在自由空间激光通信(FSO)系统中, 瞄准误差和大气湍流严重影响系统通信链路, 是链路性能恶化的两大主要因素。通过对联合信道的理论分析, 建立了信道模型, 并利用Meijer G函数推导出了直接探测系统和相干探测系统平均信道容量的表达式。通过在Matlab中的仿真结果可知, 在给定瞄准误差和大气湍流的条件下, 信号光的光束束散角并非越小越好, 而是存在最优束散角, 该束散角不仅可以保证系统性能良好, 而且使得发射系统功率取得最小值, 并且采用相干探测系统可以抑制大气湍流对系统的影响, 有效提高系统的性能。

In the free space laser communication(FSO) system, pointing error and atmospheric turbulence seriously affect the communication link of the system, which are the two main factors for the deterioration of the link performance. Based on the theoretical analysis of the joint channel, the channel model was established, and the expression of the average channel capacity of the direct detection system and coherent detection system was derived by using the Meijer G function. By comparing the simulation results in Matlab, given the pointing error and atmospheric turbulence conditions, the signal light beam divergence angle is not as small as possible, but there is an optimal beam divergence angle. The beam divergence angle can ensure the system performance, making the transmission power minimum. The coherent detection system suppress the influence of atmospheric turbulence on the system, thus the performance of the system is effectively improved.