Chapter 7 of«GSM RNP&RNO»-GSM Parameter Configuration and Adjustment-20060624-A-1.0

Chapter 7 GSM Parameter Configuration and Adjustment Internal Open

Table of Contents

Chapter 7 GSM Parameter Configuration and Adjustment.........................................................1

7.1 Network and Cell ID............................................................................................................1

7.1.1 Cell Global ID...........................................................................................................1

7.1.2 Base Station Identity Code.......................................................................................3

7.2 Paging and Access Control Parameters.............................................................................6

7.2.1 Number of Access Grant Reserved Blocks (BS_AG_BLK_RES or AG)...................6

7.2.2 Frame Number Coding Between Identical Paging....................................................7

7.2.3 Common Control Channel Configuration (CCCH-CONF).........................................8

7.2.4 Extended Transmission Slots (TX_INTEGER).........................................................9

7.2.5 Minimum Access Level of RACH............................................................................11

7.2.6 Random Access Error Threshold............................................................................12

7.2.7 Access Control Class (ACC)...................................................................................13

7.2.8 Maximum Retransmission Times (RET).................................................................14

7.2.9 Control Class of MS Maximum Transmit Power (MS-TXPWR-MAX-CCH).............15

7.2.10 Power Offset (POWEROFFSET)..........................................................................16

7.2.11 IMSI Attach/Detach Allowed.................................................................................16

7.2.12 Direct Retry (DR)..................................................................................................17

7.3 Serial Parameters of Cell Selection and Reselection........................................................18

7.3.1 cell_bar_access......................................................................................................18

7.3.2 cell_bar_qualify.......................................................................................................19

7.3.3 Minimum Received Level Allowing MS to Access (RXLEV_ACCESS_MIN)..........21

7.3.4 Additional Reselection Parameter Indicator............................................................21

7.3.5 Cell Reselection Parameter Indicator.....................................................................22

7.3.6 Cell Reselection Offset, Temporary Offset, and Penalty Time................................22

7.3.7 Cell Reselection Hysteresis (CRH).........................................................................25

7.4 Parameters Affecting Network Functions..........................................................................26

7.4.1 Newly Established Cause Indicator (NECI)............................................................26

7.4.2 Power Control Indicator (PWRC)............................................................................26

7.4.3 Discontinuous Transmit of Uplink...........................................................................27

7.4.4 Discontinuous Transmit of Downlink.......................................................................28

7.4.5 Call Resetup Allowed..............................................................................................28

7.4.6 Emergency Call Allowed.........................................................................................29

7.4.7 Early Classmark Sending Control...........................................................................30

7.5 Frequency Hopping Parameters.......................................................................................31

7.5.1 Frequency Hopping Sequence Number..................................................................31

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7.5.2 Mobile Allocation.....................................................................................................32

7.5.3 Mobile Allocation Index Offset................................................................................32

7.6 Distance Control Parameters............................................................................................33

7.6.1 Call Clearing...........................................................................................................33

7.6.2 TA Handover Threshold (MSRANGEMAX)............................................................34

7.6.3 TA Restriction (MS_BS_DIST_USED)....................................................................34

7.7 Radio Link Failure Process and Parameters.....................................................................35

7.7.1 Radio Link Failure Counter (RLC or Radio Link Timeout).......................................35

7.7.2 SACCH Multiframe (RLTO_BS)..............................................................................37

7.8 Handover and Related Parameters...................................................................................38

7.8.1 PBGT Handover Threshold (HoMargin)..................................................................38

7.8.2 Minimum Downlink Power of Handover Candidate Cells (rxLevMinCell)................39

7.8.3 Handover Threshold at Uplink Edge.......................................................................39

7.8.4 Handover Threshold at Downlink Edge..................................................................40

7.8.5 Downlink Quality Restriction of Emergency Handover............................................40

7.8.6 Uplink Quality Restriction of Emergency Handover................................................41

7.8.7 Uplink Quality Threshold of Interference Handover................................................41

7.8.8 Downlink Quality Threshold of Interference Handover............................................42

7.8.9 Uplink Received Power Threshold of Interference Handover.................................43

7.8.10 Downlink Received Power Threshold of Interference Handover...........................43

7.8.11 Maximum Repeated Times of Physical Messages (NY1).....................................44

7.8.12 Multiband Indicator (multiband_reporting)............................................................45

7.8.13 Permitted Network Color Code (ncc permitted)....................................................46

7.9 Power Control and Related Parameters............................................................................47

7.9.1 Maximum Transmit Power of MS (MSTXPWRMX).................................................47

7.9.2 Received Level Threshold of Downlink Power Increment (LDR)............................48

7.9.3 Received Level Threshold of Uplink Power Increment (LUR).................................49

7.9.4 Received Quality Threshold of Downlink Power Increment (LDR)..........................50

7.9.5 Received Quality Threshold of Uplink Power Increment (LUR)..............................50

7.9.6 Received Level Threshold of Downlink Power Decrement (UDR)..........................51

7.9.7 Received Level Threshold of Uplink Power Decrement (UUR)...............................52

7.9.8 Received Quality Threshold of Downlink Power Decrement (UDR)........................53

7.9.9 Received Quality Threshold of Uplink Power Decrement (UUR)............................54

7.9.10 Power Control Interval (INT).................................................................................55

7.9.11 Power Increment Step (INC).................................................................................55

7.9.12 Power Decrement Step (RED)..............................................................................55

7.10 Systematic Important Timers...........................................................................................56

7.10.1 T3101...................................................................................................................56

7.10.2 T3103...................................................................................................................57

7.10.3 T3105...................................................................................................................57

7.10.4 T3107...................................................................................................................58



7.10.5 T3109...................................................................................................................59

7.10.6 T3111...................................................................................................................59

7.10.7 Parameter T3212..................................................................................................60

7.10.8 T3122...................................................................................................................61

7.10.9 T3124...................................................................................................................62

7.10.10 T11..................................................................................................................... 63

7.10.11 T200...................................................................................................................63

7.10.12 N200...................................................................................................................65



Chapter 7 GSM Parameter Configuration and

Adjustment

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

predict coverage according to traffic prediction and local radio propagation

environment. This guides project design of the system and parameter configuration of

radio network.

The project design includes the following aspects:

Network topology design

Selecting the location of base station

Frequency planning

Cell parameter configuration

The RF planning determines the coverage range of a cell, and the serving range of

the 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.

7.1 Network and Cell ID

7.1.1 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 country

Each location area

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Each base station

Each cell

Numbering the previous items aims as follows:

An MS can identify the serving network so that the MS can select a network in

any environment.

The network can obtain the precise location of the MS so that the network can

process various service requests involving the MS.

The MS can report information about neighbor cells to the network during calling

to avoid call drop.

The cell global identity (CGI) is a major network identity parameter. CGI consists of

location area identity (LAI) and cell identity (CI). LAI includes mobile country code

(MCC), mobile network code (MNC), and location area code (LAC), shown in Figure

7-1.

Figure 7-1 CGI composition

The system transmits CGI information through system information (SI) transmitted by

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 65535

CI ranges from 0 to 65535.

III. Configuration and Influence

As a globally unique mobile identity, the MCC is uniformly distributed and managed

by 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 LACs

must not exist in the state network.

Equivalent CIs must not exist in the same location area.

7.1.2 Base Station Identity Code

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 control

channel (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 frequency to

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, shown in Figure 7-2.



Figure 7-2 Schematic drawing of BSIC selection

In Figure 7-2, the carriers of the cell A, B, C, D, E, and F use the same absolute

channel number, and other cells uses BCCH carriers of different channel number.

Usually, the cell A, B, C, D, E, and F use different BSIC. When the BSIC resources

are inadequate, the cells near use different BSIC.

Take cell E for example. If the BSIC resources are limited, you use different BSICs

between cell D and E, B and E, F and E for preference. You might use the same

BSIC between cell A and E, C and E.

The BSIC consists of network color code (NCC) and base station color code (BCC),

shown in Figure 7-3.

Figure 7-3 BSIC composition

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

of BSIC is as follows:

The BSIC involves in decoding process of random access channel (RACH) to

prevent base stations from connecting to the RACH sent to the neighbor cells by

the MS by error.

After the MS receives SCH messages, it judges that it has been synchronous to

the cell. Decoding information on the downlink common signaling channel

correctly requires training sequence code (TSC) used on common signaling

channel.

GSM regulations describe TSC in eight fixed formats, and the sequence number

of them is 0–7. The cell BCC determines the TSC used by the common signaling



channel of a cell. Therefore the BSIC helps inform the MS of the TSC used by

the common signaling channel of the serving cell.

In a call, the MS must measure the level of BCCH carrier of neighbor cells and

report it 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 uplink

measurement reports. When the neighbor cells of a cell include two or more cells

with the same BCCH carrier, the base station can distinguish the cells by BSIC

to avoid incorrect handover.

In a call, the MS must measure signals of neighbor cells, and sends

measurement reports to the network. The measurement report can contain

information about six neighbor 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 previously mentioned. Operators control the MS to report the

neighbor cell information permitted 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 use

different 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 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 the neighbor

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.



7.2 Paging and Access Control Parameters

7.2.1 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. Format

The 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 following principles.

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 AG

accordingly. By default the immediate assignment messages are superior to paging



messages to be sent in the network, so you need not reserve a channel for immediate

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

7.2.2 Frame Number Coding Between Identical Paging

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

I. Definition

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). Each

paging 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 paging

subchannels. 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 used

in 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.


According 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 paging

channels of the cell are (see the calculation of paging groups in GSM regulation

05.02). 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 of

the 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 is running,

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.

7.2.3 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 more

physical 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 7-1.

Table 7-1 CCCH configuration coding

CCCH_CONF MeaningNumber of CCCH message

blocks in a BCCH multiframe

000

One physical channel for

used for CCCH, not shared

with SDCCH

9

001 One physical channel for 3



used for CCCH, shared with

SDCCH

010

Two physical channels for


with SDCCH

18

100

Three physical channels for


with SDCCH

27

110

Four physical channels for


with SDCCH

36


According to Table 7-1, when the CCCH and SDCCH share one physical channel, the

CCCH has the minimum 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 has

one 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 physical

channel for paging. Otherwise, the method that CCCH and SDCCH do not share one

physical channel is used.

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. In

addition, you must consider the influence on the access grant reserved blocks.



7.2.4 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

T

It is the number of slots between two sending when the MS keeps sending

multiple channel request messages.

S

It is related to channel combination, and is an intermediate variable of access

algorithm. 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 7-2.

Table 7-2 Values of S

T

S in different CCCH combination methods

The CCCH and SDCCH

does not share a physical

channel

The 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 86

7, 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

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) between

originating immediate assignment process by MS and sending the first channel

request messages is random. Its range is {0, 1, …, MAX (T, 8) - 1}. When the

MS originates the immediate 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 a

channel request message and the next is from {S, S + 1, …, S + T - 1} according

to even 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 RACH

conflicting 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 T

freely 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 the

network); 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.

7.2.5 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 to –110 dBm

to –47 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 access

error threshold, determines whether the random access burst is valid. To configure

the 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 of

RACH affects call drop rate and access range (coverage), so you must pay attention

to the influence on access of MS.

7.2.6 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

rate is, 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.

90–100 33



101–120 34

121–140 35

141–160 36

161–175 37

176–195 38

196–221 39

222–243 40

244–250 41

0–89 or 251–255 38

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

RACH determine the validity of random access burst.

7.2.7 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

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

in accessing. 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 0–9: 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 0–9 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 class

Value range: a check option, including class 0 disabled, …, class 9 disabled.

Recommended value: all 0.

Special access control class

Value 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, a

common access class is configured to 1000000000; common users excluding class 0

users can access the network.


C0–C15 (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 testing

in some cells, configure C0–C15 (excluding C10) to 1. In this way, different users

are prevented from accessing the network, so the installing and maintenance is

less influenced.

During busy hours of cells with high traffic, congestion occurs, RACH conflicting

time increase, AGCH traffic overloads, and Abis interface traffic overloads. When

you configure class of some users to 1, you can reduce the traffic of the cell.

7.2.8 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

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 listed in

Table 7-3.

Table 7-3 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 with

high 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 7

to 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.



7.2.9 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 and reselection.

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

of MS maximum transmit power)

P: Maximum transmit power level of MS

II. Format

The range of MS-TXPWR-MAX-CCH is 0–31. 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 power

corresponding to 0–31 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 power

corresponding to 0–31 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, see protocol 0508.

The smaller it is, the greater the output power of MS is. The MS near the base station

interferes 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.



7.2.10 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 0–3 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.

7.2.11 IMSI Attach/Detach Allowed

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 off or 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 of

itself 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/detach

process 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 avoid

abnormalities 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 with

No 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.

7.2.12 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 a

function 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.

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 cell

with 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.

7.3 Serial Parameters of Cell Selection and Reselection

7.3.1 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 is

barred 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 access the network from all the cells, so cell_bar_access is configured to

0. In special situations, the operators want some cell for handover service only, so

cell_bar_access is configured to 1 (cell_bar_qualify is 0), as shown in Figure 7-4.

Figure 7-4 Schematic drawing of cell access barred



The area A in Figure 7-4 are busy areas (metropolitan commercial areas). The

microcell coverage method is used to improve the access performance in the area

with limited frequency resources. The double-layer network is used to reduce cross-

cell handover when the MS moves at a high speed, so wide-coverage base station G

(capacity can be small) is constructed to cover area A.

The MS usually works in microcells (you can configure the priority of cells and

reselection parameters to enable this). When the MS is calling while moving fast, the

network force MS to hand over to the base 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 MS will 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 the

cell_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.

7.3.2 cell_bar_qualify

I. Definition

The cell_bar_qualify determines the priority of cells, namely, it enables MS to select

some 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 7-1.

Table 7-1 Cell priorities

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 equipment room 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_qualify

only affects cell selection, without any influence on cell reselection. You must

optimize the network by combining cell_bar_qualify and C2.

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

present, the MS will select cells with low priority. Therefore when the level of the

cell 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.

7.3.3 Minimum Received Level Allowing MS to Access (RXLEV_ACCESS_MIN)

I. Definition

To avoid bad communication quality, call drop, and a waste of network radio

resources 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 from –110 dBm to –47 dBm.


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 the

effective 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 to –90 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.

7.3.4 Additional Reselection Parameter Indicator

I. 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, and equipment

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

bytes of SI4 (SI4RestOctets) are present, the MS must abstract and calculate

parameters related to C2 and related cell reselection parameter PI.



When ADDITIONAL RESELECT is configured to Y, the meaning is that the MS

must abstract and calculate parameters related to C2 and related cell reselection

parameter 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.

7.3.5 Cell Reselection Parameter Indicator

I. Definition

The cell reselection parameter indicator (CELL_RESELECT_PARAM_IND) is used in

informing MS of whether C2 is a cell reselection parameter and whether C2 is

present.

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 cell

broadcast, 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.

7.3.6 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 6 cells.



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 the

calculation as follows:

2) 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.

3) 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 cells

with 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 = C1 – CRO.

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 receiving

values 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

4) The cell reselection offset (CRO) is in decimal, with unit of dB. It ranges from 0 to

63, which means 0 to 126 dB (2 dB as the step). The recommended value is 0.

5) 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.

6) 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

for changing 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:

7) 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

from the 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 value according to the exclusive level of the cell by MS. The greater the

exclusion is, the greater the CRO is.

8) For cells with low traffic and equipment of low utilization, change the parameters

to enable MS to camp on the cell (the cell is prior). In this situation, configure

CRO to 0–20 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 helps

avoid over frequent cell reselection, the recommended value of PT is 20s or 40s.

9) 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.

7.3.7 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 that of

the serving cell.

The difference between the signal levels of the neighbor cell and the serving cell

must 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 of

neighbor 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 flow

overloads or location updating of cross location area is frequent, the cell reselection

hysteresis is increased as recommended. You must avoid abnormal coverage due to

over large location area.

IV. Precautions

Do not configure CRH to 0 dB.



7.4 Parameters Affecting Network Functions

7.4.1 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 must

confirm whether the system support half-speed TCH.

7.4.2 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 (frequency

hopping 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 each

slot on BCCH frequency is prohibited to change. The downlink power control

does not involve carrier slots for BCCH which includes the frequency hopping.

For previous causes, when the MS measures the average downlink channel level with

common methods, the measurement result is inaccurate for power control because

the 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 received

level 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.


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.

7.4.3 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.

7.4.4 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.


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.



7.4.5 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 takes

longer 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.

7.4.6 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 allowed

for 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.




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

in China. The Chinese emergency call cannot function as prescribed in GSM

regulations. 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.

7.4.7 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 a

GSM network, the MS reports Classmark1 or Classmark2 information immediately

after ESTIND<CM SERV REQ> (corresponding to L2-SABM at Um interface) is

allocated. 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, it

must 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.

7.5 Frequency Hopping Parameters

7.5.1 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, the MAI 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 continuous

frequency collision during frequency hopping by using different HSNs.

II. Format

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

0: cyclic frequency hopping

1–63: pseudo frequency hopping


You can choose any HSN in cells using frequency hopping, but you must ensure that

the 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.

7.5.2 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:

For GSM900 networks: 1–124 and 975–1023.

For GSM1800 networks: 512–885


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.



7.5.3 Mobile Allocation Index Offset

I. Definition

During communication, the air interface uses a carrier frequency, one element of MA

set. 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.

7.6 Distance Control Parameters

7.6.1 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 to cell

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 link

fails 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 this

phenomenon, define CallClearing to clear calls in island areas.

7.6.2 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.


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:

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.



7.6.3 TA Restriction (MS_BS_DIST_USED)

I. Definition

The maximum allowed access distance between base station and MS. If the distance

between 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

a proper 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 access distance

to 63, the RACH misjudgment increases (the system demodulates interference to

RACH bursts by mistake). Therefore the radio performance and traffic measurement

indexes of the cell are affected.

7.7 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.

7.7.1 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 a

radio 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

the MS 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, as shown in Figure 7-1.

Figure 7-1 Counter S process

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, as shown in Figure 7-2.

Figure 7-2 Application of radio link failure counter

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-cell

handover.

If the radio link failure counter is over great, the network releases related

resources 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 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 coverage

radium

Configure it to between 20 and 32 in areas with heavy traffic.

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.



7.7.2 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 beginning

of 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

the MS 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 7-1.

II. Format

RLT0_BS ranges from 4 to 64.


Proper configuration of radio link expiration of base station affects CDR and utilization

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 coverage

radium

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 drop

occurs frequently while the MS moves.

IV. Precautions

RLT0_BS and RLC must be consistent.



7.8 Handover and Related Parameters

7.8.1 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 cause

fluctuation 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 to –64 dB to +63

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

areas is 70 to 72.


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.

7.8.2 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 cell

level measured by MS is greater than the threshold, the BSS list the cell into

candidate cell list for handover judgment.

II. Format

It ranges from –110 dBm to –47 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

–80 dBm.

It helps allocate traffic between cells averagely.

Especially in multi-layer network structure, to maintain MS in a network layer,

you can increase the level of the cell of the network layer (such as –70 dBm),

and also decrease that in other cells.

IV. Precautions

You cannot configure rxLevMinCell over great (over –65 dBm) or over small (lower

than –95 dBm), and otherwise communication quality is affected.

7.8.3 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 to –110 dBm to –47 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


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

be lowered. When PBGT handover is disabled, and the edge handover threshold is

over low, an artificial cross-cell non-handover occurs. Therefore call drop occurs or

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

7.8.4 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 to –110 dBm to –47 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

over low, an artificial cross-cell non-handover occurs. Therefore call drop occurs or

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

7.8.5 Downlink Quality Restriction of Emergency Handover

I. Definition

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.



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 intracell

handover occurs first. If there are no other candidate cells, and the intracell handover

is enabled, the intracell handover occurs.



7.8.6 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





can configure it to 60 or 70. When emergency handover occurs, the intracell

handover occurs first. If there are no other candidate cells, and the intracell handover

is enabled, the intracell handover occurs.

7.8.7 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 of

interference handover.

The uplink received quality is lower than the uplink quality threshold of


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

preference.

II. Format







can configure it to 60 or 70. When interference handover is triggered, select the

candidates 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.

7.8.8 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 power threshold

of interference handover.

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



preference.

II. Format





can configure it to 60 or 70. When interference handover is triggered, select the

candidates 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.



7.8.9 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:

The uplink received level is higher than the uplink received power threshold of


The uplink received quality is lower than the uplink quality threshold of



preference.

II. Format

It ranges from 0 to 63, corresponding to –110 dBm to –47 dBm.



When interference handover is triggered, select the candidates 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.

7.8.10 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 power threshold

of interference handover.

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





preference.

II. Format

It ranges from 0 to 63, corresponding to –110 dBm to –47 dBm.



When interference handover is triggered, select the candidates 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.

7.8.11 Maximum Repeated Times of Physical Messages (NY1)

I. Definition

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:

10) Calculate related RF features.

11) Send physical messages (it the channel messages are encrypted, start

encryption and decryption algorithm) in unit data to MSs.

12) Start timer T3105.

If the network does not receive correct layer 2 frames sent by MS until expiration of

T3105, 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.



When 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 sends

a 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)

7.8.12 Multiband Indicator (multiband_reporting)

I. Definition

In a single band GSM network, when the MS send measurement reports of neighbor

cells to the network, it needs to report the content of the six neighbor cells with

strongest signals.

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 signal

strength 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 allowed

measurement reports of neighbor cells with strongest signals and known NCC,

with the neighbor cells in whatever band.



1: The MS must report the allowed measurement report of a neighbor cell with

known NCC and with strongest signals at each band expect for the band used by

the 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

report conditions of other neighbor cells in any band.

2: The MS must report the allowed measurement report of two neighbor cells

with known NCC and with strongest signals at each band expect for the band

used by the 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 report conditions of other neighbor cells in any band.

3: The MS must report the allowed measurement report of three neighbor cells

with known NCC and with strongest signals at each band expect for the band

used by the 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 report conditions 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 a

band intentionally, you can configure the multiband indicator to 0

If the traffic of each band is obviously different, and operators want MS to select

a band by preference, you can configure the multiband indicator to 3.

For situations between the previous two, configure multiband indicator to 1 or 2.

7.8.13 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 reporting

unselectively 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 be

measured 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.



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 the

cell, 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.

7.9 Power Control and Related Parameters

7.9.1 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 the

BSS 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 handover

might occur.

7.9.2 Received Level Threshold of Downlink Power Increment (LDR)

I. Definition

When 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.

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 downlink

power increment.

II. Format


N1 ranges from 1 to 32.

P1 ranges from 1 to 32.


The received level is between –60 dBm and –80 dBm in a GSM network, so configure

received level threshold of downlink power increment to –85 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.

7.9.3 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 base

station starts power control to increase MS transmit power.




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

power increment.

II. Format








received level threshold of uplink power increment to –85 dBm.




7.9.4 Received Quality Threshold of Downlink Power Increment (LDR)

I. Definition

When the downlink received quality 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.

The received quality threshold of downlink power increment defines the downlink

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

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



The parameter P3 means the quality of at least P3 sampling points in N3 sampling

points is smaller than the threshold prescribed by received quality threshold of

downlink power increment.

II. Format

It ranges from 0 to 7, the voice quality grade.




The received quality is 0 to 2 of quality grade in a GSM network, so configure

received quality threshold of downlink power increment to –85 dBm.






7.9.5 Received Quality Threshold of Uplink Power Increment (LUR)

I. Definition

When the uplink received quality 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.

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

quality threshold. When the uplink quality received by MS is smaller than it, the base

station starts power control to increase transmit power of MS.




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

power increment.

II. Format






received quality threshold of uplink power increment to 3.






7.9.6 Received Level Threshold of Downlink Power Decrement (UDR)

I. Definition

When the downlink received level of the serving cell is greater than a threshold, the

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

to decrease interference to radio channels.

The received level threshold of downlink power decrement defines the downlink

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

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




points is greater than the threshold prescribed by received level threshold of downlink

power decrement.

II. Format






received level threshold of downlink power decrement to –85 dBm.




7.9.7 Received Level Threshold of Uplink Power Decrement (UUR)

I. Definition

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

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

decrease interference to radio channels.



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

level threshold. When the uplink level received by MS is greater than it, the base

station starts power control to decrease transmit power of MS.




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

power decrement.

II. Format






received level threshold of uplink power decrement to –60 dBm.




7.9.8 Received Quality Threshold of Downlink Power Decrement (UDR)

I. Definition

When the downlink received quality of the serving cell is greater than a threshold, the

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

to decrease space interference.

The received quality threshold of downlink power decrement defines the downlink

received quality threshold. When the downlink quality received by MS is greater than

it, the base station starts power control to decrease transmit power of MS.






points is greater than the threshold prescribed by received quality threshold of

downlink power decrement.

II. Format






received quality threshold of downlink power decrement to 0.




7.9.9 Received Quality Threshold of Uplink Power Decrement (UUR)

I. Definition

When the uplink received quality of the serving cell is greater than a threshold, the

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

decrease space interference.

The received quality threshold of uplink power decrement defines the uplink received

quality threshold. When the uplink quality received by MS is greater than it, the base

station starts power control to decrease transmit power of MS.




points is greater than the threshold prescribed by received quality threshold of uplink

power decrement.

II. Format








received quality threshold of uplink power decrement to 0.




7.9.10 Power Control Interval (INT)

I. Definition

It takes a period from beginning of power control to detection of effect of power

control. Therefore an interval must exist between continuous two power controls;

otherwise the system becomes unstable and even call drop occurs.

The parameter power control interval (INT) configures the minimum interval between

two continuous times of power control.

II. Format

It ranges from 0 to 31s.


According to frame structure of GSM network, configure INT to about 3s.

IV. Precautions

INT cannot be smaller than 1s, and otherwise the system becomes unstable.

7.9.11 Power Increment Step (INC)

I. Definition

The INC indicates the power increment of MS or base station in power control.



II. Format

The range of INC is 2 dB, 4 dB, or 6 dB.


The recommended value is 4 dB.

7.9.12 Power Decrement Step (RED)

I. Definition

The RED indicates the power decrement of MS or base station in power control.

II. Format

The range of RED is 2 dB or 4 dB.


The recommended value of RED is 2 dB.

7.10 Systematic Important Timers

7.10.1 T3101

I. Definition

T3101 is the BSC timer controlling time of immediate assignment process.

II. Format

T3101 ranges from 0 to 255s. The recommended value is 3s.


In an immediate assignment process, the BSC requires BTS to provide SDCCH to set

up signaling channel. When the BSC sends a channel activation message, T3101

starts timing. When the BSC receives the setup instruction sent by BTS, T3101 stops

timing. When T3101 expires, the system releases corresponding SDCCH resources.



Proper configuration of T3101 reduces congestion due to dual assignment SDCCH

effectively.

The greater the T3101 is, the longer the inefficient time for using signaling resources

is. For example, if the extended transmission delay is improperly configured (usually

the sum of T and S is over small), the MS fails in responding to the network side, so

the MS resends the random access request message.

Therefore, the network side will assign SDCCH (the network cannot distinguish the

repeated sending access request from the first send). For better use of signaling

resources, especially in activating queue function, you must configure T3101 to a

smaller value. The minimum interval for sending channel activation message and

receiving setup indicator is 600ms. For non-overload BSS, the maximum interval is

1.8s.

7.10.2 T3103

I. Definition

In inter- and intra-BSS handover, the BSC determines the time for keeping TCH both

in handover-originated cell and target cell. When the time receives handover

completion (intra-BSC) or clearing (inter-BSC) message, T3103 stops.

II. Format

T3103 ranges from 0 to 255s. The recommended value is 5s.


The following paragraph is an example of inter-BSS handover.

When T3103 receives the handover command, it is reset and starts timing. When it

receives clearing command, it is reset. This means that T3103 reserves two channels

when it is timing, one channel for source BSC, and one channel for target BSC. If it is

over long, two channels are occupied for a long time and resources might be wasted.

According to the tests, if the NSS timer is properly configured, the handover process

occurs within 5s. Therefore, the recommended value is 5s.



7.10.3 T3105

I. Definition

See the protocol 0408 and 0858. When sending physical information, the network

starts T3105. If the timer expires before receiving any correct frames from MS, the

network resends physical information and restarts the T3105. The maximum repeated

times is Ny1.

II. Format

T3105 ranges from 0 to 255, with unit of 10ms.


The physical information is sent on FACCH. The time for sending four TDMA in a time

on FACCH is about 18ms. If the next physical information is just sent 18ms after the

first one, probably the first physical information is still being sent. The minimum time

for sending physical information continuously and most quickly is 20ms.

IV. Precautions

T3105 is related to the timer NY1. If T3105 is small, configure NY1 to a greater value.

If a handover trial fails and the T3105 of the target cell expires for Ny times before the

original cell receives the HANDOVER FAILURE message, the target BTS sends the

CONNECTION FAILURE INDICATION message to the target BSC.

The counter of target BSC is renewed though MS might return to the original channel.

To avoid this, the T3105 must meet the following foulard:

Ny * T3105 > T3124 + delta

Wherein, delta is the time between expiration of T3124 and receiving HANDOVER

FAILURE message by original BSC.

7.10.4 T3107

I. Definition

T3107 is a BSC timer, restricting the time for executing TCH assignment instruction. It

caters for TCH assignment of intracell handover and channel assignment of calling.



II. Format

T3107 ranges form 0s to 255s. The recommended values are as follows:

10s when channel resources are enough.

5s when channel resources are limited.


T3107 starts after the BSC sends the ASS_CMD message to BTS. It stops after the

BSC receives the ASS_CMP or ASS_FAIL message sent by BTS. If T3107 expires,

the system judges that the MS disconnects to the network, so the occupied resource

is released to other MSs. According to the measured statistics result of network, the

channel assignment is complete within 2s. If the BSC does not receive ASS_CMP

message after 2s, the assignment command fails.

If the radio link is bad and some information must be resent, the process might be

prolonged to 5s. To avoid premature disconnection, configure T3107 to 10s. In this

way, the MS can reuse the original channel when handover or assignment fails.

Therefore the call drop due to intracell handover decreases or the system service

quality of re-assignment is improved (if the system supports re-assignment function).

However, the channel resource might be wasted for several seconds. When the

network capacity is limited, you must save the resource as possible.

7.10.5 T3109

I. Definition

The BSC restricts the releasing resource of SACCH by T3109.

II. Format

T3109 ranges from 3s to 34s. The recommended T3109 is as follows:

T3109 = a + RdioLinktimeOut x 0.480s, a = 1s or 2s.


T3109 measures the time for channel releasing indicator after sending MS clearing

instructions. It starts after the BSC sends DEACT_SACCH message to BTS. It stops

after the BSC receives the REL_INC message sent by BTS. When T3109 expires, the

BSC sends the CLEAR REQUEST message to MSC.



IV. Precautions

The sum of T3111 and T3109 must be greater than RadioLinkTimeOut. If T3109 is

over small, the corresponding radio resources are re-allocated before

RadioLinkTimeOut is due (radio link is not released).

7.10.6 T3111

I. Definition

T3111 is a connection release delay timer, used in deactivation of delayed channel

after disconnection of major signaling link. T3111 aims to spare some time for

repeated disconnections. When BSC receives the REL_IND message sent by BTS,

T3111 starts. For time protection, T3111 stops until expiration and the BSC sends the

RF_CHAN_REL message to BTS.

II. Format

T3111 ranges from 0s to 5s.

The recommended value is 2s.


After the disconnection of major signaling link, T3111 delays the release of channels.

It allows the base station to retransmit the instruction for releasing radio channels to

MS within delayed time. After the base station sends a release request massage, the

radio resources remain for T3111 time.

If the system capacity is small, configure T3111 as short as possible. The minimum

value of T3111 is 2s, over five multiples of the time for resending MS the instruction

for releasing radio channel resources. A greater T3111 might be of no help, but

affects congestion of SDCCH and TCH easily.

7.10.7 Parameter T3212

I. Definition

In a GSM network, the causes to location updating are as follows:

The MS attach.

The MS detects that its location area changes.



The network forces MS to update location periodically.

The network controls how frequent the MS updates location, and the period for

location updating is determined by the parameter T3212.

II. Format

T3212 ranges from 0 to 255, with unit of 6 minutes (1/10 hour). If T3212 = 1, it means

that T3212 is 6 minutes. If T3212 = 255, it means that T3212 is 25 hours and 30

minutes. If T3212 = 0, it means that MS is not required for periodical location updating

in the cell. The recommended T3212 is 240.


As an important means, the periodical location updating enables network to connect

to MSs closely. Therefore, the short the period is, the overall service performance of

the network is. Anyhow frequent periodical location updating brings two negative

aspects:

The signaling flow of the network increases sharply and the utilization of radio

resource declines. When the period is over long, the processing capability of

network elements (NE, including MSC, BSC, and BTS) is directly affected.

The MS must transmit signals with greater power, so the average standby time is

shortened sharply.

Therefore, configure T3212 according to resource utilization in various aspects of

network.

T3212 is configured by equipment room operators. Its value depends on the flow and

processing capability of each NE. Configure T3212 as follows:

Configure T3212 to a greater value (such as 16 hours, 20 hours, or even 25

hours) in areas with heavy traffic and signaling flow.

Configure T3212 to a smaller value (such as 3 hours or 6 hours) in areas with

low traffic and signaling flow.

Configure T3212 to 0 in areas with traffic overrunning the system capacity.

To configure T3212 properly, you must permanently measure the processing

capability and flow of each UE in the running network, such as:

The processing capability of MSC and BSC

A interface, Abis interface, and Um interface

The capability of HLR and VLR

If any of the previously listed NEs is overloaded, you can consider increasing T3212.



IV. Precautions

T3212 cannot be over small. Otherwise, the signaling flow at each interface increases

sharply and the MS (especially handset) consumes increasing power. If the T3212 is

smaller than 30 minutes (excluding 0), the network will be fiercely impacted.

Configuring T3212 of different cells in the same location area to the same value is

recommended. In addition, the T3212 must be consistent with related parameters of

switching side (smaller than the implicit detach timer at switching side).

If the T3212 of different cells in the same location area is the same, in the cell

reselection, the MS continues to time according the T3212 of the original cell. If the

T3212 of the original and target cell in the same location area is different, the MS

uses the T3212 of the original cell modulo that of the serving cell.

According to the actual tests of MS in the network, if the T3212 in the same location

area is different, after the MS performs modulo algorithm based on behaviors of some

users, the MS might power on normally. However, the MS fails in originating location

updating, so the network identifies it as implicit detach. Now the MS powers on

normally, but a user has powered off prompt appears when it is called.

7.10.8 T3122

I. Definition

T3122 defines the period that the MS must wait for before the second trial calling if

the first trial calling fails. It aims to avoid congestion of SDCCH due to repeated trial

calling by MS and to relieve system load.

II. Format

T3122 ranges from 0s to 255s. The recommended value is 10s.


The value of T3122 is included in the immediate assignment reject message. After the

MS receives the immediate assignment reject message (no channels for signaling, A

interface failure, overload of central processing unit, namely, CPU), it can send new

trial calling request after T3122. T3122 aims to relieve radio signaling and voice

channel resources.

T3122 also help avoid systematic overload. When the CPU is overloaded, the system

multiplies T3122 by a factor (determined by processorLoadSupconf) to increase



T3122 through overload control. In peak load time, you can manage network access

by increasing T3122. Namely, you can increase the interval between two continuous

trial callings to relieve network load.

7.10.9 T3124

I. Definition

T3124 is used in occupation process in asynchronous handover. It is the time for MS

to receive the physical information send by network side.

II. Format

Configure it to 675ms when the channel type of assigned channel for HANDOVER

COMMAND message is SDCCH (+ SACCH). Configure it to 320ms in other

situations.


When the MS sends the HANDOVER ACCESS message on the primary DCCH,

T3124 starts. When the MS receives a PHYSICAL INFORMATION message, the MS

stops T3124, stops sending access burst, activates the PCH in sending and receiving

mode, and connects to the channel if necessary.

If the assigned channel is a SDCCH (+ SACCH), you must enable MS to receive a

correct PHYSICAL INFORMATION message sent by network side in any block. If

T3124 expires (only in asynchronization) or the low layer link fails in the new channel

before sending the HANDOVER COMPLETE message, the MS proceeds as follows:

13) Deactivate the new channel

14) Restart the original channel

15) Reconnect to TCH

16) Trigger to setup primary signaling link

Then the MS sends the HANDOVER FAILURE message on the primary signaling link

and return normal operation before trial handover. The parameters for returning the

original channel are those before response to the HANDOVER COMMAND message

(such as in encryption mode).



7.10.10 T11

I. Definition

T11 is an assignment request queue timer.

II. Format

T11 is determined by equipment room operators. It indicates the maximum queuing

delay for assignment request.


When the BSC is sending the ASSIGNMENT REQUEST message, no TCHs are

available. The ASSIGNMENT REQUEST message must be put to a queue and the

BSC sends the QUEUING INDICATION message to MSC. Meanwhile, T11 starts

timing.

When the BSC sends the ASSIGNMENT COMPLETE message (TCH is successfully

assigned) or the ASSIGNMENT FAILURE message (TCH is not assigned) to MSC,

T11 stops timing.

If T11 expires, the corresponding ASSIGNMENT REQUEST message is removed

from queue and the BSC sends a CLEAR REQUEST message with the cause of no

radio resource available to MSC to clear calling. Assignment queuing helps reduce

service rejection times due to congestion, so enabling it is recommended in a

network. Anyhow, T11 cannot be over great and it must be configured according to

customer habits.

7.10.11 T200

I. Definition

T200 is important (both the MS and base station have T200) at Um interface in data

link layer LAPDm. LAPDm has different channels, such as SDCCH, FACCH, and

SACCH, and the transmission rate of different channel is different, so T 200 must be

configured with different values. The type of the channels corresponding to T200 is

the value of the T200.



II. Format

Different channels corresponds different values of T200. According to the protocol,

when SAPI = 0 and SAPI = 3, the T200 of corresponding data link is dependently

implemented, depending on delay of synchronous processing mechanism and

process in layer 1 and layer 2.

Table 7-1 Value range and default of each type of T200

T200 MinimumMaximu

mDefault

T200_SDCCH_SAPI0 50 100 60; /* = 60 * 5 ms */

T200_FACCH_Full_Rate 40 100 50; /* = 50 * 5 ms */

T200_FACCH_Half_Rate 40 100 50; /* = 50 * 5 ms */

T200_SACCH_TCH SAPI0 120 200 150; /* = 150 * 10 ms */

T200_SACCH_TCH SAPI3 120 200 150; /* = 150 * 10 ms */

T200_SACCH_SDCCH 50 100 60; /* = 60 * 10 ms */

T200_SDCCH_SAPI3 50 100 60; /* = 60 * 5 ms */


T200 avoids deadlock in sending data in data link layer. The data link layer changes

the physical link in which error occurs easily to data link with no errors. At the two

ends of the data link communication system, a confirm-to-resend mechanism is used.

Namely, receiving a message by the receiver must be confirmed by the sender.

If it is unknown that the message is lost, both two ends wait for messages, so the

system confronts a deadlock. Therefore, T200 is used by the sender. When T200

expires, the sender judges that the receiver fails in receiving the message, so it

resends the message.

When the sender needs to confirm whether the receiver has received the message,

T200 starts. When the sender receives the response from the receiver, T200 stops.

When T200 expires, the resending mechanism starts. If the sender receives no

response from the receiver after multiple resendings, it sends ERROR INDICATION

(T200 expiration) to layer 3.



IV. Precautions

T200 must be properly configured to ensure a predictable behavior at Um interface.

The rules for configuring T200 include:

The potentially-existing lost frames in radio link must be detected as possible.

Necessary retransmission of frames must start at the earliest possible moment.

If the response is delayed due to UE failure, the T200 cannot expire before

receiving and processing the next frame from the opposite end.

If T200 expires and no other frames are sent by preference, the related frames

must be resent in the message block.

T 200 starts immediately after next PH-READY-TO-SEND.

7.10.12 N200

I. Definition

N200 is the resending times after expiration of T200.

II. Format

To configure N200, follow rules below:

17) When SAPI = 0 or 3, N200 depends on the state and the channel used.

When multiframe operation is set up, it ensures a common time value for layer 2

link failure in all channels. For layer 2 link establishment and release, configure

N200 to 5.

18) In timer recovery state, configure N200 as below:

5 (SACCH)

23 (SDCCH)

34 (FACCH of full rate)

29 (FACCH of half rate)

19) When SAPI is unequal to 0 or 3, configure N200 to 5, as shown in Table 7-1.



Table 7-1 Situations of SAPI unequal to 0 or 3

SAPI ChannelValid response

delay

Minimum

resending

delay

Maximum resending

delay

Tresp Trmin Trmax Note 3

0 SDCCH MS: 11 51 51

BSS: 32

0 FACCH/Full rate 9 26 39

0 FACCH/Half rate 10 34 44

3 SDCCH MS: 11 51 51 Note 1

BSS: 32

3 SACCH(with TCH)25/129 Note

2312 416 Note 2

The TDMA frame is the measurement unit of values in this table, equal to

120/26ms (approximately 4.615ms)

Note 1: It caters for the process without SAPI 0 transmission. Otherwise, it does not

have a upper limit due to the priority of SAPI 0 transmission.

Note 2: You can configure it to a greater value only when PCH is unavailable due to

SAPI frame transmission if SAPI = 3.

Note 3: It caters only for sending monitoring frames that are available and without F

equal to 1.


If the BSC fails in receiving lay 2 response message after multiple resending, it sends

the ERROR INDICATION message (T200 expires) to layer 3. The BSC takes

statistics of ERROR INDICATION message by corresponding traffic measurement

counter. When T200 or N200 is configured to an over small value, call drop occurs

probably due to ERROR INDICATION.


Chapter 7 of«GSM RNP&RNO»-GSM Parameter Configuration and Adjustment-20060624-A-1.0

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Transcript of Chapter 7 of«GSM RNP&RNO»-GSM Parameter Configuration and Adjustment-20060624-A-1.0