How to Reduce Call Drops in a GSM Network - TechMafia
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Transcript of How to Reduce Call Drops in a GSM Network - TechMafia
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TechMafia
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More Telecom StuffWelcome to Telecom KnowdgeAll About GSM Technology
Frequency Planning for 2GHandover Success Rate KPIImprovementHow to Improve TCHAssignment Success RateHow to reduce Call Drops Ina GSM Network
GSM OptimizationImportant KPI's for GSMNetwork PerformanceKPI Optimization CasesRadio Network PlanningPrinciple
All About GSM Technology >
How to reduce Call Drops In aGSM Networkposted Oct 13, 2009, 12:53 AM by Gulzar Singh [ updated May 9,
2011, 1:13 PM ]
MeaningThe TCH call drop rate refers to the ratio of call drops tosuccessful TCH seizures after the BSC successfullyassigns TCHs to MSs. The TCH call drop rate can bemeasured from the following aspects:
TCH call drop rate (including handover)
TCH call drop rate (excluding handover)
The TCH call drop rate, one of the most significant KPIsfor telecom operators, is related to retainability. Itindicates the probability of call drops due to variousreasons after MSs access TCHs. A too high TCH call droprate adversely affects the user's experience.
Recommended Formulas
TCH call drop rate (including handover) = Number ofcall drops on TCH/(Number of successful TCH seizures(signaling channel) + Number of successful TCHseizures (TCH) + Number of successful TCH Seizures inTCH handovers (TCH)) x 100%
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TCH call drop rate (excluding handover) = Number ofcall drops on TCH/Number of successful TCH seizures(TCH) x 100%
FactorsThatAffecttheTCHCallDropRateAccordingtousercomplaintsandnetworkoptimizationexperience,themajorfactorsthataffecttheTCHcalldroprateareasfollows:
Hardwarefailure
Transmissionproblem
Versionupgrade
Parametersetting
Intranetworkandinternetworkinterference
Coverageproblem
Antennasystemproblem
Imbalancebetweenuplinkanddownlink
Repeaterproblem
1.1 HardwareFai lureWhenaTRXoracombinerisfaulty,seizingtheTCHbecomesdifficult,andthustheTCHcalldroprateincreases.
1.2 TransmissionProblem
TheTCHcalldroprateincreasesinthefollowingconditions:
The transmission quality on the A or Abis interface ispoor for various reasons.
Transmission links are unstable.
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1.3 VersionUpgradeAftertheBTSversionorBSCversionisupgraded,theBTSversionmaybeincompatiblewiththeBSCversion,andtheparametersandalgorithmsinthenewversionmaybechanged.Inthiscase,theTCHcalldroprateincreases.
1.4 ParameterSett ingThesettingsofsomeparametersontheBSCandMSCsidesmayaffecttheTCHcalldroprate.Ifthefollowingsituationsoccur,theTCHcalldropratemayincrease:
1.The parameters SACCH Multi-Frames and RadioLink Timeout are set to too small values.
2.TheparameterRXLEV_ACCESS_MIN is set to a toosmall value.
3.The parameter RACH Min.Access Level is set toa too small value.
4.TheparametersMin DL Power on HO Candidate Celland MinAccessLevelOffsetareinappropriatelyset.
5.ThelengthoftimerT3103(thistimerissettowaitforaHandoverCompletemessage)issettoatoosmallvalue.
6.ThelengthoftimerT3109(thistimerissettowaitforaReleaseIndicationmessage)issettoatoosmallvalue.
7.ThelengthoftimerT3111(thistimerspecifiestheconnectionreleasedelay)issettoatoosmallvalue.
8.ThelengthoftimerT305/T308issettoaninvalidortoogreatvalue.
9.TheparameterTCH Traffic Busy Threshold issettoatoosmallvalue.
10.TheparameterCall Reestablishment Forbidden isset to Yes.
11.Theparametersrelatedtoedgehandoverareinappropriatelyset.
12.TheparametersrelatedtoBQhandoverareinappropriatelyset.
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13.Theparametersrelatedtointerferencehandoverareinappropriatelyset.
14.Theparametersrelatedtoconcentriccellhandoverareinappropriatelyset.
15.Theparametersrelatedtopowercontrolareinappropriatelyset.
16.T200andN200aresettotoosmallvalues.
17.Someneighboringcellrelationsarenotconfigured.
18.TheparameterMAIOisinappropriatelyset.
19.TheparameterDisconnect Handover Protect Timeris set to a too small value.
20.TheparameterTR1N is set to a too small value.
21.TheparametersSoftwareParameter13 and MAX TA are setto too small values.
22.Ifarepeaterisused,theparameterDirectly MagnifierSite FlagissettoNo.
1.5 IntraNetworkandInterNetworkInterferenceIfinternetworkinterferenceandrepeaterinterferenceexist,orifsevereintranetworkinterferenceoccursbecauseoftightfrequencyreuse,calldropsmayoccuronTCHsbecauseofpoorQoS.ThisadverselyaffectstheTCHcalldroprate.
Thefollowingtypesofinterferencemayoccur:
1.Internetworkinterferencefromscramblersorprivatelyinstalledantennas
2.InterferencefromtheCDMAnetworkofChinaUnicom
3.Repeaterinterference
4.IntermodulationinterferencefromBTSs
5.Intranetworkcochannelandadjacentchannel
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interference
1.6 CoverageProblemThefollowingcoverageproblemsmayaffecttheTCHcalldroprate.
1.Discontinuouscoverage(blindareas)
ThevoicequalityattheedgeofanisolatedBTSispoorandcallscannotbehandedovertoothercells.Inthiscase,calldropsmayoccur.
In complex terrains such asmountainous regions, the signals areblocked and thus the transmission isdiscontinuous, leading to call drops.
2.Poorindoorcoverage
Densely distributed buildings and thickwalls cause great attenuation and lowindoor signal level, which causes calldrops.
3.Crosscoverage(isolatedBTS)
Theservingcellcausescrosscoverageduetovariousreasons(suchasexcesspower).AnMScannotbehandedovertoanothercellduetonosuitableneighboringcells.Inthiscase,thesignallevelbecomeslowandthevoicequalityoftheMSdeteriorates.Thus,calldropsoccur.
4.Insufficientcoverage
If the signal from an antenna is blockedor the BCCH TRX is faulty, call dropsmay occur because of discontinuouscoverage.
1.7 AntennaSystemProblem
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ThefollowingantennasystemproblemsmayaffecttheTCHcalldroprate
1.Ifthetransmitantennasoftwocellsareimproperlyconnected,theuplinksignallevelineachcellismuchlowerthanthedownlinksignallevelinthecell.Therefore,calldropsarelikelytooccuratplacesfarawayfromtheBTS.
2.Ifadirectionalcellhasmainanddiversityantennas,theBCCHandSDCCHofthecellmaybetransmittedfromdifferentantennas.Ifthetwoantennashavedifferentpitchanglesorazimuths,thecoverageareasofthetwoantennasaredifferent.Inthiscase,thefollowingresultmayoccur:AnMScanreceivetheBCCHsignalsfromoneantennawhenacallismade,theMScannotseizetheSDCCHtransmittedbytheotherantennaandthusacalldropoccurs.
3.Ifthefeederisdamaged,waterleaksinthefeeder,orthefeederandtheconnectorarenotsecurelyconnected,boththetransmitpowerandreceiversensitivityoftheantennaarereduced.Thus,calldropsmayoccur.
1.8 ImbalanceBetweenUpl inkandDownl inkThedifferencebetweentheuplinksignallevelandthedownlinksignallevelmaybegreatinthefollowingconditions:
ThetransmitpoweroftheBTSishigh.
Thetowermountedamplifier(TMA)orBTSamplifierdoesnotworkproperly.
Theantennaandtheconnectorarenotsecurelyconnected.
Asaresult,calldropsmayoccurattheedgeoftheBTScoveragearea.
1.9 RepeaterProblemIfacellisinstalledwitharepeater,BTScoverageproblemsmayoccurinthecasethattherepeaterisfaultyorthattheuplinkanddownlinkgainisinappropriatelyset.Therefore,theTCHcalldroprateincreases.
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Ifawidefrequencyrepeaterisusedandthegainissettoagreatvalue,stronginterferencemaybecaused.Asaresult,thenetworkqualityisadverselyaffectedandtheTCHcalldroprateincreases.
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