AF中继辅助TWR-FSO通信系统的性能分析

Performance analysis of AF relay assisted TWR-FSO communication system

针对大气湍流和指向误差对自由空间光通信性能的影响会随着通信距离的增大而愈发严重,基于放大转发中继(AF),提出了一种双向中继-自由空间光通信(TWR-FSO)系统方案。该系统采用差分二进制相移键控调制,建立了一个包含大气湍流和指向误差的复合衰落信道模型,其信道衰落满足Gamma-Gamma分布。利用Meijer’s G函数推导得到TWR-FSO系统中断概率和平均误码率的闭合表达式。在不同湍流强度和阈值门限条件下,对比分析了中断概率和平均误码率性能。仿真结果表明,在受到相同指向误差的条件下,当SNR=25 dB时,AF中继相较于DF中继系统的中断概率从10^(-1)量级下降到10^(-4)量级左右。当折射率结构常数为4.0×10^(-15)m^(-2/3),SNR=40 dB时,系统的误码率可以达到10^(-8)量级以下。说明AF中继下TWR-FSO系统能有效降低大气湍流和指向误差对通信系统的影响。

Aiming at the influence of atmospheric turbulence and pointing error on the performance of free space optical communication will become more and more serious with the increase of communication distance,based on amplify and forward relay(AF),a two-way relay-free space optical communication(TWR-FSO)system scheme.The system adopts differential binary phase shift keying modulation,and establishes a composite fading channel model including atmospheric turbulence and pointing error,and its channel fading satisfies Gamma-Gamma distribution.The closed expressions of outage probability and average bit error rate of TWR-FSO system are derived by using Meijer’s G function.Under different turbulence intensity and threshold conditions,the performance of outage probability and average bit error rate is compared and analyzed.The simulation results show that,under the same pointing error,when SNR=25dB,the outage probability of AF relay system is reduced from 10^(-1) order to 10^(-4) order compared with DF relay system.When the refractive index structure constant is 4.0×10^(-15)m^(-2/3) and SNR=40dB,the bit error rate of the system can reach below the order of 10^(-8).It shows that TWR-FSO system under AF relay can effectively reduce the influence of atmospheric turbulence and pointing error on communication system.