radio network planning and dimensioning guideline

Mobile WiMAX Radio NetworkPlanning and Dimensioning Guide

DN70467472Issue 1-1 en draft30/06/2008

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Nokia Siemens Networks Mobile WiMAXSystem, Rel. WMR1.0 ED1 and ED2, Pre-release, System Library, v.1

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2 (55) # Nokia Siemens Networks DN70467472Issue 1-1 en draft

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Mobile WiMAX Radio Network Planning and Dimensioning Guide

Contents

Contents 3

1 Changes in Mobile WiMAX Radio Network Planning andDimensioning Guide 5

2 Introduction 7

3 Initial dimensioning process 93.1 Econometric data 93.2 Capacity requirements and network performance 113.3 Requirements for coverage 113.4 Dimensioning process 12

4 Coverage dimensioning 154.1 Cell range estimate 20

5 Capacity dimensioning 21

6 Planning process 256.1 Mobile WiMAX air interface characteristics 286.2 Planning tool selection 29

7 Coverage planning 317.1 Coverage thresholds 317.2 Improving coverage 32

8 Capacity planning 358.1 Network load in Mobile WiMAX 378.2 Capacity solutions 378.3 Capacity features 388.4 Capacity of a standalone cell 39

9 Optimal radio planning 419.1 Frequency reuse 429.2 Antenna tilting 439.3 Optimizing the BTS height 47

10 Verification and analysis 4910.1 RF quality 4910.2 Connectivity analysis 5110.3 Dominance areas 5110.4 Cell edge analysis 5210.5 SINR performance 54

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Contents


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1 Changes in Mobile WiMAX RadioNetwork Planning and DimensioningGuide

Changes between issues 1-0 and 1-1

Information about new features affecting Mobile WiMAX radio networkplanning and dimensioning (multiple-input and multiple-output (MIMO), fullusage of subchannels (FUSC) and fractional frequency reuse (FFR)) hasbeen added.

The following new sections have been added:

. The sections Network load in Mobile WiMAX and Capacity featuresto the chapter Capacity planning.

. The section Frequency reuse to the chapter Optimal radio planning.

The tables Dimensioning inputs, Link budget for Mobile WiMAX and Linkbudget parameters and default values have been updated.

The table SINR target (pedB 3km/h, 20%PER traffic, 1%PER MAP, 2RxMRC) has been removed.

The chapter Link budget and coverage dimensioning has been renamedCoverage dimensioning.

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Changes in Mobile WiMAX Radio Network Planning andDimensioning Guide


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2 Introduction

The aim of this document is to present Mobile WiMAX radio networkplanning and dimensioning fundamentals. The document covers the basiccoverage and capacity planning and dimensioning processes and thesystem parameters for Nokia Siemens Networks Mobile WiMAX system.

The first part (the chapters Initial dimensioning process, Coveragedimensioning and Capacity dimensioning) of the document describes theMobile WiMAX radio network dimensioning phases (general process,coverage, and capacity dimensioning).

Dimensioning is the initial phase of radio network planning. Duringdimensioning, the primary configuration estimates and requirements forcoverage, capacity, and quality of service are planned. The approximatenumber of necessary base station sites and base stations, the averagevalues for the power budget, cell size, capacity, and initial networkconfiguration are estimated at this phase.

Note that in the dimensioning phase, only average values over a part ofthe network can be calculated. Individual sites configurations aredetermined during the actual planning phase.

The second part (the chapters Planning process, Coverage planning andCapacity planning) of the document describes the Mobile WiMAX radionetwork planning phases (planning process, coverage, and capacityplanning). The detailed radio network planning process identifies specificsite locations and refines their configurations to suit the local environmentand traffic profile. Radio network planning is related to good overallnetwork performance. It depends on the actual traffic and user behaviour.

The chapters Optimal radio planning and Verification and analysis provideadditional information related to radio network configuration and qualityoptimization. The quality of a radio network plan is often described in termsof downlink signal quality. In Mobile WIMAX, the signal-to-interference-plus-noise ratio (SINR) is the key driver of the network performance. Tosupport high data rates, the radio plan must offer a very good SINRdistribution even though there may be very limited spectrum.

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Introduction

The radio network planning is carried out with a specific radio networkplanning tool such as NetAct planner. A suitable tool should be selectedbefore the planning process is initiated. Note that the detailed planningprocess depends to some extent on the selected tools and the featuressupported by the tools.


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3 Initial dimensioning process

Dimensioning is basically a part of the initial phase of radio networkplanning. Although intended to be a quick estimation of the site count invarious clutter environments, nominal network plan may be sketched outor roughly simulated in order to achieve the capacity and coverageestimates of the initial radio network configuration.

Mobile WiMAX networks are planned according to specific businesscases. The aim of the dimensioning process is to define a networkconfiguration that meets the expected revenue. The business caseinvolves coverage for target customers, supported services, servicequality, network capacity, infrastructure and operational cost, andcompliance with certain regulatory requirements. At the beginning ofdimensioning, the planner has to analyze the business inputs.Dimensioning normally provides enough top-level subscriber data such astraffic forecast and target network coverage to estimate the neededinfrastructure. The table Business inputs for dimensioning shows some ofthe data required for dimensioning.

3.1 Econometric data

The following business data is normally provided:

. Population and penetration rate – defines the maximum number ofpotential subscribers.

. Operator’s market share – the expected number of subscribers.

. Number of households and penetration rate – used in fixedbroadband applications (for example, wireless DSL-typesubscription).

. Types of subscriptions – used when the traffic calculation hasdifferent usage patterns for various subscriptions (for example, VoIP,Internet, mobile office, and fixed wireless).

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Initial dimensioning process

. Coverage area – the area where users should be able to establishradio connections with certain probability and quality criteria.

. Clutter classifications – for dimensioning purposes, the completecoverage area is divided into three clutter types: urban, suburban,and rural.

. Clutter information – needed for selecting the correct propagationmodel, penetration loss and shadowing margin for each clutter.

Note that the inputs may vary between operators. In this way, thecalculation for the total network traffic may vary. However, the goal is tocome up with the peak or average traffic for each type of service area forcapacity dimensioning. The most common business inputs aresummarized in the table Business inputs for dimensioning.

Table 1. Business inputs for dimensioning

Parameters Description Use

Population andpenetration rates

Yearly numbers Used for traffic calculation togetherwith penetration rates

Subscriber types andservices

Yearly numbers Traffic calculation

Service areas and cluttertypes

Size of each clutter area Dimensioning urban, suburban, andrural areas

User traffic profile Calling patterns and busy hourlevels

Used for peak-to-average ratiocalculation in dimensioning foruniform-user traffic model

Cell application mix Types of data applications in acell

Used for capacity benchmarking (thatis, acceptance load test)

Site type ratios Ratio of microcells versusindoor cells

To determine the number ofexpected indoor and microcells for agiven number of macrocells indimensioning

Building density andclutter data

Number of huge buildings,shopping complexes, andstadiums that require indoorcoverage

To determine the number of indoorsites

Site classifications Height, mounting, cabling, andexisting infrastructure

To determine which sites are “MobileWiMAX friendly” for integration andcommissioning cost estimation


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3.2 Capacity requirements and network performance

Spectrum efficiency and cell capacity are the crucial criteria for operatorsto accomplish their business plans. Therefore, they need to benchmark thenetwork quality in addition to the business inputs. One part of networkquality is related to capacity and network performance under loadedconditions. The other part is related to the extent of coverage. Theserequirements are essential because of a number of reasons such asregulatory issues, competition, or set as benchmarks for networkacceptance. Some of the requirements related to capacity andperformance are shown in the table Network requirements related tocapacity.

Table 2. Network requirements related to capacity


Peak user data rate(kbps)

Maximum achievable bit ratefor single user (under bestconditions)

Marketing purposes

Target cell load (%) Cell load factor to be used asbasis for QoS andperformance

QoS purposes, performancebenchmarking, uplink and downlink

Minimum data rate Guaranteed minimum data ratefor mobile users

Cell edge performance and handoverbenchmarking

Cell capacity Maximum average cellthroughput in a multi-cellenvironment

Capacity dimensioning

Subscriber per cell Maximum number of users percell (active and inactive)

Capacity based on the number ofconnections

Simultaneous VoIPusers per cell

Number of active voice-over-IP(VoIP) users per cell

VoIP capacity dimensioning

3.3 Requirements for coverage

The Mobile WiMAX coverage requirements are heavily dependent on thepropagation model and the maximum allowed path loss (MAPL). TheMAPL is determined in the link budget calculation for a specified type ofservice under certain quality conditions. It has to be balanced for uplinkand downlink data and the FCH/MAP part in the beginning of the downlinksub-frame. For example, data service coverage may be defined as 90%indoor coverage probability for the minimum required bit rate.

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Additional planning requirements, such as the use of the operator'sexisting sites for deploying Mobile WiMAX, may be provided by theoperator. The table Coverage requirements summarizes some of thecommon coverage requirements.

Table 3. Coverage requirements


Outage probability,uplink and downlink

Percentage of area or usersexperiencing signal qualitybelow threshold (SINR orRSS)

For coverage quality, (=1- CoverageProbability)

Minimum data rate atcell edge, uplink anddownlink

Planned data rate forguaranteed services such asVoIP

Quality of planned and actualcoverage; used in networkacceptance; related to handover

Target cell range Maximum cell radius in variousclutter types

To make sure that the plannednetwork can utilize existing sites

Indoor coverage Extent of indoor coverage forvarious locations (houses andbuildings)

For network planning

3.4 Dimensioning process

The dimensioning process is shown in the figure Dimensioning processbased on the dimensioning tool. The link budget analysis, capacityanalysis, and the dimensioning exercise are fairly straightforward. Theinput analysis, together with finding an appropriate network configuration,may require careful consideration because of a number of implementationconstraints such as spectrum, cost, equipment limitations, and others.

Figure 1. Dimensioning process based on the dimensioning tool

Some additional parameters are also shown in the table Dimensioninginputs.

INPUTANALYSIS

NETWORKCONFIGURATION

LINK BUDGETANALYSIS

CAPACITYANALYSIS

COST-REVENUEANALYSIS

TRAFFICANALYSIS

DIMENSIONINGEXERCISE


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Table 4. Dimensioning inputs


Site area factor Area = k x R2 where R is themaximum cell radius andK=1.95 is often considered forthree sectors (with clover-leafstructured cells)

Site area for coverage dimensioning

Channel type Tx-Rx channel to evaluateSINR-MCS performance

For capacity and coveragecalculation

Interference margin Interference increase due toco-channel interference in tightfrequency reuse scenarios

For coverage

Fading margin Fading margin because ofshadowing

For coverage

QoS The level of service that theuser will experience whenusing the network for voice ordata communication

Cell edge performance

Overbooking factor Number of users sharing achannel or multiplexing factor

Calculated based on peak-to-average bit rate and utilization factor

Noise floor and noisefigure

Additive white Gaussian noise(AWGN) for given bandwidthand the noise figure of thereceiver components

For system noise calculation

IBPL Planned in-building penetrationloss for different indoor areas(houses, and buildings)

For indoor coverage target

Measured indoor loss inSU, U and Renvironments

IBPL profiles for each cluttertype

To estimate number of buildingsrequiring indoor solutions

Additional losses andgains (for examplefeeder loss or antennagain)

Other environment/systemlosses and gains

For coverage

Propagation model Default radio propagationmodel to be used. COST 231-HATA or tuned two slopemodel.

For dimensioning (coverage)

SS type Types of subscriber station(SS) (mobile, stationary,indoor, rooftop, and antennagain)

For coverage

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4 Coverage dimensioning

The target of coverage dimensioning is the computation of the cell rangeneeded to cover a given area. In order to achieve coverage, the requiredSINR must be reached within a certain area with at least a givenprobability. This must be fulfilled by all logical channels for the system tooperate properly. The link budget is the basis for the computation of themaximum allowable path loss (MAPL). The table Link budget for MobileWiMAX shows an example of a link budget for Mobile WiMAX.

Table 5. Link budget for Mobile WiMAX

Parameters Downlink MAPDownlinkTraffic Uplink Traffic

Total Tx Power (dBm) 36 36 23

Tx Antenna gain (dBi) 18 18 0

Tx feeder loss (dB) 0.5 0.5 0

Rx antenna gain (dBi) 0 0 18

Rx feeder loss (dB) 0 0 0.5

System bandwidth (MHz) 10 10 10

FFT size 1024 1024 1024

Total number of OFDMA symbols inframe 47 47 47

TDD downlink/uplink division(number of OFDMA symbols) 32 15

MCS (modulation and codingscheme) QPSK-1/2 Rep 2 QPSK-1/2 QPSK-1/2

Frame overheads (number ofsymbols) 5 3

Symbols for data transmission 27 12

Permutation zone downlink PUSC downlink PUSC uplink PUSC

N used (number of usedsubcarriers) 841 841 841

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Coverage dimensioning

Table 5. Link budget for Mobile WiMAX (cont.)

Parameters Downlink MAPDownlinkTraffic Uplink Traffic

PUSC reuse 3 3 3

Rx diversity 2Rx MRC 2Rx MRC 2Rx MRC

BLER 1% 20 % 20 %

MAC headers (excluding FCH andMAP, %) 2.5% 2.5%

Maximum MCS throughput (kbps) 2920 1048.32

Target cell edge user throughput(kbps) 512 128.00

Capacity needed for one user 35.13% 12.86%

Effective sector bandwidth (MHz) 9.2 9.2 9.2

Noise figure (dB) 6 6 3

Effective noise power (dBm) -98.36 -98.36 -101.36

Uplink subchannellization gain (dB) 3.80

Required SINR (dB) 3 2.5 2.5

Link budget (noise limited, dB) 148.97 149.42 148.02

Interference margin (dB) 1 1 1

Link budget (interference + noiselimited, dB) 152.6 153.1 146.8

The table Link budget parameters and default values explains the mostimportant input parameters. The values used for each parameter shouldbe carefully considered during coverage dimensioning.

Table 6. Link budget parameters and default values

Parameters Description Default value

BTS Tx power Maximum average power (peak-to-average ratio considered already inthis value) of the BTS.

36dBm or 40dBm for remoteRF head, 43dBm for RF unitattached to the system unit.

SS antenna TX power Maximum average power (peak-to-average ratio considered already inthis value) of the SS antenna.

23dBm for mobile per PCMCIAcard SS, up to 27dBm foroutdoor CPE.

BTS antenna gain Antenna gain in dBi 18.5 dBi for 65 degreesantenna, 11dBi for omni.


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Table 6. Link budget parameters and default values (cont.)


BTS feeder loss Cable, connector and jumper lossespermitted

0.5dB for remote RF head, 2-3dB for RF unit attached to thesystem unit (can becompensated with MHA).

SS antenna gain Antenna gain in dBi 0dBi for mobile per PCMCIAcard SS, up to 18dBi foroutdoor CPE with externalantenna.

SS feeder loss Cable, connector and jumper lossespermitted

0dB for mobile per PCMCIAcard SS, 2-3dB outdoor CPEwith external antenna.

System bandwidth Allowed options of the bandwidthfor one carrier per cell:

Depends on network-specificpreconditions.

5 or 10MHZ for 2.5GHz band

5, 7 or 10MHz for 3.5GHz band

TDD ratio OFDMA symbols should be usedfor downlink and uplink. Forty-sevensymbols are for 5 MHz and 10 MHzsystem bandwidth and thirty-threesymbols are for 7MHz systembandwidth.

Allowed ranges for TDD ratio are:

5 and 10MHz: (downlink/uplink) 26/21 – 34/13

5 and 10MHz: (downlink/uplink)32/15

7 MHz: (downlink/uplink) 18/15 –24/9

7 MHz: (downlink/uplink) 22/11

Modulation and codingscheme for downlinkMAP

MAP always uses QPSK1/2 MCS.Repetition of 2, 4, or 6 can beselected for MAP to increase thecoverage (reduce required SINR).

Repetition 2

Modulation and codingscheme for downlinktraffic

Minimum downlink MCS is requiredat the cell edge.

QPSK1/2

Modulation and codingscheme for uplink traffic

Minimum uplink MCS is required atthe cell edge.

QPSK1/2

Frame overheads fordownlink and uplinktraffic

Downlink capacity is used for MAPand FCH.

Three symbols

Uplink capacity is used for rangingand feedback channels.

Three symbols

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Permutation scheme PUSC or/and FUSC can be usedfor downlink permutation; that is,PUSC and FUSC can theoreticallybe used simultaneously in separatezones within the downlinksubframe. PUSC is mandatory forFCH and MAP.

For downlink data FUSC can beused but not in the case of Rxdiversity = 2X2 STC, for whichPUSC is used.

In uplink only PUSC is used.

Downlink: PUSC

Uplink: PUSC

Frequency reuse forMAP, downlink traffic anduplink traffic.

Frequency reuse x means that apart of the spectrum is used oncein x cells. The part of spectrum canbe a whole carrier (in permutationschemes PUSC or FUSC) or a partof a carrier (in PUSC only). Thisparameter applies to the PUSC-onlycase.


Downlink diversityscheme

Input option for downlink diversity:

1Rx: one antenna reception is usedwith Single Input, Single Output(SISO).


2Rx MRC: two antenna receptionwith Maximum Ratio Combining(MRC) is used with Single Input,Multiple Output (SIMO).

2X2 STC: Diversity Multiple Input,Multiple Output (MIMO), Alamouticoding (You should increase Txpower 3dB for downlink traffic whenusing this option; only PUSCpermutation can be used.)

2x2 SM (Spatial Multiplexing): todouble the throughput (compared to1Rx) in optimal SINR conditions.

BLER for the firsttransmission for downlinkand uplink traffic

The block error rate is for the firsttransmission.

20%

MAC header overheadfor downlink and uplinktraffic

The standard MAC overhead is 10(6 bytes for MAC header + 4 bytesfor CRC). Additional 2 bytes can beassumed for fragmentation andpacking.

2.5% for normal mobile internettraffic

10 % for VoIP


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Target cell edge userthroughput for downlink

Required downlink throughput atthe cell edge for a single user.Required throughput should be lessthan the maximum bit rate withselected MCS.

Depends on the QoS policy ofthe network operator.

Target cell edge userthroughput for uplink

Required uplink throughput at thecell edge for a single user.

Depends on the QoS policy ofthe network operator.

Required throughput should be lessthan the maximum bit rate withselected MCS.

Decreasing uplink cell edgethroughput increases uplinkcoverage, due to increasedsubchannelisation gain.

Noise figure for BTS andSS

Noise figure is product dependent. BS: 3 dB

SS: 6 dB

Interference margin foruplink and downlink

Interference margin for theinterference comes from the othercells. This margin depends on, forexample, the frequency reuse, thenetwork load and the radio networkdeployment.

1 dB for frequency reuse 3

Required SINR

The required SINR is one of the main parameters in the link budget.However, this parameter value is linked to other input parameter values,thus it should not be freely changed.

The required SINR depends on the following aspects:

. Channel model

. Modulation and coding scheme

. Block error rate

. Radio features (CTC and HARQ)

. Diversity method

. Carrier frequency

. Permutation scheme

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4.1 Cell range estimate

The cell range estimation in the radio network dimensioning phase isbased on the link budget calculations. The link budget gives the maximumallowed path loss (MAPL) limiting the coverage. The MAPL can be limitedby downlink MAP, downlink traffic, uplink traffic or downlink FCH.

The cell range calculation takes into account all the environment lossesand fading or interference margins in order to calculate the net air-lossfrom the BTS antenna to the SS. Then the net air-loss is used to evaluatethe cell range, based on the propagation model formulas. The net air-lossis calculated as:

Airloss = HWpathloss – FadingMargin – InterferenceMargin – IBPL

The FadingMargin is selected for a given coverage probability. It takes intoaccount shadowing and the positive effect of the opportunity of receiving asignal from more than one cell at the cell edge (multi-server probability).The InterferenceMargin is subject to a number of factors such as thefrequency reuse factor, propagation model, antenna type, and load. Itmodels the noise rise above the system noise as a result of co-channelinterference.

The other environment parameters for typical propagation models are:

. Coverage probability – used to select the value for the fading margin.

. Frequency band – either 3.5 or 2.5 GHz.

. BTS height – depends on the clutter type.

. SS antenna height – 1.5 to 8 meters (4.9 to 26.2 feet)

. In buildings, the penetration loss (IBPL) is different for each clutter.

The most suitable propagation model for Mobile WiMAX depends on thefrequency band used and the propagation environment.

Typical models that can be used are:

. Cost 231-HATA model

. Erceg model

. two slope models (standard Macro Cell model)


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5 Capacity dimensioning

The Mobile WiMAX capacity largely depends on the SINR distribution inthe service area. The Modulation and Coding Schemes (MCS) varies from0.17 to 5.0 bits per subcarrier to cope with SINRs that vary by up to 25 dBbetween the minimum and maximum values. With the limited spectrum inmost cases, the task of providing decent capacity per site is a challenge forthe radio network planner. Although there are other planning qualityindicators such as multipath and handover areas, capacity planning ismainly about SINR maximization while maintaining the coverage criteria.

The Mobile WIMAX capacity is tightly coupled to its coverage. Asillustrated in the figure Relationship between MCS and distance from thesite, higher MCS are supported closer to the site where the signal quality isexpected to be higher. A typical value of the average SINR in a cell isaround 12-18 dB with a cell edge value of roughly 5dB for sectorized cells.

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Figure 2. Relationship between MCS and distance from the site

The average cell air interface capacity depends on several variables,including the following:

. Sector bandwidth

. Permutation scheme (due to its lower number of pilots, DL FUSChas higher spectral efficiency than DL PUSC and thereforesurpasses its capacity by approximately 6.7%).

. Frequency reuse factor

. Radio network deployment (antenna height, azimuth, downtilt)

Probability

64 QAM3/4

64 QAM2/3

16 QAM3/4

16 QAM1/2

QPSK3/4

QPSK1/2

SINR Values

64 QAM 3/464 QAM 2/316 QAM 3/416 QAM 1/2QPSK 3/4QPSK 1/2


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. Radio features (MIMO, HARQ, CTC)

. TDD radio

. User distribution in the cell

. Scheduler type

. Traffic model

The following table shows the average cell throughput capacity values fora sample 3-sector radio network deployment with the followingparameters:

. 10 MHz bandwidth

. 2RxMRC diversity method

. PUSC permutation

. TDD ratio 32/15

. HARQ+CTC

It is assumed that users are uniformly distributed in the cell. The higher thereuse factor, the more relaxed the interference situation and the better theSINR distribution. The highest capacity is achieved for the borderline caseof an infinite reuse factor leading to an isolated cell. An example ofaverage downlink throughputs in a cell is shown in the table An example ofaverage cell throughput capacity values.

Table 7. An example of average cell throughput capacity values

Frequency reuse Average downlinkthroughput

Mbps

Reuse factor 3 9.3

Reuse factor 4 10.7

Isolated cell 11.1

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6 Planning process

The Mobile WiMAX radio network planning includes a number of steps,ranging from pre-planning and tool setup to site survey. The process issimilar to that of any wireless network. The figure General Mobile WiMAXradio network planning process shows the general planning process forMobile WiMAX. The following properties differentiate Mobile WiMAX fromother technologies:

. The actual site configuration

. Parameters

. KPIs

A propagation environment such as Mobile WiMAX may support mobileand fixed users, where the fixed users may employ directional or rooftopantennas. Coverage and capacity planning has some Mobile WiMAXspecific items, but generally it is quite similar to HSPA planning. The mainemphasis is to ensure a SINR that meets the requirements of the networkarea.

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Planning process

Figure 3. General WiMAX radio network planning process

The final radio plan defines the site locations and their respectiveconfigurations. The configuration involves BTS height, number of sectors,assigned frequencies or major channel groups, types of antennas, azimuthand downtilt, equipment type and RF power. The final plan should betested against various KPI requirements – mainly coverage criteria andcapacity (or signal quality). The figure Detailed WiMAX radio networkplanning process can be used as a guide in developing a planningprocess. The planning process also depends on the planning tool used.

The planning process includes a test drive and verifications after the sitesurvey. This procedure is not mandatory for all sites if they are toonumerous. Usually, the site survey and KPI analysis give an indication ofthe areas that are expected to have poor RF quality, and the particularsites involved. This is usually done when the candidate sites are notlocated in ideal locations or if the site survey finds some discrepanciesbetween the candidates.

Pre-planning

Pre-planninginformation

Dimensioning

Detailed planning

Model tuning

Site selection

Coverage andcapacity planning

Configurationplanning

Parameterplanning

Optimisation

Pre-launchoptimisation

Post-launchoptimisation


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Figure 4. Detailed WiMAX radio network planning process

The task of radio network planning is to define a set of site locations andrespective BTS configurations that address the coverage and capacityfigures derived from radio network dimensioning. The starting point in radionetwork planning is the output from the radio network dimensioning,especially the calculated site densities in each clutter type. The site countderived from radio network planning often differs from the site countderived from radio network dimensioning, since the actual site coveragemay differ significantly from the assumed empirical models. There isalways a risk that the planned site count may exceed the estimated sitecount calculated during dimensioning. As a result, several planningiterations are needed to reach a reliable figure.

COVERAGE PLAN/MAP

TRAFFIC GEOGRAPHICALSPREAD

COVEARGE/CAPACITYANALYSIS

DETERMINECAPACITY SOLUTION

SITE SELECTION

CAPACITY LIMITED?PURELY COVERAGE

PLANNING

YES

NO

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Planning process

6.1 Mobile WiMAX air interface characteristics

The Mobile WiMAX radio offers modest processing gain in the form ofrepetition coding and subchannelization. These features are only exploitedwhen the signal quality demands more processing. To support high datarates, the radio network plan must offer very good SINR even with a verylimited spectrum. For example, in the absence of subchannelization andrepetition coding, the required SINR for the lower modulation and codingschemes (MCS) is around 5 dB and needs to be achieved even with a verytight frequency reuse factor of 1/3, or 1/4 in the presence of shadowing.

Another consideration in Mobile WiMAX planning is the high SINRrequirements to support high data rates. Although a site is expected tosupport high data rates for SSs closer to it, SINR values higher than 30dBare only possible in the absence of interference. This requires accuratemodelling of the propagation and RF equipments. For example, inWCDMA, the high data rates are possible even with C/(I+N) of lower than10dB, since the processing gain enables the receiver to tolerate a certainamount of interference. In Mobile WiMAX, the processing gain is onlyprovided through channel coding and limited coding repetition.

The Mobile WiMAX System uses OFDMA technology, which results intypically higher SINR values when compared with WCDMA in loadednetworks. The reason for this is that there is no own cell interference in theOFDMA systems for static and slow moving terminals. Typically, datausers are static or slow moving, thus the lack of their own cell inferenceimproves the average SINR in Mobile WiMAX networks when comparedwith WCDMA networks. For this reason, careful radio network planning tolimit inter-cell interference is essential in order to maximize the MobileWiMAX radio network performance.

Achieving high SINR

The quality of a radio plan is often described in terms of downlink signalquality. In Mobile WIMAX, the SINR is the key performance indicator forradio plan quality, which is similar to EcNo in WCDMA. The following fivemain factors affect SINR:

. Site antenna – for reducing interference

. Propagation attenuation (slope) factor

. Frequency reuse with its corresponding subcarrier allocation method

. Cell radius and the respective coverage margins

. Level of shadowing – causing interference


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The baseline configuration for a Mobile WiMAX deployment is 1+1+1macrocell. The sectorization is mandatory in order to exploit the highantenna gain of a directional (sector) antenna while at the same timeminimizing interference. It is commonly understood that the maximumpractical value for frequency reuse in a 1+1+1 configuration for MobileWiMAX is 1/3 in order to achieve the required SINR at the cell edge.Frequency reuse factors of 1/3 and 1/4 are both used during the course ofthis document.

6.2 Planning tool selection

The radio network planning normally follows the dimensioning exercise.Sometimes, the dimensioning process includes a rough plan to justify thesite count and coverage level by using some commonly acceptedpropagation models and generic Mobile WiMAX System modules in theplanning tool. In the actual planning phase, a number of inputs are neededin order to improve the quality and accuracy of the radio plan. Dependingon the selected planning tool, the full utilization of a number of inputs maybe required. For example, it is assumed that the following items havealready been well considered:

. Propagation characteristics of various areas (propagation modelstuned)

. Required inputs defined (clutter maps, terrain maps, and buildingdata)

. RF equipment parameters have been defined (antennas, RFfeatures, and AVIs)

. Options for BTS configuration (sectorized, omni, PUSC, and TDDratio)

. SS types and parameters defined (antenna types, mounting, anddiversity)

There are two important decisions related to radio network planning thathave to be considered prior to the actual planning exercise:

. The level of accuracy when it comes to coverage and capacityneeds to be considered; this depends greatly on the accuracy of thepropagation model in the planning tool.

. The planner needs to decide how much RF optimization is to beundertaken during the planning phase. This is only possible if theplanning tool, together with the planning parameters and equipmentsmodels, is accurate enough. This is often the case when

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Planning process

optimization is neglected during the planning process. The post-planning optimization exercise is often expensive and produces onlyminor improvements. It is often limited to antenna adjustments (tiltingand azimuth changes).

The following features are useful when selecting a planning tool:

. Automatic frequency selection

. Optimal site selection (when existing or candidate sites areprovided)

. Support of mixed and multiple propagation models

. Support of model tuning and user defined models

. Support of OFDMA system, including channel impairments

. Optimal downtilting

. Propagation parameters (or constants) for 2.5 and 3.5 GHz


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7 Coverage planning

The coverage planning process for Mobile WiMAX networks is practicallythe same as for other cellular networks. One particular aspect of MobileWIMAX is that it is relatively new to some planners because its coveragedepends on MCS support. Other features such as TDD, subchannelizationgains, and repetition coding are not applicable in 2G and 3G networks.The coverage planning includes the following three main areas:

. Propagation study

. Link budget

. Proper selection of sites based on cell dominance and signaloutage.

The inputs for coverage planning include mainly the following information:

. Clutter information

. Terrain information

. Building data (for dense urban)

. Candidate site locations

. Propagation data and in-building penetration losses (IBPL)

. Equipment specifications

7.1 Coverage thresholds

The parameters that can be measured with field measurement tools areused when planning the coverage; it is otherwise difficult to verify theplanning results. The Mobile WiMAX terminals measure CINR and RSSfrom the preamble symbol of the OFDMA frame. Thus, the most practicalcoverage parameters in Mobile WiMAX are preamble CINR and RSS.

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Coverage planning

The measured preamble CINR reflects well the radio network deploymentquality. The preamble symbol is transmitted in every frame. If the networkis fully synchronized, then the preamble symbol is sent at the same time byevery BS. For this reason, the preamble CINR does not depend on thetraffic load in the network. It represents CINR with 100% load. Thus, thepreamble CINR behaves differently compared with CPICH Ec/No inWCDMA, which is load dependent.

The bottleneck link in Mobile WiMAX can be downlink MAP, downlinktraffic or uplink traffic. The preamble CINR and RSS thresholds are alwaysmeasured in the downlink. This means that the coverage thresholdsshould be calculated for downlink, even when the uplink is the bottlenecklink. The link budget tool can do this calculation. However, the mobilesubscriber station (MSS) antenna and the BTS parameters (for example,maximum transmission power and antenna gain) should be carefully set toreflect the real situation in the network.

If the planning tool coverage analyses do not consider slow fading margin,then the additional margin should be added to the thresholds in order totake the slow fading into account. Slow fading margins can be calculatedwhen coverage location probability and standard deviation are defined.The building penetration loss should also be taken into account in themargin for indoor coverage if it has not already been considered in theplanning tool.

7.2 Improving coverage

It is often the case that the coverage holes are in the actual networkbecause of the unexpected blockage of signals in a severely shadowedenvironment. To some extent, coverage holes cannot be solved by simpleantenna adjustments of the surrounding sites. In this case, an additionalsite is needed. Since the frequency planning has already been done basedon the existing plan, additional sites may use any extra frequencies orspectrum.

The allocated sites with a spare frequency (or frequency not used in thenormal reuse pattern) exhibit a superior SINR-RSS property because ofthe absence of co-channel interference. Since the cell selection for cellcamping is based on SINR (or CINR measurements), the effectivedominance area of the sites using the spare frequency is much larger forthe same BTS configuration when compared with sites using frequencyreuse. The figure Coverage difference between isolated frequency and


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reused frequency describes the coverage comparisons. As shown in thefigure Scatter Plot of RSS vs. SINR, the coverage advantage of a noise-limited site against interference-limited site is more than 10 dB in a highshadowing case.

Figure 5. Coverage difference between isolated frequency and reusedfrequency

There are two ways to compensate for the coverage difference:

. To use a lower gain antenna for the added site. This can easilycompensate for more than 10 dB differences between a commonlyused 18 dBi antenna and low gain antenna.

. To use a lower EIRP at the BTS for the added site. However, thisdepends on whether or not any power reduction feature issupported.

SINR

RSS

Coverage Difference

Noise Floor

Extra Frequency (added site)

Reused Frequency

Planned Cell-Edge SINR

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8 Capacity planning

In radio network dimensioning, the areas can be generally classified aseither coverage or capacity-limited. This classification also applies to theradio network planning. In principle, it is assumed that the traffic inputs areuniformly spread in the area. For non-uniform traffic distribution, a capacitytesting feature is needed in the planning tool. In most cases, the trafficinput comes with the following three options:

. Uniform user density – users are spread equally in the planned areaand the user traffic usage level is also uniform.

. Traffic or user density map – the geographical distribution of theusers is provided as a map (input has to be taken from the map; forexample, a national housing or population survey or an availabletraffic database).

. Clutter-specific traffic level – usually expressed in Mbps per squarekilometer (Mbps per 0.6 square mile) for each clutter type during thebusy hour. The numbers can be easily estimated based on thecurrent planning values.

Generating traffic load is planning tool dependent. To test whether certainareas of the network are coverage or capacity-limited, sites can be placedin the network based on the calculated maximum cell range (or coverageplan). The planning tool can then evaluate whether individual cells orclusters of cells can carry the traffic load. Once the areas are determinedas either coverage or capacity limited, the site selection process isfollowed (see the figure Overview of coverage and capacity planning).

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Capacity planning

Figure 6. Overview of coverage and capacity planning

Planning a capacity-limited network or cluster requires both coverage andcapacity KPIs. Coverage KPIs include service outage probability, cell edgebit rates (uplink and downlink) and cell edge signal strength that areavailable in most planning tools. Capacity KPIs such as voice blocking, celloverload probability, average cell load and user data rates are morespecific planning-tool-specific.

GeographicalData/Maps

Customer Data &Services

Propagation Data

RF EquipmentsDescription

Planning ToolSetup

KPI definition

Site Locations

Site Configuration

Coverage/CapacityAnalysis

KPI Analysis

Site Survey

Test Drive &Verifications

Final Site Location& Configuration

Model Tuning


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8.1 Network load in Mobile WiMAX

Load in OFDMA systems can be described as frame filling ratio. The loadin an OFDMA network tells how efficiently the OFDMA symbols andsubchannels are used, in terms of time. It is not directly mapped to trafficthroughput as MCS changes dynamically depending on the radioconditions. The higher the load, the higher is the probability that thenearest cell on the same frequency will cause interference.

The OFDMA frame consists of symbols. In the downlink sub-frame onesymbol is always used for preamble and some symbols are used for framecontrol header and MAP messages. The rest of the symbols in a downlinksub-frame are used for data and control traffic. The load can be definedseparately for these different symbols.

. Preamble always has 100% load, as it is sent in every frame at thesame instant due to the strict synchronous TDD structure.

. MAP symbols (typically 4-6 first symbols) have higher loads thantraffic symbols.

. Traffic symbols have variable loads.

. The average traffic load can be different in uplink and downlink sub-frames.

Downlink CINR is typically measured from the preamble symbol. TheSINR experienced on other symbols can be higher than indicated by thepreamble CINR, especially with a low average traffic load.

8.2 Capacity solutions

The capacity of a Mobile WiMAX network can be increased by using thefollowing planning strategies:

. Assigning more bandwidth – bandwidth per site allocated accordingto demand.

. Adjusting the site density – making the radius smaller than thecoverage limited by cell range.

. Deploying fractional frequency reuse (FFR) with, for example, PUSCreuse 3 in outer and FUSC reuse 1 in inner sector areas.

. Planning with more than one layer – macrocells and microcells.

. Providing indoor solutions for large buildings.

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Capacity planning

In dense areas, the coverage is normally planned to support indoorcoverage. Cells are already at minimum radii and if the area is still capacitylimited, then shrinking the cells further is not applicable. Solutions fordense areas include the following:

. More bandwidth – expanding capacity as the network matures

. Splitting indoor and outdoor traffic by using macro and indoor sites

. For outdoor capacity: using macro and micro layers to address non-uniform traffic density

The options above require an additional frequency block to cater for indooror microcell layers.

In suburban and low traffic areas, the following solutions are applicable:

. Non-uniform site density

. Isolated hotspot cells – if spectrum is available

In non-uniform site density, the site radius is set according to traffic density.This requires the network to be planned for capacity at the onset (day 1). Inisolated hotspot cells, they are added as traffic increases.

8.3 Capacity features

The radio interface capacity can also be increased by introducing newcapacity features. Downlink MIMO and fractional frequency reuse (FFR)can be applied for capacity gain.

MIMO will provide the following two cell capacity improvements:

. Higher throughput for users in good radio conditions.

. Higher downlink transmit power.

MIMO gain is highly dependent on the radio conditions (SINR). In poorconditions MIMO performance is fairly equal to a maximum ratiocombining (MRC) receiver with two antennas. However, in good radioconditions MIMO can double the throughput of MRC. Thus, careful radionetwork planning to avoid excess interference is a key factor for goodMIMO performance.


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MIMO increases the BS transmit power by 3dB, as there is a separatetransmitter for both branches in Flexi WiMAX BTS. The MIMO featuregoes together with the cyclic delay diversity (CDD) feature that is used fornon-MIMO symbols (that is, preamble and MAP). CDD brings the 3dBpower increase also to non-MIMO symbols.

FFR is recommended for cases where the total bandwidth is very limitedand PUSC 1/3 reuse is applied. The downlink subframe is divided into twodownlink permutation zones. FFR will combine PUSC 1/3 and full PUSC/FUSC reuse in such way that the terminals in poor radio conditions usePUSC 1/3 (permutation zone 1) and the terminals in good radio conditionsuse full PUSC or FUSC (permutation zone 2).

8.4 Capacity of a standalone cell

The standalone cells are noise-limited. For this reason, the SINR isexpected to be much higher than those cells with reuse of 1/3 or 1/4.These include microcells, indoor sites and picocells for hotspots. Based onNokia Siemens Networks' simulations, the interference-limited cells haveroughly 30-40% more capacity than the cells with reuse of 1/3.

The cell camping on a standalone cell is controlled such a way that on amicrocell layer, certain SINR requirements must be satisfied for campingon the cell and the SINR distribution for active users is to be biasedtowards the higher values. This can significantly improve the cell capacity.For in-building solutions that are free from interference, the SINR can beplanned accordingly with much higher minimum requirements.

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9 Optimal radio planning

Site selection process

This optimization problem is typical in all kinds of wireless networks. Theproblem is to identify the sites from a set of potential (or candidate) siteswhile satisfying the following criteria:

. Site count

. Coverage KPI

. Capacity KPI

. Traffic raster

. Uplink and downlink data rates

Traditionally, the site selection is carried out manually even though it is atime-consuming process. Automatic site selection algorithms implementedin the planning tool are more advisable but their reliability depends verymuch on the propagation model (ray tracing or some physical propagationmodel).

The manual site selection is normally made using a propagationconsistency check against:

. Signal blockage (site/cell level)

. Signal spillage (site/cell level)

. BTS height uniformity (cluster of BTS)

. BTS spacing regularity (cluster of BTS)

One method used in manual site selection planning is the site eliminationmethod based on expected cell range criteria; this is in addition to thepropagation consistency check above.

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The final criteria can be decided based on dominance together with thecoverage and capacity KPIs.

Site location irregularities

The actual site locations normally deviate from the ideal (for example,hexagonal grid). For this reason, allocating certain margins for cell range isbeneficial. Typical site location irregularities result in coverage holesbecause of low RSS.

Sector azimuth irregularities

Another common factor in sectorized cells is azimuth irregularities. Theazimuth errors do not degrade the SINR dramatically. This is because offrequency reuse that allows diversity and some level of tolerance tointerference (in contrast to CDMA systems).

Optimization using azimuth adjustments

Since the SINR is tolerant towards azimuth deviation from the idealdirection, it is useful as a tool for RF optimization if there is a reasonableoverlap between sectors of the same site. The overlap is achieved byusing a relatively wider horizontal antenna beamwidth. This techniqueneeds to be used in conjunction with downtilting, since irregular sitelocations would mean different effective cell radii for various sectors.

The downtilting is applied according to the BTS height and cell radius. TheBTS has 1.5 kilometers (0.9 mile) average site distance, and a heightbetween 20 and 60 meters (65.6 to 196.9 feet).

9.1 Frequency reuse

The total frequency reuse can be implemented in the following two ways:

. PUSC reuse

. Carrier reuse

PUSC reuse refers to the case where the same carrier (for example1x10MHz) is used in each cell, but is divided into three subcarriers byusing different subchannels for each subcarrier. Each subcarrier has aneffective bandwith of 1/3 of the whole carrier bandwidth. Differentsubcarriers should be allocated to adjacent cells.


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Carrier reuse refers to the case where different carriers (for example3x10MHz) are used to provide frequency reuse. Different carriers shouldbe allocated to adjacent cells. In the case of carrier reuse, each cell usesthe whole carrier bandwidth.

These two frequency reuse schemes can also be combined in order toobtain higher frequency reuse. However, higher frequency reuse leads tolower effective carrier bandwidth, when the total bandwidth in use islimited. PUSC reuse can also be changed inside an OFDMA frame in sucha way that one part of the frame uses PUSC reuse 3 and the other partPUSC reuse 1. This is called the fractional frequency reuse scheme.

The optimal frequency reuse strategy depends on the available totalbandwidth, network capacity and coverage requirements. Typically,frequency reuse 1/3 or 1/4 is applied in the initial network planning.

In densely populated areas, the capacity can be improved by utilizing morefrequencies for reuse. The problem of poor SINR in some propagationenvironments is primarily due to the high co-channel interference causedby line-of-sight or near-line-of-sight interferers.

9.2 Antenna tilting

The antenna tilting is very effective in controlling co-channel interferenceby suppressing signal spillage. The vertical antenna pattern is also used tocompensate for the near-far effect because of propagation, which in turncan enhance the signal distribution in the cell.

In some cases, Mobile WIMAX may require aggressive downtilting in someareas because of the geometry of reuse 1/3 and 1/4. There are twomechanisms often used for downtilting: mechanical tilting and electricaltilting.

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. Electrical tilting can be controlled remotely and may be integratedinto the Operations Support System (OSS). Consequently, thechoice of antenna becomes very important since electrical andmechanical downtilting have different effects on the effective shapeof the horizontal and vertical patterns. The horizontal and verticalpatterns can be visualized clearly in a planning tool when empiricalpropagation models are used.

. Mechanical tilting is relatively cheap to implement since the antennaalways allows the mounting to be adjusted vertically. The maindrawback of mechanical tilt is its distortion in the horizontal patternsince it provides higher attenuation at the main lobe’s azimuthdirection. This is acceptable if only small tilts are required.

For larger downtilts, electrical tilting is more effective in reducing theeffective coverage across the antenna’s entire horizontal main lobe.

Mechanical downtilting produces only a significant attenuation at thehorizontal azimuth direction. As a result, the horizontal pattern is split intotwo lobes, which distorts the coverage of the sector. On the other hand,electrical tilting provides uniform attenuation for the entire sector. Becauseof this property of mechanical tilting, it is more useful for narrow beamwidthantenna (for example, 33-degree antenna) as the main lobe can beattenuated more uniformly compared with a wider beamwidth antenna.

SINR optimization by downtilting

The downtilt angle setting in Mobile WiMAX differs slightly from theconventional tilt angle calculation. This is because the traditional downtiltformula is based on maximizing the signal strength at the receiver withouttaking into account the strong co-channel interference that results fromtight frequency reuse. This sets the tilt angle at tan-1[(hb-hm)/d] where hbis the BTS height, hm is the mobile height and d is the expected cell range.This effectively optimizes the signal strength at the cell edge for a givenmobile height.


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Figure 7. Downtilting consideration for tight reuse

When dealing with co-channel interference, the suppression of the uppervertical side lobe is essential after a certain distance from the cell edge.Since the next sector that is assigned with the same frequency is usuallymore than 1.5 times the distance from the cell edge, the null of the verticalpattern almost sits on the horizon to achieve a downtilt angle thatsuppresses the interference at the horizon. Thus, the tilt angle is anywherefrom tan-1[(hb-hm)/d] to the maximum vertical beamwidth. If possible, theantenna should support a large range of electrical tilts reaching the verticalmaximum beamwidth (for example, 0-12 degrees).

RSS versus downtilting

The main change in the downtilting signal characteristics is the increase inthe effective path loss slope. The path loss slope factor (in dB/decade)affects the capacity (that is, higher SINRs with higher slopes). In this way,the RSS is well above the noise floor. Downtilting is also a suitable tool forimproving capacity. The figure Signal levels with electrical downtilt showshow downtilting increases the path loss slope curve with respect todistance.

minimizinginterference

maximizing RSSinterference suppression

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Figure 8. Signal levels with electrical downtilt

The SINR improvement by downtilting is applicable if the antenna cansuppress co-channel interference. This is an advantage for the smallercells, as there are more margins for coverage. The higher SINRimprovement is also more visible in areas closer to the site.

Impact to downtilting

The interference suppression of the antenna is another important factor inMobile WIMAX planning. Antenna’s interference suppression is dependenton the upper side lobe gain and shape, as well as the angle of the nullbetween the main lobe and the first upper side lobe. Since there is alimited number of antennas to begin with, a sensitivity test can be made ina planning tool by using a test antenna vertical pattern. The figure Antennatest model for interference suppression represents the test antenna modelby the main lobe only, and the null angle between the upper side lobe andthe main lobe. This simple antenna is easy to generate using, for example,a planning tool antenna editor. The null angle can then be adjustedaccording to the amount of downtilting to be tested.


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Figure 9. Antenna test model for interference suppression

9.3 Optimizing the BTS height

The final sites always vary in height in the actual network. Smalldifferences are not critical to the KPIs but large differences candramatically distort the dominance areas and SINR of the surroundingsites. Downtilting of higher sites can be an effective tool to improve theSINR at the cell edge. The figure Affect of different BTS heights andoptimization by downtilting shows the effect of non-uniform heights,especially to the cumulative SINR values around 2 to 4 dB in the absenceof shadowing and how downtilting can improve the outage probability. Italso shows that uniform BTS heights offer good outage probabilities (forexample, good cumulative SINRs at lower values).

RelativeAttenuation

downtilting

beamwidth

null angle

Minimumattenuation

Angle from main lobe

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Figure 10. Affect of different BTS heights and optimization by downtilting


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10 Verification and analysis

The radio plan analysis involves the KPI generation and the performancevisualization. KPI generation is mainly used to obtain cell level, clutter levelor network level statistics that are useful for comparing the planningiterations. KPI definitions and the method of calculation are tool-dependent. On the other hand, performance visualization is used mainlyfor optimizing localized RF problems, which is normally done on a clusterbasis. In this respect, most planning tools have the same capabilities (thatis, utilizing map layering functions). Mobile WiMAX radio planning is mainlySINR and RSS driven, so the analysis is very similar to that of otherwireless technologies (2G and 3G).

10.1 RF quality

The radio plan quality needs to meet certain KPIs, ranging from signalstrength to signal quality. The KPIs visualization is a good method ofidentifying certain areas that require improvement. If the frequency reuseis quite tight (such as CDMA), the signal strength versus signal qualitycriteria is a good figure of merit to characterize the RF quality. In MobileWiMAX, the RF quality is simply the RSS versus SINR scatter plot (see thefigure Scatter plot of RSS vs. SINR). The quality of the RF can be gaugedby how close the SINR is compared to the SNR (see the figureInterference analysis using scatter plot). In a network with large shadowingor high interference, there is a high variation in the SINR for a given RSS.

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Verification and analysis

Figure 11. Scatter plot of RSS vs. SINR

Figure 12. Interference analysis using scatter plot


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10.2 Connectivity analysis

The best server criteria analysis can be done in the following ways:

. Shortest distance criteria – line of sight propagation, shadowingindicator

. Highest RSS criteria – for uplink coverage limited cases

. Best SINR criteria – for capacity limited cases

The planning tools should be flexible enough to support the best servercriteria. The selection of the criteria depends on the link budget andinterference environment. The best SINR criterion is the best option forgenerally low downlink SINRs. Note that the SS uses the measured CINRfor cell camping decision. For large cell sizes with uplink coveragelimitations, the best RSS often coincide with the best SINR as the downlinkalso suffers from poor coverage. In fixed wireless applications, theconnectivity analysis is done based on predetermined user locations; thisis useful for optimization purposes.

The best server connectivity analysis is used to identify potential sectorsthat serve a given area. If the reuse is 1/3, there are theoretically up tothree potential sectors that can serve the cell edge and they are rankedaccording to best serving cell criteria.

10.3 Dominance areas

The dominance analysis is related to best server analysis, since frequencyreuse allows coverage overlap between adjacent sectors with differentfrequencies. A strong dominance means that there is only one potentialserving cell since the RSS or SINR of the second best (potential) server iswell below a given threshold or window.

Planned versus actual dominance area

The coverage of a cell is planned in order to meet certain user density ortraffic. The actual coverage may differ due to interference, severeshadowing or wrongly assumed propagation parameters.

Continuous versus fragmented coverage area

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The dominance area of a cell must be continuous. This criterion is oftenused in order to minimize unnecessary handovers. A fragmenteddominance area is an indicator of low BTS height for the intendedcoverage.

10.4 Cell edge analysis

There are two main cell edge KPIs:

. minimum SINR (determines cell edge bit rate)

. minimum RSS (determines cell edge signal level)

Spillage criteria

The spillage occurs when a signal propagates beyond the intended cellcoverage and interferes with the adjacent cells in the first tier of theinterference boundary. The spillage criterion is based on the co-channelinterference. The signal level of a potential interferer in the adjacent cell’sdominance area must be below the system noise to avoid any unwantedinterference rise in the downlink. This is described in the figure Signalspillage with respect to system noise. If a margin is provided, then the cellrange must be checked against the path loss exponent. The relationshipbetween the target interference level and the margin is simply:

Target_interference(cell edge) = System_noise – Margin, [dBm]


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Figure 13. Signal spillage with respect to system noise

SINR overlap between adjacent cells

The coverage overlaps are needed for cell selection diversity. This occursbecause the link budget allocates a fading margin for shadowing. In effect,the minimum required SINR and minimum required RSS exceed theplanned cell range.

In analyzing SINR overlaps, the criterion is to identify whether thehandover areas are served by the adjacent sectors based on the minimumrequired SINR and RSS. In small cells that are dimensioned to supporthigh SINRs at the handover areas, there is a tendency for the signal to spillbeyond the reuse distance into cells with the same frequency, thuscausing interference.

The average RSS values around -90 to -80 dBm are useful in aninterference environment. These translate to SINR higher than 10dB in theabsence of co-channel interference which allows for enough SINR overlapto enable cell selection diversity. The figure Planned cell range in ashadowing environment shows how the SINRs look like in the presence ofcoverage overlaps in the shadowing environment and how the cell range isextended beyond the planned site radius.

Spillage,dB

Spillage Marginat cell edge

1st Tier co-channel neighbour

distance

System Noise

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Figure 14. Planned cell range in a shadowing environment

10.5 SINR performance

The SINR is usually expressed in terms of sample distribution in order toextract the KPIs. For radio network planning purposes, the SINRdistribution across the cell area needs to be visualized in order to assessthe uniformity of the signal quality in the cell. The figure SINR versusdistance with different antenna types shows how the SINR varies with thedistance from the site. It compares two different antenna types (mainlyvertical patterns) in the absence of shadowing.


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Figure 15. SINR versus distance with different antenna types

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radio network planning and dimensioning guideline

Documents

officialcustomer document

mentioned hardware

documentation hasbeen

initial dimensioning

network performance

butnot limited

prior notice

software products