专业英语课后答案

ExercisesⅠ.PleasetranslatethefollowingwordsandphrasesintoChinese.Exercises1.samplefunction 样本函数2.ensembleaverage总体均值3.physicalsignificance 物理意义4.aFouriertransformpair傅里叶变换对5.deterministicwaveform 确定性波形6.inthelimit在极限情况下7.timeinvariant 时不变的8.anupperfrequencylimit 频率上限9.Parseval’stheorem巴塞瓦尔定理10.randompulses 随机脉冲Exercises1.physicalsystem 物理系统，实际系统 2.risetime 上升时间3.amountofinformation 信息量4.inprinciple 理论上，原则上5.gaussianchannel 高斯信道6.probabilitydensity 概率密度7.rootmeansquare 均方根值，均方根，8.tradeoff交替换位，折衷选择9.lowerbound 下限，下界1.equalizer均衡器11.viceversa反之亦然12.upperlimit上限Exercises1.overallperformance 总性能2.crestfactor振幅（波峰）因数（振幅与有效值之比）3.nonlinearoperation非线性运算4.inverseoperation 逆操作5.rms 均方根（值）6.PAM 振幅调制7.PDM 脉宽调制8.PPM 脉冲相位调制9.maximummagnitude最大幅值10.errorintervals 误差间隔11.Entropy 熵，平均信息量12.roundoff 舍入，用四舍五入化为整数13.quantumlevel 量化电平14.DPCM 差分脉冲编码调制Exercises1.channelcoding 信道编码2.transmissionbandwidth 传输带宽3.Singlesidednoisepowerdensity 单边带噪声功率密度4.orthogonalsignaling正交信号5.FEC 前向纠错6.logictable 逻辑表7.systematiccode 系统码8.AWGN 加性高斯白噪声9.BER 误码率，误比特率（biterrorratio）10.trellisdiagram 网格图11.constraintlength 制约长度12.vectorarray 向量数组13.algebraicfunction 代数函数14.statediagram 状态图15.cyclicshift 循环移位16.generatormatrix 生成矩阵Exercises1.AM 幅度调制（amplitudemodulation）2.DPSK 差分相位键控(differentialPSK)3.PAM 脉冲振幅调制（pulseamplitudemodulation）4.PDM 脉宽调制（pulsedurationmodulation）5.PPM 脉冲相位调制（pulsephasemodulation）6.PCM 脉冲编码调制（pulsecodemodulation）7.DPCM 差分脉冲编码调制（differentialpulsecodemodulation）8.ASK 振幅键控（amplitudeshiftkeying）9.FSK 频移键控（frequencyshiftkeying）10.FDM 频分多路复用（frequencydivisionmultiplexing）11.TDM 时分多路复用（timedivisionmultiplexing）12.codedmodulation编码调制13.suppressedcarrier 抑制载波14.modulatedsignal 已调信号 Exercises1.copperwire 铜线2.speechrecognition 语音识别3.adaptivedifferentialPCM 自适应差分脉码调制4.infiniteimpulseresponse(IIR) 无限脉冲响应5.realtimeconversation 实时交换6.digitalsignalprocessing 数字信号处理7.CELP 码激励线性预测（codeexcitedlinearprediction）8.VAD 话音激活检测器(voiceactivitydetector)9.MPE 多脉冲激励(multipulseexcitation)10.ADPCM 自适应差分脉码调制 (adaptivedifferentialPCM)11.directquantization 直接量化12.logpulsePCMquantizer 对数脉冲PCM量化器 ExercisesⅡ.PleasetranslatethefollowingwordsandphrasesintoEnglish.1.随机过程 randomprocess2.统计平均 statisticalaverage3.随机变量 randomvariable4.自相关函数 autocorrelationfunction5.傅里叶变换 Fouriertransform6.功率谱密度 powerspectraldensity7.概率密度函数 probabilitydensityfunction8.高斯过程 gaussianprocess9.平稳过程 astationaryprocess10.统计独立 statisticallyindependent11.时间平均(值) timeaverage12.统计特性 statisticalcharacteristic13.各态历经过程 ergodicprocess14.狄拉克函数 deltafunctionExercises1.通信理论 communicationtheory(theoryofcommunications)2.香农定理 Shannon’stheorem3.信道带宽 channalbandwidth4.信号波形 signalwaveform5.理想低通滤波器 ideallowpassfilter6.自相关函数 autocorrelationfunction7.无噪声高斯信道 noiselessgaussianchannel8.通信信道 communicationchannel9.信息速率 informationrate10.信噪比 signaltonoiseratio(SNR,S/N)11.信道容量 channalcapacity12.双边功率谱密度 Twosidedpowerspectraldensity13.误码率 errorprobability(probabilityfoerror)14.奈奎斯特采样速率 Nyquistsamplingrate15.限带高斯信道 bandlimitedgaussianchannel16.高斯白噪声 whiteGaussiannoiseExercises1.正脉冲 positivepulse2.脉冲编码调制 pulsecodemodulation3.解码器 decoder4.编码器 encoder5.量化步长 quantumstepsize6.峰值 peakmagnitudes7.线性函数 linearfunction8.脉冲序列 pulsetrain9.均匀量化器 uniformquanizer10.预测编码 predictivecoding11.压扩器 compandor12.压缩比 compressionratioExercises1.检错码 errordetectioncode2.信道容量channelcapacity3.分组码 blockcode4.卷积码convolutionalcode5.移位寄存器 shiftregister6.汉明距离 Hammingdistance7.码重 codeweight(weightofcode)8.树形图 treediagram9.编码增益 codinggain10.平均比特能量 averagebitenergy11.码距 codedistance(distanceofcode)12.纠错码 errorcorrectioncode13.带宽效率 bandwidthefficiency14.模2加法器 modulo2adder15.原始数据 rawdata16.编码率 coderate17.生成多项式 generatorpolynomial18.循环码 cycliccodeExercises1.带通信号 bandpasssignal2.脉冲调制 pulsemodulation3.角度调制 anglemodulation4.残留边带抑制载波调制 vestigialsidebandsuppressedcarriermodulation5.绝对带宽 absolutebandwidth6.脉冲宽度 pulseduration7.线性函数 linearfunction8.载波频率 carrierfrequency9.模拟调制 analogmodulation10.移相键控 PSK（phaseshiftkeying）11.连续波调制 continuouswave(CW)modulation12.同轴电缆 coaxialcable Exercises1.共振峰跟踪滤波器 formanttrackingfilter2.国际电信联盟 InternationalTelecommunicationsUnion(ITU)3.背景噪声 backgroundnoise4.双向通信 two-waycommunication5.基音跟踪滤波器 pitchtrackingfilter6.长时预测 long-termprediction7.语音编码 speechcoding8.声码器 vocoder9.语音增强 speechenhancement10.波形跟随编码器 waveformfollowingcoder11.参数编码器 parametriccoder12.频域编码器 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