Teaching Plan Lecturer Wangwei-zhuang Course English for Telecommunications Lesson Number Unit One  Time  Grade  Teaching Mode Lecturing  Content The Principle of PCM Class Hours 2 Periods  Teaching Objectives to know the three basic processes of PCM: Sampling Quantizing Encoding to understand that PCM is the heart of technology in communications in today’s digital world. to master the technical terms: PCM sampling quantizing encoding pulse stream…  Focal & Difficult Points Focal Points：. The three processes of PCM Difficult Points：the conversion of the analogue signals into binary form; The technical terms in the text.  Teaching Methods Applied Ways of lecturing, multimedia demonstration and speech interacting are applied to achieve the most understanding of the text intended.  Discussion, Exercises and Assignments Discussion：What is the heart of technology in communications in today’s digital world？（Topic） Exercises：共2道题 Assignments： 1. to collect the materials related to PCM. 2. to apply the principle of PCM to the practice  Bibliography Zhang Daozhen,ed.Practical English Grammar (the 3rd Revision).Shanghai: the Commercial Press,1992 Shanghai Translation Publishing House, edu. New English-Chinese Dictionary. Shanghai: Shanghai Translation Publishing House,1988. Posts and Telecom Press, edu. English-Chinese Telecommunications Technology Dictionary. Beijing: Posts and Telecom Press,1997 Zhang Xiaohua and Shi Fangwen,ed.English for Telecommunications (the 4th Version).Beijing: Beijing University of Posts and Telecommunications Press,2004 Xu Xiulan.English for Computers and Telecommunications (the 3rd Revision) .Beijing: Beijing University of Posts and Telecommunications Press,2004   Teaching Content Contents Time Teaching Apparatuses  I. Brief-Introduction to English on Telecommunications From this period on, we are going to learn English on Telecommunications, which is one of the English for special purposes. Learning this course, we will enlarge our vocabulary in the field of telecommunications and information; get familiar with the terms in it; get to know the characteristics of writing style of telecommunications English and master the translation skills of it; thus greatly improve our professional qualities and communicative competency in this globalized world in the information age. II. Pre-reading Activities Introduction to Pulse Code Modulation (PCM) Ask the Ss the following two questions related to the theme of the text: What is the heart of technology in communications in today’s digital world？ Possible answers: PCM, which is short for Pulse code modulation (to be discussed in depth later) is the heart of technology in communications in today’s digital world. It is a process in which analog signals are converted to digital form. The analog signal is represented by a series of pulses and non-pulses (1 or 0 respectively). At this stage to fully understand we can refer back to the notes on signals. Why PCM? Possible answers: The stream of pulses and non-pulse streams of 1’s and 0’s are not easily affected by interference and noise. Even in the presence of noise, the presence or absence of a pulse can be easily determined. Since PCM is digital, a more general reason would be that digital signals are easy to process by cheap standard techniques. This makes it easier to implement complicated communication systems such as telephone networks (covered later in this course). The practical implementation of PCM makes use of other processes. The processes are carried out in the order in which they appear below: Filtering Sampling Quantizing Encoding III. While-reading Activities i. New Words And Phrases principle ［'ｐｒｉｎｓｉｐｌ］n. 原理 be dependent on 依赖，取决于 sample ［'ｓ?ｍｐｌ］ vt. 采样； 样值 quantize ［'ｋｗ?ｎｔａｉｚ］ v. 量化，分层 code ［ｋｏｕｄ］v. 编码；n.码 scheme ［ｓｋｉ: ｍ］n. 方案，设计，安排 describe ［ｄｉｓ'ｋｒａｉｂ］vt. 叙述，描述 description? 叙述，描述 amplitude ［'?ｍｐｌｉｔｊｕ:ｄ］ n. 幅，幅度 binary ［'ｂａｉｎ?ｒｉ］a. 二进制的 minimum ［'ｍｉｎｉｍ?ｍ］n. ?最小值，最小量 theoretical ［θｉ?'ｒｅｔｉｋ?ｌ］a. ?理论上的i repetition ［ｒｅｐｉ'ｔｉ??ｎ］n. ?重复，反复 reexamination? 再审查，重考 maximum ［'m?ksim?ｍ］n. ?最大值 reduce ［ｒｉ: 'ｄｊｕ:ｓ］v. ?减少，缩小 interchange ［ｉｎｔ?' ?ｅｉｎ?］v. ?互换，转换 method ［'ｍｅθ?ｄ］n. ?方式，方法，手段 overcome ［ｏｕｖ?'ｋ?ｍ］v. ?克服,打败,征服 environment ［ｉｎ'ｖａｉ?ｒ?ｍ?ｎｔ］n. ?环境,周围情况 lightning ［'ｌａｉｔｎｉ?］n. ?电光，闪电，雷电 strike ［ｓｔｒａｉｋ］n. ?击，敲，打 spark ［ｓｐα:ｋ］vi. ?发火花，打火，闪光 ignition ［ｉｇ'ｎｉ??ｎ］ n. ?点火，点火装置 signal?to?noise ratio 信号噪声比 satellite ［'ｓ?ｔｉｌａｉｔ］ n.卫星 terrestrial ［ｔｉ'ｒｅｓｔｒｉ?ｌ］ a.?地球的,地面的,大地的 by comparison? 比较起来，相对之下 parameter ［ｐ?'ｒ?ｍｉｔ?］n. ?参数，系数 attenuation n. 衰减，衰耗 inherent ［ｉｎ'ｈｉ?ｒ?ｎｔ］a. ?固有的，内在的 assume ［?'ｓｊｕ:ｍ］v. ?假设，假定 decoder? 解(译)码器 codec? 编译码器 interleave ［ｉｎｔ'ｌｉ:ｖ］vt. ?交插，交错，插接 appropriate ［?'ｐｒｏｕｐｒｉｔ］ a. ?适当的，合适的 unique ［ｊｕ: 'ｎｉｋ］a. ?唯一的，独特的 reoccur? 再发生，再次发生 ii. Passage-reading Activities The Principle of PCM(1) PCM原理 PCM is dependent on (2 ) three separate operations, sampling, quantizing, and coding (2’). Many different schemes for performing (2) these three functions have evolved during recent years, and we shall describe the main ones. PCM的构成依赖于三个环节,即采样、量化和编码. 近年来,人们对这三个环节的实现提出了许多不同的方案,我们将对其中一些主要的方案进行讨论. （2）. be dependent on 依靠，依赖，取决于. （2’）. performing是perform的动名词.动名词虽为名词，但 仍保留着动词的某些特征，例如它仍可带有动词宾语.本句中的these three functions就是performing的宾语. 本课中这类例子很多，例如第四段中的最后一句中： Consequently there is an inherent advantage for overcoming noisy environments by choosing digital transmission. 句中的overcoming和choosing都是动名词且带有自己的动词宾语. 另有理论认为ＰＣＭ分为四过程，如下： The practical implementation of PCM makes use of other processes. The processes are carried out in the order in which they appear below: Filtering Sampling Quantizing Encoding The filtering stage removes frequencies above the highest signal frequency. These frequencies if not removed, may cause problems when the signal is going through the stage of sampling. Sampling of a waveform means determining instantaneous amplitudes of a signal at fixed intervals. You may have a problem in understanding what this sentence means, but if you take time to look at Figure 7 on the following Slide, you should be able to understand. 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 (3), that is, coded, as (3’) a sequence of 8 binary digits. 在这些讨论中,我们会看到话路中的语声信号是如何转换成一个幅值序列的,而每个幅值又被编码,即以8位二进制数的序列表示. （3）. each value being represented这是一种独立分词结 构，用来表示一种伴随状态，作状语.可译成：“而每一幅值被表示为”.独立分词结构在科技文章中相当常见，例如： There are many kinds of steel, each having its uses in industry. 译为：“钢有许多种，在工业中每种都有它自己的用途”. 独立分词结构还可以表示时间、原因或条件等，对主句进行补充说明.例如表示原因： The resistance being very high, the current in the circuit was low. 译为:“由于电阻很高，故电路里的电流很小”. (3’).as a sequence of 8 binary digits句中的as意为“作为，表为，成为”.该短语可译成:“(表为)8位二进制码的序列”. Furthermore (4), 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(4a). Practical equipments, however, normally use a sampling rate of 8 kHz, and if 8-digits per sample value are used, the voice channel becomes represented by a stream of pulses (4b) with a repetition rate of 64 kHz. Fig. 1-1 illustrates the sampling, quantizing, and coding processes. 而且,我们将证明,为了变换频率范围300Hz~3.4KHz的话路信号,理论上的最小采样频率为608KHz.但是,实际设备通常用8KHz的采样速率,而如果每个样值用8位码的话,则话路是由一个重复速率为64KHz的脉冲流来表示的. 图1-1表示了采样、量化和编码的过程. （4）. furthermore: adv.“而且；此外” Furthermore, these child-raising families may raise other people‘s children in addition to their own. 　而且,这些抚养孩子的家庭除了自己的孩子外也可以抚养其他人家的孩子。 The house is too small, and furthermore, it's too far from the office. 这座房子太小,而且离办公地点也太远。 同义词：again, also, besides, by the same token, in addition, likewise, similarly, then, too. (4a)。 脉冲流 (4b). occupying是occupy的现在分词. 动词的-ing形式可以作为名词用，称为动名词，本课注释(2)已对此作了介绍。动词的-ing形式亦可作形容词用(称现在分词).它一般修饰该动作的发出者，而且它亦可带有自己的宾语，例如本句中的:“a voice channel occupying the range 300Hz to 3.4kHz”. 该短语可译为:“占有300Hz到3.4kHz频率范围的话路”. Reexamination of our simple example shows us that the speech signal?of maximum (5) frequency 3.4 kHz has been represented by a signal of frequency64 kHz.? 让我们再研究一下上面提到的简单例子.可以看出 ,最高频率为3.4KHz的话音信号是用64KHZ的(脉冲流)信号来表示的. （5）. n.(pl. maximums, -ma[-mE])最大量; 最大数; 最高点极点; 最高额, 最大限度【数】极大(值); 最大(值)(发展的)顶峰时期 reach a maximum 达到顶点 The excitement was at its maximum. 兴奋到极点。 The sound has reached its maximum. 声音达到最高音位。 反义词：minimum 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, and for digital communication systems these two variables may be interchanged most efficiently. 但是,如果每个样值只用4位码表示,则传输质量会下降,而脉冲的重复速率也将减小到32KHz.因而传输质量是取决于脉冲重复速率的.对于数字通信系统,这两个量之间极明显地相互影响着. Digital transmission provides a powerful method for overcoming noisy environments. 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 (6) within the communication equipment itself. 数字传输对于克服噪声环境的影响提供了一个强有力的手段.噪声可以以多种不同的方式进入传输信道,比如说因为附近的闪电、汽车点火系统的打火或因通信设备本身低电平所致. （6）.本句中的几个词组可译为: lightning strike 打雷 sparking of a car ignition system? 汽车点火系统的打火 thermal low-level noise? 低电平的热噪声 It is the relationship of the true signal to the noise signal, known as the signal-to-noise ratio (7) which is of the most interest to (7’) the communication engineer. Basically, if the signal is very large compared to the noise level,(7a) then a perfect message can take place; however, this is not always the case (7b). 正是这种被称为信噪比的即真实信号与噪声的关系引起了通信工程师的极大的兴趣.从本质上讲,如果信号比噪声电平大得多,则信息的传输是完美的.但是,实际情况并不总是这样. （7）. known as the signal-to-noise ratio 译为“称为信号噪声比”. （7’）. Be of + n. 结构 Be of importance=be important be of the most interest to= be most interesting to （7a）. compared to the noise level 意为:“与噪声电平相比”. （7b）. this is not always the case: 实际情况并非如此． For example, the signal received from a satellite, located in far outer space (8), is very weak and is at a level only slightly above that of the noise. Alternative examples (8’) may be found within terrestrial systems where, although the message signal is strong, so is the noise power.?? 例如, 从位于遥远太空中的卫星接收的信号极其微弱,其电平仅比噪声稍高一点.地面系统则是另一类例子,尽管信号很强,噪声也很强. （8）. located in far outer space这是一种分词短语结构.located是动词的-ed形式，称为过去分词，起形容词的作用，在句中作定语.这种分词往往用来修饰原来动词动作的承受者.例如: The trees planted by me have grown up.“我种的树已长大了.” 再例如: Electromotive force results in electrical pressure, compared to water pressure.“电动势产生电压，电压好比水压” 所以课文中的这一短语可译为:“位于遥远太空中的(卫星)”. （8’）. Alternative adj.随便一个的；二者择一的 (三者或以上的选择用choice) The way was blocked, so we went by an alternative road.这条路被挡住了，因此我们走了另一条路。 n. 抉择；选择余地 I wanted to go out, but I had no money. I had no alternative but to staying at home.我想出去，可是没钱；只能待在家里。 We have no alternative but to go on.除了继续下去,我们没有选择的余地。 There was no other alternative but to fight till the victory.除了战斗直到胜利,别无选择。 ?If we consider binary transmission, the complete information about a particular message will always be obtained by simply detecting the presence or absence of the pulse. 研究二进制信号的传输可见,只要简单地去判别脉冲的”有”和”无”,我们就获得了一条消息的全部信息. By comparison, most other forms of transmission systems convey the message information using the shape, or level of the transmitted signal (9); parameters that are most easily affected by the noise and attenuation introduced by the transmission path. 相比之下,许多其他形式的传输系统是利用被传信号的波形或电平来传送信息的,而这些参数又极易受到传输途径中的噪声和衰耗的影响. （9）. By comparison? 相比之下 （9’）. using the shape, or level of transmitted signal 为现在分词短语结构，作伴随情况状语，可译为:“用传输信号的波形或电平(来传送信息)”. 类似的例子还有: The rockets rose hissing over the launching site.“火箭在发射场的上空嘶嘶地上升.” 再例如: They sat together, carefully studing the design of the circuits. “他们坐在一起仔细地研究着那些电路的设计.” 对课文中的这个句子，全句可译为:“相比之上，许多其他形式的传输系统是利用被传信号的波形或电平来传送信息的，而这些参数又极易受到传输途径中的噪声和衰耗的影响.” Consequently (10) there is an inherent advantage (10’) for overcoming noisy environments by choosing digital transmission. 因此选择数字传输系统在克服噪声环境方面有其固有的优势. （10）.consequently: adv., conj.所以，因此 Mr. Foster has never been to China. Consequently / Hence he knows very little about it. “福斯特先生从未去过中国,所以对中国了解得很少。“ 同义词：accordingly, hence, as a result, therefore. （10’）. inherent advantage 固有的优势． 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 decoder, the unit that performs the reverse operation (11). 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. 到目前为止,在这个讨论中, 我们一直假定每个话路各有一个编码器和解码器.前者是将幅度采样值变成脉冲,而后者施行相反的变换,这种设置并非必需.在实际运行的PCM系统中,单一的编、译码器为24路、30路,甚至120路所共用(注: 在当代PCM设备中,编、译码器系分路设备,即每个话路各有一套.) （11）. 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 decoder, the unit that performs the reverse operation. 本句理解和翻译应注意结构的分析．　在宾语从句that each voice channel has…中has带了两个并列的宾语coder, decoder；且这两个成分又分别带了非限制性定语从句． A high-speed electronic switch (12a) is used to present the analog information signal of each channel, taken in turn (12b), to the codec. The codec is then arranged to sequentially sample the amplitude value, and code (12c) this value into the 8-digit sequence. 一个高速的电子开关被用来将每一话路的模拟信号依次地送往编、译码器.然后编、译码器再顺序采样幅值并把这个幅值编成8位码序列. （12a）. A high-speed electronic switch : 一个高速电子开关 （14b）. taken in turn 轮流地，依次地 （12c）. Code 此处作动词，编码． 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. This unit is called a time division multiplexer (TDM), and is illustrated in Fig. 1-2 (13). The multiplexing principle that is used is known as word interleaving．Since the words, or 8-digit sequences, are interleaved in time. 因此从编译码器输出的信息就是一个分别对应于话路1, 话路2, 等等的8位码序列. 这种设备称为时分复用,如图1-2所示. 音域8位码的码字序列按时间顺序插接在一起,所以上面的复用原则称为码字插接. At the receive terminal a de-multiplexer is arranged to separate the 8-digit sequences into the appropriate (14) channels. The reader may ask, how does the de-multiplexer know which group of 8-digits relates to channel 1, 2, and so on? Clearly this is important! 接收端设置了分路设备,将8位码序列分配到相应的话路中.读者也许会问,分路设备怎么知道哪一个8位码组对应于第1路、第2路极其他各路呢?显然这是很重要的. （14）. appropriate: adj.适合的; 适当的; 相称的 appropriate example适当的例子 appropriate manners适当的态度 Write in a style appropriate to your subject.用与你的题目相称的体裁写。 Ordinary shoes are not appropriate to resist the electricity.普通鞋不适于抗电击。 The problem is easily overcome by specifying a frame format (15a), where at the start of each frame a unique sequence of pulses called the frame code (15b), or synchronization word (15c), is placed so as to(15d) identify the start of the frame. 这个问题是很容易解决的.我们只要指定一个帧格式,即在每一帧的开始放置一个被称作帧码或同步字的独特的码序列以标志每帧的起始. （15a）. specifying a frame format 指定一个帧格式 （15b）. the frame code:帧码 （15c）. synchronization word：同步字 （15d）. so as to 以便，为了. A circuit of the de-multiplexer is arranged to detect 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. 而用分路设备的一个电路去检测同步字,从而就可知道下一个8位码组对应于话路1.当最后一个话路的码字收到之后,同步码字有再次出现. IV. Post-reading Activities 1. Review the important expressions , phrases, sentences and translation skills learnt in the study of the text. 2. Guide students through some exercises in class. V. Further Development of the Theme-related Specialized Knowledge PCM原理及应用可参考网络资源： http://www.webopedia.com/TERM/P/PCM.html http://www.itu.int/search/pages/ituwebsearch/basic.asp? QuerySubmit=true&QueryText=pcm VI. Assignments（注意和首页题目总道数一致） 1.Preview Unit 02 2.Do Exercises3-5 between Page 19－22 3 mins 2 mins 60 mins 2mins 4 mins 1 mins computer， projector， loud speaker， audio-visual language teaching system， blackboard， recorder， DVD， radio， hanging chart， model.   抽样量化与编码sampling, quantizing and coding 话路 speech channel 幅值 amplitude value 抽样频率 sampling frequency 抽样速率 sampling rate 脉冲流 stream of pulses 重复率 repetition rate 编码过程 coding process 模拟信号 analog signal 传输质量 transmission quality 数字通信 digital communication 数字传输 digital transmission 含噪声的环境 noisy environment 传输路由 transmission path 信噪比 signal-to-noise ratio 信号电平 signal levels 地面系统 terrestrial systems 噪声功率 noise power 二进制传输 binary transmission 反向操作 reverse operation 8-位码序列 8-digit sequence 接收端 receiving terminal 帧格式 frame format 同步字 synchronization word 称作同步字的独特码序列 a unique sequence of pulses called synchronization word 涉及到第一，第二及其它各路的序列 a sequence relating to channel 1, 2 and so on 将抽样的幅值转换成一串脉冲的单元 the unit that converts sampled amplitude value to a set of pulses 由传输路由引入的衰减 　 the attenuation introduced by transmission path 被传信号的波形　 the shape of transmitted signal 一条特定消息中的全部信息　 the complete information about a particular message 由卫星上收到的信号　　　 the signal received from a satellite 真实信号与噪声信号间的关系 relationship of the true signal to the noise signal 实现这三项功能的方案 the schemes for performing these 3 functions 一串幅值　　　　　　　 a series of amplitude value 电话质量的话路　　　 a speech channel of telephone quality 理论上最小取样频率　　 a minimum theoretical sampling frequency 汽车点火系统的打火　 the sparking of a car ignition system 脉冲的“有”和“无”　　　 the presence or absence of the pulse 时分多路复用器　　 　 Time Division Multiplexer 高速电子开关　　　　 a high-speed electronic switch 重复率为64khz的脉冲流 the stream of the pulses with a repetition of 64 khz