GSM原理(英文)

WebProForumTutorials©TheInternationalEngineeringConsortium1/19GlobalSystemforMobileCommunication(GSM)DefinitionGlobalsystemformobilecommunication(GSM)isagloballyacceptedstandardfordigitalcellularcommunication.GSMisthenameofastandardizationgroupestablishedin1982tocreateacommonEuropeanmobiletelephonestandardthatwouldformulatespecificationsforapan-Europeanmobilecellularradiosystemoperatingat900MHz.ItisestimatedthatmanycountriesoutsideofEuropewilljointheGSMpartnership.OverviewThistutorialprovidesanintroductiontobasicGSMconcepts,specifications,networks,andservices.AshorthistoryofnetworkevolutionisprovidedinordersetthecontextforunderstandingGSM.Topics1.Introduction:TheEvolutionofMobileTelephoneSystems2.GSM3.TheGSMNetwork4.GSMNetworkAreas5.GSMSpecifications6.GSMSubscriberServicesSelf-TestCorrectAnswersAcronymGuideWebProForumTutorials©TheInternationalEngineeringConsortium2/191.Introduction:TheEvolutionofMobileTelephoneSystemsCellularisoneofthefastestgrowingandmostdemandingtelecommunicationsapplications.Today,itrepresentsacontinuouslyincreasingpercentageofallnewtelephonesubscriptionsaroundtheworld.Currentlytherearemorethan45millioncellularsubscribersworldwide,andnearly50percentofthosesubscribersarelocatedintheUnitedStates.Itisforecastedthatcellularsystemsusingadigitaltechnologywillbecometheuniversalmethodoftelecommunications.Bytheyear2005,forecasterspredictthattherewillbemorethan100millioncellularsubscribersworldwide.Ithasevenbeenestimatedthatsomecountriesmayhavemoremobilephonesthanfixedphonesbytheyear2000(seeFigure1).Figure1.CellularSubscriberGrowthWorldwideTheconceptofcellularserviceistheuseoflow-powertransmitterswherefrequenciescanbereusedwithinageographicarea.Theideaofcell-basedmobileradioservicewasformulatedintheUnitedStatesatBellLabsintheearly1970s.However,theNordiccountrieswerethefirsttointroducecellularservicesforcommercialusewiththeintroductionoftheNordicMobileTelephone(NMT)in1981.CellularsystemsbeganintheUnitedStateswiththereleaseoftheadvancedmobilephoneservice(AMPS)systemin1983.TheAMPSstandardwasadoptedbyAsia,LatinAmerica,andOceaniccountries,creatingthelargestpotentialmarketintheworldforcellular.Intheearly1980s,mostmobiletelephonesystemswereanalogratherthandigital,liketoday'snewersystems.Onechallengefacinganalogsystemswastheinabilitytohandlethegrowingcapacityneedsinacost-efficientmanner.Asaresult,digitaltechnologywaswelcomed.Theadvantagesofdigitalsystemsoveranalogsystemsincludeeaseofsignaling,lowerlevelsofinterference,integrationoftransmissionandswitching,andincreasedabilitytomeetcapacitydemands.Table1chartstheworldwidedevelopmentofmobiletelephonesystems.WebProForumTutorials©TheInternationalEngineeringConsortium3/19Table1.TheDevelopmentofMobileTelephoneSystemsYearMobileSystem1981NordicMobileTelephone(NMT)4501983AmericanMobilePhoneSystem(AMPS)1985TotalAccessCommunicationSystem(TACS)1986NordicMobileTelephony(NMT)9001991AmericanDigitalCellular(ADC)1991GlobalSystemforMobileCommunication(GSM)1992DigitalCellularSystem(DCS)18001994PersonalDigitalCellular(PDC)1995PCS1900—Canada1996PCS—UnitedStates2.GSMThroughouttheevolutionofcellulartelecommunications,varioussystemshavebeendevelopedwithoutthebenefitofstandardizedspecifications.Thispresentedmanyproblemsdirectlyrelatedtocompatibility,especiallywiththedevelopmentofdigitalradiotechnology.TheGSMstandardisintendedtoaddresstheseproblems.From1982to1985discussionswereheldtodecidebetweenbuildingananalogordigitalsystem.Aftermultiplefieldtests,adigitalsystemwasadoptedforGSM.Thenexttaskwastodecidebetweenanarroworbroadbandsolution.InMay1987,thenarrowbandtimedivisionmultipleaccess(TDMA)solutionwaschosen.AsummaryofGSMmilestonesisgiveninTable2.Table2.GSMMilestonesYearMilestone1982GSMformed1986fieldtest1987TDMAchosenasaccessmethod1988memorandumofunderstandingsignedWebProForumTutorials©TheInternationalEngineeringConsortium4/191989validationofGSMsystem1990preoperationsystem1991commercialsystemstart-up1992coverageoflargercities/airports1993coverageofmainroads1995coverageofruralareas3.TheGSMNetworkGSMprovidesrecommendations,notrequirements.TheGSMspecificationsdefinethefunctionsandinterfacerequirementsindetailbutdonotaddressthehardware.Thereasonforthisistolimitthedesignersaslittleaspossiblebutstilltomakeitpossiblefortheoperatorstobuyequipmentfromdifferentsuppliers.TheGSMnetworkisdividedintothreemajorsystems:theswitchingsystem(SS),thebasestationsystem(BSS),andtheoperationandsupportsystem(OSS).ThebasicGSMnetworkelementsareshowninFigure2.Figure2.GSMNetworkElementsWebProForumTutorials©TheInternationalEngineeringConsortium5/19TheSwitchingSystemTheswitchingsystem(SS)isresponsibleforperformingcallprocessingandsubscriber-relatedfunctions.Theswitchingsystemincludesthefollowingfunctionalunits:•homelocationregister(HLR)—TheHLRisadatabaseusedforstorageandmanagementofsubscriptions.TheHLRisconsideredthemostimportantdatabase,asitstorespermanentdataaboutsubscribers,inc