A weather-dependent UAV relay-assisted hybrid FSO/RF airborne communication system

High-altitude airborne platforms inter-connected by free-space optical (FSO) links have been widely envisioned as a promising aeronautical network architecture. The use of unmanned aerial vehicles (UAVs) as relays was proposed to significantly increase the availability for airborne optical communication links. In this work, an additional UAV as a relay is deployed to connect the FSO link from the airborne platform to the ground station to avoid cloud blockage, presenting a novel solution for the hybrid FSO/RF airborne communication under the influence of adverse weather conditions. Further, a weather-dependent link switching scheme is proposed. Additionally, we derive closed-form expressions for the outage probability and bit error rate (BER) of the considered system, under the combined effects of atmospheric attenuation, turbulence, pointing error, and the angle-of-arrival (AOA) due to the hovering UAV. Numerical results quantitatively confirm the effectiveness of our proposal under different weather conditions. Finally, effective design guidelines that can be useful for system designers are presented.