Clutter Loss Characteristics at the Line-of-Sight and Non-Line-of-Sight Boundaries in High Base Station Environments

High-Altitude Platform Station (HAPS) is a new mobile communication platform for ultra-wide coverage areas and disaster-resilient networks, since it can provide mobile communication services directly to smartphones from an altitude of 20 km via an Unmanned Aerial Vehicle (UAV). In order to design efficient cell configurations for HAPS-based services, we need radio wave propagation models considering terrain, vegetation, urban areas, suburban areas, and building entry loss. The clutter loss model described in Recommendation ITU-R (International Telecommunication Union Radio communication sector) P.2108, covers the propagation loss caused by features such as buildings on the ground. However, the model has no parameters for urban structures. Therefore, a correction that takes urban structure into account is required. A model that corrects Recommendation ITU-R P.2108 using shielding building heights as urban structure is proposed. If the shielding building heights are defined, it is important to clarify the relationship between the ground antenna height and the shielding building heights. In this paper, we carry out field measurements using a helicopter and clarify the propagation loss characteristics of the ground antenna height from below to above the roof (shielding building).