《通信与电子信息科技英语》课件unit 5.ppt

1、ModulationNew words and phrases1 categorize v.加以类别,分类2 broadly adv.概括地,大致地3 amplitude n.幅度，幅值，振幅4 cosine n.余弦5 argument n.自变量，变元6 markedly adv.显著地，明显地7 characteristic n.特征，特性8 prescribe v.指定，规定 9 quantize v.量化10 parameter n.参数,参量 Modulation11 digitize vt.将数字化12 proportional adj.比例的，成比例的 proportional

2、 to与成比例，成正比13 disperse v.分散，散开，扩展14 vestigial adj.残留的,剩余的 vestigialsideband残留边带15 integral n.积分；adj.积分的 16 collectively adv.共同地，全体地17 representative adj.典型的,有代表性的 18 simplification n.简化19 appreciable adj.可观的，可评估的20 impress v.施加，外加Modulation21 lineofsight n.视线 line of sight propagation(电波的)直线传播22 ant

3、enna n.天线23 compact adj.简洁的，简明的24 treatment n.论述，分析25 fractional adj.部分的26 designation n.指定,指示 27 complication n.复杂化28 likewise adv.同样地,照样地29 brute adj.强制的,粗暴的 brute force method 强制法30 overwhelm vt.淹没；覆盖31 contamination n.污染，杂质，污染物Modulation32 transatlantic n.横渡大西洋的33 rupture n.破裂，绝缘击穿34 tradeoff n.

4、折衷,权衡35 tune vt.调谐 36 jumble n.混杂37 simultaneous adj.同时的；同步的38 bank n.组39 nonoverlapping adj.不相重叠的40 gap n.间隙,间隔41 telemetry n.遥测，遥感勘测42 stereophonic n.立体声的Modulation1 carrier wave 载波2 more or less 差不多，或多或少3 cw(continuous wave)连续波 4 pulse duration 脉冲宽度，脉冲持续时间5 modulated signal 已调信号modulating signal

5、调制信号6 pulse train 脉冲序列，脉冲群7 round off 舍入，四舍五入8 discrete level 离散电平9 amount to 等于，实际上是10 spectral components 频（光）谱分量Modulation11 in relation to 关于关于,涉及涉及,与与相比相比12 take on 具有，呈现具有，呈现13 DM(delta modulation)调制，增量调制调制，增量调制14 ADM(adaptive delta modulation)自适应增量调制自适应增量调制15 DPCM(differential pulse code modu

6、lation)差分脉冲编码调差分脉冲编码调16 ASK(amplitudeshift keying)振幅键控振幅键控17 FSK(frequencyshift keying)移频键控移频键控18 PSK(phaseshift keying)移相键控移相键控19 DPSK(Differential PSK)差分相位键控差分相位键控20 suit to 适于，适合于适于，适合于Modulation21 electromagnetic wave 电磁波22 electromagnetic radiation 电磁辐射23.account for 说明,占,解决,得分24.in an effort t

7、o 企图，努力想25.HartleyShannon law 哈特莱香农定律26.FDM(frequency division multiplexing)频分（多路）复用27.TDM(timedivision multiplexing)时分（多路）复用28.time slot 时隙29 coaxial cable 同轴电缆Modulation Modulation is a process by which an information signal f(t)may be converted to a more useful form.It is helpful to categorize mo

8、dulation broadly accordingto three basic methods.Each method is then subdivided into various types of modulation.Carrier Wave Modulation Method One of the most common modulation methods is to alter a carrier wave of the formAcos(0t+0),(5.1)where 0 is an arbitrary constant,A is the wave peak amplitud

9、e,and 0is the carrier frequency.More or less obvious modulation approaches are to make A a function of the information signal f(t)or to add a phase term to the cosine argument which depends onf(t).These methods may be characterized as continuous wave(cw)modulation.The result of cw modulation is usua

10、lly a bandpass signal because the carrier frequency is often much higher than the largest significant frequency component in f(t).ModulationPulse Modulation Method Another modulation method,pulse modulation,involves changing some parameter of a train of pulses.For example,the amplitude of the pulses

11、 could be varied as some function of the information signal f(t).Alternatives would be to vary pulse duration or position.Pulse modulation does not involve a carrier.The resulting modulated signal is still baseband but is no longer the original information signal.Both cw and pulse modulation may be

12、classed as analog modulation which involves varying the modulated parameter continuously as a linear function of the information signal.Coded or Digital Modulation Method Coded modulation involves changing a characteristic of a pulse train but is Modulationa markedly different method from pulse modu

13、lation.The method involves first sampling the information signal,quantizing the sample by rounding off to the closest of a number of discrete levels,and finally generating a prescribed number of pulses according to a code related to the nearest discrete level.In the simplest system the code may dete

14、rmine the presence or absence of pulses in the prescribed number,or,alternatively,it may determine pulse sign.Both cases correspond to pulses having only two possible levels.More complicated systems are also feasible with pulses having a larger number of discrete levels.Quantizing and coding amounts

15、 to digitizing the signal;thus,coded modulation will also be referred to as digital modulation.It is one of the most modern and useful methods of modulation available today.Exercises.Please translate the following words and phrases into Chinese.1.AM2.DPSK3.PAM4.PDM5.PPM6.PCM7.DPCM8.ASK9.FSK10.FDM11.

16、TDM12.coded modulation13.suppressed carrier14.modulated signal幅度调制幅度调制(amplitude modulation)差分相位键控差分相位键控(Differential PSK)脉脉(冲振）幅调制冲振）幅调制(pulse amplitude modulation)脉宽调制脉宽调制(pulse duration modulation)脉（冲相）位调制脉（冲相）位调制(pulse phase modulation)脉脉(冲编冲编)码调制码调制(pulse code modulation)差分脉冲编码调制差分脉冲编码调制(differ

17、ential pulse code modulation)振幅键控振幅键控(amplitudeshift keying)移频键控移频键控(frequencyshift keying)频分（多路）复用频分（多路）复用(frequencydivision multiplexing)时分（多路）复用时分（多路）复用(timedivision multiplexing)编码调制编码调制抑制载波抑制载波已调信号已调信号Exercises.Please translate the following words and phrases into English.1.带通信号2.脉冲调制3.角度调制4.残留

18、边带抑制载波调制5.绝对带宽6.脉冲宽度7.线性函数8.载波频率9.模拟调制10.移相键控11.连续波调制12.同轴电缆bandpass signalpulse modulationangle modulationVestigial sideband suppressed carrier modulationabsolute bandwidthpulse durationlinear functioncarrier frequencyanalog modulationPSK(phase shift keying)continuous wave(cw)modulationcoaxial cabl

19、eExercises.Fill in the blanks with the missing word(s).1.The method involves first sampling the information signal,quantizing the sample by rounding off to the closest of a number of discrete levels,and finally generating a prescribed number of pulses according to a code related to the nearest discr

20、ete level.2.Coded modulation will also be referred to as digital modulation.It is one of the most modern and useful methods of modulation available today.3.In PPM pulse position is proportional to the amplitude of the message signal4.Timedivision multiplexing(TDM)uses pulse modulation to put samples

21、 of different signals in nonoverlapping time slots.For instance,the gaps between pulses could be filled with samples from other signals.5.It is often necessary to use modulation to translate the useful band of frequencies up to a large carrier frequency so that efficient electromagnetic radiation is

22、 possible from an antenna having reasonable size.Exercises6.The design of a communication system may be constrained by the cost and availability of hardware,whose performance often depends on the frequencies involved7.Fractional bandwidth considerations account for the fact that modulationunits are

23、found in receivers as well as in transmitters.8.These methods may be characterized as continuous wave(cw)modulation.9.Since each station has a different assigned carrier frequency,the desired signal can be separated from the others by filtering.10.PCM may be either binary,where pulses have only two

24、voltage levels,or -ary,where pulses may take on possible levels.11.By exploiting the frequency translation property of cw modulation,message information can be impressed on a carrier whose frequency has been selected for the desired transmission method.Exercises.Answer the following questions accord

25、ing to the text.1.Why does the cw modulation usually result in a bandpass signal?The result of cw modulation is usually a band pass signal because the carrier frequency is often much higher than the largest significant frequency component in f(t).2.Please describe the procedure of the coded modulati

26、on.The method involves first sampling the information signal,quantizing the sample by rounding off to the closest of a number of discrete levels,and finally generating a prescribed number of pulses according to a code related to the nearest discrete level.Exercises3.What are the practical benefits o

27、f modulation?The primary purpose of modulation in a communication system is to generate a modulated signal suited to the characteristics of the transmission channel.Actually,there are several practical benefits and applications of modulation briefly discussed below.1)Modulation for efficient transmi

28、ssion 2)Modulation to overcome hardware limitations3)Modulation to reduce noise and interference 4)Modulation for frequency assignment 5)Modulation for multiplexing4.How can we transmit many signals on one channel at the same time according to the text?Multiplexing is the process of combining severa

29、l signals for simultaneous transmission on one channel.Frequency division multiplexing(FDM)uses cw modulation to put each signal on a different carrier frequency,and a bank of filters separates the signals at the destination.Time division multiplexing(TDM)uses pulse modulation to put samples of different signals in nonoverlapping time slots.5.In this text modulation is classified as three categories,what are they?They are:1)Carrier Wave Modulation Method 2)Pulse Modulation Method 3)Coded or Digital Modulation Method