通信工程專業(yè)外語-unit13原文與翻譯

精選優(yōu)質(zhì)文檔-----傾情為你奉上精選優(yōu)質(zhì)文檔-----傾情為你奉上專心---專注---專業(yè)專心---專注---專業(yè)精選優(yōu)質(zhì)文檔-----傾情為你奉上專心---專注---專業(yè)Unit13ComparisonbetweenGSMandCDMAGSM與CDMA之比較UsingCDMA/FDDtechnology,subscribersofCDMAcellularmobilecommunicationsystemcantransmittheirinformationsimultaneouslythroughthesamechannel.Ontheotherhand,theGSMsystemadoptsTDMA/FDDmethodtotransmitanddistinguishinformationfromdifferentGSMmobilestations.Inaddition,infavorofQCELParithmetic,RAKEreceiver,powercontrolandsoftswitchingetc.,CDMAshowsmoreadvantagesinitssystemperformancethantheGSM,suchasgreateranti-interferencecapability,biggersystemcapacity,highersuccessfulconnectionratio,feweroff-linechances,lowprobabilityofintercept(LPI),andsoon.使用碼分多址/頻分雙工技術(shù)，用戶的蜂窩移動通信系統(tǒng)的傳輸信息的同時，通過同樣的渠道。另一方面，該系統(tǒng)采用時分多址/頻分雙工傳輸?shù)姆椒ê妥R別信息從不同的移動臺。此外，有利于中國電信集團廣州研發(fā)中心算術(shù)，耙式接收器，功率控制和軟開關(guān)等，顯示出更多的優(yōu)勢在碼分多址系統(tǒng)性能比，如更高的抗干擾能力，更大的系統(tǒng)容量，連接成功率較高，離線的機會少，低截獲概率（低截獲概率），等。1,PowerControlandRAKEReceiver功率控制和瑞克接收機WhendifferentsubscriberssendtheirinformationtothesameBS(basestation),differentsignalpowercausedbydifferenttransmittingdistanceswillconsequentiallycauseinterferencewitheachother,especiallyforthoseMSs(mobilestation)beingfarawayfromBSwillbeseriouslydisturbedbecauseoftheiralmostsubmergedsignalsbysignalsoftheclose-to-BSMSs.[2]p110Inordertosolvethisproblemandkeephighsystemperformance,powercontroltechniqueisintroducedinCDMAcommunicationsystem,whichcaneffectivelyovercomethiscross-disturbance.AsoneofthecoretechniquesinCDMAcellularmobilecommunicationsystem,powercontrolcanmakethesignalpowerfromallsubscriberstotheBSequivalentthroughadjustingthetransmittingpowerfromeachsubscriber.為解決這一問題，保持較高的系統(tǒng)性能，功率控制技術(shù)介紹了碼分多址通信系統(tǒng)，它可以有效地克服這cross-disturbance。作為一個核心技術(shù)在蜂窩移動通信系統(tǒng)的功率控制，可以使信號功率從所有用戶的學(xué)士學(xué)位相當(dāng)于通過調(diào)整發(fā)射功率，從每個用戶。Powercontrolcanbenotonlydividedtoopen-loopcontrolandclosed-loopcontrol,butalsotoforward(down)powercontrolandbackward(up)powercontrol.Foropen-loopcontrolmethod,subscriberadjustsemittingpoweraccordingtothemeasuredframeerrorprobability,whilefortheclosed-looppowercontrol,basestationmeasuresthesignal-to-noiseratioofreceivedsignalsandthenadjustthetransmittingpowerofcorrespondingMS.功率控制不僅可以分為開環(huán)控制和閉環(huán)控制，而且還提出了（下）功率控制和反向功率控制（上）。開環(huán)控制方法，用戶調(diào)整發(fā)射功率根據(jù)測量幀錯誤概率，同時為閉環(huán)功率控制，基站測量接收信號的信噪比，然后調(diào)整發(fā)射功率相應(yīng)的女士ThebackwardpowercontrolinCDMAsystemcanbedividedintotwokindsofcontroltechnique,theopen-loopbackwardpowercontrolonlyusedbymobilestation,andtheclosed-loopbackwardpowercontrolthatcanbeadoptedbybothbasestationandmobilestation.Ontheotherhand,theforwardpowercontrolisjustusedtoreducethedisturbancefromsmalladjacentdistricts.反向功率控制系統(tǒng)可分為開環(huán)控制技術(shù)，反向功率控制用的移動站，以及閉環(huán)反向功率控制，可以通過基站和移動站。另一方面，正向功率控制是用來降低干擾小附近的地區(qū)。RAKEReceptionTechnique(瑞克接收技術(shù))Fadinganddistortionareinevitableforsignalstransmittedinmobilecommunicationchannelbecauseoftheunidealcharacteristicsofchannel,andthenmakebadinfluenceonsystemperformance.變形是不可避免的衰落和信號傳輸?shù)囊苿油ㄐ判诺酪驗椴焕硐氲男诺捞匦?，進而會影響系統(tǒng)的性能。ThebasictheoryofRAKEreceptiontechniqueis:bymeansofcollectingalltransmittedsignalsfrommulti-pathandunitingthem,thereceivedsignalpowercanobtainaneffectiveenhancement,whichcanimprovetheoutputSNRandsystemperformance.[3]p110Three,fourRAKEreceiversarerespectivelysetineachMS,BSinCDMAsysteminordertoreceivethearrivingbranchsignalofthesameoriginalfromdifferenttransmittingroutes,andthencombinethemtogetanincrescentoutputSNRaftertheirrespectivelyindependentdemodulation.Thus,infavorofRAKEreceptiontechnique,thedisadvantageousfactorthatsignaltransmittedinmulti-pathbecauseanadvantageousfactorinCDMAcellularmobilecommunicationsystem.三，四的耙式接收器分別設(shè)置于每一毫秒，在碼分多址系統(tǒng)，以便接收到信號相同的原始分支從不同的傳播途徑，并結(jié)合他們得到一個增大的輸出信噪比后分別獨立解調(diào)。因此，有利于瑞克接收方法，發(fā)送信號的不利因素，因為一個有利因素在多徑碼分多址蜂窩移動通信系統(tǒng)。2BetterPerformanceofCDMA性能更好的碼分多址GreaterAnti-interferenceCapability更大的抗干擾能力Becauseofspreadspectrummodulation,bandwidthofuser’ssignalisextremelybroadenedbytheassigneduniquepseudo-randomsequence,thusthemodulatedbroadbandsignalownsspectralpropertiesclosetoGaussianwhitenoise.Receivingthiskindofspreadspectrumsignal,alltheCDMAreceiverstrytodemodulateitusingPNsequencecreatedlocally,butonlyonereceiverwiththesamelocalPNsequenceasthatinthereceivedsignalcanconvertthebroadbandnoise-likesignalintonarrowbandusefulsignal,whileotherreceiverisstilltheinsignificantbroadbandnoiseexcepttherelativedemodulatorwiththeuniquelocalPNsequence.由于擴頻調(diào)制，帶寬用戶的信號是非常擴大的分配獨特的偽隨機序列，從而調(diào)制的寬帶信號擁有光譜性能接近高斯白噪聲。接受這種擴頻信號，所有的碼分多址接收機嘗試使用偽隨機序列解調(diào)本地創(chuàng)建，但只有一個接收相同的本地偽碼序列，在接收信號可以轉(zhuǎn)換成寬帶類噪聲信號為窄帶有用信號，而其他接收器仍然是微不足道的寬帶噪聲，除了相關(guān)解調(diào)器與當(dāng)?shù)鬲毺氐膫坞S機序列。Inaddition,asfarasthenarrowbandmeaninglesssignaladditivetothereceivedsignalbytherelativereceiverwiththesameuniquepseudo-randomsequence,itismodulatedintobroadbandsignalwithextremelylessenedpowerspectraldensity.Thus,therelativereceivercanfilterthebroadbandsignalfromotherusersandmajorityofthemeaninglesssignaloutofthefilterbandwidthjustthroughanarrowbandfilter.Therefore,reservationinwithinthereceiveronlyconsistsofthenarrowbandusefulsignalandlittlemeaninglesssignalwithinthefilterbandwidth.Asaconsequentresult,theoutputsignal-to-noiseratioisimprovedlargely,thatwillnecessarilyleadstogreatersystemanti-interferencecapability.此外，至于窄帶毫無意義的信號添加劑的接收信號的相對接收相同的獨特的偽隨機序列，它是調(diào)制成寬帶信號的功率譜密度非常減少。因此，相對接收器可以過濾寬帶信號從其他用戶和廣大的毫無意義的信號進行濾波器的帶寬是通過窄帶濾波器。因此，保留在接收由窄帶有用信號和小無意義的信號在濾波器的帶寬。作為一個必然結(jié)果，輸出信噪比有較大的提高，這必然會導(dǎo)致更大的系統(tǒng)的抗干擾能力。ItcanbeprovedthatthemorehighvalueofBn/Bb,themoregreatsystemanti-interferencecapability.由于擴頻調(diào)制，帶寬用戶的信號是非常擴大的分配獨特的偽隨機序列，從而調(diào)制可以證明更高價值的Bn/Bb，更大的系統(tǒng)的抗干擾能力。BiggerSystemCapacityandHigherSuccessfulAccessRatio更大的系統(tǒng)容量和更高的接入成功率UnliketheTDMAmulti-accessmodeinGSMmobilecommunicationsystem,signalofeachCDMAsubscriberisdistinguishedbytheassigneduniquePNsequencebasedontheCDMAtechnology.Thus,eachsignalofCDMAsubscribercanbetransmittedsynchronouslyoccupyingtheentiresub-channelbandwidthdividedfromtheFDDmethod.Soundertheequalfrequencyresourcecondition,inotherword,forthesamechannelbandwidth,capacityofCDMAsystemis4~5timeslargerthanthatofGSMsystem.不同的是時分多址接入模式在移動通信系統(tǒng)中，信號的每個用戶的特點是獨特的偽隨機序列的分配基于碼分多址技術(shù)。因此，每一個信號，用戶可同步傳輸信道帶寬占整個分從故障診斷方法。所以在同等頻率資源條件，換句話說，在同一信道帶寬，碼分多址系統(tǒng)容量為4~5倍以上的系統(tǒng)。Inthenatureofthings,acommunicationsystemwithbigcapacitymusthavehighsuccessfulaccessratio.在事物的性質(zhì)，通信系統(tǒng)容量大，必須具備較高的接入成功率。Inaddition,usingCELP(CodeExcitedLinearPredictive)arithmeticforvoicecode,audiosignalinCDMAsystemcanbetransmittedwithvariablespeed,withthemaximumCELPcodedaudiosignaltransmittingvelocityis9.6kbit/swhilethesubscriberistalking,andtheminimumvelocityof1.2kbit/sfortheconversationpause.ThistechniquecalledVoiceActivationcanreducethebackgrounddisturbanceamongsubscriberscommunicatingononechannelatthesametime,andenhancesthesystemcapacity.ForGSMsystem,thisVoiceActivationtechniquecannotbeusedbecauseofthesignaltransmittingdelayatconversationpause.此外，利用線性預(yù)測（碼激勵線性預(yù)測）算法的語音編碼，音頻信號在碼分多址系統(tǒng)可以傳播速度可變，以最大線性預(yù)測編碼的音頻信號傳輸速率為9.6比特每秒而用戶說話，和最低速度的1.2比特每秒的談話暫停。這種技術(shù)稱為語音激活能降低背景干擾用戶間的通信在一個頻道在同一時間，并提高了系統(tǒng)容量。全球移動通訊系統(tǒng)，該語音激活技術(shù)無法使用，由于信號傳輸延遲談話停頓。BetterVoiceQuality更好的聲音質(zhì)量UsingadvancedCELP(CodeExcitedlinearPredictive)arithmeticforitsdigitalaudiosignalcode,and3RAKEreceiversinahandsettoreceivesignalsfromdifferentdirectionssimultaneously,itismadeextremelyabundantanddimensionalforaudiosignalspectrumfromCDMAhandset.Furthermore,vocoderbasedontheCELParithmeticinCDMAsystemcanadjustitstransmittingvelocityandchoosecorrespondingsendingpowerlevelautomaticallytoreducethedisturbanceofnoise.Thus,evenunderthecircumstancewithloudnoise,wecanmakeconversationofgoodqualitywithoutanycacophony.采用先進的線性預(yù)測（碼激勵線性預(yù)測）算法的數(shù)字音頻信號的代碼，在手機和3接收機接收來自不同方向的信號的同時，它是極其豐富和三維音頻信號頻譜從手機。此外，聲碼器的線性預(yù)測算法在碼分多址系統(tǒng)可以調(diào)整其傳輸速度和選擇相應(yīng)的發(fā)送功率電平自動減少噪聲的干擾。因此，即使在情況下的聲音，我們可以把會話質(zhì)量好無雜音。LowerProbablyofIntercept(LPI)下可能攔截（低截獲概率）Itisnecessaryforeavesdroppingsomebody'sconversionthatthetransmittedconversioninformationmustbecapturedandthendecoded.ForCDMAsystem,signalwithuser'sinformationmustbespreadspectrummodulatedbeforesenttothecommonchannelwithextremelyspreadspectrumandverylowpowerspectraldensity.ThusitistoodifficulttodetectthiskindofCDMAsignalforthelistener-inbecauseitspowerspectraldensityisevenlowerthanambientnoise,andit'salmostimpossibleforhimtodistinguishthesignalfrombackgroundnoise.這是必要的竊聽別人的轉(zhuǎn)換，傳輸轉(zhuǎn)換信息必須捕獲和解碼。用于碼分多址系統(tǒng)的信號，用戶的信息必須發(fā)送擴頻調(diào)制前的共同渠道極擴頻和非常低的功率譜密度。因此，這是很難檢測到這種信號的收聽者因為其功率譜密度甚至低于環(huán)境噪聲，它幾乎不可能為他區(qū)分信號從背景噪音。Moreover,evenifthesignaliscaptured,whatthelistener-incangetonlybroadbandnoiseofinsignificancefromhisdemodulatorbecauseofhisinaccuratelocalpseudo-randomsequence.TheprobabilityofrightPNsequencepatternnecessaryforspreadspectrumdemodulationisoneofmorethanonethousandbillion!Whatalowprobabilityforlistener-intoeavesdropother'sconversationthroughCDMAcellularmobilecommunicationsystem!此外，即使信號捕獲的聽眾，僅能獲得寬帶噪聲微不足道從解調(diào)器因為他的不準(zhǔn)確的本地偽隨機序列。概率的正確的序列模式所必需的擴頻解調(diào)是超過一千個億！什么是低概率的聽眾偷聽別人的談話通過蜂窩移動通信系統(tǒng)！FewerOff-linechances離線的機會較少Becauseofthesoft-switchingtechnique,whichmeans“connect-before-break”,it’sovercomeforCDMAthatthefrequentoccurrenceofoff-time.由于軟開關(guān)技術(shù)，即“connect-before-break”，它克服了碼分多址，頻繁發(fā)生的時間。Inmobilecommunicationsystem,BSistheguaranteeforconversation.WhensubscribersduringconversationmovingclosetoedgeoftheBS’demesne,theBSshouldmaintainthecommunicationthroughitsactiveswitching,otherwisetheprocesswillbeinterrupted.Duringswitchingperiod,BS’sdominionshouldshiftfrom“demesneofthelocalBS(suchasA)”to“demesneofAanditsneighboringBS(B)”to“demesneofB”,andsignalfromthemovingmobilestationwillautomaticallyswitchtoarelativelyidleneighboringBS.Thus,onlywhenitisapprovedthatthemovingMShasmovedtothe“demesneofB”,cantheconnectionbetweenthemovingMSanditsoriginalBS(A)beswitchedoff.SoitisnoteasyforaCDMAconversationtobeinterruptedbyoff-line.在移動通信系統(tǒng)，基站是保證談話。當(dāng)用戶在會話移動接近邊緣的學(xué)士學(xué)位的私有化，如要保持通信通過其主動開關(guān)，否則程序中斷。在切換期間，英國的主權(quán)應(yīng)該從“私有的地方本科（如）”到“私有和鄰近基站（乙）”到“私有”，和信號從移動臺移動會自動