Terrestrial Connectivity Through Constellations of High Altitude Platform Station (HAPS)

A High Altitude Platform Station (HAPS) is a aerial node operating at an altitude of about 20 km in the stratosphere, allowing for longer flight times, wider coverage areas, and links for backhauling traffic from ground base stations. Driven by technological innovations in autonomous navigation, antenna arrays, artificial intelligence, and solar power supply, HAPS has become an important component of next-generation wireless networks. In this paper, we outline the key applications of HAPS constellations and the technical challenges for successful design and deployment of this technology. Subsequently, we leverage a line-of-sight probability predicated on the obstacle penetration rate in the first Fresnel zone, resulting in an analytical formulation for the LoS probability that is dependent on the operating frequency, the transmitter and receiver heights, the horizontal distance between them, and three additional parameters describing the statistical properties of the propagation environment. The model constructed is sufficiently accurate to capture scattering aspects such as reflectivity and diffusion, yet mathematically flexible enough to allow for a smooth and physically meaningful interpretation of the performance trend of advanced radio networks including HAPS.