Multiuser diversity for mixed RF/FSO cooperative relaying in the presence of interference

This paper presents the performance of multiuser diversity over mixed radio frequency / free space optical (RF/FSO) relay network in presence of co-channel interference at relay and destination nodes. The multiuser RF link between source-to-relay experiences Nakagami-m fading, while the FSO link between relay-to-destination is assumed to be affected by α−μ distributed atmospheric turbulence. Moreover, the amplitudes of the interfering signals at relay and destination nodes are assumed to follow independent Nakagami-m fading distribution. We consider both forms of optical demodulation schemes i.e., coherent detection and intensity modulation with direct detection (IM/DD) demodulation. Novel expression of the end-to-end cumulative distribution function (CDF) for the proposed mixed RF/FSO system has been derived which is further utilized to obtain the closed-form expression for outage probability and bit-error-rate of the overall system. Additionally, we present asymptotic expressions of outage probability and bit-error-rate to yield quick insights of the system performance. Finally, the numerical results are provided to examine the effect of various system parameters which are also supported by Monte-Carlo simulations.