Capacity Planning

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Course Name

Capacity Planning

www.huawei.com

Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

Confidential Information of Huawei. No Spreading Without Permission

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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).

A=

BHC * tm T

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

A=

200 *180s = 10 Erl 3600 s


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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


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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 Traffic Model

Item

Shenyang

Dalian

Anshan

0.028

0.026

0.022

61

57

48

43

Busy Hr Call Times

1.64

1.64

1.64

1.64

Successful First Paging Ratio

80%

80%

80%

80%

Busy Hr Location Update Times

1.21

2.61

1.91

1.01

Second Paging Ratio

20%

20%

20%

20%

Average Handovers per Call

1.4

1.7

1.7

1.4

Busy Hr Short Message Receiving per User

4.6

3.2

2.0

1.5

Busy Hr Short Message Sending per User

4.2

3

1.5

1.4

10%/ 10%

10%/ 10%

10%/ 10%

10%/ 10%

Busy Hr Average Traffic per User Average Holding Time (s)

Roaming User In/Out Ratio Subscriber Active Ratio

Call Proportion

Others 0.02

100%

100%

100%

100%

Mobile-Mobile

40%

40%

40%

30%

Fix-Mobile

36%

36%

36%

38%

Mobile-Fix

24%

24%

24%

32%


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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. Traffic for specific area

At first, the subscribers in cities contribute most traffic. With the development, the subscribers in suburban areas grows fast. Consider future expansion


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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 this area 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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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.


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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 Frequency Reuse Pattern Max TRX Number of Cell Max Channel Number of Cell Erlang B Table Max Traffic (Erl) of Cell Traffic Distribution Max User No. and Coverage by One Cell Total user No. and traffic Site, Cell Number Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

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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. Block Rate

Channel Number

0.5

1.0

2

5

10

6

1.622

1.909

2.276

2.960

3.758

7

2.158

2.501

2.935

3.738

4.666

14

6.663

7.532

8.200

9.730

11.47

21

11.86

12.84

14.04

16.19

18.65

29

18.22

19.49

21.04

23.83

27.05

36

24.01

25.51

27.34

30.66

34.50


Er l ang B

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Basic Flow – By Max Coverage Coverage Planning Max Coverage per Cell Total Coverage of The Network Cell Number Traffic Distribution Traffic and User No. per Cell Erlang B Table Channel Number of Cell TRX Number of Cell Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

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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.

Interference Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

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Calculate the Coverage 3 – Sectors site

Omni site

Site Coverage Radius: R

Site Coverage Radius: R

Site distance: D=1.5R

Site distance: D=1.732R

Site Coverage Area=1.949R2

Coverage Area=2.598R2


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Erlang B Table

Erlang B table give the relationship between Channel Number , Call Block Rate (QoS) and Traffic. Block Rate

Channel Number

0.5

1.0

2

5

10

6

1.622

1.909

2.276

2.960

3.758

7

2.158

2.501

2.935

3.738

4.666

14

6.663

7.532

8.200

9.730

11.47

21

11.86

12.84

14.04

16.19

18.65

29

18.22

19.49

21.04

23.83

27.05

36

24.01

25.51

27.34

30.66

34.50


Er l ang B

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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 many TRX, cell, site is needed?


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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 many TRX, cell, site is needed?


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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.) Times in busy hour Event

Normal Cell

Internal

Boundary

Unit

Normal Location Update

0.4

0

1.2

Times/ Busy Hr

Periodic Location Update

2

2

2

/

IMSI Attach/Detach

0.2

0.2

0.2

/

Call Establish (O/D)

0.8/0.8

0.8/0.8

0.8/0.8

/

Point to Point Short Message (O/D)

2/2

2/2

2/2

/


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SDCCH Traffic Model Event

Normal Cell

Internal

Boundary

Unit

Normal Location Update

0.4

0

1.2

mErl/user

Periodic Location Update

1.8

1.8

1.8

mErl/user

IMSI Attach/Detach

0.16

0.16

0.16

mErl/user

Call Establish

1.24

1.24

1.24

mErl/user

Point to Point Short Message

6.9

6.9

6.9

mErl/user

Sum

10.5

10.1

11.3

mErl/user

Redundancy（ 20%）

12.6

12.1

13.6

mErl/user

SDCCH/TCH

50%

48%

52%

Consider 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 Conversion Conversion Trigger: Idle SDCCH < Idle SD Thrsh. SD Dynamic Allowed Yes/No Yes

Resource Check Ongoing?

No

SDCCH + 8 < Cell SD Maximum?

No Yes

Yes

System Busy? No No

Yes

SDCCH conversion allowed?

IS Idle TCH/F + idle (TCH/H)/2 ≤ 4 AND Idle TCH/F + idle (TCH/H)/2 ≤ No of TRX?

Yes Yes

Other SDCCH conversion ongoing? No

No

Stop


Select suitable TCH/F

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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).

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

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

Dynamic adjustment of other SDCCH in the cell should not be in progress (one conversion at a time).

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 Confidential Information of Huawei. No Spreading Without Permission Default: Yes

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

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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

T

T

T

T

T

T

T

T

T

T

T

T

T

S

T

S

T T

T


T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

I

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.


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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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Concentric Cell (Co-BCCH) 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

Normal dual band cells－ cells－TWO BCCH

COBCCH－ COBCCH－only one BCCH

1800M - TCH 1800M - BCCH

1800M - TCH

900M - TCH

900M - TCH

900M - BCCH

900M - BCCH

HUAWEI TECHNOLOGIES CO., LTD.

Overlaid subcell

Underlaid subcell

HUAWEI Confidential

Co-BCCH cell, also has some other names:

1、Co-Cell

2、Multiband Cell

3 、900/1800 mix cell



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Concentric Cell (Co-BCCH) Dual BCCH cell: S3+S3

CoBCCH cell: S3+3

900M

1800M

TRX Dual BCCH CoBCCH

900M: 3 1800M: 3 UL: 3 OL: 3

BCCH

SDCCH

PDCH

Available TCH

Erl

1 1 1 0

2 2 4 0

1 1 2 0

20 20 17 24 41

13.2 13.2 10.7 16.6

HUAWEI TECHNOLOGIES CO., LTD.

Total Erl

Trunking Gain

26.4 27.3 31.9

3.4% 20.08%

HUAWEI Confidential



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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. Type Assignment

Not get the MS ability or MS just support single band

Imm-assignment

Underlaid

Assignment

Underlaid

Intra-BSC HO

Underlaid

Incoming-to-BSC HO

Underlaid


MS supports dual band

Underlaid Depend on “assign optimum layer” Depend on “Prefer subcell in HO of intra BSC” Underlaid

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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 you www.huawei.com



Capacity Planning

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