多元LDPC-CPM系统中动态迭代停止算法

针对正反馈存在于短帧多元低密度奇偶校验码(low density parity check,LDPC)与高阶连续相位调制(continuous phase modulation,CPM)迭代系统中的问题,提出一种在低信噪比采用加权联合平均外信息交换、在中高信噪比采用加权外信息交换的外信息处理方式。该方式对解调器与译码器之间传递的外信息进行相应处理,可以有效控制波动过大的位概率。同时将交叉熵(cross entropy,CE)和辅助硬判决(hard decision aided,HDA)两种迭代停止准则与加权外信息处理方式结合进行动态迭代译码。理论分析和仿真结果表明,对外信息交换进行加权操作并联合动态迭代停止算法能够在有效减少正反馈的同时使迭代的收敛性得到优化,同时迭代停止算法可减少平均迭代次数,提高系统的实时性。     

Construction of time-frequency codes based on protograph LDPC codes in OFDM communication systems

This paper proposes a scheme to construct timefrequency codes based on protograph low density parity check (LDPC) codes in orthogonal frequency division multiplexing (OFDM) communication systems.This approach synthesizes two techniques:protograph LDPC codes and OFDM.One symbol of encoded information by protograph LDPC codes corresponds to one subcarrier,namely the length of encoded information equals to the number of subcarriers.The design of good protograph LDPC codes with short lengths is given,and the proposed protograph LDPC codes can be of fast encoding,which can reduce the encoding complexity and simplify encoder hardware implementation.The proposed approach provides a higher coding gain in the Rayleigh fading channel.The simulation results in the Rayleigh fading channel show that the bit error rate(BER) performance of the proposed time-frequency codes is as good as random LDPC-OFDM codes and is better than Tanner LDPC-OFDM codes under the condition of different fading coefficients.