Abstract
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.