Part 4 GSM Radio Parameters

7/30/2019 Part 4 GSM Radio Parameters

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4GSM Parameter Configuration and

AdjustmentWhen operators prepare to construct a mobile communication network, they must

predict coverage according to traffic prediction and local radio propagationenvironment. This guides project design of the system and parameter configuration

of radio network.

The project design includes the following aspects:

Network topology designSelecting the location of base stationFrequency planningCell parameter configuration

The RF planning determines the coverage range of a cell, and the serving range ofthe cell is determined based on the combination of RF planning and cell parameter

configuration. By this, the MS always enjoys optimal services and maximum

network capacity at the best cell.

This chapter discusses the meaning and effect of important parameters in GSM radio

communication. Mastering the effect and impact of these parameters helps to

configure network parameters and optimize the network in later stages.

In a GSM network, abundant radio parameters are configured according to cells or

partial areas; however, the parameter configuration might affect neighbor areas.

Therefore, while configuring and adjusting parameters, you must pay attention to the

impact of configuring parameters on other areas, especially neighbor areas.

4.1 Network and Cell ID

4.1.1 Cell Global ID

I. Definition

GSM is a global cellular mobile communication system. To ensure that each cell

corresponds to a unique ID globally, the GSM system numbers the following items:

Each GSM network in each countryEach location area

Each base stationEach cell

Numbering the previous items aims as follows:

An MS can identify the serving network so that the MS can select a network in anyenvironment.The network can obtain the precise location of the MS so that the network canprocess various service requests involving the MS.


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The MS can report information about neighbor cells to the network during calling toavoid call drop.

The cell global identity (CGI) is a major network identity parameter. CGI consists oflocation area identity (LAI) and cell identity (CI). LAI includes mobile country code

(MCC), mobile network code (MNC), and location area code (LAC).

The system transmits CGI information through system information (SI) transmittedby cell broadcast. When an MS receives SI, it demodulates SI for CGI information.The MS judge whether to camp on the cell according to the MCC and MNC. It also

judges whether the current location area changes to determine updating location.

While updating location, the MS reports LAI information to the network so that the

network can know the location area of the MS.

II. Format

The CGI is MCC-MNC-LAC-CI, with details as follows:

MCC consists of three decimal digits, ranging from 000 to 999.MNC consists of two decimal digits, ranging from 00 to 99.

LAC ranges from 0 to 65535CI ranges from 0 to 65535.

III. Configuration and Influence

As a globally unique mobile identity, the MCC is uniformly distributed and managedby international telecommunication union (ITU). The MCC for China is 460

(decimal).

The MNC is uniformly distributed by state telecommunication management organs.

Now two GSM networks exist in China. The MNC for China Mobile is 00. The

MNC for China Unicom is 01.

The method for coding LAC is ruled by each country accordingly. This caters for

China also (refer to GSM system from Ministry of Information Industry). At the

early stage of network construction, the LAC is coded and distributed. The LAC is

seldom changed in the later stages.

The coverage areas related to the LAC is vital in the network. You can configure it as

great as possible.

No special restriction is on the distribution of CI. The CI ranges from 0 to 65535(decimal). It must be ensured that two equivalent CIs exist in the same location area.

This is determined in the system design. Except for special situations (such as

constructing base stations), the CI must not be changed during the system operation.

IV. Precautions

You must pay attention to the following aspects:

The MNC is unchangeable.While configuring the LAC, you must follow related regulations. Equivalent LACsmust not exist in the state network.Equivalent CIs must not exist in the same location area.

4.1.2 Base Station Identity Code


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I. Definition

In a GSM network, each base station corresponds to a distributed local color code,

called base station identity code (BSIC). When the MS receives broadcast controlchannel (BCCH) carriers of two cells at the same time, with same channel number,

the MS distinguishes them by BSIC.

In network planning, the BCCH carriers of neighbor cells are different in frequencyto reduce intra-frequency interference. The cellular communication system features

that the BCCH carrier might be reused. Therefore, the BSIC of the cells with the

same BCCH carrier must be different.

The system transmits BSIC on synchronization channel (SCH) of each cell. The effect of BSIC is asfollows:

The BSIC involves in decoding process of random access channel (RACH) to preventbase stations from connecting to the RACH sent to the neighbor cells by the MS byerror.After the MS receives SCH messages, it judges that it has been synchronous to thecell. Decoding information on the downlink common signaling channel correctlyrequires training sequence code (TSC) used on common signaling channel.GSM regulations describe TSC in eight fixed formats, and the sequence number ofthem is 07. The cell BCC determines the TSC used by the common signaling channelof a cell. Therefore the BSIC helps inform the MS of the TSC used by the commonsignaling channel of the serving cell.In a call, the MS must measure the level of BCCH carrier of neighbor cells and reportit to the base station according to regulations to neighbor cell list of BCCH.Meanwhile, the MS must provide measured BSIC of the carrier in the uplinkmeasurement reports. When the neighbor cells of a cell include two or more cellswith the same BCCH carrier, the base station can distinguish the cells by BSIC to avoidincorrect handover.In a call, the MS must measure signals of neighbor cells, and sends measurementreports to the network. The measurement report can contain information about sixneighbor cells only, so the MS must be controlled to report the cells actually related

to handover. The first three digits of BSIC (namely, NCC) aims as previouslymentioned. Operators control the MS to report the neighbor cell informationpermitted by the serving cell NCC by broadcast parameters NCC permitted.

II. Format

The BSIC is NCC-BCC, with details as follows:

The NCC ranges from 0 to 7.The BCC ranges from 0 to 7.


Usually different GSM PLMNs use the same frequency resource, but, to some

degree, their network planning is independent. The neighbor GSM PLMNs usedifferent NCCs according to regulations. This ensures that the neighbor base stations

with same frequency use different BSICs.

The BCC is part of the BSIC. It helps identify different base stations with same

BCCH carrier number in the same GSM PLMN. The values of BCC must meet the

previous requirements. According to GSM regulations, the TSC of cell BCCH carrier


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must be same as that of cell BCC. The equipment providers must ensure the TSC

consistency.

IV. Precautions

The neighbor cells or cells nearby using the same BCCH carrier must use different

BSICs. Especially when two or more cells use the same BCCH carrier in theneighbor cell list of a cell, theses cells must use different BSIC. Pay attention to cells

at the bordering areas between provinces and cities, and otherwise cross-cell

handover might fail and abundant mistaken access problems might occur.


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4.2 Paging and Access Control Parameters

4.2.1 Number of Access Grant Reserved Blocks (BS_AG_BLK_RES or AG)

I. Definition

The common control channel consists of access grant channel (AGCH) and paging

channel (PCH).

For different CCCHs, each BCCH multiframe (including 51 frames) contains CCCH

message blocks different number. The CCCH is shared by AGCH and PCH.According g to regulations, partial message blocks on CCCH are especially reserved

for AGCH. This avoids that the AGCH messages are blocked when the PCH traffic

is great.

The number of parameter access grant reserved blocks (AG) refers to the number of

message blocks reserved for AGCH on CCCH in each BCCH multiframe.

II. FormatThe AG ranges from 0 to 2 when CCCH shares physical channel (CCCH_CONF =

1) with stand-alone dedicated control channel (SDCCH).

The AG ranges from 0 to 5 when CCCH does not share physical channel

(CCCH_CONF=0) with stand-alone dedicated control channel (SDCCH).


When the channel combination of the cell is fixed, the parameter AG adjusts the ratio

of AGCH and PCH in CCCH. When the PCH is idle, it can send immediate

assignment messages. The AGCH does not transmit paging messages. Equipment

operators can balance AGCH and PCH by adjusting AG, with the followingprinciples.

The principle for AG value is that based on no overload of AGCH, you must reduce

the parameter to shorten the time for MS to respond to paging, and to improve

system service performance. When the immediate assignment messages are superior

to paging messages to be sent, configure AG to 0.

The value of AG is recommended as follows:

AG is 1 when the CCCH and SDCCH share a physical channel. AG is 2 or 3 in other situations.

In network operation, take statistics of overload situations of AGCH and adjust AGaccordingly. By default the immediate assignment messages are superior to pagingmessages to be sent in the network, so you need not reserve a channel for immediate

assignment messages. In this situation, configure AG to 0.

4.2.2 Frame Number Coding Between Identical Paging

Frame number coding between identical paging is BS_PA_MFRMS (MFR for short).

I. Definition


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According to GSM regulations, each MS (corresponding to an IMSI) belongs to a

paging group (for calculation of paging groups, see GSM regulation 05.02). Eachpaging group in a cell corresponds to a paging subchannel. According to its IMSI, the

MS calculates the paging group that it belongs to, and then calculates the location of

paging subchannel that belongs to the paging group. The MS only receives the

signals of the paging subchannel that it belongs to, and neglects that of other pagingsubchannels. In addition, the MS even powers off some hardware of itself during

other paging subchannel to lower power cost of itself.

The number of paging channel multiframe (MFR) is the number of multiframes usedin a period of paging subchannel. The MFR determines the number of paging

subchannels that the cell PCH is divided into.

II. Format

The MFR ranges from 2 to 9, which respectively means that the same paging group

cycles in a period of 2 to 9 multiframes.

III. Configuration and InfluenceAccording to the definition of CCCH, AG, and MFT, you can calculate the number

of paging channel in each cell.

When the CCCH and SDCCH share a physical channel, there is (3 - AG) MFRs. When the CCCH and SDCCH share a physical channel, there is (9 - AG) MFRs.

According to the previous analysis, the greater the MFR is, the more the pagingchannels of the cell are (see the calculation of paging groups in GSM regulation05.02). Theoretically, the capacity of paging channels does not increase with the

increase of MFR. The number of buffers for buffering paging messages on each base

transceiver station (BTS) increases. The paging messages are sent more evenly both

in time and space, so it seldom occurs that the paging messages overflow in the

buffers so call lost occurs (related to functions by equipment providers).

However, to enjoy the previous advantages, you will have a longer delay of paging

messages on the radio channels. The greater the MFR is, the greater the delay of

paging messages in the space is, and the lower the average service performance ofthe system is. Therefore, the MFR is an important parameter in network

optimization.

The following principle caters for configuring MFR:

The configured strategy for buffers of each equipment provider is different, so you

must select the MFR properly so that the paging messages do not overflow on PCH.Based on this, configure the parameter as small as possible. In addition, you must

measurement the overflow situations of PCH periodically while the network isrunning, and adjust MFR accordingly.

IV. Precautions

Any paging message of the same location area must be sent to all cells in the location

areas at the same time, so the PCH capacity of each cell in the location area must be

equivalent or close to each other. Otherwise, you must consider smaller PCH

capacity as the evidence for designing location area.


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4.2.3 Common Control Channel Configuration (CCCH-CONF)

I. Definition

The CCCH includes AGCH and PCH. It sends immediate assignment messages and

paging messages. In each cell, all traffic channels (TCHs) share CCCH. According to

the TCH configuration and traffic model of the cell, the CCCH can be one or morephysical channels. In addition, the CCCH and SDCCH share a physical channel. The

combination methods for CCH are determined by CCCH parameter CCCH_CONF.

II. Format

The CCCH_CONF consists of three bits, with the coding methods listed in Table:

CCCH configuration coding

CCCH_CONF MeaningNumber of CCCH message blocks in

a BCCH multiframe

000

One physical channel for used

for CCCH, not shared withSDCCH

9

001One physical channel for used

for CCCH, shared with SDCCH3

010Two physical channels for used

for CCCH, not shared with

SDCCH18

100Three physical channels for

used for CCCH, not shared with

SDCCH27

110Four physical channels for usedfor CCCH, not shared with

SDCCH36


When the CCCH and SDCCH share one physical channel, the CCCH has theminimum channel capacity. When the CCCH and SDCCH do not share a physical

channel, the more physical channels that the CCCH uses, the greater the capacity is.

The CCCH_CONF is determined by the operators based on combination of cell

traffic model and paging capacity of the location area where a cell belongs to. It is

determined in system design, and adjusted in network expansion. According to

experiences, when the paging capacity in the location area is not high and cell hasone or two carriers, it is recommended that the CCCH uses one physical channel and

share it with SDCCH (in combination CCCH methods). This spares a physicalchannel for paging. Otherwise, the method that CCCH and SDCCH do not share one

physical channel is used.


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When the cell TRX exceeds 6 and CCCH OVERLOAD occurs in the cell, it is

recommended that the CCCH uses two or more basic physical channel and does not

share them with SDCCH.

IV. Precautions

The CCCH_CONF must be consistent with the actual configuration of cell CCCH. Inaddition, you must consider the influence on the access grant reserved blocks.

4.2.4 Extended Transmission Slots (TX_INTEGER)

I. Definition

In a GSM network, a random access channel (RACH) is an ALOH. To reduce the

conflicting times on RACH when an MS accesses the network, and to increase

RACH efficiency, GSM regulations (sections 3.3.1.2 of 04.08) prescribe the

compulsory access algorithm for MS. The algorithm defines three parameters as

follows:

Extended transmission slots T Maximum retransmission times RET TIt is the number of slots between two sending when the MS keeps sending multiplechannel request messages. SIt is related to channel combination, and is an intermediate variable of accessalgorithm. It is determined by T and CCCH configuration.

II. Format

The value of T is from 3 to 12, 14, 16, 20, 25, 32, and 50.

The value of S ranges as listed in Table:Values of S

T

S in different CCCH combination methods

The CCCH and SDCCH does

not share a physical channelThe CCCH and SDCCH share a

physical channel

3, 8, 14, 50 55 41

4, 9, 16 76 52

5, 10, 20 109 58

6, 11, 25 163 867, 12, 32 217 115


To access the network, the MS must originate an immediate assignment process. To

begin the process, the MS sends (RET + 1) channel request messages on RACH. To


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reduce conflicts on RACH, the time for MS to send channel request messages must

meet the following requirements:

The number of slots (not including slots for sending messages) betweenoriginating immediate assignment process by MS and sending the first channel requestmessages is random. Its range is {0, 1, , MAX (T, 8) - 1}. When the MS originates theimmediate assignment process, it takes a value from the range according to even

distribution probability. The number of slots (not including slots for sending messages) between achannel request message and the next is from {S, S + 1, , S + T - 1} according toeven distribution probability.

According to previous analysis, the greater the T is, the larger the range of intervals

between one channel request message and the next, and the less the RACHconflicting times is. The greater the S is, the greater the interval between one channel

request message and the next, the less the RACH conflicting times is, and the more

efficiently the SDCCH is used. However, the increase of T and S leads to longer time

for MS to access the network, so the access performance of the whole network

declines. Therefore you must configure T and S properly.

S is calculated by MS according to T and combination of CCH. You can configure Tfreely and sends it to MS by system information. Usually, you need configure T

properly to make T + S as small as possible (to reduce the time for MS to access thenetwork); meanwhile you must ensure an effective assignment of SDCCH to avoid

overload (for all random access requests, the system does not distinguish whether

they are from the same MS, but assigns a SDCCH). In operation, you can adjust the

value according to traffic measurement of cell immediate assignment.

4.2.5 Minimum Access Level of RACH

I. Definition

The minimum access level of RACH is the level threshold for the system to judge

whether there is a random access request.

II. Format

The minimum access level of RACH ranges from 0 to 63 (corresponding to110

dBm to47 dBm).

The unit is level grade value.


When the access burst level of RACH is greater than the threshold, the BTS judges

that there is an access request. The BTS, together with the parameter random accesserror threshold, determines whether the random access burst is valid. To configurethe parameter properly, you must combine actual sensitivity of the base station and

the parameter minimum received level permitted for MS to access. This prevents

the MS from failing in calling though there are signals. The access burst level ofRACH affects call drop rate and access range (coverage), so you must pay attention

to the influence on access of MS.


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4.2.6 Random Access Error Threshold

I. Definition

GSM protocols prescribe that by relativity of judgment training sequence (41 bits)

the system can judge whether the received signals are the random access signals of

MS.

II. Format

The value ranges from 0 to 255. The recommended value is 180.


The random access error threshold defines the relativity of training sequence. If the

smaller it is, the more errors of random access signals permitted by the network are,

the easily the MS randomly accesses the network, and the greater the report error rate

is. If the greater the random access error threshold is, the smaller the report error rateis, and the more difficult the access to the network is when signals are weak. See

protocol 0408, 0502.

The system requires the random access error threshold transferred by current bit of

41 bit training sequence.

90100 33

101120 34

121140 35

141160 36

161175 37

176195 38

196221 39

222243 40

244250 41

089 or 251

25538

The two parameters random access error threshold and minimum access level of

RACH determine the validity of random access burst.

4.2.7 Access Control Class (ACC)

I. Definition

GSM regulations (02.11) prescribe that each GSM user (common user) corresponds

to an access class, ranging from class 0 to class 9. The access class is stored in SIM


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of mobile users. For special users, GSM regulations reserves five special access

classes, ranging from class 11 to class 15. Theses classes are prior to other classes inaccessing. Special users might have one or more access classes (between 11 and 15),

which are also stored in user SIM. Users of class 11 to 15 are prior to that of class 0

to 9. However, the class between 0 and 9 or between 11 and 15 does not mean

priority.The access class is distributed as follows:

Class 09: common users Class 11: users for PLMN management Class 12: users for security departments Class 13: common business departments (in charge of water, gas) Class 14: emergency services Class 15: PLMN staff

Users of class 09 have its access rights catering for home PLMN and visited PLMN.Users of class 11 and 15 have its access rights catering for visited PLMN only. Users

of class 12, 13, and 14 have its access rights catering for in the country where home

PLMN belongs to.

II. Format

The access control class consists of two parts:

Common access control classValue range: a check option, including class 0 disabled, , class 9 disabled.Recommended value: all 0. Special access control classValue range: a check option, including class 11 disabled, , class 15 disabled.Recommended value: all 0.

If a class is configured to 1, it means that access is forbidden. For example, acommon access class is configured to 1000000000; common users excluding class 0

users can access the network.


C0C15 (excluding C10) are set by equipment room operators. Usually these bits are

configured to 1. Proper configuration contributes to network optimization as follow:

When installing a base station, starting a base station, or maintaining and testingin some cells, configure C0C15 (excluding C10) to 1. In this way, different users areprevented from accessing the network, so the installing and maintenance is lessinfluenced. During busy hours of cells with high traffic, congestion occurs, RACH conflictingtime increase, AGCH traffic overloads, and Abis interface traffic overloads. When youconfigure class of some users to 1, you can reduce the traffic of the cell.

4.2.8 Maximum Retransmission Times (RET)

I. Definition

See GSM regulation 04.08. When an MS originates an immediate assignment

process, it sends a channel request message to the network on RACH. The RACH is

an ALOH, so the MS can send multiple channel request messages before receiving


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immediate assignment messages, to increase access success rate of MS. The

maximum retransmission times M (RET) is determined by equipment room

operators, and sent to MS by SI.

II. Format

The maximum retransmission times consists of two bits, with the meanings listedin Table:

Coding of maximum transmission times M

M maximum transmission times

00 1

01 2

10 4

11 7


The greater the M is, the higher the success rate of call attempt is, and the higher the

connection rate is, but the load of RACH, CCCH, and SDCCH increase. In cell withhigh traffic, if the RET is over great, overload of radio channels and congestion

occur, so the connection rate and radio resource utilization declines sharply. If the

RET is over small, the call attempt times of MS reduces, success rate reduces, so the

connection rate reduces. Therefore, proper configuration of RET for each cell help

utilize network radio resources and improve connection rate.

For configuration of RET M, refer to the following methods:

For areas with low traffic, such as in suburban or rural areas, configure RET to 7to increase the access success rate of MS. For areas with average traffic, such as common urban areas, configure RET to 4.

For microcell with high traffic and of apparent congestion, configure RET to 1.

4.2.9 Control Class of MS Maximum Transmit Power (MS-TXPWR-MAX-CCH)

I. Definition

MS-TXPWR-MAX-CCH is sent in BCCH SIs. It affects behavior of MS in idle

mode. It is also used in calculating C1 and C2, and determines cell selection andreselection.

C1 = RLA_C - RXLEV_ACCESS_MIN - MAX((MS_TXPWR_MAX_CCH - P), 0) RLA_C: average received level by MS RXLEV_ACCESS_MIN: minimum received level permitted for MS to access MS_TXPWR_MAX_CCH: maximum power level of control channel (control class ofMS maximum transmit power) P: Maximum transmit power level of MS


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II. Format

The range of MS-TXPWR-MAX-CCH is 031. For cells of GSM900 and GSM1800,

the dBm values corresponding to the control class are different.

In a GSM900 network, the 32 control class of maximum transmit powercorresponding to 031 is as follows:

{39, 39, 39, 37, 35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 5, 5, 5, 5, 5,5, 5, 5, 5, 5, 5, 5} In a GSM1800 network, the 32 control class of maximum transmit powercorresponding to 031 is as follows:{30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 36, 34, 32}

Recommended values are 5 for GSM900 and 0 for GSM1800.


MS-TXPWR-MAX-CCH determines the power class used before MS receives power

control messages. For details, seeprotocol 0508.

The smaller it is, the greater the output power of MS is. The MS near the base stationinterferes with neighbor channels of the cell, so the access to the network by other

MSs and communication quality are influenced. The greater it is, the smaller the

output power of MS is, and the lower the access success rate of MS at cell borders is.You must configure MS-TXPWR-MAX-CCH properly according to the serving

range of the cell.

4.2.10 Power Offset (POWEROFFSET)

I. Definition

When the MS accesses the network and before it receives the initial power control

messages, all GSM900 MSs and type 1 and type 2 DCS1800 MSs use

MS_TXPWR_MX_CCH of BCCH. If the MS_TXPWR_MX_CCH exceeds the

maximum transmit power of MS, the MS uses the closest power.

The parameter POWEROFFSET is effective to type 3 DCS1800 MSs. When the type

3 DCS1800 MS accesses the network, it use total power of MS_TXPWR_MX_CCH

+ POWEROFFSET before receiving the initial power control message. See protocol

GSM0508.

II. Format

The values of 03 correspond to 0 dB, 2 dB, 4 dB, and 6 dB.

The recommended value is 2.


The greater the parameter is, the more easily the type 3 DCS1800 MS accesses the

network. A great POWEROFFSET enables MS to access the network afar, but does

not help control cross-cell interference, so the network quality is influenced.

4.2.11 IMSI Attach/Detach Allowed


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I. Definition

The IMSI detach means that the MS informs the network of itself work state

changing from working to non-working. Usually it refers to when the MS powers offor the SIM is taken off MS. After receiving the inform from MS, the network sets the

IMSI as in non-working state.

The IMSI attach is opposite of IMSI detach. It means that MS informs the network ofitself work state changing to working. Usually it refers to when the MS powers on or

the SIM is put into MS again. After the MS turns to working state again, it detects

whether the current location areas (LAI) is the same as that recorded in MS at last.

If yes, the MS starts IMSI attach process (this is one of location updating). If no, the MS starts location updating process of cross location area.

After receiving the location updating message or IMSI message from MS, the

network sets the IMSI as in working state.

The parameter IMSI attach/detach allowed (ATT) is used for informing MS of the

IMSI attach/detach process.

II. Format

The value of ATT includes YES/NO. NO means that starting IMSI attach/detachprocess by MS is forbidden. YES means that starting IMSI attach/detach process by

MS is compulsory.


Usually configure ATT to YES so that the network will not process the proceeding of

the MS after the MS powers off. This frees system resources (such as PCH).

IV. Precautions

The ATT of different cells in the same location area must be the same to avoidabnormalities while the MS is called. For example, in a cell with YES as the value of

ATT, when the MS powers off, it starts IMSI detach process. Therefore the network

records that the MS is in non-working state, so it does not page the MS. In a cell withNo as the value of ATT and the cell being different from the one where the MS

powers off, when the MS powers on again in the cell, the MS does not start IMSI

attach process. In this situation, the MS cannot be called normally until it starts

location updating process.

4.2.12 Direct Retry (DR)

I. Definition

During the assignment process of call setup, congestion might cause assignment

failure. The assignment failure causes failure of the whole call. GSM networks has afunction to avoid such failures, namely, DR. The DR is that the BSS directly assign

MS to TCH of neighbor cells. The parameter is used by system to set whether to

allow direct retry function.


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II. Format

The value of DR includes YES and NO. YES means that the system allows

directional retry. NO means that the system does not support direction retry function.


DR improves call success rate. If conditions are ready, start DR. On the contrary, DR

is that the BSS directly assign MS to TCH of neighbor cells when congestion occurs

in the cell where the MS camps, so the MS can originates a call in the non-best cellwith lowest received level, and extra interference might be brought about in

frequency reuse networks. Therefore, you must use the function properly according

to comprehensive network situations.


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4.3 Serial Parameters of Cell Selection andReselection

4.3.1 cell_bar_access

I. Definition

In the SI broadcasted in each cell, a bit indicates whether the MS is allowed to access

the network in the cell, namely, cell_bar_access.

II. Format

The value of cell_bar_access includes 1 and 0. The value 0 indicates that MS is

allowed to access the network from the cell. The value 1 indicates that the MS isbarred to access the network from the cell. Actually whether to allow MS to access

the network from the cell is determined by both cell_bar_access and

cell_bar_qualify.


The cell_bar_access is configured by equipment room operators. Usually the MS is allowed to accessthe network from all the cells, so cell_bar_access is configured to 0. In special situations, the operatorswant some cell for handover service only, so cell_bar_access is configured to 1

The MS usually works in microcells (you can configure the priority of cells and reselection parametersto enable this). When the MS is calling while moving fast, the network force MS to hand over to thebase station G. The signals of base station G are stronger than microcell base station in most areas.When the call terminates, the MS just camps near base station G and at edge of microcell cells, the MSwill not reselect a cell according to GSM regulations, therefore the MS cannot return to microcell.

The capacity of base station G is usually small, so the previous phenomenon leads to

congestion of base station G. To solve the problem, you can configure thecell_bar_access to 1, namely, to forbid MS directly accessing base station G. In area

A, handover is allowed to base station G.

IV. Precautions

The cell_bar_access is used only in some special areas. For common cells, it is

configured to 0.

4.3.2 cell_bar_qualify

I. Definition

The cell_bar_qualify determines the priority of cells, namely, it enables MS to selectsome cell by preference.

II. Format

The value of cell_bar_qualify includes 1 and 0. The cell_bar_qualify and

cell_bar_access determine the priority state of cells, as listed in Table 1-4.

Table 7-1 Cell priorities


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cell_bar_qualify cell_bar_access Cell selection priority Cell reselection state

0 0 Normal Normal

0 1 Barred Barred

1 0 Low Normal

1 1 Low Normal

An exception is that the cell selection priority and cell reselection state are normal

when the following conditions are met:

The cell belongs to the PLMN which the MS belongs to. The MS is in cell test operation mode. The cell_bar_access is 1. The cell_bar_qualify is 0. The access control class 15 is disabled.


The priority of all the cells are usually configured to normal, namely,cell_bar_qualify = 0. In microcell and dualband networking, operators might want

MS to camps on the cell of some type by preference. In this situation, the equipmentroom operators can configure the priority of these cells to normal and other cells

to low.

During cell selection, when the proper cells with normal as the priority is not present

(proper cells means that all parameters meet the conditions for cell selection, namely,

C1 > 0, and the cell is allowed to access), the MS will select cells with low priority.

IV. Precautions

Pay attention to the following aspects:

When cell priority is used as a method to optimize network, the cell_bar_qualifyonly affects cell selection, without any influence on cell reselection. You mustoptimize the network by combining cell_bar_qualify and C2. During cell selection, when the proper cells with normal as the priority is notpresent, the MS will select cells with low priority. Therefore when the level of thecell with normal priority is low, and cells with low priority and high level are present,the MS will access the network slowly while powering on.

4.3.3 Minimum Received Level Allowing MS to Access (RXLEV_ACCESS_MIN)

I. Definition

To avoid bad communication quality, call drop, and a waste of network radioresources due to MS accessing the network at low received signal level, GSM

regulations prescribe that when an MS accesses the network the received level must

be greater than the threshold level, namely, the minimum received level allowing MS

to access.

II. Format

The value range of RXLEV_ACCESS_MIN is from110 dBm to47 dBm.


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The recommended RXLEV_ACCESS_MIN needs to be approximately equal to the

receiving sensitivity of MS. The RXLEV_ACCESS_MIN affects cell selection

parameter C1, so it is important to traffic adjustment and network optimization.

For cells with over high traffic and severe congestion, you can increase

RXLEV_ACCESS_MIN. In this way, the C1 and C2 of the cells decrease, and theeffective coverage range decreases. You must not configure RXLEV_ACCESS_MIN

over great, because this might cause non-seamless coverage and complaints for

signal fluctuation. It is recommended that the RXLEV_ACCESS_MIN is smaller

than or equal to90 dBm.

IV. Precautions

Except for areas of high density of base stations and of qualified coverage, adjusting

cell traffic by RXLEV_ACCESS_MIN is not recommended.

4.3.4 Additional Reselection Parameter IndicatorI. Definition

The cell selection and reselection by MS depends on the parameters C1 and C2.Whether C2 is the cell reselection parameter is determined by network operators.

Additional reselection parameter indicator (ADDITIONAL RESELECT) informs

MS of whether to use C2 in cell reselection.

II. Format

ADDITIONAL RESELECT consists of 1 bit. In SI3, it is meaningless, andequipment manufacturers configure it to N. The MS uses ADDITIONAL

RESELECT of SI4.

When ADDITIONAL RESELECT is configured to N, the meaning is: if the rest bytesof SI4 (SI4RestOctets) are present, the MS must abstract and calculate parametersrelated to C2 and related cell reselection parameter PI. When ADDITIONAL RESELECT is configured to Y, the meaning is that the MS mustabstract and calculate parameters related to C2 and related cell reselectionparameter PI.


Cells seldom use SI7 and SI8, so you can configure ADDITIONAL RESELECT to

N. When cells use SI7 and SI8, and the parameter C2 is used in cell reselection, you

can configure ADDITIONAL RESELECT to Y.

4.3.5 Cell Reselection Parameter Indicator

I. Definition

The cell reselection parameter indicator (CELL_RESELECT_PARAM_IND) is usedin informing MS of whether C2 is a cell reselection parameter and whether C2 is

present.


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II. Format

The value of CELL_RESELECT_PARAM_IND includes Y and N, with the

meanings as follows:

Y: The MS must calculate C2 by abstracting parameters from SIs of cellbroadcast, and set C2 as the standard for cell reselection.

N: The MS must set C1 as the standard, namely, C2 = C1.


The equipment room operators determine the value of PI. Configure PI to Y if related

cells set C2 as the standard for cell reselection; otherwise, configure it to N.

4.3.6 Cell Reselection Offset, Temporary Offset, and Penalty Time

I. Definition

After the MS selects a cell, without great change of all the conditions, the MS will

camp on the selected cell. Meanwhile, it does as follow: Starts measuring signals level of BCCH carrier in neighbor cells. Records the 6 neighbor cells with greatest signal level. Abstract various SI and control information of each neighbor cell from the 6cells.

When conditions are met, the MS hands over from the selected cell to another. This

process is called cell reselection. The conditions include:

Cell priority Whether the cell is barred to access Radio channel level (important)

When the signal level of neighbor cells exceeds that of the serving cell, cell

reselection occurs. The channel level standard used in cell reselection is C2, with thecalculation as follows:

1) When PENELTY_TIME 11111:C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET * H (PENALTY_TIME - T)Wherein, if PENALTY_TIME - T (x) < 0, the function H(x) = 0; if x 0, H(x) = 1.2) When PENELTY_TIME = 11111:C2 = C1 - CELL_RESELECT_OFFSET

T is a timer, with 0 as the initial value. When a cell is listed by MS in the list of cellswith maximum signal level, start T with step of 4.62ms (a TDMA frame). When the

cell is removed from the list, the associated T is reset.

After cell reselection, the T of original cell works as PENALTY_TIME. Namely,

temporary offset is not performed on the original cell.CELL_RESELECT_OFFSET (CRO) modifies cell reselecting time C2.

TEMPORARY_OFFSET (TO) is supplemented to C2 from starting working of T to

the prescribed time.

PENALTY_TIME is the time for TEMPORARY_OFFSET having effect on C2.

When PENALTY_TIME = 11111, the MS is informed of using C2 = C1CRO.


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CELL_RESELECT_OFFSET, TEMPORARY_OFFSET, and PENALTY_TIME are

cell reselection parameters.

When the cell reselection parameter PI is 1, the MS is informed of receivingvalues of three parameters on BCCH. If PI is 0, the MS judges that the previous three parameters are 0, namely C2 =C1.

If the C2 of a cell (in the same location area as the serving cell) calculated by MS is

greater than the C2 of the cell where MS camps, and this lasts for over 5s, the MS

reselects to camp on the cell.

If the C2 of a cell (in different location area as the serving cell) calculated by MS is

greater than the sum of C2 of the cell where MS camps and cell reselect hysteresis,

and this lasts for over 5s, the MS reselects to camp on the cell.

The interval between two reselections is at least 15s, and this avoids frequent cell

reselection by MS.

C2 is formed on the combination of C1 and artificial offset parameters. The artificial

offset parameters help MS camp on or prevent MS from camping on some cell. This

balances the traffic of the network.

II. Format

1) The cell reselection offset (CRO) is in decimal, with unit of dB. It ranges from 0to 63, which means 0 to 126 dB (2 dB as the step). The recommended value is 0.2) The temporary offset (TO) is in decimal, with unit of dB. It ranges from 0 to 7,which means 0 to 70 dB (10 dB as the step). The recommended value is 0.3) The penalty time (PT) is in decimal, with unit of second. It ranges from 0 to 31.The value 0 to 30 means 20s to 620s (20s as the step). The value 31 is reserved forchanging the effect direction of C2 by CRO. The recommended value is 0.

III. Configurationa and Influence

The previous parameters can be adjusted accordingly in the following three

situations:

1) When the communication quality is bad due to heavy traffic or other causes,change the parameters to enable MS not camps on the cell (the cell is exclusive fromthe MS). For this situation, configure PT to 31, so TO is ineffective. C2 = C1 CRO.The C2 is artificially lowered. So the probability for MS to reselect the cell decreases.In addition, the equipment room operators can configure CRO to a proper valueaccording to the exclusive level of the cell by MS. The greater the exclusion is, thegreater the CRO is.2) For cells with low traffic and equipment of low utilization, change theparameters to enable MS to camp on the cell (the cell is prior). In this situation,configure CRO to 020 dB according to the priority. The higher the priority is, the

greater the CRO is. TO is configured the same as or a little greater than CRO. PT helpsavoid over frequent cell reselection, the recommended value of PT is 20s or 40s.3) For cell with average traffic, configure CRO to 0, PT to 11111 so that C2 = C1.No artificial influence is on the cell.

IV. Precautions

In whatever situations, the CRO must not be greater than 30 dB, because over great

CRO leads to unstable network, such as complaints about signal fluctuation.


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4.3.7 Cell Reselection Hysteresis (CRH)

I. Definition

CRH affects cell reselection of cross location area. The MS starts cell reselection if

the following conditions are met:

The signal level of neighbor cell (in different location area) is greater than thatof the serving cell. The difference between the signal levels of the neighbor cell and the serving cellmust be greater than the value prescribed by cell reselection hysteresis.

The difference is based on the cell reselection methods used by MS. If the MS

reselects a cell with C2, then compare values of C2.

II. Format

CRH is in decimal, with unit of dB. The range is 0 to 14, with step of 2 dB. The

recommended value is 4.


If the original cell and target cell belongs to different location areas, the MS must

originate a location updating process after cell reselection. Due to the attenuation

feature of radio channels, the C2 of two cells measured at the bordering area ofneighbor cells fluctuates much, so the MS reselect cells frequently. The interval

between two reselections is over 15s, which is rather short for location updating. The

signal flow of network increases sharply, radio resources cannot be fully utilized.

During location updating, the MS cannot respond to paging, so the connection rate

decreases. Adjust CRH according to signal flow and coverage. When signal flowoverloads or location updating of cross location area is frequent, the cell reselection

hysteresis is increased as recommended. You must avoid abnormal coverage due toover large location area.

IV. Precautions

Do not configure CRH to 0 dB.


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4.4 Parameters Affecting Network Functions

4.4.1 Newly Established Cause Indicator (NECI)

I. Definition

In a GSM network, the traffic channel (TCH) consists of full-speed TCH and half-

speed TCH. When the network supports half-speed TCH, the MS is informed of

whether the area supports half-speed TCH by NECI.

II. Format

The value of NECI includes Y and N, with the meaning as follows:

Y means that the area support half-speed TCH. N means that the area cannot support half-speed TCH.


Half-speed TCHs enable each carrier to support more traffic channel, but you mustconfirm whether the system support half-speed TCH.

4.4.2 Power Control Indicator (PWRC)

I. Definition

The PWRC informs MS of whether to take statistics of downlink level of BCCH

carrier slot for measuring average value when the BCCH frequency participates in

frequency hopping. The causes to configuring PWRC are as follows:

GSM regulations allow frequency hopping channels to use BCCH (frequencyhopping not in BCCH slots) . GSM regulations allow downlink power control over frequency hopping channels. The MS needs signal level of the measured neighbor cells, so the power of eachslot on BCCH frequency is prohibited to change. The downlink power control does notinvolve carrier slots for BCCH which includes the frequency hopping.

For previous causes, when the MS measures the average downlink channel level withcommon methods, the measurement result is inaccurate for power control becausethe average value includes the downlink received level of BCCH carriers the power

of which are not controlled, so the measurement report is inaccurate for power

control.

To avoid the influence on power control, when the MS calculates average receivedlevel during frequency hopping, the received level obtained from BCCH carrier slot

must be removed (see GSM regulations 05.08).

II. Format

The value of PWRC includes 0 and 1, with meanings as follows:

When PWRC is 0, the measurement result by MS includes BCCH carrier. When PWRC is 1, the measurement result by MS does not include BCCH carrier.



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The PWRC is usually configured to 0. Configure it to 1 if all the following

conditions are met:

Channels have frequency hopping on two or more frequencies. One of the frequency is BCCH carrier frequency. The system uses downlink power control.

IV. Precautions

The value of PWRC depends actually on the following parameters:

Whether to use frequency hopping. Whether the hopping frequency includes BCCH carrier. Whether the system uses downlink power control.

4.4.3 Discontinuous Transmit of Uplink

I. Definition

Discontinuous transmit of uplink (DTXU) refers to the process for MS not to

transmit signals during silent period (see description about DTX in Chapter 2).

II. Format

Whether the network allows uplink to use discontinuous transmit (DTX) is set by

equipment room operators. DTX ranges from 0 to 2, with the following meanings:

0: MS can use DTXU. 1: MS must use DTXU. 2: MS cannot use DTXU.


Using uplink DTX affects call quality, but it is helpful in the following aspects:

Lower interference to radio channels.Due to this, the average call quality of network is improved. Cut power consumption by MS

For the previous advantages, DTX is recommended to use.

4.4.4 Discontinuous Transmit of Downlink

I. Defintion

Discontinuous transmit of downlink (DTXD) means the network does not transmit

signals during silent period.

II. Definition

DTXD is in string, and the range is YES and NO. The meanings are as follows:

YES: Downlink uses DTX. NO: Downlink does not use DTX.



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Using downlink DTX affects call quality in a limit scale, but it is helpful in the

following aspects:

Lower interference to radio channels.Due to this, the average call quality of network is improved. Reduce load of base station CPU

Therefore, if possible, you use DTX.IV. Precautions

According to GSM regulations, downlink DTX is optional. If the base station

equipment supports DTXD, then use it. However, you must ensure that voice

transcoder is available to support DTXD.

4.4.5 Call Resetup Allowed

I. Definition

When coverage voids cause radio link failure, consequently call drop, the MS starts

to resetup the call for recovery. Whether resetting up the call is allowed depends on

the parameter call resetup allowed (RE).

II. Format

The values of call resetup allowed are 1 and 0, with meanings as follows:

1: Call resetup is allowed in the cell. 0: Call resetup is forbidden in the cell.


When a connected MS passes coverage voids, call drop occurs easily. If call resetup

is allowed, the average call drop rate (CDR) is lowered. However, call resetup takeslonger time, and most users disconnects before completion of call resetup. Therefore

call resetup is difficult to achieve, and even wastes abundant radio resources. In a

word, call resetup is disabled.

4.4.6 Emergency Call Allowed

I. Definition

The following MSs cannot enjoy various services:

MS without SIM MS with ACC as one of C0 to C9 and with cell_bar_access

The parameter emergency call allowed (EC) determines whether the MS is allowedfor emergency calls, such as police emergency call.

II. Format

EC consists of 1 bit. For the MS with ACC of C0 to C9 or without SIM, the EC is

NO, meaning emergency call forbidden. YES means emergency call allowed. For the

MS with ACC of C11 to C15, when both the access control bit and EC are

configured to forbidden, it is forbidden for emergency calls.


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According to the GSM regulations, the emergency number is 112, different from that

in China. The Chinese emergency call cannot function as prescribed in GSMregulations. For international roaming users, set 112 to answerphone to inform users

of various special service numbers. Therefore, setting emergency call must be

allowed through configuring radio parameters, namely, configure EC to 1.

4.4.7 Early Classmark Sending Control

I. Definition

In a GSM network, the MS classmark marks the following aspects:

Service capacity Supported frequency band Power capacity Encryption capacity

Classmark consists of classmark1, classmark2, and classmark3. A GSM MS. In aGSM network, the MS reports Classmark1 or Classmark2 information immediately

after ESTIND (corresponding to L2-SABM at Um interface) isallocated. Classmark3 (CM3) information includes power information of various

frequency band of multi-frequency MS.

During handover between different bands, the power class must be correctly

described. When the GSM system pages and transmits BA2 in different bands, itmust know the CM3 message. In GSM regulation Phase2plus, early classmark

sending control (ECSC) is added. ECSC means that by SI the system informs MS of

reporting Classmark3 after link setup. This avoids querying process by network.

II. Format

The values of ECSC are Y and N, with the following meanings:

Y: The MS reports Classmark3 to the network immediately after link setup. N: The MS is forbidden to report its Classmark3 to network initiatively.


The major information of Classmark3 is for dualband network, so do as follows:

Configure ECSC to N in single frequency GSM application areas. Configure ECSC to Y in dualband GSM application areas.

IV. Precautions

In a dualband network, configure the parameter of all cell to the same value.Configuring the parameter to different values in one or more cells is forbidden;

otherwise, the network quality declines.


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4.5 Frequency Hopping Parameters

4.5.1 Frequency Hopping Sequence Number

I. Definition

In a GSM network, the cell allocation (CA) means the set of carriers used by each

cell, recorded as {R0, R1, , Rn - 1}. Wherein, Ri indicates the absolute channel

number. For each communication process, the set of carriers used by base station and

MS is mobile allocation (MA), recorded as {M0, M1, , Mn - 1}. Wherein, Mi

indicates the absolute channel number. Obviously MA is a subset of CA.

During a communication process, the air interface uses a carrier number, one element

of MA. The variable mobile allocation index (MAI) determines an exact element of

MA. According to the frequency hopping algorithm in GSM regulation 05.02, theMAI is the TDMA frame number (RN) or reduced frame number (RFN), frequency

hopping sequence number (HSN), and mobile allocation index offset (MAIO).

Wherein, the HSN determines two aspects: Track of frequency points during frequency hopping The asynchronous neighbor cells using the same MA can avoid continuousfrequency collision during frequency hopping by using different HSNs.

II. Format

HSN is in decimal, ranging from 0 to 63, wherein:

0: cyclic frequency hopping 163: pseudo frequency hopping


You can choose any HSN in cells using frequency hopping, but you must ensure thatthe cells using same frequency group must use different HSN. The following

paragraph is an exception:

In an 1X1 network, three cells under a base station use the same frequency group, but

they are synchronous cells because of same FN. Therefore the three cells use the

same HSN. You must plan MAIO properly to avoid frequency collision of the three

cells under the same base station.

4.5.2 Mobile Allocation

I. Definition

The mobile allocation (MA) in the GSM network indicates a frequency set for

frequency hopping. Namely, when the MA of a cell is fixed, the communication

frequency points of the cell performs transient in the set by MA according to rules.

The parameter MA determines all the elements in MA.

II. Format

MA is a set, with all GSM frequency points as its element, namely:


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For GSM900 networks: 1124 and 9751023. For GSM1800 networks: 512885


MA is configured according to network designing requirements.

IV. Precautions

Chinese GSM networks do not cover all available frequency bands of GSM system,

so configure MA in available frequency bands.

The number of elements in each MA set cannot exceed 63.

The MA cannot include BCCH carriers.

The number of MA must not be multiples of 13 if all the following conditions are

met:

Using DTX HSN = 0 (cyclic frequency hopping)

You must avoid SACCH to appear usually at the same frequency point.

4.5.3 Mobile Allocation Index Offset

I. Definition

During communication, the air interface uses a carrier frequency, one element of MAset. MIO determines an exact element of MA set. According to the frequency

hopping algorithm in GSM regulation 05.02, the MAI is the TDMA frame number

(RN) or reduced frame number (RFN), frequency hopping sequence number (HSN),

and mobile allocation index offset (MAIO). MAIO is an initial offset of MAI, and it

aims to avoid multiple channels to use the same frequency carrier in the same time.

II. Format

MAIO ranges from 0 to 63.


MAIO is configured by equipment room operators.

IV. Precautions

The different cells using same group of MA must use consistent MAIO.

Using different MAIOs enables different sectors in the same location to use the same

frequency group (MA) without frequency collision.


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4.6 Distance Control Parameters

4.6.1 Call Clearing

I. Definition

Call clearing (CallClearing) means that the maximum allowed distance threshold is

cleared between MS and base station in talk.

II. Format

CallClearing ranges from 0 to 63, with unit of TA.


Configure CallClearing according to actual coverage range of a cell. Proper

configuration of CallClearing helps check whether the handover threshold of the cell

is properly defined, especially for urban cells.

If the call is frequently cleared after CallClearing threshold is defined according tocell radium, probably the handover threshold is improperly configured. This is due to

that the MS cannot hand over to the best server cell after exceeding designed

coverage range.

Define CallClearing according to msRangeMax, namely, CallClearing >

msRangeMax.

In actual network operation, call clearing is unusually performed, because radio linkfails due to over poor coverage before call clearing. Defining CallClearing aims to

restrict the distance between MS and base station and to avoid MSs in allowed

coverage range to interfere other MSs, especially in areas with complex landform.

The cell coverage range is irregular, so island effect might occur. For thisphenomenon, define CallClearing to clear calls in island areas.

4.6.2 TA Handover Threshold (MSRANGEMAX)

I. Defintion

When the distance between MS and base station reaches or exceeds

MSRANGEMAX, distance handover is triggered.

II. Format

MSRANGEMAX ranges from 0 to 63, with unit of TA. The reference is 63.III. Configuration and Influence

MSRANGEMAX must be smaller than CallClearing, and otherwise the handover

function will be actually unavailable. While configuring MSRANGEMAX, you must

adjust the threshold of other types of handover; otherwise ping-pong handover

occurs. one occasion might be as follows:


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The distance between MS and the serving cell exceeds the threshold, but the signals

of target cell are weaker than that of original cell. Consequently the PowerBudget

handover is triggered immediately after distance handover is triggered.

4.6.3 TA Restriction (MS_BS_DIST_USED)

I. Definition

The maximum allowed access distance between base station and MS. If the distancebetween an MS and base station exceeds the maximum allowed access distance, the

MS is forbidden to access cells.

II. Format

The range is 0 to 63, with unit of TA. The reference is 63.


For its configuration, refer to the method for configuring CallClearing. Adjust the

parameter to enable it consistent with the geographic coverage range of the cell. Set aproper threshold to filter pseudo RACH requests to avoid unnecessary assigning

SDCCH.

According to tests, for mountain-mounted base stations, the coverage and

interference is difficult to control. If you define the maximum allowed accessdistance to 63, the RACH misjudgment increases (the system demodulatesinterference to RACH bursts by mistake). Therefore the radio performance and

traffic measurement indexes of the cell are affected.


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4.7 Radio Link Failure Process and Parameters

The radio link failure is detected from uplink and downlink. The MS completes

downlink detection, while the base station completes uplink detection.

4.7.1 Radio Link Failure Counter (RLC or Radio Link Timeout)

I. Definition

The MS originates call resetup or disconnects by force if all the following conditions

are met:

The voice or data quality is too poor to be received. Power control and handover cannot help to improve the quality.

A disconnection by force actually brings about a call drop, so the MS considers it aradio link failure that the voice or data service is actually too poor to be received.

GSM regulations provide solutions to the previous problems as follows:

Set a counter S in the MS. The initial value of S is provided at the beginning of talk,and it is the value of the parameter radio link failure counter. S changes as follows:

S decreases by 1 if the MS fails in decoding a correct SACCH message when theMS should receive the SACCH message. S increases by 2 if the MS succeed in decoding a correct SACCH message.

S cannot exceed the value for radio link failure counter. When S equals to 0, the MS

originates call resetup or disconnects by force.

II. Format

The step from 4 to 64 is 4, with unit of SACCH period as follows:

For TCH, the SACCH period is 480ms. For SDCCH, the SACCH period is 470ms.


The value of the parameter radio link failure counter affects CDR and utilization of

radio resources.

Assume that cell A is a neighbor cell to cell B and the bordering coverage is poor.

When an MS moves from P to Q while in talk,

If the radio link failure counter is over small, call drop occurs before cross-cellhandover. If the radio link failure counter is over great, the network releases relatedresources until radio link expires, though the voice quality is too poor when MS camps

on cell B near P. Therefore, the utilization of radio resources declines.

Proper configuration of radio link failure counter is important, and is related to theactual situations. To configure radio link failure counter, refer to the following rules:

Configure it to between 52 and 64 in areas with over low traffic. Configure it to between 36 and 48 in areas with low traffic and great coverageradium Configure it to between 20 and 32 in areas with heavy traffic.


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IV. Precautions

Configure radioLinkTimeout to smaller than T3109. This contributes to success of

call resetup and avoids the following situation effectively:

Before the MS releases radio resources due to expiration, the network side completes

releasing channels resources and reallocates resources to other MSs. Therefore two

MSs might use the same slot and this causes interferences even call drop.

4.7.2 SACCH Multiframe (RLTO_BS)

I. Definition

Refer to the description of radio link failure counter. A counter is set accordingly to

radio link at base station side for managing radio link failures. The solutions vary due

to different equipment providers, but a general method is as follows:

Set a counter S in the base station. The initial value of S is provided at the beginningof talk, and it is the value of the parameter radio link failure expiration. S changes as

follows:

S decreases by 1 if the MS fails in decoding a correct SACCH message when theMS should receive the SACCH message. S increases by 2 if the MS succeed in decoding a correct SACCH message.

S cannot exceed the value for radio link expiration of base station. When S equals to

0, the MS originates call resetup or disconnects by force, as shown in Figure 1-5.

II. Format

RLT0_BS ranges from 4 to 64.


Proper configuration of radio link expiration of base station affects CDR andutilization of radio resources. It is related to the actual situations. To configure radio

link failure counter, refer to the following rules:

Configure it to between 52 and 64 in areas with over low traffic. Configure it to between 36 and 48 in areas with low traffic and great coverageradium Configure it to between 20 and 32 in areas with heavy traffic. Configure it to a greater value in areas with apparent voids or where call dropoccurs frequently while the MS moves.

IV. Precautions

RLT0_BS and RLC must be consistent.


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4.8 Handover and Related Parameters

4.8.1 PBGT Handover Threshold (HoMargin)

I. Definition

The PBGT handover threshold is power handover tolerance (handover in serving

areas). When the signal level of neighbor cell is hoMargin (dB) higher than that of

the serving cell, handover occurs. Complex radio propagation conditions causefluctuation of signal level. Using handover tolerance avoids frequent handover at

bordering areas. The PBGT handover threshold is similar to HO_MARGIN (GSM

05.08).

II. Format

The PBGT handover threshold ranges from 0 to 127, corresponding to64 dB to +63

dB. The reference value for suburban areas is 68. The reference value for urban areas

is 70 to 72.III. Configuration and Influence

The PBGT handover threshold aims to adjust handover difficulty properly, and to

avoid ping-pong handover. If it is configured over great, the handover is delayed and

handover is less efficient. When it is smaller than 64, the MS hands over from the

serving cell to the neighbor cell with lower level.

4.8.2 Minimum Downlink Power of Handover Candidate Cells (rxLevMinCell)

I. Definition

It is the minimum allowed access level for a cell to be a neighbor cell. When the celllevel measured by MS is greater than the threshold, the BSS list the cell into

candidate cell list for handover judgment.

II. Format

It ranges from110 dBm to47 dBm.


It is helpful in the following two aspects:

It guarantees communication quality.For a common single layer network structure, the value ranges from 90 dBm to 80dBm. It helps allocate traffic between cells averagely.Especially in multi-layer network structure, to maintain MS in a network layer, youcan increase the level of the cell of the network layer (such as 70 dBm), and alsodecrease that in other cells.

IV. Precautions


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You cannot configure rxLevMinCell over great (over65 dBm) or over small (lower

than95 dBm), and otherwise communication quality is affected.

4.8.3 Handover Threshold at Uplink Edge

I. Definition

If the uplink received level keeps being smaller than the handover threshold at uplink

edge for a period, edge handover can be performed.

II. Format

It ranges from 0 to 63, corresponding to110 dBm to47 dBm. The recommended

values are as follows:

Configure it to 25 in urban areas without PBGT handover. Configure it to 20 in single site of suburban areas. Configure it to 20 in urban areas with PBGT handover

III. Configuration and InfluenceWhen PBGT handover is enabled, the corresponding edge handover threshold can be

lowered. When PBGT handover is disabled, and the edge handover threshold is overlow, an artificial cross-cell non-handover occurs. Therefore call drop occurs or intra-

frequency and side interference occur due to cross-cell talk.

4.8.4 Handover Threshold at Downlink Edge

I. Definition

If the downlink received level keeps being smaller than the handover threshold at

downlink edge for a period, edge handover can be performed.II. Format

It ranges from 0 to 63, corresponding to110 dBm to47 dBm. The recommended

values are as follows:

Configure it to 30 in urban areas without PBGT handover. Configure it to 25 in single site of suburban areas. Configure it to 25 in urban areas with PBGT handover


When PBGT handover is enabled, the corresponding edge handover threshold can be

lowered. When PBGT handover is disabled, and the edge handover threshold is overlow, an artificial cross-cell non-handover occurs. Therefore call drop occurs or intra-

frequency and side interference occur due to cross-cell talk.

4.8.5 Downlink Quality Restriction of Emergency Handover

I. Definition


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If the downlink received quality is lower than the threshold of downlink quality

restriction of emergency handover, the quality difference emergency handover

occurs.

II. Format

It ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.The recommended value is 50.


When frequency hopping is enabled, the voice quality is better with the same RQ,

you can configure it to 60 or 70. When emergency handover occurs, the intracellhandover occurs first. If there are no other candidate cells, and the intracell handover

is enabled, the intracell handover occurs.

4.8.6 Uplink Quality Restriction of Emergency Handover

I. Definition

If the uplink received quality is lower than it, quality difference emergency handover

is triggered.

II. Format

It ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.




you can configure it to 60 or 70. When emergency handover occurs, the intracellhandover occurs first. If there are no other candidate cells, and the intracell handover

is enabled, the intracell handover occurs.

4.8.7 Uplink Quality Threshold of Interference Handover

I. Definition

It is the uplink received quality threshold of the serving cell that triggers interference

handover. The interference handover is triggered if all the following conditions are

met:

The uplink received level is higher than the uplink received power threshold ofinterference handover. The uplink received quality is lower than the uplink quality threshold ofinterference handover.

When handover switch is enabled, the interference handover occurs within the cell

by preference.

II. Format


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you can configure it to 60 or 70. When interference handover is triggered, select thecandidates according to the sorted result. If the serving cell ranks first and its

intracell handover is enabled, the MS selects the serving cell; otherwise it selects the

second candidate cell.

4.8.8 Downlink Quality Threshold of Interference Handover

I. Definition

It is the downlink received quality threshold of the serving cell that triggers

interference handover. The interference handover is triggered if all the following

conditions are met:

The downlink received level is higher than the downlink received powerthreshold of interference handover. The downlink received quality is lower than the downlink quality threshold ofinterference handover.


by preference.

II. Format





you can configure it to 60 or 70. When interference handover is triggered, select thecandidates according to the sorted result. If the serving cell ranks first and its

intracell handover is enabled, the MS selects the serving cell; otherwise it selects the

second candidate cell.

IV. Precautions

The interference handover quality must be better than emergency handover quality.

4.8.9 Uplink Received Power Threshold of Interference Handover

I. Definition

If interference handover occurs due to uplink quality, the serving cell must reach the

minimum uplink received power threshold. If this is met, the system judges that

uplink is interfered, so interference handover is triggered.

The interference handover is triggered if all the following conditions are met:


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The uplink received level is higher than the uplink received power threshold ofinterference handover. The uplink received quality is lower than the uplink quality threshold ofinterference handover.


by preference.

II. Format

It ranges from 0 to 63, corresponding to110 dBm to47 dBm.



When interference handover is triggered, select the candidates according to the sortedresult. If the serving cell ranks first and its intracell handover is enabled, the MS

selects the serving cell; otherwise it selects the second candidate cell.

4.8.10 Downlink Received Power Threshold of Interference Handover

I. Definition

If interference handover occurs due to uplink quality, the serving cell must reach the

minimum downlink received power threshold. If this is met, the system judges that

downlink is interfered, so interference handover is triggered.

The interference handover is triggered if all the following conditions are met:

The downlink received level is higher than the downlink received powerthreshold of interference handover. The downlink received quality is lower than the downlink quality threshold ofinterference handover.


by preference.

II. Format

It ranges from 0 to 63, corresponding to110 dBm to47 dBm.



When interference handover is triggered, select the candidates according to the sortedresult. If the serving cell ranks first and its intracell handover is enabled, the MS

selects the serving cell; otherwise it selects the second candidate cell.

4.8.11 Maximum Repeated Times of Physical Messages (NY1)

I. Definition


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In asynchronous handover process of GSM system, when the MS receives handover

messages of the network, it sends handover access messages on the target channel.

After the network receives the message, it does as follows:

1) Calculate related RF features.2) Send physical messages (it the channel messages are encrypted, start encryptionand decryption algorithm) in unit data to MSs.3) Start timer T3105.

If the network does not receive correct layer 2 frames sent by MS until expiration ofT3105, the network will resend the physical message and restart T3105. The

maximum times for resending physical messages is determined by the parameter

maximum repeated times of physical messages (NY1)

II. Format

NY1 ranges from 0 to 254.


III. Configuration and InfluenceWhen the network receives the handover access messages sent by MS, the physical

channel (PCH) needs to be synchronous. If the communication quality on channels is

guaranteed, the MS can receive physical messages correctly and send layer 2 frames

to the network.

If the physical messages are sent multiple times, and the network cannot receive

layer 2 frames sent by MS, the PCH is too poor to communicate normally. Though

link is setup after multiple trials, the communication quality is not guaranteed. This

lowers the utilization of radio resources. Therefore configure NY1 to a smaller value.

IV. Precautions

Configuring NY1 is affected by T3105. If T3105 is configured to a short value, then

the NY1 needs to be increased accordingly.

If a handover trial fails before the original cell receives the HANDOVER FAILURE

message, and the T3105 of the target cell expires for Ny times, the target BTS sendsa CONNECTION FAILURE INDICATION message to the target BSC. Though the

MS might return to the original channel, the traffic measurement counters from

multiple vendors will take statistics of connection failure.

To avoid the previous phenomenon, configure T3105 as follows:

Ny * T3105 > T3124 + delta (delta: the time between expiration of T3124 and

receiving HANDOVER FAILURE message by original BTS)

4.8.12 Multiband Indicator (multiband_reporting)

I. Definition

In a single band GSM network, when the MS send measurement reports of neighborcells to the network, it needs to report the content of the six neighbor cells with

strongest signals.


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In a multiband network, operators wish that MS uses a band by preference in cross-

cell handover. Therefore the MS sends measurement reports according to signalstrength and signal band. The parameter multiband indicator indicates MS to report

content of multiband neighbor cells.

II. Format

The multiband indicator ranges from 0 to 3, with meanings as follows:

0: According to signal strength of neighbor cells, the MS must report six allowedmeasurement reports of neighbor cells with strongest signals and known NCC, withthe neighbor cells in whatever band. 1: The MS must report the allowed measurement report of a neighbor cell withknown NCC and with strongest signals at each band expect for the band used by theserving cell. The MS must also report the neighbor cells of the band used by theserving cell in rest locations. If there are other rest locations, the MS must reportconditions of other neighbor cells in any band. 2: The MS must report the allowed measurement report of two neighbor cellswith known NCC and with strongest signals at each band expect for the band used bythe serving cell. The MS must also report the neighbor cells of the band used by the

serving cell in rest locations. If there are other rest locations, the MS must reportconditions of other neighbor cells in any band. 3: The MS must report the allowed measurement report of three neighbor cellswith known NCC and with strongest signals at each band expect for the band used bythe serving cell. The MS must also report the neighbor cells of the band used by theserving cell in rest locations. If there are other rest locations, the MS must reportconditions of other neighbor cells in any band.


In multiband networks, it is related to traffic of each band. For configuration, refer to

the following rules:

If the traffic of each band is approximately equal, and operators do not select aband intentionally, you can configure the multiband indicator to 0 If the traffic of each band is obviously different, and operators want MS to selecta band by preference, you can configure the multiband indicator to 3. For situations between the previous two, configure multiband indicator to 1 or2.

4.8.13 Permitted Network Color Code (ncc permitted)

I. Definition

During a talk, the MS must report the measured signals of neighbor cells to the base

station, but each report includes only six neighbor cells. Therefore the MS is

configured to report the potential handover target neighbor cells, instead of reportingunselectively and according to signal level.

To enable previous functions, restrict MS to measure the cells with the fixed network

color code (NCC). The NNC allowed by parameters list the NCCs of the cells to bemeasured by MS. The MS compares the measured NCC of neighbor cells and NCCs

set allowed by parameters. If the measured NCC is in the set, the MS reports the

NCC to the base station; otherwise, the MS discard the measurement report.


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II. Format

The parameter ncc permitted is a bit mapping value, consisting of 8 bits. The most

significant bit is bit 7 while the least significant bit is bit 0. Each bit corresponds to

an NCC code 0 to 7 (see GSM regulations 03.03 and 04.08).

If the bit N is 0 (N ranges from 0 to 7), the MS needs not to measure the level of the

cell with NCC of N. Namely, it only measures the signal quality and level of the cells

corresponding to bit number of 1 in NCC and ncc permitted configuration.


Each area is allocated with one or more NCCs. In the parameter ncc permitted of thecell, the local NCC is absolutely and only included. If excluded, abnormal handover

and call drop occur. For normal roaming between areas, the NCC of neighbor areas

must be included in the edge cells of an area.

IV. Precautions

Improper configuration of the parameter causes normal handover and even call drop.The parameter only affects behaviors of MS.


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4.9 Power Control and Related Parameters

4.9.1 Maximum Transmit Power of MS (MSTXPWRMX)

I. Definition

The transmit power of MS in communication is controlled by BTS. According to the

uplink signal strength and quality, power budget result, the BTS controls MS to

increase or decrease its transmit power.

Note:

In any situation, power control is prior to related handover for BSS. Only when theBSS fails to improve uplink signal strength and voice quality to the prescribed level,

it starts handover.

To reduce interference between neighbor cells, the power control of MS is restricted.Namely, the BTS controls MS to transmit power within the threshold.

MSTXPWRMX is the maximum transmit power of MS controlled by BTS.

II. Format

MSTXPWRMX ranges from 0 to 31.

The dBm values corresponding to GSM900 and GSM1800 cells are different:

The 32 maximum transmit power control classes for GSM900 are {39, 39, 39, 37,35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,5} The 32 maximum transmit power control classes for GSM900 are {30, 28, 26, 24,

22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 36, 34, 32}


Configuring MSTXPWRMX helps control interferences between neighbor cells,

because:

If MSTXPWRMX is over great, the interference between neighbor cells increases. If MSTXPWRMX is over small, the voice quality declines and improper handovermight occur.

4.9.2 Received Level Threshold of Downlink Power Increment (LDR)

I. DefinitionWhen the downlink received level of the serving cell is smaller than a threshold, the

network must start power control to increase the transmit power of base station and

to guarantee communication quality of MS.

The received level threshold of downlink power increment defines the downlink

received level threshold. When the downlink level received by MS is smaller than it,

the base station starts power control to increase its transmit power.


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The parameter N1 means that at lease N1 sampling points must be measured before

starting handover algorithm.

The parameter P1 means the level of at least P1 sampling points in N1 samplingpoints is smaller than the threshold prescribed by received level threshold of

downlink power increment.

II. Format


N1 ranges from 1 to 32.

P1 ranges from 1 to 32.


The received level is between60 dBm and80 dBm in a GSM network, so

configure received level threshold of downlink power increment to85 dBm.

N1 is related to propagation quality of radio channels within cell coverage range. To

reduce influence by attenuation, configure N1 to between 3 and 5.

Configure P1 to about 2/3 of N1.

4.9.3 Received Level Threshold of Uplink Power Increment (LUR)

I. Definition

When the uplink received level of the serving cell is smaller than a threshold, the

network must start power control to increase the transmit power of MS and to

guarantee communication quality of MS.

The received level threshold of uplink power increment defines the uplink received

level threshold. When the uplink level received by MS is smaller than it, the basestation starts power control to increase MS transmit power.

The parameter N1 means that at lease N1 sampling points must be measured before

starting handover algorithm.

The parameter P1 means the level of at least P1 sampling points in N1 sampling

points is smaller than the threshold prescribed by received level threshold of uplink

power increment.

II. Format


N1 ranges from 1 to 32.P1 ranges from 1 to 32.


The received level is between60 dBm and80 dBm in a GSM network, so

configure received level threshold of uplink power increment to85 dBm.


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N1 is related to propagation quality of radio channels within cell coverage range. To

reduce influence by attenuation, configure N1 to between 3 and 5.

Configure P1 to about 2/3 of N1.

4.9.4 Received Qu

Documents

Part 4 GSM Radio Parameters