Unit 3：Pulse Code Modulation.ppt

1、Specialized English,通信工程专业英语,Unit 3：,第二部分 通信技术,Pulse Code Modulation,脉冲编码调制,1.词汇和句型： 词汇是语言的基础，科技英语中的词汇可分为四类: 普通词汇、专业词汇、专业缩写词汇和转意词汇。,普通词汇：这些词汇在科技英语中的意义和用法与在普通英语中基本是一致的。 冠词、动词、副词、介词、形容词、数词、连接词、名词、代词,科技英语中的几个关键问题,专业英语基础知识,专业词汇：在通信技术中常用的专业词汇,electron、amplifier、electromagnetic wave、transceiver、frequency、

2、parameter.,专业缩写词汇：在通信技术中常用的专业缩写词汇,PCM pulse code modulation,SSB single side band,LASER light amplification by stimulated emission of radiation,LAN local area network,WWW world wide web,Fig. Figure,DSP digital signal processing,转义词汇：从普通词汇中借用、移植过来的，并赋予它们不同于普通应用时的专门含义。,专业英语基础知识,转意词 普通含义 专业含义,current 水流

3、，气流，趋势，当前的 电流,circuit 周围，巡回，绕行 电路,carrier 运载工具 载波，载流子,modulator 调节者 调制器,flip-flop 翻跟斗 触发器,NEW WORDS AND PHRASES,NEW WORDS AND PHRASES,NEW WORDS AND PHRASES,Provided these pulses were regenerated before they become impaired beyond recognition, then it would be possible, in principle, to transmit the

4、signal over infinitely long distances with no deterioration, except the approximation inherent in converting an analogue signal into a digital signal and back again in principle 为插入语； except theback again: 介词短语作状语 只要在脉冲变得无法识别之前重新再生它，那么，除了把模拟信号转换为数字信号及把数字信号转换为模拟信号时内在的近似过程，原则上信号可以无衰减的传输无限长的距离。,TEXT,Th

5、e sampling theorem tells us that we need to sample the signal at a rate equivalent to at least twice the highest frequency present in the signal if we are to reconstitute the signal at the receiver without distortion that we needwithout distortion: 宾语从句； if wewithout distortion:宾语从句中的条件状语从句。 抽样定律告诉我

6、们：如果想要在接收端无失真的重建信号，抽样频率需要至少是信号中最高频率的两倍。,The next question we have to answer is how many quantization levels do we need to provide in order to represent the signal amplitude with sufficient accuracy? 复杂句 how manywith sufficient accuracy:表语从句，与“is”一起构成复合谓语。 “do”提到“we need”之前,加强语气，强调谓语动词“need”表示的动作。 我们

7、要回答的下一个问题是：为了有足够的精确度来代表信号幅度，我们需要提供多少量化级？,In North America and Japan the primary level of multiplexing consists of 24 speech signals with a single bit of synchronizing information for every 248 bit frame , giving a frame size of 193 bits “the primarymultiplexing”作主语； “consists”作谓语，“of 24 speech signa

8、ls with248 bit frame”作状语； “giving”是现在分词短语作伴随状语，其逻辑主语是句子的主语。 在北美和日本,复用的一次群包括24个语音信号和为每248比特帧同步的一个比特，（故）帧的大小为193比特。,With modern digital switching systems it is possible to make more efficient use of the signaling channel by using it simply as a message transmission facility，the formatting of the signa

9、ling information being the responsibility of the exchange equipment “it”为形式主语，“to make morefacility”是真正的主语 “the signaling channel”作宾语，“efficient” 是“use的定语； the formattingequipment:分词独立结构，作伴随状语 利用现代数字交换系统，把信令信道仅仅作为信息传输工具（设备）使其利用率更高是可能的，信令信息的初始化是交换设备的功能。,To alleviate these problems，line codes are empl

10、oyed which modify the spectrum shape and introduce additional transitions into the line signal Toproblems:目的状语； which modifysignal: “which” 引导的限制性定语从句，修饰“line codes”(有句子成分分隔现象) 为了解决这些问题，使用了能修改频谱形状的、引入额外信号形状转变的线路码。,To avoid this confusion，any violation pulse which is of opposite polarity to the prece

11、ding mark pulse，whether genuine or a violation, is forced into violation by the insertion of a “parity” pulse substituted for the first zero immediately following the preceding mark To avoid confusion:目的状语； 为了避免混淆，任何与前面的标记脉冲极性相反的冲突脉冲，无论其是真的或假的冲突脉冲，都会被强制为冲突（形式）。这种强制冲突是通过插入相同极性脉冲来替代紧跟在前面标记脉冲之后的第一个“0”来实现的。,4B3T has found its chief application transmission systems that have been converted to 30 channel PCM from the earlier 24 channel system thatsystem:“that”引导