OMP110040 GSM Location Area Planning ISSUE1.50

Location Area 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.




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

Contents

1. Location Area Overview

2. Location Area Planning Principle

3. Paging Strategies in Location Area

4. LAC capacity calculation



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Definition of Location Area

In GSM protocols, a mobile communication network is divided into multiple service areas according to the codes of location areas. Thus the network pages a mobile subscriber through paging its location area.

Location area is the basic unit of paging areas in a GSM system. That is, 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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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.

When MS is powered on or LAC of current cell is found to be different from its originally stored contents, MS will inform network of the current location area via location update, and the network uses the LAI for paging. Generally the allocation and coding of LAC is set at the early stage of network construction, and seldom modified during the operation.

The size of location area (LA) is one of key factors in the system. If the LA coverage is too small, the chances for MS to update location increase, and this will increase the signaling load in the system. If the LA coverage is too large, when network conducts paging to the MS, the same paging information will be transmitted in a large number of cells, and this will lead to the heavy load on CCCH. The adjustment of LA size has no unified standard. Operating departments can decide whether to adjust the size according to the currently running network. If the CCCH signaling load is heavy because of too big LA coverage, then reduce the size of LA, and vice versa. It is generally recommended to set the LA as large as possible. The calculation of LA is related with the paging strategies of different manufacturers. If Huawei equipment is employed, it is recommended to set the TRX number within the range of 300 in one location area. In the early stage of network construction, the traffic is not heavy, so the TRX number in one LA can be larger than this value. It is necessary to monitor the PCH load and the increase of traffic in a long term. If necessary, PCH capacity can be increased by adding one extended BCCH channel.

While making LA planning, try to make use of the geographical distribution and behaviors of mobile subscribers to allocate the LA, so as to achieve the objective of reducing the times of location update at the boundary between location areas. Please note that LAC in cell parameters must be in consistent with that in MSC. Otherwise, call setup failure will occur.



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Definition of Location Update

The Time of location update

To inform the system the LA in which the MS is to facilitate paging

The Purpose of location update

Normal location updatingPeriodical location updatingIMSI attach

First of all, we should know the 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? There are three cases:The first one: Getting into a new LA. This type of location update is called forced location update. The second one: regular update, it is also called periodical location update. Even if the MS doesn’t enter a new location area, GSM system will also require the MS to perform regular location update, thus to grasp the MS current status.The third one: IMSI attach

The location update signaling be sent on SDCCH channel.Normal location updatingThe normal location updating procedure is used to update the registration of the actual Location Area of a mobile station in the network. The location updating type information element in the LOCATION UPDATING REQUEST message shall indicate normal location updating.The normal location updating procedure shall also be started if the network indicates that the mobile station is unknown in the VLR as a response to MM connection establishment request.To limit the number of location updating attempts made, where location updating is unsuccessful, an attempt counter is used. The attempt counter is reset when a mobile station is switched on or a SIM card is inserted.Upon successful location updating the mobile station sets the update status to UPDATED in the SIM, and stores the received Location Area Identification in the SIM. The attempt counter shall be reset. Periodic updatingPeriodic updating may be used to notify periodically the availability of the mobile station to the network. Periodic updating is performed by using the location updating procedure. The location updating type information element in the LOCATION UPDATING REQUEST message shall indicate periodic updating.The procedure is controlled by the timer T3212 in the mobile station. If the timer is not already started, the timer is started each time the mobile station enters the MM IDLE substate NORMAL SERVICE or ATTEMPTing TO UPDATE. When the MS leaves the MM Idle State the timer T3212 shall continue running until explicitly stopped. IMSI attach procedureThe IMSI attach procedure is the complement of the IMSI detach procedure (see section 4.3.4). It is used to indicate the IMSI as active in the network. A flag (ATT) is broadcast in the SYSTEM INFORMATION TYPE 3 message. It indicates whether the attach and detach procedures are required to be used or not.The IMSI attach procedure is invoked if the detach/attach procedures are required by the network and an IMSI is activated in a mobile station (i.e. activation of a mobile station with plug-in SIM, insertion of a card in a card-operated mobile station etc.) within coverage area from the network or a mobile station with an IMSI activated outside the coverage area enters the coverage area. The IMSI attach procedure is used only if the update status is UPDATED and if the stored Location Area Identification is the same as the one which is actually broadcasted on the BCCH of the current serving cell. Otherwise a normal location updating procedure is invoked independently of the ATT flag indication.IMSI attach is performed by using the location updating procedure. The location updating type information element in the LOCATION UPDATING REQUEST message shall in this case indicate IMSI attach.



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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



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Contents







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Location Area Planning Principle

1. It is no suggested that the size of LA is too large or too small.

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.

It is no suggested that the size of LA is too large or too small.

The size of a location area, plays a key role in a GSM system. If the coverage area of a location area is too small, the mobile station will perform frequent location update. In this case, the signaling flow in the system will increase, SDCCH channel perhaps be congestion..If the coverage of a location area is too larger, however, the network will send a paging

message in multiple cells until the mobile station is paged. In this case, the paging traffic will be higher, perhaps PCH will be congestion and the signaling flow at the Abis interface will increase. .



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2. In order to reduce the number of location update at the edge of LA,

MS’s geography distributing and behavior should be fully used

to design LA

LAC1

LAC2

LAC3

LAC4

LAC5

LACn

Suburban 4

LACn

Suburban 3

LACnSuburban n

LACn

Suburban1

LACnSuburban 2

Urban

In order to reduce the number of location update at the edge of LA, MS’sgeography distributing and behavior should be used enough to design LAC (shown as the figure)

Application scene: Dense Urban

If there are more than two location areas in a big city with great traffic, the landforms (such as mountains and rivers) within this city can be used as edges of LA. If no such landforms available within this city, the areas (such as streets and shopping centers) withgreat traffic cannot be used as edges of LA.

In the intersected areas between urban and suburban, where the edges of LA should not be located, while should be on the other side of the BTS, in order to avoid frequent location update.

Application scene: Suburban

When the coverage area between urban and suburban is not continued, it’s possible that a MS can not perform the periodical location update on time, so when the protect time expires (set in MSC side), implicit detach occurs to the MS. Now, suppose this MS enters urban which has the same LAC with the suburban, so it should not perform the normal location update, then it happens that the although the MS has good signal but not in the serving area. That is why the distribution of location areas in cities and suburbs is different. Generally, suburban areas or counties occupy independent location areas. In cities, the distribution of location areas is similar to a concentric circle. (The areas in the internal circle can be divided into several location areas due to the requirements on capacity. The concentric circle can be divided into several fragments.)

Practice has proved that if the location areas are divided according to the previous methods, as shown in the Figure in the slide both coverage and call connected ration can be



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3. LA should be a continue area, avoiding or reducing BTS hybrid

networking

4. Location area design for dual-band network (please refer to the

next page)



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Location Area Design For Dual-band

There are three dual-band networking modes

MSC MSC

BSC BSC

900BTS

1800BTS

MSC

BSC BSC

900BTS

1800BTS

MSC

BSC

900BTS

1800BTS

900/1800BTS

Independent MSC Networking

Co-MSC/ Independent BSC Networking

Co-BSC Networking

Independent Networking Hybrid Networking

There are three dual-band networking modes, namely, independent MSC networking, co-MSC/independent BSC networking, and co-BSC networking, among which the former two are called independent networking, and the later is called hybrid networking.



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Independent MSC Networking

1800 cell

MSCMSC

BSCBSC

MSCMSC

BSCBSC BSCBSC

1800 cell

900 cell

900 cell

LA1

LA2

BSCBSC

Location Update between GSM900 and DCS1800 is easily to happen

Handover between GSM900 and DCS1800 is inter MSC handover

If 1800 MHz cells and 900 MHz cells are under the control of two MSCs respectively, their location areas are different. Therefore, you must set related parameters 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. Meanwhile, when designing signaling channels, you must fully consider the load resulted from location update.



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Co-MSC/Independent BSC Networking

1800 cell

MSCMSC

BSCBSC

900 cell

BSCBSCBSCBSC BSCBSC

1800 cell

900 cellLA2LA1

Location Update between GSM900 and DCS1800 is not easily to happen

Handover between GSM900 and DCS1800 is inter BSC handover while not inter MSC

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.



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Co-MSC/Independent BSC Networking

In the early network construction stage, it is 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 frequency band or

geographic location, as shown in figure.

900M Cell 900M Cell 900M Cell

LA1 LA2

900M Cell

1800M 1800M 1800M 1800M 1800M 1800M1800M Cell



LA2

LA1

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, you 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, you must carefully design the edges of the location areas.

If the location area is divided in terms of band, because frequent location updates are resulted from inter-band handover and cell reselection, you must set related parameters 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. Meanwhile, when designing signaling channels, you must fully consider the load resulted from location update.



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Co-BSC Networking

MSCMSC

BSCBSC BSCBSCBSCBSC BSCBSC

1800 cell

900 cell

1800 cell

900 cell

LA2LA1

Location Update between GSM900 and DCS1800 is not easily to happen

Handover between GSM900 and DCS1800 is intra BSC while not inter MSC handover



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Contents







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Contents


3.1 Characteristics of the Paging Message

3.2 Paging Strategies

3.3 Paging Channel and Paging Group

3.4 Parameters Related to Location Area



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Characteristics of the Paging Message

•the BSC and BTS receive many paging messages, which may lead to overload

•Unacknowledged mode on the LAPDm layer of the Um interface

Characteristics of the Paging Message

•The assignment message and paging message (CS paging and PS paging) share the downlink CCCH

•TMSI paging strategy

•IMSI paging strategy

The paging message has the following characteristics:

Both the TMSI paging and the IMSI paging can be used. The IMSI paging has higher reliability. The TMSI paging can avoid eavesdropping of IMSI paging and increase the paging combination ratio on the radio channels, but the TMSIs of some MSs may be incorrect temporarily and cannot be paged.

The message on the downlink CCCH is transferred in unacknowledged mode on the LAPDm layer of the Um interface. There is a risk of message loss.

The paging message to an MS is sent in all the cells of the location area where the MS is located. Therefore, the BSC and BTS receive many paging messages, which may lead to overload.

The assignment message and paging message (CS paging and PS paging) share the downlink CCCH. The paging message can be sent only on the PCH, while the assignment message can be sent on the AGCH or PCH. Proper scheduling is required.



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Contents








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Paging Strategies

LA paging or global paging

IMSI paging or TMSI paging

Paging time and paging duration setting

IMSI implicit detach timer setting

If MS’s LA is available in VLR, paging message will be delivered to all the cells in local LA registered, it is called LA paging. If the paging message is delivered to all the cells in the whole MSC, it is called global paging.

HUAWEI MSC supports paging retransmission in 5 times at most, and can set TMSI strategy or IMSI strategy for each paging.



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Paging Strategies

LA paging or global paging

The following solution is adopted according to local LA distribution

condition and subscribers’ behavior

Dense urban

– It takes an obvious effect to adopt the whole network paging at the last time

Marginal areas

– There is no obvious effect to adopt the whole network paging

Network where PCH is about to overload or already overload

– It is suggested to adopt LA paging at the second or third time

Segmental network

– It may adopt the whole network paging at the last time if paging capacity is enough

The planning of the LA and the distribution of subscribers determine whether to choose the LA paging or the global paging.

For the dense urban areas where the coverage of the LA is small and the cross-LA paging is possible, the global paging is recommended for the last paging.

For marginal areas where the coverage of the LA is large and the cross-LA paging can be avoided, the global paging is not the best choice.

If the PCHs are or will be overloaded, the LA paging is recommended for the second or third paging.

For the segmental network where cells in the same LA are not in continuous coverage and the planning cannot be modified, the global paging is recommended for the last paging when possible.



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Paging Strategies

IMSI paging

There is only IMSI while no TMSI information in paging message

TMSI paging

It needs to carry TMSI and IMSI (used to calculate paging group by BSC) information in paging message.

Depending on the MSC paging strategy

IMSI paging or TMSI paging

When the PCHs are or will be overloaded, the TMSI paging is recommended to lower the possibility of the PCH overloading.

Generally, when the TMSI paging is used, some mistakes may occur and the MS may not respond to the paging. Therefore, the TMSI paging is recommended for the first paging and the IMSI paging is recommended for the second and third paging.



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Paging Strategies

Paging time and paging duration setting

Paging time and paging duration setting is based on signaling analysis in

A interface

It is suggested to set the paging time to be more than 2 times

Generally, paging duration is suggested to set to around 10s, no more

than 20s

signaling analysis in A interface

Paging Response Delay

The Second Paging Response Paging Time

Paging Duration

Also available in MSC side

The paging time and paging duration is calculated by analyzing the signaling flow on the A interface. For example, the paging times and paging duration are set according to the paging response delay (the majority paging delay and the longest paging delay) and the second paging response. The paging times are recommended to be more than 2 times, and the total paging duration is recommended to be 10s, no more than 20s.



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Paging Strategies

IMSI implicit detach timer (in MSC) setting

If the duration of the periodic

location update is less than 30s,

the duration of this timer is

recommended to be set to five

minutes plus twice the duration

of the periodic location update.

If the duration of the periodic

location update is more than

30s, the duration of this timer is

recommended to be set to 5-10

minutes plus the duration of the

periodic location update.

Therefore, it is advised to set the duration of the IMSI Implicit Off-line Timer to 1.1-2.1 times as the duration of periodic location update in the BSC.

According to RNO experience, if IMSI implicit detach timer in MSC more than 2 hours, it takes an obvious effect to increase paging successful raion by reducing this duration. Because less the timer duration is, more quickly the network knows the MS’s network drop status. Paging message will not be delivered to the MS in implicit detach, so the chance of failing to page is reduced. But at the same time, the time of “the subscriber you dialed is powered off” will also increased when successful paging ratio is increased.

Therefore, it is advised to set the duration of the IMSI Implicit Off-line Timer to 1.1-2.1 times as the duration of periodic location update in the BSC.

If the duration of the periodic location update is less than 30s, the duration of this timer is recommended to be set to five minutes plus twice the duration of the periodic location update.

If the duration of the periodic location update is more than 30s, the duration of this timer is recommended to be set to 5-10 minutes plus the duration of the periodic location update.



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Paging Combination

Paging combination is used to improve the utilization of the Um interface.

Paging command1

Paging command2

Paging command3

Paging command4

BTS BSC

Paging command 1&2&3&4

MS1

MS2

MS3MS4

The paging command issued by the BSC to the BTS

contains the information of only one MS

The BTS combines the most possible paging commands for

the MSs that belong to the same paging group and sends one paging request to these

MSs

Paging combination is used to improve the utilization of the Um interface. The paging command issued by the BSC to the BTS contains the information of only one MS. The BTS combines the most possible paging commands for the MSs that belong to the same paging group and sends one paging request to these MSs. In other words, one paging request contains the TMSI or IMSI information of multiple MSs. One TMSI consists of 3 Arabic numerals, and one IMSI consists of 15 Arabic numerals. The length of the paging request is limited. The combination capability depends on whether the combined paging commands use the IMSI paging or TMSI paging. The MS determines whether to respond to the paging request by resolving the Mobile Identity field (including the TMSI or IMSI) in the paging request.

The protocols specify three paging request types. Their combination modes are as follows:

Paging request type I (one or two paging commands are combined in one paging request message)

IMSI

IMSI+IMSI

IMSI+TMSI/P

TMSI/P

TMSI/P+TMSI/P



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Paging request type II (two or three paging commands are combined in one paging request message)

TMSI/P+TMSI/P

TMSI/P+TMSI/P+IMSI

TMSI/P+TMSI/P+TMSI/P

Paging request type III (four paging commands are combined in one paging request message)

TMSI/P+TMSI/P+TMSI/P+TMSI/P

Therefore, the efficiency of paging combination depends on whether the TMSI paging or the IMSI paging is used. This strategy is configured on the MSC side. Usually, the last paging retransmission uses the IMSI paging (the TMSI of the MS is considered to be faulty)



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Speech Service Paging Preferred

Basic Principle

Performance Analysis

This function helps to ensure the quality of speech services in paging

overload conditions where groups of short messages are transmitted.

However, the quality of short message services and PS services may be

affected.

PCH3

CS Paging1

SM Paging1

PS Paging1

SM Paging2

CS Paging2

…

CS Paging3

Paging queue is full

New CS Paging

The first non-CS paging (SM paging or PS

paging) is replaced by the CS paging message

…

Speech Service Paging Preferred

Basic Principle

This function is performed to ensure that the speech service paging is preferred. If the PCH queue is full when the BTS receives a speech service paging message from the BSC, the BTS searches for a short message or PS service message starting from the head of the PCH queue. If such a message exists, it is replaced by the CS paging message. If such a message does not exist, the speech service paging message is discarded.

Short Message Paging Procedure

The short message paging procedure is similar to the speech paging procedure. The only difference is that the CHAN NEED field in the short message paging command is the SDCCH request. The BTS distinguishes short message paging and speech paging through this field.

PS Paging Procedure

The PS paging procedure is similar to the speech paging procedure. During the PS paging procedure, the function of the SGSN is similar to that of the MSC. The paging strategy of the SGSN determines whether the P-TMSI or IMSI is used for paging.

Only the MS in the STANDBY state can be paged. The SGSN obtains the Routing Area (RA) of the MS and sends a paging message to the entire RA.



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Contents








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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

As shown above, CCCH=PCH+RACH+AGCH; downlink CCCH=PCH+AGCH; and uplink CCCH=RACH. In the above combinations, combination 3 and 4 must be allocated to slot 0 of the BCCH carrier configured for the cell; while combination 5 must be allocated to timeslots 2, 4 and 6 of the BCCH carrier. The FACCH works in the frame stealing mode, for which no fixed time sequence will be allocated. In addition, the cyclic multiframe period of SACCH/C4 and SACCH/C8 is 102 frames.



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Structure of Main BCCH

5046-

4942-45

4

1

4

020-39

16-

19

12-

15

1

1106-92-510

Frame

Number

ICX4CX4SF……CX4CX4SFCX4BX4SFChannel

Grpup5

Group3,4

(same as

Group2)

Group2Group1Group

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

504

9

4

84713-461211109876543210

Frame

Number

RRRRR……RRRRRRRRRRRRRRChannel

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

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

The TDMA/FDMA multiplexing is used in GSM, the information needed in the synchronization between MS and BTS is provided by FCCH+SCH.

The MS determines the frequency of the BCCH carrier by searching for the frequency correction Burst transmitted via FCCH; then it finds the SCH (synchronization channel) according to the relationship between SCH and FCCH and decodes the current frame number and BSIC for synchronization with BTS. Furthermore, it determines whether the cell is barred or not and decodes the system information on BCCH.

In the structure diagram of extended BCCH, except that the F and S timeslots are replaced by Idle timeslots, the rest of the structures are the same as that of the main BCCH.



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Structure of Combined BCCH

50

46

-

49

42

-

45

4140

36

-

39

32

-

35

3130

26

-

29

22

-

25

2120

16

-

19

12

-

15

11106-

9

2-

510

Frame

Number

I

A3

×4

A2

×4

SF

D3

×4

D2

×4

SF

D1

×4

D0

×4

SF

C

×4

C

×4

SF

C

×4

B

×4

SFChannel

I

A1

×4

A0

×4

SF

D3

×4

D2

×4

SF

D1

×4

D0

×4

SF

C

×4

C

×4

SF

C

×4

B

×4

SFChannel

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

It is used in the configuration of cells of low traffic density and small capacity. The Combined BCCH is only configured at timeslot 0.

Channel combination: FCCH＋SCH＋BCCH＋CCCH+SDCCH/4+SACCH/4

SDCCH/4: Stand-alone dedicated control channel. Each TDMA multiframe with 51 frames has 4 SDCCH;

SACCH/4: Slow SDCCH/4 associated control channel;

Compared with the main BCCH channel, 4 signaling channels are added to the 51 frames. The functions of these 4 signaling channels are the same as those of the SDCCH8 channel. Therefore, this channel combination can be taken as a combination of the functions of the above two channels. This combination take effect on two aspects: first, this reduced the quantity of AGCH+PCH on CCCH and only a small-capacity system is provided; second, this combination provides a certain quantity of signaling channels in timeslot 0. Thus, it is unnecessary to assign SDCCH8 channels in a small-capacity system. This channel suitable for small-capacity systems. And it is also an example of the flexible GSM network configuration.



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Structure of Logical Channel Combination Frame-Main SDCCH

5

0

4

948

44-

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

IIIA3×4

A2×4

A1×4

Channel

A0×4

D7×4

D6×4

D5×4

D4×4

D3×4

D2×4

D1×4

D0×4

IIIA7×4

A6×4

A5×4

Channel


D:SDCCH; A:SACCH; I:IDLE

Channel combination: SDCCH/8+ SACCH/C8

SDCCH/8: Stand-alone dedicated control channel. Each TDMA multiframe with 102 frames has 8 SDCCH.

SACCH/C8: Slow SDCCH/8 associated control channel.



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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.

In GSM system, the downlink common control channel mainly includes Access Granted Channel (AGCH) and Paging Channel (PCH). It serves to send the access granted (immediate assignment) and paging messages. CCCH is shared. According to the configuration of traffic channel and traffic model, CCCH can be carried by either one or multiple physical channels. Moreover, CCCH and SDCCH can share one physical channel. The MS needs to know how the CCCH(s) is/are configured, so that it can find and select one to listen to. The CCCH_CONF is just used to tell the MS about this matter.

When CCCH is a physical channel which combined with SDCCH, the capacity of CCCH is the lowest. When CCCH is a physical channel which is not combined with SDCCH, the capacity is higher. For other cases, the more the physical channels are used as CCCH, the higher the CCCH capacity is.

Configuration of CCCH_CONF is specified according to the traffic model. This model is closely related to the cell location and environment. According to experiences, when TRX quantity in the cell is 1 or 2, it is recommended to use a combined CCCH as the common control channel. When TRX quantity in the cell is 3 or 4, it is recommended to use a non-combined CCCH as the common control channel.

Currently CCCH can be configured according to actual traffic load. If the paging load is very heavy, the paging traffic of cell should be distributed via multiple CCCH physical channels other way. Special attention should be paid to PCH in CCCH. Generally PCH capacities of various cells under one LAC must be the same.



P-34


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)

As downlink CCCH includes both AGCH and PCH, it is necessary to set the number of blocks, which are reserved for AGCH among CCCH message blocks. To let MS know such configuration information, the system information of each cell includes a configuration parameter, which is the number of access granted blocks reserved (BS_AG_BLKS_RES). This parameter actually assigns the proportion of AGCH and PCH on CCCH. It affects the time of MS’s response to the paging.

The network operator can adjust this parameter to balance the traffic of AGCH and PCH by referring to the following principles:

1. Principle for BS_AG_BLKS_RES: make this parameter as small as possible withoutcausing overload of AGCH, so as to increase the capability of paging and improve the system performance.2. Generally it is recommended to select 1 (when CCCH_CONF is 1 combined CCCH), 2

or 3 (when CCCH_CONF is one of other values) for BS_AG_BLKS_RES.3. During operation, observe the statistics of AGCH overload and adjust

BS_AG_BLKS_RES properly.

Note: In Huawei system, when AGCH has been all occupied, if PCH is free, it can be used to send the immediate assignment command. If AGCH blocks reserved is set as 0, the immediate assignment would be sent only when there is free PCH channel. Therefore, a fixed capacity reserved for AGCH is necessary.



P-35


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

This parameter specifies the number of paging sub-channels that are assigned in a cell. In the network, MS only monitors the paging sub-channel it belongs and ignores the content of the others. When this parameter is set larger, there will be more paging sub-channels in the cell and accordingly there will be less MS in each paging sub-channel. Therefore, the bearing capability of PCH will be more (theoretically the capacity of each PCH does not increase, but the buffer that buffers paging message in each BTS is increased, which makes the sending of paging messages more even in the time domain), and the lifetime of MS battery will be longer. The value of this parameter should be as small as possible under the condition that the overload on PCH does not occur. In the operation, the PCH load should be measured regularly and the value of this parameter should be adjusted properly according to the PCH load. In a location area, paging is sent in all the cells. Therefore, all cells in the same location area should have the same or nearly the same PCH capacity (number of paging sub-channels). In the area where the PCH bears a medium or large load, it is suggested to be set as 6 or 7 (6 or 7 multi-frames are used as a cycle of paging). For the area with a small load, it is set as 4 or 5. Besides, it is often set as 2.Note:1. One CCCH block (four consecutive CCCH timeslots) can bear the information of two

IMSI pagings or four TMSI pagings or two AGCH immediate assignments.2. In idle mode MS camps in a cell. The DSC is initialized to the integer part of 90/N (N

is BS_PA_MFARMES, with the value range: 2~9). when MS can successfully decode the message on paging sub-channel, DSC will increase by 1, but it will not exceed initially value. If decoding fails, DSC will decrease by 4. If DSC<=0, the downlink signaling link fails, resulting in cell reselection.



P-36


CCCH Configuration

The CCCH can be configured on the TS0 of C0 in BCCH+CCCH mode, or on the three

extended group sets on the TS2, TS4, and TS6 in CCCH mode.

The CCCH configuration is indicated by CCCH_CONF parameter. The code must be consistent

with the actual configuration of CCCH.

36Four physical channels are used for the CCCH but not combined with the SDCCH.110

27Three physical channels are used for the CCCH but not combined with the SDCCH.100

18Two physical channels are used for the CCCH but not combined with the SDCCH.010

3One physical channel is used for the CCCH and combined with the SDCCH.001

9One physical channel is used for the CCCH but not combined with the SDCCH.000

Number of CCCH Blocks in One BCCH Multi-FrameMeaningCCCH-CONF Code

For a CCCH, the number of paging sub-channels (represented by N) is calculated as follows:

CCCH CONF = 001: N = (3 - BS AG BLKS RES) x BS PA MFRMS

CCCH CONF = others: N = (9 - BS AG BLKS RES) x BS PA MFRMS



P-37


PAGING_GROUP

The GSM system supports a maximum of 9×9=81 paging groups. the MS can be

divided into 81 sub-groups at most from the opinion of the paging group.

No matter what kind of combination mode is adopted, the number of blocks used

for paging in every 51 multi-frame does not exceed 9. The system enables the 51

multi-frame to cycle again , with a quantity of “BS-PA-MFRAMS” (number of frames

of the same paging) of 51 multi-frames as a period.

Suppose that the number of frames of the same paging is 7 and the number of

paging blocks (9or3-BS_AG_BLKS_RES: number of access granted reserved blocks)

of each 51 multi-frame is 4. Then the paging group number cycles between 0-27 (28

in total).

The number of paging blocks in each 51 multiframe is calculated according to the following formula:

If the CCCH and SDCCH are combined in one physical channel:

Number of paging groups per super-group=3－number of access granted reserved blocks

in other cases, i.e. the CCCH is not combined with the SDCCH:

Number of paging groups per super-group =9－ number of access granted reserved blocks

Both the above two parameters: “BS_AG_BLKS_RES” and the “BS-PA-MFRAMS”are broadcasted in system information



P-38


PAGING_GROUP

PCH10....

PCH10

1

2

9

10

The First

Pagingperiod

8

AGCH AGCH

PCH56

16PCH56

AGCH AGCH

AGCH AGCH

AGCH AGCH

AGCH AGCH

AGCH AGCH

BS_PA_MFRAMES= 8 Multi-frame period (51 frames)

.

.

.

.

.

.

.

.

BS_AG_BLKS_RES=2

8 Multi-frame form one

period

（PCH N—the Nth paging channel）

PCH1

PCH1

1 Non-Compounding CCCH

.

.

.

.

.

.

.

.

The second Pagingperiod

Both assignment message and paging message share downlink CCCH channel.

Assignment message can be transmit either by AGCH or PCH, while paging message can be sent only by PCH.



P-39


Determination of CCCH_GROUP and PAGING_GROUP for MS in Idle Mode

MS’s CCCH_GROUP(0，...，BS_CC_CHANS -1)

=((IMSI mod 1000) mod (BS_CC_CHANS x N ))div N

MS’s PAGING_GROUP(0，…， N-1)

=((IMSI mod 1000) mod (BS_CC_CHANS x N)) mod N

where

N =

IMSI = International Mobile Subscriber Identity

mod = Modulo.

div = Integer division.

MFRMS-PA-BS)_( ×− AGBCONFCCCH

For example：Channel configuration is Main BCCH＋SDCCH+ extended BCCH+TCH+ extended BCCH+TCH+TCH+TCH，BS_AG_BLKS_RES =7， BS_PA_MFRAMES =2。Two IMSIs is 460042709000034, 4600427090037

Then

MS1: CCCH _GROUP: ((460042709000034 mod 1000) mod (3*(9-7)*2))div ((9-7)*2) = 2

PAGING_GROUP: ((460042709000034 mod 1000) mod (3*(9-7)*2))mod ((9-7)*2) = 2

MS1: CCCH _GROUP: ((460042709000037 mod 1000) mod (3*(9-7)*2))div ((9-7)*2) = 0

PAGING_GROUP: ((460042709000037 mod 1000) mod (3*(9-7)*2))mod ((9-7)*2) = 1

MS1 accesses in TS2, and listens to the paging message in 2th PAGING_GROUP, while MS2 accesses in TS0, and listens to the paging message in the first PAGING_GROUP.



P-40


Contents








P-41


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

Detach process (IMSI) refers to the process that MS informs the network that it is shifting from working state to non-working state (usually a power-off process), or the SIM card is being taken out from MS. Upon receiving the notice from MS, the network knows that the IMSI subscriber is in non-working state. Therefore, if the MS is called, the call connection will be implemented.

IMSI attach process is opposite to detach process. It is the process that MS informs the network it has entered the service area (usually a power-on process) or SIM card has been inserted into MS. After entering service state again, MS will test whether the current location area (LAI) is the same with the latest LAI recorded in MS. If yes, MS will start IMSI attach process. Otherwise MS will start location update process, upon receiving the location update or IMSI attach process, the network will indicate that this IMSI subscriber is in working state.

Note that ATT configuration of different cells in the same LAI must be the same. It is because IMSI detach process will be started when MS is power-off in the cell with ATT set as yes. The network will record that this subscriber is in non-working state and reject all the called connection requests to this subscriber. When MS is power-on again, if it is in the same LAI as it was power-off (thus the LAI update process will not be started) but in another cell, and ATT of the cell is set as no, then the MS will not start IMSI attach process. In this case, this subscriber can not be called normally until the MS starts the location update process.



P-42


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)

MS will make location update when detecting the change of location. Besides, MS will make periodic location update controlled by parameter T3212. Once MS read T3212 from system information, it will store it in SIM card. When the time reaches T3212 value, the location update process will be triggered. The shorter the period is, the better the performance is. But it will bring more signaling load for system. On setting of this parameter, the processing capability of MSC and BSC, the flux of A interface, Abis interface and Um interface, the flux of HLR and VLR should be considered. Generally this parameter is set as a larger value for urban area and smaller for suburb, countryside or the place with poor coverage.

Large T3212( 16 hours 20 hours) is recommended for the area with heavy traffic, and small T3212 (3 hours, 2 hours) for the area with normal traffic. For the area where the traffic exceeds the system capacity, it is recommended to set T3212 as 0 (no periodic location update). To set the value of T3212 properly, it’s necessary to conduct long-term measurement on the processing capability and flux of each entity in the system. If any overload occurs, increase the value T3212.

Note that this value should be smaller than the period by which the network queries the IMSI attached subscriber. Otherwise, the following situation occurs: When MS has not done any operation in a certain time, and it is not yet the time for periodic location update, the network will set IMSI flag of MS as detached, because its query result shows that MS has not done any operation. Thus, the network will not process the paging of this MS. So, before MS initiates another round of periodic location update, once there is a call to the MS, the network will voice the calling party that the called MS is has been powered off. As usual, the T3212 is set smaller than one third of the MSC’s check time.

When MS reselects a cell in a different location area, it will make a non-periodic location update and reset T3212 in the new cell. If it reselects in the same location area, then the timer value will be remainder of the original one divided by the new T3212.



P-43


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

This parameter aims to prevent the frequent location update that may increase the network signaling flow and to reduce the possibility of paging message loss. If the value of this parameter is too small, the location update will have “ping-pong” effect and the signaling load on SDCCH will increase. Moreover, the call setup successful rate of the system will become lower because MS will not respond paging during location update. When it is too large, the cell where MS resides for a long time may not be the best when MS enters a new location area. When MS reselects a cell from a different location, MS will start a location update. Due to the fading of radio channel, C2 values of two cells at the their edges will fluctuate, which causes MS to reselect frequently. To reduce the influence, GSM specifications define a parameter called cell reselection hysteresis. It is required that MS start cell reselection only when C2 value of the adjacent cell (in a different location area) is greater than that of serving cell and their difference is greater than the value of reselection hysteresis.

Appropriate cell reselection hysteresis is important for network optimization. Usually it is recommended to be 8~10dB and can be adjusted in the following cases:When the traffic of an area is very heavy and the signaling overload often occurs, it is

recommended to increase the value of cell reselection hysteresis of the adjacent cells belonging to different LACs.When the overlapping coverage of the adjacent cells belonging to different LAC are wide, it

is recommended to increase the value of cell reselection hysteresis.



P-44


Contents







P-45


Location Area Planning Procedure

The number of paging blocks sent in each second (set to N)

Paging time in each paging block (set to B) Erlang in each LA (set to T)

The number of TRXs in each LA (set to NTRX）

The number of subscribers in

each LA (set to S)

×

1

2

3

4

5

6

The maximum paging times in each second (set to P)



P-46



Step1: The number of paging blocks sent in each second (set to N)

1 frame = 4.61ms

1 multiframe = 51 frames = 0.2354s

For non-combined BCCH：

For combined BCCH：

)/)(_(25.4

)/(2345.0

)_(

SPBAGBCONFCCCH

SPBAGBCONFCCCHN

−×=

−=

)/)(9(25.4 SPBAGBN −×＝

)/)(3(25.4 SPBAGBN −×＝

As a result, the number of paging times in each hour, the traffic allowed in each location area, and the number of carriers supported in each location area can be deducted.

The calculation of location areas varies with the paging strategies designed by different carriers.

During early network construction stage, the traffic is not great, so a location area can accommodate more TRXs. However, it is still necessary to monitor the PCH load and traffic growth.

When the traffic grows great, enhance the PCH capacity by adding a BCCH to the system, but the number of TCH channels is reduced by one .

PB is Paging Block



P-47



Step2: Paging time sent in each paging block (set to B)

For IMSI paging strategy，B=2 (PT/PB）

For TMSI paging strategy, B=4 (PT/PB）

2 IMSI pagings

2 TMSI and 1 IMSI pagings

4 TMSI pagings

1 2 3Each Paging Block

According to protocols, each paging block has 23 bytes, and can send 2 IMSI pagings, or 2 TMSI and 1 IMSI pagings, or 4 TMSI pagings.

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)

PT is Paging Time



P-48



Step3:The maximum paging times in each second (set to P)

For non-combined BCCH：

For combined BCCH：

）（ PBPTBSPBAGBCONFCCCHP /)/)(_(25.4 ×−×=

）（ PBPTBSPBAGBP /)/)(9(25.4 ×−×=

）（ PBPTBSPBAGBP /)/)(3(25.4 ×−×=



P-49



Step4: Traffic volume in each LA (set to T)

For expansion network

Check traffic statistics ”Paging Measurement per BSC\Abis Interface

Paging Measurement per Cell\Delivered Paging Message for CS Service”,

and calculate paging time/second, which should not more than the value

basing on the step before, besides, it’s suggested to check ”Call

Measurement\Flow Control Measurement per Cell\OVERLOAD rate of

paging”

For new-built network

Calculate basing on a traffic model supposed (refer to the next slide)



P-50



For new-built network

Average holding time: D seconds

MOC:MTC:PTP SM (receiver) = E:F:G

Call times corresponding to each paging:

Paging resend ratio: C= 1+Sencond Paging Ratio

Average paging load: M ( that is to say, paging channel may be congested

when more than maximum paging capacity M )

GFFE

++

)()()9(25.4

GFCMDFEBAGBT

+××+××−×

=Then

orratioMTCratiopagingondthe

MDratiopagingCSBAGBT_)__sec_1(

)__()9(25.4×+

××××−×=



P-51



Step5: The number of TRXs in each LA (set to NTRX）

Step6: The number of subscribers in each LA (set to S)

Busy hour traffic volume per subscriber: G Erlang

) TRXper Volume Traffic Average()Ratio TCHH1( ×+TNTRX＝

Site Type

Channel Number

Average Traffic Volume per cell

Average Traffic Volume per TRX

Erlangtable

GTS＝



P-52


Question1

non-combined BCCH, AGB=2

IMSI paging:50%TMSI paging:50%

Average paging load: 50%

MSC paging resend ratio: 1.1

MOC:MTC:SM(receiver)=5:5:1

Average holding time: 60s

Given Condition

How much Traffic volume is there in each LA?

( )paging blocks in 1 multiframe( ) paging blocks can be sent in a second

( )paging times can be sent in each paging block

( )paging times can be sent in each second

( ) paging times

( )paging times in an hour

Traffic volume is ( )ERL for each call

( )ERL corresponds( )paging times



P-53


Busy hour traffic volume per subscriber: 0.03ERL

TCHH ratio: 70％

Traffic volume per TRX: 4.8Erlang

support( )subscribers

support( )TRXsHow many TRXs can be

support in each LA？

How many subscribers in each LA？

Question1



P-54


Given Condition

50%Call times corresponding to each paging

50%Average Paging Load

TMSIPaging Strategy

4.8Average Traffic Volume per TRX

58Average Holding Time70%TCHH Ratio

50%MTC ratio15%The second Paging Ratio

2BS PA MFRMS2BS AG BLKS RES9CCCH CONF

1.How much Traffic volume(Erl) is there in each LA?

2.How many TRXs can be support in each LA？

Question2



P-55


non-combined BCCH, AGB=2

TMSI paging strategy

Average Paging Load: 50%

MSC paging resend ratio: 1.25

the ratio of MS successful MTO times to total call times: 30％

Average Holding Time: 60s

Given Condition

1.How much Traffic volume(Erl) is there in each LA?

2.How many TRXs can be support in each LA？(Without TCHH)?

( )call times/(s.Erl) in 60s

( )paging times/(S.Erl)

( )successful MOC/(s.Erl)

s.Erl is Erlang/second

( )paging blocks in 1 multiframe( ) paging blocks can be sent in a second

( )paging times can be sent in each paging block

( )maximum paging times can be sent in each second

( )paging times in a second

Question3



P-56

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Documents

OMP110040 GSM Location Area Planning ISSUE1.50