GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Product Name G3BSC Product VersionGSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Prepared by Reviewed by Reviewed by Approved by Date Date Date Date 2012-3-5 Page 1 of 25 GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Contents 1.1 Definition..................................................................................................................................................................5 1.2 Recommended Formula............................................................................................................................................5 1.3 Signaling Procedure and Measurement Points.........................................................................................................6 2.1 Hardware Failure......................................................................................................................................................7 2.2 Transmission.............................................................................................................................................................7 2.3 Version Upgrade.......................................................................................................................................................7 2.4 Parameter Setting......................................................................................................................................................7 2.5 Intra-Network and Inter-Network Interference........................................................................................................8 2.6 Coverage Problem....................................................................................................................................................8 2.7 Antenna System........................................................................................................................................................9 2.8 Imbalance Between Uplink and Downlink...............................................................................................................9 2.9 Repeater....................................................................................................................................................................9 3.1 Analysis Process.....................................................................................................................................................10 3.2 Solutions to High SDCCH Call Drop Rate............................................................................................................12 3.2.1 Checking the Hardware....................................................................................................................................13 3.2.2 Checking the Transmission...............................................................................................................................14 3.2.3 Checking the BSC and BTS Version Upgrade.................................................................................................15 3.2.4 Checking the Parameter Settings......................................................................................................................15 3.2.5 Checking the Interference.................................................................................................................................17 3.2.6 Checking the Coverage, Antenna System, and Balance Between Uplink and Downlink................................17 3.2.7 Checking the Repeaters....................................................................................................................................18 6.1 Case 1: SDCCH Call Drop in a Synchronous Network.........................................................................................22 6.2 Case 2: Call Drop Due to Imbalance Between Uplink and Downlink...................................................................22 6.3 Case 3: Call Drop Due to Antenna System Problem..............................................................................................23 6.4 Case 4: Call Drop Due to Transmission Problem...................................................................................................24 2012-3-5 Page 2 of 25 ....................GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Figures Number of successful SDCCH seizures.6 Number of successful SDCCH seizures in the signaling channel handover .........6 2012-3-5 Page 3 of 25 ............................................................................................................................. 0 Change Description Draft completed. Acronyms and Abbreviations: Acronym and Abbreviation SDCCH MS BSC KPI TCH Full Spelling Standalone Dedicated Control Channel Mobile Station Base Station Controller Key Performance Index Traffic Channel 2012-3-5 Page 4 of 25 . test method. and optimization method of the SDCCH call drop rate. KPI Abstract: This document describes the definition.20050311-A-1. Author Du Jian References SN 1 2 3 4 5 6 Document G-Guide to Eliminating Interference .GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Revision Record Date 2008-8-25 Revision Version V1.0 GSM BSS Network KPI (Network Coverage) Optimization Manual GSM BSS Network KPI (SDCCH Call Drop Rate) Baseline GSM BSS Network KPI (Uplink and Downlink Balance) Optimization Manual Guide to Solving Call Drop Problems GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual Author Chen Baolin Xie Haibin Wu Zhen Yang Jixiang Yang Bin Su Shi Date 2005-3-11 2008-6-18 2007-6-22 2008-3-26 2002-3-7 2008-6-20 GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Keywords: SDCCH call drop rate. The recommended formula is as follows: Call Drop Rate on SDCCH = (Call Drops on SDCCH/Successful SDCCH Seizures + Successful SDCCH Seizures in the signaling channel handover) x 100% Compared with the formula of the BSC32. see the GSM BSS Network KPI (SDCCH Call Drop Rate) Baseline.2 Recommended Formula The SDCCH call drop rate is obtained on the basis of the traffic measurement results. As few call drops due to release indication occur in the existing network. user experience is adversely affected. If the value of this KPI is high. This KPI reflects the seizure condition of signaling channels.1 Definition The SDCCH call drop rate indicates the probability of call drops when the MS occupies the SDCCH. 2012-3-5 Page 5 of 25 . the formula of the BSC6000 adds the measurement of the number of call drops due to release indication received on the SDCCH in stable state. The SDCCH call drop rate is one of accessibility KPIs. For details. 1. the measurement values of the BSC32 and BSC6000 are the same in the formula.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 1 Overview of SDCCH Call Drop Rate 1. 1 Number of successful SDCCH seizures Figure 1. B indicates the number of successful SDCCH seizures in the signaling channel handover 2012-3-5 Page 6 of 25 .2 Number of successful SDCCH seizures in the signaling channel handover The measurement points illustrated in Figure 2 are described as follows: A indicates the number of successful SDCCH seizures.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 1.3 Signaling Procedure and Measurement Points Figure 1. and the parameters and algorithms in the new version may be changed. the major factors that affect the SDCCH call drop rate are as follows: Hardware failure Transmission Version upgrade Parameter setting Intra-network and inter-network interference Coverage. 2. If the following situations occur. the BTS version may be incompatible with the BSC version. the SDCCH call drop rate may increase: 2012-3-5 Page 7 of 25 . antenna system.4 Parameter Setting The settings of some parameters on the BSC and MSC sides may affect the SDCCH call drop rate.1 Hardware Failure When a TRX or a combiner is faulty. the SDCCH call drop rate increases. seizing the TCH becomes difficult. and thus the SDCCH call drop rate increases.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 2 Factors That Affect SDCCH Call Drop Rate According to user complaints and network optimization experience. 2. (2) Transmission links are unstable. and imbalance between uplink and downlink 2. In this case.2 Transmission The SDCCH call drop rate increases in any of the following conditions: (1) The transmission quality is poor on the A or Abis interface due to various reasons.3 Version Upgrade After the BTS version or BSC version is upgraded. 2. 1. Software Parameter 13 and MAX TA are set to too small values. MAIO is set improperly.Access Level(dBm) is set to a too small value. or if severe intra-network interference occurs because of tight frequency reuse. 2. Handover parameters: SDCCH HO Allowed is set to Yes. Inter-network interference from scramblers or privately installed antennas Interference from the CDMA network Repeater interference Intermodulation interference from BTSs Intra-network co-channel and adjacent-channel interference 2. The following types of interference may occur: 1. T200 SDCCH(5ms) and N200 of SDCCH are set to too small values.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Radio link and cell parameters: SACCH Multi-Frames (SACCH period (480ms)) and Radio Link Timeout(SACCH period (480ms)) are set to too small values. 3. 2. T3111(ms) is set to a too small value. Disconnect Handover Protect Timer is set to a too small value. Coverage failure 2012-3-5 Page 8 of 25 . call drops may occur on SDCCHs due to poor QoS. T3109(ms) is set to a too small value. T3103A(ms) and T3103C(ms) are set to too small values.6 Coverage Problem The following coverage problems may affect the SDCCH call drop rate. which causes call drops.5 Intra-Network and Inter-Network Interference If inter-network interference and repeater interference exist. 5. Poor indoor coverage Densely distributed buildings and thick walls cause great attenuation and low indoor signal level. 4. The network planning is improper after the Um interface is synchronized. RACH Min. This affects the SDCCH call drop rate. The length of timer T305/T308 is set to an invalid or too great value. 2. As a result. If the two antennas have different pitch angles or azimuths. 2012-3-5 Page 9 of 25 . If a directional cell has main and diversity antennas. if water runs into the feeder. 3. when a call is made. call drops may occur at the edge of the BTS coverage area.7 Antenna System The following antenna system problems may affect the SDCCH call drop rate 1. call drops probably occur. call drops are likely to occur at a place far away from the BTS. Therefore. the antenna and the connector are not securely connected. the call drop rate increases. Therefore.9 Repeater If a cell is installed with a repeater. the BCCH and SDCCH of the cell may be transmitted from different antennas. the uplink signal level in each cell is much lower than the downlink signal level in the cell.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual If the signal from an antenna is blocked or the BCCH TRX is faulty. 2. If the feeder is damaged. the coverage areas of the two antennas are different. the tower mounted amplifier (TMA) or BTS amplifier does not work properly.8 Imbalance Between Uplink and Downlink The difference between the uplink signal level and the downlink signal level may be great in the following conditions: The transmit power of the BTS is high. the network quality is adversely affected and the call drop rate increases. Thus. In this case. BTS coverage problems may occur in the case that the repeater is faulty or that the uplink and downlink gain is inappropriately set. If the transmit antennas of two cells are misconnected. call drops may occur. or if the feeder and the connector are not securely connected. 2. 2. As a result. 2. strong interference may be caused. the MS cannot seize the SDCCH transmitted by the other antenna and thus a call drop occurs. the following result may occur: An MS can receive the BCCH signals from one antenna. If a wide-frequency repeater is used and the gain is set to a great value. both the transmit power and receiver sensitivity of the antenna are reduced. 1 Analysis Process 2012-3-5 Page 10 of 25 .GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 3 Analysis of and Solutions to High SDCCH Call Drop Rate 3. GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 开始 确定掉话率高小 区 否 传输或硬件是 否存在问题 否 是否由于版本 升级 否 数据配置是否 存在问题 否 是否存在干扰 否 覆盖是否存在 问题 否 天馈是否存在 问题 否 是否上下行不 平衡 否 直放战是否存 在问题 否 掉话率问题是 否解决 是 解决直放战问题 是 根据指导书优化 上下行不平衡问 题 是 调整天馈 是 根据覆盖关化指 关关关化覆盖 是 是否是网内干 扰 否 是 调整切换功控等 相关参数 排查外部干扰 是 检查版本BU G 更换版本或打补 丁 是 解决硬件或传输 问题 是 检查频率规划情 况 结束 2012-3-5 Page 11 of 25 . you should find out the difference between the actual SDCCH call drop rate and the expected value. You should also find out the influence of the problems and the related KPIs. you need to check configuration parameters and network interference. If no obvious causes are found. The following table lists the distribution of call drops based on the type of call drop and the cause for call drop in the traffic statistics. you can locate the fault by performing the corresponding procedure. Call Drops due to Abis Terrestrial Link Failure Call Drops Due to Equipment Failure Call Drops due to Forced Handover Call Drops due to Resource Check Clear Requests Sent on the A Interface M303 M304 M305 M306 M309 According to the traffic statistics. For Um causes.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 3.2 Solutions to High SDCCH Call Drop Rate Before analyzing the causes of high SDCCH call drop rates. If a certain type of call drop accounts for a large proportion of call drops. transmission. For hardware causes. Number of call drops on the SDCCH due to transmission and equipment causes Interface Distribution The sum of the counter and the number of call drops due to SDCCH handover failure is the number of call drops on radio interface (SDCCH). you need to check hardware. the call drop may not occur. Analyzing the traffic statistics based on the cause for call drop Type of Call Drop Call Drops due to CONN FAIL Received on SDCCH in Stable State Cause for Call Drop Radio Link Failure HO Access Failure OM Intervention Radio Resource Unavailable Other Causes Call Drops due to ERR IND Received on SDCCH in Stable State T200 Expired Unsolicited DM Response Sequence Error Call Drops due to REL IND Received on SDCCH Call Drops due to No MRs from MS for a Long Time Release Indication Measurement Code M3001A M3001B M3001C M3001D M3001E M3000A M3000B M3000C M3002 M302 As the seizure duration of the SDCCH is short. and equipment failure. You can analyze the distribution of call drops based on the related traffic measurement results. you can perform the procedures shown in the 2012-3-5 Page 12 of 25 . you can obtain the distribution of SDCCH call drops due to Um and non Um causes. 2. Alarm ID 1000 2204 4414 3606 Alarm Name LAPD OML Fault TRX Communication Alarm TRX VSWR Alarm DRU Hardware Alarm In addition.2 (check the transmission) 3.1 (check hardware failure) M3001D (radio resource unavailable) M303 (Abis terrestrial link failure) M304 (equipment failure) The following sections describe the solutions to high SDCCH call drop rates.2. seizing the SDCCH becomes difficult.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual preceding figure.1 Checking the Hardware If a TRX or a combiner is faulty or if an RF cable is incorrectly connected.2.1 (check hardware failure) 3. The following table lists the mapping between the traffic measurement counters and the troubleshooting procedures. and thus the SDCCH call drop rate increases.2.2.4 (check whether the radio link failure counter and the number of SACCH multi-frames are set properly) 3. you can locate the fault by checking the traffic measurement related to hardware failures. 3. Traffic Measurement Counter M3000A (T200 expired) M3001A (radio link failure) Troubleshooting Procedure 3.4 (check whether the T200 and N200 are set properly) 3. 2012-3-5 Page 13 of 25 . You can check whether hardware is faulty by viewing BTS alarms or viewing the hardware state on the Site Device Panel tab page of the LMT. The following table lists the major BSC alarms related to hardware failures. The traffic measurement counters and parameters in this document are the same as those in the BSC6000V9R8C01B051 version.2. 2. You can check the transmission conditions by viewing the alarms related to transmission.2 Checking the Transmission Poor transmission quality. you should check the transmission connections. or insufficient resources on the Abis or A interface may lead to the increase of the SDCCH call drop rate. Alarm ID 1000 11270 11278 11280 20081 20082 Alarm Name LAPD OML Fault LAPD Alarm E1 Local Alarm E1 Remote Alarm Loss of E1/T1 Signals (LOS) Loss of E1/T1 Frames (LOF) In addition. unstable transmission links. you can infer that transmission failures occur. If a large number of transmission alarms are generated. The following table lists the BSC alarms related to transmission failures. Cause Transmiss ion failure BSC-Level BSC Measurement -> LAPD Measurement Cell-Level Call Measurement: -> Channel Activation Measurement per Cell CHAN ACTIV NACK Messages Sent by BTS Channel Activation Timeouts Call Measurement -> :Call Drop Measurement per Cell Measurement of Call Drops Due to Abis Terrestrial Link Failure 2012-3-5 Page 14 of 25 .GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual Cause Equipment Faults BSC-Level BSC Measurement -> Access measurement per BSC -> Congestion Ratio on SDCCH per BSC Call Drop Ratio on SDCCH per BSC SDCCH Availability per BSC Cell-Level Channel Measurement -> Analyzed Measurement of Available Channels (SDCCH) Call Drop Measurement per Cell in Call Measurement: Call Drops due to Equipment Failure (Signaling Channel) 3. Then. you can locate the fault by checking the traffic measurement related to transmission failures. If this parameter is set to a too small value. the counter decreases by 1. Radio Link Timeout (SACCH period(480ms)) This parameter determines whether a downlink radio link is faulty. see the BSC6000 Upgrade Guide. 3. or provide the feedback for the R&D department to learn whether the new version has known defects.Access Level This parameter determines whether an MS can access the network over the RACH. RXLEV_ACCESS_MIN This parameter specifies the minimum receive level of an MS to access the BSS. The counters related to traffic volume. are affected. In the traffic measurement.3 Checking the BSC and BTS Version Upgrade If the SDCCH call drop rate increases after the BSC version or BTS version is upgraded. SACCH Multi-Frames (SACCH period (480 ms)) This parameter determines whether an uplink radio link is faulty. Each time the BTS successfully decodes the measurement report on the SACCH. you can infer that the radio propagation conditions are poor. For details.2. you can infer that the radio propagation conditions are poor. if this parameter is set to a too small value. the counter increases by 2. however. 2012-3-5 Page 15 of 25 . When the value of this parameter is 0. are accordingly affected. In the traffic measurement. if there are many call drops (M3001A) related to radio link failure. If this parameter is set to a too small value. RACH Min. if there are many call drops (M3001A) related to radio link failure. You should check the settings of the following parameters for a cell with a high SDCCH call drop rate. Each time the BTS fails to decode the measurement report on the SACCH from the MS. you should replace it with another version or install the patch. You can set this parameter to a great value to reduce the SDCCH call drop rate.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 3. In this case. If this parameter is set to a too great value. Min DL Power on HO Candidate Cell and Min Access Level Offset The sum of the values of the two parameters specifies the minimum downlink receive level of a candidate neighboring cell for a handover. you can check the version description document and the related documents. the BTS regards the radio link as faulty. the counter increases by 2. however. an unwanted cell may become the candidate cell. In this case. Each time the BTS successfully decodes the measurement report on the SACCH. You should check whether the BTS version is compatible with the BSC version and whether the parameters and algorithms in the new version are changed. some MSs with low signal levels may access the network and call drops are likely to occur. the BTS regards the radio link as faulty. some MSs with low receive levels may access the network and call drops are likely to occur. Each time the BTS fails to decode the measurement report on the SACCH from the MS. You can set this parameter to a great value to reduce the SDCCH call drop rate. If the new version has defects. some desired cells may be excluded from the candidate cells. you can set this parameter to a greater value. The counters such as call setup success rate and paging success rate. Both conditions may lead to the increase of call drops. you can set this parameter to a greater value.4 Checking the Parameter Settings The parameter settings on the BSC side and MSC side may affect the SDCCH call drop rate.2. the counter decreases by 1. When the value of this parameter is 0. To locate the problem. After the T3103 and Radio Link Timeout timers expire. T3109(ms) This parameter specifies the period for waiting for a Release Indication message after the BSC sends a Channel Release message to the BTS. the BSC cannot hand over the MS within the period specified by this parameter. If timers T305 and T308 are set to invalid or great values. a great error decoding probability occurs in the area covered by the 2012-3-5 Page 16 of 25 . If this parameter is set to a too small value. Thus. the call drop rate increases. call drops occur. If the TSC is planned improperly for a cell in the synchronous network. You are advised to set this parameter properly. the BSC considers that the radio link in the originating cell is faulty. a call drop occurs. The purpose is to reserve a period of time for repeated link disconnections. channel resources are wasted and TCH congestion occurs. Neighboring relationships should be configured completely on the basis of the drive test data and electronic map (for example. the MS cannot be put on hook because it does not receive a release acknowledgement message. you can set this parameter to a greater value. data links are disconnected too early. Nastar) to minimize the call drops due to no available neighboring cells. Therefore. you can increase the values of T200 and N200 properly. Disconnect Handover Protect Timer This parameter is a software parameter of the BSC. Timer T305 specifies the period during which the MSC monitors the on-hook procedure. the MSC clears the call a long time after the MS hangs up.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual T3103A(ms) and T3103C(ms) Timer T3103 series consists of T3103A. the link may be released before the Release Indication message is received. the following case can be avoided: After being handed over to the target cell. It is recommended that timer T3109 be set to 1–2 seconds longer than timer Radio Link Timeout. probably no message is received when timer T3103 series expires. a channel may be deactivated too early. Note that the modification of the data in the timer table does not take effect. T200 SDCCH(5ms) and N200 of SDCCH If T200 SDCCH(5ms) and N200 of SDCCH are set to too small values. If the lengths of the timers are set to small values. call drops are likely to occur. After receiving a DISCONNECT message from an MS. You should set the two parameters when adding BSC data. the BSC releases the channel in the originating cell. Then. MA and TSC settings in Um synchronization The settings involve the AISS function. In this case. As a result. Neighboring relationship (affecting call drops in SDCCH handover when the signaling channel handover is enabled) If the neighboring cells configured in the BA2 table are incomplete. Thus. T3111(ms) This parameter specifies the interval between the time that the main signaling link is disconnected and the time that a channel is deactivated. Timers T305 and T308 Timers T305 and T308 are used on the MSC side. These timers are started to wait for a handover complete message. the number of call drops is increased and thus the call drop rate is significantly affected. T3103C. If this timer is set to a too small value. and T8. If call drops occur because of T200 expiry (M3400A). if many call drops are related to handovers (CM361: Call Drops on Radio Interface in Handover State). call drops are likely to occur in the case of no suitable neighboring cell for handover and progressive deterioration in the voice quality. Timer T308 specifies the period during which the MSC monitors the resource release procedure. If this parameter is set to a too great value. You can set this parameter to a greater value to reduce the SDCCH call drop rate. Thus. In the traffic measurement. GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual cells with the same BCCH or MA. The interference elimination can be classified into intra-network interference elimination and inter-network interference elimination. the channel is released when the TA of a call exceeds the value of MAX TA. In this case. If the cases (such as too low DL receive level. Antenna System. see the GGuide to Eliminating Interference. the error decoding causes ERR_IND reporting by the BTS. call drops may occur on SDCCHs due to poor QoS. It is recommended that Software Parameter 13 should not be enabled.2. For details about interference elimination. In this case. When the multi-frame link is set up or the signaling is transmitted at layer 2. The higher percentage of band level 3-5 indicates that serious UL interference exists. damaged feeder. you need to view the distribution of interference bands in the SDCCH measurement report of the TRX. you can check its coverage by the DT and CQT. MAIO If FH is used in a cell. you can analyze the cell coverage according to the DT route and geographical conditions and then check the antenna system. Software Parameter 13 and MAX TA When Software Parameter 13 is enabled and MAX TA is set to a too small value. 3. call drops occur. the frequencies collide during the FH. and MAIO is set improperly (for example.6 Checking the Coverage. In addition. call drops occur. lost DL measurement reports.2. the call drop rate increases. and Balance Between Uplink and Downlink For a cell with a high SDCCH call drop rate. In this case. For the problematic cell. you need to optimize TOP cells. In this case. water running into the feeder. the call setup success rate and handover success rate slightly fall and the receive quality becomes poor. poor level quality. and long call access time) occur. Cause Interference TRX-Level MR Measurement -> Interference Band Measurement per TRX Mean Number of SDCCHs in Interference Band 1 Mean Number of SDCCHs in Interference Band 2 Mean Number of SDCCHs in Interference Band 3 Mean Number of SDCCHs in Interference Band 4 Mean Number of SDCCHs in Interference Band 5 3. The information on UL interference can be obtained by checking the interference bands in the traffic statistics. it indicates that the problems with the coverage and imbalance between uplink and downlink occur in the cell. This affects the SDCCH call drop rate. and 2012-3-5 Page 17 of 25 . down tilt. Some problems with the coverage and imbalance between uplink and downlink are caused by the reasons such as the antenna coverage direction. the FH offsets of different TRXs in a cell are set to the same value). or if severe intra-network interference occurs because of tight frequency reuse. great difference between the UL and DL levels. If the value of "Call Drops due to ERR IND Received on SDCCH in Stable State" is great.5 Checking the Interference If inter-network interference and repeater interference exist. you should check whether a repeater is faulty and whether the uplink/downlink gain is set to a too great/small value. The following table lists the traffic measurement counters related to repeaters. you should check whether they are wide-frequency repeaters. If repeaters are installed. Cause Repeater Cell-Level None TRX-Level MR Measurement -> Number of MRs Based on TA 2012-3-5 Page 18 of 25 . If the parameters are set to Yes. If the parameters are set to No.2. If repeater problems exist in a cell.7 Checking the Repeaters Check whether Directly Magnifier Site Flag is set to Yes and SDCCH HO Allowed is set to Yes in the data configuration on the LMT. If such problems exist. 3. see the GSM BSS Network KPI (Network Coverage) Optimization Manual and the GSM BSS Network KPI (Uplink and Downlink Balance) Optimization Manual. the TA distribution varies greatly in the traffic measurement results. In addition. the coverage area of the BTS changes. Ensure that the amplification coefficient is properly set. If a repeater has an impact on the SDCCH call drop rate. and check whether the uplink/downlink amplification coefficient is too great. Thus. the SDCCH call drop rate increases.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual insecurely connected connector. For solutions for the problems. you can infer that the cell is configured with repeaters. you should check whether other operators' repeaters are installed near the cell. you should switch off the repeater. vendors and mobile operators use different formulas to calculate the SDCCH call drop rate.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 4 Test Method The SDCCH call drop rate is one of accessibility KPIs. In actual measurement. thus leading to different values of this counter. which can be measured through registration or reporting of the related traffic measurement KPIs. you should register the specific counters and use an appropriate formula to calculate the value of this counter. Currently. 2012-3-5 Page 19 of 25 . Then. as shown in the following figure. Then. generate the signaling tracing file on the LMT or through the Signal Analyze Tool. and then choose Call Trace from the shortcut menu. From the following figure.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 5 Remarks About the Signaling Analysis of the SDCCH Call Drop Rate Trace the RSL signaling on the Abis interface. right-click a piece of signaling of a call and choose Show Chart from the shortcut menu. Obtain ”CONN_FAIL” and “ERROR_IND” signaling. as shown in the following figure. you can view such information as the uplink and downlink receive 2012-3-5 Page 20 of 25 . Based on the information. TA. such as insufficient downlink coverage and interference.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual level of the serving cell. you can find out the causes for call drops. MS power. 2012-3-5 Page 21 of 25 . and BTS power. downlink receive level of neighboring cells. uplink and downlink signal quality of the serving cell. 2 Case 2: Call Drop Due to Imbalance Between Uplink and Downlink Description: The following symptoms occur during the DT: After the test MS camps on a cell. it cannot make calls. After the TSC is modified for cross coverage signals. According to the analysis of a TOP cell. Fault point: The TSC is planned improperly in a synchronous network. Cause analysis and handling: When the uplink signal level is much lower than the downlink signal level.1 Case 1: SDCCH Call Drop in a Synchronous Network Description: The 1x3 radio FH mode is used in a BTS. In this case. the MS can only receive calls. the BTS reports an Error Indication message when the MS is authenticated. In this case. Cause analysis and handling: According to the call drop signaling.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 6 Cases for SDCCH Call Drop Rate Optimization 6. the error decoding probability greatly increases when the signaling is transmitted at layer 2 in a synchronous network. 2012-3-5 Page 22 of 25 . the SDCCH call drop rate reaches a normal value. The counter item is M3000C. the authentication or assignment procedure cannot be completed. call drops occur frequently at a certain distance from the antenna. 6. According to the traffic measurement. After the synchronization. an error is reported after the specified threshold is exceeded. the cell and another cell (cross coverage) in the synchronous area use the same main BCCH and BCC settings. the power may not be balanced. In this case. if the serial number V(r) carried in the I frame received by the receive end is different from the expected value. the SDCCH call drop rate increases. an error occurs when the BTS and MS transmit the information with serial numbers to be acknowledged on the Um interface. According to the analysis of the layer 2 procedure. the counter "Call Drops due to ERR IND Received on SDCCH in Stable State (Sequence Error)" increases. Because TRX 2 (main BCCH TRX) in cell 1 and TRX 6 (main BCCH TRX) in cell 2 transmit the signal through the TXA port of the DDPU in the sector independently. and level 3 are large. After the wrong connection between TRX 3 and TRX 7 is adjusted. The jumpers of the two non-main BCCH TRXs may be misconnected. After the BTS3012 is put into operation. therefore. call drops occur. 6. TRX 3 and TRX 7 are the second TRX in cell 1 and cell 2 respectively. Cause analysis and handling: According to the analysis of the traffic measurement results of TRX-level radio link performance in busy hours. These counters in cell 3 are normal. which indicates that the downlink loss is too great and the downlink transmit power is too small. the number of abnormal radio links on both TRX 3 (TRX 2 and TRX 3 are configured for cell 1) and TRX 7 (TRX 6 and TRX 7 are configured for cell 2) is great. When the call is assigned on the channel in the non BCCH TRX. the transmit power decreases sharply and incurs the call drop due to the inverse transmission of TRX 3 and TRX 7. the proportions of the TRX 3 in cell 1 and TRX 7 in cell 2 at level 1. Therefore.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual The tracing result (as shown in the previous figure) shows that the uplink signal level is much lower than the downlink signal level. 2012-3-5 Page 23 of 25 . they are connected to the TXB channel of the DDPU in the corresponding cell. the number of TCH call drops in cell 1 and cell 2 in busy hours reaches 20 and the number of SDCCH call drops reaches 1.3 Case 3: Call Drop Due to Antenna System Problem Description: A new BTS3012 is deployed at a site and the cell configuration is S2/2/2. the number of call drops on the TCH and the SDCCH in two cells is normal.000. According to the analysis of the traffic measurement results related to the uplink and downlink balance performance. level 2. when a subscriber makes a call. a message is displayed. As a result. the number of Successful SDCCH Seizure Requests is over 7. A detailed check shows that the E1 connector on top of the BTS cabinet is made improperly. 2012-3-5 Page 24 of 25 .4 Case 4: Call Drop Due to Transmission Problem Description: At a certain site. indicating that the process is disrupted and that the communication expires. the transmission bit error rate is high and the BTS cannot be completely initialized. the TCH traffic volume is small and the TCH call drop rate is high. Some parameters of the BTS cannot be initialized. In addition.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 6. the traffic measurement results show that the value of the counter SDCCH Seizure Request is not normal: The maximum number of SDCCH seizure requests reaches 9. assigning a TCH is difficult. The possible cause is that the E1 connector is made improperly. Huawei engineers replace only the transmission cable between the transmission equipment room and the Huawei BSC and use a new E1 connector to fix the DDF transmission cable to the E1 port on top of the BTS cabinet. the MOTO BTS is replaced with Huawei BTS and the cell configuration is S2/2/2. the problem is solved. making a call is difficult on site. the on-site engineer powers off the BTS and loads the data again.000. During the initialization of the BTS. most of the transmission cables are the original ones. Before the replacement. calls are made normally and drive tests show that all performance counters are normal. The traffic measurement results within a measurement period of 15 minutes show that MS-originated and MS-terminated calls are made normally and handovers are performed normally. and the number of Failed SDCCH Seizures due to Busy SDCCH is over 900. some subscribers complain that it is difficult to make calls after the replacement. In this case. The BTS hardware is normal and the cable connections are proper. After a proper E1 connector is used. After obtaining the consent from the customer. Cause analysis and handling: According to the check of the hardware on site.000. After the replacement. the transmission is normal. At the night of the replacement. Compared with the similar SDCCH counters. After a week of operation. Check whether these alarms are generated in the cell. Check the causes for call drops. Measure SDCCH call drops.cell site) or *. you need to fill in the following form. determine whether interference or coverage problems exist.ant file Engineering parameter table and electronic map Purpose Check whether the software version is faulty.GSM BSS Network KPI (SDCCH Call Drop Rate) Optimization Manual 7 Check Item Software version Data configuration Alarm information Traffic measurement Traffic measurement Signaling DT data Others Feedback Form for SDCCH Call Drop Rate If the SDCCH call drop rate is high and technical support is required. clock. Clear the alarms if they are generated. 2012-3-5 Page 25 of 25 . and transmission alarms (self-check) Cause for call drop Traffic measurement results related to the voice quality and the balance between uplink and downlink RSL signaling tracing data *. Check the geographical information through the Nastar software. Check whether interference and imbalance between uplink and downlink exist. Based on the DT data.dat file Hardware.log (*. Check the network optimization parameters and power configuration. Remarks Software versions of the BSC and BTS *.