Huawei GSM Capacity Planning

5/21/2018 Huawei GSM Capacity Planning

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Capacity Planning

Confidential Information of Huawei. No Spreading Without Permission

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www.huawei.com

Copyright 2009 Huawei Technologies Co., Ltd. All rights reserved.

Capacity Planning


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Page2Copyright 2009 Huawei Technologies Co., Ltd. All rights reserved.

Foreword

Capacity planning is very important of network QoS.

Good planning reduce further RNO work and capacity

expansion.


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Contents

1. Traffic Prediction

2. TCH Capacity Planning

3. SDCCH Capacity Planning

4. Capacity Enhancement Technology


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Traffic and Erlang

A is offered traffic, BHCis busy hour call times, tm is user

mean hold time, Tis 1Hr (3600s).

200 users call in busy hr, average holding time 180s, the

traffic is:

T

tBHCA

m*=

Erls

sA 10

3600

180*200==


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Traffic Prediction

In traffic prediction, we should consider many factors:

Population

Family income

Subscription ratio of fixed phone

National economy development

City construction

Future policy of fee

The network construction requires the consideration of economic feasibility andrationality. Therefore, a reasonable investment decision must be based on the predictionof the network capacity of the early and late stage.


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TCH Traffic Model Example

32%24%24%24%Mobile-Fix

38%36%36%36%Fix-Mobile

30%40%40%40%Mobile-Mobile

Call Proportion

100%100%100%100%Subscriber Active Ratio

10%/ 10%10%/ 10%10%/ 10%10%/ 10%Roaming User In/Out Ratio

1.41.534.2Busy Hr Short Message Sending per User

1.52.03.24.6Busy Hr Short Message Receiving per User

1.41.71.71.4Average Handovers per Call

20%20%20%20%Second Paging Ratio

1.011.912.611.21Busy Hr Location Update Times

80%80%80%80%Successful First Paging Ratio

1.641.641.641.64Busy Hr Call Times

43485761Average Holding Time (s)

0.020.0220.0260.028Busy Hr Average Traffic per User

OthersAnshanDalianShenyang

Traffic ModelTraffic ModelItem


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Traffic Prediction

After predicting the total network traffic, then predict the

subscriber distribution.

Generally, base stations are constructed in urban areas,

suburban areas, and transport arteries.

At first, the subscribers in cities contribute most traffic. With

the development, the subscribers in suburban areas grows

fast.

In busy hr, the traffic of each subscriber is 0.025 Erl in urban areas and 0.020 Erl in

suburban areas.


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Considerations

For important areas, consider back up stations and TRX.

The dynamic factors, such as roaming ratio, subscriber

mobility should be considered.

For the areas of burst traffic, such as the play ground and

seasonal tourism spots, you must prepare backup

equipments (such as carriers and micro cells).

Prepare the some carriers, micro base stations for

emergency and future optimization.


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Contents






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Overview

According to different situation, we have two method for

planning: Fixed Site Locationand Fixed Frequency Reuse.

By Frequency Reuse:

The type of frequency reuse is given.

By Max Coverage:

The max coverage of cell is given.

By Frequency Reuse: The type of frequency reuse is given. It decides max TRXnumber of every cell. By traffic prediction, calculate max user number per cell. Accordingto the total traffic and user number, Obtain site and cell number.

By Max Coverage:By coverage planning, obtain the max coverage of one cell. By thetotal area of whole network, calculate the required cell number. By traffic prediction,

obtain the traffic of every cell, then calculate the TRX number.


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Basic Flow - By Frequency Reuse

Max Channel Number of Cell

Max User No. and Coverage by One Cell

Max TRX Number of Cell

Frequency Reuse Pattern

ErlangErlangB TableB Table

Site, Cell Number

Max Traffic (Erl) of Cell

Total user No. and trafficTotal user No. and traffic

Traffic DistributionTraffic Distribution


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By Frequency Reuse (Cont.)

According to the bandwidth and allowed interference level,

get the acceptable reuse mode.

Obtain the max number of TRX in one cell, then one Site.

For example, there are 4.8MHZ: 7.2/0.2=36 frequency

If reuse density is 4X3: 36/(4*3)= 3 frequency, in other

word, each cell has 3 TRX


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Each TRX has 8 channels. Obtain the voice channel

numbers by detracting the SDCCH required. Typically each

two TRX need a SDCCH.

For example, each cell 3 TRX, 2 SDCCH channels should

be configured. So total TCH are: 3X8=24 channels

24-1(BCCH)-2(SDCCH)=21 TCH channels


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By number of voice channels and call loss ratio (generally

2% dense traffic areas), you can obtain the maximum traffic

of one cell by Erlang B table.

For example, 21TCH according 2% block rate, each cell can

support 14.04 erl.


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Erlang B Table

Erlang B table give the relationship between Channel

Number, Call Block Rate (QoS) and Traffic.

Block RateChannel

Number

30.66

23.83

16.19

9.730

3.738

2.960

5

34.5027.3425.5124.0136

27.0521.0419.4918.2229

18.6514.0412.8411.8621

11.478.2007.5326.66314

4.6662.9352.5012.1587

3.7582.2761.9091.6226

1021.00.5


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By Frequency Reuse

If there are 1 million MS, and each MS traffic is 0.025erlduring the busy hour. So the whole traffic is 25000 erl

25000/14.04=1780.6 cells =1781 cells


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Basic Flow By Max Coverage

Channel Number of Cell

TRX Number of Cell

Traffic and User No. per Cell

Max Coverage per Cell

ErlangErlangB TableB Table

Traffic DistributionTraffic Distribution

Coverage PlanningCoverage Planning

Total Coverage of The NetworkTotal Coverage of The Network

Cell Number


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By Max Coverage

By Coverage Planning, obtain the maximum coverage range

per cell.

By total area of the whole network, calculate cell number.

According to Traffic Prediction, decide how many user and

traffic in each cell.

With Erlang B table, decide the channel number required in

each cell.

Calculate the TRX number required in each cell.

InterferenceInterference


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Site Coverage Radius: R

Site distance: D=1.5RSite Coverage Area=1.949R2

Site Coverage Radius: R

Site distance: D=1.732RCoverage Area=2.598R2

3 Sectors site Omni site

Calculate the Coverage


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Erlang B Table

Erlang B table give the relationship between Channel

Number, Call Block Rate (QoS) and Traffic.

Block RateChannel

Number

30.66

23.83

16.19

9.730

3.738

2.960

5

34.5027.3425.5124.0136

27.0521.0419.4918.2229

18.6514.0412.8411.8621

11.478.2007.5326.66314

4.6662.9352.5012.1587

3.7582.2761.9091.6226

1021.00.5


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Practice

Suppose 100000 subscriber in city, 80% urban, 20%

suburban. Busy Hr traffic is 25/20mErl per user.

Frequency 10-50 is available.

Use3-sector site.

If by Frequency Reuse, BCCH use 4*3, TCH use 2*3. How

many TRX, cell, site is needed?

If by Max Coverage, max radius 1 km, total 300km2. How



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Practice

Suppose 100000 subscriber in city, 80% urban, 20%

suburban. Busy Hr traffic is 25/20mErl per user.

Frequency 10-50 is available.

Use3-sector site.

If by Frequency Reuse, BCCH use 4*3, TCH use 1*3. HR is

used here.1X3 and all the TRX can work in HR mode. How



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Contents






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SDCCH Traffic Source

Location Update

Normal/Periodical 3.5 s/ times

Power Off/On

IMSI Detach/Attach 2.9/3.5 s/times

Call

Original/Destination 2.7/2.9 s/times

Short Message

Sending/Receiving 6.2 s/times


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SDCCH Traffic Model (Cont.)

/2/22/22/2Point to Point ShortMessage (O/D)

/0.8/0.80.8/0.80.8/0.8Call Establish (O/D)

/0.20.20.2IMSI Attach/Detach

/222Periodic Location Update

Times/Busy Hr1.200.4Normal Location Update

UnitUnitBoundaryBoundaryInternalInternalNormal CellNormal CellEventEvent

Times in busy hourTimes in busy hour


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SDCCH Traffic Model

52%48%50%SDCCH/TCH

mErl/user13.612.112.6Redundancy20%

mErl/user11.310.110.5Sum

mErl/user6.96.96.9Point to Point Short Message

mErl/user1.241.241.24Call Establish

mErl/user0.160.160.16IMSI Attach/Detach

mErl/user1.81.81.8Periodic Location Update

mErl/user1.200.4Normal Location Update

UnitUnitBoundaryBoundaryInternalInternalNormal CellNormal CellEventEvent

Consider TCH Traffic 25mErl/userConsider TCH Traffic 25mErl/user


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Other Considerations

The following steps is similar to TCH planning.

The traffic analysis of SDCCH is very difficult, normally

not accurate.

Commonly used configuration is 1SDCCH per 2TRX, a

value by experience.

Now we use the Dynamic SDCCH, which largely

expand the flexibility of SDCCH configuration.


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TCH to SDCCH ConversionConversion Trigger:

Idle SDCCH < Idle SD Thrsh.

Resource CheckOngoing?

SDCCH + 8 10, all the channels in the cell can be

configured as TCHFs. TCH Traffic Busy Threshold can be

set to 100.


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Examples

According to the Erlang B table, when the traffic volume in

the cell is Y the number of channels required in the cell is 17and the number of TCHs required is 13.

Because 13 x 2 > 17 > 13, the number of TCHFs to be

configured in the cell is 9 (2 x 13 - 17) and other channels

should be configured as TCHHs.

TCH Traffic Busy Threshold is set to 70 (100 x [2 x 13 -

17]/13)


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Examples

Based on ERLANG B, if the traffic volume in the cell is Z,

the number of configured channels is 28 and the number of

channels that can be used as TCHs in the cell is 13.

Because 28 > 13 x2, all the channels in the cell should be

configured as TCHHs. At the same time, Huawei

recommends that a user should perform an expansion.

The TCH Traffic Busy Threshold is set to 0.


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Exercise

If cell A has 12 TCHs, traffic volume is 8.3 erl, the required

block rate is 1% ,so the TCH Traffic Busy Threshold is set

to ( ? )

If cell B has 10 TCHs, traffic volume is 16.2 erl, the required

block rate is 2% ,so the TCH Traffic Busy Threshold is set

to ( ? )


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What is Co-BCCH cell In the same cellthere are 900M carriers and

1800M carriers, just one BCCH channel, only a CGI. Co-BCCH cell should be configured as concentric

cell

Overlaid subcell

Underlaid subcell

Concentric Cell (Co-BCCH)

Co-BCCH cell, also has some other names:

1Co-Cell

2Multiband Cell

3 900/1800 mix cell


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Dual BCCH cell: S3+S3

900M

1800M

CoBCCH cell: S3+3

20.08%31.941 3.4%27.316.624000OL: 3

10.717241UL: 3CoBCC

H

26.413.2201211800M:

3

13.220121900M: 3

Dual

BCCH

Trunking

Gain

Total

ErlErl

Available

TCHPDCH

SDCC

H

BCC

HTRX

Concentric Cell (Co-BCCH)


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Assignment GSM900M/DCS1800M Co-cell assignment must conform to the policies of

concentric cell. As the MS may be a non-dual-band one, the band supportingcapability of the MS must be judged before the channel assignment.

UnderlaidUnderlaidIncoming-to-BSC HO

Depend on Prefer subcell

in HO of intra BSCUnderlaidIntra-BSC HO

Depend on assign

optimum layerUnderlaidAssignment

UnderlaidUnderlaidImm-assignment

MS supports dual bandNot get the MS ability or MS

just support single bandAssignment

Type

When the MS supports the frequencies of both the overlay and underlay cells,assign the channel according to the channel assignment policy of the concentriccell. Otherwise, assign the channel in the overlay cell only.


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Configuration

When adding a new cellit should beconfigured as GMS900&DCS1800


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Configuration


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Configuration


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Others

Dual Band Network

900MHz -> 900MHz/1800MHz

DTX (Discontinuous Transmission)

Frequency hopping


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Summary

In this course, we have learned:

Traffic analysis and prediction

How to do TCH channel dimensioning

How to do SDCCH channel dimensioning

Capacity Enhancement Technology


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Erl Table


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Huawei GSM Capacity Planning