Over-Harbor Channel Modeling with Directional Ground Station Antennas for the Air-Ground Channel

As use of unmanned aircraft systems (UAS) is expected to dramatically increase in the coming years, and two new frequency bands (960-977 MHz in L-band and 5030-5091 MHz in C-band) have been allocated for future control and non-payload communications for UAS civil applications, characterization of the air-ground channel becomes essential. Directional ground station (GS) antennas are expected to be used, hence the UAS is likely to fly into the GS back lobe area in some conditions. In this paper, dual-band single-input multiple-output (SIMO) data is employed to estimate channel characteristics. This data was taken over a harbor in Oxnard, CA where the aircraft was outside the half power main beam of the GS antennas. We analyze and compare results with those taken within the main beam. Although the results depend on specific antenna pattern, the statistical models provide a useful evaluation of this AG channel. In the back lobe area the path loss is 15 dB larger (in C-band) and 20 dB larger (in L-band) than free space path loss, the fading is rapid and severe (worse than Rayleigh), and the root mean square delay spread (RMS-DS) is on average 35 ns with maximum 400 ns, whereas the RMS-DS in the main beam over water setting is only 10 ns. The number of multipath components (MPCs), MPC excess delay, and the path loss of the line of sight (LOS) component all increase in the back lobe area.