4 GSM Parameter Configuration and AdjustmentWhen 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:l Network topology designl Selecting the location of base station l Frequency planningl Cell parameter configurationThe 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.4.1 Network and Cell ID4.1.1 Cell Global IDI. DefinitionGSM 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:l Each GSM network in each countryl Each location areal Each base stationl Each cellNumbering the previous items aims as follows:l An MS can identify the serving network so that the MS can select a network in any environment.l The network can obtain the precise location of the MS so that the network can process various service requests involving the MS.l 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).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. FormatThe CGI is MCC-MNC-LAC-CI, with details as follows:l MCC consists of three decimal digits, ranging from 000 to 999.l MNC consists of two decimal digits, ranging from 00 to 99.l LAC ranges from 0 to 65535l CI ranges from 0 to 65535.III. Configuration and InfluenceAs 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. PrecautionsYou must pay attention to the following aspects:l The MNC is unchangeable.l While configuring the LAC, you must follow related regulations. Equivalent LACs must not exist in the state network. l Equivalent CIs must not exist in the same location area.4.1.2 Base Station Identity CodeI. DefinitionIn 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.The system transmits BSIC on synchronization channel (SCH) of each cell. The effect of BSIC is as follows: l 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.l 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 07. 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.l 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.l 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. FormatThe BSIC is NCC-BCC, with details as follows:l The NCC ranges from 0 to 7.l The BCC ranges from 0 to 7.III. Configuration and InfluenceUsually 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. PrecautionsThe 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.4.2 Paging and Access Control Parameters4.2.1 Number of Access Grant Reserved Blocks (BS_AG_BLK_RES or AG)I. DefinitionThe common control channel consists of access grant channel (AGCH) and paging channel (PCH).For different CCCHs, each BCCH multiframe (including 51 frames) contains CCCH message blocks different number. The CCCH is shared by AGCH and PCH. According g to regulations, partial message blocks on CCCH are especially reserved for AGCH. This avoids that the AGCH messages are blocked when the PCH traffic is great.The number of parameter access grant reserved blocks (AG) refers to the number of message blocks reserved for AGCH on CCCH in each BCCH multiframe.II. FormatThe AG ranges from 0 to 2 when CCCH shares physical channel (CCCH_CONF = 1) with stand-alone dedicated control channel (SDCCH).The AG ranges from 0 to 5 when CCCH does not share physical channel (CCCH_CONF=0) with stand-alone dedicated control channel (SDCCH).III. Configuration and InfluenceWhen 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:l AG is 1 when the CCCH and SDCCH share a physical channel.l 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 0.4.2.2 Frame Number Coding Between Identical PagingFrame number coding between identical paging is BS_PA_MFRMS (MFR for short).I. DefinitionAccording 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. FormatThe MFR ranges from 2 to 9, which respectively means that the same paging group cycles in a period of 2 to 9 multiframes.III. Configuration and InfluenceAccording to the definition of CCCH, AG, and MFT, you can calculate the number of paging channel in each cell.l When the CCCH and SDCCH share a physical channel, there is (3 - AG) MFRs.l 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. PrecautionsAny 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.4.2.3 Common Control Channel Configuration (CCCH-CONF)I. DefinitionThe 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. FormatThe CCCH_CONF consists of three bits, with the coding methods listed in Table:CCCH configuration codingCCCH_CONFMeaningNumber of CCCH message blocks in a BCCH multiframe

000One physical channel for used for CCCH, not shared with SDCCH9

001One physical channel for used for CCCH, shared with SDCCH3

010Two physical channels for used for CCCH, not shared with SDCCH18

100Three physical channels for used for CCCH, not shared with SDCCH27

110Four physical channels for used for CCCH, not shared with SDCCH36

III. Configuration and InfluenceWhen 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. PrecautionsThe 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.4.2.4 Extended Transmission Slots (TX_INTEGER)I. DefinitionIn 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:l Extended transmission slots Tl Maximum retransmission times RETl TIt is the number of slots between two sending when the MS keeps sending multiple channel request messages.l SIt is related to channel combination, and is an intermediate variable of access algorithm. It is determined by T and CCCH configuration.II. FormatThe value of T is from 3 to 12, 14, 16, 20, 25, 32, and 50.The value of S ranges as listed in Table:Values of STS in different CCCH combination methods

The CCCH and SDCCH does not share a physical channelThe CCCH and SDCCH share a physical channel

3, 8, 14, 505541

4, 9, 167652

5, 10, 2010958

6, 11, 2516386

7, 12, 32217115

III. Configuration and InfluenceTo 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:l 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.l 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.4.2.5 Minimum Access Level of RACHI. DefinitionThe minimum access level of RACH is the level threshold for the system to judge whether there is a random access request.II. FormatThe minimum access level of RACH ranges from 0 to 63 (corresponding to 110 dBm to 47 dBm).The unit is level grade value.III. Configuration and InfluenceWhen 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.4.2.6 Random Access Error ThresholdI. DefinitionGSM 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. FormatThe value ranges from 0 to 255. The recommended value is 180.III. Configuration and InfluenceThe 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.9010033

10112034

12114035

14116036

16117537

17619538

19622139

22224340

24425041

089 or 25125538

The two parameters random access error threshold and minimum access level of RACH determine the validity of random access burst.4.2.7 Access Control Class (ACC)I. DefinitionGSM 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:l Class 09: common usersl Class 11: users for PLMN managementl Class 12: users for security departmentsl Class 13: common business departments (in charge of water, gas)l Class 14: emergency servicesl Class 15: PLMN staffUsers of class 09 have its access rights catering for home PLMN and visited PLMN. Users of class 11 and 15 have its access rights catering for visited PLMN only. Users of class 12, 13, and 14 have its access rights catering for in the country where home PLMN belongs to.II. FormatThe access control class consists of two parts:l Common access control classValue range: a check option, including class 0 disabled, , class 9 disabled.Recommended value: all 0.l Special access control classValue range: a check option, including class 11 disabled, , class 15 disabled.Recommended value: all 0.If a class is configured to 1, it means that access is forbidden. For example, a common access class is configured to 1000000000; common users excluding class 0 users can access the network.III. Configuration and InfluenceC0C15 (excluding C10) are set by equipment room operators. Usually these bits are configured to 1. Proper configuration contributes to network optimization as follow:l When installing a base station, starting a base station, or maintaining and testing in some cells, configure C0C15 (excluding C10) to 1. In this way, different users are prevented from accessing the network, so the installing and maintenance is less influenced.l 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.4.2.8 Maximum Retransmission Times (RET)I. DefinitionSee 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. FormatThe maximum retransmission times consists of two bits, with the meanings listed in Table:Coding of maximum transmission times MMmaximum transmission times

001

012

104

117

III. Configuration and InfluenceThe 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:l For areas with low traffic, such as in suburban or rural areas, configure RET to 7 to increase the access success rate of MS.l For areas with average traffic, such as common urban areas, configure RET to 4.For microcell with high traffic and of apparent congestion, configure RET to 1.4.2.9 Control Class of MS Maximum Transmit Power (MS-TXPWR-MAX-CCH)I. DefinitionMS-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.l C1 = RLA_C - RXLEV_ACCESS_MIN - MAX((MS_TXPWR_MAX_CCH - P), 0)l RLA_C: average received level by MSl RXLEV_ACCESS_MIN: minimum received level permitted for MS to accessl MS_TXPWR_MAX_CCH: maximum power level of control channel (control class of MS maximum transmit power)l P: Maximum transmit power level of MSII. FormatThe range of MS-TXPWR-MAX-CCH is 031. For cells of GSM900 and GSM1800, the dBm values corresponding to the control class are different.l In a GSM900 network, the 32 control class of maximum transmit power corresponding to 031 is as follows:{39, 39, 39, 37, 35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5}l In a GSM1800 network, the 32 control class of maximum transmit power corresponding to 031 is as follows:{30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 36, 34, 32}Recommended values are 5 for GSM900 and 0 for GSM1800.III. Configuration and InfluenceMS-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.4.2.10 Power Offset (POWEROFFSET)I. DefinitionWhen 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. FormatThe values of 03 correspond to 0 dB, 2 dB, 4 dB, and 6 dB. The recommended value is 2.III. Configuration and InfluenceThe greater the parameter is, the more easily the type 3 DCS1800 MS accesses the network. A great POWEROFFSET enables MS to access the network afar, but does not help control cross-cell interference, so the network quality is influenced.4.2.11 IMSI Attach/Detach AllowedI. DefinitionThe 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.l If yes, the MS starts IMSI attach process (this is one of location updating).l 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. FormatThe 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.III. Configuration and InfluenceUsually 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. PrecautionsThe 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.4.2.12 Direct Retry (DR)I. DefinitionDuring 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. FormatThe 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.III. Configuration and InfluenceDR 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.4.3 Serial Parameters of Cell Selection and Reselection4.3.1 cell_bar_accessI. DefinitionIn 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. FormatThe 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.III. Configuration and InfluenceThe 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 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. PrecautionsThe cell_bar_access is used only in some special areas. For common cells, it is configured to 0.4.3.2 cell_bar_qualifyI. DefinitionThe cell_bar_qualify determines the priority of cells, namely, it enables MS to select some cell by preference.II. FormatThe value of cell_bar_qualify includes 1 and 0. The cell_bar_qualify and cell_bar_access determine the priority state of cells, as listed in Table 1-4.Table 7-1 Cell prioritiescell_bar_qualifycell_bar_accessCell selection priorityCell reselection state

00NormalNormal

01BarredBarred

10LowNormal

11LowNormal

An exception is that the cell selection priority and cell reselection state are normal when the following conditions are met:l The cell belongs to the PLMN which the MS belongs to.l The MS is in cell test operation mode.l The cell_bar_access is 1.l The cell_bar_qualify is 0.l The access control class 15 is disabled.III. Configuration and InfluenceThe 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. PrecautionsPay attention to the following aspects:l 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.l 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.4.3.3 Minimum Received Level Allowing MS to Access (RXLEV_ACCESS_MIN)I. DefinitionTo 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. FormatThe value range of RXLEV_ACCESS_MIN is from 110 dBm to 47 dBm.III. Configuration and InfluenceThe 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. PrecautionsExcept for areas of high density of base stations and of qualified coverage, adjusting cell traffic by RXLEV_ACCESS_MIN is not recommended.4.3.4 Additional Reselection Parameter IndicatorI. DefinitionThe 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. FormatADDITIONAL RESELECT consists of 1 bit. In SI3, it is meaningless, and equipment manufacturers configure it to N. The MS uses ADDITIONAL RESELECT of SI4. l 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.l 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.III. Configuration and InfluenceCells seldom use SI7 and SI8, so you can configure ADDITIONAL RESELECT to N. When cells use SI7 and SI8, and the parameter C2 is used in cell reselection, you can configure ADDITIONAL RESELECT to Y.4.3.5 Cell Reselection Parameter IndicatorI. DefinitionThe 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. FormatThe value of CELL_RESELECT_PARAM_IND includes Y and N, with the meanings as follows:l Y: The MS must calculate C2 by abstracting parameters from SIs of cell broadcast, and set C2 as the standard for cell reselection.l N: The MS must set C1 as the standard, namely, C2 = C1.III. Configuration and InfluenceThe equipment room operators determine the value of PI. Configure PI to Y if related cells set C2 as the standard for cell reselection; otherwise, configure it to N.4.3.6 Cell Reselection Offset, Temporary Offset, and Penalty TimeI. DefinitionAfter 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:l Starts measuring signals level of BCCH carrier in neighbor cells.l Records the 6 neighbor cells with greatest signal level.l 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:l Cell priorityl Whether the cell is barred to accessl 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:1) When PENELTY_TIME 11111:C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET * H (PENALTY_TIME - T)Wherein, if PENALTY_TIME - T (x) < 0, the function H(x) = 0; if x 0, H(x) = 1.2) When PENELTY_TIME = 11111:C2 = C1 - CELL_RESELECT_OFFSETT 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. l When the cell reselection parameter PI is 1, the MS is informed of receiving values of three parameters on BCCH. l 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. Format1) 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 0.2) The temporary offset (TO) is in decimal, with unit of dB. It ranges from 0 to 7, which means 0 to 70 dB (10 dB as the step). The recommended value is 0.3) The penalty time (PT) is in decimal, with unit of second. It ranges from 0 to 31. The value 0 to 30 means 20s to 620s (20s as the step). The value 31 is reserved for changing the effect direction of C2 by CRO. The recommended value is 0.III. Configurationa and InfluenceThe previous parameters can be adjusted accordingly in the following three situations:1) When the communication quality is bad due to heavy traffic or other causes, change the parameters to enable MS not camps on the cell (the cell is exclusive 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. 2) 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 020 dB according to the priority. The higher the priority is, the greater the CRO is. TO is configured the same as or a little greater than CRO. PT helps avoid over frequent cell reselection, the recommended value of PT is 20s or 40s.3) For cell with average traffic, configure CRO to 0, PT to 11111 so that C2 = C1. No artificial influence is on the cell.IV. PrecautionsIn 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.4.3.7 Cell Reselection Hysteresis (CRH)I. DefinitionCRH affects cell reselection of cross location area. The MS starts cell reselection if the following conditions are met:l The signal level of neighbor cell (in different location area) is greater than that of the serving cell.l 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. FormatCRH is in decimal, with unit of dB. The range is 0 to 14, with step of 2 dB. The recommended value is 4.III. Configuration and InfluenceIf 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. PrecautionsDo not configure CRH to 0 dB.4.4 Parameters Affecting Network Functions4.4.1 Newly Established Cause Indicator (NECI)I. DefinitionIn 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. FormatThe value of NECI includes Y and N, with the meaning as follows:l Y means that the area support half-speed TCH.l N means that the area cannot support half-speed TCH.III. Configuration and InfluenceHalf-speed TCHs enable each carrier to support more traffic channel, but you must confirm whether the system support half-speed TCH.4.4.2 Power Control Indicator (PWRC)I. DefinitionThe 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:l GSM regulations allow frequency hopping channels to use BCCH (frequency hopping not in BCCH slots) .l GSM regulations allow downlink power control over frequency hopping channels.l 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. FormatThe value of PWRC includes 0 and 1, with meanings as follows:l When PWRC is 0, the measurement result by MS includes BCCH carrier.l When PWRC is 1, the measurement result by MS does not include BCCH carrier.III. Configuration and InfluenceThe PWRC is usually configured to 0. Configure it to 1 if all the following conditions are met:l Channels have frequency hopping on two or more frequencies.l One of the frequency is BCCH carrier frequency.l The system uses downlink power control.IV. PrecautionsThe value of PWRC depends actually on the following parameters:l Whether to use frequency hopping.l Whether the hopping frequency includes BCCH carrier.l Whether the system uses downlink power control.4.4.3 Discontinuous Transmit of UplinkI. DefinitionDiscontinuous 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. FormatWhether 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:l 0: MS can use DTXU.l 1: MS must use DTXU.l 2: MS cannot use DTXU.III. Configuration and InfluenceUsing uplink DTX affects call quality, but it is helpful in the following aspects:l Lower interference to radio channels.Due to this, the average call quality of network is improved.l Cut power consumption by MSFor the previous advantages, DTX is recommended to use.4.4.4 Discontinuous Transmit of DownlinkI. DefintionDiscontinuous transmit of downlink (DTXD) means the network does not transmit signals during silent period.II. DefinitionDTXD is in string, and the range is YES and NO. The meanings are as follows:l YES: Downlink uses DTX.l NO: Downlink does not use DTX.III. Configuration and InfluenceUsing downlink DTX affects call quality in a limit scale, but it is helpful in the following aspects:l Lower interference to radio channels.Due to this, the average call quality of network is improved.l Reduce load of base station CPUTherefore, if possible, you use DTX.IV. PrecautionsAccording to GSM regulations, downlink DTX is optional. If the base station equipment supports DTXD, then use it. However, you must ensure that voice transcoder is available to support DTXD.4.4.5 Call Resetup AllowedI. DefinitionWhen 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. FormatThe values of call resetup allowed are 1 and 0, with meanings as follows:l 1: Call resetup is allowed in the cell.l 0: Call resetup is forbidden in the cell.III. Configuration and InfluenceWhen 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.4.4.6 Emergency Call AllowedI. DefinitionThe following MSs cannot enjoy various services:l MS without SIMl MS with ACC as one of C0 to C9 and with cell_bar_accessThe parameter emergency call allowed (EC) determines whether the MS is allowed for emergency calls, such as police emergency call.II. FormatEC 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.III. Configuration and InfluenceAccording 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 1.4.4.7 Early Classmark Sending ControlI. DefinitionIn a GSM network, the MS classmark marks the following aspects:l Service capacityl Supported frequency bandl Power capacityl Encryption capacityClassmark consists of classmark1, classmark2, and classmark3. A GSM MS. In a GSM network, the MS reports Classmark1 or Classmark2 information immediately after ESTIND (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. FormatThe values of ECSC are Y and N, with the following meanings:l Y: The MS reports Classmark3 to the network immediately after link setup.l N: The MS is forbidden to report its Classmark3 to network initiatively.III. Configuration and InfluenceThe major information of Classmark3 is for dualband network, so do as follows:l Configure ECSC to N in single frequency GSM application areas.l Configure ECSC to Y in dualband GSM application areas.IV. PrecautionsIn 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.4.5 Frequency Hopping Parameters4.5.1 Frequency Hopping Sequence NumberI. DefinitionIn 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:l Track of frequency points during frequency hoppingl The asynchronous neighbor cells using the same MA can avoid continuous frequency collision during frequency hopping by using different HSNs. II. FormatHSN is in decimal, ranging from 0 to 63, wherein:l 0: cyclic frequency hoppingl 163: pseudo frequency hoppingIII. Configuration and InfluenceYou 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.4.5.2 Mobile AllocationI. DefinitionThe 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. FormatMA is a set, with all GSM frequency points as its element, namely:l For GSM900 networks: 1124 and 9751023.l For GSM1800 networks: 512885III. Configuration and InfluenceMA is configured according to network designing requirements.IV. PrecautionsChinese 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:l Using DTXl HSN = 0 (cyclic frequency hopping)You must avoid SACCH to appear usually at the same frequency point.4.5.3 Mobile Allocation Index OffsetI. DefinitionDuring 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. FormatMAIO ranges from 0 to 63.III. Configuration and InfluenceMAIO is configured by equipment room operators.IV. PrecautionsThe 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.4.6 Distance Control Parameters4.6.1 Call ClearingI. DefinitionCall clearing (CallClearing) means that the maximum allowed distance threshold is cleared between MS and base station in talk.II. FormatCallClearing ranges from 0 to 63, with unit of TA.III. Configuration and InfluenceConfigure 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.4.6.2 TA Handover Threshold (MSRANGEMAX)I. DefintionWhen the distance between MS and base station reaches or exceeds MSRANGEMAX, distance handover is triggered.II. FormatMSRANGEMAX ranges from 0 to 63, with unit of TA. The reference is 63.III. Configuration and InfluenceMSRANGEMAX 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. 4.6.3 TA Restriction (MS_BS_DIST_USED)I. DefinitionThe 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. FormatThe range is 0 to 63, with unit of TA. The reference is 63.III. Configuration and InfluenceFor 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.4.7 Radio Link Failure Process and ParametersThe radio link failure is detected from uplink and downlink. The MS completes downlink detection, while the base station completes uplink detection.4.7.1 Radio Link Failure Counter (RLC or Radio Link Timeout)I. DefinitionThe MS originates call resetup or disconnects by force if all the following conditions are met:l The voice or data quality is too poor to be received.l 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:l S decreases by 1 if the MS fails in decoding a correct SACCH message when the MS should receive the SACCH message.l S increases by 2 if the MS succeed in decoding a correct SACCH message.S cannot exceed the value for radio link failure counter. When S equals to 0, the MS originates call resetup or disconnects by force.II. FormatThe step from 4 to 64 is 4, with unit of SACCH period as follows:l For TCH, the SACCH period is 480ms.l For SDCCH, the SACCH period is 470ms.III. Configuration and InfluenceThe value of the parameter radio link failure counter affects CDR and utilization of radio resources.Assume that cell A is a neighbor cell to cell B and the bordering coverage is poor. When an MS moves from P to Q while in talk,l If the radio link failure counter is over small, call drop occurs before cross-cell handover.l 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:l Configure it to between 52 and 64 in areas with over low traffic.l Configure it to between 36 and 48 in areas with low traffic and great coverage radiuml Configure it to between 20 and 32 in areas with heavy traffic.IV. PrecautionsConfigure radioLinkTimeout to smaller than T3109. This contributes to success of call resetup and avoids the following situation effectively:Before the MS releases radio resources due to expiration, the network side completes releasing channels resources and reallocates resources to other MSs. Therefore two MSs might use the same slot and this causes interferences even call drop.4.7.2 SACCH Multiframe (RLTO_BS)I. DefinitionRefer 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:l S decreases by 1 if the MS fails in decoding a correct SACCH message when the MS should receive the SACCH message.l S increases by 2 if the MS succeed in decoding a correct SACCH message.S cannot exceed the value for radio link expiration of base station. When S equals to 0, the MS originates call resetup or disconnects by force, as shown in Figure 1-5.II. FormatRLT0_BS ranges from 4 to 64.III. Configuration and InfluenceProper 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:l Configure it to between 52 and 64 in areas with over low traffic.l Configure it to between 36 and 48 in areas with low traffic and great coverage radiuml Configure it to between 20 and 32 in areas with heavy traffic.l Configure it to a greater value in areas with apparent voids or where call drop occurs frequently while the MS moves.IV. PrecautionsRLT0_BS and RLC must be consistent.4.8 Handover and Related Parameters4.8.1 PBGT Handover Threshold (HoMargin)I. DefinitionThe 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. FormatThe 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.III. Configuration and InfluenceThe PBGT handover threshold aims to adjust handover difficulty properly, and to avoid ping-pong handover. If it is configured over great, the handover is delayed and handover is less efficient. When it is smaller than 64, the MS hands over from the serving cell to the neighbor cell with lower level.4.8.2 Minimum Downlink Power of Handover Candidate Cells (rxLevMinCell)I. DefinitionIt 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. FormatIt ranges from 110 dBm to 47 dBm.III. Configuration and InfluenceIt is helpful in the following two aspects:l It guarantees communication quality.For a common single layer network structure, the value ranges from 90 dBm to 80 dBm. l 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. PrecautionsYou cannot configure rxLevMinCell over great (over 65 dBm) or over small (lower than 95 dBm), and otherwise communication quality is affected.4.8.3 Handover Threshold at Uplink EdgeI. DefinitionIf the uplink received level keeps being smaller than the handover threshold at uplink edge for a period, edge handover can be performed.II. FormatIt ranges from 0 to 63, corresponding to 110 dBm to 47 dBm. The recommended values are as follows:l Configure it to 25 in urban areas without PBGT handover.l Configure it to 20 in single site of suburban areas.l Configure it to 20 in urban areas with PBGT handoverIII. Configuration and InfluenceWhen PBGT handover is enabled, the corresponding edge handover threshold can be lowered. When PBGT handover is disabled, and the edge handover threshold is 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.4.8.4 Handover Threshold at Downlink EdgeI. DefinitionIf the downlink received level keeps being smaller than the handover threshold at downlink edge for a period, edge handover can be performed. II. FormatIt ranges from 0 to 63, corresponding to 110 dBm to 47 dBm. The recommended values are as follows:l Configure it to 30 in urban areas without PBGT handover.l Configure it to 25 in single site of suburban areas.l Configure it to 25 in urban areas with PBGT handoverIII. Configuration and InfluenceWhen PBGT handover is enabled, the corresponding edge handover threshold can be lowered. When PBGT handover is disabled, and the edge handover threshold is 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.4.8.5 Downlink Quality Restriction of Emergency HandoverI. DefinitionIf the downlink received quality is lower than the threshold of downlink quality restriction of emergency handover, the quality difference emergency handover occurs.II. FormatIt ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.The recommended value is 50.III. Configuration and InfluenceWhen 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.4.8.6 Uplink Quality Restriction of Emergency HandoverI. DefinitionIf the uplink received quality is lower than it, quality difference emergency handover is triggered.II. FormatIt ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.The recommended value is 50.III. Configuration and InfluenceWhen 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.4.8.7 Uplink Quality Threshold of Interference HandoverI. DefinitionIt 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:l The uplink received level is higher than the uplink received power threshold of interference handover.l The uplink received quality is lower than the uplink quality threshold of interference handover.When handover switch is enabled, the interference handover occurs within the cell by preference.II. FormatIt ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.The recommended value is 50.III. Configuration and InfluenceWhen frequency hopping is enabled, the voice quality is better with the same RQ, you 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.4.8.8 Downlink Quality Threshold of Interference HandoverI. DefinitionIt 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:l The downlink received level is higher than the downlink received power threshold of interference handover.l The downlink received quality is lower than the downlink quality threshold of interference handover.When handover switch is enabled, the interference handover occurs within the cell by preference.II. FormatIt ranges from 0 to 70, corresponding to RQ (QoS 0 to 7) x 10.The recommended value is 50.III. Configuration and InfluenceWhen frequency hopping is enabled, the voice quality is better with the same RQ, you 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. PrecautionsThe interference handover quality must be better than emergency handover quality.4.8.9 Uplink Received Power Threshold of Interference HandoverI. DefinitionIf 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:l The uplink received level is higher than the uplink received power threshold of interference handover.l The uplink received quality is lower than the uplink quality threshold of interference handover.When handover switch is enabled, the interference handover occurs within the cell by preference.II. FormatIt ranges from 0 to 63, corresponding to 110 dBm to 47 dBm.The recommended value is 25.III. Configurationa and InfluenceWhen 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.4.8.10 Downlink Received Power Threshold of Interference HandoverI. DefinitionIf 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:l The downlink received level is higher than the downlink received power threshold of interference handover.l The downlink received quality is lower than the downlink quality threshold of interference handover.When handover switch is enabled, the interference handover occurs within the cell by preference.II. FormatIt ranges from 0 to 63, corresponding to 110 dBm to 47 dBm.The recommended value is 30.III. Configurationa and InfluenceWhen 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.4.8.11 Maximum Repeated Times of Physical Messages (NY1)I. DefinitionIn asynchronous handover process of GSM system, when the MS receives handover messages of the network, it sends handover access messages on the target channel. After the network receives the message, it does as follows:1) Calculate related RF features.2) Send physical messages (it the channel messages are encrypted, start encryption and decryption algorithm) in unit data to MSs.3) Start timer T3105.If the network does not receive correct layer 2 frames sent by MS until expiration 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. FormatNY1 ranges from 0 to 254.The recommended value is 20.III. Configuration and InfluenceWhen the network receives the handover access messages sent by MS, the physical channel (PCH) needs to be synchronous. If the communication quality on channels is guaranteed, the MS can receive physical messages correctly and send layer 2 frames to the network.If the physical messages are sent multiple times, and the network cannot receive layer 2 frames sent by MS, the PCH is too poor to communicate normally. Though link is setup after multiple trials, the communication quality is not guaranteed. This lowers the utilization of radio resources. Therefore configure NY1 to a smaller value.IV. PrecautionsConfiguring 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)4.8.12 Multiband Indicator (multiband_reporting)I. DefinitionIn 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. FormatThe multiband indicator ranges from 0 to 3, with meanings as follows:l 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.l 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.l 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.l 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.III. Configuration and InfluenceIn multiband networks, it is related to traffic of each band. For configuration, refer to the following rules:l If the traffic of each band is approximately equal, and operators do not select a band intentionally, you can configure the multiband indicator to 0l 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.l For situations between the previous two, configure multiband indicator to 1 or 2.4.8.13 Permitted Network Color Code (ncc permitted)I. DefinitionDuring 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. FormatThe 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.III. Configuration and InfluenceEach 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. PrecautionsImproper configuration of the parameter causes normal handover and even call drop. The parameter only affects behaviors of MS.4.9 Power Control and Related Parameters4.9.1 Maximum Transmit Power of MS (MSTXPWRMX)I. DefinitionThe 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. FormatMSTXPWRMX ranges from 0 to 31.The dBm values corresponding to GSM900 and GSM1800 cells are different:l 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}l 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}III. Configuration and InfluenceConfiguring MSTXPWRMX helps control interferences between neighbor cells, because:l If MSTXPWRMX is over great, the interference between neighbor cells increases.l If MSTXPWRMX is over small, the voice quality declines and improper handover might occur.4.9.2 Received Level Threshold of Downlink Power Increment (LDR)I. DefinitionWhen the downlink received level of the serving cell is smaller than a threshold, the network must start power control to increase the transmit power of base station and to guarantee communication quality of MS.The received level threshold of downlink power increment defines the downlink received level threshold. When the downlink level received by MS is smaller than it, the base station starts power control to increase its transmit power.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. FormatIt ranges from 110 dBm to 47 dBm.N1 ranges from 1 to 32.P1 ranges from 1 to 32.III. Configuration and InfluenceThe 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 N1.4.9.3 Received Level Threshold of Uplink Power Increment (LUR)I. DefinitionWhen 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.The parameter N1 means that at lease N1 sampling points must be measured before starting handover algorithm.The parameter P1 means the level of at least P1 sampling points in N1 sampling points is smaller than the threshold prescribed by received level threshold of uplink power increment. II. FormatIt ranges from 110 dBm to 47 dBm.N1 ranges from 1 to 32.P1 ranges from 1 to 32.III. Configuration and InfluenceThe received level is between 60 dBm and 80 dBm in a GSM network, so configure received level threshold of uplink 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 N1.4.9.4 Received Quality Threshold of Downlink Power Increment (LDR)I. DefinitionWhen 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 N3 means that at lease N3 sampling points must be measured before starting handover algorithm. 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. FormatIt ranges from 0 to 7, the voice quality grade.N3 ranges from 1 to 32.P3 ranges from 1 to 32.III. Configuration and InfluenceThe 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.N3 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N3 to between 3 and 5.Configure P3 to about 2/3 of N3.4.9.5 Received Quality Threshold of Uplink Power Increment (LUR)I. DefinitionWhen 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.The parameter N3 means that at lease N3 sampling points must be measured before starting handover algorithm.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 uplink power increment. II. FormatIt ranges from 0 to 7, the voice quality grade.N3 ranges from 1 to 32.P3 ranges from 1 to 32.III. Configuration and InfluenceThe received quality is 0 to 2 of quality grade in a GSM network, so configure received quality threshold of uplink power increment to 3.N3 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N3 to between 3 and 5.Configure P3 to about 2/3 of N3.4.9.6 Received Level Threshold of Downlink Power Decrement (UDR)I. DefinitionWhen 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.The parameter N2 means that at lease N2 sampling points must be measured before starting handover algorithm.The parameter P2 means the level of at least P2 sampling points in N2 sampling points is greater than the threshold prescribed by received level threshold of downlink power decrement. II. FormatIt ranges from 110 dBm to 47 dBm.N1 ranges from 1 to 32.P1 ranges from 1 to 32.III. Configuration and InfluenceThe received level is between 60 dBm and 80 dBm in a GSM network, so configure received level threshold of downlink power decrement to 85 dBm.N2 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N2 to between 3 and 5.Configure P2 to about 2/3 of N2.4.9.7 Received Level Threshold of Uplink Power Decrement (UUR)I. DefinitionWhen 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.The parameter N2 means that at lease N2 sampling points must be measured before starting handover algorithm.The parameter P2 means the level of at least P2 sampling points in N2 sampling points is greater than the threshold prescribed by received level threshold of uplink power decrement.II. FormatIt ranges from 110 dBm to 47 dBm.N2 ranges from 1 to 32.P2 ranges from 1 to 32.III. Configuration and InfluenceThe received level is between 60 dBm and 80 dBm in a GSM network, so configure received level threshold of uplink power decrement to 60 dBm.N2 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N2 to between 3 and 5.Configure P2 to about 2/3 of N2.4.9.8 Received Quality Threshold of Downlink Power Decrement (UDR)I. DefinitionWhen 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.The parameter N4 means that at lease N4 sampling points must be measured before starting handover algorithm.The parameter P4 means the quality of at least P4 sampling points in N2 sampling points is greater than the threshold prescribed by received quality threshold of downlink power decrement.II. FormatIt ranges from 0 to 7, the voice quality grade.N4 ranges from 1 to 32.P4 ranges from 1 to 32.III. Configuration and InfluenceThe received quality is 0 to 2 of quality grade in a GSM network, so configure received quality threshold of downlink power decrement to 0.N4 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N4 to between 3 and 5.Configure P4 to about 2/3 of N4.4.9.9 Received Quality Threshold of Uplink Power Decrement (UUR)I. DefinitionWhen 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.The parameter N4 means that at lease N4 sampling points must be measured before starting handover algorithm.The parameter P4 means the quality of at least P4 sampling points in N4 sampling points is greater than the threshold prescribed by received quality threshold of uplink power decrement.II. FormatIt ranges from 0 to 7, the voice quality grade.N4 ranges from 1 to 32.P4 ranges from 1 to 32.III. Configuration and InfluenceThe received quality is 0 to 2 of quality grade in a GSM network, so configure received quality threshold of uplink power decrement to 0.N4 is related to propagation quality of radio channels within cell coverage range. To reduce influence by attenuation, configure N4 to between 3 and 5.Configure P4 to about 2/3 of N4.4.9.10 Power Control Interval (INT)I. DefinitionIt 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. FormatIt ranges from 0 to 31s.III. Configuration and InfluenceAccording to frame structure of GSM network, configure INT to about 3s.IV. PrecautionsINT cannot be smaller than 1s, and otherwise the system becomes unstable.4.9.11 Power Increment Step (INC)I. DefinitionThe INC indicates the power increment of MS or base station in power control.II. FormatThe range of INC is 2 dB, 4 dB, or 6 dB.III. Configuration and InfluenceThe recommended value is 4 dB.4.9.12 Power Decrement Step (RED)I. DefinitionThe RED indicates the power decrement of MS or base station in power control.II. FormatThe range of RED is 2 dB or 4 dB.III. Configuration and InfluenceThe recommended value of RED is 2 dB.

4.10 Systematic Important Timers

4.10.1 T3101I. DefinitionT3101 is the BSC timer controlling time of immediate assignment process.II. FormatT3101 ranges from 0 to 255s. The recommended value is 3s.III. Configuration and InfluenceIn 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 re