1Overview of SDCCH Call DropRate1.1 DefinitionThe SDCCH call drop rate indicates the probability of calldrops when the MS occupies theSDCCH. The SDCCH call drop rate is one ofaccessibility KPIs. This KPI reflects the seizurecondition of signaling channels. If the value of thisKPI is high, user experience is adverselyaffected.1.2 Recommended FormulaThe SDCCH call drop rate is obtained onthe basis of the traffic measurement results. Therecommended 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, theformula of the BSC6000 adds the measurementof the number of call drops dueto release indication received on the SDCCH in stable state.As few call drops due to release indication occur inthe existing network, the measurementvalues of the BSC32 and BSC6000 are thesame in the formula.For details, see the GSM BSS Network KPI (SDCCH Call Drop Rate) Baseline.

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 6 of 26

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNAL1.3 Signaling Procedure and MeasurementPointsFigure 1.1Number of successful SDCCH seizuresFigure 1.2Number of successful SDCCH seizures in the signaling channel handoverThe measurement points illustrated in Figure 2 are described as follows:A indicates the number of successful SDCCH seizures.B indicates the number of successful SDCCH seizures in the signaling channel handover

2GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNALRadio link and cellparameters:SACCH Multi-Frames (SACCH period (480ms))and

Radio Link Timeout(SACCHperiod(

480ms)) are set to too small

values.

RACH Min.Access Level(dBm)is set to a too small value.

T200 SDCCH(5ms)and

N200 of SDCCHare set to too smallvalues.MAIO is set improperly.Handover parameters:SDCCH HO Allowedis set to

Yes.

T3103A(ms)and

T3103C(ms)are set to too smallvalues.

T3109(ms)is set to a too small value.

T3111(ms)is set to a too small value.The length of timer T305/T308 is set toan invalid or too great value.Disconnect Handover Protect Timeris set to a too small value.The network planning is improper after the Um interface is synchronized.

Software Parameter 13and

MAX TAare set to too smallvalues.

2.5 Intra-Network and Inter-NetworkInterferenceIf inter-network interference and repeater interference exist, orif severe intra-networkinterference occurs because of tight frequency reuse, call drops may occur on SDCCHsdue topoor QoS. This affects the SDCCH call drop rate.The following types ofinterference may occur:1.Inter-networkinterferencefromscramblers orprivatelyinstalledantennas2.Interferencefrom theCDMA network3.Repeaterinterference4.Intermodulation interference from BTSs5.Intra-networkco-channelandadjacent-channelinterference2.6 Coverage ProblemThe following coverage problems may affect theSDCCH call drop rate.1. Poor indoorcoverageDensely distributed buildings and thick walls cause great attenuation and low indoorsignallevel, which causes call drops.2. Coverage failure

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 9 of 26

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNALIf the signal from an antenna isblocked or the BCCH TRX isfaulty, call drops may occur.

2.7 Antenna SystemThe following antenna system problems may affect the SDCCH call drop rate1.If thetransmit antennas of two cellsare misconnected, the uplink signal level ineachcellis much lower than the downlink signal level in the cell. Therefore, call drops are likelyto occur at a place far away from theBTS.2.If a directional cell has main and diversity antennas, the BCCH and SDCCH of the cellmay be transmitted from different antennas. If the two antennas have different pitchangles or azimuths, the coverage areas of the two antennas are different. In this case, thefollowing result may occur: An MS can receive the BCCH signals from one antenna;when a call is made, the MS cannot seize the SDCCH transmitted by the other antennaand thus a call drop occurs.3.If thefeeder is damaged, if water runs into the feeder, or if the feeder and the connectorare notsecurely connected, boththe transmit power andreceiver sensitivity oftheantenna are reduced. Thus, call dropsprobably occur.

2.8 Imbalance Between Uplink and DownlinkThe difference between the uplink signal level andthe downlink signal level may begreat inthe following conditions: The transmit power of the BTS ishigh; the tower mounted amplifier(TMA) or BTS amplifier does not work properly; the antenna and theconnector are notsecurely connected.As a result, call drops mayoccur at the edge of the BTS coverage area.

2.9 RepeaterIf a cell is installed witha repeater, BTS coverage problems may occur in the case that therepeater is faulty or that the uplinkand downlink gain is inappropriately set. Therefore, thecall drop rate increases.If a wide-frequency repeater is used and the gain is setto a great value, strong interferencemay be caused. As a result, the network quality is adversely affected and the call drop rateincreases

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNALthe cells with the same BCCHor MA. When the multi-frame link is set upor thesignaling is transmitted at layer 2, theerror decoding causes ERR_IND reporting by theBTS. In this case, call drops occur. If the value of "Call Drops dueto ERR IND Receivedon SDCCH in Stable State" is great, youneed to optimize TOP cells.

MAIOIf FH is used in a cell, and

MAIOis set improperly (for example, the FH offsets ofdifferent TRXs in a cell are set to the same value), the frequencies collide during the FH.In this case, the call droprate increases.

Software Parameter 13 and MAX TAWhenSoftware Parameter 13is enabled and

MAX TAis set to a too small value, thechannel is released when the TA of a call exceeds the value ofMAX TA. In this case,call drops occur. It is recommended that

Software Parameter 13should not be enabled.

3.2.5 Checking theInterferenceIf inter-network interference and repeater interference exist, orif severe intra-networkinterference occurs because of tight frequency reuse, call drops may occur on SDCCHsdue topoor QoS. This affects the SDCCH call drop rate.The information on UL interference can beobtained by checking the interference bands inthetraffic statistics. The higher percentage of band level 3-5 indicates thatserious ULinterference exists. In this case, you need to view thedistribution of interference bands in theSDCCH measurement report of the TRX.The interference elimination can be classified intointra-network interference elimination andinter-network interference elimination. For detailsabout interference elimination, see the

G-Guide to Eliminating Interference.

CauseTRX-LevelInterferenceMRMeasurement->Interference BandMeasurement per TRXMean Number of SDCCHs in Interference Band 1Mean Number of SDCCHs in Interference Band 2Mean Number of SDCCHs in Interference Band 3Mean Number of SDCCHs in Interference Band 4Mean Number of SDCCHs in Interference Band 5

3.2.6 Checking the Coverage, Antenna System, andBalance Between Uplink andDownlinkFor a cell with a highSDCCH call drop rate, you can check itscoverage by the DT and CQT.If the cases (suchas too lowDL receive level, great difference between the UL and DL levels,poor level quality, lost DL measurement reports, and longcall access time) occur, it indicatesthat the problems with the coverage and imbalance between uplink and downlink occur inthecell.For the problematic cell, the call setup success rate and handover success rate slightly fallandthe receive quality becomes poor. In addition, youcan analyze the cellcoverage according tothe DT route and geographical conditions and then check the antenna system. Some problemswith the coverage and imbalance between uplink and downlink are caused by the reasons suchas the antenna coverage direction, downtilt, damaged feeder, water running into thefeeder,

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 18 of 26

INCLUDEPICTURE "http://htmlimg3.scribdassets.com/5n57knwwcg12euv6/images/18-17d98b88a2.jpg" \* MERGEFORMATINET

INCLUDEPICTURE "http://htmlimg3.scribdassets.com/5n57knwwcg12euv6/images/18-17d98b88a2.jpg" \* MERGEFORMATINET

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNALand insecurelyconnected connector.For solutions for the problems, see the

GSM BSS Network KPI (Network Coverage)Optimization Manualand the

GSM BSS Network KPI (Uplink and Downlink Balance)Optimization Manual.

3.2.7 Checking the RepeatersCheck whether

Directly Magnifier Site Flagis set to

Yesand

SDCCH HO Allowedis set to

Yesin the data configuration on the LMT. If the parameters are set to

Yes, you can infer thatthe cell is configured with repeaters. If the parameters are set to

No, you should checkwhether other operators' repeaters are installed near thecell.If repeaters are installed, you shouldcheck whether they are wide-frequency repeaters, andcheck whether the uplink/downlink amplification coefficient is toogreat. Ensure that theamplification coefficient is properly set. Ifa repeater has an impact on the SDCCH call droprate, you shouldswitch off the repeater.In addition, you should check whether a repeater is faulty andwhether the uplink/downlinkgain is set toa too great/small value. If such problems exist, thecoverage area of the BTSchanges. Thus, the SDCCH calldrop rate increases.If repeater problems exist ina cell, the TA distribution varies greatly in the trafficmeasurement results. The following table liststhe traffic measurement counters related torepeaters.

CauseCell-LevelTRX-LevelRepeaterNoneMRMeasurement->Number of MRs Based on TA2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 19 of 26

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNALThe tracing result (as shown in theprevious figure) shows that the uplink signal levelis muchlower than the downlinksignal level. Therefore, call drops occur.

6.3 Case 3: Call Drop Due to Antenna SystemProblemDescription:A new BTS3012 is deployed at a site and the cellconfiguration is S2/2/2. Afterthe BTS3012 is put intooperation, the number of TCH call drops in cell1 and cell 2 inbusyhours reaches 20 and the number of SDCCH call drops reaches 1,000. These counters in cell3are normal.

Cause analysis and handling:According to the analysis of the traffic measurement results ofTRX-level radio link performance in busy hours, the number of abnormal radio linkson bothTRX 3 (TRX 2 and TRX3 are configured for cell 1) and TRX 7 (TRX6 and TRX 7 areconfigured for cell 2) is great. TRX 3 and TRX 7are the second TRX in cell 1 andcell 2respectively; therefore, they are connected to the TXB channel of theDDPU in thecorresponding cell. The jumpers of the two non-main BCCH TRXs may be misconnected.According to the analysis of the traffic measurement results related to the uplink anddownlink balance performance, the proportions of the TRX 3 in cell 1 and TRX7 in cell 2atlevel 1, level 2, and level3 are large, which indicates that the downlink loss istoo great andthe downlink transmit power is toosmall. Because TRX 2 (main BCCH TRX) in cell1 andTRX 6 (main BCCH TRX) incell 2 transmit the signalthrough the TXA port of the DDPU inthe sector independently. When the call is assigned on thechannel in the non BCCH TRX, thetransmit power decreases sharply and incurs the call drop due to theinverse transmission ofTRX 3 and TRX 7. After the wrong connection between TRX 3 and TRX 7 isadjusted, thenumber of call drops on the TCH andthe SDCCH in two cells isnormal.

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 24 of 26

INCLUDEPICTURE "http://htmlimg3.scribdassets.com/5n57knwwcg12euv6/images/24-e850fb82cb.jpg" \* MERGEFORMATINET

INCLUDEPICTURE "http://htmlimg3.scribdassets.com/5n57knwwcg12euv6/images/24-e850fb82cb.jpg" \* MERGEFORMATINET

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNAL6.4 Case 4: Call Drop Due to TransmissionProblemDescription:At a certain site, the MOTO BTS isreplaced with Huawei BTS and the cellconfiguration is S2/2/2. At the night of the replacement, calls are made normally and drivetests show thatall performance counters are normal. The traffic measurement results withinameasurement period of 15 minutes show that MS-originated and MS-terminated calls aremade normally and handovers are performed normally. After a week of operation, the trafficmeasurement results show that the value of the counter SDCCH Seizure Request is notnormal: The maximum number of SDCCH seizure requests reaches 9,000, the number ofSuccessful SDCCH Seizure Requests is over 7,000, and the number of Failed SDCCHSeizures due to Busy SDCCH is over 900.Compared with the similar SDCCH counters, theTCH traffic volume is small and the TCH call droprate is high.

Cause analysis and handling:According to the check of the hardware on site, makinga callis difficult on site. In addition, somesubscribers complain that it is difficult to make callsafterthe replacement. After obtaining theconsent from the customer, the on-siteengineer powersoff the BTS and loads the data again. Duringthe initialization of the BTS, a message isdisplayed, indicating that the process is disrupted and thatthe communication expires. Someparameters of the BTS cannot be initialized. The BTS hardware is normal and the cableconnections are proper.Before the replacement, the transmission isnormal. After the replacement, most of thetransmission cables are the original ones. Huawei engineers replace only the transmissioncable between the transmission equipment room and the Huawei BSC and use anew E1connector to fix the DDF transmission cable to theE1 port on topof the BTS cabinet. Thepossible cause is that the E1connector is made improperly. In this case, the transmission biterror rate is high and the BTScannot be completely initialized. As a result, when a subscribermakes a call, assigninga TCH is difficult. A detailed check shows that theE1 connector ontop of the BTS cabinet ismade improperly. After a proper E1 connector is used, the problemis solved.

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 25 of 26

INCLUDEPICTURE "http://htmlimg2.scribdassets.com/5n57knwwcg12euv6/images/25-212ff0b5f5.jpg" \* MERGEFORMATINET

GSMBSSNetworkKPI(SDCCHCallDropRate)OptimizationManualINTERNAL7Feedback Form for SDCCH CallDrop RateIf the SDCCH call drop rate ishigh and technical support is required, you need tofill in thefollowing form.

CheckItemRemarksPurposeSoftwareversionSoftwareversions of the BSC andBTSCheck whether the software version isfaulty.Dataconfiguration*.datfileCheckthenetworkoptimizationparametersandpower configuration.AlarminformationHardware, clock, and transmissionalarms (self-check)Check whether these alarms are generated inthecell. Clear the alarms if they are generated.TrafficmeasurementCauseforcalldropMeasureSDCCHcalldrops.TrafficmeasurementTraffic measurement results relatedto the voice quality and thebalancebetween uplink and downlinkCheck whether interference and imbalancebetweenuplink and downlink exist.SignalingRSLsignalingtracingdataCheckthecausesforcalldrops.DTdata*.log(*.cellsite)or*.antfileBasedontheDTdata,determinewhetherinterference or coverage problems exist.OthersEngineeringparametertableandelectronic mapCheck the geographical information through theNastar software.

2011-8-4HuaweiProprietaryandConfidentialCopyright Huawei Technologies Co.,LtdPage 26 of 26

INCLUDEPICTURE "http://htmlimg2.scribdassets.com/5n57knwwcg12euv6/images/26-242d83af40.jpg" \* MERGEFORMATINET

INCLUDEPICTURE "http://htmlimg2.scribdassets.com/5n57knwwcg12euv6/images/26-242d83af40.jpg" \* MERGEFORMATINET