中文摘要：

分析了在Gamma-Gamma信道下基于脉冲位置调制（PPM）的多输入多输出自由空间光通信（MIMO-FSO）系统模型。理论上分析LT码原理,研究了不同湍流环境下LDPC码与LT码对MIMO-FSO系统性能的影响,同时比较不同度分布时的LT码对该系统性能的影响。通过仿真实验验证了在不同湍流环境下,LT码对于该系统的性能有较大的提升,且在强湍流环境下,采用修正转移鲁棒孤子分布（ISRSD）的LT码能有效地降低译码开销,进一步提升该系统的性能。

英文摘要：

The model of MIMO-FSO system based on PPM in Gamma-Gamma channel is analyzed. Theoretically,the paper analyzes the LT code. The influence of LDPC code and LT code on the performance of MIMO-FSO system is stuied under different turbulence environments,and the influence of LT code with different degree distributions on the performance of MIMO-FSO system is also discussed. The simulation results show that LT code for the performance of the system is greatly improved in different turbulence environments,and the LT code with the improved shifted robust soliton distribution（ ISRSD） can effectively reduce the decoding overhead,and further improve the performance of the system.