光通信中基于BCJR的BCH译码算法研究

首先从理论上分析了硬判决译码算法和软判决译码算法的性能然后对BCH(Bose,Ray-Chaudhuri,Hocquenghem)码的网格结构以及BCJR(Bahl,Cocke,Jelinek and Raviv)算法进行了详细地分析及推导。实验结果表明,在光信道环境中,在误比特率为10-5时,当仅提高最小汉明距离码率相同或者仅减小码率最小汉明距离相同时,BCJR算法相对于硬判决译码算法的编码增益分别在之前的编码增益基础上又增加了0.15dB和0.25dB。因此设计级联码方案时,应尽可能选择纠错能力较大的内码。此外也可以采用适当增加内码的冗余度相应减小外码的冗余度的方法,在获得更高的编码增益的同时保证整个系统的带宽利用率不变。

Research on BCJR-based BCH decoding algorithm in optical communication

In this paper,the performances of the hard-decision and the soft-decision decoding algorithms for BCH(Bose,Ray-Chaudhuri,Hocquenghem) codes are analyzed in theory firstly.Then the trellis structure of BCH codes is introduced and the Bahl,Cocke,Jelinek and Raviv(BCJR) algorithm based on trellis is deduced.The experimental results show that in optical channel,as the bit-error-ratio reaches 10-5,the coding gain difference between the BCJR algorithm and the hard-decision algorithm is increased by 0.15 dB when only increasing the minimum Hamming distance and by 0.25 dB when only reducing the code rate.Therefore,for a concatenated code design in optical communication,the inner code with larger error correcting capability should be selected as possible.In addition,in order to obtain the higher coding gain and ensure the system bandwidth utilization rate unchanged,the method appropriately increasing the redundancy of inner code and decreasing the redundancy of outer code correspondingly is suggested.