Angular Spread Analysis and Modeling of UAV Air-to-Ground Channels at 3.5 GHz

Use of Unmanned Aerial Vehicles (UAVs) for multiple applications in the fifth generation (5G) mobile communication systems is expected to grow dramatically in the coming future, due to the low cost and larger connectivity range. Hence, temporal and spatial air-to-ground (A2G) channel characteristics will be required to ensure high-reliability A2G links. In this paper, we present a measurement and modeling campaign on the A2G channel at 3.5 GHz in a rural macrocell (RMa) scenario using a three-dimensional propagation multipath channel sounder. The channels were sounded with the horizontal ranges of 300 meters. The transmitter (TX) equipped with two omnidirectional antennas was placed on a quad-rotor UAV which flew horizontally at six altitudes from 50 to 300 meters. The receiver (RX) emulated a user equipment (UE) and placed on the ground. We measured the elevation/azimuth of arrival (EoA/AoA) of the multipath components (MPCs) and obtained the elevation/azimuth rootmean-square spread of arrival (ESA/ASA). We analyze the variation of ESA and ASA with the UAV height, which can support the A2G channel model with height-dependent parameters. Furthermore, we adopt the lognormal probability density function (PDF) to model the ESA and ASA distributions based on the measurement data and compare the proposed models with the 3GPP model. This work provides a reference for the design of the air-borne access networks using the sub-6 GHz (sub-6G) band.