Initial results for air-ground channel measurements & modeling for unmanned aircraft systems: Over-sea

As is widely known, unmanned aircraft systems (UAS) are expected to greatly expand in use within the national airspace system over the coming decades. With UAS civil spectral allocations planned for two bands-L-band (960-977 MHz) and C-band (5030-5091 MHz)-work is already being conducted on air interfaces and network design for control and non-payload communications (CNPC). Since most prior work studied the narrowband air-ground (AG) channel with very tall ground-site towers in open, clear areas, key wideband channel characteristics for UAS have not been thoroughly addressed. In this paper we provide some of our initial results on measurements and modeling of the AG channel, for a project sponsored by NASA Glenn Research Center. The measurements on which we report were conducted with a ground site in a coastal setting, with flights over the Pacific Ocean. These measurements were of the simultaneous channel impulse responses in both bands, and employed two receivers for each band to assess antenna diversity as well as differences across the bands. After a brief discussion of project goals, test equipment, and the measurement campaign, we provide analysis of power delay profiles and path loss, for several flight paths that cover moderate and low-elevation-angle conditions. We report on delay dispersion statistics, and channel parameter correlations across frequency and antennas for the over-sea setting. We also briefly discuss how our measured profiles will be used to develop statistical models for the AG channel. These models will be of use for communication system engineers conducting analysis, simulations, and design of future UAS CNPC systems.