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 need to correct the corresponding decoding algorithm according to the specific channel model when decoding. This paper analyzes the decoding method and decoding performance of QC-LDPC codes under the avalanche photodiode (APD) receiver in space optical communication, and proposes to calculate the log-likelihood required for decoding initialization under the APD receiver channel (LLR) method. The simulation results show that the QC-LDPC codes have better decoding performance than the approximate Webb-Gaussian model under the condition of no additional complexity after the decoding in the APD receiver channel is corrected Asymmetric Gaussian model. When the BER is 10-6, the net coding gain of more than 1dB is compared with that of the asymmetric Gaussian model.