TechMafia

Techmafia

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%

Search web

Frequency & NeighborPlanning

Telecom TechnologiesKnow More about 2GKnow more about 3GWi MaX

Videos on GSM NEWS andTechnologySitemap

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.

StartDownloadConvertAnyFiletoaPDF.GettheFreeFromDoctoPdfApp!

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.

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

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

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.

Ifawidefrequencyrepeaterisusedandthegainissettoagreatvalue,stronginterferencemaybecaused.Asaresult,thenetworkqualityisadverselyaffectedandtheTCHcalldroprateincreases.

Sign in | Recent Site Activity | Report Abuse | Print Page | Powered By Google Sites

Comments

Youdonothavepermissiontoaddcomments.