UAV-based Multi-cell HAPS Communication: System Design and Performance Evaluation

Technology advances have enabled unmanned aerial vehicles (UAV) to stay afloat in the stratosphere for several months as base station platforms with the communication payload powered by solar energy. These UAV-based High Altitude Platform Stations (HAPS) can provide i) connectivity for remote areas not served by terrestrial networks, ii) global coverage for IoT devices, and iii) services for public safety and transportation industries. At a typical altitude of 20 Km, an HAPS can cover a large service area with a higher throughput and a lower latency compared to satellite links.In this paper, we present a reference design of a New Radio (NR) HAPS communication system comprised of both service and feeder links that can serve multiple cells within a large coverage area. The use of an adaptive antenna array with beam steering enables the system to continuously serve users from the same cell while the aircraft conducts a repetitive flight pattern above the fixed service area. Achievable capacity and coverage of the service link design at a sub-6 GHz carrier frequency are first estimated in a link budget analysis and then evaluated through Monte Carlo simulations. We observe that good spectral efficiency and coverage can be expected for outdoor line-of-sight users in the downlink, while the uplink performance is limited by the transmit power and antenna gain of the user terminal. We also demonstrate that 5G NR in the mmWave band can be used for the feeder link and can satisfy the throughput and availability requirement.