高阶调制系统下LDPC码优化设计

为了提高编码调制系统的整体编码增益,提出一种高阶调制系统下LDPC码的度分布优化方法.根据高阶调制符号中不同比特的误比特特性,将调制符号所经历信道建模为一组对称二进制输入加性高斯信道.在此基础上,推导了高阶调制系统下LDPC码高斯近似密度进化分析方法,并得到译码收敛条件.结合度分布约束关系及译码收敛条件,提出高阶调制系统下LDPC码的度分布优化问题及差分进化实现方法.仿真结果表明,设计的LDPC码在高阶调制系统中的渐进性能和误码性能优于基于比特优化映射的编码调制方案.

Optimized LDPC Codes for high-order modulation systems

Abstract:In order to improve the coding gain of coded modulation systems, a method to optimize the degree distribution of the LDPC codes in high order modulation system is proposed. As the error rate performance of the bits in a QAM symbol is different, a QAM symbol can be modeled as a series of symmetric binary-input additive white Gaussian noise sub-channels. Based on this model, the Gaussian approximate density evolution algorithm for LDPC coded modulation system is deduced. Combining the degree distribution constraints and decoding convergence conditions, the degree distribution optimization problem and its differential evolution realization of the LDPC code in the high order modulation system is presented. The simulation results show that both asymptotic properties and BER performance of the proposed method are superior to the selective bit mapping scheme.