Capacity analysis of amplify-and-forward based dual-hop free space optical communication system with backup RF link

In this paper, we present an amplify and forward based dual-hop free space optical communication (FSO) system with a radio frequency (RF) backup link. In which, the dual-hop FSO links are modeled by log-normal distribution turbulence, and the RF link is assumed to follow the Rayleigh distribution. For the proposed system, analytical expressions for the cumula­tive distribution function and the probability density function of the end-to-end signal-to-noise ratio are derived. Based on these expressions, closed-form expression for the ergodic capacity is derived. The effect of the fading strength on the system capacity is presented. A Comparison with a dual-hop FSO without backup RF link is performed. Finally, computer simulation results are presented to verify our mathematical analysis.