Outage Performance of HAP-UAV FSO Links with Gaussian Beam and UAV Hovering

This paper focuses on the free-space optics (FSO) links between high-altitude platforms (HAPs) and unmanned aerial vehicles (UAVs) which have not been addressed in the literature. In the considered system model, a HAP and a UAV play the roles as a transmitter and a receiver, respectively. The UAV is in operation when it is within the beam coverage of the HAP. This work aims to model the HAP-UAV FSO channel taking into account the effects of both the atmospheric turbulence and the pointing error caused by the UAV's hovering. A Gaussian beam model is assumed for the laser transmitted from the HAP and the log-normal distribution is adopted for the atmospheric turbulence-induced fading. For performance analysis, the outage probability and outage capacity versus the distance from the UAV to the center of the received Gaussian beam footprint are numerically investigated. Moreover, Monte-Carlo simulations are also performed to verify the numerical results.