QC-LDPC编码OFDM系统的码优化及迭代译码

Code Optimization and Iterative Decoding of QC-LDPC Coded OFDM System

为解决在多径环境下,部分正交频分复用(OFDM)子载波可能遭受深衰落而导致系统性能严重下降的问题,该文提出了一种准循环低密度奇偶校验(QC-LDPC)编码的OFDM系统。在该系统中,编码后的校验比特被映射到更高阶的星座图中,并在迭代译码中采用Group Shuf-fled消息传递调度。根据码字比特映射方式的不同,利用基于Group Shuffled置信传播的密度演进的高斯近似对QC-LDPC码进行了优化。加性高斯白噪声和Rayleigh衰落信道下的仿真结果表明,该系统具有更好的纠错性能和更快的译码收敛速度。

In the multi-paths environment, since the performance of orthogonal frequency division multiplexing （OFDM） system may be severely degraded by the sub-carriers in deep fading, powerful error-correcting codes have to be applied to OFDM. This paper presents a novel quasi-cyclic low density parity check （QC-LDPC） coded OFDM system. In this system, the redundant bits of code- word are mapped to higher-order constellation, and a group shuffled message passing scheduling is used in the iterative decoding. According to the mapping scheme, the QC-LDPC code is optimized by density evolution based on group shuffled message passing with Gaussian approximation. Simulation results show that the proposed system can achieve better error rate performance and faster decoding convergence than conventional approaches on both additive white Gaussian noise （AWGN） and Rayleigh fading channels.