LDPC编码MC-LDS系统联合因子图的改进PEG设计

作为非正交多址（Non-orthogonal Multiple Access，NOMA）技术之一，基于稀疏因子图的多载波低密度序列（Multi-carrier Low-density Signature,MC-LDS）技术由于其译码复杂度较低，可以与同样基于稀疏因子图的低密度奇偶校验码（Low Density Parity Check Code，LDPC）同时使用。MC-LDS技术的检测算法和LDPC 的译码算法都是基于稀疏因子图上的消息传递算法（Message Passing Algorithm，MPA），但现有研究中，对于MC-LDS和LDPC稀疏因子图的设计一般独立进行，得到的结果往往不是最优的。为此，提出一种将LDPC与MC-LDS稀疏因子图进行联合分析设计的方法，采用改进的渐进边增长(Progressive Edge Growth，PEG)方法，消除了MC-LDS与LDPC联合因子图中各自的因子图之间互相耦合导致的短环，构建了性能良好的联合稀疏因子图。仿真结果表明，对于不同的LDPC码长，所提方案获得了0.5~0.6 dB的性能增益。

Improved PEG Design of Joint Factor Graph for LDPC Coded MC-LDS Systems

As one of the non-orthogonal multiple access(NOMA) technologies,the multi-carrier low-density signature(MC-LDS) technology based on the sparse factor graph can be used simultaneously with low density parity check(LDPC) code since both of them are based on the sparse factor graph.The detection algorithm of MC-LDS technology and the decoding algorithm of LDPC are both based on the message passing algorithm(MPA) on the sparse factor graph.However,in existing researches,MC-LDS and LDPC sparse factor graphs are generally designed independently.The results obtained are often not optimal.Therefore,a method for joint analysis and design of LDPC and MC-LDS sparse factor graphs is proposed.The improved progressive edge growth(PEG) method is used to eliminate the short loop caused by mutual coupling between the factor graphs of LDPC and MC-LDS.Therefore,a joint sparse factor graph with good performance is constructed.The simulation results show that the proposed scheme obtains 0.5~0.6 dB bit error rate gain for LDPC codes with different length.