UAV-enabled triple-hop mixed RF/FSO networks: reliability and altitude optimization

Abstract This paper presents a detailed performance analysis of a UAV-assisted three-hop mixed radio frequency (RF)/free-space optical (FSO) wireless communication system employing decode-and-forward (DF) relaying. The system comprises a source node communicating with a mobile UAV relay over an RF link subject to generalized Rician fading, followed by an FSO link from the UAV to a ground-based relay experiencing Gamma–Gamma atmospheric turbulence with pointing errors. The final hop from the relay to the destination user is modeled as an RF link undergoing Rayleigh fading, with opportunistic user scheduling to enhance link reliability. Closed-form expressions for the end-to-end outage probability are derived, along with an asymptotic analysis that provides insights into the diversity and coding gains. Furthermore, a location optimization framework is proposed, wherein the UAV’s altitude and corresponding elevation angle are jointly optimized to minimize the asymptotic outage probability. Simulation results corroborate the analytical findings, verified through extensive Monte Carlo trials and reveal the significant impact of fading severity, pointing error, UAV altitude, and scheduling strategy on overall system performance. The proposed model offers valuable design guidelines for next-generation UAV-enabled hybrid RF/FSO communication systems.