Satellite-Guided Non-uniformed Beamforming for Direct Air-to-Ground Communications

Abstract

The global airline is experiencing exceptional growth, and passengers onboard request Internet access to utilize their valuable in-flight time. Direct air-to-ground communication (DA2GC) attracts considerable attention for its low latency, high capacity, and low cost. In order to compensate for the high path loss and efficiently use the spectrum resources, beamforming technique has been introduced to DA2GC systems. However, directional communication causes inherent blindness problem, and the high mobility in the DA2GC scenario leads to frequent beam-realignment. Therefore, feedback overheads and risks of outages increase significantly with traditional beamforming schemes in the DA2GC scenario. Different from traditional receiving ends, airplanes have already been equipped with satellite antennas to keep a global connection, and have enough space and power to carry massive antenna arrays and computing processors to perform adaptive receiver (RX) beam adjustment. Based on this observation, we propose a satellite-guided DA2GC network architecture where the mobility management of airplanes is separated to relatively stable satellite links, and data streaming is carried by DA2GC links. Under the guidance of satellites, a wide transmitter (TX) beamforming scheme and corresponding adaptive RX beamforming scheme are proposed. In the wide TX beamforming, the widest TX beam satisfying basic receiving sensibility is used to extend each TX beam's service time. Within the TX beam, the RX beam autonomously adjusts its direction and beamwidth to keep the final received SNR at a high and stable level. Finally, simulations are performed to validate the proposed scheme.