通信工程專業(yè)外語(yǔ)-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(dòng)通信系統(tǒng)的傳輸信息的同時(shí)，通過(guò)同樣的渠道。另一方面，該系統(tǒng)采用時(shí)分多址/頻分雙工傳輸?shù)姆椒ê妥R(shí)別信息從不同的移動(dòng)臺(tái)。此外，有利于中國(guó)電信集團(tuán)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(shì)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(jī)會(huì)少，低截獲概率（低截獲概率），等。1,PowerControlandRAKEReceiver功率控制和瑞克接收機(jī)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(gè)核心技術(shù)在蜂窩移動(dòng)通信系統(tǒng)的功率控制，可以使信號(hào)功率從所有用戶的學(xué)士學(xué)位相當(dāng)于通過(guò)調(diào)整發(fā)射功率，從每個(gè)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(cè)量幀錯(cuò)誤概率，同時(shí)為閉環(huán)功率控制，基站測(cè)量接收信號(hào)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(dòng)站，以及閉環(huán)反向功率控制，可以通過(guò)基站和移動(dòng)站。另一方面，正向功率控制是用來(lái)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(hào)傳輸?shù)囊苿?dòng)通信信道因?yàn)椴焕硐氲男诺捞匦裕M(jìn)而會(huì)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(hào)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(gè)增大的輸出信噪比后分別獨(dú)立解調(diào)。因此，有利于瑞克接收方法，發(fā)送信號(hào)的不利因素，因?yàn)橐粋€(gè)有利因素在多徑碼分多址蜂窩移動(dòng)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(kuò)頻調(diào)制，帶寬用戶的信號(hào)是非常擴(kuò)大的分配獨(dú)特的偽隨機(jī)序列，從而調(diào)制的寬帶信號(hào)擁有光譜性能接近高斯白噪聲。接受這種擴(kuò)頻信號(hào)，所有的碼分多址接收機(jī)嘗試使用偽隨機(jī)序列解調(diào)本地創(chuàng)建，但只有一個(gè)接收相同的本地偽碼序列，在接收信號(hào)可以轉(zhuǎn)換成寬帶類噪聲信號(hào)為窄帶有用信號(hào)，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?dú)特的偽隨機(jī)序列。Inaddition,asfarasthenarrowbandmeaninglesssignaladditivetothereceivedsignalbytherelativereceiverwiththesameuniquepseudo-randomsequence,itismodulatedintobroadbandsignalwithextremelylessenedpowerspectraldensity.Thus,therelativereceivercanfilterthebroadbandsignalfromotherusersandmajorityofthemeaninglesssignaloutofthefilterbandwidthjustthroughanarrowbandfilter.Therefore,reservationinwithinthereceiveronlyconsistsofthenarrowbandusefulsignalandlittlemeaninglesssignalwithinthefilterbandwidth.Asaconsequentresult,theoutputsignal-to-noiseratioisimprovedlargely,thatwillnecessarilyleadstogreatersystemanti-interferencecapability.此外，至于窄帶毫無(wú)意義的信號(hào)添加劑的接收信號(hào)的相對(duì)接收相同的獨(dú)特的偽隨機(jī)序列，它是調(diào)制成寬帶信號(hào)的功率譜密度非常減少。因此，相對(duì)接收器可以過(guò)濾寬帶信號(hào)從其他用戶和廣大的毫無(wú)意義的信號(hào)進(jìn)行濾波器的帶寬是通過(guò)窄帶濾波器。因此，保留在接收由窄帶有用信號(hào)和小無(wú)意義的信號(hào)在濾波器的帶寬。作為一個(gè)必然結(jié)果，輸出信噪比有較大的提高，這必然會(huì)導(dǎo)致更大的系統(tǒng)的抗干擾能力。ItcanbeprovedthatthemorehighvalueofBn/Bb,themoregreatsystemanti-interferencecapability.由于擴(kuò)頻調(diào)制，帶寬用戶的信號(hào)是非常擴(kuò)大的分配獨(dú)特的偽隨機(jī)序列，從而調(diào)制可以證明更高價(jià)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(shí)分多址接入模式在移動(dòng)通信系統(tǒng)中，信號(hào)的每個(gè)用戶的特點(diǎn)是獨(dú)特的偽隨機(jī)序列的分配基于碼分多址技術(shù)。因此，每一個(gè)信號(hào)，用戶可同步傳輸信道帶寬占整個(gè)分從故障診斷方法。所以在同等頻率資源條件，換句話說(shuō)，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(cè)（碼激勵(lì)線性預(yù)測(cè)）算法的語(yǔ)音編碼，音頻信號(hào)在碼分多址系統(tǒng)可以傳播速度可變，以最大線性預(yù)測(cè)編碼的音頻信號(hào)傳輸速率為9.6比特每秒而用戶說(shuō)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(yǔ)音激活能降低背景干擾用戶間的通信在一個(gè)頻道在同一時(shí)間，并提高了系統(tǒng)容量。全球移動(dòng)通訊系統(tǒng)，該語(yǔ)音激活技術(shù)無(wú)法使用，由于信號(hào)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(jìn)的線性預(yù)測(cè)（碼激勵(lì)線性預(yù)測(cè)）算法的數(shù)字音頻信號(hào)的代碼，在手機(jī)和3接收機(jī)接收來(lái)自不同方向的信號(hào)的同時(shí)，它是極其豐富和三維音頻信號(hào)頻譜從手機(jī)。此外，聲碼器的線性預(yù)測(cè)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(dòng)減少噪聲的干擾。因此，即使在情況下的聲音，我們可以把會(huì)話質(zhì)量好無(wú)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(hào)，用戶的信息必須發(fā)送擴(kuò)頻調(diào)制前的共同渠道極擴(kuò)頻和非常低的功率譜密度。因此，這是很難檢測(cè)到這種信號(hào)的收聽者因?yàn)槠涔β首V密度甚至低于環(huán)境噪聲，它幾乎不可能為他區(qū)分信號(hào)從背景噪音。Moreover,evenifthesignaliscaptured,whatthelistener-incangetonlybroadbandnoiseofinsignificancefromhisdemodulatorbecauseofhisinaccuratelocalpseudo-randomsequence.TheprobabilityofrightPNsequencepatternnecessaryforspreadspectrumdemodulationisoneofmorethanonethousandbillion!Whatalowprobabilityforlistener-intoeavesdropother'sconversationthroughCDMAcellularmobilecommunicationsystem!此外，即使信號(hào)捕獲的聽眾，僅能獲得寬帶噪聲微不足道從解調(diào)器因?yàn)樗牟粶?zhǔn)確的本地偽隨機(jī)序列。概率的正確的序列模式所必需的擴(kuò)頻解調(diào)是超過(guò)一千個(gè)億！什么是低概率的聽眾偷聽別人的談話通過(guò)蜂窩移動(dòng)通信系統(tǒng)！FewerOff-linechances離線的機(jī)會(huì)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(shí)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(dòng)通信系統(tǒng)，基站是保證談話。當(dāng)用戶在會(huì)話移動(dòng)接近邊緣的學(xué)士學(xué)位的私有化，如要保持通信通過(guò)其主動(dòng)開關(guān)，否則程序中斷。在切換期間，英國(guó)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(hào)從移動(dòng)臺(tái)移動(dòng)會(huì)自動(dòng)