无线通信原理第二章

2020/6/7,1,TheCellularConcept：SystemDesignFundamentals,2020/6/7,2,CellularNetworks,2020/6/7,3,Cellshape,Circle:Equilateraltriangle:Square:Hexagon:,2020/6/7,4,Cellularcoveragerepresentation,2020/6/7,5,Macrocelllarge,coveringawiderangeofseveralhundredkmtotenkmmostlydeployedinruralandsparselypopulatedareasMicrocellmediumcell,coverageareasmallerthaninmacrocellsrangeofseveralhundredmetrestoacoupleofmetresdeployedmostlyincrowdedareas,stadiums,shoppingmallsPicocellsmall,coveringaverysmallarearangeofseveraltensofmetreslowpowerantennas,indoor,Thesizeofacell,2020/6/7,6,2020/6/7,7,Basestationtransmitters,Inhexagonalcells,basestationstransmittersareeither:centre-excited,basestationisatthecentreofthecelledge-excited,basestationat3ofthe6cellvertices,centre-excited,edge-excited,2020/6/7,8,Cellularcoveragerepresentation,Ccanbeusedasameasureofcapacity,2020/6/7,9,Amobilecommunicationsystemusesafrequencyreusefactorof1/7and420channelsavailable.If21channelsareallocatedascontrolchannels,assumeatrafficchannelsupports8users,computethenumberofsimultaneoususerspercellChannelsavailableforallocation=420-21=399ChannelNumberofacell=399/7=57Numberofsimultaneoususerspercell=8x57=456,Example1,2020/6/7,10,Methodoflocatingco-channelcells,2020/6/7,11,ChannelAssignmentStrategies,TwoassignmentapproachesFixedandstatic(mostcommon)DynamicFixedchannelassignmentallchannelsinacellcouldbeinuseallthetimenewcallsarethenblocked(nochannelsleft)maybesolvedbyborrowingsparechannelsfromnearbycells,2020/6/7,12,DynamicchannelassignmentMSCallocatesfrequencieswhenacallismadeProvideshighchannelutilizationTodothisitneedsreal-timeinformationonchanneloccupancytrafficdistributionradiosignalstrengthindication(RSSI)highcomputationalloadandincreasedstorage,2020/6/7,13,Handoff,ProvidescontinuityofcommunicationacrosscellsDifficultydroppingacallbeforereconnectingisunacceptabledifferentcellsusedifferentfrequenciesmobilephoneusersusuallymovefromplacetoplaceandveryquickly,2020/6/7,14,HandoffProcess,ReceivedsignalweakensasmobilemovesoutofcellCellsiteatsomepointrequestshandofftocellwithstrongersignalstrengthMSCswitchescalltonewcellafterallocatingchannels.,2020/6/7,15,HandoffProcess,HandoffmustnotbetoofrequentorsystemiskeptbusyservicinghandoffrequestshandoffthresholdissetslightlystrongerMinimumusablesignallevelisnormallysettobebetween-90dBmand-100dBm,2020/6/7,16,ChoosingHandoffMargins,Handoffmargin=Prhandoff-PrminimumusableIfistoolargeunnecessaryhandoffwilloccur,burdeningtheMSCIfistoosmall,theremaybeinsufficienttimetocompletethehandoffbeforeacallislostduetoweaksignalsThereforeischosencarefully,2020/6/7,17,SettingHandoffThresholds,2020/6/7,18,Handoffindifferentsystem(p64),1GsignalstrengthmeasurementsaremadebythebasestationsandsupervisedbytheMSCGSMMAHOhandoffdecisionsaremobileassistedCDMApilotchannel,softhandoff,2020/6/7,19,TypesofHandoffs,Hardhandoff:“breakbeforemake”connection,HardHandoffbetweentheMSandBSs,2020/6/7,20,TypesofHandoffs,Softhandoff:“make-before-break”connection.Mobiledirectedhandoff.Multiwaysandsofterhandoffs,SoftHandoffbetweenMSandBSTs,2020/6/7,21,InterferenceandSystemCapacity,2020/6/7,22,SixEffectiveInterferingCellsofCell1,2020/6/7,23,Co-channelreuseratioQ,2020/6/7,24,7-cellreusepattern,2020/6/7,25,12-cellreusepattern,2020/6/7,26,19-cellreusepattern,2020/6/7,27,Co-channelreuseratiovs.frequencyreusepattern,2020/6/7,28,Co-channelreuseratiovs.frequencyreusepattern,2020/6/7,29,Propagationmodel,2020/6/7,30,Co-channelinterferenceratio,2020/6/7,31,Example2,2020/6/7,32,Moreexactgeometrylayout,2020/6/7,33,Closelyapproximatelyas,2020/6/7,34,Adjacentchannelinterference,2020/6/7,35,TrunkingandGradeofService(GOS),2020/6/7,36,GradeofService(GOS),2020/6/7,37,AboutErlang,2020/6/7,38,ErlangBformula,whereCisthenumberoftrunkedchannelsofferedbyatrunkedradiosystemandAisthetotalofferedtraffic.,2020/6/7,39,Trunkedmobilenetworkprovidecellularserviceinthisarea.Systemhas394cellswith19channelseach.Findthenumberofusersthatcanbesupportedat2%blockingifeachuseraveragestwocallsperhouratanaveragecalldurationofthreeminutes.Computethetotalnumberofsubscribersthatcanbesupportedbythissystem.Probabilityofblocking=2%=0.02Numberofchannelspercellusedinthesystem,C=19Trafficintensityperuser,Au=H=2x(3/60)=0.1ErlangsfromtheErlangBchart,thetotalcarriedtraffic,A,isobtainedas12Erlangs.Therefore,thenumberofusersthatcanbesupportedpercellisU=AIAu=12/0.1=120Sincethereare394cells,thetotalnumberofsubscribersthatcanbesupportedbySystemAisequalto120 x394=47280,Example3,2020/6/7,40,OftenlargecellsneedtobesplitintosmalleronesbecausethepopulationofusersinthebigcellhasincreasedbeyondwhatitcansupportCellsplittingincreasessystemcapacityIsusedinhighdensitysubscriberareasResultstoincreasedcosts(eg.newbasestations),ImprovingCapacityinCellularSystem,2020/6/7,41,Cellsplitting,cellsplittingistheprocessofsubdividingacongestedcellintosmallercells.eachwithitsownbasestationandacorrespondingreductioninantennaheightandtransmitterpower.Cellsplittingincreasesthecapacityofacellularsystemsinceitincreasesthenumberoftimesthatchannelsarereused.Theincreasednumberofcellswouldincreasethenumberofclusterswhichinturnwouldincreasethenumberofchannels,andcapacity.Cellsplittingallowsasystemtogrowbyreplacinglargecellswithsmallercells,whilenotupsettingthechannelallocationschemerequiredtomaintaintheminimumco-channelreuseratioQbetweenco-channelcells,2020/6/7,42,2020/6/7,43,2020/6/7,44,CellSplitting,2020/6/7,45,Sectoring,2020/6/7,46,Acellularsystem:anaveragecalllaststwominutes,andtheprobabilityofblockingistobenomorethan1%.Everysubscribermakesonecallperhour,onaverage.Ifthereareatotalof395trafficchannelsforaseven-cellreusesystem,therewillbeabout57trafficchannelspercell.AssumethatblockedcallsareclearedsotheblockingisdescribedbytheErlangBdistribution.FromtheErlangBdistribution,itcanbefoundthattheunsectoredsystemmayhandle44.2Erlangsor1326callsperhour.Ifemploying120sectoring,thereareonly19channelsperantennasector(57/3antennas).Forthesameprobabilityofblockingandaveragecalllength,itcanbefoundfromtheErlangBdistributionthatea