RadioNetworkOptimisation
2.9.1GSMRadioNetworkOptimisationProcess
Oncesomehundredsofsitesareonair,itbecomesnecessarytoperformoptimisationonthenetworkin
ordertomaximisebenefitswhileminimisingcapitalandoperationcostsforoperators.Thissection,in
fact,dealswithallaspectsofoptimisingaGSMnetworkstartingfromstandardoperationsandending
withspecifictrials,studiesandfine-tuning.Beforethenetworkiscommerciallylaunched,theradio
networkoptimisationprocessstartsandthencontinuesduringthelifeofthenetwork.
ThemainapplicationinGSMtechnologyismobiletelephony.Operatorsareworriedaboutthequality
perceivedbytheenduser.Theircompetitivenessreliesverycloselyonthisaspectinparallelwiththe
pricingpolicy.
GSMstandardsofferthepossibilityofmonitoringthenetworkbycomputingstatistics.Dependingon
thetypeofnetworkmanagementsystem,eitherintheBSCorintheBTS,eachcellreportsthousands
ofstatisticsaboutallrelevantbehaviours(numberofattempts,failures,successes,duringcall,handover,
setup,etc.).ThesestatisticsarereportedtotheNetworkManagementSystem(NMS)ascounters.To
facilitateinterpretationofthebehaviour,asetofkeyperformanceindicators(KPIs)isdefinedoutof
formulasusingpurecounters.EachoperatorchoosesitsownKPIsandsets,accordingtospecificcriteria,
someobjectivestobemetinordertoachieveagoodenduserperceptionoftheserviceofferedandalso
inordertobenchmarkonenetworkwithotheroperators.
Anotheraspectthatisimportantintheoptimisationphasedealswithdrivetests.Infact,whilestatistics
giveageneralideaofthecell’sbehaviouratacertainperiod,fieldmeasurementsgiveaoneinstantscenario
ofonearea’sbehaviourduringacall.Differenttoolscanbeusedtoperformdrivetests.Eachspecific
toolisabletoreportmeasurementssuchasMOS(meanopinionscore),FER(frameerasurerate)and
BER(biterrorrate)inadditiontostandardreportingatthesignallevel,qualityandsiteinformation(cell
identity,BCCH,mobileallocationlist,bestneighbours,etc.).
Statisticsanddrivetestsarethemainmethodsusedtomonitorthenetwork’sperformance.However,
otherspecificmethodscanalsobeused.
Tracingcatchesoneobject’sbehaviour(TRX,cell,BTSorBSC)duringacertainperiodandregarding
aspecificevent(SDCCHallocation,conversationphaseofavoicecall,etc.)orasetofsuccessfulevents
(IMSIattach,paging,callsetup,locationupdate,etc.).Alarmmonitoring,transmissionnetworkauditing
andnetworkswitchingsubsystem(NSS)performancefollow-uparealsoimportantinthesensethatthey
giveanideaofhardwareproblemsorparametererrors,whichdefinitelyaffecttheenduserperception
ofthenetwork.
Afterdeepanalysis,actionsarethentakentocorrectandimproveperformance.Alltheabove-described
methodshelptheoptimisationengineerstoidentifytheoriginoftheproblemfromtheofficewhile
applyingseveralanalysismethods.Anotheraspectis,however,veryimportant:fieldknowledge.Correct
sitere-engineeringisthebasisforagoodperformingnetwork.Frequencyplanningreviewisalsoakey
stepintheprocess.