低密度校验码在瑞利衰落信道中的性能分析

Performance of Low-Density Parity-Check Codes over Rayleigh Fading Channels

低密度校验 (L DPC)码具有编码增益高、译码速度快、可并行译码等特点 ,是当前编码界的一个研究热点 ,但是目前已有的研究成果都集中在高斯信道上 .该文分析和讨论了 L DPC码在瑞利衰落信道下的性能 ,应用联合界技术推导了一个规则码的性能限 ,并给出了仿真结果 ,且发现 L DPC码在瑞利衰落信道下也具有非常好的性能 .

This paper investigates the performance and design of Low-density parity-check (LDPC) codes with coherent BPSK signaling on the Rayleigh fading channel. First, the fully interleaved case is considered in both situations of perfect channel state information (CSI) and non-channel state information (NCSI). LDPC codes perform well in the CSI channels, and when decoded with the average fading amplitude as an estimate of the NCSI channel, LDPC codes are not degraded too much compared to the CSI channel. Second, the correlated fading channel is considered. We find that LDPC codes are not severely sensitive to the fading speed of correlated channels and in this sense LDPC codes outperform turbo codes. In the simulation, for a BER of 10 -4 , LDPC codes offer coding gains of 2.2 dB at fading speed BT s =0.01 and 8.2 dB at fading speed BT s =0.001 compared to turbo codes, where the code rate R=1/3 and blocklength N=1260 . Finally, we present and demonstrate an upper bound of performance of regular LDPC codes by using the union bound technique in combination with the weight spectrum function of regular codes. The bound results give indications of achievable performance as well as the effects of block length and channels. From our results, we believe that LDPC codes are powerful in Rayleigh fading channels and might be potential candidates for the mobile communication systems.