低重量种子序列对Turbo码低码重分布的影响

Influence of Low-weight Seed Sequences on Low-Weight Distributions of Turbo Codes

用概率的方法,分析了不同重量的种子序列经过交织后仍为种子序列的概率,讨论了低重量的种子自结尾输入序列对Turbo码的低码重分布的影响.通过分析讨论指出,如果Turbo码生成多项式中的反馈多项式的周期较长,重2输入序列产生的码字重量就会较大,而其他重量的种子输入序列,尤其是重量为3,4的种子输入序列,产生的码字重量就很有可能低于重2输入序列产生的码字重量.交织器的长度越短,出现这种情况的概率就越大.

Using the probaility method,the probabilities of a seed sequence is still a seed sequence after interleaving are calculated.The influence of the low-weight seed sequences on the low weight distributions of Turbo codes is discussed.The results show that the longer the period of the feedback polynomial of the generating matrix is, the heavier the weight of the codewords caused by the weight-2 input sequences is,and therefore the weights of the codewords caused by other kinds of input sequences,such as weight - 3 or weight - 4 seed sequences,maybe exceed that by the weight - 2 input sequences.The shorter the period,the more probably this case happens.