Through-Cloud Relaying to Mitigate Cloud-Induced Attenuation in Optical Satellite Downlinks

High-speed optical satellite-ground feeder links are expected to play a significant role in providing efficient backhauling for the next generation of mobile networks. In addition, their capability to serve rural and remote areas where establishing fiber backhauling is prohibitively expensive is especially attractive. However, attenuation from clouds is a major weather-related impairment that can degrade and often disrupt these optical satellite feeder links. The most common approach to mitigate the impact of clouds is to deploy multiple ground stations to achieve ground station diversity. However, this solution is often not possible due to the infeasibility and high cost of installing fiber cables between various ground stations. In this paper, we propose the use of high-altitude platform (HAP) stations and unmanned aerial vehicles (UAVs) as decode-and-forward relays through clouds. The effects of clouds and wind on the proposed approach are analyzed, and a heuristic optimization algorithm is presented to maximize link availability with the minimum number of UAVs. Using the ERA5 database, which provides wind and cloud measurements, we evaluate the performance of the proposed approach in northern Canada.