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1、GSM（GlobalSystemforMobileCommunication）Thesuccessofmobilesystemsacrosstheworldisasignthatcommunicationismovingtowardsamorepersonalized,convenientsystem.Peoplewhohavetouseamobilephoneonbusinesssoonbegintorealizethattheabilitytophoneanytime,anyplaceinone'sperson
2、alliferapidlybecomesanecessity,notaconvenience.Thespeedandrapiditywithwhichthepersonalcommunicationsrevolutiontakesplaceis,unlikefixedtransmissionsystems,highlydependentontechnologyandcommunicationstandards.Formobilethethreekeyelementstoachievingservicetake-up
3、arethecost,thesizeandtheweightofthephone,andthecostandqualityofthelink.3Ifanyofthesearewrong,especiallythefirsttwo,thenmarketgrowthisliabletobeseverelyrestricted.Thefixedtelephoneserviceisglobalandtheinterconnectionvariesfromcoaxialcabletoopticalfibreandsatell
4、ite.Thenationalstandardsaredifferent,butwithcommoninterfacesandinterfaceconversion,interconnectioncantakeplace.Formobiletheproblemisfarmorecomplex,withtheneedtoroamcreatinganeedforcomplexnetworksandsystems.Thusinmobilethequestionofstandardsisfarmorecrucialtosu
5、ccessthanfixedsystems.4Inaddition,thereisalsothevexedquestionofspectrumallocationinthemobilearea. Mobilesystemsoriginallyoperatedinanalogmodeinthe450MHzband,movinglaterto900MHzwithdigitalGSMandthento1,800MHzwithpersonalcommunicationsystems.Thehistoryofmobility
6、cansplitintogenerations.Thefirstgenerationsystemsweretheadvancedmobilephonesystems(AMPS)intheUS,totalaccesscommunicationsystem(TACS)inmostofEuropeandNordicmobiletelephonesystem(NMT);whichwereallanaloguesystems.Thesecondgenerationisvarymuchdominatedbythestandar
7、dfirstsetoutinEuropebythegroupspecialmobile(GSM)committee,whichwasdesignedasaglobalmobilecommunicationsystem.TheGSMsystemisbasedonacellularcommunicationsprinciplewhichwasfirstproposedasaconceptinthe1940sbyBellSystemengineersintheUS.Theideacameoutoftheneedtoinc
8、reasenetworkcapacityandgotroundthefactthatbroadcastmobilenetworks,operatingindenselypopulatedareas,couldbejammedbyaverysmallnumberofsimultaneouscalls.5Thepowerofthecellularsystemwa
