1、Specialized English,通信工程专业英语,：译文必须通顺流畅，符合语言规范，不应有文理不通、逐词死译和生硬晦涩等现象。,：译文必须符合原意，准确地、完整地、科学地表达原文的内容，不得有任何篡改。,通顺（Smooth）,不是用译者的意思来代替原文的意思,第一部分 专业英语基础知识,专业英语的翻译（Translating）,忠实（True）,1.翻译的标准,翻译：用一种语言把另一种语言所表达的思想内容准确而又完整地再现的语言活动。,把原文意思用译语准确无误地传达出来,句子结构上有差异,词汇上很少对等,直译：基本上保留原文的表达形式及内容，不做大的改动，同时译出的文字又明白易懂； 意
2、译：在正确理解原意的基础上，重新遣词造句，把原文的意思用通顺的汉语表达出来。,专业英语的翻译,照译：基本上保留原文的结构形式，语序上未作大的变动；保留原文词语的字面意思，未加引伸和转换。,2.翻译方法,Computers are of great help to our work.计算机对我们的工作有很大帮助。 Compounds are composed of elements.化合物是由元素构成的。,专业英语的翻译,转换：词义引伸和词性转换（意义上的转换）；语序的变动，句子结构和句子表达方式的转换（形式上的转换）。,The miniature receiving antenna was d
3、eveloped as an alternative to that larger one.这种小型接收天线是为取代那种大型接收天线而研制的。 （译文把原文中的名词转换成了动词） The reliability can be further improved by using error-detecting and error-correcting codes.利用检错和纠错编码能进一步提高可靠性。（被动语态转译为主动语态）,专业英语的翻译,省略：根据汉语语法的修辞习惯，将原文中的某些词语略去不译。（如英语中的冠词、代词和连词）,Air is a fluid but not a liquid.
4、空气是流体, 不是液体。（省略冠词） If you know the frequency, you can find the wave length.如果知道频率，就能求出波长。（泛指的人称代词you可省略不译）,专业英语的翻译,增补：按照汉语语言习惯，在译文中适当添加原文中所没有的词语，以更明确的表达原文的含义和满足汉语语法的修辞需要。,This is what we must resolve at first.这是我们必须首先解决的问题。(增补宾语),专业英语的翻译,Unit 2：,第二部分 通信技术,Digital Communication System,数字通信系统,相关背景知识,N
5、EW WORDS AND PHRASES,immune adj. 免除的,不受影响的,可避免的 threshold n. 门槛,门限 intertlace v. 使交织,使交错 hierarchy n. 等级,体系,系列 crosstalk n. 串话 feasible adj. 可行的,行得通的 elimination n. 消除,排除,淘汰 interval n 间隔时间 supervision n. 监督,监管 overvoltage n. 超压,过电压 suppress v. 抑制 nonlinearly ad. 非线性地 resolution n. 分析,分辨 polarity n.
6、 极性,The use of digital methods for the transmission of analog signals is becoming increasingly common in telecommunication systems. There are two major reasons for this. digital :数字的, 数位的 analog:模拟（的） telecommunication电讯, 长途通讯 在通信系统中使用数字方式来传输模拟信号正变得越来越普遍，这主要由两种原因引起。,TEXT,First, if digital rather tha
7、n analog signals are transmitted, then the system remains nearly immune to noise as long as it is below a threshold level. rather than ：而不是 immune to ：可避免的,不受影响的 as long as ：只要, 在.的时候 threshold level：门限电平 第一,如果传输的是数字信号而不是模拟信号,则只要噪声电平低于门限电平,系统就几乎不受影响。,This is due to the fact that for long-distance tr
8、ansmission the digital signal can be regenerated at each repeater, creating a new, noise-free signal. Thus, noise does not accumulate as it would in a comparable analog system. due to ：由于, 应归于 regenerate：再生，重建 repeater：中继器，再生器 accumulate：积累 这是因为：对于长距离传输，数字信号可以在再生器中重新生成，从而产生一个新的、无噪声的信号，因此噪声不会像在模拟系统中那
9、样积累。,Second, the components of a digital system lend themselves well to integrated implementation using large-scale-integrated (LSI) circuits. component：组成，成分 lend oneself to：适合于 implementation：落实，实施，实际应用，执行, 履行; large-scale-integrated (LSI) circuits：大规模集成电路 第二，数字系统的组成使其适合于采用大规模集成电路实际应用场合。,Even in s
10、uch a digital transmission system, however, many signals which are being processed are usually analog in nature. There analog signals need therefore to be converted into digital format. in nature：实际上, 本质上 convert into：使转变（转换）成. format ：形式, 格式, 版式 然而，即使在这样的数字传输系统中，所处理的许多信号通常在本质上是模拟的。因此，需要将这些模拟信号转化为数字
11、形式。,There are various modulation schemes to accomplish this, including pulse-width modulation (PWM), pulse amplitude modulation (PAM),and pulse code modulation (PCM) . PCM is currently the most commonly used modulation system in digital telecommunication systems. pulse-width modulation (PWM):脉宽调制 pu
12、lse amplitude modulation (PAM) :脉幅调制 pulse code modulation (PCM) :脉码调制 有多种调制手段以实现这种转换,包括脉宽调制、脉幅调制以及脉码调制. PCM是当前数字通信系统中最普通的调制手段。,The PCM signal is generated by sampling, quantizing, and coding an analog signal. The result is a stream of binary digits (bits), that is, an alternation of high and low vo
13、ltage levels in the signal. This stream can then be applied, frequency modulation. sampling ：取样 quantizing：量化 coding：编码 alternation：交替, 变换; 间隔 PCM信号是通过对模拟信号取样、量化、编码产生的。结果是产生一系列的二进制比特流，即交替的高低电平。,The process of sampling an analog voltage V (t) consists of developing a pulse train in which the amplitud
14、e of the nth pulse equals the amplitude of V(t) at t= nT. consists of ：由.组成 pulse train ：脉冲串 amplitude：幅值，振幅，幅度 对模拟电压V(t)采样过程包括生成一个脉冲串,在这个脉冲串中,第n个脉冲的幅度等于V(t)在t=nT时的幅值。,In order for the pulse train to represent uniquely the information contained in V(t), the sampling rate fc=1/T must be at least twic
15、e as large as the highest frequency component in the spectrum of V(t), the amplitudes of the pulses in the sampled signal are then quantized and converted into a set of bits, called a digital word. sampling rate:抽样（频）率 spectrum：谱，光谱，频谱 为了让脉冲序列唯一表示V(t)包含的信息，抽样频率fc=1/T至少为V(t)频谱中最高频率成分的2倍，然后对抽样信号中的脉冲幅值
16、进行量化并转化为一系列的比特，称作码字。,The transmission of digital words in a practical PCM telecommunication system often utilizes time-division multiplexing (TDM). In a TDM system, the digital words taken from several channels are transmitted interlaced over the same line. time-division multiplexing (TDM) ：时分复用 int
17、erlaced：交织的,交错的 在实际的PCM长途通信系统中经常利用时分复用方式来传输码字。在TDM系统中，来自几个信道的码字交错着在一条线路上传输。,In voice-frequency (telephone) systems, usually 24 or 32 voice channels are thus multiplexed onto a single pair of wires. voice-frequency (telephone) systems：音频（电话）系统 multiplex：复用 在音频（电话）系统中，通常将24或32路话路复用到一对线路中传输。,The Intern
18、ational Telegraph and Telephone Consultative Committee (CCITT) had recommended two main architectures (“hierarchies”), which now many nationwide PCM transmission network use. CCITT ：国际电话与电报顾问委员会 architectures ：体系机构 hierarchy ：体系制, 系统，数据层次 nationwide ：全国性的 CCITT推介了两种主要的体系，现在许多全国的PCM传输网络都在采用。,The firs
19、t one, shown schematically in Fig.1, has been adopted mostly in Europe, Africa, Australia, and South America. In this system, the input multiplexers (MUX) interleave 32 digital words. Of these, 30 words represent the signal amplitudes in 30 voice channels, while the remaining two time slots contain
20、signaling and synchronization information. schematically ：示意性地 multiplexers ：多路(复用)器 interleave：使交织替, 插 time slots ：时间的空当，时隙 synchronization：同步 在这种体系中，输入复用器将32路信息码交插在一起。其中30路码字代表30路语音信道，其余2路时隙包含随路信令和同步码。,The second hierarchy, used mainly in the United States, Canada, and Japan, is illustrated in Fig
21、. 2. In this system, 24 voice channels are multiplexed at the input section. illustrate：举例说明, 图解multiplex：多路传输，多路复用 第二种体系由图2所示，主要用在美国、加拿大和日本。在这种系统中，24路语音信号在输入端复用在一起。,There are two main tasks performed in a digital telecommunication system: transmission and switching. Transmission involves sending th
22、e digitally coded voice signal from one 1ocation to another, while switching consists of establishing the desired connection between two voice channels which carry digital signals. perform ：履行, 执行，完成任务 switching：交换 1ocation：地点 传输包括把数字编码的语音信号从一个地方发送到另一个地方，而交换包括建立两个话音信道的有效连接，这两个信道是（用来）承载数字信号的。,The uni
23、t which performs the pulse code modulation and demodulation of the signals in a digital transmission system is called a coder-decoder, or, in abbreviated form, a codec. demodulation ：解调, 反调制, 检波 coder-decoder ：编/解码器 abbreviated ：省略的, 缩写的 codec ：数字信号编解码器 在数字传输系统中，对信号进行脉码调制和解调的单元被称作编/解码器，或缩写为codec.,In
24、 early digital systems, the switching was done in an analog form, using such analog devices as the electromechanical crossbar mechanism. electromechanical ：电动机械的,机电的crossbar mechanism ：纵横机械组装 在早期的数字系统中，通过使用像纵横交换机这样的模拟设备，在模拟形式中进行交换.,Then, the analog voice signal channels were time-multiplexed into gr
25、oups of 24 or 30 channels. Each group was next converted into digital form by a single high speed codec. time-multiplexed ：时分复用 然后，将单个的模拟语音话路时分复用为24路或30路的组合。接下来，通过一个高速的数字信号编解码器将每一组合转化为数字形式。,This arrangement resulted in some savings in terms of the number of components; however, the design of the sha
26、red codec with a sufficiently low line-to-line crosstalk and noise, as well as the required high speed in a fully integrated form represented a very difficult design problem. line-to-line crosstalk ：线间串话 integrated ：集成的 这种排列导致了器件数量的一些减少，但是，具有足够低的线间串话和噪声,同时又具有所需很高速度的全集成(各路)共用编解码器的设计代表了一个很难的设计问题。,In a
27、ddition, any failure of the codec resulted in the loss of service to all lines serviced by that unit. Also, the system required a large number of analog switches, which were bulky and slow. failure ：故障 bulky：庞大的, 体积大的, 笨重的, 占地方的 此外，编解码器的任何故障都会导致这个单元所服务的所有线路丢失其所需的服务。而且，这种系统需要大量笨重且低速的模拟转换器。,Finally, t
28、he analog multiplexing needed was more difficult to perform and less flexible than digital multiplexing would have been. analog multiplexing ：模拟多路复用 flexible ：灵活的, 柔软的 digital multiplexing ：数字多路复用 最终，所需的模拟多路复用与数字多路复用相比,在实现上更为困难,灵活性亦更差,With the recent availability of low-cost and high-performance int
29、egrated circuits, it became feasible to allocate one codec to each voice channel, rather than to a group of channels. availability ：可用性, 有效性, 实用性 high-performance：高性能 integrated circuits ：集成电路 allocate：分配，配给，分派 随着近来低成本、高性能集成电路的实用化，可以为每一路语音信道分配一个编解码器，而不是一组信道使用一个编解码器 。,The voice signal in each channel
30、 is thus first digitized, and the subsequent switching and multiplexing are performed by digital systems which can use low-cost digital logic and memory circuits. digitize ：将（例如数据）数字化 subsequent ：后来的, 并发的，随后的 因此，首先将每个信道中的语音信号数字化，随后的交换和复用是由数字系统完成的，数字系统可以使用廉价的数字逻辑电路和存储电路。,Such a “per-channel codec” sy
31、stem results in a considerable reduction of crosstalk and noise. Also, there is a significant saving in size and cost, due to the elimination of most of the bulky and expensive electromechanical components. considerable ：相当大(或多)的, 相当可观的 significant ：有意义的, 重大的, 重要的 elimination ：排除, 除去, 消除 bulky ：大的,
32、容量大的, 体积大的 每信道一个编解码器的系统，显著减少了串话和噪声的影响 。此外，由于除去了使用体积庞大且贵重的电动机械的部件而显著节省了空间和成本。,The standard sampling rate fc recommended by the CCITT for the usual 3003400 Hz voice channel is 8000Hz.recommended ：被推荐的 sampling rate ：取样频率 对于通常的3003400 Hz 的语音信道，CCITT推荐的标准取样频率为8000Hz。,In the per-channel codec system, the
33、 analog signal is thus sampled at intervals of 1/8000Hz=1.2510-4S=125s, and the amplitude of the sample is converted into an eight-bit digital word is then transmitted serially to the multiplexer. at intervals of ：相隔, 每隔 serially ：连续地 在每信道一个编解码器的系统，每隔125s对模拟信号取样一次，将样值的幅度转化成一个8比特的码字，然后再连续的传输给复用器。,The
34、 125-s-long time interval available for the conversion is called a frame. interval ：时间间隔 frame ：帧 将这个用来转换的125s长的时间间隔称作一帧。,The digital multiplexer places all the bits corresponding to one sample of each of 24 or 30 channels (depending on the hierarchy used) into a single frame, and transmits the resu
35、lting serial bit stream. 数字复用器把对应于24路或30路各路样值的全部比特放在一个帧中，然后传输结果串行比特流。,To mark the beginning and the end of each frame at the receiver, some identifying signal should be added to the transmitted bit steam. mark ：做标记于, 标志 identifying signal ：识别信号 为了在接收机处能够对每一帧的帧头和帧尾进行标识，应该在传输的比特流中加入一些识别信号。,For example
36、, in the 24-channel eight-bit PCM system called D2 developed by AT&T, an additional bit is appended to the bits of each frame. appended to ：附加，添加，贴上 例如，在被AT&T称作D2 的24信道8比特PCM系统中，给每一帧中附加了一个比特。,Thus, a frame in the D2 system contains 248+1=193 bits. Hence, the data rate of the transmitted signal is 19
37、3 bits per 125s, which corresponds to 1.544106bit/s. interval ：时间间隔 frame ：帧 从而，在D2系统中，每一帧包含248+1=193 bits 。因此，所传输信号的数据率为193 bits/125s,对应 1.544106bit/s的速率。,In the transmit direction, the subscribed line is connected to the subscriber-line interface circuit (SLIC). The SLIC performs the two-to-four w
38、ire conversion, the battery feed, the line supervision, and also provides ringing access and over voltage protection. SLIC ：subscriber-line interface circuit 用户线接口电路 battery feed ：远端供电 line supervision ：线路监测 ringing access ：铃流接入 over voltage protection：过压保护,The signal then passes through the transmi
39、t filter, which limits its spectrum to (approximately) 3400Hz.The transmit filter thus removes the part of the spectrum which extends over 4kHz,and thus makes it possible to sample the signal at an 8 kHz rate without introducing aliasing. transmit filter：发送滤波器 approximately：近似地, 大约 aliasing：混淆现象 信号接
40、着通过发送滤波器，发送滤波器将信号频谱限制在3400Hz附近，因此去掉了超出4kHz的频谱，从而使得以8 kHz 的频率对信号抽样而不出现混频成为可能。,In addition, the low-frequency portion (below 300Hz)of the spectrum is also suppressed by the transmit filter, to prevent power-line frequency (50 or 60 Hz) noise from being transmitted. low-frequency portion ：低频部分 suppress
41、ed ：抑制, 压制 power-line frequency ：传输线频率 prevent. from：使.不做某事, 阻止.做某事 此外，频谱的低频部分（300Hz以下）也被发送滤波器抑制掉，以阻止传输线频率噪声。,The filtered signal, now band limited to the 300 to 3400 Hz range, is then sampled at an 8 kHz rate, and then converted (encoded) into eight-bit PCM data. This conversion is performed nonlin
42、early; that is, the resolution of the resulting digital signal is finer for small signals than for large ones. nonlinearly ：非线性地, 非直线(型)地 resolution ：分辨率, 清晰度 经过滤波的信号，频带被限制在300 to 3400 Hz 范围内，然后以8 kHz 的频率对其进行抽样，转换（编码）为8bit的PCM数据。这种转换是非线性的，即对小信号其生产的数字信号的分辨率要优于大信号。,The output of the nonlinear A/D conv
43、erter is a specially coded eight-bit digital word. The first bit indicates the sign of the input x, with“1”representing positive and“0”negative polarity. The next seven bits provide the amplitude value of the signal. A/D converter ：模拟/数字转换器 positive ：正的;阳性的 negative：负的;阴极的; 非线性模/数转换器输出经过特殊编码的8bit码字，
44、其中第一个bit表示输入x的符号，1表示正极性，0表示负极性，后7位bit表示信号的幅值。,Returning to the block diagram of Fig.4, the digital output of the encoder is then time-division multiplexed with the outputs from the other lines, and the resulting bit stream is transmitted over the channel. block diagram ：方框图，结构图 time-division multipl
45、ex：时分复用 positive ：正的;阳性的 negative：负的;阴极的; 编码器的数字输出与其他线路的输出通过时分复用，产生的bit流在信道中传输。,At the receiver side, the incoming data are demultiplexed, that is, distributed among the various channels, and decoded (i.e., D/A converted). The analog output is then sampled-and-held, and passed through the receive fi
46、lter. incoming data ：输入数据 demultiplex ：解复用，分离 D/A convert ：数/模转换 negative：负的;阴极的; sampled-and-held ： 在接收端，对输入数据进行解复用，即在各个通路间分配并解码（数/模转换 ）。,The latter is a low-pass smoothing filter, which removes the high-frequency “side lobes” of the signal spectrum, and hence smoothes out the staircase noise in th
47、e signal. It is also often used to equalize for the sin x/x amplitude distortion introduced by the sample-and-hold stage. low-pass smoothing filter ：低通滤波器 side lobes ：旁瓣, 副瓣 smoothe out ：消除, 使平滑staircase noise ：阶梯噪声 equalize ：使均衡; 调整,After four-to-two wire convention, the voice signal is transmitted into the handset of the subscribers telephone, and thus the one-way communication is completed. handset ：电话听筒 subscriber ：用户，预约者, 订购者 one-way ：单线的，单方向的， 单行道的 在接收端，对输入数据进行解复用，即在各个通路间分配并解码（数/模转换 ）。,小 结,专业英语翻译的标准忠实（True）通顺（Smooth） 专业英语的翻译方法照译 转译 省译 赠补 Digital Communication System,
