基于LDPC/Turbo双模译码器的自适应迭代译码算法研究

针对现有WIMAX标准中LDPC/Turbo双模译码器设计在精确计算时未充分考虑迭代次数的问题，提出了一种适用于LDPC和Turbo码的自适应迭代译码算法，可灵活应用于由FPGA技术实现的双模译码器.该算法通过跟踪中间消息计算错误概率，根据多条件判定精确计算迭代次数，从而实现译码算法与错误概率变化特征的自适应性；通过改进的预判决机制减少平均迭代次数.利用Matlab搭建WIMAX系统测试链路，对TDMP多种算法的误码性能与迭代次数的关系进行测试，实现了12个SISO处理单元并行的LDPC/Turbo双模译码器.结果表明，所设计的译码器减少了算法中冗余的迭代过程，并且完全满足该标准下最大码长的要求.

Research on adaptive iterative decoding algorithm based on LDPC/Turbo dual-mode decoder

In view of the shortcoming that the design of LDPC/Turbo dual-mode decoder does not fully consider the precise calculation of iteration number, we propose a adaptive iterative decoding algorithm which is suitable for LDPC and Turbo codes. The algorithm is used to calculate the error probability by tracking the middle messages, and to calculate the number of iterations according to multi-conditions, thus we can achieve the self-adaptability of the variation of the decoding algorithm according to the error probability. We reduce the average number of iterations by applying an improved predecision mechanism, and build the test link of WIMAX system on Matlab platform to test the relationship between the BER performance of the multi-algorithms and iteration number, and implement the LDPC/Turbo dual-mode decoder with 12 SISOs parallel processing units. The result shows that the design of the decoder fully satisfies the requirement of the maximum code length under the standard, and can reduce the redundant iterative process.