Air-ground channel measurements and modeling for UAS

Unmanned aircraft systems (UAS) are expected to be used in greatly increasing numbers in the near future. To safely integrate them into the National Airspace System (NAS) [1] requires highly reliable communication links for control and nonpayload communications (CNPC) [2]. Although spectrum allocations for UAS appear to be in place, UAS missions can differ markedly from those of conventional piloted aircraft, and new challenges will appear. One of these challenges is the potential detrimental effects of the air-ground (AG) channel [3]. For past systems that used elevated ground site (GS) antennas in open areas, multipath propagation was minimal. Data rates and bandwidths of past systems were also small, rendering the multipath issue either inconsequential or easily overcome by (sometimes large) transmit power increases or longer latencies. Legacy voice communication systems are also comparatively low rate and forgiving of delay and can usually resort to repetition to improve reliability.