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

Location Area Planning

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

Definition of Location Area

� GSM mobile communication network is divided into multiple

service areas according to the codes of location areas.

� Location area is the basic unit of paging areas in GSM system.

The paging message of a subscriber is sent in all cells of a

location area.

� A location area contains one or more BSCs, but it belongs to one

MSC only.

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Definition of Location Area


Location Area Code LAC

� Definition

� To locate the location of MS, the whole area covered by each

GSM PLMN is divided into different location areas. LAC is used

to identify different location areas.

� Format

� LAI contains LAC, which is composed of two bytes. LAC

adopts hexadecimal coding. The available range is from 0001H

to FFFEH. The code 0000H and FFFFH cannot be used

(please refer to specification GSM0303, 0408, and 1111). One

location area can contain one or more cells.

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Location Update

� Purpose of location update:

� To inform the system the LA in which the MS is to

facilitate paging

� When need the MS perform location update

� Getting into a new LA

� Periodical location update


Size of location areas

� The size of a location area, plays a key role in a GSM system.

� If the size of location area is too big, the paging traffic will be higher,

perhaps PCH will be congestion.

� If the size of location area is too small, the MS will occur more

location update process. The signaling traffic is higher, SDCCH

channel perhaps be congestion.

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Paging VS Location update Traffic

Paging Location update

# of cells in Loc. area

signalingtraffic

optimum numberof cells in Loc. area

minimize signaling trafficoptimum varies with network evolution


Division of location areas� If two or more location areas are present in a big city of great

traffic, the landforms, such as mountains and rivers within this city

can be used as edges of the location areas.

� If no such landforms available within this city, the areas (such as

streets and shopping centers) with great traffic cannot be used as

edges of the location areas.

� In the intersected areas of urban areas and suburban areas, to

avoid frequent location update, should design the edges of

location areas near the outer base stations.

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Location Area Design For Dual-band

� If 1800 MHz cells and 900 MHz cells are under the control of two

MSCs respectively, their location areas are different.

� Related parameters should be set to maintain the mobile stations

stay in the 1800 MHz cells where the traffic is absorbed. In this

case, the times for the mobile station to handover between the two

bands and reselect cells will decrease.

� Designing signaling channels, fully consider the load resulted from

location update.



� If 1800 MHz cells and 900 MHz cells share a MSC, at the early

network construction stage, they are suggested to use the same

location area without affecting the network capacity.

� If the restriction on paging capacity is present, two location areas

must be divided for them either in terms of band or geographic

location, as shown in Figure .

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� If the location is divided in terms of geographic location, the

frequent location updates resulted from inter-band handover and

cell reselection can be avoided.

� However, need to modify the related data of the original 900 MHz

network. In addition, at the edges of the location areas, because

the location updates caused by intra-band and inter-band

handover and cell reselection is present simultaneously, the

signaling flow is huge at these edges. As a result, carefully design

the edges of the location areas.


26-frame multi-frameTCH/F+SACCH/F (full-rate TCH)

TCH/H+SACCH/H (half-rate TCH)

51-frames multi-frameFCCH+SCH+BCCH+CCCH (main BCCH)

FCCH+SCH+BCCH+CCCH+SDCCH/4+SACCH/4 (combined BCCH)

BCCH+CCCH (extended BCCH)

SDCCH/8+SACCH/8 (main SDCCH)

Physical Combination of Logical Channel

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Structure of Main BCCH

5046-4942-45414020-3916-1912-1511106-92-510Frame

Number

ICX4CX4SF……CX4CX4SFCX4BX4SFChannel

Grpup5

Group3,4

(same as

Group2)

Group2Group1Group

1 multi-frame (51TDMA Frames) 235.38ms Downlink

5049484713-461211109876543210Frame

Number

RRRRR……RRRRRRRRRRRRRRChannel

1 multi-frame (51TDMA Frames) 235.38ms Uplink

F:FCCH; S:SCH; B:BCCH; C:CCCH; I:IDLE; R:RACH


Structure of Combined BCCH

5046-49

42-45

414036-39

32-35

313026-29

22-25

212016-19

12-15

11106-92-510Frame

Number

IA3

�4A2

�4SF

D3

�4D2

�4SF

D1

�4D0

�4SF

C

�4C

�4SF

C

�4B

�4SFChannel

IA1

�4A0

�4SF

D3

�4D2

�4SF

D1

�4D0

�4SF

C

�4C

�4SF

C

�4B

�4SFChannel

Grpup5Group4Group3Group2Group1Group


47-50464541-4437-4014-3610-136-9540-3Frame Number

D2�4RRD1�4D0�4R……RA1�4A0�4RRD0�4Channel

D2�4RRD1�4D0�4R……RA3�4A2�4RRD3�4Channel


F:FCCH; S:SCH; B:BCCH; C:CCCH; D:SDCCH ;A:SACCH; I:IDLE; R:RACH

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Structure of Logical Channel Combination Frame-Main SDCCH

50494844-

47

40-

43

36-

39

32-

35

28-

31

24-

27

20-

23

16-

19

12-

158-114-70-3

Frame

Number

IIIA7�

4

A6�

4

A5�

4

A4�

4

D7�

4

D6�

4

D5�

4

D4�

4

D3�

4

D2�

4

D1�

4

D0�

4Channel

IIIA3�

4

A2�

4

A1�

4

A0�

4

D7�

4

D6�

4

D5�

4

D4�

4

D3�

4

D2�

4

D1�

4

D0�

4Channel


47-50

43-46

39-42

35-38

31-34

27-30

23-26

19-22

15-18

1413128-114-70-3Frame

Number

A4�4

D7�4

D6�4

D5�4

D4�4

D3�4

D2�4

D1�4

D0�4

IIIA3�

4A2�

4A1�4

Channel

A0�4

D7�4

D6�4

D5�4

D4�4

D3�4

D2�4

D1�4

D0�4

IIIA7�

4A6�

4A5�4

Channel


D:SDCCH; A:SACCH; I:IDLE


ATT

� Value range: Yes, No

� Content It is used to inform MS whether IMSI attach-detach is

allowed in this cell. If it is set to “Yes”, the network will not

process the connection to the called mobile subscriber when MS

is power-off. Thus network processing time and radio resources

are saved. Otherwise the network will process the connection

even though the MS has been powered off.

� Recommendation Yes

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CCCH_CONF � Value range: 1 Non-Compounding CCCH, 1 Compounding CCCH, 2

Non-Compounding CCCHs, 3 Non-compounding CCCHs, 4 Non-

compounding CCCHs.

� Content: It is “Common Control Channel Configuration”. CCCH

configuration determines the capacity of PCH, AGCH and RACH. This

parameter can be automatically configured by the BSC Data Auto

Configuration System according to the TRX channel configuration.

� Recommendation: When there is one TRX in the cell, one combined

CCCH is recommended (in a system with few paging messages in

location area). For others, it is configured according to the number of

TRX in the cell.


BS_AG_BLKS_RES

� Value range: 0~2 (1 combined CCCH), 0~7 (others)

� Unit: Block

� Content: It is also called Access Granted Blocks Reserved. It is

the number of CCCH channel message blocks that are reserved

in one multi-frame for access granted channels (AGCH).

� Recommendation: 2 (non-combined CCCH)

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BS_PA_MFRAMES

� Value range: 2 9

� Unit: Multi-frame period (51 frames)

� Content: It is Paging Channel Multi-frames. It defines the

number of multi-frames used as a cycle of paging sub-

channels.

� Recommendation: 2


T3212

� Value range: 0~255

� Unit: 6 minutes

� Content: It is the Periodic Location Update Timer. It defines the

interval of periodic location update.

� Recommendation: 30 (for urban area), 20 (for suburban area)

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CRH

� Value Range: 0~14, the step size is 2dB

� Unit: dB

� Default Value: 6

� Description: Cell Reselection Hysteresis. It is the parameter used

when cell reselection happens between two location areas.

� Location: Cell Attributes/Idle Mode/Basic Idle Parameters


TCH Immediate Assignment

� Value Range: Yes, No

� Default Value : No

� Description: Option "Yes" means that TCH channel can be

immediately assigned as signaling and traffic channel when

SDCCH has no available resource. The option "No" means that

only SDCCH can be assigned.

� Location: Cell Attributes

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Calculating For Location Area

� Generally, the capacity of a location area is calculated as

follows:

The number of paging blocks sent in each second � the

number of paging messages sent in each paging block =

the maximum paging times in each second.



The number of paging blocks sent in each second

1 frame = 4.61ms,

1 multiframe = 51 frames = 0.2354s;

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� suppose the number of access grant blocks is AGB, the number of

blocks, the number of paging blocks sent in each second is

calculated by the following formulas:

� For non-combined BCCH, the number of paging blocks sent in

each second = (9 – AGB)/0.2345 (paging block/second).

� For non-combined BCCH, the AGB is 2 according to Huawei BSC.

Therefore, the number of paging blocks sent in each second is 29.7

(paging block/second).



� suppose the number of access grant blocks is AGB, the number of

blocks, the number of paging blocks sent in each second is

calculated by the following formulas:

� For combined BCCH, the number of paging blocks sent in each

second = (3 – AGB)/0.2345 (paging block/second).

� For combined-BCCH, the AGB is 1, so the number of paging blocks

sent in each second is 8.5 (paging blocks/second).

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� The number of paging messages sent in each paging block

(X)

� According to protocols, each paging block has 23 bytes, and

can send 2 IMSI pages, or 2 TMSI and 1 IMSI pages, or 4

TMSI pages.

� According to the paging strategies of Huawei MSC, if the IMSI

paging mechanism is adopted, the number of paging

messages sent in each paging blocks is 2 (paging times/paging

block); if the TMSI paging mechanism is adopted, it is 4

(paging times/paging block)


Calculating For Location Area� If the IMSI paging mechanism is adopted, for non-combined

BCCH

when AGB = 2, P = 59.47 (paging times/second);

� For combined-BCCH


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Calculating For Location Area� If the TMSI paging mechanism is adopted, for non-combined

BCCH,


� For combined BCCH,




� Paging Capability (Hour)= [(CCCH CONF-BS AG BLKS

RES)�Paging Strategy�3600] / [51�TDMA period

�(1+Sencond Paging Ratio)]

� Paging Strategy: IMSI paging or TMSI paging

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� LAC Capability (ERL)= [(CCCH CONF-BS AG BLKS

RES)�Paging Strategy� Average Holding Time �Average

Paging Load at BTS ] / [51�TDMA period�(1+Sencond

Paging Ratio) � MTC Ratio]

� Paging Strategy: IMSI paging or TMSI paging



� LAC Capability (TRX)= LAC Capability (ERL) / Average

Traffic Volume per TRX � (1+TCHH Ratio) ]

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TMSIPaging Strategy

15%Sencond Paging Ratio

5BS AG BLKS RES

Main BCCHCCCH CONF



50%Average Paging Load at BTS

TMSIPaging Strategy

4.8Average Traffic Volume per TRX

58Average Holding Time

70%TCHH Ratio

50%MTC Ratio

15%Sencond Paging Ratio

2BS PA MFRMS

2BS AG BLKS RES

9CCCH CONF

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LAC Capability (TRX)= 6006 / 4.8 � (1+ 0.7) ] =736

( ) 3728130.15120.0046151

3600]422)-[(9 (Hour) Capability Paging =

+××××××=

( ) 60065.00.1510.0046151

5.0 58]42)-[(9 (ERL) Capability LAC =

×+×××××=


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