激光诱导荧光检测系统设计外文翻译

1、一、外 文 资 料Analog and Digital Types of Communication analysisTypically, in the design of a communication system the information source, communication channel, and information sink (end user) are all specified. The challenge is to design the transmitter and the receiver with the following guidelines in

2、 mind: Encode/modulate the message signal generated by the source of information, transmit it over the channel, and produce an “estimate” of it at the receiver output that satisfies the requirements of the end user. Do all of this at an affordable cost. Consider first the case of a digital communica

3、tion system represented by the block diagram of Figure 9, the rationale for which is rooted in information theory. The functional blocks of the transmitter and the receiver, starting from the far end of the channel, are paired as following: Source encoder - decoder. Channel encoder-decoder. Modulato

4、r - demodulator.The source encoder removes redundant information from the message signal and is responsible for the efficient use of the channel. The resulting sequence of symbols is called the source code word. The data stream is processed next by the channel code word. The channel code word is lon

5、ger than the source code word by virtue of the controlled redundancy built into its construction. Finally, the modulator represents each symbol of the channel code word by a corresponding analog symbol, appropriately selected from a finite set of possible analog symbols. The sequence of analog symbo

6、ls produced by the modulator is called a waveform, which is suitable for transmission over the channel. At the receiver, the channel output (received signal) is processed in reverse order to that in the transmitter, thereby reconstructing a recognizable version of the original message signal. The re

7、constructed message signal is finally delivered to the user of information at the destination. From this description it is apparent that the design of a digital communication system is rather complex in conceptual terms but easy to build. Moreover, the system is robust, offering greater tolerance of

8、 physical effects than its analog counterpart. In contrast, the design of an analog communication system is simple in conceptual terms but difficult to build because of stringent requirements on linearity and system adjustment. For example, voice communication requires nonlinear distortion products

9、at least 40dB below the wanted message signal. In signal-processing terms, the transmitter consists of a modulator and the receiver consists of a demodulator. The conceptual simplicity of analog communications is due to the analog modulation techniques, exemplified by their wide use in radio and tel

10、evision, make relatively superficial changes to the message signal in order to prepare it for transmission over the channel. More specifically, there is no significant effort made by the system designer to tailor the waveform of transmitted signal to suit the channel at any deeper level. On the othe

11、r hand, digital communication theory endeavors to find a finite set of waveforms that are closely matched to the characteristics of the channel and which are therefore more tolerant of channel impairments. In so doing, reliable communication is established over the channel. FIGURE 9 Block diagram of

12、 digital communication system. 二、译 文模拟通信与数字通信分析一般来讲，设计通信系统时，信息源、信道、信宿均已确定。我们的目标是按以下原则设计发射器、接收器： 对信源产生的信息进行编码、调制处理，并通过信道传输，在接收端产生其估计。 考虑经济开销。首先考虑数字通信系统。它是以信息理论为理论基础。数字通信系统包含以下模块： 信源编码解码器。 信道编码解码器。调制解调器。信源编码用于去除原始消息的冗余信息，体现有效性。经其处理之后的符号序列，称为信源码字。该数据流接着送入信道，产生信道码字。比起信源码字，信道码字更长。以为其引入了受控的冗余信息。最后，信道码字经由调制器调制，产生适合信道传输的波形。在接受端，信道输出（接收信号）以与发射端相反的次序被处理。故可重新产生原始消息的副本。该再生信号最终送与用户。从以上描述可见，数字通信系统设计概念复杂，却易于构建。而且，系统具有鲁棒性。与模拟系统相比，数字系统抗干扰能力更强。 对比而言，模拟通信系统设计概念简单，却难于构建。例如，音频通信在40dB以下产生