信息科学与电子工程专业英语课后答案 .doc

Unit 1 Exercises(1) Translate the following sentences into Chinese.1. As with series resonance, the greater the resistance in the circuit the lower the Q and, accordingly, the flatter and broader the resonance curve of either line current or circuit impedance.对于串联谐振，电路中的电阻愈大Q值就愈低，相应地线路电流或电路阻抗的谐振曲线也就愈平、愈宽。2. A wire carrying a current looks exactly the same and weighs exactly the same as it does when it is not carrying a current.一根带电的导线其外表与重量都与不带电导线完全一样。3. Click mouse on the waveform and drag it to change the pulse repetition rate, or directly enter a new value of the period in the provided dialogue box, while keeping the pulse width unchanged.在波形上点击鼠标并拖动来改变脉冲重复频率，或者在提供的对话框中直接输入新的周期值，而保持脉冲宽度不变。 4. Electronics is the science and the technology of the passage of charged particles in a gas, in a vacuum, or in a semiconductor. Please note that particle motion confined within a metal only is not considered electronics.电子学是一门有关带电粒子在气体、真空或半导体中运动的科学技术。注意，在本书中粒子运动仅限于金属的情况不属于电子学。5. Hardware technologies have played vital roles in our ability to use electronic properties to process information, but software and data processing aspects have not developed at the same speed.硬件技术在我们使用电子特性来处理信息的能力中一直起着重要作用，而软件及数字处理方面却没能与硬件同步发展。6. However, in a properly designed DC amplifier the effect of transistor parameter variation, other than Ico, may be practically eliminated if the operation point of each stage is adjusted so that it remains in the linear operation range of the transistor as temperature varies.然而在设计得当的直流放大器中，若调节每一级的工作点使之在温度变化时保持在晶体管线性区，就能在实际上消除Ico以外的晶体管参数变化所造成的影响。Unit 2 Exercises (1) Translate the following sentences into Chinese.1. If analog signals are to be transmitted digitally, they first have to be sampled at a specified rate and further converted to discrete amplitude samples by quantization.如果要以数字方式传输模拟信号，首先必须以一定的频率对信号进行采样，然后通过量化进一步将它们转换为离散的幅度样本。2. Linear filters amplify or attenuate selected spatial frequencies, can achieve such effects as smoothing and sharpening, and usually form the basis of re-sampling and boundary detection algorithms. 线性滤波器放大或衰减选择的空间频率，能够实现像平滑和锐化这些效果，通常是重采样和边缘检测算法的基础。3. Stability and repeatability are fundamental attributes of digital circuits, however, and the necessary accuracy can be obtained in a digital version of the modulator by an appropriate choice of word length to represent the signals.不过稳定性和可重复性是数字电路的基本性质，在数字式调制器中必要的精度可通过适当地选择代表信号的字长而获得。4. The first observation is made on the fundamental relationship between the nature of system and the periodicity of its frequency response: a continuous system has an aperiodic frequency response, while a discrete system has a periodic frequency response.从系统性质和它频率响应的周期性之间的基本关系中首先可以看到：连续系统有非周期性的频率响应，而离散系统有周期性的频率响应。5. The main function of the receiver is to extract the input message signal from the degraded version of the transmitted signal coming from the channel.接收器的主要功能是从由信道传输来的退化了的信号中提取出输入消息。 Unit 3 Exercises(1) Translate the following sentences into Chinese.1. A very commonly used method of microwave measurements is based on the study of a standing wave pattern formed along the line because of the interference of incident and reflected waves.一个很常用的微波测量方法是基于对驻波图型的研究，这种驻波是由入射波和反射波之间的干涉而沿着传输线形成的。2. Computations show a reduction of 6dB in the EM field intensity with the distance doubled, and an increase of 3dB in the intensity with the transmitted power doubled. This result provides verification to the algorithm used.计算表明，当距离增大一倍时，电磁场强度减小6分贝；而发射功率增大一倍时，场强则增加3分贝。这一结果验证了所用算法的正确性。3. Like transfer of heat by conduction, convection and radiation, microwave heating can be considered as another mode of heat transfer, in which heat is produced directly at the location of the dielectric losses. 就像通过传导、对流、辐射来传递热量一样，微波加热可以看作热传递的另一种方式，即热量直接产生于发生介电损耗的地方。4. Operation of the radar is based on the measurement of the time it takes for a pulse transmitted from an antenna to get reflected by the object to be detected and to return at the antenna and the receiver.雷达的工作是基于对天线发出的脉冲被所要探测的目标反射，（然后）回到天线和接收机所需时间的测量。5. Other motivations for using CAD in circuit design includes the wish to acquire confidence in a design that was accomplished by other means, and, not least in importance, a sense of curiosity or perhaps a desire to discover the unexpected.在电路设计中使用CAD的其它动机包括：想要验证用别的方法设计出来的电路；满足好奇心或者可能是想发现预想不到的现象。后一个动机并非是最不重要的。（取得信心，并非最不重要，意料之外的事）6. The spacing between the repeating amplifiers is a function of the cable attenuation and the system bandwidth so that the gain provided by these amplifiers compensates for the loss introduced by the cable.中继放大器之间的间距是电缆衰减和系统带宽的函数，以便这些放大器提供的增益补偿电缆引起的损耗。7. When the cut-off frequency is no less than the maximal frequency of the original signal, nor is it greater than the difference between the sampling frequency and the maximal frequency, the original signal may be completely rebuilt.当截止频率不小于原始信号的最高频率，也不大于采样频率和最高频率之差，原始信号可以完整地重建。8. While the politics of the last one hundred years centered around Industrial Age technology, the politics of the future will be based on Information Age concerns oriented towards the storage, protection and exchange of information.尽管近百年来的政治活动是以工业时代的技术为中心的，未来的政治活动将基于信息时代的事物，面向信息的存储、保护和交换。Unit 4 Exercises (1) Translate the following passages into Chinese.1. Communication may be broadly defined as the transfer of information from one point to another. When the information is to be conveyed over any distance a communication system is usually required. Within a communication system the information transfer is frequently achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal. This modulated carrier is then transmitted to the required destination where it is received and the original information signal is obtained by demodulation. Sophisticated techniques have been developed for this process by using electromagnetic carrier waves operating at radio frequencies as well as microwave and millimeter wave frequencies. However, communication may also be achieved by using an electromagnetic carrier that is selected from the optical range of frequencies.通信可以广义地定义为从一处到另一处的信息传递。当要将信息传输到任何距离以外时就需要有一个通信系统。在通信系统内部，信息的传输经常通过将信息叠加或调制到作为信号载体的电磁波上来实现。经调制的载波然后被传送到要求的目的地，在那里被接收，原始信号通过解调被恢复出来。为了实现这一过程，已经利用工作在射频、微波以及毫米波频率上的电磁载波开发了复杂的技术。不过通信也可以用光波频段上的电磁载波来实现。2. Electronic communications is the transfer and movement of data between locations through the use of computers. An electronic communication system includes the equipment needed to support the movement of information, the communication lines and media to carry the information, the computer software and programs to control the flow of information, the personnel to plan, implement, and operate communications, and the management of all these resources. Electronic communications establishes links between people as well as computers.电子通信就是通过使用计算机在不同的地点之间传输数据。一个电子通信系统包括：支持信息流动所需要的设备，承载信息的通信线路和媒介，控制信息流的计算机软件和程序，计划、实施、操作通信系统的人员，以及对所有这些资源的管理。电子通信建立起人和人、计算机和计算机之间的联系。3. First generation communications systems can be characterized by the use of analog transmission techniques, and the use of simple multiplex access techniques such as frequency division multiple access (FDMA). They suffered from a low user capacity, and security problems due to the simple radio interface used. Second generation systems were introduced in the early 1990s, and all use digital technology. This provided an increase in the user capacity of around three times, achieved by compressing the voice waveforms before transmission. Third generation systems are an extension on the complexity of second-generation systems and are to be introduced after the year 2000. The system capacity will be increased to over ten times original first generation systems, achieved by using complex multiplex access techniques such as code division multiplex access (CDMA), or an extension of TDMA, and by improving flexibility of services available.第一代通信系统以模拟传输技术和简单复用技术如频分复用为特征。这些系统用户容量低，而且因为使用简单的无线电接口而存在安全问题。第二代通信系统于20世纪90年代初开始引入，全部使用数字技术。通过在传输前将话音波形压缩使得用户容量提高了三倍。第三代通信系统是对第二代系统在复杂性方面的扩展，预计于2000年以后启用。通过使用复杂的复用技术如CDMA或TDMA的扩展，并提高服务的灵活性使得系统容量比原来的第一代系统提高10倍。4. For each combination of communication (modulation/detection) type, channel fading model, and diversity type, the average bit error rate (BER) and/or symbol error rate (SER) of the system is obtained and represented by an expression in a form that can readily be evaluated. All cases considered correspond to real practical channels, and in many instances the BER and SER expressions obtained can be evaluated numerically on a hand-held calculator.对于通信（调制/检测）类型、信道衰落模型、分集类型的每一种组合，得到系统的平均误码率（BER）和符号错误率（SER），并以容易求值的形式表示。所有考虑的相应于实际信道的情况，以及许多情况下得到的BER和SER表达式均可用手持计算器来计算。5. Modulation is the systematic variation of some attribute of a carrier waveform such as the amplitude, phase, or frequency in accordance with a function of the message signal. It is used in communication systems for matching signal characteristics to channel characteristics, for reducing noise and interference, for simultaneously transmitting several signals over a single channel, and for overcoming some equipment limitations. A considerable portion of this book is devoted to the study of how modulation schemes are deigned to achieve the above tasks. The success of a communication system depends to a large extent on the modulation.调制是载波波形的某些属性，例如幅度、相位和频率，根据消息信号的函数有规则的变化。它用于通信系统以使信号特性匹配信道特性，减少噪声和干扰，在单个信道上同时传输多个信号，并克服某些设备的限制。本书相当大部分内容是研究如何设计调制方案以实现上述任务。一个通信系统的成功很大程度上依赖于调制。Unit 5 Exercises (1) Translate the following passage into Chinese.OFDM consists of a large number of subcarriers equally spaced in a frequency band, each may be digitally modulated by a same scheme such as PSK, QAM, etc., or by different schemes. A serially transmitted sequence is divided into a number of sections, each having N symbols, and the N symbols in each section are used to modulate N carriers for simultaneous transmission. Therefore OFDM is essentially a parallel modulation system. When the number of subcarriers is sufficiently large, the system can resist multipath interference. This is because that, in the time domain, a symbol duration longer than the multipath delay can be chosen, while in the frequency domain, each symbol only occupies a small portion of the channels frequency band. Thus, the effect of multipath fading spreads over many symbols, resulting in slight distortion to many symbols rather than complete destroy of a few symbols. In this way, correct demodulation is not affected so that the signal can be accurately recovered at the receiver. In an OFDM system, the principle of choosing the subcarrier interval is to make the subcarriers mutually orthogonal within the entire symbol period. Thus, even if spectral overlap exists between the subcarriers, the symbols can still be recovered without loss. In order to realize maximum spectral efficiency, the interval between subcarriers is usually chosen to equal the reciprocal of the symbol duration T. Therefore the subcarrier frequencies in the base band are fn = n/T, (n = 0, 1, . , N-1). Denoting the n-th modulating symbol as X(n), the OFDM waveform within a symbol duration can be expressed as:(1)Sampling this waveform at t = T/N yields(2)It is observed from the above expression that x(k) and X(n) form a discrete Fourier transform pair, therefore the baseband OFDM waveform can be generated from the discrete Fourier transform of N modulating symbols. When N=2m where m is an integer, the fast algorithm of IDFT is easy to implement.OFDM由大量在频率上等间隔的子载波构成。每个子载波可用同样的方案，如PSK，QAM等，或者用不同的方案数字调制。将串行传输的符号序列分成许多段，每一段有N个符号，每段的N个符号被用来分别调制N个载波同时发送。因此，OFDM本质上是一个并行调制系统，当载波数足够大时，这种系统具有抗多径干扰的能力。这是因为在时域上符号周期能选取得比多径延迟时间长，而在频域上每个符号只占整个信道带宽的一小部分，因此多径衰落的影响被分散到许多符号上，其结果是许多符号都发生轻度的畸变，而不是使某些符号被完全破坏。这样，不影响正确的解调，信号能在接收器中准确地恢复。在OFDM系统中，选择子载波间隔的原则是使子载波在整个符号周期内相互正交，这样。即使在子载波间存在频谱部分重叠，符号仍能无损失地恢复。为了实现最大的频谱效率，子载波之间的间隔通常选取为符号周期的倒数。因此基带子载波频率为fn = n/T, (n = 0, 1, . , N-1)，第n个调制符号记为X(n)，在一个符号周期内的OFDM波形可表示：(1)在t = T/N 时刻采样这个波形得到：(2)从上面的表示中可以看到，x(k) 和X(n)构成了一对离散傅里叶变换，因此基带OFDM波形可根据N个调制符号的离散傅里叶变换来生成。当N=2m，其中m为整数，IDFT的快速算法很容易实现。Unit 6 Exercises (1) Translate the following sentences into Chinese.1. Communication is the transmission of information from one point to another. This transmission requires the ability to vary signals with time in a manner which is unpredictable to the receiver.通信就是信息从一点传送到另一点。这种传送要求信号随时间发生的变化不能在接收端预测。2. It is true of any communication system that the shape and amplitude of the transmitted signal will be continuously degraded by the introduction of noise, and the attenuation along the transmission path.传输的信号会不断地被噪声的引入和线路上的衰减所损伤，对任何通信系统都是如此。3. Since the very beginning, communications systems have consisted of three major parts, namely, the equipment, the medium, and the protocol. It is still the case today. However, the close link of telecommunications with the computer technology has brought about tremendous changes in communications, from the concepts, to the contents and the methods.从一开始通信系统就由设备、媒介和协议三个要素组成。至今依然如此。然而电信与计算机技术的紧密联系使得通信从概念到内容和手段都发生了重大的变化。4. The availability of such a large collection of system performance curves in a single compilation allows the researcher or system designer to perform trade-off studies among the various communication type/fading channel/diversity combinations so as to determine the optimum choice in the face of his or her available constraints.在一本书中提供如此大量的系统性能曲线，使研究者或系统设计者能在各种通信类型、衰落信道、分集组合之间进行比较研究，从而在他或她所面临的限制之下做出最佳的选择。5. The channel provides the electrical connection between the information source and the user. The channel can have many different forms such as a microwave radio link over free space, a pair of wires, or an optical fiber.信道提供信息源和用户之间的电路联接。信道可以有许多不同的形式，比如自由空间里的微波联接，一对电线，或者一根光纤。6. The degradation of the transmitted signal is a result of signal distortion due to imperfect response of the channel and due to undesirable electrical signals (noise) and interference. Noise and signal distortion are two basic problems of electrical communication.传输信号的退化是信号失真的结果，而这种失真又是由信道的非理想响应及不想要的电信号（噪声）和干扰引起的。噪声和信号畸变是电子通信的两个基本问题。Unit 8 Exercises (1) Translate the following sentences into Chinese.1. Early in the twentieth century, it was found that light could cause atoms to emit electrons and that, when light released an electron from an atom, the energy possessed by the electron very greatly exceeded that which the atom could, according to the electromagnetic wave theory, have received.在二十世纪早期，人们发现光能够使原子放出电子，而且当光从原子中释放一个电子时，电子所包含的能量大大超过由电磁波理论得到的原子所接收的能量。2. Pulse broadening determines the minimum separation between adjacent pulses, which in turn determines the maximum information-carrying capacity of the optical fiber.脉冲的展宽决定了相邻脉冲之间的最小间隔，这一间隔进而又决定了光纤的最大信息容量。3. If one were to transmi