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

摘要

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.%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, SIMOPPM and M1MOPPM 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.