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1、GSM(GlobalSystemforMobileCommunication)Thesuccessofmobilesystemsacrosstheworldisasignthatcommunicationismovingtowardsamorepersonalized,convenientsystem.Peoplewhohavetouseamobilephoneonbusinesssoonbegintorealizethattheabilitytophoneanytime,anyplaceino
2、ne'spersonalliferapidlybecomesanecessity,notaconvenience.Thespeedandrapiditywithwhichthepersonalcommunicationsrevolutiontakesplaceis,unlikefixedtransmissionsystems,highlydependentontechnologyandcommunicationstandards.Formobilethethreekeyelementstoach
3、ievingservicetake-uparethecost,thesizeandtheweightofthephone,andthecostandqualityofthelink.3Ifanyofthesearewrong,especiallythefirsttwo,thenmarketgrowthisliabletobeseverelyrestricted.Thefixedtelephoneserviceisglobalandtheinterconnectionvariesfromcoaxi
4、alcabletoopticalfibreandsatellite.Thenationalstandardsaredifferent,butwithcommoninterfacesandinterfaceconversion,interconnectioncantakeplace.Formobiletheproblemisfarmorecomplex,withtheneedtoroamcreatinganeedforcomplexnetworksandsystems.Thusinmobileth
5、equestionofstandardsisfarmorecrucialtosuccessthanfixedsystems.4Inaddition,thereisalsothevexedquestionofspectrumallocationinthemobilearea. Mobilesystemsoriginallyoperatedinanalogmodeinthe450MHzband,movinglaterto900MHzwithdigitalGSMandthento1,800MHzwit
6、hpersonalcommunicationsystems.Thehistoryofmobilitycansplitintogenerations.Thefirstgenerationsystemsweretheadvancedmobilephonesystems(AMPS)intheUS,totalaccesscommunicationsystem(TACS)inmostofEuropeandNordicmobiletelephonesystem(NMT);whichwereallanalog
7、uesystems.ThesecondgenerationisvarymuchdominatedbythestandardfirstsetoutinEuropebythegroupspecialmobile(GSM)committee,whichwasdesignedasaglobalmobilecommunicationsystem.TheGSMsystemisbasedonacellularcommunicationsprinciplewhichwasfirstproposedasaconc
8、eptinthe1940sbyBellSystemengineersintheUS.Theideacameoutoftheneedtoincreasenetworkcapacityandgotroundthefactthatbroadcastmobilenetworks,operatingindenselypopulatedareas,couldbejammedbyaverysmallnumberofsimultaneouscalls.5Thepowerofthecellularsystemwa