软信息辅助硬判决译码在自由空间光通信中的应用

A Soft-Aided Hard-Decision Decoder for Free-Space Optical Communications

由于在性能和复杂度之间的良好折中,软信息辅助硬判决译码近年来受到了光通信领域的高度关注,其中包括了软信息辅助比特标记(Soft-Aided Bit-Marking,SABM)算法.为了易于硬件实现,本文基于阶梯码(Staircase Code,SCC)提出了一种改进型SABM算法(improved SABM,iSABM),称为iSABM-SCC.iSABM-SCC利用信道软信息,通过两个可信度阈值将硬判决输出比特标记为三种可信度等级,用以辅助硬判决译码识别译码错误和扩展纠错能力,达到提升阶梯码性能的目的.在受大气湍流影响的自由空间光通信中的仿真表明,iSABM-SCC性能显著优于标准SCC和RS码.以强湍流信道为例,码率为0.75的iSABM-SCC在4-PAM调制下较标准SCC产生的性能增益可达4.37 dB,在8-PAM调制下较RS码产生的性能增益可达11.06 dB.

Due to a good trade-off between performance and complexity,a new class of decoding schemes,called soft-aided hard-decision(SA-HD)decoders,has become particularly interesting to optical communication fields in recent years.Soft-aided bit-marking(SABM)algorithm is one of the popular ones.To be friendly for hardware implementation,this paper proposes an improved SABM(iSABM)algorithm for staircase codes(SCCs),which we call iSABM-SCC.With the help of channel soft information,iSABM-SCC marks bits into three types according to their reliabilities using two thresholds.The marked information is then used to assist the staircase decoder to prevent miscorrections and to extend the error-correcting capability,thus improving the performance of SCCs.The simulation results for free-space optical communications show that the proposed iSABM-SCC scheme achieves higher performance gains over standard SCC(S-SCC)and RS code in turbulence channels.For instance,iSABM-SCC with code rate of 0.75 has been shown to yield up to 4.37 dB performance gain when compared to S-SCC for 4-PAM and up to 11.06 dB performance gain when compared to RS code for 8-PAM in a strong turbulence channel.