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毕业设计论文英文原文
毕业设计(论文)英文翻译原文
院(系):
信息与通信学院
专业:
电子信息工程
学生姓名:
张晨
学号:
030220606
指导教师:
田克纯
职称:
高级工程师
2007年6月6日
UMTS
Foreffective,efficientcommunications,standardizationiscritical,andnowhereisthismoreevidentthanintheareasofmobilecomputingandcellulartelephony.
Ifyouneeddataaccessore-mailthroughyourcellphone,you’relikelytobeusingoneoftwodifferenttechnologies:
CodeDivisionMultipleAccess(CDMA)orGlobalServiceofMobileCommunication(GSM).
BothCDMAandGSMaresecond-generation(2G)technologies,andtheyhaveco-existedforseveralyears.Eachtechnologyhasitssupporters.CDMAphonesareengineeredspecificallyforanindividualcarrier,whereasGSMphonesmakeuseofaremovablememorycardcalledtheSubscriberIdentityModule(SIM).ASIMcardcontainsallthekeyinformationrequiredtoactivateaphone,includingtheuser’stelephonenumber,personalidentificationnumber,addressbookandencodednetworkidentificationdetails.AusercaneasilymoveaSIMfromonephonetoanother.
ThoughGSMphonesareinteroperablewithoneanother,differentcountriesusedifferentpartsofthefrequencyspectrum,so“worldphones”typicallymustbecapableofusingseveralfrequencies.
Today,thefastest-growinguseofcellularnetworksisforthetransmissionofallkindsofdataandrichmedia,includingWebsites,video,music,images,andmapsanddrivingdirections.Theolder2Gnetworkssimplycouldn’thandlethatvolumeoftraffic,andtheycouldn’tofferthespeedneededfortransmittinglargefiles.Theanswerwastomaketheservicesfasterandbuildoutthenetworkstodealwithmoretraffic.
Here,too,theCDMAandGSMpathscontinuedtheirseparatebutparalleldevelopment.CDMAbroughtusCDMA2000and1xRTTnetworks.Themostrecentdevelopmentsare1xEvolutionDataOptimized,orEV-DO,and1xEvolutionData/Voice,orEV-DV.
Similarly,GSMbegatGeneralPacketRadioService,orGPRS,whichbegatenhanceddataratesforGSMevolution,orEDGE.EDGEwasdevelopedtoenablethetransmissionoflargeamountsofdataatahighspeed,384Kbit/sec.ThelatestgenerationiscalledWidebandCodeDivisionMultipleAccess(WCDMA).
AndthisfinallybringsustoUniversalMobileTelecommunicationsSystem.
TheInternationalTelecommunicationUnion(ITU),aspecializedagencyoftheUnitedNations,hasattemptedtocoordinatethesecompetingtechnologiestoimprovethroughputandincreaseinteroperability.TheInternationalMobileTelecommunications2000standardisathird-generationdigitalcommunicationsspecificationfromtheITU.AndtheEuropean(i.e.,GSM-based)implementationofIMT-2000isUMTS,whichisbasedonWCDMA.Previouscellulartelephonedatasystemsweremostlycircuit-switched,requiringadedicatedconnection.WCDMAispacket-switched,usingtheInternetProtocol.ThefirstcommercialWCDMAnetworkwaslaunchedinJapanin2001.
UMTShasbeenspecifiedasanintegratedapplicationformobilevoiceanddatasystemswithwide-areacoverage.aUsinggloballyharmonizedspectruminpairedandunpairedbands,earlyimplementationsofUMTSoffertheoreticalbitratesofupto384Kbit/sec.insituationswherethemobiledeviceisactuallymoving.Thecurrentgoalistoachieve2Mbit/sec.whenbothendsoftheconnectionare(atleasttemporarily)stationary.
UMTSoperatesonradiofrequenciesidentifiedbytheITUIMT-2000specificationdocumentandlicensedtooperators,usinga5-MHz-widechannelthatsimplifiesdeploymentfornetworkprovidersthathavebeengrantedlarge,contiguousblocksofspectrum.MostUMTSsystemsusefrequenciesbetween1,885and2,025MHz.
UMTSassignsseparatecarrierfrequenciestoincomingandoutboundsignals,aprocesscalledfrequencydivisionduplexing(FDD).Forsymmetrictraffic,suchastwo-wayvideophones,FDDishighlyefficient,allowinguplinkanddownloaddataratestobeequal,incontrasttotechnologiessuchasAsymmetricDigitalSubscriberLineservice,whichtypicallyoffersuploadratesthataremuchslowerthanitsdownloadrates.FDDreducesinterferenceandwastesnobandwidthinswitchingfromtransmittingtoreceiving.
Ongoingworkwithinthe3rdGenerationPartnershipProjectpromisesincreasedthroughputspeedsovertheWCDMARadioAccessNetwork.High-SpeedDownlinkPacketAccessandHigh-SpeedUplinkPacketAccesstechnologiesarealreadystandardized,andcommercialoperatorsinAsiaandNorthAmericaareputtingthemthroughnetworktrials.Withtheoreticaldownloadspeedsashighas14.4Mbit/sec.anduplinkspeedsofupto5.8Mbit/sec.,thesetechnologieswillmakeitpossibleforUMTStoofferdatatransmissionspeedscomparabletothoseofhard-wiredEthernet-basednetworks.
DATACOMMUNICATIONS
AsimplifiedblockdiagramofadatacommunicationlinkisshowninFig.14-1.Althoughonlyonesecondaryisshown[1],itrepresentsatypicalsecondaryinamultipointsystem.Oneofthefunctionsofthehostcomputeristostoretheapplicationsprogramsforthevarioussecondaries.
Theendequipmentwhicheithergeneratesthedigitalinformationfortransmissionorusesthereceiveddigitaldatacanbecomputers,printers,keyboards,CRTs,andsoon.Thisequipmentgenerallymanipulatesdigitalinformationinternallyinwordunits一allthebitsthatmakeupawordinaparticularpieceofequipmentaretransferredinparallel.Digitaldata,whentransmitted,areinserialform.Paralleltransmissionofan8-bitwordwouldrequireeightpairsoftransmissionlines—notatallcost-effective[3].Dataterminalequipment(DTE)isageneralphraseencompassingallofthecircuitrynecessarytoperformparallel-to-serialandserial-to-parallelconversionsfortransmissionandreceptionrespectivelyandfordatalinkmanagement.TheDART(UniversalAsynchronousReceiver/Transmitter)andUSART(UniversalSynchronous/AsynchronousReceiver/Transmitter)arethedevicesthatperformtheparallel-to-serialandserial-to-parallelconversions.TheprimaryDTEincludesalinecontrolunit(LCUorLinCo)whichcontrolstheflowofinformationinamultipointdatalinksystem.Astationcontroller(STACO)isthecorrespondingunitatthesecondaries.IfthereissoftwareassociatedwiththeLCU,itisthencalledafront-endprocessor(FEP).Atonetime,theDTEwasthelastpieceofequipmentthatbelongedtothesubscriberinadatalinksystem.BetweentheDTEs,startingwiththemodems,wascommunicationsequipmentownedandmaintainedbyTelco[4].RecentjudgmentshaveremovedmodemsfromtherealmofexclusiveTelcoproperty.
Datacommunicationsequipment(DCE)[5]acceptstheserialdatastreamfromtheDTEandconvertsittosomeformofanalogsignalsuitablefortransmissiononvoice-gradelines.Atthereceiveend,theDCEperformsthereversefunctionofconvertingthereceivedanalogsignaltoaserialdigitaldatastream.ThesimplestformofDCEisamodem(modulator/demodulator)ordataset.Atthetransmitend,themodemcanbeconsideredaformofdigital-to-analogconverter,whileatthereceiveend,itcanbeconsideredaformofanalog-to-digitalconverter.Themostcommonofmodulationbymodemsarefrequencyshiftkeying(FSK),phaseshiftkeying(PSK),andquadratureamplitudemodulation(QAM).Thisisatypicallydatatransmissionmodeusingtheanalogtelephonelines,seethebottomlinebetweenthetwoDCEsinFig.14-1.Ifyoutransmitdatabydigitalchannel(sometimesitiscalled“DigitalT-carrier[6]”),aPulseCodeModulation(PCM)equipmentmustbeused,seethemiddlepartofFig.14-1.Amicrowavetransmissionsystemcanalsobeusedforthedatacommunication.Finally,youcanusethesatellitecommunicationsystemfordatatransmission,non-showninFig.14-1.
IfthecablesandsignallevelsusedtointerconnecttheDTEandDCEwereleftunregulated,thevariationsgeneratedwouldprobablybeproportionaltothenumberofmanufacturers.ElectronicsindustriesAssociation(EIA),anorganizationofmanufacturersconcernedwithestablishingindustrystandards,haveagreedontheRS-232CasthestandardinterfacebetweentheDTEandthemodem.Thisisa25-pincable[7]whosepinshavedesignatedfunctionsandspecifiedsignallevels.TheRS-232Cisanticipatedtobereplacedbyanupdatedstandard.
DataCommunicationSystems
Therearefivebasictypesofdatacommunicationsystem:
Off-linedatatransmissionissimplytheuseofatelephoneorsimilarlinktotransmitdatawithoutinvolvingacomputersystem.Theequipmentusedatbothendsofsuchalinkisnotpartofacomputer,oratleastdoesnotimmediatelymakethedataavailableforcomputerprocess,thatis,thedatawhensentand/orreceivedare'off-line'.Thistypeofdatacommunicationisrelativelycheapandsimple.
Remotebatchisthetermusedforthewayinwhichdatacommunicationtechnologyisusedgeographicallytoseparatetheinputand/oroutputofdatafromthecomputeronwhichtheyareprocessedinbatchmode.
On-linedatacollectionisthemethodofusingcommunicationstechnologytoprovideinputdatatoacomputerassuchinputarises-thedataarethenstoredinthecomputer(sayonamagneticdisk)andprocessedeitheratpredeterminedintervalsorasrequired.
Enquiry-responsesystemsprovide,asthetermsuggests,thefacilityforausertoextractinformationfromacomputer.Theenquiryfacilityispassive,thatis,doesnotmodifytheinformationstored.Theinterrogationmaybesimple,forexample,'RETRIEVETHERECORDFOREMPLOYEENUMBER1234'orcomplex.Suchsystemsmayuseterminalsproducinghardcopyand/orvisualdisplays.
Real-timesystemsarethoseinwhichinformationismadeavailabletoandprocessedbyacomputersysteminadynamicmannersothateitherthecomputermaycauseactiontobetakentoinfluenceeventsastheyoccur(forexampleas