Outage Probability of Mixed Satellite RF / Terrestrial FSO Cooperative System

In this paper, we analyse the outage performance of a cooperative communication system consisting of a satellite-to-ground link in radio frequency (RF) domain and terrestrial free-space optical (FSO) link. Over the first link there are signal envelope variations caused by simultaneous effects of multipath propagation and shadowing. These effects are characterised by probability density function (PDF) taking into account that both line-of-sight and diffuse components are shadowed. The signal is decoded at the ground station and forwarded to a destination. The composite Gamma-Gamma PDF that takes scintillation and pointing errors into account describes the FSO link. We give analytical expressions for the overall outage probability and present numerical results with appropriate comments. The existence of outage floor is noticed. We estimate the value of outage floor and region of signal power where this floor appears. The results could be useful in general designing energy efficient systems.