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从研究APD光电检测接收机被检测光场的量子统计模型出发,构造了一种适用于强度调制/直接检测的自由空间光通信系统中LDPC译码的精确实现方法。该方法在APD接收机输出统计模型(Webb-Gaussian模型)的基础上,推导了M-PPM的LDPC译码算法中初始似然比值的精确计算方法,并给出了详细的译码过程。理论分析和仿真结果表明,与目前普遍采用的APD近似非对称Gaussian统计模型下的译码性能相比较,在相同的信道条件下,该方法可以获得大约1~2 d B的性能增益。这为进一步提高自由空间光通信系统的性能提供了一定的理论依据。
Based on the study of the quantum statistical model of APD photodetector, a precise implementation of LDPC decoding in free-space optical communication system for intensity modulation / direct detection is proposed. Based on the APD receiver output statistical model (Webb-Gaussian model), this method deduces the exact calculation method of the initial likelihood ratio in the M-PPM LDPC decoding algorithm and gives a detailed decoding process. The theoretical analysis and simulation results show that this method can obtain the performance gain of about 1 ~ 2 d B under the same channel conditions compared with the decoding performance under the approximate asymmetric Gaussian statistical model of APD currently prevailing. This provides a certain theoretical basis for further improving the performance of free space optical communication system.