基于EXIT图的Turbo均衡LDPC码性能分析及优化研究

EXIT图是用来分析级联系统中外信息迭代交换的重要工具,本文将Brink的基于EXIT图的优化MIMO信道LDPC码的思想推广到用于Turbo均衡的LDPC码性能分析及码结构设计优化中。文章首先给出了基于互信息的接收机具体分析模型,接着分别讨论了接收机分析模型中两个单元的EXIT曲线:线性MMSE均衡器和VND(variable node decoder)的联合EXIT曲线,CND(check node variable)的EXIT曲线的详细计算步骤。进一步以获得的EXIT曲线为基础,提出了用于Tur- bo均衡的LDPC码的码结构优化算法,EQVAC-EXIT(EQVAC:equalizer VND and CND)算法,算法能够自动地进行码集噪声门限值计算及优化次数分布对的搜索。最后的数值仿真结果表明,(3,6)正则码及优化得到的非正则码的噪声门限值距离Narayanan的结果仅相差0．03dB左右,优化得到的边的次数分布及节点的次数分布与Narayanan的结果相比也很接近。

Performance Analysis and Optimization of LDPC Codes for Turbo Equalization Based on EXIT Chart

The exchange of extrinsic information for the concatenated systems could be analyzed by EXIT (EXtrinsic Information Transfer) charts.Optimization of LDPC cedes based on (EXIT) chart for MIMO channel is recently proposed by Brink.This paper ex- tended Brink's idea to the optimization of LDPC codes for MMSE turbo equalization.The receiver was partitioned into two blocks,one is the equalizer and VND (variable node decoder),the other is CND (check node decoder).The algorithm to obtain the EXIT curves of the two blocks was given first.Furthermore,this paper proposed an algorithm based on the obtaining EXIT curves to optimize the degree distribution of LDPC codes and calculate the corresponding noise threshold,EQVAC-EXIT algorithm.Simulation results shows good per- formance for the proposed algorithm.