为了克服大气湍流所造成的信道衰落效应, 分析了在弱湍流信道模型下基于强度检测脉冲位置调制方式的自由空间光通信空间(FSO)分集接收系统模型, 推导了无分集系统的误时隙率计算公式。然后以此作为参考, 在独立同分布的情况下, 采用数值仿真的方法, 分别对比分析了最大比合并(MRC)、等增益合并(EGC)和选择性合并(SC)的误时隙率性能。结果表明, 3种合并技术中, 误时隙率性能改善最优的是MRC, 其次是EGC, 而SC的改善性能最差, 但是SC实现相对容易。利用分集接收合并技术可以有效改善FSO系统的性能, 并且具有较好的抗大气信道衰落能力, 在无线光通信中将有一定的应用前景。

In order to overcome the channel fade effect caused by the atmospheric turbulence, the free space optical (FSO) system model with spatial diversity was analyzed based on intensity detection pulse position modulation (PPM) in weak turbulence atmosphere. The calculating formula of slot error rate (SER) of the system without diversity was derived under PPM firstly. Then as a benchmark, under the case of independent and identical distribution, the average slot error rates of three linear combining technologies, i.e., the maximal ratio combing (MRC), equal gain combining (EGC) and selection combining (SC) were compared by means of numerical simulation. The results show that the improvement of system by MRC is the best, followed by EGC and SC is poor. However, SC is simpler and more convenient. The technology of spatial diversity receiver combination is efficient to improve the performance of FSO and has strong ability of resistance to atmospheric channel fade, and is suited for optical wireless communications systems.