Optimization of HAPS placement in hybrid FSO/RF space-air-ground integrated networks

In the 6G era, non-terrestrial networks capable of providing communication services to the entire earth have garnered significant attention. As the area covered by satellites and airborne platforms such as high-altitude platform stations (HAPS) increases, the transmission capacity of the system needs to be increased. Therefore, the integration of free-space optical communications, which offer large capacity but are affected by atmospheric instability, with radio frequency communications, known for their stability but limited capacity, is expected to be a viable solution for satellite communications. In this paper, we propose a placement control method for HAPS that maximises the spectral efficiency of space-air-ground integrated networks. Simulations showed that the spectral efficiency of the system can be maximised by considering both the satellite orbits and the traffic demand distribution when deploying HAPS.