專業(yè)英語(yǔ)課后答案

ExercisesⅠ.PleasetranslatethefollowingwordsandphrasesintoChinese.Exercises1.samplefunction 樣本函數(shù)2.ensembleaverage總體均值3.physicalsignificance 物理意義4.aFouriertransformpair傅里葉變換對(duì)5.deterministicwaveform 確定性波形6.inthelimit在極限情況下7.timeinvariant 時(shí)不變的8.anupperfrequencylimit 頻率上限9.Parseval’stheorem巴塞瓦爾定理10.randompulses 隨機(jī)脈沖Exercises1.physicalsystem 物理系統(tǒng)，實(shí)際系統(tǒng) 2.risetime 上升時(shí)間3.amountofinformation 信息量4.inprinciple 理論上，原則上5.gaussianchannel 高斯信道6.probabilitydensity 概率密度7.rootmeansquare 均方根值，均方根，8.tradeoff交替換位，折衷選擇9.lowerbound 下限，下界1.equalizer均衡器11.viceversa反之亦然12.upperlimit上限Exercises1.overallperformance 總性能2.crestfactor振幅（波峰）因數(shù)（振幅與有效值之比）3.nonlinearoperation非線性運(yùn)算4.inverseoperation 逆操作5.rms 均方根（值）6.PAM 振幅調(diào)制7.PDM 脈寬調(diào)制8.PPM 脈沖相位調(diào)制9.maximummagnitude最大幅值10.errorintervals 誤差間隔11.Entropy 熵，平均信息量12.roundoff 舍入，用四舍五入化為整數(shù)13.quantumlevel 量化電平14.DPCM 差分脈沖編碼調(diào)制Exercises1.channelcoding 信道編碼2.transmissionbandwidth 傳輸帶寬3.Singlesidednoisepowerdensity 單邊帶噪聲功率密度4.orthogonalsignaling正交信號(hào)5.FEC 前向糾錯(cuò)6.logictable 邏輯表7.systematiccode 系統(tǒng)碼8.AWGN 加性高斯白噪聲9.BER 誤碼率，誤比特率（biterrorratio）10.trellisdiagram 網(wǎng)格圖11.constraintlength 制約長(zhǎng)度12.vectorarray 向量數(shù)組13.algebraicfunction 代數(shù)函數(shù)14.statediagram 狀態(tài)圖15.cyclicshift 循環(huán)移位16.generatormatrix 生成矩陣Exercises1.AM 幅度調(diào)制（amplitudemodulation）2.DPSK 差分相位鍵控(differentialPSK)3.PAM 脈沖振幅調(diào)制（pulseamplitudemodulation）4.PDM 脈寬調(diào)制（pulsedurationmodulation）5.PPM 脈沖相位調(diào)制（pulsephasemodulation）6.PCM 脈沖編碼調(diào)制（pulsecodemodulation）7.DPCM 差分脈沖編碼調(diào)制（differentialpulsecodemodulation）8.ASK 振幅鍵控（amplitudeshiftkeying）9.FSK 頻移鍵控（frequencyshiftkeying）10.FDM 頻分多路復(fù)用（frequencydivisionmultiplexing）11.TDM 時(shí)分多路復(fù)用（timedivisionmultiplexing）12.codedmodulation編碼調(diào)制13.suppressedcarrier 抑制載波14.modulatedsignal 已調(diào)信號(hào) Exercises1.copperwire 銅線2.speechrecognition 語(yǔ)音識(shí)別3.adaptivedifferentialPCM 自適應(yīng)差分脈碼調(diào)制4.infiniteimpulseresponse(IIR) 無(wú)限脈沖響應(yīng)5.realtimeconversation 實(shí)時(shí)交換6.digitalsignalprocessing 數(shù)字信號(hào)處理7.CELP 碼激勵(lì)線性預(yù)測(cè)（codeexcitedlinearprediction）8.VAD 話音激活檢測(cè)器(voiceactivitydetector)9.MPE 多脈沖激勵(lì)(multipulseexcitation)10.ADPCM 自適應(yīng)差分脈碼調(diào)制 (adaptivedifferentialPCM)11.directquantization 直接量化12.logpulsePCMquantizer 對(duì)數(shù)脈沖PCM量化器 ExercisesⅡ.PleasetranslatethefollowingwordsandphrasesintoEnglish.1.隨機(jī)過(guò)程 randomprocess2.統(tǒng)計(jì)平均 statisticalaverage3.隨機(jī)變量 randomvariable4.自相關(guān)函數(shù) autocorrelationfunction5.傅里葉變換 Fouriertransform6.功率譜密度 powerspectraldensity7.概率密度函數(shù) probabilitydensityfunction8.高斯過(guò)程 gaussianprocess9.平穩(wěn)過(guò)程 astationaryprocess10.統(tǒng)計(jì)獨(dú)立 statisticallyindependent11.時(shí)間平均(值) timeaverage12.統(tǒng)計(jì)特性 statisticalcharacteristic13.各態(tài)歷經(jīng)過(guò)程 ergodicprocess14.狄拉克函數(shù) deltafunctionExercises1.通信理論 communicationtheory(theoryofcommunications)2.香農(nóng)定理 Shannon’stheorem3.信道帶寬 channalbandwidth4.信號(hào)波形 signalwaveform5.理想低通濾波器 ideallowpassfilter6.自相關(guān)函數(shù) autocorrelationfunction7.無(wú)噪聲高斯信道 noiselessgaussianchannel8.通信信道 communicationchannel9.信息速率 informationrate10.信噪比 signaltonoiseratio(SNR,S/N)11.信道容量 channalcapacity12.雙邊功率譜密度 Twosidedpowerspectraldensity13.誤碼率 errorprobability(probabilityfoerror)14.奈奎斯特采樣速率 Nyquistsamplingrate15.限帶高斯信道 bandlimitedgaussianchannel16.高斯白噪聲 whiteGaussiannoiseExercises1.正脈沖 positivepulse2.脈沖編碼調(diào)制 pulsecodemodulation3.解碼器 decoder4.編碼器 encoder5.量化步長(zhǎng) quantumstepsize6.峰值 peakmagnitudes7.線性函數(shù) linearfunction8.脈沖序列 pulsetrain9.均勻量化器 uniformquanizer10.預(yù)測(cè)編碼 predictivecoding11.壓擴(kuò)器 compandor12.壓縮比 compressionratioExercises1.檢錯(cuò)碼 errordetectioncode2.信道容量channelcapacity3.分組碼 blockcode4.卷積碼convolutionalcode5.移位寄存器 shiftregister6.漢明距離 Hammingdistance7.碼重 codeweight(weightofcode)8.樹形圖 treediagram9.編碼增益 codinggain10.平均比特能量 averagebitenergy11.碼距 codedistance(distanceofcode)12.糾錯(cuò)碼 errorcorrectioncode13.帶寬效率 bandwidthefficiency14.模2加法器 modulo2adder15.原始數(shù)據(jù) rawdata16.編碼率 coderate17.生成多項(xiàng)式 generatorpolynomial18.循環(huán)碼 cycliccodeExercises1.帶通信號(hào) bandpasssignal2.脈沖調(diào)制 pulsemodulation3.角度調(diào)制 anglemodulation4.殘留邊帶抑制載波調(diào)制 vestigialsidebandsuppressedcarriermodulation5.絕對(duì)帶寬 absolutebandwidth6.脈沖寬度 pulseduration7.線性函數(shù) linearfunction8.載波頻率 carrierfrequency9.模擬調(diào)制 analogmodulation10.移相鍵控 PSK（phaseshiftkeying）11.連續(xù)波調(diào)制 continuouswave(CW)modulation12.同軸電纜 coaxialcable Exercises1.共振峰跟蹤濾波器 formanttrackingfilter2.國(guó)際電信聯(lián)盟 InternationalTelecommunicationsUnion(ITU)3.背景噪聲 backgroundnoise4.雙向通信 two-waycommunication5.基音跟蹤濾波器 pitchtrackingfilter6.長(zhǎng)時(shí)預(yù)測(cè) long-termprediction7.語(yǔ)音編碼 speechcoding8.聲碼器 vocoder9.語(yǔ)音增強(qiáng) speechenhancement10.波形跟隨編碼器 waveformfollowingcoder11.參數(shù)編碼器 parametriccoder12.頻域編碼器 frequencydomaincodeExercisesⅢ.Fillintheblankswiththemissingword(s).1.Theensembleaverageswillbeidenticalwiththestatisticalaveragesandmayberepresentedbythesamesymbols.2.TheaveragesdeterminedbymeasurementsonasinglesampleFunctionatsuccessivetimeswillyieldatimeaverage,whichwerepresentasn2(t1).3.Suppose,forexample,thatthestatisticalcharacteristicsofthesampleFunctionsintheensemblewerechangingwithtime.4.Foritmayhappenthatwhileeachsamplefunctionisstationarytheindividualsamplefunctionsmaydifferstatisticallyfromoneanother.5.Asanextensionofthatresultweshalldefinethepowerspectraldensityofarandomprocessinthesameway.6.ItisofinteresttoinquirewhetherG(f)definedinEq.(1.2)forarandomprocesshasaphysicalsignificancewhichcorrespondstothephysicalsignificanceofG(f)fordeterministicwaveforms.8.Hence,ifweshouldselectsomesamplefunction,aknowledgeofthevalueofn(t)attimetwouldbeofnoassistanceinimprovingourabilitytopredictthevalueattainedbythatsamesamplefunctionattimet+τ.9.Hence,wheneverwemakeanobservationormeasurementofthepulsewaveformwhichextendsoveradurationlongenoughsothattheaverageobservedpulseshape,suchastheiramplitudes,widths,andspacingsarerepresentativeofthewaveformgenerally,weshallfindthatEq.(1.12)applies.10.Letusselectasectionofthiswaveformwhichextendsfrom-T/2to-T/2.11.Sincewehaveassumedanergodicprocess,weareatlibertytoperform(perform,performing)theaveragingoveranysamplefunctionoftheensemble,sinceeverysamplefunctionwillyieldthesameresult.Exercises1.ThereisanegativestatementassociatedwithonShannon’stheorem.2.thepurposeoftransmissionoverthechannel,themessagesarerepresentedbyfixedvoltagelevels.3.SincethetransmissionofanyoftheMmessagesisequallylikely,H=log2M,thusourchannelistransferringinformationatarateR=rH.4.Forafixedsignalpowerandinthepresenceofwhitegaussiannoisethechannelcapacityapproachesanupperlimitwithincreasingbandwidth.5.Itisofgreatinteresttorecognizethatthetradeoffbetweenbandwidthandsignaltonoiseratioisnotlimitedbyalowerlimitinbandwidth.6.ThesignalistransmittedinachannelwhichcanberepresentedasalowpassRCcircuitwithcutoffat1Hz.7.Ifthereisnonoise,thenweareentirelyfreetomakeasfortheattenuationbytheuseofanamplifierandtocorrectthefrequencydistortionbytheuseofanequalizer.8.Thatis,weneedtoestimatetheintervalTwhichshouldbeassignedtoeachmessagetoallowthetransmittedlevelstoberecognizedIndividuallyoverthereceiver,eventhoughthebandwidthBofthechannelislimited.9.Therefore,the25percentreductioninbandwidthrequiresa60percentincreaseofsignalpower.10.Whilewehaveusedthetermcommunicationchannelinmanyoccasions,itiswelltoemphasizeatthispoint,thattheterm,whichisSomethingasanabstraction,isintendedtoencompassallthefeaturesandcomponentpartsofthetransmissionsystemwhichintroducenoiseorlimitthebandwidth.11.TheprobabilityoferrorisclosetounityforeverypossiblesetofMtransmittersignals.12.ItturnsoutthattheresultsobtainedforagaussianchanneloftenprovidealowerboundintheperformanceofasystemOperatinginanongaussianchannel.ExercisesⅢ.Fillintheblankswiththemissingword(s).1.PCMisawidelydifferentformofmodulationcomparedwiththeanalogpulsetypessuchasPAM,PDM,andPPM.2.Thecharacteristicsofthepulsegrouparerelatedtothemessagesamplethroughoperationscalledquantizationandcoding.3.Thetermsymbolcoderdistingnishesthiscodingoperationfromtheoverallsourceencodingprocess.Inmostcases,avariablelengthcodeisusedtorepresentthemappedandquantizeddataset.Itassignstheshortestcodewordstothemostfrequentlyoccuring(occurring,occure,occurred)outputvaluesandthusreducescodingredundancy.4.Thus,aquantizationerrorexistsinPCMand,aswillbeseen,istheBasiclimitationinperformance.5.Quantizationandsamplingproducethesameresultassamplingandquantizing.6.Forequalpeakmagnitudes,signalswithlargecrestfactorsgivepoorerperformancethanthosewithsmallKcr.7.Inthereceivertheinverseoperationisimplementedbyanexpandortorestoretheoriginalmessage.8.Thedigitaldataisfedseriallyintothedecoder.9.astheratedrops,samplesaremadelessfrequentlyandstepsizesincrease.10.Theactualcompressionratioresultingfromthismethodisnomorethananorderof4∶1.11.Inanattempttoreduce（reduce，reducing）thenumberofcodessentbyaPCMsystem,aslightvarianceonsamplingmethodisusedbyasystemknownasDifferentialPulseCodeModulation(DPCM). ExercisesⅢ.Fillintheblankswiththemissingword(s).1.Channelcodingprotectsdigitaldatafromerrorsbyselectivelyintroducingredundanciesinthetransmitteddata.2.Byproperencodingoftheinformation,errorsinducedbyanoisychannelcanbereducedtoanydesiredlevelwithoutsacrificingtherateofinformationtransfer.3.Errorcontrolcodingwaveforms,ontheotherhand,havebandwidthexpansionfactorsthatgrowonlylinearlywiththecodeblocklength.4.Inablockencoder,kinformationbitsareencodedintoncodebits.5.Theblockcodeisreferredtoasan(n,k)code,andtherateofthecodeisdefinedasRc=k/nandisequaltotherateofinformationdividedbytherawchannelrate.6.Convolutionalcodesarefundamentallydifferentfromnblockcodesinthatinformationsequencesarenotgroupedintodistinctblocksandencoded.7.Thetreediagramshowsthestructureoftheencoderintheformofatreewiththebranchesrepresenting（represent，represented，representing）thevariousstatesandtheoutputsofthecoder.8.ThisreducesthebandwidthefficiencyofthelinkinhighSNRconditions,butprovidesexcellentBERperformanceatlowSNRvalues.9.Asystematiccodeisoneinwhichtheparitybitsareappendedtotheendoftheinformationbits.10.Achannelcoderoperatesondigitalmessage(orsource)databyencodingthesourceinformationintoacodesequencefortransmissionthroughthechannel. ExercisesⅢ.Fillintheblankswiththemissingword(s).1.Themethodinvolvesfirstsamplingtheinformationsignal,quantizingthesamplebyroundingofftotheclosestofanumberofdiscretelevels,andfinallygeneratingaprescribednumberofpulsesaccordingtoacoderelatedtothenearestdiscretelevel.2.Codedmodulationwillalsobereferredtoasdigitalmodulation.Itisoneofthemostmodernandusefulmethodsofmodulationavailabletoday.3.InPPMpulsepositionisproportionaltotheamplitudeofthemessagesignal4.Timedivisionmultiplexing(TDM)usespulsemodulationtoputsamplesofdifferentsignalsinnonoverlappingtimeslots.Forinstance,thegapsbetweenpulsescouldbefilledwithsamplesfromothersignals.5.Itisoftennecessarytousemodulationtotranslatetheusefulbandoffrequenciesuptoalargecarrierfrequencysothatefficientelectromagneticradiationispossiblefromanantennahavingreasonablesize.6.Thedesignofacommunicationsystemmaybeconstrainedbythecostandavailabilityofhardware,whoseperformanceoftendependsonthefrequenciesinvolved7.Fractionalbandwidthconsiderationsaccountforthefactthatmodulationunitsarefoundinreceiversaswellasintransmitters.8.Thesemethodsmaybecharacterizedascontinuouswave(cw)modulation.9.Sinceeachstationhasadifferentassignedcarrierfrequency,thedesiredsignalcanbeseparatedfromtheothersbyfiltering.10.PCMmaybeeitherbinary,wherepulseshaveonlytwovoltagelevels,orμ-ary,wherepulsesmaytakeonμpossiblelevels.11.Byexploitingthefrequencytranslationpropertyofcwmodulation,messageinformationcanbeimpressedonacarrierwhosefrequencyhasbeenselectedforthedesiredtransmissionmethod. ExercisesⅢ.Fillintheblankswiththemissingword(s).1.Speechcodingisafundamentaltechnologythathasexistedformorethan60years,beginninginthe1930swithDudley’soriginalvocoder.2.Speechcodingisdistin