Experimental Channel Statistics of Drone-to-Ground Retro-Reflected FSO Links with Fine-Tracking Systems

The utilization of drones as flying base stations (BSs) in the sixth-generation (6G) cellular networks has attracted much attention recently. In this context, free-space optical (FSO) systems could be deployed to provide high-capacity fronthaul/backhaul links between drones and ground BSs. Particularly, a drone-to-ground FSO communication link can be established by equipping the drone with a modulating retro-reflector (MRR) to modulate the incoming optical beam and reflect the modulated beam back along the same path. This helps to alleviate stringent pointing requirements from the drone while satisfying the limited size, weight, and power (SWaP) consumption requirements. Nevertheless, the underlying physical channel effects of this aerial retro-reflected FSO system have never been experimentally explored in the literature. In this paper, we report, for the first time, the experimental channel statistics of a drone-to-ground retro-reflected FSO link, offering practical insights into the angle-of-arrival (AoA) fluctuations at the receiver, the channel coherence time, the probability of fade, the level crossing rate, the average fade duration, and the time-frequency channel characteristics. Our results are expected to serve as practical sources of reference for the theoretical performance analyses and engineering designs of drone-based retro-reflected FSO systems.