Design of High Speed FSO Feeder Links for HAPS based on COTS Components

High Altitude Platform Stations (HAPSs) will be key nodes of future Non-Terrestrial Networks (NTNs). As an example, they could provide high-speed wireless connectivity to remote areas, either unserved or in emergency conditions. To establish a high-capacity feeder link ($10 \mathrm{Gbit} / \mathrm{s}$ or higher) from ground to HAPS, optical solutions are being proposed. Here, we present a design analysis of a link from ground to HAPS, based on Free Space Optics (FSO) with capacity of $10 \mathrm{Gbit} / \mathrm{s}$ or $100 \mathrm{Gbit} / \mathrm{s}$, considered as short-term and long-term objectives, respectively. Here the key impairments affecting an optical beam under strong turbulence conditions are investigated, including on-axis scintillation, beam wandering, and pointing errors, along with their impacts on link reliability. The results demonstrate that these communication links can be successfully attained, leveraging upon existing fiber-communication Commercial Off-the-Shelf (COTS) components. A key element will be the realization of very accurate pointing solutions.