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1、Unit 1 basics of communication,Text AA Mathematical Theory of Communication,Unit 1,原文:The recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication.,译文:各种调制方法，如PCM和PPM，能
2、够完成带宽与信噪比的交换，它们的发展增强了通信理论的重要性。,Unit 1,原文:A basis for such a theory is contained in the important papers of Nyquist and Hartley on the subject.,译文:在本学科，Nyquist和Hartley的重要论文中包含了这种理论的基础。,Unit 1,原文:In this paper we will extend the theory to include a number of new factor,in particular the effect of nois
3、e in the channel,and the savings possible due to the statistical structure of the original message and due to the nature of the final destination of information.,译文:在本文中，我们将这些理论进行扩展，包括许多新的因素，尤其是信道中噪声的影响，以及可能由于原始信息的统计结构和信宿的特性所导致的信息存储。,Unit 1,原文:The fundamental problem of communication is that of repr
4、oducing at one point either exactly or approximately a message selected at another point.,译文:通信的基本问题是如何在一点精确或近似的再生来自另一点的信息。,Unit 1,原文:Frequently the messages have meaning,that is they refer to or are correlated according to some system with certain physical or conceptual entities.,译文:信息通常有具体含义，按照一定的
5、物理或概念实体，其含义与这些系统相互关联。,Unit 1,原文:These semantic aspects of communication are irrelevant to the engineering problem.A significant aspect is that the actual message is one selected from a set of possible messages.,译文:这些通信的语义方面与工程问题不相干。一个重要的方面是那个实际的消息是从一组可能的消息中选出来的。,原文:These semantic aspects of communic
6、ation are irrelevant to the engineering problem.A significant aspect is that the actual message is one selected from a set of possible messages.,译文:这些通信的语义方面与工程问题不相干。一个重要的方面是那个实际的消息是从一组可能的消息中选出来的。,Unit 1,原文:The system must be designed to operate for each possible selection,not just the one which wil
7、l actually be chosen since this is unknown at the time of design.,译文:系统必须被设计成为每个可能的选择进行运行，而不仅仅是那个实际上将被抽中的，因为这在设计时是未知的。,Unit 1,原文:If the number of messages in the set is finite then this number or any monotonic function of the number can be regarded as a measure of the information produced when one m
8、essage is chosen from the set,all choices being equally like.,译文:如果集合中信息的数量是有限的，那么当一个信息被从所有的选择是等概的集合中抽出时，这个数或这个数的任何单调函数可被认为是信息的量被出示。,Unit 1,原文:As was pointed out by Hartley the most natural choice is the logarithmic function.,译文:如Hartley所指出的，最自然的选择是个对数函数。,Unit 1,原文:Although this definition must be g
9、eneralized considerably when we consider the influence of the statistics of the message and when we have a continuous range of messages,we will in all cases use an essentially logarithmic measure.,译文:尽管当我们考虑到这个消息统计的影响力以及当我们有了连续一套的信息，这个定义必须被广义地概括，不论什么情况下我们将使用一个本质地对数测量。,Unit 1,原文:The logarithmic measu
10、re is more convenient for various reasons:1.It is practically more useful.Parameters of engineering importance such as time,bandwidth,the number of relays,etc.,tend to vary linearly with the logarithm of the number of possibilities.,译文:对数测量更加方便，理由如下：1.对数测量实际上更加有用。工程的重要参数，如时间、带宽、继电器数，等等，趋向于随可能数字的对数线性
11、改变。,Unit 1,原文:For example,adding one relay to a group doubles the number of possible states of the relays.It adds 1 to the base 2 logarithm of this number.Doubling the time roughly squares the number of possible messages,or doubles the logarithm,etc.,译文:例如，加一个继电器到一个组中会使继电器的可能形态的数量翻倍。它加了1到这个以2为底的数的对数
12、。翻倍时间大约是将可能信息的数量平方，或将对数翻倍，等等。,Unit 1,原文:2.It is nearer to our intuitive feeling as to the proper measure.This is closely related to(1)since we intuitively measures entities by linear comparison with common standards.,译文:2.这更接近我们关于合适尺寸的直观感受。这与（1）紧密相关，因为我们用通用标准的线性比较直观地测量实体对象。,Unit 1,原文:One feels,for e
13、xample,that two punched cards should have twice the capacity of one for information storage,and two identical channels twice the capacity of one for transmitting information.,译文:一种感觉，例如，一人感觉两张穿孔卡片应该有两倍的一张卡的信息贮存量，两条相同的通道两倍于一条的传输信息量。,Unit 1,原文:3.It is mathematically more suitable.Many of the limiting
14、operations are simple in terms of the logarithm but would require clumsy restatement in terms of the number of possibilities.,译文:3.它在算数上更合适。许多限制操作就对数而言是简单的但是就可能性的数量而言将需要笨拙的再声明。,Unit 1,原文:The choice of a logarithmic base corresponds to the choice of a unit for measuring information.If the base 2 is u
15、sed,the resulting units may be called binary digits,or more briefly bits,a word suggested by J.W.Tukey.,译文:对数底的选择对应测量信息单位的选择。如果以2为底，产生的单元可以叫二进制数字，或更简要地叫比特，一个由建议的词。,Unit 1,原文:A device with two stable positions,such as a relay or a flip-flop circuit,can store one bit of information.N such devices can
16、store N bits,since the total number of possible states is 2N and.If the base 10 is used,the units may be called decimal digits.,译文:一个有两个稳定状态的设备，如一个继电器或一个触发电路能储存一比特信息。N个这样的设备能储存N比特信息，因为所有可能形式的数量是2N且。如果以10为底产生的单元可以被称为十进制数字。,Unit 1,原文:Since（1.1）,译文:因为（1.1）,Unit 1,原文:A decimal digit is about bits.A digi
17、t wheel on a desk computing machine has ten stable positions and therefore has a storage capacity of one decimal digit.,译文:一个十进制数大约比特。一个台式计算机器的数字轮有十个稳定状态且由此它有一个十进制数的储存容量。,Unit 1,原文:In analytical work where integration and differentiation are involved the base e is sometimes useful.The resulting unit
18、s of information will be called natural units.Change from the base a to base b merely requires multiplication by.,译文:以e为底在涉及积分微分的分析工作时有时是有用的。信息单元的结果将被命名为自然单元。从以a为底变到以b为底仅仅只要乘以。,message,message,Noisesource,receiver,transmitter,Receiversignal,signal,Figure 1.1 Schematic diagram of a general communicat
19、ion system,Unit 1,原文:By a communication system we will mean a system of the type indicated schematically in Figure 1.1.It is consists of essentially five parts:,译文:我们用示意图图1.1表明类型的系统说明通信系统。它包含了5重要的部分：,Unit 1,原文:1.An information source which produces a message or sequence序列 of messages to be communica
20、ted to the receiving（terminal末端的，终端的）.The message may be of various types.,译文:1.一个信息来源，产生一个被送至接收端的消息或消息序列。这个消息可能有各种类型。,Unit 1,原文:(a)A sequence of letters as in a telegraph of（teletype system电报系统）;(b)A single function of time f(t)as in radio or telephony;,译文:（a）在一个电报系统的电报的一个字母序列如；（b）在收音机或电话中的一个单一时间函数
21、f（t）；,Unit 1,原文:(c)A function of time and other variables as in black and white televisionhere the message may be thought of as a function f(x,y,t)of two space coordinates 坐标and time,the light intensity 强度at point(x,y)and time t on a pickup tube plate管板;,译文:（c）一个时间函数和在黑白电视机的其他变量这里信息可能被认为一个两个空间坐标和时间的
22、函数f（x，y，t），在点（x，y）的光强度和在一个摄像管的板子上的时间t；,Unit 1,原文:(d)Two or more functions of time,say f(t),g(t),h(t)this is the case in three dimensional 空间sound transmission or if the system is intended to service several individual channels in multiplex;,译文:（d）两个或更多的时间函数，像f（t）、g（t）、h（t）这是三维音频传输的形式或如果系统想维护多路复用系统中的
23、几条单独信道；,Unit 1,原文:(e)Several functions of several variablesin color television the message consists of three functions f(x,y,t),g(x,y,t)and h(x,y,t)defined in a three-dimensional 三维continuum连续,译文:（e）几个多变量的函数在彩色电视机中，信息包含在一个三位连续统中定义的三个函数f（x，y，t）、g（x，y，t）和h（x，y，t）,Unit 1,原文:we may also think of these t
24、hree functions as 作为 components of a vector field defined in the region地区similarly相似的,several black and white television sources would produce产生 messages consisting of a number of functions of three variables变量;,译文:我们或许还认为这三个函数作为一个域内定义的矢量场的成分相似的，几台黑白电视机信息来源将产生包含许多三变量的函数的信息；,Unit 1,原文:(f)Various comb
25、inations组合 also occur,for example,in television with an associated audio音频 channel 信道.,译文:（f）许多组合同样出现，例如，电视中有关联的音频信道。,Unit 1,原文:2.A transmitter发射机 which operates on the message in some way to produce a signal信号 suitable for transmission over the channel.In telephony this operation consists merely仅仅
26、of changing sound pressure into a proportional比例 electrical current.,译文:2.一个发送器将消息用些方法处理产生适用在信道中传输的信号。在电话中这个操作仅仅包含改变声压为一个成比例的电流。,Unit 1,原文:In telegraphy we have an encoding operation which produces a sequence of dots,dashes and spaces on the channel corresponding相应 to the message.,译文:在电报中我们有一个编码操作产生
27、相符于信息的一些连续的点、破折号和空格在信道中。,Unit 1,原文:In a multiplex PCM system the different speech functions must be sampled,compressed,quantized and encoded,and finally interleaved 交叉properly to construct构建 the signal.,译文:在一个多路复用PCM系统中不同的语音函数必须被抽样、压缩、量化和编码，且最终被适当地交叉存取来构造信号。,Unit 1,原文:Vocoder systems,television and
28、frequency modulation are other examples of complex operations applied to the message to obtain获得 the signal.,译文:语音编码器系统、电视和频率调制器是其他复杂操作用于信息来获得信号的例子。,Unit 1,原文:3.The channel is merely the medium used to transmit the signal from transmitter to receiver.It may be a pair of wires,a coaxial cable,a band
29、of radio frequencies,and a beam of light,ect.,译文:3.信道仅仅是从发送器传送信号到接收器的媒介。它或许是一双金属丝，一条同轴缆，一波段的收音机频率和一束光，等等。,Unit 1,原文:4.The receiver ordinarily performs the inverse operation of that done by the transmitter,reconstructing the message from the signal.5.The destination is the person(or thing)for whom th
30、e message is intended.,译文:4.接收器通常完成反向操作发送器做的事，重构来自信号的信息。5.目的地是信息计划的人（或物）。,Unit 1,原文:We wish to consider certain general problems involving 涉及communication通信 systems.To do this it is first necessary to represent the various elements involved as mathematical entities,suitably idealized理想化 from their p
31、hysical counterparts.,译文:我们希望考虑确凿的普遍的涉及通信系统的问题。做这些首先需要提出许多相关的因素作为数字实体，适当地从它们的物理对应物借鉴。,Unit 1,原文:We may roughly classify communication systems into three main categories:discrete,continuous and mixed.By a discrete离散 system we will mean one in which both the message and the signal are a sequence of di
32、screte symbols符号.,译文:我们可以大概的将通信系统分成主要三类：离散的、连续的和混合的。离散系统对于我们就意味着信息和信号是一系列的离散符号。,Unit 1,原文:A typical case is telegraphy where the message is a sequence of letters字母 and the signal is a sequence of dots,dashes and spaces.,译文:电报是一个典型的例子，系统中信息是一系列的字母且信号时一系列的原点、破折号及空格。,Unit 1,原文:A continuous system is on
33、e in which the message and the signal are both treated as continuous functions,e.g.,redio or television.A mixed system is one in which both discrete and continuous variables appear,e.g.,PCM transmission of speech.,译文:一个连续系统中信息和信号都能处理为连续的函数，如，收音机或电视。一个混合的系统中离散、连续变量均会出现，如，PCM语音传输。,Unit 1 basics of com
34、munication,Text BInformation Theory,Unit 1,原文:Claude Shannon laid the foundation of information theory in 1948.His paper“A Mathematical Theory of Communication”published in Bell System Technical Journal is the basis for the entire telecommunications developments that have taken place during the last
35、 five decades.,译文:在1948年，Clsude Shannon建立了信息论的基础。他的论文通信的数学理论发表在贝尔系统技术杂志上，改论文是近50年整个通信发展的基础。,Unit 1,原文:A good understanding of the concepts概念 proposed by Shannon is a must for every budding telecommunication professional.,译文:每个通信从业人员，必须对Shannon所提出的概念有很好的理解。,Unit 1,原文:In any communication system,there
36、 will be an information source that produces information in some form,and an information sink absorbs the information.,译文:在任何通信系统中，都包括以一定形式产生信息的信源，以及获取信息的信宿。,Unit 1,原文:The communication medium connects the source and the sink.The purpose目的 of a communication system is to transmit the information fro
37、m the source to the sink without errors.,译文:传输媒体连接信源和信宿。通信系统的目的，是无差别地将信息从信源传送至信宿。,Unit 1,原文:However,the communication medium always introduces some errors because of noise.The fundamental requirement of communication system is to transmit the information without errors in spite of the noise.,译文:但是，由
38、于噪声的存在，传送媒体往往会引入一些误差。尽管有噪声寻在，但对通信系统的基本要求是无差错地传送信息。,Unit 1,原文:The requirement of a communication system is to transmit the information from the source to the sink without errors,in spite of the fact that noise is always introduced in the communication medium.,译文:通信系统的要求是把信息没有错误的从信源传到信宿,尽管事实上噪音总是引入传播媒
39、介中。,Unit 1,原文:In a generic communication system,the information source produces symbols(such as English letters字母,speech语音,video视频,ect.)that are sent through the transmission medium by the transmitter 发射器.,译文:在一个通用的通信系统中，信息源产生符号(如英文字母、语音、视频等等)通过传输介质的发送器发出。,Unit 1,原文:The communication medium introduc
40、es noise,and so errors are introduced in the transmitted date.At the receiving end,the receiver decodes the data and gives it to the information sink.,译文:通信介质产生噪声,因此错误被引入了传输数据。在接收端,接收端解码数据信息并将其发给信宿。,Unit 1,原文:As an example,consider an information source that produces two symbols A and B.The transmit
41、ter codes the data into a bit stream.,译文:举一个例子，考虑一个信源产生两个符号A和B。发射机将数据编码在一个比特流。,Unit 1,原文:For example,A can coded as 1 and B as 0.The stream of 1s and 0s is transmitted through the medium.Because of noise,1 may became 0 or 0 may became 1 at random places,as illustrated加插图 below.,译文:例如，A可以编码为1和B作为0。1s
42、 和 0s的比特流通过媒介被发送。因为噪音，在任意位置1可能变为0或0可能变成1的地方，就像以下插图。,Unit 1,原文:At the receiver,one bit is received in error.How to ensure that the received data can be made error free?Shannon provides the answer.,译文:在接受端，一比特接收错误。怎样保证接收数据不会出错？Shannon给出了答案。,Unit 1,原文:In this block diagram(Figure 1.2),the information s
43、ource produces the symbols that are coded using two types of codingsource encoding and channel encodingand then modulated and sent over the medium.,译文:在这个框图(图1.2)，信源产生的符号编码使用两种类型的编码信源编码和信道编码然后将其调制并送入在媒质中。,Unit 1,原文:At the receiving end,the modulated signal is demodulated,and the inverse逆 operations
44、of channel encoding and source encoding(channel decoding and source decoding)are performed执行.Then the information is presented呈现 to the information sink.,译文:在接收终端，调制信号被解调，且进行信道编码和信源编码的逆操作(信道解码和信源解码)执行。然后这些信息就被呈现在信宿。,Unit 1,原文:As proposed主张 by Shannon,the communication system consists of source encod
45、er,channel encoder and modulator at the transmitting end,and demodulator,channel decoder and source decoder at the receiving end.,译文:如香农主张的，通信系统由发送终端的信源编码器、信道编码、调制器和接收终端的调制解调器、信道解码器和信源解码器。,Figure 1.2 The communication system model,Unit 1,原文:Information source:The information source produces the symb
46、ols.If the information source is,for example,a microphone,the signal is in analog模拟 form.If the source is a computer,the signal is in digital form(a set of一套 symbols).,译文:信源：信源产生符号。如果信源是，例如，一个麦克风，信号是模拟形式。如果信源是一个计算机，信号是数字形式(一套符号)。,Unit 1,原文:Source encoder:The source encoder converts转换 the signal prod
47、uced by the information source into a data stream.If the input signal is analog,it can be converted into digital form using an analog-to-digital converter.,译文:信源编码器：信源编码器把信源所产生的信号转化为数据流。若输入信号是模拟的，它可以转换成数字形式使用一个模数转换器。,Unit 1,原文:If the input to the source encoder is a stream of symbols,it can be conve
48、rted into a stream of 1 and 0 using some type of coding mechanism.For instance例如,if the source produces the symbols A and B,A can be coded as 1 and B as 0.,译文:如果输入信源编码器是一串的符号，它可以变成一组1和0使用某种类型的编码机制。例如，如果信源产生符号A和B，A可以被编码为1和B编为0。,Unit 1,原文:Shannons source coding theorem tells us how to de this coding e
49、fficiently.Source encoding is done to reduce the redundancy冗余 in the signal.,译文:香农的信源编码定理告诉我们如何有效地编码。信源编码减少信号中的冗余。,Unit 1,原文:Source coding techniques can be divided into lossless无损 encoding techniques and lossy有损 encoding techniques.In lossy encoding techniques,some information is lost.,译文:信源编码技术可分为
50、无损编码技术和有损编码技术。在有损编码技术，有些信息会丢失。,Unit 1,原文:In source coding,there are two types of codinglossless coding and lossy coding.In lossless coding,no information is lost.,译文:在信源编码中，有两种形式的编码无损编码和有损编码。在无损编码时，信息不会丢失。,Unit 1,原文:When we compress our computer files using a compression technique(for instance,WinZi
