激光誘導(dǎo)熒光檢測系統(tǒng)設(shè)計外文翻譯

1、一、外 文 資 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、譯 文模擬通信與數(shù)字通信分析一般來講，設(shè)計通信系統(tǒng)時，信息源、信道、信宿均已確定。我們的目標(biāo)是按以下原則設(shè)計發(fā)射器、接收器： 對信源產(chǎn)生的信息進行編碼、調(diào)制處理，并通過信道傳輸，在接收端產(chǎn)生其估計。 考慮經(jīng)濟開銷。首先考慮數(shù)字通信系統(tǒng)。它是以信息理論為理論基礎(chǔ)。數(shù)字通信系統(tǒng)包含以下模塊： 信源編碼解碼器。 信道編碼解碼器。調(diào)制解調(diào)器。信源編碼用于去除原始消息的冗余信息，體現(xiàn)有效性。經(jīng)其處理之后的符號序列，稱為信源碼字。該數(shù)據(jù)流接著送入信道，產(chǎn)生信道碼字。比起信源碼字，信道碼字更長。以為其引入了受控的冗余信息。最后，信道碼字經(jīng)由調(diào)制器調(diào)制，產(chǎn)生適合信道傳輸?shù)牟ㄐ巍Ｔ诮邮芏?，信道輸出（接收信號）以與發(fā)射端相反的次序被處理。故可重新產(chǎn)生原始消息的副本。該再生信號最終送與用戶。從以上描述可見，數(shù)字通信系統(tǒng)設(shè)計概念復(fù)雜，卻易于構(gòu)建。而且，系統(tǒng)具有魯棒性。與模擬系統(tǒng)相比，數(shù)字系統(tǒng)抗干擾能力更強。 對比而言，模擬通信系統(tǒng)設(shè)計概念簡單，卻難于構(gòu)建。例如，音頻通信在40dB以下產(chǎn)生