Gamma-Gamma模型下采用PPM调制的MIMO-FSO系统误时隙率分析

分析了在Gamma-Gamma分布下基于脉冲位置调制(pulse position modulation, PPM)方式的多输入输出自由空间光学（multiple input multiple output free space optics, MIMO-FSO）通信系统模型。首先推导了单输入单输出（single input single output, SISO)-PPM系统的误时隙率（slot error rate, SER）计算公式，以此作为参考，在独立同分布和独立分布参数不同情况下，分别推导出MISO-PPM、SIMO-PPM和MIMO-PPM系统的平均SER计算公式，并用数值仿真的方法，分析了它们的平均SER性能。仿真结果表明，在Gamma-Gamma分布模型下，采用多发多收的方法确实能有效提高FSO系统的平均SER性能，如在误时隙率为10 ^-4 时，M = 2、N =2 的MIMO-PPM系统在信道分布参数相同和不同时，与SISO-PPM相比，分别能节省信噪比50 dB和65 dB左右。实际应用中，M 和N 分别取3或4就基本足够，对无线光通信系统的理论分析和系统设计具有一定的指导意义。

Performance analysis of MIMO-FSO systems based on PPM modulation and Gamma-Gamma distribution model

The multiple input multiple output free space optics(MIMO-FSO) system model is analyzed under the Gamma-Gamma distribution channels and pulse position modulation(PPM).The SER calculating formula of single input single output(SISO)-PPM systems is derived firstly,then as a benchmark,under the cases of both independent with identical distribution(IID) and independent with different distributions(IDD),the average slot error rates(SER) of MISO-PPM,SIMO-PPM and MIMO-PPM systems are derived respectively.Simulations of the average SER performances of these systems are done.The simulation results show that,under Gamma-Gamma distribution,the average SER is indeed improved in MIMO systems.When SER is at 10-4,the average SER of the MIMO-PPM system with M=2 and N=2 is improved by about 50 dB and 65 dB under IID and IDD respectively.In practical designs,M and N are enough to set to 3 or 4 respectively.The obtained conclusion is significant to the analysis and design of FSO systems.