Outage Analysis of Adaptive Combining Scheme for Hybrid FSO/RF Communication

In this paper, we analyse the outage performance of an adaptive combining scheme for hybrid free space optics (FSO) / radio frequency (RF) system considering both terrestrial communication and uplink satellite communication (SATCOM) scenarios. Adaptive combining involves keeping the FSO link active all the time and activating the RF link based on the quality of the FSO link. The outage analysis has been carried out by modeling the atmospheric turbulence of FSO link using Gamma-Gamma distribution. Further, Nakagami-m and Ricean distributions are used for modeling the small-scale fading of RF link for terrestrial communication and SATCOM scenarios, respectively. The exact expression of outage probability for the adaptive-combining-based hybrid FSO/RF system has been derived. Further, a range for optimum switching threshold has been determined. Asymptotic analysis along with the calculation of diversity gain has also been carried out for both scenarios. The outage performance of adaptive combining scheme is compared with that of hard switching scheme and single-link FSO system.