蜂窝无线通信系统的研究英文翻译Word文档下载推荐.docx
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蜂窝无线通信系统的研究英文翻译Word文档下载推荐.docx
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题目蜂窝无线通信系统的研究
学生姓名杨迪
专业班级通信工程
学号P0*******
院(系)电子信息工程学院
指导教师(职称)杨洋
RESEARCHOFCELLULARWIRELESSCOMMUNATIONSYSTEM
一:
Conception
AbstractCellularsystemsisalsocalledthe"
village"
system.Isalltheareascoveredbydividedintoseveralvillage,eachdistricttheradiusofthevisualuserdistributiondensityin1~10kmorso.Setupabasestationineverycommunityserviceforuserswithinthescopeofthisarea.Andthroughthedistrictdivisiontofurtherimprovethesystemcapacity.Thissystembymobileservicesswitchingcenter(MSC),basestation(BS)equipmentandmobilestation(MS)(theuserequipment)andtheexchangecentertothebasestationofatransmissionline,asshowninthefigurebelow.Atpresentintheoperationofthe900MHZ(TACS)firstgenerationmobilecommunicationsystemsimulationsystemandthesecondgenerationmobilecommunication(GSM)digitalsystembelongtothiscategory.Isthemovementofthemobilestationexchangecenterandthepublictelephonenetwork(PSTN)iswhatweusuallycalltelephonenetworkislinkedtogether,betweenthemobileswitchingcenterisresponsiblefortheconnectionbetweenthebasestationcommunication,callprocess,themobilestation(suchasmobilephones)andsubordinatetothebasestationtoestablishcontact,bythebasestationconnectedtothemobileswitchingcenteragain,finallyaccesstothepublictelephonenetwork.
Cellularcommunicationsystemsallowalargenumberofmobileuserstoseamlesslyandsimultaneouslycommunicatetowirelessmodemsatfixedbasestationsusingalimitedamountofradiofrequency(RF)spectrum.TheRFtransmissionsreceivedatthebasestationsfromeachmobilearetranslatedtobaseband,ortoawidebandmicrowavelink,andrelayedtomobileswitchingcenters(MSC),whichconnectthemobiletransmissionswiththePublicSwitchedTelephoneNetwork(PSTN).Similarly,communicationsfromthePSTNaresenttothebasestation,wheretheyaretransmittedtothemobile.Cellularsystemsemployeitherfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),codedivisionmultipleaccess(CDMA),orspatialdivisionmultipleaccess(SDMA).
二:
Introduction
Awidevarietyofwirelesscommunicationsystemshavebeendevelopedtoprovideaccesstothecommunicationsinfrastructureformobileorfixedusersinamyriadofoperatingenvironments.Mostoftoday’swirelesssystemsarebasedonthecellularradioconcept.Cellularcommunicationsystemsallowalargenumberofmobileuserstoseamlesslyandsimultaneouslycommunicatetowirelessmodemsatfixedbasestationsusingalimitedamountofradiofrequency(RF)spectrum.TheRFtransmissionsreceivedatthebasestationsfromeachmobilearetranslatedtobaseband,ortoawidebandmicrowavelink,andrelayedtomobileswitchingcenters(MSC),whichconnectthemobiletransmissionswiththePublicSwitchedTelephoneNetwork(PSTN).Similarly,communicationsfromthePSTNaresenttothebasestation,wheretheyaretransmittedtothemobile.Cellularsystemsemployeitherfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),codedivisionmultipleaccess(CDMA),orspatialdivisionmultipleaccess(SDMA).
Wirelesscommunicationlinksexperiencehostilephysicalchannelcharacteristics,suchastime-varyingmultipathandshadowingduetolargeobjectsinthepropagationpath.Inaddition,theperformanceofwirelesscellularsystemstendstobelimitedbyinterferencefromotherusers,andforthatreason,itisimportanttohaveaccuratetechniquesformodelinginterference.Thesecomplexchannelconditionsaredifficulttodescribewithasimpleanalyticalmodel,althoughseveralmodelsdoprovideanalyticaltractabilitywithreasonableagreementtomeasuredchanneldata.However,evenwhenthechannelismodeledinananalyticallyelegantmanner,inthevastmajorityofsituationsitisstilldifficultorimpossibletoconstructanalyticalsolutionsforlinkperformancewhenerrorcontrolcoding,equalization,diversity,andnetworkmodelsarefactoredintothelinkmodel.Simulationapproaches,therefore,areusuallyrequiredwhenanalyzingtheperformanceofcellularcommunicationlinks.
Likewirelesslinks,thesystemperformanceofacellularradiosystemismosteffectivelymodeledusingsimulation,duetothedifficultyinmodelingalargenumberofrandomeventsovertimeandspace.Theserandomevents,suchasthelocationofusers,thenumberofsimultaneoususersinthesystem,thepropagationconditions,interferenceandpowerlevelsettingsofeachuser,andthetrafficdemandsofeachuser,combinetogethertoimpacttheoverallperformanceseenbyatypicaluserinthecellularsystem.Theaforementionedvariablesarejustasmallsamplingofthemanykeyphysicalmechanismsthatdictatetheinstantaneousperformanceofaparticularuseratanytimewithinthesystem.Thetermcellularradiosystem,therefore,referstotheentirepopulationofmobileusersandbasestationsthroughoutthegeographicservicearea,asopposedtoasinglelinkthatconnectsasinglemobileusertoasinglebasestation.Todesignforaparticularsystem-levelperformance,suchasthelikelihoodofaparticularuserhavingacceptableservicethroughoutthesystem,itisnecessarytoconsiderthecomplexityofmultipleusersthataresimultaneouslyusingthesystemthroughoutthecoveragearea.Thus,simulationisneededtoconsiderthemulti-usereffectsuponanyoftheindividuallinksbetweenthemobileandthebasestation.
Thelinkperformanceisasmall-scalephenomenon,whichdealswiththeinstantaneouschangesinthechanneloverasmalllocalarea,orsmalltimeduration,overwhichtheaveragereceivedpowerisassumedconstant.Suchassumptionsaresensibleinthedesignoferrorcontrolcodes,equalizers,andothercomponentsthatservetomitigatethetransienteffectscreatedbythechannel.However,inordertodeterminetheoverallsystemperformanceofalargenumberofusersspreadoverawidegeographicarea,itisnecessarytoincorporatelarge-scaleeffectssuchasthestatisticalbehaviorofinterferenceandsignallevelsexperiencedbyindividualusersoverlargedistances,whileignoringthetransientchannelcharacteristics.Onemaythinkoflink-levelsimulationasbeingavernieradjustmentontheperformanceofacommunicationsystem,andthesystem-levelsimulationasbeingacoarse,yetimportant,approximationoftheoveralllevelofqualitythatanyusercouldexpectatanytime.
Cellularsystemsachievehighcapacity(e.g.,servealargenumberofusers)byallowingthemobilestationstoshare,orreuseacommunicationchannelindifferentregionsofthegeographicservicearea.Channelreuseleadstoco-channelinterferenceamonguserssharingthesamechannel,whichisrecognizedasoneofthemajorlimitingfactorsofperformanceandcapacityofacellularsystem.Anappropriateunderstandingoftheeffectsofco-channelinterferenceonthecapacityandperformanceisthereforerequiredwhendeployingcellularsystems,orwhenanalyzinganddesigningsystemmethodologiesthatmitigatetheundesiredeffectsofco-channelinterference.Theseeffectsarestronglydependentonsystemaspectsofthecommunicationsystem,suchasthenumberofuserssharingthechannelandtheirlocations.Otheraspects,morerelatedtothepropagationchannel,suchaspathloss,shadowfading(orshadowing),andantennaradiationpatternsarealsoimportantinthecontextofsystemperformance,sincetheseeffectsalsovarywiththelocationsofparticularusers.Inthischapter,wewilldiscusstheapplicationofsystem-levelsimulationintheanalysisoftheperformanceofacellularcommunicationsystemundertheeffectsofco-channelinterference.Wewillanalyzeasimplemultiple-usercellularsystem,includingtheantennaandpropagationeffectsofatypicalsystem.Despitethesimplicityoftheexamplesystemconsideredinthischapter,theanalysispresentedcaneasilybeextendedtoincludeotherfeaturesofacellularsystem.
三:
CellularRadioSystem
System-LevelDescription:
CellularsystemsprovidewirelesscoverageoverageographicserviceareabydividingthegeographicareaintosegmentscalledcellsasshowninFigure2-1.Theavailablefrequencyspectrumisalsodividedintoanumberofchannelswithagroupofchannelsassignedtoeachcell.Basestationslocatedineachcellareequippedwithwirelessmodemsthatcancommunicatewithmobileusers.Radiofrequencychannelsusedinthetransmissiondirectionfromthebasestationtothemobilearereferredtoasforwardchannels,whilechannelsusedinthedirectionfromthemobiletothebasestationarereferredtoasreversechannels.Theforwardandreversechannelstogetheridentifyaduplexcellularchannel.Whenfrequencydivisionduplex(FDD)isused,theforwardandreversechannelsaresplitinfrequency.Alternatively,whentimedivisionduplex(TDD)isused,theforwardandreversechannelsareonthesamefrequency,butusedifferenttimeslotsfortransmission.
Figure2-1Basicarchitectureofacellularcommunicationssystem
High-capacitycellularsystemsemployfrequencyreuseamongcells.Thisrequiresthatco-channelcells(cellssharingthesamefrequency)aresufficientlyfarapartfromeachothertomitigateco-channelinterference.ChannelreuseisimplementedbycoveringthegeographicserviceareawithclustersofNcells,asshowninFigure2-2,whereNisknownastheclustersize.
Figure2-2Cellclustering:
Depictionofathree-cellreusepattern
TheRFspectrumavailableforthegeographicserviceareaisassignedtoeachcluster,suchthatcellswithinaclusterdonotshareanychannel.IfMchannelsmakeup
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