HAPS (High-Altitude Platform Station), which provides wireless communication services from an altitude of approximately 20 km using a balloon, an UAV (Unmanned Aerial Vehicle) or other aircraft, is attracting attention as a new mobile communication platform that that makes it possible to form an ultra-wide service area of around 200 km in diameter. In order to use HAPS to construct an efficient cellular network for wireless communication services, it is necessary to develop a radiowave propagation model that takes into account the factors of propagation loss such as the environment around the ground station, which includes terrain, vegetation, clutter, BEL (Building Entry Loss), and so on. In this paper, we clarify the characteristic of BEL based on measurements from outside to inside a high-rise building for various elevation and azimuth angles, indoor antenna heights and antenna positions. Furthermore, we propose a site-specific model of BEL.
