Switching-based hybrid FSO/RF transmission for DF relaying system

In this paper, we propose a novel switching scheme for hybrid free-space optical (FSO)/radio frequency (RF) system. The outage probability and average bit error rate (BER) expressions are derived for the proposed hybrid system considering decode-and-forward (DF) relaying dual-hop (DH) scenario with and without a direct link. For the scenario with direct link, selection combining (SC) scheme is assumed at the destination. Specifically, the system transmits over FSO channel as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. If it falls below the threshold, then the system switches its transmission over millimeter wave (mmW) RF channel. Moreover, Gamma-Gamma and Nakagami-m distributions are used to characterize FSO and mmW RF links, respectively. The exact theoretical expressions are derived in closed-form and validated by Monte-carlo simulations for the proposed system. Finally, to confirm the efficiency of the proposed switching scheme, the performance of the hybrid FSO/RF system is compared with the performance of the FSO system.