1. Lecture 6 Communication System 第六课 通信系统

2. Exercises Please read the text and complete the exercises in 30 minutes. 1.Answer the following questions according to the text. What basic elements does the communication system involve? ——It involves information source, transmitter (encoder, modulator), channel (transmission medium), receiver (demodulator, decoder), and information sink. Try to take some examples about the application of communication in our daily life. ——Telephones, radios, televisions, computers, etc.

3. Please describe the functions of modulator and demodulator in a communication system. ——Modulator is designed to impress the information signal onto the wave form to be transmitted which produces a varying signal at its output proportional in some way to the signal appearing across its input terminal, while the demodulator performs the inverse operation of the modulator. Take some examples about the transmission medium. ——The ionosphere, the troposphere, free space, cable, fiber optical cable, etc.

4. 2.Translate the following phrases and expressions. 无线通信系统 ——wireless communication system the conveying or transmission of information from one point to another —— 从一地到另一地的信息传输 vary the amplitude or frequency in direct proportion to the voltage input —— 使幅度或频率随输入电压成比例地变化

5. to optimize the error-free detection —— 使无差错检测最佳化 调制解调器 ——modem 计算机终端设备 ——computer terminals

6. 3.Choose the best answer. The _____ chooses the best form for the signal in order to optimize its detection at the output. A. decoder B. encoder C. coding The radios and televisions, the computer terminals with access to the Internet are all capable of _____ rapid communications from every corner of the globe. A. providing B. provide C. provision The _____ of the signals is determined by several factors. A. intensive B. intense C. intensity B C A

7. The decoder performs the inverse operation to make the best decision that a given message was indeed sent. Here the word “inverse” can be replaced by ______. A. contrary B. opposition C. versatile Scientists have found ______ good methods for communications by using new technologies. A. variation B. vary C. various The distortion is caused by the channel ______. A. perfection B. imperfection C. imperfect A C B

8. 4.Judge true or false according to the text. Not every communication system makes use of a transmission medium of some kind. ( ) The decoder makes the best decision that a given message was indeed sent according to the available signals. ( ) The modulator produces a constant signal which is proportional in some way to the signal appearing across its output terminals. ( ) The roles of the encoder and the demodulator are almost the same in that both prepare the signal for more efficient transmission. ( ) A transmission line is one of the simplest transmission medium. ( ) F F T T T

9. 5.Match Column A with Column B. Column A (1)transmitter (2) receiver (3) noise (4) information source (5) channel Column B (a)an equipment which converts the message into a signal suitable for transmission over the channel (b) message which may written words, or spoken words, or some form of data (c) the medium used to transmit the signal from the transmitter to the receiver (d) an equipment which can change the received signal back into a message and passes the message onto its destination (e) the unwanted which may cause distortions of sound in a telephone, or errors in telegraph message or data

10. 6.Translate the following sentences into English. 信号在传输过程中不可避免地会产生衰减与失真。 ——Attenuation and distortion are introduced inevitably in the process of information transmission. 通信系统主要由发射机、接收机和信道三部分组成 ——Communication system consists of three main parts: transmitter, receiver and channel. 调制器使正弦信号的振幅、频率和相位与输入电压 成正比。 —— Modulator varies the amplitude, frequency and phase of a sinusoidal in direct proportion to the voltage input.

11. Key words and Technical terms communication system 通信系统 convey 运输，输送 transmission 发射，传送，传输 ——information transmission precise 精确的，准确的 multitude of 众多的 facet 方面 computer terminals 计算机终端 access to 接入 high seas 公海

12. wireless telephone 无线电话 sensor 传感器 diagram 框图 —— diagram of the system signal source 信源 signal sink 信宿 transmitter 发送设备 receiver 接收设备 channel 信道

13. transmission medium 传输介质 encoder 编码器 optimize 使最优化 detection 检测 ——error-free detection decoder 解码器 inverse 倒转的，反转的 ——inverse operation make the best decision 最佳判断 description 描述 ——mathematical description

14. motive 动机，目的；发动的，运动的 coding system 编码系统 modulator 调制器 demodulator 解调器 sinus/sinusoidal 正弦波 error-free detection 无差错检测 ——error-free reception modem 调制解调器 crucial 至关重要的 ——crucial link

15. ionosphere 电离层 troposphere 对流层 free space 自由空间 transmission line 传输线 attenuation 衰减 distortion 失真 noise signal 噪声信号 interfere with 干扰 the message-bearing signal 有用信号

16. Expressions be capable of … 能够 … ——Telephones, radios, televisions, computer terminals with access to the Internet, and our newspapers are all capable of providing rapid communications from every corner of the world. keeps…in touch with… 与 … 保持联系 ——Communication through a wireless telephone keeps a car driver in touch with the office or home miles away.

17. make use of… 使用 … ——Not every communication system makes use of all the elements. in order to … 为了 … ——The encoder chooses the best form for the signal in order to optimize its detection at the output. rely on 依靠 ——The design of the encoder and decoder must rely on a detailed mathematical description of information transmission. be proportional to … 与 … 成比例 ——The modulator produces a varying signal at its output which is proportional in some way to the signal appearing across its input terminals.

18. Core Sentences Translation In the most fundamental sense, “communication” means the conveying or transmission of information from one point to another through a succession of processes. —— 从根本上讲，通信指从一地到另一地的信息连续 传输。 Communication provides the senses of ships on the high seas, aircraft in flight, and rockets and satellites in space. —— 通信可以为公海上的船只、航行中的飞机及太空 中的火箭和卫星提供感测信息。

19. The encoder chooses the best form for the signal in order to optimize its detection at the output. —— 编码器选择最佳的信号（编码）形式以在输出端 优化检测。 The decoder performs the inverse operation to make the best decision, based on the available signals. —— 解码器完成相反的操作，它根据提供的信号作出 最佳判决。 While the subject of coding often carries with it an air of secrecy, a more important motive in many modern coding systems is the improved efficiency in conveying information. —— 尽管编码的内容通常是加密的，而在许多现代编 码系统中更重要的目的是提高传输信息的效率。

20. A sinusoidal modulator may vary the amplitude, frequency, or phase of a sinusoidal in direct proportion to the voltage input. —— 正弦调制器可使正弦波的幅度、频率、相位随 输入电压成比例地变化。 The process of coding is designed to optimize the error-free detection that a given message is being sent, whereas the process of modulation is designed to impress the information signal onto the waveform to be transmitted. —— 编码过程是为了使无差错检测最佳化从而发送 给定信息，而调制过程是将消息加载到被发送的 （信号）波形上去。

21. In any case, attenuation and distortion, as well as noise signals generated in the media and the transmitting and receiving equipment, are introduced. —— 不管怎样，系统中都会产生衰减、失真以及由介 质、发送和接收设备产生的噪声信号。 For our purpose, noise signals are any electrical signals (voltages or currents) which interfere with the error- free reception of the message-bearing signal. —— 在我们的实际应用中，噪声信号通常是电信号（ 电压、电流），它会干扰有用信号的无差错接收。