capacity planning

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Capacity Planning

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Page1Copyright © 2008 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, BHC is busy hour call times, tm is user

mean hold time, T is 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 and

rationality. Therefore, a reasonable investment decision must be based on the prediction

of 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

1.52.0 3.24.6Busy 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.

Traffic for specific areaTraffic for specific area

Consider future expansionConsider future expansion

� 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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Example� Capacity needs expansion. According to the service development,

population growth and mobile popularity, the subscribers in thisarea are expected to reach 100,000 in 2 years.

� Roaming factor = 10%.

� Mobile factor (moves within the local network) = 10%.

� Dynamic factor (with burst traffic considered) = 15%.

� The network capacity = 100000 * (1 + 10% + 10% + 15%) = 135,000.

� However, consider the congestion, the max traffic taken by the 85% of the value by Erl B table.

� The network capacity = 135, 000/85% = 158,800, about 160,000.


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Contents






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Overview� According to different situation, we have two method for

planning: Fixed Site Location and 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 TRX

number of every cell. By traffic prediction, calculate max user number per cell. According

to 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 the

total 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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Estimate Number of BTS Needed

� Given: amount of subscriber, bandwidth available,

reused density, traffic model

� total operator’s bandwidth/planned freq. reuse rate

� ==>number of TRX per cell

� ==>channel per cell

� ==>subscriber per cell

� ==>number of BTS needed for traffic reasons

� VERY rough initial estimation!


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How Many Subscribers should a Cell Support?

� Given: Number of subscribers in area, Traffic load per subscriber,

Coverage area, radius

� Total traffic volume

� ==> traffic per sq.km

� ==> traffic per cell

� ==> number of TRX needed per BTS

� Allow extra capacity for roamer and busy hour traffic

Transmission should not be the bottleneck of the system


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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

ErlangErlang B 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.

� Each TRX has 8 channels. Obtain the voice channel

numbers by detracting the SDCCH required. Typically use

7.2 TCH per TRX.

� By number of voice channels and call loss ratio (generally

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

of one base station by Erlang B table.


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By Frequency Reuse� Dividing the Erl number by the average busy-hour traffic per

subscribers (for example, 25/20 mErl in urban/suburban),

obtain the max number of subscriber of one base station.

� According to subscriber density, obtain the coverage area of

the base station.

� Calculate the number of base stations by total user number

or total traffic of the area.


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Erlang B Table� Erlang B table give the relationship between Channel

Number , Call Block Rate (QoS) and Traffic.

Er l ang B

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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Basic Flow – By Max Coverage

Channel Number of Cell

TRX Number of Cell

Traffic and User No. per Cell

Max Coverage per Cell

ErlangErlang B 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=1.5R

Site Coverage Area=1.949R 2

Site Coverage Radius: R

Site distance: D=1.732R

Coverage Area=2.598R 2

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.

Er l ang B

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 Short Message (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/user13.612.112.6Redundancy（（（（20%））））

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 Check Ongoing?

SDCCH + 8 <Cell SD Maximum?

ISIdle TCH/F + idle (TCH/H)/2 ≤ 4

ANDIdle TCH/F + idle (TCH/H)/2 ≤ No of TRX?

Stop Select suitable TCH/F

System Busy?

SDCCH conversionallowed?

Other SDCCH conversion ongoing?

No

Yes

Yes

No

Yes

Yes

Yes

No

Yes

No

No

No

SD DynamicAllowed Yes/No

� After the SDCCH dynamic adjustment process is triggered, dynamic

adjustment can be started under the following conditions:

� There should not be a resource check ongoing (usually at night during low traffic hour).

� The BSC internal flow control level should be less than 0 (i.e. the BSC is not in overload).

� Dynamic adjustment of other SDCCH in the cell should not be in progress (one

conversion at a time).

� “SD Dynamic Allocation Allowed” should be “Yes” (feature enabled).

� The number of the SDCCHs +8 should be less than “Cell SD Maximum”.

� IF the number of the cell idle TCH/F + (the number of the cell idle TCH/H)/2 ≤ 4 AND ≤

the number of the TRXs in the cell THEN the dynamic SDCCH adjustment is not allowed.

ELSE allowed.

� Then a suitable TCH/F should be selected for conversion.

� Parameter: Cell SD Maximum

� Range:0~255

� Default: Configured SDCCHs + 8 (i.e single dynamic)

� Description: The maximum number of SDCCHs in the cell.

� Parameter: SD Dynamic Allocation Allowed

� Range: Yes, No

� Default: Yes

� Description: Indicates whether SDCCH dynamic allocation is allowed.PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com

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Contents






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Tight Frequency Reuse (Cont.)� 2*3 or 1*3 or 1*1

� With the same frequency band, Tight Frequency Reuse

increase the TRX number per cell, which decides the

capacity of the cell.


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Half Rate� Half rate voice coding uses new coding algorithm to reduce

the coding rate to half that of full rate. Thus, one physical

channel that can only support one call now can support two

calls by half rate.

� If the half rate service is used, the voice capacity expands

twice without adding TRX.


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The Function of HR

T T T T T T T T T T T S T T T T T T T T T T T T IT

T T T T T T S T T T T T T

T T T T T T T T T T T T S


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Estimation of the Number TCHF

� Some situations, need to estimate the number of TCHFs

and TCHHs available in a cell.

� With the estimated proportion between the TCHFs and

TCHHs you can set the TCH Traffic Busy Threshold more

accurately.

� The estimation of the number of TCHFs and TCHHs in a cell paves the way for the

proper configuration of the TCHFs and TCHHs in the cell. Also, with the estimated

proportion between the TCHFs and TCHHs you can set the TCH Traffic Busy

Threshold more accurately.


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Estimation of the Number TCHF

� Providing the traffic volume (1 Erl) and the allowed call loss

rate (B%), the number of channels required in the cell (n)

can be calculated according to the Erlang B table.

� Suppose that a cell has two TRXs and the cell is configured

with one BCCH and two SDCCHs.


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Examples

� According to the Erlang B table, when the traffic volume is X

the number of channels required in the cell is 10.

� The number of channels that can be configured as TCHs in

the cell is 13 (2 x 8 - 3).

� Because 13 > 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 17

and 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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HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

� What is Co-BCCH cell？� In the same cell，there 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)

1800M 1800M 1800M 1800M ---- TCHTCHTCHTCH

1800M 1800M 1800M 1800M ---- BCCHBCCHBCCHBCCH



Normal dual band cellsNormal dual band cellsNormal dual band cellsNormal dual band cells－－－－TWO BCCHTWO BCCHTWO BCCHTWO BCCH




COBCCHCOBCCHCOBCCHCOBCCH－－－－only one BCCHonly one BCCHonly one BCCHonly one BCCH

Co-BCCH cell, also has some other names:

� 1、Co-Cell

� 2、Multiband Cell

� 3 、900/1800 mix cell


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HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

Dual BCCH cell: S3+S3

900M

1800M

CoBCCH cell: S3+3

20.08%31.941

3.4%27.316.624000OL: 3

10.717241UL: 3CoBCCH

26.413.2201211800M: 3

13.220121900M: 3Dual BCCH

Trunking GainTotal ErlErlAvailable TCHPDCHSDCCHBCCHTRX

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 supporting

capability of the MS must be judged before the channel assignment.

UnderlaidUnderlaidIncoming-to-BSC HO

Depend on “Prefer subcell

in HO of intra BSC”UnderlaidIntra-BSC HO

Depend on “assign

optimum layer”UnderlaidAssignment

UnderlaidUnderlaidImm-assignment

MS supports dual bandNot get the MS ability or MS

just support single bandAssignmentType

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


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Configuration

When adding a new cell，it should be configured 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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Thank youwww.huawei.com


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