激光誘导荧光检测系统设计外文翻译.docVIP

一、外 文 资 料 Analog and Digital Types of Communication analysis Typically, 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 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 communication 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. Modulator - 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 longer 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 symbols 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 reconstructed message signal is finally delivered to the user of information at the destination. From this description it is apparent that the design o