上海海事大學(xué)信息工程學(xué)院

上海海事大學(xué)信息工程學(xué)院Unit11IntroductiontodigitalcommunicationBackgroundWordsandexpressionsTextandnotesGrammarExercisesReadingmaterial上海海事大學(xué)信息工程學(xué)院IntroductiontoTelecommunicationcordlessphone無繩電話basestation基站mobilestation移動站上海海事大學(xué)信息工程學(xué)院IntroductiontoTelecommunication天線Ametallicapparatusforsendingorreceivingelectromagneticwaves.alsocalledaerial上海海事大學(xué)信息工程學(xué)院TheHistoryofMobileRadioCommunication1880:Hertz–Initialdemonstrationofpracticalradiocommunication1897:Marconi–Radiotransmissiontoatugboatoveran18mipath1921:DetroitPoliceDepartment:--Policecarradiodispatch(2MHz frequencyband)1933:FCC(FederalCommunicationsCommission)–Authorizedfourchannelsinthe30to40MHzrange1938:FCC–Ruledforregularservice1946:BellTelephoneLaboratories–152MHz(Simplex)1956:FCC–450MHz(Simplex)1959:BellTelephoneLaboratories–Suggested32MHzbandforhigh capacitymobileradiocommunication1964:FCC–152MHz(FullDuplex)1964:BellTelephoneLaboratories–Activeresearchat800MHz1969:FCC–450MHz(FullDuplex)上海海事大學(xué)信息工程學(xué)院TheHistoryofMobileRadioCommunication1974:FCC–40MHzbandwidthallocationinthe800to900MHzrange1981:FCC–Releaseofcellularlandmobilephoneserviceinthe40MHzbandwidthinthe800to900MHzrangeforcommercialoperation1981:AT&TandRCC(RadioCommonCarrier)reachanagreementtosplit40MHzspectrumintotwo20MHzbands.BandAbelongsto nonwirelineoperators(RCC),andBandBbelongstowireline operators(telephonecompanies).Eachmarkethastwooperators.1982:AT&T

isdivested,andsevenRBOCs(RegionalBellOperating Companies)areformedtomanagethecellularoperations上海海事大學(xué)信息工程學(xué)院TheHistoryofMobileRadioCommunication1988:TDMA(TimeDivisionMultipleAccess)votedasadigitalcellularstandardinNorthAmerica1992:GSM(GlobalSystemforMobileCommunications

)operableinGermanyD2system1993:CDMA(CodeDivisionMultipleAccess)votedasanotherdigitalcellularstandardinNorthAmerica1994:AmericanCDMAoperableinSeattle,Washington1994:PDC(PersonalDigitalCellular)operableinTokyo,Japan上海海事大學(xué)信息工程學(xué)院TheHistoryofMobileRadioCommunication1995:CDMAoperableinHongKong1997:BroadbandCDMAconsideredasoneofthethirdgenerationmobilecommunicationtechnologiesforUMTS(UniversalMobile TelecommunicationSystems)duringtheUMTSworkshopconferenceheldinKorea1999:ITU(InternationalTelecommunicationUnion)decidesthenext generationmobilecommunicationsystems(e.g.,W-CDMA, cdma2000,etc)通信技術(shù)發(fā)展歷史回顧

有線通信1799年Volta發(fā)明電池；1837年S.Morse發(fā)明電報（變長度信源碼）；1844年華盛頓——巴爾的摩電報演示；1858年第一條橫跨大西洋的越洋電報電纜建成；1875年E.Baudet發(fā)明定長信源碼；1876年Bell申請電話專利；1877年建立Bell電話公司；1906年DeForest發(fā)明電子三極管放大；1915年實現(xiàn)橫跨美洲大陸的電話；二次大戰(zhàn)和經(jīng)濟大蕭條推遲了越洋電話業(yè)務(wù)；

1953年建立第一條橫越大西洋電話電纜；1960年Bell實驗室發(fā)明數(shù)字交換；在過去50年中電話有極大發(fā)展，光纖代替銅纜；

無線通信歷史

1820年Oersted

發(fā)現(xiàn)電流產(chǎn)生磁場；1831年Faraday發(fā)現(xiàn)導(dǎo)線作切割磁力線運動產(chǎn)生感應(yīng)電流；1864年Maxwell提出電磁場方程，預(yù)言電磁波存在；1894年O.Lodge發(fā)明粉末檢波器，在牛津檢測到150碼遠發(fā)出的無線信號；

1895年Marconi發(fā)明的無線電報，傳輸2公里；1897年Marconi申請無線電報專利，建立無線電報公司；1901年12月12日Marconi在加拿大紐芬蘭島收到從英國Cornwall發(fā)出的無線信號，傳輸距離1700mile.1900年專利《調(diào)諧電話》獲得批準，專利號為

No.7777；同年公司改名為Marconi公司；1907年獲諾貝爾物理獎1904年Flemin發(fā)明電子二極管；1906年DeForest發(fā)明電子三極管放大；1920年AM廣播在美國Pittsburgh開通；在一次大戰(zhàn)中E.Armstrong發(fā)明超外差A(yù)M接收機；1933年E.Armstrong發(fā)明FM；1929年美國人Zworykin發(fā)明電視；1933年英國BBC廣播電視開通；近50年來通信的發(fā)展

1947年Brattain,Bardeen,Shockley發(fā)明晶體管；

W.SHOCKLEY(1910-1989)J.BARDEEN(1908-1991)W.H.BRATTAIN(1902-1987)1955年Bell實驗室皮爾斯（Pirece）提出衛(wèi)星通信；1962年TelstarI衛(wèi)星發(fā)射，轉(zhuǎn)播歐、美之間電視廣播；1965年發(fā)射商用通信衛(wèi)星；1958年Townes,Schawlow發(fā)明激光；1966年英國學(xué)者高昆（K.C.Kao）與霍克汗姆（G.A.Hockham）預(yù)言光纖損耗可以降到20db/km以下，使光纖通信成為可能；1958年Kilby發(fā)明集成電路；70年代末Bell實驗室提出蜂窩式無線公眾移動通信網(wǎng)；目前2G→3G→B3G；Clinton總統(tǒng)給R.Frenkiel

授獎通信系統(tǒng)理論

1924年奈奎斯特（Nyquist）研究表明帶寬為W的信道最多可以支持每秒2W個符號的無碼間干擾傳輸，現(xiàn)代數(shù)字通信的開端。1928年維納（Wiener）提出濾波理論和預(yù)測理論，奠定了控制論；1943年諾斯（D.O.North）提出了匹配濾波器理論；1947年蘇聯(lián)學(xué)者卡捷爾尼可夫（Kotelnikov）發(fā)展了信號的幾何表示理論，并建立了信號的潛在抗干擾理論；上世紀40年代，賴斯（O.Rice）關(guān)于隨機噪聲的數(shù)學(xué)研究；1948年Shannon建立信息論（通信的數(shù)學(xué)理論）1950年Hamming提出糾錯編碼；之后在Shannon理論指導(dǎo)下，各種信道糾錯編碼，信源壓縮編碼，調(diào)制方式，多用戶通信理論，網(wǎng)絡(luò)理論，擴譜理論，多天線理論，合作通信理論等蓬勃發(fā)展起來；

上海海事大學(xué)信息工程學(xué)院BackgroundBellLaboratories:BellLaboratories(alsoknownasBellLabsandformerlyknownasAT&TBellLaboratoriesandBellTelephoneLaboratories)istheresearchanddevelopmentorganizationofAlcatel-LucentandpreviouslyoftheAmericanTelephone&TelegraphCompany(AT&T).BellLaboratoriesoperatesitsheadquartersatMurrayHill,NewJersey,andhasresearchanddevelopmentfacilitiesthroughouttheworld.上海海事大學(xué)信息工程學(xué)院BackgroundBellLaboratories:TheCprogramminglanguagewasdevelopedatBellLaboratoriesin1970Thefirsttransistor,apoint-contact

germaniumdevice,wasinventedatBellLaboratoriesin1947.Thisimageshowsareplica.上海海事大學(xué)信息工程學(xué)院backgroundClaudeElwoodShannon(April30,1916–February24,2001),anAmerican

electronicengineerandmathematician,isknownas"thefatherofinformationtheory".[1]Shannonisfamousforhavingfoundedinformationtheorywithonelandmarkpaperpublishedin1948.Butheisalsocreditedwithfoundingbothdigitalcomputeranddigitalcircuitdesigntheoryin1937,when,asa21-year-oldmaster'sstudentatMIT,hewroteathesisdemonstratingthatelectricalapplicationofBooleanalgebracouldconstructandresolveanylogical,numericalrelationship.Ithasbeenclaimedthatthiswasthemostimportantmaster'sthesisofalltime.[2]上海海事大學(xué)信息工程學(xué)院Wordsandexpressionscharacteristic adj.特有的，典型的；n.特性，特色redundancy n.過剩；冗余；裁員encode v.

把……編碼，譯碼compression n.

壓縮，濃縮；壓榨，壓迫interference n.干擾；干涉；干預(yù)；介入；沖突reliability n.可靠性fidelity listeningtest

n.保真度；忠誠；盡責；精確

trivial adj.

不重要的，瑣碎的；微不足道的sophisticated adj.復(fù)雜的，精密的；富有經(jīng)驗的map n.地圖，圖；v.映射；繪制地圖；計劃sequence n.

序列；有次序的事情、數(shù)字、行動等reciprocal adj.互相給予的；互惠的；相互的modulator n.

調(diào)制器，調(diào)節(jié)的人elaborateadj.復(fù)雜的；精心制作的；v.詳盡闡述

transmittern.發(fā)射機，發(fā)射臺；發(fā)報臺；傳輸者上海海事大學(xué)信息工程學(xué)院Wordsandexpressionsreceiver n.接收器；無限電接收機；接受者mechanism n.機械裝置；機理，機制；工作方式ignition n.點火；著火；點火開關(guān)demodulator n.解調(diào)器distortion n.扭曲，變形，失真，曲解precursor n.先驅(qū)，前導(dǎo)，先鋒；預(yù)兆；前身constraint n.限制，拘束感interpolationn.竄改，添寫，插補，【數(shù)學(xué)】插值法resolutionn.分辨率；決心；決議；解析；解決capacityn.容量；能力；能量；資格coherentadj.

緊密結(jié)合的；（各部分之間）一致的

協(xié)調(diào)的；【物理學(xué)、光學(xué)】相干的geometricaladj.

幾何學(xué)的，幾何的detrimentaladj.

有害的，不利的；n.有害的人或物benchmarkn.標準檢查程序，基準，參照；v.檢測上海海事大學(xué)信息工程學(xué)院WordsandexpressionsM-arymodulationM進制調(diào)制stemfrom是……的結(jié)果；起源于lead…into…帶領(lǐng)，引導(dǎo)；通往；致使samplingtheorem采樣定理mean-squareapproximation均方估算beassociatedwith與……有關(guān)，與……有關(guān)系；涉及additivewhiteGaussiannoise加性高斯白噪聲上海海事大學(xué)信息工程學(xué)院TextandnotesOfparticularimportanceintheanalysisanddesignofcommunicationsystemsarethecharacteristicsofthephysicalchannelsthroughwhichtheinformationistransmitted.分析和設(shè)計通信系統(tǒng)的特別重要性在于傳遞信息的物理信道的特性。上海海事大學(xué)信息工程學(xué)院TextandnotesThepurposeofthechannelencoderistointroduce,inacontrolledmanner,someredundancyinthebinaryinformationsequencethatcanbeusedatthereceivertoovercometheeffectsofnoiseandinterferenceencounteredinthetransmissionofthesignalthroughthechannel.信道編碼器的作用是以控制的形式在二進制信息序列中引入一些冗余，使在接收器端能克服信號在信道中傳輸時所遇到的噪聲和干擾的影響。上海海事大學(xué)信息工程學(xué)院TextandnotesAlthoughMorseisresponsibleforthedevelopmentofthefirstelectricaldigitalcomunicationsystem(telegraphy),thebeginningsofwhatwenowregardasmoderndigitalcommunicationsstemfromtheworkofNyquist(1924),whoinvestigatedtheproblemofdeterminingthemaximumsignalingratethatcanbeusedoveratelegraphchannelofagivenbandwidthwithoutintersymbolinterference.雖然摩爾斯發(fā)明了首個電氣數(shù)字通信系統(tǒng)（電報），但我們現(xiàn)在所認為的現(xiàn)代數(shù)字通信起源于1924年奈奎斯特的工作，他研究了如何確定在一個給定帶寬的信道上無符號干擾發(fā)生的最大信號速率。上海海事大學(xué)信息工程學(xué)院TextandnotesNyquistsetouttodeterminetheoptimumpulseshapethatwasband-limitedtoWHzandmaximizedthebitrateundertheconstraintthatthepulsecausednointersymbolinterferenceatthesamplingtimek/T,k=0,±1,±2…...奈奎斯特著手于確定帶限為W赫茲的最優(yōu)脈沖圖形，并保證在采樣時間為k/T,k=0,±1,±2…...時，脈沖不會導(dǎo)致字符間相互干擾條件下，將比特率最大化。上海海事大學(xué)信息工程學(xué)院TextandnotesHealsodemonstratedthattheeffectofatransmitterpowerconstraint,abandwidthconstraint,andadditivenoisecanbeassociatedwith

thechannelandincorporatedintoasingleparameter,calledthechannelcapacity.他還演示了傳輸功率約束、帶寬約束及疊加噪聲的影響能與信道結(jié)合，并能歸結(jié)到一個稱為信道容量的參數(shù)。上海海事大學(xué)信息工程學(xué)院TextandnotesInthecourseofthesedevelopments,Shannon’soriginalresultsandthegeneralizationofhisresultsonmaximumtransmissionlimitsoverachannelandonboundsontheperformanceachievedhaveservedasbenchmarksforanygivencommunicationsystemdesign.在這些發(fā)展的過程中，香農(nóng)的原始結(jié)論和其結(jié)論在信道上的傳輸最大限制和獲得的性能界限方面的歸納可以作為任何給定通信系統(tǒng)設(shè)計的基礎(chǔ)。上海海事大學(xué)信息工程學(xué)院Grammar－定語從句定語從句修飾句中的某以名詞或代詞，用在先行詞之后。引導(dǎo)定語從句的關(guān)系詞有who,whom,whose,that,how,when,where,whyandwhich.定語從句可以分為限制性定語從句和非限制性定語從句兩種。1、限制性定語從句限制性定語從句對所修飾的先行詞起限制作用，在意義上與先行詞密切不可分，一般不可用逗號與主句分割。Oncethesignalsareconvertedtolight,theytraveldownthefiberuntiltheyreachadetectorwhichchangesthelightsignalsbackintoelectricalsignals.上海海事大學(xué)信息工程學(xué)院Grammar－定語從句Sourcesareoftendescribedintermsofthefrequencythattheyoccupy.Thereaderwhoisimpatienttogetontodigitalsystemsrealizethatmanydigitalsystemsalsorequireanalogtechnologytofunction.APONisapassiveopticalnetworkwhereATMisadoptedtotransmitbroadbandandnarrowbandcellsviatheSDHframestructure.注：當引導(dǎo)定語從句的先行詞前有all,any,no,little,much,very,first等詞，或先行詞前為形容詞最高級、序數(shù)詞所修飾時，或先行詞為all,anything,nothing,everything時，從句的引導(dǎo)詞只能用that.上海海事大學(xué)信息工程學(xué)院Grammar－定語從句Thisisoneoftheveryfewbooksatanylevelthatpresentsaformulaforfindinganyvoltageorcurrentinthedc-excitedRC(orRL)circuitsthataresoimportantintimes.Noisesignalsareanyelectricalsignalsthatinterferewiththeerror-freereceptionofthemessage-bearingsignal.上海海事大學(xué)信息工程學(xué)院Grammar－定語從句2、非限定性定語從句非限定性定語從句僅對先行詞進行解釋或補充說明，有時含有原因、讓步、時間、條件、結(jié)果等意義，從句要用逗號與主句分開，關(guān)系代詞不能省略，通常用which(不用that),who,when

等引導(dǎo)。Microwaves,whichhaveahigherfrequencythanordinaryradiowaves,areusedroutinelyinsendingthousandsoftelephonecallsandtelevisionprogramsacrosslongdistances.Foraradiowaveinfreespace,thevelocityisthesameasthatoflight,whichisapproximately300×106meterspersecond.上海海事大學(xué)信息工程學(xué)院Grammar－定語從句3、介詞＋which,whom,whose從句Firstofall,letusintroduceyoutosomeofthecircuitsthatarecommonlyfoundinradio-frequencysystemsandwithwhichyoumaynotbefamiliar.Amagnetcancauseanelectriccurrentinawirenearwhichitismoved.上海海事大學(xué)信息工程學(xué)院Grammar－定語從句4、代詞/名詞＋介詞＋which從句Directcurrentisanelectriccurrentthechargesofwhichmoveinonedirectiononly.Theanalogworldisfullofrelativenumbers,tradeoffs,andapproximations,allofwhichdependheavilyonthebasicsemiconductorproperties.上海海事大學(xué)信息工程學(xué)院常用寫作句型……分成兩大類……fallinto(aredividedinto,areclassifiedinto,areof)twomajor(general,broad)groups(classes,categories).Therearetwomajor(general,broad)groups(classes,categories)of……上海海事大學(xué)信息工程學(xué)院常用寫作句型該項目研究的主要目的在于……Thechief(main,primary,major,principle)aim(purpose,object,objective,goal)ofthestudyis……Thestudyhasbeenstartedinthehopeof(withaviewto,inorderto,totheendthat,sothat)……Thestudyisintended(designed)to(do)……Performingthestudywehope(intendtodo,expect)……上海海事大學(xué)信息工程學(xué)院常用寫作句型……在……范圍之內(nèi)（外）?！璱s(lies,goes,comes,falls)within(beyond)……這是與……有關(guān)的問題。Thisisaproblemconcernedwith(concerning,relatedto,relatingto,bearingon,dealingwith)……句子翻譯練習(xí)這篇文章主要研究基于壓縮傳感技術(shù)的紅外小目標檢測算法。大目標檢測不是本文的研究目標。機器學(xué)習(xí)方法可以分為有監(jiān)督和無監(jiān)督兩大類。接收機前端電路的噪聲可能對通信系統(tǒng)產(chǎn)生很大的影響。上海海事大學(xué)信息工程學(xué)院句子翻譯練習(xí)無線電的發(fā)明使人類有可能進行遠距離通信。每個邊帶通過該系統(tǒng)后，它就會相對于載波被旋轉(zhuǎn)了一個角度。本文提出了設(shè)計天線結(jié)構(gòu)的一種新方法。上海海事大學(xué)信息工程學(xué)院句子翻譯練習(xí)Quadratureamplitudemodulation(QAM)andfrequencydivisionmultiplexing(FDM)aretheprecursorsofmanyofthenewcommunicationsystems.QAMandFDMareofgreatinterestfortheirefficientuseoftheradiospectrum.上海海事大學(xué)信息工程學(xué)院WordsinlisteningmaterialSmart：智能的Self-drivingcar：自動駕駛車Geometric：幾何的Driverless:無人駕駛的Driverassistancesystem:駕駛輔助系統(tǒng)上海海事大學(xué)信息工程學(xué)院聽力練習(xí)TI公司產(chǎn)品介紹DavidLang:我的水下機器人無人駕駛汽車是如何看清路況的上海海事大學(xué)信息工程學(xué)院Exercises1.Choosethebestanswerforeachofthefollowingquestions.(1)Intheanalysisanddesignofcommunicationsystems,_____isparticularlyimportant. a.thecharacteristicsofthephysicalchannels b.thesourceoutput c.thebinaryinformationsequence d.theamountofredundancyintroduced上海海事大學(xué)信息工程學(xué)院aExercises1.Choosethebestanswerforeachofthefollowingquestions.(2)Thepurposeofthechannelencoderisto_____. a.convertmessagesintoasequenceofbinarydigits roduceredundancytoovercometheeffectsofnoiseandinterference c.seekanefficientrepresentationofthesourceoutput d.mapthebinaryinformationsequenceintosignalwaveforms上海海事大學(xué)信息工程學(xué)院bExercises1.Choosethebestanswerforeachofthefollowingquestions.(3)Theprimarypurposeof_____istomapthebinaryinformationsequenceintosignalwaveforms. a.sourceencoder b.channelencoder c.digitalmodulator d.digitaldemodulator上海海事大學(xué)信息工程學(xué)院cExercises1.Choosethebestanswerforeachofthefollowingquestions.(4)ThesamplingtheoremstatesthatasignalofbandwidthWcanbereconstructedfromsamplestakenattheNyquistrateof_____. a.W b.2W c.3W d.4W上海海事大學(xué)信息工程學(xué)院bExercises1.Choosethebestanswerforeachofthefollowingquestions.(5)AccordingtoShannon’sinformationtheory,thecapacityofanidealband-limitedchannelisrelevantto_____. a.bandwidth b.averagetransmittedpower c.additivenoise d.allofabove上海海事大學(xué)信息工程學(xué)院dExercises2.Substituteunderliningwordwiththemostappropriatechoice.(1)Toelaborateonthispoint,letussupposethatthecodedinformationsequenceistobetransmittedonbitatatimeatsomeuniformrateRbitspersecond(bits/s). a.abbreviate b.collaborate c.workout d.respect上海海事大學(xué)信息工程學(xué)院cExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(2)Inotherwords,weseekanefficientrepresentationofthesourceoutputthatresultsinlittleornoredundancy.a.recover b.leadto c.couplewith d.contributeto上海海事大學(xué)信息工程學(xué)院bExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(3)Ineffect,redundancyintheinformationsequenceaidstothereceiverindecodingthedesiredinformationsequence. a.help b.prevent c.disturb d.decrease上海海事大學(xué)信息工程學(xué)院aExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(4)Alternatively,themodulatormaytransmitbcodedinformationbitsatatimebyusingM=2b

distinctwaveformsSi(t),i=0,1,…,M01,onewaveformforeachofthe2bpossibleb-bitsequences._____ a.meaningful b.ambiguous c.similar d.different上海海事大學(xué)信息工程學(xué)院dExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(5)Morsedevisedthevariable-lengthbinarycodeinwhichlettersoftheEnglishalphabetarerepresentedbyasequenceofdotsanddashes(codewords). a.create b.change c.study d.demonstrate上海海事大學(xué)信息工程學(xué)院aExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(6)Nyquistsetouttodeterminetheoptimumpulseshapethatwasband-limitedtoWHzandmaximizedthebitrateundertheconstraintthatpulsecausednointersymbolinterferenceatthesamplingtimek/T,k=0,+/-1,+/-2,….Hisstudiesledhimtoconcludethatthemaximumpulserateis2Wpulses/s. a.worst b.suitable c.optimal d.efficient上海海事大學(xué)信息工程學(xué)院cExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(7)AnotherimportantcontributiontothefieldofdigitalcommunicationistheworkofKotelinikov(1947),whoprovidedacoherentanalysisofthevariousdigitalcommunicationsystemsbasedonageometricalapproach. a.consistent b.difficult prehensive d.useful上海海事大學(xué)信息工程學(xué)院aExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(8)Theincreaseindemandfordatatransmissionduringthelastfourdecades,coupledwiththedevelopmentofmoresophisticatedintegratedcircuits,hasledtothedevelopmentofveryefficientandmorereliabledigitalcommunicationsystems. a.simple plicated c.reliable d.advanced上海海事大學(xué)信息工程學(xué)院bExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(9)Inthecourseofthesedevelopments,Shannon’soriginalresultsandthegeneralizationofhisresultsonmaximumtransmissionlimitsoverachannelandonboundsontheperformanceachievedhaveservedasbenchmarksforanygivencommunicationsystem. a.criterion b.result c.demand d.analysis上海海事大學(xué)信息工程學(xué)院aExercises2.Substitutetheunderliningwordswiththemostappropriatechoice.(10)ThetheoreticallimitsderivedbyShannonandotherresearchersthatcontributedtothedevelopmentofinformationtheoryserveasanultimategoalinthecontinuingeffortstodesignanddevelopmoreefficientdigitalcommunicationsystems. a.practical b.first c.impossible d.final上海海事大學(xué)信息工程學(xué)院dExercises3. TranslatethefollowingsentencesintoChinese.(1)Whateverthenatureofthesource,theoutputfromthesourcewillbemodeledasasamplefunctionofarandomprocess.Itisnotobviouswhytheinputstocommunicationsystemsshouldbemodeledasrandom,andinfactthiswasnotappreciatedbeforeShannondevelopedinformationtheoryin1948.上海海事大學(xué)信息工程學(xué)院Exercises3. TranslatethefollowingsentencesintoChinese.(2)Asinthestudyofanytypeofsystem,achannelisusuallyviewedintermsofitspossibleinputs,itspossibleoutputs,andadescriptionofhowtheinputaffectstheoutput.Thisdescriptionisusuallyprobabilistic.(3)Thechannelcapacityisafunctionoftheprobabilisticdescriptionoftheoutputconditionaloneachpossibleinput.Conversely,itisnotpossibletoachievelowerrorprobabilityatratesabovethechannelcapacity.上海海事大學(xué)信息工程學(xué)院Exercises3. TranslatethefollowingsentencesintoChinese.(4)TheDLCalsoprovidesprotectionagainstdecodingerrorsmadebythechanneldecoder.Typicallythisisdonebyusingasetof16or32paritychecksintheframetrailer.Eachparitycheckspecifieswhetheragivensubsetofbitsintheframecontainsanevenoroddnumberof1’s.Thusiferrorsoccurintransmission,itishighlylikelythatatleastoneoftheseparitycheckswillfailinthereceivingDLC.上海海事大學(xué)信息工程學(xué)院Exercises3. TranslatethefollowingsentencesintoChinese.(5)Theblocksofbinarydigitscanbegeneralizedintovariable-lengthsequencesofbinarydigits.Weshallfindthatanygivendiscretesource,characterizedbyitsalphabetandprobabilisticdescription,hasaquantitycalledentropyassociatedwithit.上海海事大學(xué)信息工程學(xué)院Exercises4. Completethefollowingsentenceswithrelativeclause.

(1)Radio,telephone,andtelegrapharemeans____________________________________________

________________.

無線電、電話和電報是人們用以擴大自身聽與說感官范圍的手段。上海海事大學(xué)信息工程學(xué)院bywhichmanhasextendedtherangeofhissensesofhearingandspeechExercises4. Completethefollowingsentenceswithrelativeclause. (2)Wefirstdealwithwaves________________

________.

我們首先討論頻率恒定的波。上海海事大學(xué)信息工程學(xué)院 whosefrequencyisconstantExercises4. Completethefollowingsentenceswithrelativeclause.

(3)Oneoftheadvantagesofdigitalcommunicationistheabilitytoregenerateasignal____________

___________