在通信系统中，信源编码器要尽可能压缩信源冗余度，提高编码效率。但是信源编码在实际信道中传输时，要受到噪声和衰减的影响，就会出现差错。因此信源码还必须经信道编码器再编码，然后再经信道传输至信道译码器，检出和纠正出现的差错，以提高信道传输的可靠性，这就是信道编码的目的。-In the communication system, source encoder to compress as much as possible source redundancy, improve coding efficiency. However, the actual source code in the transmission channel, subject to noise and attenuation, there will be errors. Therefore, the letter also must be approved source channel encoder and then encoded and then transmitted through the channel to the channel decoder, error detection and correction appears to improve the reliability of transmission channel, which is the purpose of channel coding.