Outage Analysis of q-Duplex RF/FSO Relaying

In this paper, we propose and analyze a novel q duplex radio frequency/free space optical (RE/FS()) relaying protocol for a mixed RF and hybrid RE/ESO communication system. In our scheme, several mobile users transmit their data over an RF link to a relay node (e.g. a small cell base station) and the relay forwards the information to a destination (e.g. a macro cell base station) over a hybrid RE/ESO backhaul link. The RF links are full-duplex with respect to the FS() link and half-duplex with respect to each other, i.e., either the user-relay RE link or the relay destination RE link is active. Depending on the channel statistics, the q-duplex relaying protocol may reduce to full-duplex relaying, when the quality of the FSO link is sufficiently high, or to half duplex relaying, when the FS0 link becomes unavailable due to severe atmospheric conditions. We derive an analytical expression for the end-to-end outage probability of the proposed protocol when the fading for the user-relay RF link, the relay-destination RF link, and the relay-destination ISO link are modelled as Rayleigh, Ricean, and Gamma-Gamma distributed, respectively. Our simulation results confirm the analytical derivations and reveal the effectiveness of the proposed q-duplex protocol and its superiority compared to existing schemes.