GSM System Information

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ISSUE

GSM System Information


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System InformationOverview

Parameters

Introduction

CaseStudy

Course Contents


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System information (SYS INFO) contains network

parameters sent to MS through Um interface network identity parameters, cell selection parameters system control parameters network function parameters

System information can be sent through two kinds of

logical channels System information on BCCH System information on SACCH

System Information Overview


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SYS INFO 1

SYS INFO 1 Cell Channel Description

(cell channel description format) RACH Control Parameter(random access channel controlparameter)

Content

SYS INFO 1

It contains random access control information(RACH) and cell frequency allocation table (i.e. CAtable). It is transmitted on BCCH.


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SYS INFO 1 - Control Parameter

These control parameters include: Maximum re-transmitting times (MAX retrans) Extended transmission timeslots (Tx_interger) Common access control level (AC) Call reestablish permitted (RE) Emergency call permitted (EC)


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SYS INFO2

It contains access control information (RACH), network color codepermitted (NCC Permitted), and neighbor cell frequency allocationlist (BA1 list). It is transmitted on BCCH. Generally speaking, SYSINFO 2, 2BIS, 2TER contains different parts of the neighbor cellBCCH frequencies. Via reading and decoding BA1 list, MS canperform cell reselection in idle mode. For a MS of GSM900 PHASE

I, it only reads the neighbor cell BCCH frequencies defined in SYSINFO 2, and ignores those carried by 2BIS and 2TER.

SYS INFO

2

Conten

t SYS INFO 2 Neighbor cell BCCH frequency description NCC permitted RACH Control Parameter


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SYS INFO2BIS

2BIS contains RACH control data and neighbor cell BCCHfrequencies (part of BA1 list). It is optional and transmitted onBCCH. As the number of frequencies in BA1 list carried by SYSINFO 2 is limited, SYS INFO 2BIS carries the rest of the BCCHfrequencies in the BA1 list that are from the same band as in

SYS INFO 2.

SYS INFO

2BIS

Content

SYS INFO 2BIS

Neighbor Cell Desc. RACH Control Parameter (Same as those in SYS INFO

1.)


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2TER contains neighbor BCCH frequencies (part of BA1 list). Itis transmitted on BCCH. Only dual band MS can read thisinformation, and single band 900 or 1800 MS will ignore it.Since this information carries BCCH frequencies that belong to

different band other than those in SYS INFO 2, it isunnecessary for single band MS to read.

SYS INFO 2TER - - Neighbor Cell Description

(extended)

SYS INFO2TER

Content

SYS INFO 2TER


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It contains LAI, cell identity, RACH control parameters and cellselection related parameters. It is transmitted on BCCH. It isone of the most important information.

SYS INFO 3 - - Cell Identity

- - LAI( location area identity)

- - Control Channel Description

- - Cell OptionBCCH- - Cell Selection Parameter

- - RACH Control Parameter

SYS INFO 3

Content

SYS INFO 3


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Cell Identity and Location Area Identity

Cell Global Identity (CGI) consists of Location Area Identity (LAI) andCell Identity (CI). And LAI includes Mobile Country Code (MCC), MobileNetwork Code (MNC), and Location Area Code (LAC). SYS INFO 3, 6,and 4 contain all or part of the information of CGI. According to thereceived SYS INFO, MS decodes the CGI, and decide whether it can

register in the network based on the MCC and MNC indicated by CGI.At the same time, it can judge whether the current location area ischanged, so as to decide whether it is necessary to start the locationupdating process.


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Control Channel Description

Control channel description includes the followingparameters

IMSI Attach-Detach Allowed (ATT) Common Control Channel Configuration (CCCH_CONF) Access Granted Blocks Reserved (BS_AG_BLKS_RES) Paging Channel Multi-frames (BS_PA_MFRAMES) Periodic Location Update Timer (T3212)


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Cell Option

Cell option contains the following parameters: Power control indication (PWRC) Discontinuous transmission (DTX) Radio link timeout


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Cell Selection Parameter

Cell selection parameters indicate how the MS shouldbehave after the MS is powered on. It includes the followingparameters:

Cell Reselection Hysteresis (CRH) Maximum power level of control channel

(MS_TXPWR_MAX_CCH) Minimum receiving level of MS permitted to access

(RXLEV_ACCESS_MIN) Additional reselection parameter indicator (ACS) Half-rate supported (Support Half-Rate)


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SYS INFO

4

Content

SYS INFO 4 - - LAI

- - Cell Selection Parameters

- - RACH Control Parameters

- - CBCH Channel Description (optional)

- - CBCH Mobile Allocation (optional)

- - SI4 Rest Octets (parameters related to cell reselection)

SYS INFO 4

It consists LAI, RACH control parameters, cell selection parametersand optional CBCH channel information. It is transmitted on BCCH.When the system supports cell broadcast function, CBCH togetherwith the CBCH MA describe the configuration of CBCH and therelevant frequency information.


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CBCH Channel Description and CBCHMA

These two parameters are optional. When system supports cellbroadcast, CBCH Channel Description explains the CBCHchannel configuration situation. When CBCH Channel is infrequency hopping mode, CBCH MA is also needed.


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SI4 Rest Octets

It contains the following parameters: Cell Reselection Parameter Indicator (PI) Cell Bar Qualify (CBQ) Cell Bar Access (CBA) Cell Reselect Offset (CRO) Temporary Offset (TO)

Penalty Time (PT)


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Content

SYS INFO 5 - - Neighbor CellDescription

SYS INFO 5

SYS INFO 5 It describes the neighbor cell BCCH frequencies(BA2 list). It is

mandatory and is transmitted on SACCH. Different from SYSINFO 2, MS can read the frequency described in SYS INFO 5in dedicated mode, report the relevant information of neighborcells in measurement reports, and use it as the basis for

handover. Similarly, for 900 MS of PHASE 1, it onlyrecognizes the neighbor cell frequencies described by SYSINFO 5, and ignores those carried by SYS INFO 5BIS and5TER.


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SYS INFO 5BIS

SYS INFO 5BIS 5BIS describes neighbor cells BCCH frequencies.These

frequencies are part of BA2 list. It is optional and istransmitted on SACCH. Generally, as the number of

frequencies which can be described by SYS INFO 5 is limited,SYS INFO 5BIS carries the rest BCCH frequencies in the BA2which belong to the same band as SYS INFO 5.

Content SYS INFO 5BIS - - Neighbor Cell Description


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SYS INFO5TER

Content

SYS INFO 5TER - - Neighbor Cell Description (Extended)

SYS INFO 5TER

5TER describes neighbor cells BCCH frequencies, thesefrequencies are also a part of the BA2 list. It is transmittedon SACCH. Similarly, only dual band MS can read thisinformation, and single band GSM900 or GSM1800 MS will

ignore it. It carries the BCCH frequencies of neighbor cellswhose band are different from the serving cells.


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SYS INFO6

Content

SYS INFO 6 - - Cell Identity

- - LAI- - Cell Option

- - NCC Permitted

SYS INFO 6

It describes LAI, cell identity, and some parametersdescribing the cells functions. It is transmitted onSACCH. It is also one of the most important systeminformation.


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Parameters

IntroductionCaseStudy

Course Contents


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Introduction to SYS INFO Parameters

Huawei GSM System Information Parameters: Network Identity Parameters System Control Parameters Cell Selection Parameters Network Functional Parameters


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Network Identity Parameter CGI

Network identity parameters mainly include cell globalidentity (CGI) and base station identity code (BSIC).

CGI=MCC+MNC+LAC+CI

Once MS receives SYS INFO, it decodes the CGI information, anddecides whether it can stay in the cell according to the MCC and

MNC indicated by CGI. At the same time, it judges whether thecurrent location area is changed, so as to decide whether toexecute location update. During the location update process, MSwill report the new LAI to the network, so that the network canknow the LA in which MS is currently located.


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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 sameBCCH by the help of BSIC. In network planning, effort shouldbe made to make sure that BCCH of neighbor cells aredifferent from the serving cells BCCH to reduce the

interference. Practically it is still possible that a same BCCH isre-used in the surrounding cells. For cells using the sameBCCH in a relevant near distance, their BSIC must bedifferent so that MS can identify two neighbor cells with sameBCCH.


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Mobile Country Code MCC

MCC is composed of 3 decimal numbers. Thecoding range is decimal 000-999.

Definition MCC consists of 3 decimal numbers. It

indicates the home country of the mobilesubscriber.

Format


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Mobile Network Code MNC

MNC is composed of two decimal numbers. Thecoding range is decimal 00-99.

MNC is used to uniquely identify a specific GSMPLMN network in a certain country (decided byMCC).

Definition

Format


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Location Area Code LAC

LAI contains LAC, which is composed of two bytes.LAC adopts hexadecimal coding. The available rangeis from 0001H to FFFEH. The code 0000H and FFFFH

cannot be used (please refer to specificationGSM0303, 0408, and 1111). One location area cancontain one or more cells.

To locate the location of MS, the whole area coveredby each GSM PLMN is divided into different locationareas. LAC is used to identify different location areas.

Definition

Format


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Cell Identity CI

CI is composed of 16 bits, The available range isfrom 0 to 65535.

To uniquely identify each cell in the GSM PLMN, thenetwork operator needs to allocate one code for eachcell, which is the cell identity (CI). Cell identity, togetherwith LAI, is used for identity of each cell in the world.

(specification 0303).

Definition

For

mat


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Network Color Code NCC

NCC is composed of 3 bits, with

the range of 0 to 7.

NCC is a part of BSIC. MS uses it to distinguishadjacent BTS that belong to different GSMPLMN.

Format

Definition


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BS Color Code BCC

BCC is composed of 3 bits. Theavailable range is from 0 to 7.

BCC is a part of BSIC. For its function, pleaserefer to above sections.

Format

Definition


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ATT CCCH_CONF BS_AG_BLKS_RES BS_PAMFRAMES T3212 Radio Link Timeout Neighbor Cell Description NCC Allowed

MS MAX Retrans TX-Integer Common Access Control Class MBR ECSC Power Deviation Indication Power Deviation

System Control Parameters


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ATT

Value range:Yes, No ContentIt is used to inform MS whether IMSI attach-detach

is allowed in this cell. If it is set to Yes, the network will notprocess the connection to the called mobile subscriber whenMS is power-off. Thus network processing time and radio

resources are saved. Otherwise the network will process theconnection even though the MS has been powered off.

RecommendationYes


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CCCH_CONF

Value range: 1 Non-Compounding CCCH, 1 CompoundingCCCH, 2 Non-Compounding CCCHs, 3 Non-compoundingCCCHs, 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 configuredby the BSC Data Auto Configuration System according to theTRX channel configuration.

Recommendation: When there is one TRX in the cell, onecombined CCCH is recommended (in a system with fewpaging messages in location area). For others, it is configuredaccording to the number of TRX in the cell.


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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 accessgranted channels (AGCH).

Recommendation: 2 (non-combined CCCH)


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BS_PA_MFRAMES

Value range: 29 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


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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 (forsuburban area)


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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 Thesubscriber you dialed is powered off.

A B

T3212=4

T3212=

8

LAC

Ping-pongReselect


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Radio Link Timeout

Value range: 4~64, the step size is 4 Unit: SACCH period (480ms) Content: This parameter is used for MS to decide down-

link disconnection in case of SACCH decoding failures.

Recommendation: 20~56


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Application of Radio Link Timeout

Impact of radio linktimeout

A B

P Q

Poorcoverage


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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. Table BA2 describes BCCH frequencies of the adjacent

cells to be measured when the MS is in dedicated mode.


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Application of Neighbor CellDescription

Theoretical NeighborCells

Actual NeighborCells

B

CA

D

B

CA

D


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B

C

A

Application of Neighbor CellDescription

A


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NCC Allowed

Value range: Check box, including options 0~7. Content: Network Color Code, sent in system information 2

and 6. It lists NCC that need be measured by MS. If aneighbor cells NCC is permitted, MS will report MRs of it to

the network. Recommendation: Subject to the concrete conditions.


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MS MAX Retrans

Value range: 1, 2, 4, 7

Unit: Time Content: It is one of the random access control parameters. MS

MAX Retrans is the upper limit of times that MS is allowed tosend Channel Request in one immediate assignment procedure.

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) Content: Used to calculate the number of timeslots in the interval

between multiple channel requests sent by MS.

Recommendation: 20 (If the cell immediate assignment successrate is low, set the S with a larger value. Select 32 for satellitetransmission, so as to reduce satellite transmission delay).


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Calculation of S

ST

CombinedCCCH

Non-combinedCCCH

3

,

8

,

14

,

5

0

5

5

4

14,

9,

16

76

52

5,

10,

20

109

58

6

,

11

,

2

5

16

3

8

67,

12,

32

217

115


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Common Access Control Class

Value range: Check box, including level 0 forbidden,lever 1forbidden,, till level 9 forbidden

Content: One of the parameters of random access controlinformation. 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.

Recommendation: 0000000000


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Special Access Control Class

Value range: Check box, including level 11 forbidden,level12forbidden,, till level 15 forbidden

Content: It is used for load control, permitting or forbidding thenetwork access of some special level users. 1 stands for

forbidden and 0 for permitted. Recommendation: 00000


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MBR

Value range: 0~3 Content: Multi-band Reporting. It is used to inform MS

to report the adjacent cells in a controllable way. It issent in the System Information 2ter and 5ter.


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Application of MBR


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ECSC

Value range: Yes, No Content: Early Classmark Sending Control. It indicates if an

MS in the cell is allowed to use early Classmark sending.See Protocol 0408.

Recommendation: No.


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Cell Selection Parameter

CBQ(Cell Bar Qualify) CBA (Cell Bar Access) MS_TXPWR_MAX_CCH RXLEV_ACCESS_MIN PI (Cell Reselect Parameters Indication)

CRO(Cell Reselection Offset) TO(Temporary Offset) PT(Penalty Time) CRH( Cell Reselection Hysteresis)

C ll S l i P


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Cell Selection Process

There are two kinds of cell selection. Normal cell selection Stored list cell selection

In fact, the process might be different for different MSs

C ll R l ti P


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Cell Reselection Process

Cell reselection for cells in 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 tunesto 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 thecell reselection process will be performed.

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

If current serving cell is prohibited, or down link fails, or C1 is less than 0continuously for 5s, cell reselection will also be triggered.

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

CBQ


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CBQ

Value range: Yes(1) , No(0) Unit: None Content: Cell Bar Qualify. CBQ only affects the

selection of cells but is not related to cell reselection.It works with CBA to define the access priorities ofcells.

Recommendation: No.

CBA


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CBA

Value range: Yes, No Content: Cell Bar Access, worked together with CBQ to set

the priority status of the cell in idle mode for cell selectionand reselection.

Recommendation: Yes

A li ti f CBQ


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Application of CBQ

The traffic of cell A and B is heavy. Set these two cells withCBA=No, CBQ=No.

A B

A li ti f CBA


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Application of CBA

B is a micro cell. Set B to Normal and A toLow.

B

A

A li ti f CBA


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Application of CBA

CBQ(A) =NOCBA(A) = NO

A

C

B

D

MS TXPWR MAX CCH


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MS TXPWR_MAX_CCH

Value range: 0~31 Unit: level Content: This parameter determines the maximum

allowed output power of the MS when it begins to access acell and has not yet received power control command.

Recommendation: 5(900MHz), 0(1800MHz)

RXLEV ACCESS MIN


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RXLEV_ACCESS_MIN

Value range: 0~63 Unit: Level Content: It means the minimum receive signal level

required for MS to access a cell.

Recommendation: 8

PI


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PI

Value range: Yes (1), No (0). Unit: None Content: Cell Reselect Parameters Indication, sent on

the broadcast channel of the cell. It is an indication to theexistence of Cell Reselect Offset(CRO), TemporaryOffset(TO) and Penalty Time(PT).

Recommendation: Yes.

CRO


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CRO

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

Unit: None Content: Cell Reselect Offset. It is a parameter in C2

calculation to give an intentional modification in MS cell

reselection. Recommendation: 0

TO


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TO

Value range: 0~7 , the corresponding value is 0~60dB, 7corresponds to Infinite.

Unit: None Content: Cell Reselect Temporary Offset. It is a parameter

in C2 criterion to give a temporary modification within PTtime.

Recommendation: 0

PT


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PT

Value range: 0~31, the corresponding time is 20~620s.31 is to change the formula of C2.

Unit: None Content: Cell Reselect Penalty Time.

Recommendation: 0

CRH


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CRH

Value range: 0~14 , the step size is 2 Unit: dB Content: Cell Reselection Hysteresis. It is the parameter

used when cell reselection happens between two locationareas.

Recommendation: 4

Network Function Parameter


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Network Function Parameter

PWRC (Power Control Permitted) UL DTX (Uplink Discontinuous Transmission) Support Half-Rate (New-Establishment Cause

Indication)

Call Re-establishment Allowed (RE) EC Allowed (Emergency Call Allowed)

PWRC


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PWRC

Value range: Yes, No. Unit: None Content: It is used to indicate MS weather to reduce

received level value obtained from the timeslots ofBCCH when MS measures receiving level during baseband hopping mode. When it is set to No, it means the

influence of receiving level on BCCH is not inconsideration. If it is set to Yes, process it in the waymentioned above.

Recommendation: Yes

UL DTX


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UL DTX

Value range: May use, Shall use, Shall not use. Unit: None Content: It is used to indicate whether MS uses DTX

function. In System Information 3, it is 2-bit coding. InSystem Information 6, it is 3-bit coding. It shows theDTX state of the MS in the previous measurementperiod.

Recommendation: Shall use.

Support Half-Rate


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Support Half-Rate

Value range: Yes, No. Unit: None Content: Informing MS whether half-rate service are

supported in the cell.

Call Re-establishment Allowed


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Call Re-establishment Allowed

Value range: Yes, No Unit: None Content: Informing MS whether call reestablishment is

allowed or not.

Recommendation: No

EC Allowed


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EC Allowed

Value range: Yes, No Unit: None Content: Emergence Call Allowed . When EC

Allowed is set to Yes, it means emergency call ispermitted. Otherwise it is prohibited.

Recommendation: Yes.

Others in Data Configuration System


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Others in Data Configuration System

System Information Usage Regular Transmission Regular Transmission Interval

System Information Usage


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System Information Usage

Value Range: It is a check box, including system information1~12, 2bis, 2ter, 5bis, 5ter, 10bis.

Unit: None Content: It is used to determine whether a type of system

information should be sent. A selected box means to send.

Recommendation: Select system information 1~6, 2bis,2ter, 5bis, 5ter

Regular Transmission


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Regular Transmission

Value range: Yes, No Unit: None Content: It shows whether BSC chooses to update system

information contents transmitted by BTS. If it is Yes, BSCwill send system information to BTS at a certain interval (it isdecided by Regular Transmission Interval). Otherwise,

system information can only be updated manually by usingBSC maintenance system.

Recommendation: Yes

Regular Transmission Interval


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Regular Transmission Interval

Value range: 0~255 Unit: Minute Content: It stipulates the time interval that BSC

updates system information to BTS.

Recommendation: 10 minutes

Course Contents


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ParametersIntroduction

CaseStudy

Course Contents

Case Study


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Case Study

Case Description During the process of optimization in a certain area, it is found out thatthe signal is poor in a certain section of suburban highway. The signalstrength measured is less than -95dBm.

Handling Procedure Modify the data in BSC. Add neighbor relationship to Cell A and B for

each other. The coverage problem is thus solved.

Case 1: Island

effect

C

B

A-92

-80 -9

5

Case Study


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Case Study

Case description The subscriber complained that MS could not register to the network,or it was difficult to register to the network between BTS A and B, orno network mark was displayed on the MS, but MS indicated that thesignal was very good. Some subscribers also complained that MScould make MTC could not make MOC.

Cause analysis

CGI of the cell was modified. So the network register flow was notnormal. Although the signal was very good, MS could not getregistered in the network.

Recommendation and summary CGI is a very important parameter and should be configured correctly,

thus to ensured that the CGI data in BSC and MSC are the same.

Case 2: Incorrect CGI causes MS unable to register on the

network.

Case Study


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Case Study

Case description Subscribers complain that the signal fluctuates in a certain area. On-site test shows that this phenomenon does exist. From the testingmobile, we can see that there are a lot of cells signals in this area.Some frequencies are the suburb BTS signals far away from thisarea. The cell reselection of MS is rather frequent.

Handling procedure

Modify parameter RXLEV_ACCESS_MIN of all cells in urban areaand make them consistent with each other. The problem of signalfluctuation is solved.

Recommendation and summary In area with complicated coverage, the RXLEV_ACCESS_MIN of

each cell should be kept same.

Case 3: RXLEV_ACCESS_MIN causes signal

fluctuation.

Case Study


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Case description A local GSM network has more than 6000 subscribers. There are four

BTSs. The network has been working properly. But from sometime on,some MS often lost connection with network suddenly. The complaint fromsubscribers in urban area increased.

Handling procedure Modify T3212 to 10, i.e. 60 minutes. Modify the corresponding time of MSCto 180 minutes. Two days observation shows no subscriber complaint andthe problem is solved.

Case 4Too small T3212 causes MS lose connection with network.

Case Study


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Documents

GSM System Information