Performance Analysis of Hybrid FSO/RF Systems Using ℳ Distribution and Markov Function

In Passive Defense, security of communication is very important. Free Space Optic (FSO) communication has a lot of advantages such as high security and high bandwidth. But it suffers from atmospheric turbulence. For mitigation of this effect on FSO performance some methods have been proposed, such as transmitting with the Adaptive Rate (AR) and Automatic Repeat Request (ARQ). In this paper, the performance of hybrid FSO/RF systems with multi-layer design by transmitting AR and ARQ in different conditions of atmospheric turbulence is evaluated by using the ℳ distribution model for optical channel. For two designs (multi-layer with AR and standard-ARQ, and multi-layer with AR and ARQ by frame combining), the Spectral Efficiency criteria, the Average Expected Number and the Level Crossing Rate (LCR) have been compared. The simulation results show that at the first transmission rate, maximum LCR= 80, occurs at the SNR equals to 6dB and 2dB, for the first and the second designs, respectively. Also, at average Spectral Efficiency (3.5 bits /sym), at the persistence level k=2, occurs at the SNR equals to 25dB and 20dB, for the first and the second designs, respectively; which shows the advantages of the second design over the first. Although for these advantages we have to spend more cost. For example, when SNR equals to 20 dB, the Average Expected Number will be 1.00057 in the first and will be 1.35 in the second design, which indicates the higher energy consumption of the second design.