Air-Ground Channel Characterization for Unmanned Aircraft Systems: the Near-Urban Environment

Use of unmanned aircraft systems (UAS) (or, drones) is expected to grow dramatically in the coming decades. For civil UAS that must share airspace with piloted aircraft, safety is paramount. Hence, requirements for a highly-reliable control and non-payload communication (CNPC) link are under development. Since designing a reliable link requires accurate knowledge of the channel characteristics, validated models for the air-ground (AG) channel are essential. In this paper we report results of SIMO AG measurements made for a NASA project in a near-urban environment (Cleveland, OH), for the two bands recently allocated for civil UAS CNPC: L-band (similar to 970 MHz) and C-band (similar to 5.06 GHz). Example channel characteristics are provided for a single flight track. For this flight track, path loss exponents were found to be 1.6 in L-band and 1.9 in C-band. Small scale fading Ricean K factors were 13 dB in L-band and 27 dB in C-band. The C-band root mean square delay spread was approximately 10 ns for most of the time, but reached 180 ns when reflections from buildings in the urban area were present. Spatial and inter-band correlation statistics are also reported. Tapped delay line models for near-urban AG channels will be presented in the near future.