How Do Non-Ideal UAV Antennas Affect Air-to-Ground Communications?

Analysis of the performance of Unmanned Aerial Vehicle (UAV)-enabled communications systems often relies upon idealized antenna characteristic, where the side-lobe gain of UAVs' antenna is ignored. In practice, however, side-lobe cause inevitable interference to the ground users. We investigate the impact of UAVs' antenna side-lobe on the performance of UAV-enabled communication. Our analysis shows that even for a very small antenna's side-lobe gain, the ground receiver can experience substantial interference. We further show that a rather large exclusion zone is required to ensure a sufficient level of protection for the ground receiver. Nevertheless, in a multiple-antenna setting for the ground users, even when such a large exclusion zone was in place, UAVs' antenna side-lobe creates a high level of correlation among the interference signals received across receive antennas. Such a correlation limits the system ability to exploit channel diversity in a multiple-antenna setting for improving capacity. We then quantify the impact of UAVs' antenna side-lobes on the overall system performance by deriving the corresponding loss of the achieved capacity in various communications environments. We provide a new quantitative insight on the cost of adopting non-ideal UAV antenna on the overall capacity. Our analysis also shows that the capacity loss can be confined by careful selection of system parameters.

I. Introduction

Using Unmanned Aerial Vehicles (UAVs) equipped with wireless transceivers acting as drone base-stations (BSs) is proposed to enhance the ground users’ connectivity in 4G & 5G systems, and beyond [1]–[3]. UAVs’ potential for enhancing capacity/coverage of LTE/LTE-A has also been demonstrated in cases of UAV-assisted communications and cellular-connected drones [4]–[6].