毕业设计论文英文原文Word格式文档下载.docx

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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