通信与电子信息工程专业英语第二单元TEXTAB.pptVIP

Unit 2Modulation Technology;Modulation Technology 调制技术 ;原文：Formula (2.1) introduced the basic function of a sine wave which already indicates the three basic modulation schemes (typically通常, the cosine 余弦function is used for explanation说明): 译文：公式（2.1）引入了一个基本的正弦函数，它可以表示三种基本调制方案（通常用余弦函数来说明）： ;Unit 2;原文：Digital 数字modulation调制 is required if digital data has to be transmitted over a medium that only allows for analog模拟 transmission传输. 译文：如果数字信号必须在只允许模拟信号传输的媒介中传输，则要求进行数字调制。 ;原文：One example for wired networks有线网络 is the old analog telephone system —to connect a computer to this system a modem调制解调器 is needed .The modem then performs the translation of digital data into analog signals vice versa. 译文：模拟电话系统是有线网络的一个例子，它需要用一个调制解调器将计算机与系统相连。调制解调器完成调制解调模数转换的任务。数字传输在有线局域网或计算机内部是很有用的。 ;原文：Apart from the translation of digital data into analog signals, wireless transmission无线传输 requires an additional modulation, an analog modulation that shifts转变 the center frequency of the base-band signal generated产生 by the digital modulation up to the radio carrier无线电载波. 译文：除了数模转换外，无线传输还需要一个附加的模拟调制，将普通基带信号的中心频率通过数字调制提高形成无线电载波。;原文：For example digital modulation translates a 1 Mbps bit-steam into a base-band signal with a bandwidth of 1MHz.There are several reasons why this base-band signal cannot be directly transmitted in a wireless system无线系统: 译文：例如，通过数字调制，将一个1Mbps比特流转换成1MHz带宽的基带信号。基带信号之所有以不能直接在无线系统中传输有如下几个原因： ;原文：Digital transmission数字传输 is used, for example, in wired local area networks or within a computer. In wireless networks, however, digital transmission cannot be used. Here, the binary bit-steam has to be translated into an analog signal first. 译文：然而，在无线网络中，二进制比特流首先必须被转换成模拟信号，因此，不一定必须用到数字传输。 ;原文：The three basic methods for this translation are amplitude shift keying 幅移键控(ASK), frequency shift keying 频移键控(FSK), and phase shift keying 相移键控(PSK). These are discussed in more detail in the following sections部分. 译文：三种基本的数字调制是幅移键控（ASK）、频移键控（FSK）和相移键控（PSK）。下面我们要分别详细讨论。 ;原文：Apart from the t