Passive Reflectors for Enhancing Cellular UAV Coverage

Current fourth-generation (4G) long-term evolution (LTE) base-stations (BSs) that are not capable of performing elevation beamforming are down-tilted in order to optimize the throughput of ground user equipment (GUE). As a consequence of this down-tilt, unmanned aerial vehicles (UAVs), especially those at higher altitudes, are forced to connect with the BS side-lobes, resulting in increased transmit powers and interference to other GUEs and UAVs. In this paper, we propose using passive reflectors placed close to the BS as a low-cost alternative to elevation beamforming to compensate for the reduced antenna gain, and consequently, the increased pathloss between the BS and UAVs. The effectiveness of such reflectors in lowering the interference and increasing throughputs is tested through extensive simulations using the recently introduced third-generation partnership project aerial channel models.