Direct Air to Ground Communications for Flying Vehicles: Measurement and Scaling Study for 5G

Broadband connectivity in the sky for unmanned aerial vehicles (UAVs) and commercial aircraft is the next step toward the ambitious goal of connectivity anywhere. To achieve it, direct air-to-ground communications (DA2GC) is a more promising solution than satellite communications due to its lower latency and higher throughput capabilities. In this paper, we develop a DA2GC system with tilted up directional antennas at ground base station and perform a measurement campaign using a UAV at low altitudes to study the DA2GC link at a carrier frequency of 3.7 GHz in terms of signal-to-noise ratio and throughput. Our designed DA2GC system is a general setup that can enable new frequency spectrum and new applications for 5G implementation. We also scale the obtained results from the measurements to a scenario of an aircraft flying at an altitude of 13 km. We study the physical limits of current cellular networks and analyze link budget for the scaling. A maximum of 14 Mbps is achieved during the measurement campaign. By scaling the measurement results with existing communications techniques such as carrier aggregation and techniques toward 5G such as higher antenna gains due to beamforming, extrapolated throughput could reach up to 257 Mbps with a maximum inter-site distance of 200 km due to limitations of current cellular networks. These results show that cellular networks with communication techniques toward 5G can be utilized for providing high-capacity connectivity for current aircraft at high altitudes as well as next-generation flying vehicles at low altitudes.