Technical Guide for WCDMA LAC Planning(v1.1) ZTE

Internal Use Only

Technical Guide for WCDMA LAC Planning

Version v10

Release 2007-11-6 Implementation 2007-11-6

Released by Network Planning amp Optimization Dept ZTE Corp

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

Internal Use Only

Modification Record

File NoDrafter

ModifierMajor Points Modified

Update

DateVersion

Reason for

modification

1 WANG Feng 2007-3-6 V10 Guide

establishment

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

Contents

1 OVERVIEW1

2 PAGING PRINCIPLE PAGING CHANNEL PARAMETER AND SYSTEM

PARAMETER1

21 PAGING PRINCIPLE1

22 PAGING CHANNEL PARAMETER1

23 SYSTEM PARAMETER2

3 PAGING CAPACITY CALCULATION2

31 PCH CAPACITY CALCULATION2

311 Channel Number Confirmation2

312 GOS Confirmation2

313 Channel Capacity Calculation3

32 EACH UErsquoS PAGING TRAFFIC CALCULATION ON BUSY HOUR3

321 CS Traffic Model3

33 CALCULATION OF THE MAXIMUM SUBSCRIBER NUMBER THAT EACH LAC

SUPPORTS5

4 LAC DIVISION PRINCIPLE6

5 FEASIBILITY ANALYSIS OF WCDMA AND GSM CO-USE LAC7

51 WCDMA PAGING CAPACITY CALCULATION7

52 GSM PAGING CAPACITY CALCULATION7

53 ADVANTAGE AND DISADVANTAGE OF WCDMA AND GSM CO-USE LAC AS WELL AS

SUGGESTIONS8

6 LIBYA LAC DIVISION CASE9

Internal Use Only

1 Overview

The guide introduces WCDMA paging channel capacity calculation from which deduces the

maximum number of sectors that can be supported by each LAC with different traffic model as

well as general suggestions for LAC division the guide provides instructions for LAC planning on

the phase of WCDMA radio network planning

The guide includes paging principle paging capacity calculation and LAC division principle

2 Paging Principle Paging Channel Parameter and System

Parameter

21 Paging Principle

LAC is an abbreviation for Location Area Code a parameter represents UE paging location

When a UE is paged CN will send paging request through RNC to all NodeB that use the

corresponding LAC One LAC may be used by tens or hundreds of cells so the number of paging

message sent to RNC may be astonishing NodeB has to send paging request through limited PCH

to UE therefore too many NodeB that use one same LAC may cause NodeB paging overload

even signaling congestion and paging message drop But if too less NodeB use one same LAC

then there will be many boundaries of areas with different LAC that make it easy for UE on these

boundaries to update location frequently among areas with different LAC if UE is moving to an

area with different LAC and carrying out location update when a paging message is sent then UE

canrsquot receive the paging message sent to the area with the original LAC during the location update

period and therefore UE canrsquot be connected

22 Paging Channel Parameter

In 3G network paging happens in PCCH Logical channel PCCH is mapped to transmission

channel PCH and transmission channel PCH is mapped to physical channel SCCPCH so paging is

transmitted in physical channel SCCPCH

Related PCCH parameters are defined in Criterion 34108 Two modes 240bit10ms and

80bit10ms are transmitted in PCCH We usually use the mode 240bit10ms According to the

definition in the protocol the length of IMSI-GSM-MAP is 60bits with further consideration of

selection bits and paging reason bits one PCCH frame can carry 3 IMSI The length of TMSI-

GSM-MAP or PTMSI-GSM-MAP is 32bits therefore one 10ms PCCH frame comprises at most 5

TMSI paging or PTMSI paging

Paging channel of each cell includes one of the following combinations

1048727 3 IMSI paging

1048727 2 IMSI paging＋ at most 2 TMSI paging

1048727 1 IMSI paging + at most 4 TMSI paging

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

1

Internal Use Only

1048727 At most 5 TMSI paging

The maximum paging number in one Paging Type1 Record is 8 （ refer to 25331

maxpage1） therefore when it is IMSI paging the maximum paging capacity of each paging

channel of each cell is Min(38)=3 when it is TMSI paging the maximum paging capacity of each

paging channel of each cell is Min(58)=5

23 System Parameter

The present system parameter default settings are

Paging period is 640ms

Radio paging repeats 4 times

CN paging is resent once total sending times is twice

CN paging resending interval is 3 seconds

Paging total congestion rate is set as 02

3 Paging Capacity Calculation

31 PCH Capacity Calculation

311 Channel Number Confirmation

3 IMSI coding paging messages or 5 TMSI coding paging messages can be put in 1X240

PCH FP transmission therefore the maximum number of paging message that can be put in each

FP is defined as 5 Take the worst situation into account we define sub-channel number of each

PCCH is 3 which can be adjusted dynamically

312 GOS Confirmation

For improving paging success rate RNC uses multi-retransmission therefore the

corresponding relationship between call loss of multi-retransmission and call loss of single

retransmission needs to be calculated Presently systemrsquos RNC retransmission times are 4

Suppose that the call completion ratio first time is x1 call loss is s1 then x1=1-s1

Suppose that the call completion ratio second time is x2 call loss is s2 then x1=1-s2

Suppose that the call completion ratio third time is x3 call loss is s3 then x1=1-s3

Suppose that the call completion ratio forth time is x4 call loss is s4 then x1=1-s4

Then the call incompletion probability in these 4 times is

(1- x1)(1-x2)(1-x3)(1-x4) = s1s2s3s4

Suppose that call loss ratios each time are the same then

GoS single call lose = Power (actual call loss in RNC multi-retransmission 1RNC

retransmission times)

Here Power means multiplied by itself a certain number of times or extraction of a root

It is given that the actual RNC multi-retransmission call loss rate is 02 so GoS single call

lose = (0002)14＝0211474

Notice the proper actual RNC multi-retransmission call loss rate needs to be discussed

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

2

Internal Use Only

313 Channel Capacity Calculation

Erlang B formula requires average call loss of GoS in multi-paging because RNC repeat

multi-transmission and paging ratio is independent here we can regard that the average call loss of

GoS in multi-paging is equal to single call loss of GoS

Channel number (equivalent sub-channel number) and congestion rate are given we can

calculate PCH traffic according to Erlang B formula which is shown as follows

Here is average received call times in unit period of time is average call

duration which is the traffic

Actual Erlang B formula calculation is according to recursive algorithm

B(0rho)=1

B(Serversrho)=(rhoB(Servers -1rho) Servers)(1+rhoB(Servers -1rho) Servers)

Servers = Number of telephone lines

Intensity rho= Arrival rate of calls Completion rate of calls

Arrival rate = the number of calls arriving per hour

Completion rate = the number of calls completed per hour

We already know paging congestion rate is 0211474 when all uses IMSI paging sub-

channel number is 3 when all uses TMSI paging sub-channel number is 5 Input those into

Erlang B formula we can calculate paging traffic that PCH supports

IMSI paging paging traffic ＝200633(erl)

TMSI paging paging traffic ＝413931(erl)

32 Each UErsquos Paging Traffic Calculation on Busy Hour

321 CS Traffic Model

CS domain uses traditional call model represented by traffic on busy hour mainly includes

the following parameters

BHCA（A）Busy Hour Call Attempts

Holding Time（B）Each callrsquos duration unit s

Then single subscriberrsquos average traffic on busy hour ＝AtimesB3600（Erl）CS traffic model refers to voice service model in ZXWR Radio Performance Indicator

Technical Guide V40 which is shown in the following table Table 3-1 Traffic Density of Voice Service

Area3G UE density

Activated UE

proportion on busy

hour

Activated UE density

on busy hour

Single UErsquos traffic（Erl）

Traffic density（Erlkm2）

Initial phase

Dense urban

1200 100 1200 003 36

Mean urban 300 100 300 0013 39

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

3

Internal Use Only

Developing phase

Dense urban

3600 100 3600 004 144

Mean urban 900 100 900 0018 162

Stable phase

Dense urban

7500 100 7500 0045 3375

Mean urban 1950 100 1950 002 39

Table 3-2 Traffic Density of Visual Telephone

Area3G UE density

Activated UE

proportion on busy

hour

Activated UE density

on busy hour

Single UErsquos traffic (mErl)

Traffic density(mErlkm2)

Initial phase

Dense urban

1200 5 60 075 45

Mean urban 300 2 6 035 21

Developing phase

Dense urban

3600 8 288 15 432

Mean urban 900 5 45 07 315

Stable phase

Dense urban

7500 10 750 34 2550

Mean urban 1950 8 156 15 234

Paging traffic calculation on busy hour requires call times and call duration that converted by

traffic on busy hour in traditional traffic model CS122K call duration is set as 72 seconds

CS64K call duration is set as 60 seconds and then converted traffic model is shown in the

following table Table 3-3 CS Traffic Model after Conversion

Area

CS122K voice traffic CS64K visual telephone service

BHCA Call Duration(s) BHCA Call Duration(s)

Initial phaseDense urban 15 72 0045 60

Mean urban 065 72 0021 60

Developing phase

Dense urban 2 72 009 60

Mean urban 09 72 0042 60

Stable phase

Dense urban 225 72 0204 60

Mean urban 1 72 009 60

Notice BHCA and Call Duration need to be filled according to the actual situation of

countries and operators As to each subscriberrsquos traffic on busy hour in traditional CS traffic

model different BHCA will dramatically vary subscriber number that each LAC supports

BHCA in traffic model is counted bilaterally including MOC and MTC Therefore when

counting paging BHCA paging times shall be the half of call attempts which is shown in the

following table

Table 3-4 Paging BHCA Model

AreaCS122K paging

BHCA（timeshour）

CS64K paging BHCA（timeshour

）

CS domain paging BHCA（timeshou

r）

Initial phase

Dense urban 075 00225 07725

Mean urban 0325 00105 03355

Developing phase

Dense urban 1 0045 1045

Mean urban 045 0021 0471

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

4

Internal Use Only

Stable phase

Dense urban 1125 0102 1227

Mean urban 05 0045 0545

Paging traffic in RNC once paging can be calculated through paging BHCA model which is

equal to BHCA x paging duration (10ms one frame of PCCH)

Now ZTE RNC radio paging retransmission times is set as 4 RNC retransmission times is

set as 2 CN paging interval between two paging is 3 seconds CN twice paging proportion is 25

RNC transmits each paging for four times therefore each subscriberrsquos paging traffic is equal

to the sum of all paging traffic in the four paging initiated by RNC as well as two paging traffic

initiated by CN But the proportion of CN twice paging is not 100 so the paging traffic of CN

twice paging is lower which is the true situation in actual network Each subscriberrsquos CS paging

traffic on busy hour = (the first paging traffic initiated by RNC + the second paging traffic

initiated by RNC + the third paging traffic initiated by RNC + the forth paging traffic initiated by

RNC)(1+ the proportion of CN twice paging) The calculation result is shown in the following

table

Table 3-5 Each Subscriberrsquos CS Paging Traffic on Busy Hour

AreaThe first paging traffic

initiated by RNC（Erl）

The second paging traffic initiated by

CN（Erl）

Each Subscriberrsquos CS Paging Traffic

on Busy Hour（Erl）

Initial phase

Dense urban 214583E-06 536458E-07 911979E-06

Mean urban 931944E-07 232986E-07 396076E-06

Developing phase

Dense urban 290278E-06 725694E-07 123368E-05

Mean urban 130833E-06 327083E-07 556042E-06

Stable phase

Dense urban 340833E-06 852083E-07 144854E-05

Mean urban 151389E-06 378472E-07 643403E-06

33 Calculation of the Maximum Subscriber Number that Each LAC Supports

When network is configured with one PCH which is the common configuration in most

actual networks and RNC retransmission congestion rate is 02 if we use IMSI paging paging

traffic that PCH supports ＝200633(erl) if we use TMSI paging paging traffic that PCH supports

＝413931(erl) Therefore the subscriber number that each LAC supports = paging traffic that

PCH supportseach subscriberrsquos paging traffic on busy hour As to IMSI paging and TMSI paging

the subscriber number that each LAC supports is shown in the following table

Table 3-6 Maximum Subscriber Number that Each LAC Supports

Area

CS domain paging traffic of each

subscriber on busy hour (Erl)

Subscriber number that each LAC

supports in IMSI paging

Subscriber number that each LAC

supports in TMSI paging

Initial phase

Dense urban 912E-06 220000 454000

Mean urban 396E-06 507000 1050000

Developing phase

Dense urban 123E-05 163000 336000

Mean urban 556E-06 361000 744000

Stable Dense urban 145E-05 139000 286000

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

5

Internal Use Only

phase Mean urban 643E-06 312000 643000

4 LAC Division Principle

1) In LAC division the upper limit of LAC is determined by paging capacity of each cell

lower limit of LAC is determined by LAC update frequency If LAC is too large paging

times in the network will be increased dramatically even congestion will occur and

network paging success rate will be decreased If LAC is too small LAC update will be too

frequent and network signaling load will be increased Therefore these two factors need to

be considered in LAC division and LAC shall be divided properly according to actual

network situation

2) LACs of areas with different traffic characteristics vary Generally LAC of dense urban lt

LAC of mean urban lt LAC of suburb lt LAC of rural

3) Geographic characteristic and UE distribution shall be taken into account in LAC boundary

selection for decreasing LAC update frequency Generally LAC boundary is located in

areas that have lesser subscribers or lower handover probability

4) Try to avoid LAC boundary locating in areas that have group subscriber or VIP clients

5) Impact from load increase shall be considered in LAC division

6) NodeBs that use multi-carriers shall belong to one same LAC

7) NodeBs coverage shall be continuous in one same LAC

8) In principle LAC setting methods of 2G and 3G system are generally the same therefore

3G LAC planning can refer to 2G LAC planning Firstly calculate paging capacity in radio

interfaces according to paging process and channel characteristic secondly figure out

traffic that one LAC can support according to traffic model and finally set LAC according

to actual or estimated traffic in the network

9) RNC capacity in 3G network is generally larger than BSC capacity in 2G network thus the

number of RNC is smaller than that of BSC and one LAC will not step across BSC

therefore existing network LAC configuration and BSC traffic situation shall be taken into

account while planning 3G network LAC 3G LAC can be the combination of the existing

network LACs according to traffic balance principle 3G LAC boundary shall be better the

same with the boundary of the outer layer of combined 2G LACs

5 Feasibility Analysis of WCDMA and GSM co-use LAC

This section offers calculation of paging capacity without consideration of factors such as

paging congestion rate RNC multi-paging times and CN second paging but brief comparison of

ideal paging capacity of WCDMA and GSM system so as to analyze whether co-using LAC is

feasible as well as what advantages and disadvantages it may introduce

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

6

Internal Use Only

51 WCDMA Paging Capacity Calculation

3 IMSI coding paging messages or 5 TMSI coding paging messages can be put in 1X240

PCH FP transmission therefore the maximum number of paging message that can be put in each

FP is defined as 5

WCDMA maximum paging capacity per second the whole network uses TMSI paging one

10ms PCCHPCH frame includes 5 paging messages 100 PCCHPCH frames can be transmitted

on one PCH each second totally 500 paging messages

WCDMA minimum paging capacity per second the whole network uses IMSI paging one

10ms PCCHPCH frame includes 3 paging messages 100 PCCHPCH frames can be transmitted

on one PCH each second totally 300 paging messages

52 GSM Paging Capacity Calculation

According to GSM criterion as to Combined BCCHSDCCH cell each 235ms multi-frame

transmits 3 paging groups but as to Non-Combined BCCHSDCCH cell each 235ms multi-frame

transmits 9 paging groups BTS broadcasts paging request through paging group The following is

probable configuration in one paging request

2 IMSIs

1 IMSI and 2 TMSIs

4 TMSIs

Suppose all paging groups are used by PCH (extreme situation)

In IMSI paging as to Combined BCCHSDCCH cell each PCH each second transmits

10235=425 multi-frames each multi-frame has 3 paging groups each paging group has 2 paging

messages therefore 42532=25 paging messages are sent each second

In IMSI paging as to Non-Combined BCCHSDCCH cell each PCH each second transmits

10235=425 multi-frames each multi-frame has 9 paging groups each paging group has 2 paging

messages therefore 42592=76 paging messages are sent each second

In TMSI paging as to Combined BCCHSDCCH cell each PCH each second transmits

10235=425 multi-frames each multi-frame has 3 paging groups each paging group has 4 paging

messages therefore 42534=51 paging messages are sent each second

In TMSI paging as to Non-Combined BCCHSDCCH cell each PCH each second transmits

10235=425 multi-frames each multi-frame has 9 paging groups each paging group has 4 paging

messages therefore 42594=153 paging messages are sent each second

In different combination paging capacity comparison of WCDMA and GSM system is

shown in the following table

WCDMA GSM(Combined BCCH SDCCH cell)

GSM(Non-Combined BCCH SDCCH cell)

IMSI 300 25 76

TMSI 500 51 153From the upper table we can see that in the situation of general parameter configuration

WCDMA paging capacity is obviously stronger than that of GSM therefore traffic that WCDMA

each LAC supports is much higher than that of GSM

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

7

Internal Use Only

53 Advantage and Disadvantage of WCDMA and GSM co-use LAC as well as Suggestions

1）Advantage of GSM900 GSM1800 and WCDMA co-use LAC

When WCDMA and GSM are co-constructed especially when most WCDMA sites co-site

with GSM sites WCDMA uses the same LAC planning with that of GSM for speeding up data

configuration in network commissioning that facilitates fast commissioning of commercialized

WCDMA network

After long-term optimization GSM LAC planning project is mature and LAC division is

reasonable It accelerates LAC optimization process and decrease LAC optimization pressure if

WCDMA network uses the same LAC planning with that of GSM network

GSM LAC division reflects existing networkrsquos traffic distribution and paging load WCDMA

network is generally constructed after GSM network construction then unreasonable LAC

division caused by inexact traffic estimation will be decreased if WCDMA uses the same LAC

planning with that of GSM network

2）Disadvantage of GSM900 GSM1800 and WCDMA co-use LAC

WCDMA paging capacity is stronger than that of GSM so WCDMA paging capacity cannot

be used fully when WCDMA uses the same LAC planning with that of GSM network

Too small WCDMA LAC will cause frequent LAC update and heave signaling load UE on

the boundary may even not receive paging

Subscriber location and operation of WCDMA and GSM network may not the same so

GSM LAC planning may not comply with characteristic of WCDMA service statistic

3）Suggestions for LAC division when GSM900 GSM1800 co-exist with WCDMA

WCDMA LAC division can be operated separately from reference to GSM LAC division

which includes

WCDMA LAC boundary location refers to that of GSM GSM LAC boundaries are usually

on cells with low traffic and less handover times WCDMA LAC is larger than that of GSM but

WCDMA LAC boundary selection can refer to that of GSM completely One important reason to

take GSM LAC boundary as a reference is that WCDMA traffic is low in the initial phase and its

traffic distribution has no statistic meaning

The WCDMA LAC division refers to GSM LAC paging load statistics try to balance each

LACrsquos paging load GSM network is mature and GSM subscriber number increases slowly so it

will be more accurate in balancing WCDMA LAC paging load according to GSM existing

network traffic statistics

6 Libya LAC Division Case

There are totally 260 sites in the phase one and phase two Libya Tripoli network and they

belong to 7 LACs RNC10 has 2 LACs RNC1 has 5 LACs It is hard to avoid areas with high

traffic becoming LAC boundary due to too many LACs which will surly impact call performance

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

8

Internal Use Only

DT KPI is regulated in Libya acceptance including Call Setup Success Rate which will inevitably

be impacted by too many LACs

As to commercialized network stability is the primary demand Therefore we use this

project while combining LAC Sites controlled by RNC1 are classified into 2 LACs sites

controlled by RNC10 are classified into 1 LAC so the original 7 LACs now turn out to be the

present 3 LACs and then LAC update requests decrease dramatically The project is shown in the

following figure

Figure 1 LAC Combination Illustration

We use concentric circles mode to re-plan LAC LAC1080 and LAC1090 of RNC10 are

combined as one LAC LAC1010 LAC1020 and LAC1030 of RNC1 are combined as one LAC

LAC1050 and LAC1070 are combined as one LAC

In order to validate whether the maximum paging times of combined LAC exceeds

equipment capacity in OMCR LMT choose a cell randomly in each LAC to test and calculate

each LACrsquos maximum paging times on busy hour after combination so as to observe each LACrsquos

paging load The maximum paging times of RNC10 after combination on busy hour is 18+16=34

per second average paging times is 575+398=973 RNC1 has 2 LACs after combination the

total maximum paging times of LAC1010 LAC1020 and LAC1030 on busy hour is

165+21+19=565 per second average paging times is 514+517+584=1615 the total maximum

paging times of LAC1050 and LAC1070 after combination on busy hour is 165+14=305 per

second while average paging times is 504+379=883 System maximally supports 100 times

paging per second therefore after combination peak value of each LACrsquos paging channel

utilization ratio are separately 34 565 and 305 While average paging channel utilization

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

9

Internal Use Only

ratio are separately 973 1615 and 883

NoticeHere is a problem The sum of the maximum paging times of each LAC is larger

than the actual maximum paging times because it is impossible that all LACsrsquo paging times reach

their peak values at the same time the total maximum paging times is just estimation

Now the number of active subscriber in VLR in Libya is only around 30000 after RNC1

combination one of its LACrsquos paging utilization ratio is over 50 paging load is obviously too

large The RampD Dept has not provided a reasonable explanation or solution for the situation

therefore the combination project is temporarily suspended in the field

The PCH paging times calculation in the table is according to Section 624 in 25435－700

Protocol Two consecutive PCH frames carry paging indication information and paging message

separately and the two compose a complete paging message Related description in the protocol is

as follows

The PCH DATA FRAME includes the paging indication information and paging messages [FDD -

To page one User Equipment two consecutive PCH DATA FRAMEs with consecutive CFN

numbers are transmitted the first frame contains the Paging Indication Information and the second

contains the Paging Message] [TDD ndash To page one User Equipment one or more PCH DATA

FRAMEs are transmitted]

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements

10