Cellular Mobile Radio Systems.1998 .pdf

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1、1IntroductionThepotentialofcommunicatingwithmovingvehicleswithouttheuseofwirewassoonrecognizedfollowingtheinventionofradioequipmentbytheendofthenineteenthcenturyanditsdevelopmentinthebeginningofthetwentiethcentury[1.1,1.2].However,itisonlytheavailabil

2、ityofcompactandrelativelycheapradioequipmentwhichhasledtotherapidexpansionintheuseoflandmobileradiosystems.Landmobileradiosystemsarenowbecomingsopopular,forbothbusinessanddomesticuse,thattheavailablefrequencybandsarebecomingsaturatedwithoutmeetingeven

3、afractionoftheincreasingdemand.Togiveanexample,theestimatednumberofmobileradiosinusein1984wasabout540000withagrowthrateofabout10%perannumintheUK;estimatesofgrowthratesupto20%havebeenmadeforotherEuropeancountries[1.3].Usingthesefiguresleadstoestimateso

4、fapproximately2.5millionUKusersbytheendofthiscentury.Agrowthrateof20%annuallywouldleadtomorethan13millionusersworldwidebytheyear2000.Suchafigureiscomparabletothe11millionbusinessand18millionresidentialfixedtelephoneinuseatpresent[1.3].IntroductionSolu

5、tionstospectralcongestioninthelandmobileradioenviron-mentcanbeenvisagedinthefollowingways.0a)TheCellularConceptIncellularsystems,spectralefficiencyisachievedbyemployingspatialfrequencyre-usetechniquesonaninterference-limitedbasis.Frequencyre-userefers

6、totheuseofradiochannelsonthesamecarrierfrequencytocoverdifferentareaswhichareseparatedfromoneanotherbyasufficientdistancesothatco-channelinterferenceisnotobjectionable[1.4].Thisisachievedbydividingtheserviceareaintosmaller`cells',ideallywithnogapsorov

7、erlaps,eachcellbeing12INTRODUCTIONservedbyitsownbasestationandasetofchannelfrequencies.Thepowertransmittedbyeachstationiscontrolledinsuchawaythatthelocalmobilestationsinthecellareservedwhileco-channelinterfer-ence,inthecellsusingthesamesetofradiochann

8、elfrequencies,iskeptacceptablyminimal.Anaddedcharacteristicfeatureofacellularsystemisitsabilitytoadjusttotheincreasingtrafficdemandsthroughcellsplitting.Byfurtherdividingasinglecellintosmallercells,asetofchannelfrequenciesisre-usedmoreoften,le