无线通信与网络chap10ppt课件

.,CellularWirelessNetworks,Chapter10,CellularNetworkOrganization,Usemultiplelow-powertransmitters(100Worless)AreasdividedintocellsEachservedbyitsownantennaServedbybasestationconsistingoftransmitter,receiver,andcontrolunitBandoffrequenciesallocatedCellssetupsuchthatantennasofallneighborsareequidistant(hexagonalpattern),FrequencyReuse,AdjacentcellsassigneddifferentfrequenciestoavoidinterferenceorcrosstalkObjectiveistoreusefrequencyinnearbycells10to50frequenciesassignedtoeachcellTransmissionpowercontrolledtolimitpoweratthatfrequencyescapingtoadjacentcellsTheissueistodeterminehowmanycellsmustintervenebetweentwocellsusingthesamefrequency,ApproachestoCopewithIncreasingCapacity,AddingnewchannelsFrequencyborrowingfrequenciesaretakenfromadjacentcellsbycongestedcellsCellsplittingcellsinareasofhighusagecanbesplitintosmallercellsCellsectoringcellsaredividedintoanumberofwedge-shapedsectors,eachwiththeirownsetofchannelsMicrocellsantennasmovetobuildings,hills,andlampposts,CellularSystemOverview,CellularSystemsTerms,BaseStation(BS)includesanantenna,acontroller,andanumberofreceiversMobiletelecommunicationsswitchingoffice(MTSO)connectscallsbetweenmobileunitsTwotypesofchannelsavailablebetweenmobileunitandBSControlchannelsusedtoexchangeinformationhavingtodowithsettingupandmaintainingcallsTrafficchannelscarryvoiceordataconnectionbetweenusers,StepsinanMTSOControlledCallbetweenMobileUsers,MobileunitinitializationMobile-originatedcallPagingCallacceptedOngoingcallHandoff,AdditionalFunctionsinanMTSOControlledCall,CallblockingCallterminationCalldropCallsto/fromfixedandremotemobilesubscriber,MobileRadioPropagationEffects,SignalstrengthMustbestrongenoughbetweenbasestationandmobileunittomaintainsignalqualityatthereceiverMustnotbesostrongastocreatetoomuchcochannelinterferencewithchannelsinanothercellusingthesamefrequencybandFadingSignalpropagationeffectsmaydisruptthesignalandcauseerrors,HandoffPerformanceMetrics,CellblockingprobabilityprobabilityofanewcallbeingblockedCalldroppingprobabilityprobabilitythatacallisterminatedduetoahandoffCallcompletionprobabilityprobabilitythatanadmittedcallisnotdroppedbeforeitterminatesProbabilityofunsuccessfulhandoffprobabilitythatahandoffisexecutedwhilethereceptionconditionsareinadequate,HandoffPerformanceMetrics,HandoffblockingprobabilityprobabilitythatahandoffcannotbesuccessfullycompletedHandoffprobabilityprobabilitythatahandoffoccursbeforecallterminationRateofhandoffnumberofhandoffsperunittimeInterruptiondurationdurationoftimeduringahandoffinwhichamobileisnotconnectedtoeitherbasestationHandoffdelaydistancethemobilemovesfromthepointatwhichthehandoffshouldoccurtothepointatwhichitdoesoccur,HandoffStrategiesUsedtoDetermineInstantofHandoff,RelativesignalstrengthRelativesignalstrengthwiththresholdRelativesignalstrengthwithhysteresisRelativesignalstrengthwithhysteresisandthresholdPredictiontechniques,PowerControl,DesignissuesmakingitdesirabletoincludedynamicpowercontrolinacellularsystemReceivedpowermustbesufficientlyabovethebackgroundnoiseforeffectivecommunicationDesirabletominimizepowerinthetransmittedsignalfromthemobileReducecochannelinterference,alleviatehealthconcerns,savebatterypowerInSSsystemsusingCDMA,itsdesirabletoequalizethereceivedpowerlevelfromallmobileunitsattheBS,TypesofPowerControl,Open-looppowercontrolDependssolelyonmobileunitNofeedbackfromBSNotasaccurateasclosed-loop,butcanreactquickertofluctuationsinsignalstrengthClosed-looppowercontrolAdjustssignalstrengthinreversechannelbasedonmetricofperformanceBSmakespoweradjustmentdecisionandcommunicatestomobileoncontrolchannel,TrafficEngineering,Ideally,availablechannelswouldequalnumberofsubscribersactiveatonetimeInpractice,notfeasibletohavecapacityhandleallpossibleloadForNsimultaneoususercapacityandLsubscribersLNblockingsystem,BlockingSystemPerformanceQuestions,Probabilitythatcallrequestisblocked?Whatcapacityisneededtoachieveacertainupperboundonprobabilityofblocking?Whatistheaveragedelay?Whatcapacityisneededtoachieveacertainaveragedelay?,TrafficIntensity,Loadpresentedtoasystem:=meanrateofcallsattemptedperunittimeh=meanholdingtimepersuccessfulcallA=averagenumberofcallsarrivingduringaverageholdingperiod,fornormalized,FactorsthatDeterminetheNatureoftheTrafficModel,MannerinwhichblockedcallsarehandledLostcallsdelayed(LCD)blockedcallsputinaqueueawaitingafreechannelBlockedcallsrejectedanddroppedLostcallscleared(LCC)userwaitsbeforeanotherattemptLostcallsheld(LCH)userrepeatedlyattemptscallingNumberoftrafficsourcesWhethernumberofusersisassumedtobefiniteorinfinite,First-GenerationAnalog,AdvancedMobilePhoneService(AMPS)InNorthAmerica,two25-MHzbandsallocatedtoAMPSOnefortransmissionfrombasetomobileunitOnefortransmissionfrommobileunittobaseEachbandsplitintwotoencouragecompetitionFrequencyreuseexploited,AMPSOperation,SubscriberinitiatescallbykeyinginphonenumberandpressessendkeyMTSOverifiesnumberandauthorizesuserMTSOissuesmessagetouserscellphoneindicatingsendandreceivetrafficchannelsMTSOsendsringingsignaltocalledpartyPartyanswers;MTSOestablishescircuitandinitiatesbillinginformationEitherpartyhangsup;MTSOreleasescircuit,freeschannels,completesbilling,DifferencesBetweenFirstandSecondGenerationSystems,Digitaltrafficchannelsfirst-generationsystemsarealmostpurelyanalog;second-generationsystemsaredigitalEncryptionallsecondgenerationsystemsprovideencryptiontopreventeavesdroppingErrordetectionandcorrectionsecond-generationdigitaltrafficallowsfordetectionandcorrection,givingclearvoicereceptionChannelaccesssecond-generationsystemsallowchannelstobedynamicallysharedbyanumberofusers,MobileWirelessTDMADesignConsiderations,Numberoflogicalchannels(numberoftimeslotsinTDMAframe):8Maximumcellradius(R):35kmFrequency:regionaround900MHzMaximumvehiclespeed(Vm):250km/hrMaximumcodingdelay:approx.20msMaximumdelayspread(m):10sBandwidth:Nottoexceed200kHz(25kHzperchannel),StepsinDesignofTDMATimeslot,GSMNetworkArchitecture,MobileStation,MobilestationcommunicatesacrossUminterface(airinterface)withbasestationtransceiverinsamecellasmobileunitMobileequipment(ME)physicalterminal,suchasatelephoneorPCSMEincludesradiotransceiver,digitalsignalprocessorsandsubscriberidentitymodule(SIM)GSMsubscriberunitsaregenericuntilSIMisinsertedSIMsroam,notnecessarilythesubscriberdevices,BaseStationSubsystem(BSS),BSSconsistsofbasestationcontrollerandoneormorebasetransceiverstations(BTS)EachBTSdefinesasinglecellIncludesradioantenna,radiotransceiverandalinktoabasestationcontroller(BSC)BSCreservesradiofrequencies,manageshandoffofmobileunitfromonecelltoanotherwithinBSS,andcontrolspaging,NetworkSubsystem(NS),NSprovideslinkbetweencellularnetworkandpublicswitchedtelecommunicationsnetworksControlshandoffsbetweencellsindifferentBSSsAuthenticatesusersandvalidatesaccountsEnablesworldwideroamingofmobileusersCentralelementofNSisthemobileswitchingcenter(MSC),MobileSwitchingCenter(MSC)Databases,Homelocationregister(HLR)databasestoresinformationabouteachsubscriberthatbelongstoitVisitorlocationregister(VLR)databasemaintainsinformationaboutsubscriberscurrentlyphysicallyintheregionAuthenticationcenterdatabase(AuC)usedforauthenticationactivities,holdsencryptionkeysEquipmentidentityregisterdatabase(EIR)keepstrackofthetypeofequipmentthatexistsatthemobilestation,TDMAFormatTimeSlotFields,TrailbitsallowsynchronizationoftransmissionsfrommobileunitsEncryptedbitsencrypteddataStealingbit-indicateswhetherblockcontainsdataorisstolenTrainingsequenceusedtoadaptparametersofreceivertothecurrentpathpropagationcharacteristicsStrongestsignalselectedincaseofmultipathpropagationGuardbitsusedtoavoidoverlappingwithotherbursts,GSMSpeechSignalProcessing,GSMSignalingProtocolArchitecture,FunctionsProvidedbyProtocols,ProtocolsabovethelinklayeroftheGSMsignalingprotocolarchitectureprovidespecificfunctions:RadioresourcemanagementMobilitymanagementConnectionmanagementMobileapplicationpart(MAP)BTSmanagement,AdvantagesofCDMACellular,Frequencydiversityfrequency-dependenttransmissionimpairmentshavelesseffectonsignalMultipathresistancechippingcodesusedforCDMAexhibitlowcrosscorrelationandlowautocorrelationPrivacyprivacyisinherentsincespreadspectrumisobtainedbyuseofnoise-likesignalsGracefuldegradationsystemonlygraduallydegradesasmoreusersaccessthesystem,DrawbacksofCDMACellular,Self-jammingarrivingtransmissionsfrommultipleusersnotalignedonchipboundariesunlessusersareperfectlysynchronizedNear-farproblemsignalsclosertothereceiverarereceivedwithlessattenuationthansignalsfartherawaySofthandoffrequiresthatthemobileacquiresthenewcellbeforeitrelinquishestheold;thisismorecomplexthanhardhandoffusedinFDMAandTDMAschemes,MobileWirelessCDMADesignConsiderations,RAKEreceiverwhenmultipleversionsofasignalarrivemorethanonechipintervalapart,RAKEreceiverattemptstorecoversignalsfrommultiplepathsandcombinethemThismethodachievesbetterperformancethansimplyrecoveringdominantsignalandtreatingremainingsignalsasnoiseSoftHandoffmobilestationtemporarilyconnectedtomorethanonebasestationsimultaneously,PrincipleofRAKEReceiver,TypesofChannelsSupportedbyForwardLink,Pilot(channel0)-allowsthemobileunittoacquiretiminginformation,providesphasereferenceandprovidesmeansforsignalstrengthcomparisonSynchronization(channel32)-usedbymobilestationtoobtainidentificationinformationaboutcellularsystemPaging(channels1to7)-containmessagesforoneormoremobilestationsTraffic(channels8to31and33to63)theforwardchannelsupports55trafficchannels,ForwardTrafficChannelProcessingSteps,Speechisencodedatarateof8550bpsAdditionalbitsaddedforerrordetectionDatatransmittedin2-msblockswithforwarderrorcorrectionprovidedbyaconvolutionalencoderDatainterleavedinblockstoreduceeffectsoferrorsDatabitsarescrambled,servingasaprivacymask,ForwardTrafficChannelProcessingSteps(cont.),PowercontrolinformationinsertedintotrafficchannelDS-SSfunctionspreadsthe19.2kbpstoarateof1.2288Mbpsusingonerowof64x64Walshmatrix