CCSDS近地LDPC译码算法研究

针对CCSDS（空间数据系统咨询委员会）推荐的近地LDPC（低密度奇偶校验）码技术进行了研究,建立了和积译码算法、对数似然和积译码算法、最小和译码算法的数学模型,并对上述译码算法的译码复杂度和译码性能进行了仿真分析.分析结果表明,和积译码算法与对数似然和积译码算法的译码性能距离香农限1.2 dB,最小和译码算法的译码性能距离香农限1.45 dB.因此,提出基于最小和译码算法的改进算法——偏移最小和译码算法与归一化最小和译码算法,并分析了这2种译码算法的译码复杂度,同时进行了大量仿真实验.实验结果表明,当偏移因子β=0.15时,偏移最小和译码算法性能达到最优,译码性能距离香农限1.25 dB;当归一化因子α=0.741 2时,归一化译码算法的译码性能达到最优,译码性能距离香农限1.2 dB.归一化译码算法具有优异的译码性能和合理的复杂度,可以遴选作为CCSDSLDPC的译码算法用于工程实现.此外,还研究了迭代次数对译码性能的影响,结果表明,当迭代次数大于10次时,译码性能提升不再明显,故工程实现时迭代次数应设置为10次.

Research on Near-Earth LDPC Decoding Algorithms for CCSDS

Research is done on LDPC （Low-Density Parity-Check Code） recommendations of CCSDS （Consultative Committee for Space Data Systems） for near-earth applications.Mathematical models are constructed for BP decoding algorithm,LLR_BP decoding algorithm and min_sum decoding algorithm,and simulation and analysis is done on their complexity and decoding performance.The results show,for rate 7/8 LDPC code,the performance of BP decoding and LLR_BP decoding algorithm has a threshold within 1.2 dB of the Shannon limit of the binary-input ad ditive white Gaussian noise channel; the performance of min_sum decoding algorithm has a threshold within 1.45 dB of the Shannon limit.Based on min_sum decoding algorithm,two improved algorithms-offset min_sum decoding algorithm and normalized min sum decoding algorithm are proposed.Decoding complexity of the two decoding algorithms are analyzed and simulated.When the offset factor β=0.15,the offset min_sum decoding algorithm reaches a threshold within 1.25 dB of the Shannon limit.When the normalized factor α=0.741 2,the normalized min_sum decoding algorithm reaches a threshold within 1.2 dB of the Shannon limit.Striking a good balance between decoding performance and complexity,the normalized decoding algorithm is a good candidate for LDPC of CCSDS for engineering implementation.The influence of the number of iterations on decoding performance is also analyzed and the results show that 10 iterations is the best choice for engineering implementation.