance

simulation

Basic coverage planning

?


The Need for Simulation

Although basic coverage planning has been the mainstay of planning for 2G networks, and in manycases for 3G networks too, the multitude of options available to the LTE planner could benefit from somereference to more detailed network simulation.

Network simulation can be used to test a variety of implementation and planning assumptions togenerate confidence in the efficacy of the selected rollout strategy. It can also be very useful foridentifying strategies to deal with increasing network load and traffic type variation over time.

However, careful consideration must be given to the best way of incorporating simulation into theplanning work flow. This is because simulation can be very time consuming and, unless used in astructured way, the results can be difficult to interpret. It is also crucial that anyone using simulation fullyunderstands the underlying approach used by their particular planning tool developer in order that theycan have confidence in the simulation results.


Traffic Map

User profiles Mobility categories

UE types

Service types

Subscriberdensities

Usageassumptions

Terrain

Radio parameters and feature

configuration

Channel configuration

Antennaconfiguration

Propagationmodel

MIMO

Bandwidth

Clutter

Bearertypes

SINRrequirements

Transmitpower Scheduling

Weighted Poisson distribution of users

Application of algorithm for service

success

Snapshot 1 Snapshot 2 Snapshot n

Combined result


Monte Carlo Simulation

The Monte Carlo simulation is a general term for a mathematical approach to solving problems having alarge number of random characteristics. It was originally formulated during the Los Alamos nuclearresearch programme but is now applied in a wide range of engineering scenarios, one of which is tomodel cellular network behaviour.

To simulate network operation it is necessary to account for the effects of interference between users inboth the uplink and downlink directions. It is also necessary to model the effects of power control,channel adaptation and mixed traffic. To do this, the Monte Carlo simulation creates a series ofsnapshots (or drops). For each of these snapshots users are randomly scattered over the ground areawith weightings for expected traffic density. The tool then uses defined radio parameters to estimatetransmitted power, cell load, interference, channel adaptation and, ultimately, connection success rate. Anumber of snapshots are then combined to produce a statistical analysis of the probability of coveragefor various service types.

Tools vary in the way traffic profiles are entered, but typically traffic layers are built up by mappingservices to user types and then user types to geographical areas. The result is a map showing thecombined requirement for different services across the map area. Numerous radio parameters may berequired. Many are related to site configuration and radio transceiver performance capabilities.



Simulation Preparation – Traffic Map

In general, a traffic map suitable for simulation needs to reflect the traffic mix expected in the builtnetwork as closely as possible. For example it would be reasonable to expect that it would be possible todefine user types, terminal types and service types and then relate likely combinations of these in termsof traffic density to a ground map showing typical clutter categories by area.

The example planning tool offers a number of ways to generate a traffic map. Firstly, it may be donefollowing the definition of one or more ‘environment’ types. Each environment type is represented as apolygon in which users, services, mobility and terminal combinations are mapped in different proportionsto different clutter categories. Allowance can also be made for the proportion of connection attempts thatmay be made indoors.

Alternatively traffic load may be defined directly per cell. Often the information for such an approach maycome from existing legacy network traffic statistics. Once the LTE network is built and operating thisapproach could use real traffic data to simulate the effect of proposed new optimal features such as theintroduction of MIMO. Another possibility is the definition of a traffic map by individual weightings for eachuser, service, mobility and terminal type.



Radio and Feature Setting

Most of the settings required for simulation are likely to be in place through the basic planning process.However, if a strict coverage planning only strategy has been employed up to the point of simulation thenthere may be additional parameters to set.

The simulation will need path loss predictions to have been performed, and again, it is highly likely thatthis will already have been done. Thus the main additional parameters relate to specific LTE items suchas control channel settings, channel bandwidth options, physical cell ID allocation, frequency plan andadaptive bearer selection criteria.



Starting a Simulation

It is very important for the user to understand where a simulation will source the inputs for thecalculations that it will perform. Without a thorough understanding of this and the way these inputs areused in the calculation it is impossible to interpret correctly what is influencing the output result andtherefore the potential effect on the built network.

The simulation itself is an iterative process so there are some parameters relating to the way it behavesin this respect that must be set before the simulation can start. The key parameters are an upper limit foriterations while it searches for convergence and the number of snapshots (referred to as simulations inthe example tool) that will be produced.



Snapshot Output

The diagram shows a screen shot of a single snapshot produced as part of a Monte Carlo simulation.User, device and service distribution have been considered in the selection of locations for the snapshotbased on a three-frequency network and 5 MHz bandwidth. In each case the tool has calculated thelikely best bearer service available in each location.



Multiple Snapshots

This screenshot shows the superposition of 50 snapshots all based on the same traffic and radioassumptions. At this stage the results have not been merged but it still gives some indication of serviceavailability.



Simulation Detailed Analysis

The Atoll tool can merge results from multiple snapshots in two ways. The first, a partial example ofwhich is shown in the diagram, involves the statistical analysis of the performance on each cellexpressed in a tabular form. The second involves the use of snapshots from a simulation as the maininput for the production of a coverage prediction.



Merged Simulation Results

The diagram shows the result of producing a coverage prediction from averaged snapshot simulations. Itis displayed in exactly the same way as a standard prediction, but the result now more fully representsexpected network behaviour.



Difference – Simulation and Direct Prediction

The diagram shows a comparison between directly predicted coverage results for a three-frequencynetwork based on 5 MHz bandwidth and a prediction from averaged simulated snapshots. Grey areasare common to both predictions. Coloured areas represent differences.


SECTION 7

THE LTE PLANNING PROCESS



Who Does The Planning? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.1

Consideration for HCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.2

Infrastructure Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.3

Site Sharing Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.4

Co-Site Choice of Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.5

Co-Site Interference Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.6

Planning Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.7

Bid Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.8

Rollout Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.9

Development Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.10

RF Exposure Limits and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.11

Defining Signal Level for Exposure Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.12

Estimating Exposure Limit Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.13

CONTENTS

The LTE Planning Process



differentiate between the different types of planning work that may be required as an LTE

project develops

identify and discuss the different approaches that may be appropriate for different stages in

an LTE project

evaluate considerations for and against existing site reuse and site sharing

describe different architectural strategies that may be used for ongoing network

development

discuss the options for LTE planning workflows

assess the compliance of an LTE site with relevant regional radio signal exposure limits

OBJECTIVES



OwnedRAN

Operator

Ownedshared RAN

Operator A Operator B

Shared company plans network

Leasedshared RAN

RAN Service company plans

network

Operator A

Operator B

Operator D

Operator C


Who Does The Planning?

The traditional market model where each individual operator has a complete engineering function and acomplete and independent infrastructure build is changing. In some cases networks may be planned andbuilt by and for an individual operator but in most cases some form of pooled resource will beincorporated into the planning process.

There are many possibilities for resource and infrastructure sharing in the planning process. One modelthat has been used extensively in 3G network builds is for two or more operators to form a commonlyowed separate company. This company employs engineering staff from all concerned operators and istasked with the planning, build, optimization and maintenance of a shared RAN (Radio Access Network).

A development of this approach is the emergence of specialized RAN service companies, often spun outfrom equipment manufacturers. These companies may take on part or all of the functions associated withthe creation and operation of a shared RAN. In some markets it is conceivable that all competingoperators would use a single common RAN.

It is worth noting that there are engineering as well as cost-saving justifications for the shared-RANapproach. For example, a common radio architecture for all competing operators provides the optimalconfigurations for interference reduction between operators and a corresponding liberation of morecapacity.


Macrocells

Microcells

PicocellsSelf-install femtocells

Rollout

Cell splitting

Network development


Consideration for HCS

As for 2G and 3G networks, at some point in network development the need for capacity andcomprehensive radio coverage may result in a strategy involving some form of HCS (Hierarchical CellStructure) arrangement.

Initial rollout of any LTE network is generally based on a single cell layer and therefore, by definition, allthe outdoor cells can be considered macrocells, although by comparison to the initial 2G rollouts theymay be very small macrocells. Once the required coverage has been achieved as defined by the rolloutplanning requirements an operator may consider how service provision, connection reliability andcapacity can be improved. They must decide whether this is best achieved using cell splitting in a singlemicrocell layer or to introduce an overlaid microcell layer in traffic hot spots. In most cases a differentapproach will be appropriate in different areas. The use of part-time cell splits or microcells may also beconsidered.

Indoor coverage is also critical for LTE and as such should be an integral part of any rollout plan. Evenwhen a common RAN has been built there are some cases, for example with large corporate contracts,when operators may build individual indoor schemes. However in most public buildings indoor schemesfor LTE are typically common-build shared schemes. In new buildings the indoor coverage distributionnetwork will be part of the building plan. Connection to the distribution network may then be negotiatedeither individually or collectively by operators interested in using it.

A further development in indoor coverage is the femtocell. These are self-install and therefore not directlypart of the rollout planning workflow. However, their effect on network performance may be factored intoplanning assumptions.


eNB

Operator A(15 MHz)

Operator C(15 MHz)

Operator B(15 MHz)

spectrum licence pooling (3FN-using 45 MHz)large selection of available existing sitescommon planning assumptionsminimized inter-operator interference

one eNBone physical cell IDone channel allocationone backhaul resource

Multiple PLMN IDs


Infrastructure Sharing

In infrastructure sharing scenarios for LTE it is possible to integrate fully the resources of multipleoperators into a single hardware build. This means that a single eNB can advertise multiple PLMNidentities on the same frequency. Thus it is possible to pool the bandwidth resources of multiple licencesin a single radio access network. This gives the potential for much more frequency demarcation flexibilityin terms of its application with an HCS architecture, and in terms of the possibility of access to the moreefficient wide bandwidth LTE channel configurations.


Space for equipment cabinets

Antenna space

Antenna type

Interference scenarios

Feeder space

Mast strength

Power supply capability

Power backup capability

Air conditioning capability

Transmission for backhaul capability

GSM/GPRS/EDGE CDMA2000 1x

UMTS/HSPA 1xEV-DO

LTE

Multiple operators?Other non-cellular technologies


Site Sharing Considerations

Reusing existing sites for LTE is attractive both for time saving and cost reduction. However, there aremany important considerations in addition to a site’s applicability from a coverage point of view.

Chiefly, these considerations relate to civil engineering considerations, such as space or mast suitability,and to technology considerations, such as interference problems or transmission capacity. All thesefactors must be taken into account when assessing whether an existing site is suitable for inclusion in theLTE plan.


Type of UMTS AntennaConsideration

Separate Integrated/Multiband(Broadband)

Low visual impact

Low cost

Low wind loading

Low maintenance

Rapid fitting

Different azimuths

Different downtilts

Separately optimized

Separately upgraded


Co-Site Choice of Antenna

An integrated, multiband antenna offers a relatively compact and low-cost solution. Low visual impact,together with ease of installation and relatively low ongoing maintenance, make it a popular choice. Windloading is also low.

However, such antennas confine the operator to using the same azimuth bearing and downtilt for bothlegacy and LTE (within most current antenna design limits). Separate upgrade and optimization cannotbe carried out.


Transmitter Spurious Emissions

Frequency

TX RX

Receiver Blocking

Frequency

TX

RX

Intermodulation Products

Frequency

TX TX RX


Co-Site Interference Considerations

Co-location of systems may cause interference resulting in performance degradation. In order tominimize this performance degradation to an acceptable defined level, decoupling between the systemsis required. The most important interference mechanisms are transmitter spurious emissions, receiverblocking and intermodulation products:

The transmitter noise floor or transmitter spurious emissions of system A within the receive band ofsystem B cause interference of system B’s receiver and vice versa. This could be avoided by increasingthe stop band attenuation of system A’s antenna network in the transmit path for the receive band ofsystem B, or by increasing decoupling between the two systems, either the air decoupling or thedecoupling provided by the diplexer.

Receiver blocking occurs when the transmit signals of system A are not sufficiently rejected by thereceiver of system B and vice versa. This could be avoided by increasing the stop band attenuation ofsystem B’s antenna network in the receive path for transmit frequencies of system A, or by increasing thedecoupling between the two systems (air or diplexer decoupling).

Intermodulation products can cause interference for the receivers of one or both systems. Significantintermodulation products are generated in non-linear devices (especially mixers and amplifiers but alsoconnectors), if two or more strong signals are applied. In most cases the strong signals will be differenttransmit carriers either from system A or from system B or a combination of system A’s and system B’stransmit carriers.


Bid Plan

Rollout PlanDevelopment

Plan


Planning Types

In most cases there are a number of stages that occur in the overall network progression from green-fieldto full optimized mature network. Different priorities need to be accounted for at each stage, which mayresult in different planning processes. The diagram shows three typically different planning stages.


Set minimum performance requirement

Perform UL and DL link budgets and then balance for basic cell configuration

Derive minimum required DL signal level

Estimate cell radius for typical clutter

types

Plan with hexagons or quick cell placement with

signal strength predictions


Bid Planning

Bid planning is used to make a fast but realistic estimate of the number and typical configurationrequirements of sites in a new network. It forms the basis for the calculation of a business plan and maybe used internally by an operator, but in most cases will form part of the bid itself.

A minimalist approach is used in the planning process, but it is important that assumptions are based onthe most accurate information available. Thus where possible a trusted propagation model should beused with realistic traffic estimates.

The planning itself may in some case be based only on a hexagonal tessellation with a cell size derivedfrom link budgets. Alternatively, some degree of coverage calculation based on potential sites, oftenbased on existing sites where the operator already has a network based on a legacy technology, will bemade. This latter approach has the advantage that much of the work effort may be reusable when theformal rollout planning begins. The more realistic the initial assumption, the more useful the result will befor the rollout planning phase.


Set minimum performance requirement

Perform UL and DL link budgets and then balance

Determine expected cell load and noise rise levels Create traffic map

Set detailed standard cell radio configurations

Test planning assumptions with simulations in small example areas

Use link budgets to set minimum DL signal level

Use simulation results to set minimum DL signal level

Plan on real site locations using tuned propagation model

Perform frequency planning and interference analysis

Check service availability with direct predictions

Make physical cell ID and neighbour allocations


Rollout Planning

The rollout plan is the formal plan for the physical network that will be built thus it is necessary to turninitial planning assumptions into formalized plan requirements. The pre-planning elements are veryimportant because any decisions made at this point will have very long lasting consequences. Often timeis limited, but the more time that can be given at this stage to testing planning assumptions andformulating the most appropriate configuration strategy the better the network is likely to perform in thefuture with fewer problems needing the attention of optimizers. The two most significant constraints willbe the need to reuse existing sites and any limitations in radio configuration with any givenmanufacturer’s equipment.

Reuse of existing sites will always be important and a sensible approach would be to identify which siteswill be useful for LTE at an early stage in the plan. Proposed new locations for LTE-only sites can thenbe planned around existing sites.

Anther option open to an operator in the early planning stage is the use of full simulation. This can betime consuming, but may be used on small test areas to gain confidence in overall planning assumptions.In effect, simulation can be used as a form of tuning for the quicker and simpler direct predictions that aremore likely to be used in the general planning process.


Coverage Extension

As for rollout

Plan on real site locations using tuned propagation model

Perform frequency planning and interference analysis

Check service availability with direct predictions

Make physical cell ID and neighbour allocations

Revise cell load and radio configuration in link budgets

Apply multiplying factor to traffic map

Use simulation to estimate new cell edge radius

Use direct predictions to estimate new cell edge radius

Capacity increase

Decide on cell splitting or HCS approach

Redefine band segmentation as required for chosen approach


Development Plan

Once the initial rollout phase is complete the planners’ attention will be turned to the ongoingdevelopment of the network. Essentially, there are two different considerations in this respect; coverageextension and capacity increase. These two different aspects are not completely unrelated, new in-building systems provide both for example, but in the network as a whole they need slightly differentapproaches.

Basic coverage extension can be treated exactly as a continuation of the initial rollout phase. However, itwould be wise to assess whether any planning assumptions need to be changed before the projectbegins. For example, new cell equipment may offer more configuration or feature options and some realtraffic statistics will be available to modify the traffic model.

For capacity increase it is necessary to decide on a strategy, either cell splitting or the introduction HCS,or some combination of both. In most cases this will require some reconsideration of the bandsegmentation strategy. Once again simulations of small representative areas in the network may be usedto test assumptions for different approaches.


Occupational Exposure General Public Exposure

m/Vf3=E m/Vf573.1=E

S = f/40 W/m2 S = f/200 W/m2

E = 137 V/m E = 61 V/m

S = 50 W/m2 S = 10 W/m2

400-2000 MHz

2-300 GHz

ICNIRP Guidelines for 400 MHz to 300 GHz

f is entered in MHzvalues are averaged over any six-minute period

Occupational Exposure General Public Exposure

UL = 131.5-133.5 UL = 60.3-61.2

DL = 137 DL = 61

UL = 48-49.5 UL = 9.6-9.9

DL = 50 DL = 10

E (V/m)

S (W/m2)

Example for LTE Band 1


RF Exposure Limits and Safety

The level of radio signal power radiated from a site is governed by two factors; licence conditions andsafety considerations. The operator’s licence will limit the EIRP per radio channel. In most countries, theoperator may also be legally obliged to demonstrate that emissions from the site comply with guidelinesfor limiting human exposure to the time-varying electromagnetic fields emitted from the site.

Each country or region has its own radiation limit guidelines. Many countries use, or are influenced by,the recommendations set by ICNIRP (International Commission on Non-Ionizing Radiation Protection)guidelines. However, the limits applicable in specific countries may vary considerably on these levels,some being as much as an order of magnitude lower.

At the frequencies used by cellular systems, the guidelines define basic restrictions on exposure, basedon SAR (Specific Absorption Rate) Watts per kilogram of body tissue. These can be equated to referencelevels expressed as field strength or power density. The table in the diagram is an example from theICNIRP guidelines with exposure levels expressed as electric field strength (V/m) and power density(W/m2).

In this example the basic restrictions for exposure of the general public are five times lower (in terms ofpower density) than the levels for exposure of groups exposed as part of their occupation. This is basedon factors such as the potentially poorer health of the general public (e.g. older age profile) and thevulnerability of babies and children. Also, occupational groups are more aware of health and safetyprecautions to be employed.



Defining Signal Level for Exposure Limits

Most exposure limits are expressed as field strength or power density. However, most planning linkbudgets are worked on received signal levels. Unfortunately there is not a direct relationship between thetwo so confirming compliance with exposure limits can be difficult. The performance of the antenna willdetermine how much of the radio signal is ultimately coupled onto the feeder in the receive device.

The equations in the diagram can be used to convert between signal levels in dBm or dBW into electricfield strength or power density. However, knowledge of the system antenna performance is required.

A very useful website capable of performing these and other similar calculations can be found at:

http://www.giangrandi.ch/electronics/anttool/field.html


Example

UMTS – EIRP = 53 dBmLTE – EIRP = 53 dBm

53 dBm is 200 W

There are two transmitters, so for total EIRP:

2 x 200 = 400 W

The ICNIRP public exposure limit for LTE band 1 is 61 v/m

Applying the estimation formula:

Formula For the estimation of compliance distance

EIRP is in WattsE is in volts per meterd is in meters

where:

d= 30 x 400612

d= 1.8 m

d= 30.EIRPE2


Estimating Exposure Limit Distance

The equation shown in the diagram can be used to estimate the distance beyond which compliance witha given exposure limit, expressed in electric field strength, is met. However, it is important to note that theonly way to be sure of compliance is to test the working site with calibrated measurement equipment.The above equation should only be considered indicative.

An example is given for a cell fitted with one LTE radio carrier and one UMTS radio carrier. Both systemsare assumed to have an EIRP of 53 dBm. Note that for the ICNIRP guidelines it is necessary to add thesystems’ powers. Some regulatory authorities may only require assessment for each individual system.


CELL PLANNING FOR LTE NETWORKS

GLOSSARY OF TERMS



LT2901/v2 G.1© Wray Castle Limited

BCCH Broadcast Control ChannelBER Bit Error RateBLER Block Error RateBPSK Binary Phase Shift Keying

CDMA Code Division Multiple AccessCQI Channel Quality IndicatorCRC Cyclic Redundancy Check

DL DownlinkDRS Demodulation Reference Signals

EARFCN E-UTRA Absolute Radio Frequency Channel NumberEIRP Equivalent Isotropically Radiated PowereNB Evolved Node BEPC Evolved Packet CoreEPS Evolved Packet SystemE-UTRA Evolved Universal Terrestrial Radio AccessE-UTRAN Evolved UMTS Terrestrial Radio Access Network

FCC Federal Communication CommissionFDD Frequency Division DuplexFEC Forward Error CorrectionFTP File Transfer Protocol

GBR Guaranteed Bit RateGSM Global System for Mobile Communications

HCS Hierarchical Cell StructureHSPA High Speed Packet Access

ICNIRP International Commission on Non-Ionizing Radiation ProtectionIP-CAN IP Connectivity Access NetworkIM Implementation Margin

LTE Long Term Evolution

MAC Medium Access ControlMBSFN Multicast/Broadcast Single Frequency NetworkMIMO Multiple Input Multiple OutputMIMO Multiple Input Multiple OutputMU-MIMO Multi User MIMO

OFDMA Orthogonal Frequency Division Multiple Access

PBCH Physical Broadcast Channel 8PCFICH Physical Control Format Indicator ChannelPCS PDN Connectivity ServicePDCCH Physical Downlink Control ChannelPDN Packet Data NetworkPDN-GW PDN GatewayPDSCH Physical Downlink Shared ChannelPHICH Physical Hybrid ARQ Indicator ChannelPMI Pre-coding Matrix IndicatorsPRACH Physical Random Access ChannelPSS Primary Synchronization SignalPUCCH Physical Uplink Control Channel


LT2901/v2G.2 © Wray Castle Limited

QAM Quadrature Amplitude ModulationQCI QoS Class IdentifierQoS Quality of ServiceQPSK Quadrature Phase Shift Keying

RAN Radio Access NetworkRB Resource BlockRB Resource BlockRLC Radio Link ControlRRC Radio Resource ControlRX Receiver

SAR Specific Absorption RateSDF Service Data FloSFN Single Frequency NetworkSFN Single Frequency NetworkSINAD Signal to Interference Noise And DistortionSINR Signal to Interference and Noise RatioSISO Single Input Single OutputSNR Signal to Noise RatioSRS Sounding Reference SignalsSSS Secondary Synchronization SignalSU-MIMO Single User MIMO

TDD Time Division DuplexTTI Transmission Time Interval

UE User EquipmentUMTS Universal Mobile Telecommunications System

WiMAX Worldwide Interoperability for Microwave Access


cell planning for lte networks - lt2901 - v2

Documents

coverage planning

planning constraints1

lte courses

interrelatedfor lte

lte cell parameterssection

lte networkscourse code

writing of wray castle

coverage requirements