空间光通信APD接收机下LDPC码译码方法及性能分析

Decoding technology and performance analysis of LDPC code over APD receiver for space optical communication

准循环-低密度奇偶校验(QC-LDPC)码具有优异的性能,但在译码时需根据具体的信道模型修正对应的译码算法。本文分析了QC-LDPC码在空间光通信中的雪崩光电二极管(APD)接收机下的译码方法及译码性能,提出了在APD接收机信道下计算译码初始化所需的对数似然比(LLR)的方法。仿真结果表明,对APD接收机信道下的译码进行修正后,基本上不增加额外复杂度情况下,QC-LDPC码在精确的韦伯-高斯(Webb-Gaussian)模型下译码性能优于近似的非对称高斯模型;在信道比较理想的条件下,误码率(BER)为10-6时,韦伯-高斯模型与非对称高斯模型译码性能相比有1dB以上的净编码增益。

Quasi-cyclic low-density parity-check （QC-LDPC） codes have excellent performance, but in order to obtain the optimal performance on a specific channel, the decoding method needs to be modified to adapt to the corresponding channel model. In this paper, we apply QC-LDPC codes into the channel based on avalanche photodiode （APD） receiver in the space optical communication systerru The main work is to analyze the error performance and modify the belief propagation （BP） iterative decoding algorithm that uses probability density function （PDF） of the output sequences in the multiplicative noise channel mod- el. We introduce a new method to compute the logqikelihood ratio （LLR） initialization for the LLR-BP decoding in the APD receiver channel. The simulation results show that the adaptation of QC-LDPC decoding on the accurate Webb-Gaussian model has better performance than that on approximate asymmetric Gaussian model, and almost no additional hardware complexity is increased. Moreover, the former can bring more than 1 dB net coding gain compared with the latter at the hit error rate （BER） of 10-6 under ideal channel conditions.