《通信与电子信息科技英语》课件unit 10

Characteristics of Data Transmission CirsuitsNew words and phrases1 sophisticated adj.复杂的2 repetition n.重复,循环3 intelligibility n.可懂度，清晰度4 attenuate vt.衰减attenuationn.衰减5 dibit n.双位6 drawback n.缺点,障碍7 compromise vt.危害；损害（名誉）8 Hartley n.哈特莱ShannonHartley law香农哈特莱定律9 expectation n.期望(值)ideal expectation理想期望值10 nonetheless adv.虽然如此,但是11 minimum adj.最小的,最低的12 preclude vt.避免、阻止；使不可能Characteristics of Data Transmission Cirsuits13 impairment n.损害,损伤14 decibel n.分贝15 crosstalk n.串话16 pronounced adj.显著的,明显的17 interaction n.交互作用,交感 electromagnetic interaction 电磁交感，电磁相互作用18 braided adj.编织的19 foil n.箔,金属薄片metal foil金属箔20 shield vt.屏蔽,保护；n.屏蔽,防护罩 shielded cable屏蔽电缆21 echo n.回声22 suppressor n.抑制器echo suppressor回波抑制器23 intact adj.原封不动的，完整的24 bidirectional adj.双向的Characteristics of Data Transmission Cirsuits25 disable vt.禁止;使失效26 reactivate v.复原，重激活，重新使用27 abnormality n.不正常，畸形28 alter v.改变29 commence v.开始30 thereafter adv.此后；后来31 preset adj.；vt.预置32 lease vt.出租,租出33 equalization n.均衡adaptive equalization自适应均衡34 dedicated adj.专用的dedicated circuit专用电路 35 understandably adv.可理解地Characteristics of Data Transmission Cirsuits1 data stream 数据流2 square wave signal 矩形波信号3 HF(high frequency)高频4 submarine cable 海底电缆5 audible spectrum 声谱6 data transfer 数据传送7 multilevel encoding 多电平编码8 baud rate 波特率9 information transfer 信息传递Characteristics of Data Transmission Cirsuits10 signaling pulse 信号脉冲11 signaling speed 通信速度,发码速率12 distortionless transmission 无失真传输13 bit rate 比特率14 transmission efficiency 传输效率15 voice grade channel 话音级信道，电话线路16 bps（bits per second）比特/秒 17 noise free channel 无噪信道Characteristics of Data Transmission Cirsuits18 signaltonoise ratio 信噪比19 envelope delay 包络延迟，群时延 envelope delay distortion 包络线延迟失真(畸变)20 transformer winding 变压器绕组21 electromagnetic radiation 电磁辐射22 balanced circuit 平衡电路23 twisted pair 双绞线24 outofphase 异相地,不协调地25 in phase 同相地,协调地26 bidirectional transmission 双向传输Characteristics of Data Transmission Cirsuits27 frequency component 频率成分28 phase delay 相位延迟29 time slot 时隙30 intersymbol interference 码间干扰,符号间干扰31 react to 对作出反应32 drain off 渐渐枯竭33 be conditioned to 习惯于Characteristics of Data Transmission Cirsuits Data communications became important when the rapid transfer of data became both necessary and feasible.In other words,data communications emerged as a natural result of the development of sophisticated computer systems.Bandwidth requirementsData in most instances consists of pulse type energy.The data stream is similar to a square wave signal with rapid transitions from one voltage level to another,with the repetition rate depending on the binary representation of the data word.For instance,if an 8bit word has the value 0101 0101,the resulting voltage would appear as a series of four square waves with each negative half cycle equal to each positive half cycle.If,however,the data word has the form 0000 1111,the voltage graph would appear as a single square wave with negative and positive half cycles equal but longer than the first example.NoiseThe ShannonHartley law is related to random noise,but impulse noise can also be harmful to signals.The sampling theorem Characteristics of Data Transmission Cirsuitsshows that all values of a signal can be determined by sampling the signal at a rate equal to at least twice the bandwidth.Noise affects this sampling process because the noise pulse will be interpreted as a data bit(see Fig.10.1),if the noise impulse occurs at the time a sample is taken,and has an amplitude equal to or exceeding the minimum level recognized by the system as a mark.The potential for impulse noise to become a source of errors increases with the number of levels of each Characteristics of Data Transmission Cirsuitscode element.To achieve the 30 880 bps rate mentioned in the above example,it may be shown that five levels would be required for each code element.A noise free channel would be necessary to preclude noise induced data errors,but noisefree channels do not exist in practice.It is noise,among other impairments,which tends to limit the actual 4 kHz channel data speeds to 10 800 bps or less.It can be shown that a system using a threelevel code must have a signal to noise ratio of 8.5 dB,or 3.7 dB greater,for equal performance in the same channel.A fourlevel code requires a signaltonoise performance of 11.7 dB.Improvement in the signaltonoise ratio makes use of multilevel encoding feasible.DistortionCommunication channels tend to react to signals of different speedswithin their passband in different ways.Characteristics of Data Transmission CirsuitsSpecifically,signals of different frequencies can be passed by the channel with different values of amplitude attenuation and at different propagation speeds.The result is distortion.Of great importance to systems using phase modulation is phase delay(or envelope delay)distortion.Phase delay distortion occurs in a channel when signals of one frequency are passed through the circuit at a different speed than other signals.The resulting disto