4.8 GHz Band Radio Channel Measurement by Unmanned Aerial Vehicle-Based Virtual Array Channel Sounding System

Recently, Unmanned Aerial Vehicles (UAVs) have been widely utilized for various industry applications, and it is expected to be one of the key elements in the next-generation mobile communication system. For the design and evaluation of the mobile communication system in the sky, the air-to-ground (A2G) propagation channel characteristics have been investigated by the UAV-based measurement systems. However, there is a measurement resolution issue due to the limitation of the UAV payload. In this paper, we propose the UAV-based virtual array channel sounding system in the 4.8 GHz band to solve this limitation. In our system, the channel data are continuously measured by the receiver, which is mounted on the UAV station, while the UAV station flies along the measurement course. The data are combined offline, and they are processed virtually as data of large array antenna for investigation of angular characteristics of the propagation channel. A great advantage of our system is to be able to configure an arbitrary virtual antenna array in the air. To mitigate the UAV position error, 3D UAV positions are tracked by laser equipment and used in the array signal processing. The experiment was conducted in an indoor workshop space in the 4.85 GHz band. The half power beam width (HPBW) of the angular power spectrum was 3.2 deg., which was quite a sharp value in this frequency band. The azimuth angular estimation errors of the incident radio wave were from 0.12 deg. to 0.42 deg. Future works will include conducting experiments in various radio propagation environments and analyzing more detailed channel characteristics.