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1、SIMULATIONOFACELLULARRADIOSYSTEM———takenfrom《PrenticeHall-PrinciplesOfCommunicationSystemsSimulationWithWirelessAplications》page672-6761.IntroductionAwidevarietyofwirelesscommunicationsystemshavebeendevelopedtoprovideaccesstothecommunicationsinfrastructure
2、formobileorfixedusersinamyriadofoperatingenvironments.Mostoftoday'swirelesssystemsarebasedonthecellularradioconcept.Cellularcommunicationsystemsallowalargenumberofmobileuserstoseamlesslyandsimultaneouslycommunicatetowirelessmodemsatfixedbasestationsusingal
3、imitedamountofradiofrequency(RF)spectrum.TheRFtransmissionsreceivedatthebasestationsfromeachmobilearetranslatedtobaseband,ortoawidebandmicrowavelink,andrelayedtomobileswitchingcenters(MSC),whichconnectthemobiletransmissionswiththePublicSwitchedTelephoneNet
4、work(PSTN).Similarly,communicationsfromthePSTNaresenttothebasestation,wheretheyaretransmittedtothemobile.Cellularsystemsemployeitherfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),codedivisionmultipleaccess(CDMA),orspatialdivisionmul
5、tipleaccess(SDMA).Wirelesscommunicationlinksexperiencehostilephysicalchannelcharacteristics,suchastime-varyingmultipathandshadowingduetolargeobjectsinthepropagationpath.Inaddition,theperformanceofwirelesscellularsystemstendstobelimitedbyinterferencefromoth
6、erusers,andforthatreason,itisimportanttohaveaccuratetechniquesformodelinginterference.Thesecomplexchannelconditionsaredifficulttodescribewithasimpleanalyticalmodel,althoughseveralmodelsdoprovideanalyticaltractabilitywithreasonableagreementtomeasuredchannel
7、data.However,evenwhenthechannelismodeledinananalyticallyelegantmanner,inthevastmajorityofsituationsitisstilldifficultorimpossibletoconstructanalyticalsolutionsforlinkperformancewhenerrorcontrolcoding,equalization,diversity,andnetworkmodelsarefactoredintoth
8、elinkmodel.Simulationapproaches,therefore,areusuallyrequiredwhenanalyzingtheperformanceof7cellularcommunicationlinks.Likewirelesslinks,thesystemperformanceofacellularradiosystemismosteffectivelymodeledusingsi
