Gsm Cell Parameters Huwaie 1

8/9/2019 Gsm Cell Parameters Huwaie 1

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GSM Cell Parameters N-1

Confidential Information of Huawei. No Spreading Without Permission

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

GSM Cell Parameters


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

Descriptions

1. Cell Parameters Overview

2. Cell Parameters Introduction

3. Case Study


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Cell Parameters Overview

Cell Parameters include the most of radio network parameters

transmitted via Um interface.

Via receiving cell parameters, MS is able to exactly select,

access and coordinate with the network through which

different kinds of service is provided.

Via reasonably cell parameters, BTS can run in high point and

whole system can be effectively utilized to provide more and

better services although basing on limited resources.

By reading cell parameters, MS can access the network, perform cell

selection and reselection, fully utilize various services provided by the

network, and achieve favorable cooperation with the network.


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Cell Parameters Overview

Cell Parameters can be sent through two kinds of logical channels

BCCH (in idle mode)

SACCH (in dedicated mode)

Cell parameters can be divided into two parts:

Cell parameters is sent on BCCH, which are used in idle mode.

Cell parameters is sent on SACCH, which are used in dedicated mode.


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Descriptions

1. Cell Parameters Overview

2. Cell Parameters Introduction

3. Case Study


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Introduction to Cell Parameters

Huawei GSM cell parameters:

Network Identity Parameters

Idle Mode Parameters

Call Control Parameters

Cell Selection and Reselection Parameters

Other Parameters


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Cell Data Mapping in Different Statuses of MS

Power on

Select Network

(Network Identity Para. )

Cell Selection

(Cell Selection Para.)

Paging Mode

(Idle Mode Para.)

Dedicated Mode

(Call Control Para.)

Cell Reselection Mode

(Cell Reselection Para.)

Idle Mode

(Idle Mode Para.)

Access Network

(Call Control Para.)


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Network Identity Parameter — CGI

Network identity parameters mainly include

Cell Global Identity (CGI)

Base Station Identity Code (BSIC)

As a global cellular mobile communication system, GSM conducts strict coding for each

GSM network in every country, and even every location area, BTS, and cell, so as to

ensure that each cell corresponds to a unique number all over the world. The adoption ofthis coding scheme can achieve the following objectives:

1. Ensure that MS can correctly identify the current network, so that MS can accurately

select the network expected by subscribers and operators.

2. Ensure that the network can know the real-time position of MS, so that the network can

provide various service requests from the MS.

3. Ensure that the MS can report correct neighbor cells’ information to the network during

conversation, so that network can perform handover when necessary to keep continuous

conversation for the mobile subscribers.


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Network Identity Parameter — CGI

CGI=MCC+MNC+LAC+CI

Once MS receives SYS INFO, it decodes the CGI information, and

decides whether it can stay in the cell according to the MCC and MNC

indicated by CGI.

At the same time, it judges whether the current location area is

changed, so as to decide whether to execute location update. During

the location update process, MS will report the new LAI to the network,

so that the network can know the LA in which MS is currently located.

As a global cellular mobile communication system, GSM conducts strict coding for each

GSM network in every country, and even every location area, BTS, and cell, so as to

ensure that each cell corresponds to a unique number all over the world. The adoption ofthis coding scheme can achieve the following objectives:

1. Ensure that MS can correctly identify the current network, so that MS can accurately

select the network expected by subscribers and operators.

2. Ensure that the network can know the real-time position of MS, so that the network can

provide various service requests from the MS.

3. Ensure that the MS can report correct neighbor cells’ information to the network during

conversation, so that network can perform handover when necessary to keep continuous

conversation for the mobile subscribers.


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Mobile Country Code（MCC）

Definition: MCC consists of 3 decimal numbers. It indicates the home

country of the mobile subscriber.

Format: MCC is composed of 3 decimal numbers. The coding range is

decimal 000~999.

Location: Cell Attributes

MCC is used in international mobile subscriber identity (IMSI) and

location area identity (LAI).

1. LAI. It is periodically transmitted in cell parameters of each cell.

MCC indicates the home country of GSM PLMN. MS uses the

received information as the important basis for network selection.

2. IMSI of MS. MS’s IMSI also contains MCC. It shows the resident

country of the mobile subscriber. When MS logs on the network or

applies for a certain service, it must report its IMSI to the network

(When TMSI is unavailable.). The network uses the MCC in IMSI to

judge whether this subscriber is an international roaming subscriber.

As the unique country identity standard, MCCs are allocated and

managed by the International Telecommunication Union (ITU). ITU

Default Value E.212 (blue book) stipulated the MCC number for

every country. The MCC of China is 460 (decimal). Due to the

special meaning of MCC, modification is prohibited once it has been

set in the network.


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Mobile Network Code（MNC）

Definition: MNC is used to uniquely identify a specific GSM PLMN

network in a certain country (decided by MCC).

Format: MNC is composed of two decimal numbers. The coding range

is decimal 00~999.


MNC is used in international mobile subscriber identity (IMSI) and location area

identity (LAI).

LAI. It is periodically transmitted in each cell. Here, MNC indicates the network

number of GSM PLMN. MS uses the received information as an important basis

for network selection.

IMSI also contains MNC. It shows the home GSM PLMN network of the subscriber.

When MS logs on the network or applies for a certain service, it must report IMSI

to the network (When TMSI is unavailable.). The network judges whether this

subscriber is a roaming subscriber according to the MNC in IMSI, and uses it as

one of the important parameters for addressing to subscriber HLR.

If a country has more than one GSM PLMN, different networks must have different

MNC. MNC is allocated by relevant telecommunication management department

of the country. One operator can have one or more MNC (which regards to the

scale provided by the service, usually one operator has one MNC.). Different

operators can share the same MNC. Currently, China have two GSM networks,

which are operated by China Mobile and China Unicom. Their MNC are 00 and 01

respectively. Due to the special meaning of MNC, modification is prohibited once it

has been set in the network.


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Location Area Code（LAC）

Definition: To locate the location of MS, the whole area covered by eachGSM 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 Descriptions, 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 networkconstruction, 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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Cell Identity（CI）

Definition: To uniquely identify each cell in the GSM PLMN, the

network operator needs to allocate one code for each cell, which is

the cell identity (CI). Cell identity, together with LAI, is used for

identity of each cell in the world.

Format: CI is composed of 16 bits, The available range is 0~65535.


Cell Identity (CI) is one part of Cell Global Identity (CGI), transmitted

in each cell.

There is generally no restriction for the allocation of CI. Value from 0

to 65535 (decimal) can be obtained. But it should be ensured that

one location area cannot have two cells with the same CI.

CI is usually determined in the network design. Except for some

special cases, CI value should not be changed during the operation

of the system.

Please note that one location area is not permitted to have two or

more cells using the same CI. CI on MSC should be the same as

that on BSC. Otherwise, MS cannot make calls in this cell.


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Network Identity Parameter — BSIC

BSIC=NCC+BCC

In GSM system, each BTS is allocated with a color code, which is called

BSIC. MS can identify two cells with the same BCCH by the help of BSIC.

In network planning, make sure that BCCH of neighbor cells are

different from the serving cell’s BCCH to reduce the interference.

Practically it is still possible that a same BCCH is re-used in the

surrounding cells. For cells using the same BCCH in a relevant near

distance, their BSIC must be different so that MS can identify twoneighbor cells with same BCCH.

BSIC is transmitted on Synchronous Channel (SCH) of each cell. Its functions are as

below:

1. If MS have read SCH, it is considered as being synchronous with that cell. However, to

correctly read the information on the downlink common signaling channel, MS must get

the TSC (Training Sequent Code) that is adopted by the common signaling channel.

According to GSM specification, TS (Training Sequent) has eight fixed formats, which are

represented by TSC ranged 0~7 respectively. TSC number adopted by common signaling

channel of each cell is just the BCC of the cell. So one of the functions of BSIC is to

inform MS of the TSC adopted by the common signaling channel of the cell.

2. Since BSIC attends the coding process of information bits in random access burst, it

can be used to prevent the BTS from accepting a RACH transmitted from MS in a

neighbor cell as the access signal from the MS of the serving cell.

3. When MS is in dedicated mode, it must measure the BCCH level of the neighbor cells

and report it to BTS according to BA2 that is sent on SACCH, including their respective

BSIC. In special circumstance, when there are two or more cells using the same BCCH in

the neighbor cells, BSC can use BSIC to distinguish these cells and avoid wrong

handover or even handover failure.

4. MS must measure the BCCH signals of neighbor cells in dedicated mode, and report

the results to the network. Since MS sends measurement report which contain the

Descriptions of a maximum of 6 neighbor cells each time, it is necessary to control MS to

report only the cells which have neighbor relationships with the serving cell. The NCC is

used for the above purpose. Network operators can use parameter “ NCC Permitted” tocontrol MS to report the neighbor cells with NCC permitted in the serving cell only.


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Network Color Code（NCC）

Definition: NCC is a part of BSIC. MS uses it to distinguish adjacent

BTS that belong to different GSM PLMN.

Format: NCC is composed of 3 bits, with the range of 0 to 7.


NCC and BCC together form the base station identity code (BSIC),

transmitted on synchronous channel of each cell.

In many cases, different GSM PLMNs have the identical coverage in

many But their network planning are independent from each other.

To ensure that adjacent BTSs have different BSICs, it is generally

regulated that adjacent GSM PLMN select different NCC.

Adjacent or close cells with the same BCCH frequency must have

different BSIC. Special attention should be paid to the configuration

of cells in boundary areas.


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BTS Color Code（BCC）

Definition: BCC is a part of BSIC. For its function, please refer to

above sections.

Format: BCC is composed of 3 bits. The available range is 0~7.


BSIC includes BCC and NCC which is transmitted on SCH. BCC is a part of BSIC,

used to identify different cell with the same BCCH in the same GSM system.

According to the requirements of GSM specification, TSC of BCCH in each cell

should be the same with BCC of the cell. Generally this consistency must be

ensured by manufacturers. Adjacent or close cells using the same BCCH must

have different BSIC, otherwise, inter cell handover might be unsuccessful.

BCC planning has three solutions. All of them have taken distance principle into

consideration to avoid collisions of adjacent cells with the same BCCH and same

BSIC.

1. Based on the existing BCC set, select one of the BCC that has been used by

other cell, ensure at the same time that BCC selected will not cause BSIC/BCCH

collision with adjacent cells. The advantage of this solution is that it can ensure

BCC be evenly distributed in the whole network. However, if done manually, this

solution is time-consuming and troublesome, we can use automatic distributiontools.

2. When defining BCC, try to assign the value from 0. When causes BSIC/BCCH

collision, expand the value range. The advantage is that the number of BCC used

is kept to the smallest. So when adding a new BTS, in order to avoid the

BSIC/BCCH collision, a new BCC can be selected without modifying the BCC of

original cells around.

3. Allocate BCC according to its reuse model. That is to use the same BCC within

one cluster. It means that adjacent cells cannot use the same BCCH with the

service cell. This solution is frequently used, and also the simplest one.


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Idle Mode Parameters

ATT

CCCH Conf

BS_AG_BLKS_RES

BS_PA_MFRAMES

Period of Periodic Location Update(T3212)

Neighbor Cell Description (BA Table)

There are a lot of parameters in GSM system, they are usually

transmitted to MS from BTS via Um interface. It aims to maintain

favorable cooperation between MS and BTS. On the other hand, thevalues of these parameters directly affect the traffic load and

signaling flow of each part of the system. Therefore, proper

configuration of these parameters is important to the favorable and

stable operation of the system. The following will elaborate on the

definitions, value ranges, and effects on the system of these system

control parameters.


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ATT

Value Range: Yes, No

Default Value：Yes

Description: It is Attach-detach allowed. 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.

Location: Cell Attributes/Idle Mode/Basic Idle Parameters

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 theIMSI 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.


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CCCH Conf

Value Range: 1 Compounding CCCH , 1 Non-Compounding CCCH, 2Non-Compounding CCCHs, 3 Non-compounding CCCHs, 4 Non-

compounding CCCHs.

Default Value: 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.

Description: It is Common Control Channel Configuration. CCCH

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

parameter can be automatically configured by system according to the TRX

channel configuration.


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 isclosely 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.


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BS_AG_BLKS_RES

Value Range: 0~7 (Non-Compounding CCCHs), 0~2 (1 combined

CCCH)

Unit: Block

Default Value: 2 (Non-combined CCCH), 1(1 combined CCCH)

Description: 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).


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 cell parameter of each cell includes a configurationparameter, 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 without

causing 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.


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BS_PA_MFRAMES

Value Range: 2~9

Unit: Multi-frame period (51 frames)

Default Value: 2 Multi-frame period

Description: It is Paging Channel Multi-frames. It defines the number

of multi-frames used as a cycle of paging sub-channels.


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

Description of the others. When this parameter is set larger, there will be more pagingsub-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


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Period of Periodic Location Update(T3212)

Value Range: 0~255

Unit: 6 minutes

Default Value: 20

Description: It is the Periodic Location Update Timer. It defines the

interval of periodic location update.


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 cell

parameter, it will store it in SIM card. When the time reaches T3212 value, the location updateprocess 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-termmeasurement 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.


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LA 1

LA 2

Definition of Location Update

Inform the system the LA (Location Area) where the MS is to be paged.


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LA 2

LA 3

Condition of Location Update

Periodical location update

Moving into a new LA

LA 1


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Procedure of Location Update

BSC

MSC

MS

1 Hour 1 Hour 1 Hour

≥ ++ ++ +


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Abnormal Occasion

LA 3

LA 2

LA 1

But I am alwayspowered on

The subscriber youdialed has beenpowered off


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Reason1 of Abnormal Occasion

BSC

MSC

MS

1 Hour 1 Hour1 Hour


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Reason2 of Abnormal Occasion

BSC

MSC

MS

1 Hour 1 Hour 1 Hour

≤


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Application of T3212

Even if T3212 setting is less than the system (MSC) query time, the system

will still sometimes voice “The subscriber you dialed is powered off”.

A B

T3212=4 T3212=8

LAC

“ Ping-pong Reselect”

Let us make the following assumption. The system query time is set to 1 hour, T3212

value of cell A is set to 4 (0.4 hour), and T3212 value of the adjacent cell B is set to 8 (0.8

hour), and they are in the same location area. MS reselects B when the periodic locationupdate status in A is 3/4, and the MS periodic location update status in B changes to 3/8.

If MS stays in B for some time and the location update status reaches 7/8, then MS

reselects A. At this time, it can be seen that in cell A, MS reselection status changes to

“7/4”, i.e. 3/4. If MS reselects to B at this time, the status will change to 3/8 instead of 7/8.

The above analysis shows that if the above case occurs (the probability is high), though

T3212 values of both cells are smaller than the system query time, the MS’s frequent cell

reselection leads to the final equivalent time is greater than system query time. Thus the

subscriber will be considered as a power-off subscriber within certain time even it is in

normal idle mode.


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Neighbor Cell Description

There are table BA1 and table BA2.

Table BA1 describes BCCH frequencies of the adjacent cells to be

measured when the MS is in idle mode.

Location: Cell Attributes/Idle Mode/Advanced

Table BA2 describes BCCH frequencies of the adjacent cells to be

measured when the MS is in dedicated mode.

Location: Cell Attributes/Handover data/Advanced

MS keeps on measuring the BCCH signal level of the serving cell and the neighbor cells. In

order to know the adjacent cells, neighbor cell description information will be broadcast

periodically in cell parameter of each cell. This information lists the BCCH of all neighbor cells.MS extracts the information from cell parameter and use it as basis for neighbor cell

measurement.

For GSM network, the neighbor relationship between cells is accomplished when designing

the network topology. During the network construction, the neighbor cell relationship must be

configured in accordance with the topology design that has been planned. Moreover, after the

commission of network, neighbor relationship should be modified according to the data of

drive test and traffic measurement. When the network’s architecture is changed (e.g. adding

BTSs or changing the network frequency configuration.), the network operator must strictly

follow the changed-cell-neighbor-relationship, re-set and verify it. Improper neighbor celldescription is usually one of the main reasons of call drop. Besides, since the actual network

topology structure is often greatly different from the theoretical calculation result, and network

is in ever-changing environment, the network operator must configure the neighbor cell

description according to the actual situation.


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Theoretical Neighbor Cells Actual Neighbor Cells

B

CA

D

B

CA

D

Application of Neighbor Cell Description

In theoretical calculated neighbor cell relationship, cell A and cell C are not adjacent cells.

Assume that one MS moves from cell A to cell C during the conversation, theoretically,

MS needs twice of inter-cell handovers. Assume that the interference in cell D is rather serious, call drop is may occur during this period. But in fact, the coverage of A, B, C, and

D is not the case as the theory. A and C have overlapping coverage. If A and C are

regarded as adjacent cells here, that is to say, add the BCCH of C and A respectively to

the neighbor cell description of A and C, then when MS passes from A to C, only one

handover happens. What’s more, call drop could be avoided because of the good quality

of cell C.


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B

C

A

A

Application of Neighbor Cell Description

Part of the signals from cell A leaks out and covers some areas far away from this cell. It

is overshooting. If MS is in dedicated mode in the shady area and moves from this area

towards B and C, since there are no BCCH of cell B and C in cell A’s neighbor celldescription, call drop is unavoidable. If the antenna of BTS is located too high, or the

transmitting power is too large, overshooting will occur. BTSs built at the early stage of

GSM construction usually have this problem, because coverage is the major purpose at

that time and the antenna height is very high. The best solution for this phenomenon is to

adjust the location and downtilt of the antenna, or to adjust the transmitting power of the

BTS to eliminate the BTS’s over-covered area. In real situation, it is hard or even

impossible to change the location of antenna. So one more simple and applicable method

is to add BCCH of B and C to the neighbor cell description of cell A (no need to add A’s

BCCH to B and C). But it must be ensured that there are no cells which are all neighbor

cells of cell A and using the same frequency and same BSIC with cell B and C. Generally,

this method is not recommended.


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Call Control Parameters

MS MAX Retrans

TX-integer

RACH Min. Access Level

NCC Allowed

RLT

SACCH Multi-Frames

Common Access Control Class

Special Access Control Class

MBR

ECSC

Emergent Call Disable

There are a lot of parameters in GSM system, they are usually

transmitted to MS from BTS via Um interface. It aims to maintain

favorable cooperation between MS and BTS. On the other hand, thevalues of these parameters directly affect the traffic load and

signaling flow of each part of the system. Therefore, proper

configuration of these parameters is important to the favorable and

stable operation of the system. The following will elaborate on the

definitions, value ranges, and effects on the system of these system

control parameters.


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MS MAX Retrans

Value Range: 1, 2, 4, 7

Unit: Time(s)

Default Value: 4 Times

Description: It is one of the random access control parameters. MS MAX

Retrans is the upper limit of times that MS is allowed to send “Channel

Request” in one immediate assignment procedure.

Location: Cell Attributes/Call Control/Basic Call Control Parameters

After initiating immediate assignment process, MS keeps monitoring messages on BCCH and CCCH group it

belongs to. If the network does not send Immediate Assignment or Immediate Assignment Extend message, MS will

resend the channel request message at a certain time interval. The larger this parameter is, the higher the call

setup success rate is, but also the heavier the load of RACH and SDCCH is.

When MS initiates immediate assignment, it will send the “channel request” message to the network via RACH. As

RACH is an ALOHA channel, the network is incapable of controlling the access time of MS. Thus in heavy traffic

spot, it is unavoidable that several MSs may simultaneously make access request and cause collision which will

lead to two results: one is when one request signal level is obviously higher than the others’ access signals, the

access request with higher level will be handled; the other is the network can recognize none of them due to

mutual-interference. As the traffic is increasing, access request loss due to collision will increase, too. To make sure

that the system can correctly receive the access request and increase the access success rate, the network allows

MS to send several channel requests before receiving an immediate assignment message so as to achieve a higher

access success probability. MS will return to idle mode if it fails to receive an immediate assignment command after

the MAX Retrans exceeds. Once MS sends a channel request, it will start timer T3120 and wait on the downlink

CCCH. When T3120 times out and RACH resend times are not more than “MAX Retrans.”, MS will resend channel

request message (containing one new random reference), and restart T3120 with a random value. When T3120 is

times out and “MAX Retrans” is reached, MS will start T3126. If MS still fails to receive a response from the network

after T3126 times out, it will give up the access. If MS receives the access rejection, it will stop T3120 and start

T3122. Within T3122, no new access attempt will be allowed.

Recommendation:

Set to 7 for areas with low traffic (suburban or rural area) and the cell radius more than 3 km.

Set to 4 for areas with ordinary traffic (non-busy area in the city) and the cell radius is less than 3km.

Set to 2 for micro-cell

Set to 1 for micro-cell with heavy traffic or with obvious congestion.

Set to 4 or 7 for satellite transmission BTS.


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TX-integer

Value Range: 3~12, 14, 16, 20, 25, 32, 50

Unit: RACH Timeslot (equals to a TDMA frame, 4.615ms)

Default Value: 32

Description: Used to calculate the number of timeslots in the interval

between multiple channel requests sent by MS.


It is set to reduce the collisions on RACH. It mainly affects the execution

efficiency of the immediate assignment process. The value of this

parameter is related to CCCH configuration mode, both of them together

determine the parameter S (see the next page). The MS sends the first

random access burst at a random TS in the set {0, 1, …, MAX(T, 8)--1}.

And the TS number between any two adjacent channel request messages

is a random value in the set {S, S+1, …, S+T-1}.

Generally, parameter T+S should be as small as possible (in order to

shorten the access time of MS), but AGCH and SDCCH must not be

overloaded. If AGCH or SDCCH of the cell is overloaded, then parameterT can be changed to make parameter S larger, until AGCH or SDCCH of

the cell is not overloaded.

When the RACH collisions is serious, value T should be large. When the

number of RACH collisions is small, value T should be as small as

possible.


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Calculation of S

STX-integer

Non-Combined CCCH Combined CCCH

3, 8, 14, 50 55 41

4, 9, 16 76 52

5, 10, 20 109 58

6, 11, 25 163 86

7, 12, 32 217 115

When T becomes larger, the interval range between channel request messages sent by

different MSs will increase and RACH collisions will be reduced. When value S becomes

larger, the interval between channel request messages sent by the same MS will increase,collisions on RACH will be reduced and the availability of AGCH and SDCCH will

increase. But the increase of either will prolong the access duration of MS, resulting in

deterioration of access performance of the entire network. Generally, value T should be

selected to make S as small as possible (in order to shorten MS access time), but AGCH

and SDCCH must not be overloaded.


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RACH Min. Access Level

Value Range: -121~-47

Unit: dbm

Default Value: -115

Description: The parameter affects the access of an MS. That is to say, the

BTS determines the threshold of the level for the random access of the MS.

When the receive level of the RACH burst is lower than the threshold, the

BTS regards this access as an invalid access and no decoding is performed.

Only when the receive level for the burst timeslot of the random access is

greater than the threshold, the BTS regards that this timeslot has an access

request.

Location: Cell Attributes/Call Control/Advanced/Access Control

To avoid MS being unable to set up call even it is in the coverage area,

consideration should be given to BTS sensitivity and MS

RXLEV_ACCESS_MIN during the setting of this parameter.

A too small value for this parameter makes MSs easily to access but the

call drop rate may rise.

A too big value for this parameter may cause some MSs unable to make

calls.


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Radio Link Timeout

Value Range: 4~64, the step size is 4

Unit: SACCH period (480ms)

Default Value: 52

Description: This parameter is used for MS to decide downlink

disconnection in case of SACCH decoding failures.


Once assigned with a dedicated channel, MS will start counter S. From then on, S will

decrease by 1 when a SACCH message fails to be decoded, and will increase by 2 when

decoded correctly. When S decreases to 0, there will be a radio link failure. This allowseither re-establishment or release of the connection. If the value of this parameter is too

small, the radio link will easily get failed which will result in call drops. If it is too large, MS

will not release for a long time which will lower the availability of resources (this

parameter functions for the downlink).

For area with little traffic (remote area), it is recommended to be between 52~64.

For area with light traffic and large coverage(suburb or countryside), it is recommended to

be between 36~48.

For area with heavy traffic (urban), it is recommended to be between 20~32.

For the area with very heavy traffic (area covered by microcell), it is recommended to be

between 4~16.

For the cell with obvious coverage hole or the area where the call drops is serious during

movement, this parameter can be increased appropriately in order to increase the

possibility to resume the conversation.

Note: Radio link timeout is the parameter used to judge the downlink failure. Likewise, the

uplink will be monitored at BTS, either based on the uplink SACCH error or based on the

receiving level and quality of the uplink.


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Application of Radio Link Timeout

Impact of radio link timeout

A B

P Q

Poor coverage

If cell A and B are adjacent to each other, assume that one MS moves from point P to

point Q during a conversation, usually an outgoing cell handover will occur. If the value of

parameter “radio link timeout” is too small and the quality of signal at the edge of cells Aand B is poor, the radio link will time out before the handover occurs, thus resulting in call

drops.


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Radio Link Timeout

To increase the robustness of the SACCH channel, to improve the AMR

network coverage performance, and to lower the call drop rate, in practice

the AMR FR/HR RLT should be set higher.

Normal Call Radio Link Timeout (SACCH period(480ms))

AMR FR AFR Radio Link Timeout (SACCH period(480ms))

AMR HR AHR Radio Link Timeout (SACCH period(480ms))

Default Value

52

Call Type Parameter

64

52

•Because the robustness of the AMR voice frames is not at the same

level with that of SACCH frames, the GSM specification only

improves the robustness of the AMR voice frames but not that of theSACCH frames. Therefore, the actual coverage capability of AMR is

determined by the coverage capability of the SACCH.

•In application, the data——[RLT] and [SACCH Multi-Frames]

should be set to higher values for AMR channels to increase the

robustness of the SACCH. Thus the network coverage performance

of AMR is improved and the call drop rate is reduced.

•"Robustness" indicates the anti-interference capability. Protocols in

3GPP R6 version provide several new technologies to enhance the

robustness of the SACCH. The problem about low robustness of the

SACCH is expected to be solved with the evolution of technologies.


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SACCH Multi-Frames Value Range: 0~63

Unit: SACCH period (480ms)

Default Value: 31

Description: It is a timer used to determine whether the uplink radio link

connection fails. BSS judges the uplink radio link failure according to uplink

SACCH BER.

Every time BTS fails to decode the MR sent from MS, this timer decreases by 1;

Every time BTS succeeds to decode the MR, this timer increases by 2.

When this timer reaches 0, BTS judges that the uplink radio connection fails, then

BTS sends a radio connection failure message to BSC. This parameter and the radio link timeout (RLT) are used to judge the

uplink/downlink radio connection failure.



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SACCH Multi-Frames

To increase the robustness of the SACCH channel, to improve the AMR

network coverage performance, and to lower the call drop rate, in practice

the AMR FR/HR SACCH Multi-Frames should be set higher.

Normal Call SACCH Multi-Frames (SACCH period(480ms))

AMR FR AFR SACCH Multi-Frames (SACCH period(480ms))

AMR HR AHR SACCH Multi-Frames (SACCH period(480ms))

Default Value

31

Call Type Parameter

48

32


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NCC Permitted

Value Range: □Selection of 0~7 Perm.

Default Value: 11111111

Description: Network Color Code. It lists NCC that need be measured

by MS. If a neighbor cell’s NCC is permitted, MS will report MRs of it

to the network.


In working status, MS needs to measure adjacent cells BCCH signals and

report them to network. But each report can only include a maximum of six

adjacent cells. Thus it is necessary to make MS only report the potential

target cells for handover, instead of reporting all according to the signal

level (usually MS does not report the signals of cells from other GSM

PLMN). The above function can be implemented by making MS only

measure the cells whose NCC are selected. Parameter “NCC Permitted ”

lists the NCCs of the cells that the MS needs to measure.

BSIC is transmitted continuously on SCH of each cell and the higher three

bits of BSIC are NCC. MS only needs to compare the measured NCC ofthe adjacent cell with parameter NCC Allowed. If it is allowed, MS will

report it to BTS, otherwise it will discard the measurement result.

Note: Improper setting of this parameter will lead to lots of call drops.


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Common Access Control Class

Value Range:□Level 0~9 Forbidden


Description: One of the parameters of random access control information.

It is used for load control of ordinary subscribers, to permit or forbid the

network access of some common level users. “1” stands for forbidden

and “0” for permitted.


In some special case, the operator expects to prohibit all or part of the MSs from sending

access requests or paging response. For example, emergency status occurs or a serious

fault occurs to a GSM PLMN. Therefore, GSM specification 0211 requires to assign anaccess level for each common GSM subscriber. The common access level is divided into

level 0~9, which is stored in the SIM card of MS, and has nothing to do with access

priority.

Some cells with extremely heavy traffic may be congested during busy hour, resulting in a

large number of RACH collisions, AGCH overload, Abis interface overload, etc. GSM

specifications provide a variety of ways for dealing with the overload and congestion, but

most of them will lower the availability of equipment resources. The network operator can

set the access control parameter (C0-C9) properly to control the traffic inside the cell. For

example, when the cell suffers traffic overload or congestion, Ci can be set as 0 toprohibit MS with this access level from accessing this cell (change of Ci will not affect MS

in dedicated mode), thus reducing the traffic of the cell. To solve this problem, values of

C0-C9 in the cell can be changed periodically. For example, at intervals of five minutes,

alternatively allow the access of MS with odd access levels and those with even access

levels.

For example, 1000000000 indicates to allow the access of subscribers with the levels

other than 0. During installation and commissioning of BTS or during maintenance test for

some cells, they all can be set to “1” to prohibit the access of subscribers.


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Special Access Control Class

Value Range:□ Level 10~14 Forbidden


Description: It is used for load control, permitting or forbidding the

network access of some special level users. “1” stands for forbidden and

“0” for permitted.


For some special subscribers, GSM specifications have reserved five special access levels 11-15,

which usually have higher access priority. A special subscriber can have one or multiple access

levels (between 11 and 15) at the same time, which are also stored in the SIM card of the

subscriber.

Class15——PLMN Staff;

Class14——Emergency Services;

Class13——Public Utilities (e.g. water/gas suppliers);

Class12——Security Services;

Class11——For PLMN Use.

For subscribers with the access levels 0~9, their access right is also applicable to the home PLMN

and visit PLMN. For subscribers with the access levels 11-15, their access right is only applicable

to the home PLMN. For subscribers with the access levels 12, 13 and 14, their access right is

applicable to the area of the country to which the PLMN belongs.

Subscribers with the access level 11~15 have a higher access priority than those with the access

levels 0~9.

The access level control parameter consists of 16 bits: C0-C15, which respectively corresponds to

15 access levels in bit mapping mode (C10 is used for permitting emergency call). When a bit is 1,

it indicates not to allow MS with the corresponding level to access then cell. Otherwise it indicates

to allow the access.


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Application of MBR

-92dBm -82dBm A B

C -68dBm

D -90dBm

E -78dBm

F -88dBm

G -96dBm

H -84dBm

GSM1800

GSM900

S

S is a GSM900 cell, cells A~H are adjacent to cell S. Of them, A and B are GSM1800

cells and others are GSM900 cells. The above diagram shows the influences of different

MBR parameters as follows:

1)When MBR = 0, MS will report six adjacent cells with strongest signals without

considering the bands, the report result is: C, E, B, H, F, D.

2)When MBR = 1, the result is: C, B, E, H, F, D.

3)When MBR = 2, the result is: C, E, B, A, H, F.

4)When MBR = 3, the result is: C, E, H, B, A, F (3 GSM1800 cells should be reported. But

there are only 2 currently, so 2 GSM1800 cells are reported. For the rest, GSM900 cells

will be reported).


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ECSC


Default Value: No

Description: Early Classmark Sending Control. It indicates if an MS in the

cell is allowed to use early Classmark sending.

Yes: The MS reports Classmark3 to the network immediately after

link setup.

No: The MS is forbidden to report its Classmark3 to network

initiatively.


In GSM network, MS’s service capability, supported band, power capability,

encryption capability and so on are described by classmarks. There are three

classmarks which are classmark1, classmark2 and classmark3. The network can

know the MS’s capability by checking the classmarks of the MS. After receiving

the class mark enquiry message, MS will send classmark change message to the

network as soon as possible. CM3 (Classmark 3) includes the information about

MS power, multiband and/or multislot capability. To perform handover between

different bands, the power level must be described correctly. In the process of

paging and sending of the BA2 information between different bands, the CM3

message must be known.

Note:

1) ECSC is invalid for single-band MS. For dual-band MS, when ECSC is not

used, after the MS sends EST IND , MSC will still send the CLASSMARK

REQUEST message, and MS will response with the CLASSMARK UPDATE

message, and other functions are not affected. For the dual-band MS, when this

parameter is set to Yes, the connection time between different MS will be

obviously shortened.

2) When the encryption function is enable, The parameter must be set to "Yes".

3) M900/M1800 hybrid cells sharing BCCH are advised to be configured as "yes",


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Definition of Classmark In GSM system, the abilities that MS supports, such as service ability, band

ability, power ability, encryption ability, is described by the classmark. BSC

decodes the information according to the requirement of network and

transfer to the network.

There are 3 kinds of classmark:Classmark1、Classmark2、Classmark3.

Network knows about abilities of MS either via inquiring for MS’s CLASSMARK

or via requiring MS to report CLASSMARK3 immediately by itself after link

setup.


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Information about Classmark 2/3


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Emergent Call Disable


Default Value: No

Description: Emergence Call Disable. When EC Disable is set to “No”, it

means emergency call is permitted. Otherwise it is prohibited.


For MS with common access control class 0~9, when “Emergent Call Disable” is “Yes”, it

indicates not to allow an emergency call.

For MS with access levels 11~15, the emergency call will not be allowed only when the

corresponding access control class bit is set to “0” and “Emergent Call Disable” is set to

“Yes” at the same time.


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Cell Selection/Reselection Parameters

RXLEV_ACCESS_MIN

MS_TXPWR_MAX_CCH

CBQ (Cell_Bar_Qualify)

CBA (Cell_Bar_Access)

CRO (Cell Reselection Offset)

TO (Temporary Offset)

PT (Penalty Time)

PI (Cell Reselect Parameters Indication)

CRH ( Cell Reselection Hysteresis)

When MS is powered on, it will try to find a GSM PLMN. MS will select an appropriate cell

and read cell parameter. This process is called cell selection. The “appropriate cell” is

restricted by many factors. For example, whether this cell belongs to the selected network(under manual network selection mode), whether the cell is barred, the cell selection priority

of the cell, whether the access level of MS is prohibited by the cell, whether the quality of

radio channel meets the requirement of communication, etc. Among them, the quality of

radio channel is one important factor of cell selection. GSM specification stipulates one

parameter called path loss principle C1. The appropriate cell must ensure the C1>0. C1 is

obtained by the calculation of receiving level and the cell selection parameters.

After MS selects cell, MS will settle in the selected cell. At the same time it begins to

measure the signal level of BCCH of neighbor cells. It records six neighbor cells with the

strongest signals (refresh at least every 60s), extracts various cell parameter and controlinformation of each neighbor cell. (MS must conduct data block decoding for all the six

strongest BCCH of neighbor cells within 5 minutes, including parameters affecting cell

reselection. When MS regards a new neighbor BCCH as one of the six strongest BCCHs, it

will conduct data block decoding for this new BCCH at least every 30s). Moreover, MS must

check one of the six strongest at least every 30s. If BSIC has any changes, it will be

regarded as a new BCCH and data decoding will be conducted again. During this process,

MS will not stop monitoring PCH. When a certain condition is satisfied, MS will move from

current cell to anther cell. This process is called cell reselection. The condition includes

many factors, and they are all related to the quality of radio channels. When a neighbor

cell’s radio channel quality is better than current cell’s, cell reselection occurs. The channel

quality standard for cell reselection is C2. C2 is obtained by calculation of the receiving level

and a number of parameters.


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Cell Selection Process

There are two kinds of cell selection

Stored list cell selection

Normal cell selection

In fact, the process might be different for different MSs

If the SIM card of MS has not stored any BCCH (usually it is a new SIM card), it will search all the 124

RF channels and 374 more GSM1800 channels for dual-band MS, and measures the receiving signal

level of each. The whole process lasts about 3s to 5s. During this period, MS obtains at least 5

measurement samples from each RF channel. Then MS tunes to the carrier with strongest receivinglevel, and judge whether it is BCCH (by searching for FCCH). If yes, MS tries to decode SCH and

makes itself synchronous with that BCCH, then the MS reads cell parameter on it. If MS can correctly

read the cell parameter and verify this cell belongs to the selected PLMN and its C1 is larger than 0,

and also its cell selection priority is normal, then MS conducts location update. After passing, MS

resides in that cell. Otherwise, MS will tune to second strongest BCCH and go on with the same

procedure. If after trying the strongest 30 (single-band) or 40 (dual-band) carriers it still can’t find a

suitable cell to reside in, the MS will try to access the cells with low cell selection priority. If still

unsuccessful, the MS will try the cells of other PLMNs which are allowed by the SIM card. If failed

again, MS will stay at a cell (signal is the strongest, C1 is larger than 0, cell selection priority is not

prohibited.) without considering the PLMN and enter the emergency call mode (service bar mode).

Meanwhile, the MS keeps on monitoring all RF channels.

Note:

1. When MS access level is prohibited by this cell, cell selection algorithm is not affected. If the

condition is fulfilled, MS will still try to reside in this cell.

2. MS belongs to the PLMN selected, but is prohibited from access, or C1


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Stored List Cell Selection

Search the BCCH

which have been stored

Normal cell selectionCan decode

any frequency?

Come into

idle mode

Yes

No

Can reside in

any cell ?

No Try to reside in its

neighbor cell?

Yes

No

Yes

When MS is powered off, it will store some BCCH carrier information. When MS is powered

on, it will first search the BCCHs which have been stored. If MS can decode the BCCH data of

this cell but cannot reside, it will check the BA table of this cell and try these BCCHs. If it stillcannot pass, MS will start the cell selection process without BCCH list.


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Normal Cell SelectionSearch all

frequency

Rank according to

receiving level

Come into

idle mode

Is it a BCCH carrier?

Right PLMN&C1>0&

priority is Normal ?

Select the next frequency

with the higher Rx_level

YES No

YES

Try the cell of other PLMN

allowed in the SIM card

Stay in a cell(RX-LEV is strongest, C1>0 ,

cell priority is not prohibited) without

considering the PLMN

All frequency not satisfy

No

YES

Emergency call

mode

Select the frequency with

the highest Rx_level

Decode SCH, read

cell para. on BCCH

No

All frequency not satisfy

No

No YES

Right PLMN&C1>0&

priority is Low ?

Search all frequency

Judge whether it is BCCH

If MS can correctly read the cell parameter and verify this cell belongs to the selected

PLMN and its C1 is larger than 0, and also its cell selection priority is normal, then MS

conducts location update. After passing, MS resides in that cell.

Otherwise, MS will tune to second strongest BCCH and go on with the same procedure.

If after trying the strongest 30 (single-band) or 40 (dual-band) carriers it still can’t find a

suitable cell to reside in, the MS will try to access the cells with low cell selection

priority.

If still unsuccessful, the MS will try the cells of other PLMNs which are allowed by the

SIM card.

If failed again, MS will stay at a cell (signal is the strongest, C1 is larger than 0, cell

selection priority is not prohibited.) without considering the PLMN and enter the

emergency call mode (service bar mode).


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RXLEV_ACCESS_MIN

Value Range: 0~63 (-110 dBm ~ -47 dBm)

Default Value: 8

Description: It means the minimum receive signal level

required for MS to access a cell.


To prevent MS from accessing the system when the receiving signal level is

very low (this will make unsatisfactory communication quality and waste the

radio resources of the network), GSM specifications require that the MS’sreceiving level must be greater than a threshold when it needs to register in

the network. The threshold is the RXLEV_ACCESS_MIN.

For some cells with high traffic, this parameter can be increased

appropriately to lower the values of C1 and C2 of this cell. Accordingly the

effective coverage range of the cell will be reduced. But the value of

RXLEV_ACCESS_MIN should not be too big, otherwise coverage hole (with

regard to idle mode MS) will be created at the edge of the cell. When this

method is used to balance the traffic, the value of RXLEV_ACCESS_MIN isrecommended to be no more than 20.

Except for the areas with densely distributed BTS and good coverage,

generally it is not recommended to use RXLEV_ACCESS_MIN to adjust the

traffic of the cell. For isolated BTS or BTS with poor coverage, this value

should be set properly, otherwise the call drop rate may increase and QoS

will be affected.


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MS_TXPWR_MAX_CCH Value Range: 0~19

Unit: level

Default Value: 5 (900MHz cell),0 (1800/1900MHz cell)

Description: This parameter determines the maximum transmit

power level of the MS when it begins to access a cell and has not

yet received power control command.

Location: Cell Attributes/Other Attributes/Advanced/Public Channel

Control

During MS’s communication with BTS, its transmitting power is controlled by the network

via power control command. This command is transmit in SACCH (There are two head

bytes. One is power control byte, the other is time advance). MS must get the powercontrol head from the downlink SACCH, and output the power as is indicated in the in the

power control header. If the MS cannot support the power level in the power control

header, it will use the nearest power level it supports.

Since SACCH is associated signaling channel, it must be combined with other channels,

such as SDCCH or TCH. Therefore, the control of MS’s power begins after MS receives

SACCH. While the power level used by MS before it receives SACCH (power used when

RACH is sent) is determined by the “MS TXPWR_MAX_CCH “ (maximum power level of

control channel).

This parameter will affect cell selection and cell reselection.

C1 = RLA_C - RXLEV_ACCESS_MIN - MAX((MS_TXPWR_MAX_CCH - P), 0)

RLA_C: mean receiving level of MS

RXLEV_ACCESS_MIN: minimum receiving level of MS permitted to access

P: maximum physical supported transmitting power of MS.


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CBA

Value Range: No, Yes

Default Value: No

Description: Cell_Bar_Access, worked together with CBQ to set the

priority status of the cell in idle mode for cell selection and reselection.


The network operator can set the cell access is permitted or not by the parameter.

Usually all cells allow MS to access, thus it is set as “No”. But in the special cases, the

operator may want a cell to be used for handover service only, which can be realized bysetting the parameter as “Yes” (CBQ should be “No” in this case).


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CBQ

Value Range: No, Yes

Default Value: No

Description: Cell_Bar_Qualify. CBQ only affects the cell selection,

but is not related to cell reselection. It works with CBA to define the

access priorities of cells.


For the area overlapped by cells, the operator often wants MS to

preferably select certain cell during cell selection according to the cell

capacity, traffic and cell functions, i.e. setting the cell priority. This function

can be implemented by setting parameter “cell bar quality”. It works with

parameters “cell bar access” together to determine the cell selection and

cell reselection priority of the cell.

Usually the priorities of all cells should be set as “Normal”. But in some

special cases such as micro-cell and dual-band network, the operator may

expect MS to preferably enter the cells of a certain type. In this case, the

network operator can set the priority of this type of cell as “Normal” whilesetting the other cells as “Low”. MS will select the cell with lower priority

only when there is no appropriate cell with the priority as “Normal”. During

the network optimization by means of cell priority, it is necessary to note

that CBQ only influences the cell selection. Therefore, in order to achieve

the target, C2 (cell reselection parameter) must be taken into

consideration.


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Application of CBA and CBQ

NormalLowYesYes

NormalLowYesNo

ForbiddenForbiddenNoYes

NormalNormalNoNo

Cell Reselection

Priority

Cell Selection

Priority

BQB


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Application of CBQ

The traffic of cell A and B is heavy. Set these two cells with

CBA=“Yes”, CBQ=“No”.

A B

Each circle in the diagram indicates a cell. For some causes, the traffic in cell A and that

of cell B are obviously higher than those of the adjacent cells. To make the traffic of the

entire area distributed on average, set the priorities of cell A and cell B as “Prohibited”and those of other cells as “Normal”. In this way, the services in the shadow areas in the

diagram will be shared by the adjacent cells. It must be pointed out that this setting will

reduce the actual coverage areas of cell A and cell B, which is different from decreasing

the transmitting powers of cell A and cell B.


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Application of CBA

B is a micro cell. Set B to “Normal” and A to “Low”.

B

A

Assume that micro-cell B and macro-cell A together cover an area. In order to make

micro-cell B share more traffic of macro-cell A, the priority of cell B can be set as “Normal”

and that of cell A as “Low”. Thus in the coverage area of cell B, MS will select cell B aslong as the level of cell B reaches the RXLEV_ACCESS_MIN, no matter cell B has a

lower signal level than cell A’s or not. And then reselection parameters can be set

appropriately to make MS not to reselect cell A.


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Cell Reselection Process Cell reselection for cells in the same location area

If the C2 value of the target cell is higher than that of the serving cell for longer

than 5 seconds, a cell reselection process will be performed and the MS tunes to

the new cell.

Cell reselection for cells in different location areas

If the C2 value of the target cell is higher than that of the serving cell by at least

the value of CRH for longer than 5 seconds, a location update process and the cell

reselection process will be performed.

Two consecutive cell reselections caused by C2 have a time interval of 15 seconds.

In other words to say, if because of C2 a MS reselected to a cell, then the MS

cannot reselect to another cell by the cause of C2 within 15 seconds.

If current serving cell is prohibited, or down link fails, or C1 is less than 0

continuously for 5s, cell reselection will also be triggered.

MS starts a cell reselection if the access times exceed the MAX retrans.


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Cell Reselection Parameter

C2=C1+CRO-TO*H(PT-T) When PT is not equal to 31

C2=C1-CRO When PT is equal to 31

For neighbor cell:

H(PT-T)=0, when PT-T


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CRO

Value Range: 0~63( the corresponding level value: 0~126dB,stepped every 2dB).

Unit: 2dB

Default Value: 0

Description: Cell Reselect Offset. It is a parameter in C2 calculation

to give an intentional modification in MS cell reselection.


After cell selection, MS will reselect another better cell in idle mode. It is C2 parameter

that determines cell reselection. The principle for MS reselection is: select the cell with

the maximum C2 as the serving cell. C2 is determined by the following factors:

C2=C1+CRO-TO*H(PT-T) (PT


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TO

Value Range: 0~7 (the corresponding value is 0~60dB, 7 correspondsto “Infinite”).

Default Value: 0

Description: Cell Reselect Temporary Offset. It is a parameter in C2

criterion to give a temporary modification within PT time.

Location: Cell Attributes/Idle Mode/Advanced/Idle Parameter

TO indicates the temporary modification on C2. Temporary means that it functions for C2

only within a duration which is determined by PT parameter. Setting of this parameter

only affects MS of GSM Phase II and above.


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Documents

Gsm Cell Parameters Huwaie 1