Angular Distribution of Cellular Signals for UAVs in Urban and Rural Scenarios

Spatial channel characterization of a cellular Unmanned Aerial Vehicle (UAV) Air-to-Ground (AG) communication link is a vital step to understand the potential of beam-forming in the take-off zone, when a UAV flies in the vicinity of other objects. In this paper, we evaluate the variation of mean Angle of Arrival (AoA) and Angular Spread (AS) with height based on the experimental measurements using live Long Term Evolution (LTE) networks. The LTE signals are recorded at different heights from a ground level up to 40 m in rural and urban environments. Space-Alternating Generalized Expectation-Maximization (SAGE) algorithm is used for the estimation of the angular parameters. Results show similar mean AoA at different heights, with less than 55 degrees deviation in urban environment and no more than 20 degrees change in rural scenarios. Observed AS is reduced to less than 30 degrees at increasing heights as the Line of Sight (LoS) propagation becomes dominant. However the comparison between urban and rural environments clearly indicates the presence of relevant multipath components in the urban scenarios even 20 m above the rooftops level.