通信英语教学课件汇总完整版电子教案全书课件(最新)

1、 通 信 英 语1、通信专业基础知识2、基础英语知识 专业英语学习的要素：通信英语学习的三个要点： 1、常见语法现象 2、构词方法 3、翻译方法和技巧 重要提示：1、网上作业提交2、综合练习3、课后练习 The Principle of PCM 专业背景介绍 PCM is dependent on three separate operations, sampling, quantizing, and coding. dependent adj. 依靠，依赖 onseparate adj. 不同的operation n. 操作，运算，手术sample v. 取样quantize v. 量化co

2、de v. 编码Many different schemes for performing these three functions have evolved during recent years, and we shall describe the main ones.scheme n. 方案，计划perform v. 执行，完成function n. 功能evolve v. 发展，演化recent adj. 近来describe v. 描述In these descriptions we shall see how a speech channel of telephone quali

3、ty may be conveyed as a series of amplitude values, each value being represented, that is, coded, as a sequence of 8 binary digits. description n. 描述channel n. 信道，话路convey v. 转化，传达amplitude n. 幅度represent v. 表示，代表sequence n. 序列binary adj. 二进制的Furthermore, we shall prove that a minimum theoretical sa

4、mpling frequency of order 6.8 kilohertz (kHz) is required to convey a voice channel occupying the range 300 Hz to 3.4 kHz. prove v. 证明minimum n. 最小值frequency n. 频率order n. 数量级，命令 occupy v. 占据，占用range n. 范围Practical equipments, however, normally use a sampling rate of 8 kHz, and if 8-digits per sampl

5、e value are used, the voice channel becomes represented by a stream of pulses with a repetition rate of 64 kHz. equipment n. 设备normally adv. 通常地rates n. 速率stream n. 流repetition n. 重复Reexamination of our simple example shows us that the speech signal of maximum frequency 3.4 kHz has been represented

6、by a signal of frequency 64 kHz. reexamination n. 再审查，再看show v. 展示，表演maximum n. 最大值However, if only 4-digits per sample value had been used, the quality of transmission would drop, and the repetition rate of the pulses would be reduced to 32 kHz. quality n. 质量transmission n. 传输drop v. 下降reduce v.减少

7、Thus the quality of transmission is dependent on the pulse repetition rate, and for digital communication systems these two variables may be interchanged most efficiently.variable n. 变量interchange v.相互转换efficiently adv. 有效的Digital transmission provides a powerful method for overcoming noisy environm

8、ents. powerful adj. 有力的，method n.方法overcome v. 克服environment n. 环境Noise can be introduced into transmission path in many different ways: perhaps via a nearby lightning strike, the sparking of a car ignition system, or the thermal low-level noise within the communication equipment itself. Introduce v

9、. 引入，介绍Lightning n. 闪电strike n. 打，打击spark v.闪烁，打火球ignition n. 点火thermal adj. 热的level n. 电平It is the relationship of the true signal to the noise signal, known as the signal-to-noise ratio, which is of the most interest to the communication engineer. relationship n. 关系Basically, if the signal is very

10、 large compared to the noise level, then a perfect message can take place; however, this is not always the case. basically adv. 基本上的compare to 比作perfect adj. 完美的message n. 消息，信息take place 发生For example, the signal received from a satellite, located in far outer space, is very weak and is at a level

11、only slightly above that of the noise. satellite n. 卫星locate v. 位于slightly adv. 稍微noise n. 噪声Alternative examples may be found within terrestrial systems where, although the message signal is strong, so is the noise power.alternative adj. 替代的，迂回的terrestrial adj. 地面的If we consider binary transmission

12、, the complete information about a particular message will always be obtained by simply detecting the presence or absence of the pulse. consider v.考虑complete adj. 完整的obtain v. 获得detect v. 检测presence n.出席，到场absence n. 缺席，不在By comparison, most other forms of transmission systems convey the message inf

13、ormation using the shape, or level of the transmitted signal; parameters that are most easily affected by the noise and attenuation introduced by the transmission path. by comparison 相比之下shape n. 波形，形状parameter n. 参数affect v. 影响attenuation v. 衰减path n. 路径Consequently there is an inherent advantage f

14、or overcoming noisy environments by choosing digital transmission.consequently adv. 因而inherent adj. 固有的，本质的advantage n. 优势choose v. 选择So far in this discussion we have assumed that each voice channel has a separate coder, the unit that converts sampled amplitude values to a set of pulses; and decode

15、r, the unit that performs the reverse operation. so far 至此，迄今为止assume v. 假定This need not be so, and systems are in operation where a single codec (i.e., coder and its associated decoder) is shared between 24, 30, or even 120 separate channels. in operation 运转着，生效codec 编解码器associate v. 使发生联系，使联合share

16、 v. 共用，分享A high-speed electronic switch is used to present the analog information signal of each channel, taken in turn, to the codec. switch n. 开关present v. 引见, 给 , 上演, 提出, 呈现information n. 信息 take in turn 轮流The codec is then arranged to sequentially sample the amplitude value, and code this value

17、into the 8-digit sequence. arrange v. 安排sequentially adv. 顺序的sample v. 取样Thus the output to the codec may be seen as a sequence of 8 pulses relating to channel 1, then channel 2, and so on. output 输出relate to 涉及，对应 This unit is called a time division multiplexer (TDM), and is illustrated in Fig. 1-2

18、. division n. 分开multiplexer n. 复用器illustrate v. 描述，说明The multiplexing principle that is used is known as word interleaving, since the words, or 8-digit sequences, are interleaved in time.be known as 被称作，被认为interleave v. 复用，间插The reader may ask, how does the demultiplexer know which group of 8-digits

19、 relates to channel 1, 2, and so on? Clearly this is important!demultiplexer n. 分路器At the receive terminal a demultiplexer is arranged to separate the 8-digit sequences into the appropriate channels. terminal n. 终端separate v. 分开appropriate adj. 适当的The problem is easily overcome by specifying a frame

20、 format, where at the start of each frame a unique sequence of pulses called the frame code, or synchronization word, is placed so as to identify the start of the frame. specify v. 指定，详细说明frame n.帧unique adj. 唯一的，独特的synchronization n. 同步字identify v. 标识A circuit of the demultiplexer is arranged to de

21、tect the synchronization word, and thereby it knows that the next group of 8-digits corresponds to channel 1. The synchronization word reoccurs once again after the last channel has been received.reoccur v. 再发生，再出现 翻译要点：1、被动句翻译2、词类转换3、定语从句翻译4、宾语从句翻译5、状语从句翻译 UNIT 2 Asynchronous Serial Data transmissi

22、on 背景介绍By far the most popular serial interface between a computer and its CRT terminal is the asynchronous serial interface. by far 用来修饰比较级和最高级interface n.接口CRT 阴极射线管asynchronous 异步的This interface is so called because the transmitted data and the received data are not synchronized over any extended

23、 period and therefore no special means of synchronizing the clocks at the transmitter and receiver is necessary. synchronize v.使同步extend v.扩展，延伸special adj.特殊的means n.手段，方法clock n.时钟In fact, the asynchronous serial data link is a very old form of data transmission system and has its origin in the er

24、a of teleprinter.in fact 事实上 link n.链路，线路，中继线origin n.起源，开始teleprinter n.电传打字机Serial data transmission systems have been around for a long time and are found in the telephone (human speech), Morse code, semaphore, and even the smoke signals once used by native Americans. semaphore n.旗语smoke signal 烽

25、火The fundamental problem encountered by all serial data transmission systems is how to split the incoming data stream into individual units (i.e., bits) and how to group these units into characters. fundamental adj.基本的，根本的encounter v.遇到split v.分开incoming adj.输入的，进来的individual n.个别的，单个的unit n.单元，部件ch

26、aracter n.字符For example, in Morse code the dots and dashes of a character are separated by an inter-symbol space, while the individual characters are separated by an inter-character space, which is three times the duration of an inter-symbol space. dot n.点dash n.短划线separate v.分开inter-symbol 符号间inter

27、-character 字符间space n.空间，间隔duration n.持续时间First we examine how the data stream is divided into individual bits and the bits grouped into characters in an asynchronous serial data link. The key to the operation of this type of link is both simple and ingenious. Fig. 2-1 gives the format of data trans

28、mitted over such a link.examine v.检查，查看stream n.流divide v.分开key n.要点，关键ingenious adj.精巧的An asynchronous serial data link is said to be character oriented, as information is transmitted in the form of groups of bits called characters. oriented v.面向，朝向These characters are invariable units comprising 7

29、 or 8 bits of “information” plus 2 to 4 control bits and frequently correspond to ASCII-encoded characters. invariable adj.固定不变的comprising 包括frequently 通常的correspond to 对应ASCII Initially, when no information is being transmitted, the line is in an idle state. Traditionally, the idle state is referre

30、d to as the mark level. By convention this corresponds to a logical 1 level.initially adv.开始的idle adj. 空闲的，懒散的traditionally adv. 传统的refer to 称作mark n.传号convention 宗教会议 by 习惯logical adj.逻辑的When the transmitter wishes to send data, it first places the line in a space level (i.e., the complement of a m

31、ark) for one element period. This element is called the start bit and has a duration of T seconds. wish v.希望place v.设置space n.空号 element n.元素，单元The transmitter then sends the character, 1 bit at a time, by placing each successive bit on the line for a duration of T seconds, until all bits have been

32、transmitted. successive adj.连续的Then a single parity bit is calculated by the transmitter and sent after the data bits. Finally, the transmitter sends a stop bit at a mark level (i.e., the same level as the idle state) for one or two bit periods. Now the transmitter may send another character wheneve

33、r it wishes.parity n.奇偶校验，calculate n.计算At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit. Once the start bit has been detected, the receiver waits until the end of the start bit and then samples the next N bits at their cent

34、ers, using a clock generated locally by the receiver. continually adv.连续的monitor v.监测look for 寻找detect v.检测end n.结束generate v.产生As each incoming bit is sampled, it is used to construct a new character. When the received character has been assembled, its parity is calculated and compared with the rec

35、eived parity bit following the character. If they are not equal, a parity error flag is set to indicate a transmission error.construct v.建设，组成assemble v.装配，汇齐compare v.比较equal adj.相等的error n.差错flag n.标志indicate v.指示The most critical aspect of the system is the receiver timing. The falling edge of th

36、e start bit triggers the receivers local clock, which samples each incoming bit at its nominal center. critical adj.紧要的，关键的aspect n.方面timing n.定时edge n.边，沿trigger v.触发，启动nominal adj.标称的，名义的Suppose the receiver clock waits T/2 seconds from the falling edge of the start bit and samples the incoming da

37、ta every T seconds thereafter until the stop bit has been sampled. Fig. 2-2 shows this situation. As the receivers clock is not synchronized with the transmitter clock, the sampling is not exact. suppose v.假设situation n.情况exact adj.精确的The most obvious disadvantage of asynchronous data transmission i

38、s the need for a start, parity, and stop bit for each transmitted character. If 7 bit characters are used, the overall efficiency is only 70%. obvious adj.明显的disadvantage n.缺点overall adj.整个的efficiency n.效率A less obvious disadvantage is due to the character-oriented nature of the data link. Whenever

39、the data link connects a CRT terminal to a computer, few problems arise, as the terminal is itself character oriented. However, if the data link is being used to, say, dump binary data to a magnetic tape, problems arise.due to 由于nature n.特性dump v.倾倒，转储 magnetic adj.磁的 UNIT 4 Internet 背 景 介 绍The Inte

40、rnet is a giant network of computers located all over the world that communicate with each other.giant a.巨大的locate v.位于The Internet is an international collection of computer networks that all understand a standard system of addresses and commands, connected together through backbone systems. collec

41、tion n.收集，聚集standard n.标准address n.地址command n.命令backbone n.骨干It was started in 1969, when the U.S. Department of Defense established a nationwide network to connect a handful of universities and contractors. Department of Defense 国防部establish v.建立nationwide a.全国性的handful n.少数，少量university n.大学contr

42、actor n.订阅人，承包人The original idea was to increase computing capacity that could be shared by users in many locations and to find out what it would take for computer networks to survive a nuclear war or other disaster by providing multiple path between users. Original a.最初的，开始的Increase v.增加Compute v.计

43、算Capacity n.容量Share v.分享，共用Find out 找出，发现，查明survive v.幸免于，幸存，生还nuclear a.原子能的，核的 disaster n.灾难，天灾 multiple a.许多的path n.路径People on the ARPNET quickly discovered that they could exchange messages and conduct electronic “conferences” with distant colleagues for purposes that had nothing to do with the

44、 military industrial complex. exchange v.交换conduct v.进行，从事conference n.会议military a. 军事的complex a.复杂的; n.综合企业If somebody else had something interesting stored on his or her computer, it was a simple matter to obtain a copy.obtain v.获得copy n.拷贝Over the years, additional networks joined which added ac

45、cess to more and more computers. The first international connection, to Norway and England, were added in 1973.Today thousands of networks and millions of computers are connected to the Internet. It is growing so quickly that nobody can say exactly how many users On the Net5.The Internet is the larg

46、est repository of information which can provide very very large network resources. The network resources can be divided into network facilities resources and network information resources. The network facilities resources provide us the ability of remote computation and communication. The network in

47、formation resources provide us all kinds of information services, such as science, education, business, history, haw, art, and entertainment, etc.repository n. 仓库，资料丰富的地方resource n. 资源facility n. 设备，工具entertainment n. 娱乐，乐趣The goal of your use of the Internet is exchanging messages or obtaining info

48、rmation. What you need to know is that you can exchange message with other computers on the Internet and use your computer as a remote terminal on distant computers6. But the internal details of the link are less important, as long as it works. If you connect computers together on a network, each co

49、mputer must have a unique address, which could be either a word or a number. For example, the address of Sams computer could be Sam, or a number.The Internet is a huge interconnected system, but it uses just a handful of method to move data around. Until the recent explosion of public interest in th

50、e Internet, the vast majority of the computers on the Net use the Unix operating system. As a result, the standard Unix commands for certain Internet services have entered the online communitys languages as both nouns and verbs to describe the services themselves. Some of the services that the Inter

51、net can provide are: Mail, Remote use of another computer (Telnet), File Transfer (FTP), News, and Live conversation.explosion n. 爆炸，扩张，激增majority n. 多数，大多数The most commonly used network service is electronic mail (E-mail), or simply as mail. Mail permits network users to send textual messages to ea

52、ch other. Computers and networks handle delivering the mail, so that7 communicating mail users do not have to handle details of delivery, and do not have to be present at the same time or place.The simplest way to access a file on another host is to copy it across the network to your local host. FTP

53、 can do this.Presently, a user with an account on any Internet machine can establish a live connection to any other machine on the Net from the terminal in his own office or laboratory. It8 is only necessary to use the Unix command that sets up a remote terminal connection (Telnet), followed by the

54、address of the distant machine.Before you can use the Internet, you must choose a way to move data between the Internet and your PC. This link may be a high-speed data communication circuits, a local area network (LAN), a telephone line or a radio channel. Most likely, you will use a Modem attached

55、to your telephone line to talk to the Internet. Naturally, the quality of your Internet connection and service, like many other things in life9, is dictated by the amount of money you are willing to spend.choose v. 选择，挑选attach v. 缚，系，附加modem n. 调制解调器dictate v. 命令，支配Although all these services can we

56、ll satisfy the needs of the users for information exchange, a definite requirement is needed for the users. Not only should the users know where the resources locate, but also he should know some operating commands concerned10.To ease the searching burden of the users, recently some convenient searc

57、hing tools appear, such as Gopher, WWW and Netscape.satisfy vt. 满足，使满意definite a. 明确的，确切的，肯定的requirement n. 需要，要求World Wide Web (WWW) is a networked hypertext protocol and user interface. It provides access to multiple services and documents like Gopher does but is more ambitious in its method. A ju

58、mp to other Internet service can be triggered by a mouse click on a “hot-linked” word, image, or icon on the Web page.hypertext n. 超级文本interface n. 接口，界面ambitious n. 有抱负的，雄心勃勃的trigger vt. 发射，引起icon n. 画像，肖像，图标As11 more and more systems join the Internet, and as more and more forms of information can

59、 be converted to digital form, the amount of stuff available to Internet users continues to grow. At some points very soon after the nationwide (and later worldwide) Internet started to grow, people began to treat the Net as a community, with its own tradition and customs.stuff n. 原料，资料，东西community

60、n. 团体，社会tradition n. 传统，惯例. For example, somebody would ask a question in a conference, and a complete stranger would send back an answer: after the same questions were repeated several times by people who hadnt seen the original answers, somebody else gathered a list of “frequently asked questions”