A Study on Antenna Beamforming Method Considering Movement of Solar Plane in HAPS System

High-altitude platform station (HAPS) has attracted considerable attention as a new promising platform to provide mobile wireless communication services with ultra-wide coverage and resilience against disaster. Because of its low-delay characteristics, HAPS can provide wireless service directly to smartphones used in terrestrial networks. In a HAPS system, it is required to employ multiple cells to accommodate high communication traffic. Furthermore, the HAPS movement caused by its turning flight or variations in the stratospheric wind is known to result in the displacement of cells projected on the ground. Therefore, the HAPS movement with multicells configuration results in several handovers and disconnections. Some research has shown that this challenge can be addressed by employing antenna beamforming based on a planar or flat-shaped array antenna. Because the target diameters of coverages are only 60 to 80 km, these simple antennas can easily cover the whole coverage area; thus, they can compensate for the displacement easily. However, to achieve ultra-wide coverage over 80-km diameter, drastic change of its antenna design is needed. Therefore, this paper proposes a new antenna structure and its beamforming methods assuming a solar-plane- based HAPS with a 200-km diameter. Computer simulation quantitatively reveals that the proposed antenna can well compensate for the effect of a displaced cell.