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1、,ENGLISH ON TELECOMMUNICATIONS,课程名称：通信专业外语,UNIT 1 The Principle of PCM,1,2,3,4,UNIT 5 Introduction to Optical Fiber Communication,UNIT 4 Internet,UNIT 2 Asynchronous Serial Data Transmission,5,6,7,UNIT 10 GSM,UNIT 8 Cellular Mobile Telephone System,UNIT 7 WDM,UNIT 11 Circuit Switching and Packet Swi
2、tching,11,UNIT 16 Current Situation and the Future In the Telecommunication World,16,1,The Principle of PCM,Unit 1 The Principle of PCM NEW WORDS AND PHRASESprinciple n. 原理be dependent on 依赖，取决于sample v. 采样quantize v. 量化，分层code v. 编码 n.码scheme n. 方案，设计，安排 describe vt叙述，描述 description n叙述，描述 amplitud
3、e n幅，幅度 binary a二进制的 minimum n最小值，最小量,1,The Principle of PCM,Unit 1 The Principle of PCM NEW WORDS AND PHRASES theoretical a理论上的 repetition n重复，反复 reexamination n再审查，重考 maximum n最大值 reduce vt；vi减少，缩小 interchange y互换，转换，相互影响 method n方式方法，手段 overcome vt克服，打败，征服 environment n环境，周围情况 lightning n电光，闪电，雷电
4、 strike v击，敲，打 spark v发火花，打火，闪光,1,The Principle of PCM,Unit 1 The Principle of PCM NEW WORDS AND PHRASES ignition n点火，点火装置 signal-to-noise ratio 信噪比 satellite n卫星 terrestrial a地球的，地面的，大地的 by comparison 比较起来，相对之下 parameter prmit n参数，系数technical parameter 技术参数parameter estimation 参数估计key parameter 关键参
5、数,1,The Principle of PCM,Unit 1 The Principle of PCM NEW WORDS AND PHRASESattenuation n衰减，衰耗 attenuation coefficient 衰减系数 attenuation distortion 衰减失真 inherent a固有的，内在的 assume vt假设，假定 decoder n解(译)码器 codec n编译码器,1,The Principle of PCM,Unit 1 The Principle of PCM NEW WORDS AND PHRASES interleave vt交插，
6、交错，插接 appropriate a适当的，合适的 unique a惟一的，独特的unique solution 唯一解In some ways, each of us is like ervey person; and in some ways, each of us is unique. reoccur vi再发生，再次发生,1,PCM is dependent on three separate operations, sampling, quantizing, and coding. Many different schemes for performing these three
7、functions have evolved during recent years, and we shall describe the main ones. In these descriptions we shall see how a speech channel of telephone quality may be conveyed as a series of amplitude values, each value being represented, that is, coded, as a sequence of 8 binary digits.,PASSAGE,1,The
8、 Principle of PCM,1,Furthermore, we shall prove that a minimum theoretical sampling frequency of order 6.8 kilohertz (kHz) is required to convey a voice channel occupying the range 300 Hz to 3.4 kHz. Practical equipments, however, normally use a sampling rate of 8 kHz, and if 8-digits per sample val
9、ue are used, the voice channel becomes represented by a stream of pulses with a repetition rate of 64 kHz. Fig. 1-1 illustrates the sampling, quantizing, and coding processes.,PASSAGE,1,The Principle of PCM,1,Reexamination of our simple example shows us that the speech signal of maximum frequency 3.
10、4 kHz has been represented by a signal of frequency 64 kHz. 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. Thus the quality of transmission is dependent on the pulse repetition rate,
11、and for digital communication systems these two variables may be interchanged most efficiently.,PASSAGE,2,The Principle of PCM,1,Digital transmission provides a powerful method for overcoming noisy environments. Noise can be introduced into transmission path in many different ways: perhaps via a nea
12、rby lightning strike, the sparking of a car ignition system, or the thermal low-level noise within the communication equipment itself. 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.,PASSA
13、GE,3,The Principle of PCM,1,Basically, if the signal is very large compared to the noise level, then a perfect message can take place; however, this is not always the case. For example, the signal received from a satellite, located in far outer space, is very weak and is at a level only slightly abo
14、ve that of the noise. Alternative examples may be found within terrestrial systems where, although the message signal is strong, so is the noise power .,PASSAGE,3,The Principle of PCM,1,If we consider binary transmission, the complete information about a particular message will always be obtained by
15、 simply detecting the presence or absence of the pulse. By comparison, most other forms of transmission systems convey the message information using the shape, or level of the transmitted signal; parameters that are most easily affected by the noise and attenuation introduced by the transmission pat
16、h. Consequently there is an inherent advantage for overcoming noisy environments by choosing digital transmission.,PASSAGE,4,The Principle of PCM,1,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 puls
17、es; and decoder, the unit that performs the reverse operation. 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. A high-speed electronic switch is used to present the analog inform
18、ation signal of each channel, taken in turn, to the codec.,PASSAGE,5,The Principle of PCM,1,The codec is then arranged to sequentially sample the amplitude value, and code this value into the 8-digit sequence. Thus the output to the codec may be seen as a sequence of 8 pulses relating to channel 1,
19、then channel 2, and so on. This unit is called a time division multiplexer (TDM), and is illustrated in Fig. 1-2. The multiplexing principle that is used is known as word interleaving. Since the words, or 8-digit sequences, are interleaved in time.,PASSAGE,5,The Principle of PCM,1,At the receive ter
20、minal a demultiplexer is arranged to separate the 8-digit sequences into the appropriate channels. The reader may ask, how does the demultiplexer know which group of 8-digits relates to channel 1, 2, and so on? Clearly this is important! The problem is easily overcomed by specifying a frame format,
21、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.,PASSAGE,6,The Principle of PCM,1,A circuit of the demultiplexer is arranged to detect the synchronization word, and thereby it knows that t
22、he next group of 8-digits corresponds to channel 1. The synchronization word reoccurs once again after the last channel has been received.,PASSAGE,6,The Principle of PCM,OVER,1,synchronization wordFrame formatReceiving terminal8-digit sequenceReverse operationBinary transmissionNoise power,EXERCISE,
23、The Principle of PCM,Signal levelTerrestrial systemSignal-to-noise ratioTransmission pathNoisy envionment,1,digital transmissionTransmission qualityAnalog signalCoding processRepetition rateStream of pulseSampling frequency,EXERCISE,The Principle of PCM,Amplitude valueSpeech channelSampling, quantiz
24、ing and codingThe presence or absence of the pulseThe time division multiplexer,检验,课本 25页 第四大题选择正确答案并说出其大概意思,exercise,Superposition principle,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESAsynchronous a异步的serial a串行的，串联的transmission n传输，发送i
25、nterface n接口receive v接收，收到synchronize v(使)同步，(使)同时或同速进行period n周期，循环，时期，阶段，时间间隔，时间clock n时钟transmitter n发送器，发射机receiver n接收器，接收机,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESnecessary a必要的，必需的，必须做的link n连接，耦合，线路，链路teleprinter n电传打字机Morse c
26、ode n莫尔斯电码Signal n信号Native a当地的，天生的Fundamental a基本的，根本的，(十分)重要的Split vt分开，劈开，分割，分离incoming a进来的，入射的，输入的stream n流，束，潮流，倾向,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESindividual a分别的，各个的，单独的，个体的，独立的unit n单元，元件，成分，装置，设备，组(合)，机组，块体group v组合，分
27、组，群聚，聚集character n字母，字符，符号，字，电码组合，角色，人物dot n圆点，小数点dash n破折号，长划线，猛冲，冲锋separate v(使)分离，隔开，区分，分类intersymbol a码间的，符号间的,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESintercharacter a字符间的duration n持续时间，延续时间examine v检查，审查，实验，研究，探讨，测验，考试divide v分开，
28、分配，分割，划分，等分bit n比特ingenious a精巧的，精致的format n格式，形式orient vt定向，定(方)位，标定，(使)适应，朝向,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESinvariably ad不变地，总是，一定，永恒地comprise vt包含，包括，由组成plus prep加上；a正的control n控制frequently ad时常，频繁地correspond vt相当，对应，符合，一致
29、correspond to 相当于，与相对应，与相吻合,与一致encode vt编码initially ad最初，开头，一开始,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESidle a闲置的，空闲的traditionally ad传统地，惯例地mark leveI信号电平logical a逻辑的space level空号电平successive a连续的，顺序进行的，逐次性的parity n奇偶性calculate v计算con
30、tinually ad屡次地再三地，频频地，连续地monitor n；V监视(器)，监测(器),2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESdetect vt发觉，觉察；n检测器，侦察器sample n样品，取样；vt抽样，采样assemble v集合，收集，装配，组装flag n旗，标志。标志位critical a决定性的，关键的，危险的，临界的aspect n方面，方位，外貌，样子edge n边，边缘，界限，边界，刀刃，刀口
31、trigger v触发，起动，扣扳机，发射；n起动，触发，扳机nominal a标称的，额定的,2,Asynchronous Serial Data Transmission,Unit 2 Asynchronous Serial Data Transmission NEW WORDS AND PHRASESthereafter ad此后，其后situation n位置，地点，场所，形势，情况，环境，局面obvious a明显的，明白的，显而易见的disadvantage n不利条件，不利方面，有害，缺点whenever ad无论何时，随时，每当terminal n终端dump V倾倒，翻卸，转
32、储binary a二进制的,2,By far the most popular serial interface between a computer and its CRT terminal is the asynchronous serial interface. This interface is socalled because the transmitted data and the received data are not synchronized over any extended period and therefore no special means of synchro
33、nizing the clocks at the transmitter and receiver is necessary. In fact, the asynchronous serial data link is a very old form of data transmission system and has its origin in the era of teleprinter.,PASSAGE,1,Asynchronous Serial Data Transmission,2,Serial data transmission systems have been around
34、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. 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
35、how to group these units into characters. For example, in Morse code the dots and dashes of a character are separated by an intersymbol space, while the individual characters are separated by an intercharacter space, which is three times the duration of an intersymbol space.,PASSAGE,2,Asynchronous S
36、erial Data Transmission,2, 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 transmitted over suc
37、h a link.,PASSAGE,3,Asynchronous Serial Data Transmission,2, An asynchronous serial data link is said to be character oriented, as information is transmitted in the form of groups of bits called characters. These characters are invariable units comprising 7 or 8 bits of information plus 2 to 4 contr
38、ol bit and frequently correspond to ASCII-encoded characters. Initially, when no information is being transmitted, the line is in an idle state. Traditionally, the idle state is referred to as the mark level. By convention this corresponds to a logical 1 level.,PASSAGE,4,Asynchronous Serial Data Tra
39、nsmission,2, When the transmitter wishes to send data, it first places the line in a space level (i. e., the complement of a mark) for one element period. This element is called the start bit and has a duration of T seconds. The transmitter then sends the character, 1 bit at a time, by placing each
40、successive bit on the line for a duration of T seconds, until all bits have been transmitted. 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
41、 periods. Now the transmitter may send another character whenever it wishes.,PASSAGE,5,Asynchronous Serial Data Transmission,2, 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 rece
42、iver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receivers. 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 compar
43、ed with the received parity bit following the character. If they are not equal, a parity error flag is set to indicate a transmission error.,PASSAGE,6,Asynchronous Serial Data Transmission,2, The most critical aspect of the system is the receiver timing. The falling edge of the start bit triggers th
44、e receivers local clock, which samples each incoming bit at its nominal center. Suppose the receiver clock waits T/2 seconds from the falling edge of the start bit and samples the incoming data every T seconds thereafter until the stop bit has been sampled. Fig.2-2 shows this situationAs the receive
45、rs clock is not synchronized with the transmitter clock， the sampling is not exact,PASSAGE,7,Asynchronous Serial Data Transmission,2, The most obvious disadvantage of asynchronous data transmission is the need for a start，parity，and stop bit for each transmitted characterIf 7 bit characters are used
46、, the overall efficiency is only 70A less obvious disadvantage is due to the character oriented nature of the data linkWhenever the data link connects a CRT terminal to a computer, few problems arise，as the terminal is itself character orientedHowever，if the data link is being used to，say，dump binar
47、y data to a magnetic tape，problems arise,PASSAGE,8,Asynchronous Serial Data Transmission,asynchronous serial data transmissionThe falling edge of the start bit Serial interface,Transmitter and receiverData transimissionData streamThe idle state,Mark level Space levelStart bit Stop bit Duration of T
48、seconds,parity bit Error flagFalling edge Inter-symbol space,Last one,下课前,Receiver timingLocal clockControl bitLogical 1 levelBinary dataObvious disadvantage,检验,课本 37页 第四大题选择正确答案并说出其大概意思,enjoiy,http:/,4,Internet,Unit 4 Internet NEW WORDS AND PHRASESgiant 巨大的collection 收集address 地址backbone 主干，支柱contr
49、actor 承包商，订约人survive 幸免于disaster 灾难conference 会议purpose n目的，意图complex n合成物，综合企业,4,Internet,NEW WORDS AND PHRASESexactly ad确切地，精确地repository n仓库，资源丰富的地方resource n资源facility n设备，工具entertainment n娱乐，乐趣explosion n爆炸，扩张，激增majority n多数，大多数account n账目，账户choose vt选择，挑选attach V缚，系，附加modem n调制解调器 dictate V命令，
50、支配,4,Internet,NEW WORDS AND PHRASESsatisfy vt满足，使满意definite a明确的，确切的，肯定的requirement n需要，要求convenient a方便的，便利的hypertext n超文本interface n接口，界面ambitious a有抱负的，雄心勃勃的trigger vt发射，引起icon n. 画像，肖像，图标stuff n原料，资料，东西community n团体，社会tradition n传统，惯例,4,Internet,The Internet is a giant network of computers locat
