中文摘要：

分析了独立的双伽马衰落信道下采用分集接收技术的相干光通信系统的平均输出信噪比（SNR）、通信中断概率和平均误比特率。首先，利用多项式定理推导平均输出SNR的精确表达式；其次利用正随机变量的平均值不等式推导出SNR下界的概率密度函数（PDF），并进而得出通信中断概率和外差同步二进制相移键控（BPSK）平均误比特率的联合上界。回避了直接求取sNR的PDF，降低了性能分析的复杂度。结果表明，分集接收有效地克服了大气湍流对系统性能的影响，且分集路数越多，性能改善越明显，但强弱湍流区的性能差异也越大；所得到的性能上界与已有的Monte—Carlo模拟结果十分接近。

英文摘要：

The average output signal-to-noise ratio （SNR） ,outage probability and average bit error probability of coherent optical communication system with diversity receiving are analyzed under independent Gamma-Gamma fading channel. Firstly, exact closed-form expression of average output SNR is derived based on multi-nomial theorem. Then, the probability density function （PDF） of the lower boundary of the SNR is calclated by applying the well-known inequality between arithmetic and geometric means of positive random variables （RVs）. Furthermore,new upper boundaries for outage probability and the average bit error probability of heterodyne synchronous binary phase shift keying （BPSK） are derived. The problem of calculating the PDF of the SNR directly is avoided and the complexity of analysis is lower in contrast to the previous methods. The results show that the impacts of atmospheric turbulence on the performance of system are effectively overcome by diversity receiving technology. The more its branches, the better its performance. The difference of performance is larger between strong and weak turbulence conditions. Compared with the simulation results by Monte-Carlo method, the proposed union upper boundary is almost the same.