为了减小大气衰减效应和大气湍流效应对自由空间光通信的影响，采用了多输入多输出技术。假定自由空间光通信系统采用开关键控强度调制直接探测，信道独立同分布、无记忆平稳遍历并且具有加性高斯白噪声，在发射端和接收端都可以获取理想信道状态信息；建立了综合大气效应下多输入多输出信道模型和系统模型，推导了等增益分集合并下自由空间光通信系统的遍历容量和中断概率闭合表达式，仿真分析了各种天气条件和大气湍流对空间光通信链路的影响，结果显示随着发射孔径和接收孔径的数目增多，大气效应的影响逐渐减小，通信系统性能随之提高。从系统复杂度及性能提高程度综合考虑，选择2个发射孔径、2个接收孔径较为合适。

Multiple input multiple output (MIMO) is used in order to decrease the effects of atmospheric attenuation and turbulence on free space optical communication (FSO). It is assumed that the intensity modulation direct detection (ID/DD) with on-off keying (OOK) is used in the FSO communication systems. The channel is memoryless, stationary ergodic, identically independent and distributed with additive white Gaussian noise (AWGN). The perfect channel state information (CSI) is available to both the transmitter and the receiver. Based on the hypothesis, the multiple input multiple output channel model and systems model are established under the integrated atmospheric effects. The closed form expressions of ergodic capacity and outage probability of FSO system with the equal gain diversity combined technique are derived. The influences of various weather conditions and turbulence strength on space optical communication link are analyzed. The results indicate that the performance of the communication system is increased and the atmospheric effect is decreased with the increase of the number of transmit aperture and receiving aperture. Considering the complexity and the increasing performance of the system, 2 transmission apertures and 2 receiving apertures are more suitable for FSO.