Base Station Association and Handover for Cellular-Connected Multi-Antenna UAVs

In this paper, we investigate coverage enhancement, base station (BS) association, and BS handover management schemes for cellular-connected unmanned aerial vehicles (UAVs) equipped with beamforming capabilities. Specifically, we consider the following characteristics of cellular-connected UAVs: 1) They can receive signals from more BSs than ground terminals, but they also experience greater interference. 2) They often reside at locations with in zero or low power directions of BSs, resulting in unstable reference signal received power (RSRP). These characteristics lead to issues such as poor coverage for cellular-connected UAVs and frequent BS handovers. We have therefore in this paper established a multi-antenna cellular-connected UAV system, where the UAV can perform beamforming based on predefined beamforming vectors. Subsequently, we considered two communications scenarios: UAV being associated with a single BS and multiple BSs cooperating to serve the UAV. In each scenario, we proposed corresponding BS association, UAV beamforming and handover strategies to enhance the UAV's coverage probability in cellular networks and to some extent reduce the number of handovers for the UAV. Finally, we validated the effectiveness of the proposed methods in both scenarios through simulations.