Exercises

I. 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.

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.

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 1990's, 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.

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.

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.

Ⅱ. Choose the word or phrase that is closest in meaning to the underlined part.

1. The receiving device would have the wrong time that had been agreed in the protocol for sending/receiving data, so some bytes could become corrupted by losing bits.

A. that had been consistent with the protocol of data exchange

B. that had been the same as the protocol for sending/receiving data

C. that had been in agreement with the protocol of data transmission

D. that had been defined in the data transmission protocol

2. Synchronous transmission uses no start and stop bits but instead synchronizes transmission speeds at both the receiving and sending end of the transmission using clock signals built into each component.

A. using synchronization signals to build each component

B. using timing pulses that are incorporated in each component

C. using timing signals in order to build each component

D. using clocks that can build signal components

3. Information theory, however, does not involve message importance or meaning, as these are matters of the quality of data rather than the quantity of data, the latter of which is determined solely by probabilities.

A. which is the later one of the determined probabilities

B. the later one being probably deterministic

C. in which the later one is deterministic rather than probabilistic

D. the data quantity being determined by probabilities only

4. Any small deformations in the height or width of the pulses are irrelevant since it is only necessary to know whether the pulse is present or absent in order to retrieve the original message.

A. to reform the original information

B. to recover the original signal

C. to re-obtain the original information

D. to represent the original signal

5. Consequently, electronic equipment is constantly subjected to unwanted sources of energy and is constantly producing energy that adjacent equipment is not designed to accept.

A. continually making unaccepted interference to adjacent equipment

B. continuously causing neighboring equipment not to accept expected energy

C. constantly producing energy that is acceptable only to neighboring equipment

D. ceaselessly generating energy that is considered acceptable in the design of adjacent equipment

6. Earlier we introduced the concept that the identity of an amplitude modulated message signal may under certain circumstances be communicated by transmitting regular samples of the message, rather than the continuous signal.

A. may transmit samples that are regular in communications under some conditions

B. may be in the circumstances that regular message samples are communicated

C. may be conveyed by sending signal sampled at regular intervals under some conditions

D. may communicate with certain customers by sending regular samples of the message

7. For each of the building blocks of the RF transceiver, which has been broken into separate chapters, a list of essential reference publications also guarantees depth and academic value of the research achievements presented.

A. each of the basic components of the RF transceiver

B. each of the groups that are built into the RF transceiver

C. the individual elements in the RF transceiver

D. each of the buildings that blocks the RF transceiver

8. We are to develop a code such that fewer bits are assigned to code words representing gray levels having higher probability of occurrence, and vice versa.

A. in other words, gray levels that more frequently occur are given more bits

B. and more bits are used for gray levels of lower probability of occurrence

C. otherwise, more bits are needed in the similar case

D. in other words, more probable gray levels require shorter code words