电子与通信专业英语CDMAversusTDMA

CDMAversusTDMACDMAVsTDMAintravel:BothGSMandCDMAcanbefoundacrossUnitedStates,whichdoesn’tmeanthatitdoesn’tmatterwhichtechnologywechoose.Whenwetraveldomesticallyitispossibletheatwereachareaswheredigitalserviceisnotavailable.Whiletravelingbetweenplacesitispossiblethatwereachcertainruralareaswereonlyanalogaccessisoffered.CDMAhandsetsofferanalogcapabilitieswhichtheGSMdon’toffer.AnotherdifferencebetweenGSMandCDMAisinthedatatransfermethods.GSM’shigh-speedwirelessdatatechnology,GPRS(GeneralPacketRadioService),usuallyoffersaslowerdatabandwidthforwirelessdataconnectionthanCDMA’shigh-speedtechnology,whichhasthecapabilityofprovidingISDN(IntegratedServicesDigitalNetwork)withspeedsasmuchas144Kbps.GSM’sbenefitsovertheCDMAindomesticpurposearethatGSMusesSIMcardthatidentifiesauserandstorestheinformationinthehandset.TheSIMcardcanbeswappedbetweenhandsets,whichenabletomoveallthecontactstothenewhandsetwithease.CDMAcanhavethisflexibilitywiththeirownservicethatstoresdataontheoperator’sdatabase.Thisserviceallowstheusertoswapdata’sbetweentwohandsetswithalittletrouble,buttheadvantageisitcanbedonewhenthehandsetisevenlostbutinGSMtechnology,whenahandsetislost,SIMcardisalsolostwithit.WhenitcomesforinternationalroaminghandsetswithGSMisfarbetterthanCDMAhandsetsbecauseGSMisusedinmostthemarketsacrosstheglobe.Usersusingtri-bandorquad-bandcantraveltoEurope,IndiaandmostofAsiaandstillcanusetheircellphone.CDMAdoesnothavethismultibandcapability,thuscannotbeusedmultiplecountrieswithease.ThesummaryofCDMACDMAistheEnglishabbreviationforCodeDivisionMultipleAccess(CodeDivisionMultipleAccess),itisdigitaltechnologyatabranchSpreadspectrumcommunicationtechnologyhasdevelopedanewandsophisticatedwirelesscommunicationstechnology.CDMAtechnologyisbasedontheprincipleofspreadspectrumtechnology,soontobesentmusthavetheinformationsignalbandwidthdata,withabandwidthmuchlargerthansignalbandwidth,high-speedpseudorandomcodemodulation,sothatthebandwidthoftheoriginaldatasignalstobeextended,andthenbythecarriermodulationandsent.Receiverusethesamepseudo-randomcode,andreceivebandwidthfortheassociatedsignalprocessing,widebandsignalputintotheoriginalinformationofthenarrowbanddatasignalthatisde-spreadinordertoachieveinformationandcommunication.CDMAisaspreadspectrumcommunication,spreadspectrumcommunicationwithhimthefollowingcharacteristics:(1)anti-interferenceability.Thisisthebasiccharacteristicsofspreadspectrumcommunication,allcommunicationsaresecondtonone.(2)broadbandtransmission,anti-fadingability.(3)becauseoftheuseofbroadbandtransmission,inthechanneltransmissionpowerratioofusefulsignalinterferencesignalpowerismuchlower,soifthesignalhiddeninnoise;thatis,ifthepowerdensityisrelativelylow,thereisinfavorofcovertsignals.(4)theuseofspreadingcodestoobtaintherelevanceoftheuser'sinformation,theabilityofanti-interception.(5)multipleuserssimultaneouslyreceiving,sendingsimultaneously.CDMAmobilephonehasthefollowingadvantages:A,CDMAmobilephonescanbesaidtobetherealgreen,itstransmissionpowerextremelysmall(2mw),wejustusetheGSMmobilephone(125mw)of1/60,evenlowerthantheTVscreentheradiationpower;Second,CDMAmobilephoneshaveadoptedadvancedswitchingtechnology,softswitchtechnology(thatis,theswitchisinthefirstaftertheinterruption),maketheCDMAmobilephonecallscanbecomparabletofixedtelephone,andthere'snoGSMmobilephonedropphenomenon;Three,useCDMAnetwork,operatorsoflessinvestment,itisleftemptyforCDMAmobilecut;Four,becausebasedonextensionfrequencyonthebasisofcommunicationisakindofmodulationandmultipleaccesscommunicationmode,itscapacityis10timeshigherthanthesimulationtechnology,4timesmorethantheGSMnetwork;Five,moreimportantly,basedonthetechnologyofbroadbandCDMAthatmakesitpossibletovideoapplicationsinmobilecommunication,enablingfromnarrowcanonlymakeaphonecallandsendashortmessageservicetowardsthebroadbandmultimediaapplications.ThesummaryofTDMATDMA(Timedivisionmultipleaccess,abbreviated:TDMA),isaSharedtransmissionmediumtoachieveradiofield(usually)ornetworkcommunicationtechnology.Itallowsmultipleusersindifferenttimeslices(2)tousethesamefrequency.ItisdividedintocyclicaltimeFrame(Frame),eachFrameandthendividedintoseveraltimeslotsendsasignaltothebasestationundertheconditionofmeettimingandsynchronization,thebasestationcanberespectivelyineachtimeslotofeachmobileterminalreceivesthesignalandnotconfused.Userstoquicklytransfer,onebyone,eachusertousetheirowntime.Thisallowsmultipleuserstosharethesametransmissionmedia(radiofrequency).TDMAinTheUnitedStatesisoftenreferredtoasthesecondgeneration(2g)mobilephonestandard,specificallyreferstotheIS-136andD-AMPS,thesestandardsusingTDMAtechnologysharingthebandwidthofthecarrier.TDMAsystemdividesthespectrumaccordingtothetimeslot,andineachtimeslotonlyallowsauser,eitherreceiveorsend.ThedisadvantageofTDMAisachievablecarrierchannelnumberislimited.WesternEuropeGSMandtheUnitedStatesmorematureusersareusingthecombinationofFDMA/TDMAnarrowbandsystem.TDMAsystemmainlyhasadvancedmobilephonesystem(AMPS)Americandigitalcellulardigitalcellularsystem(USDC)andJapan(JDC)andglobalsystemformobilecommunications(