LOS-to-NLOS Channel Transition Measurements, Analysis and Characterization for the 90 GHz Band

Millimeter wave (mmWave) communication systems can employ a large amount of spectrum, and can consequently offer large data rates, e.g., multi-Gigabits-per-second. These systems employ directional antennas to enable acceptable link distances. Directional receiver antennas hence rotate in azimuth to capture the strongest received signal in non-line-of-sight (NLOS) regions. In this paper, we present our measurement results for the 90 GHz band for three different scenarios: indoor, outdoor, and an unusual environment: an airport maintenance hangar. We address line-of-sight (LOS), NLOS, mixed, and LOS-to-NLOS transitions. We used a 500 MHz bandwidth chirp signal and estimate parameters for the close-in free space reference distance path loss model using both simulated (ray-tracing software) and measured data. Path loss exponents are 1.6 for outdoor and 1.8 for indoors, smaller than for free space. We also estimate channel delay dispersion, and statistical stationarity distance for some channel transitions. We observed rapid path loss changes in the LOS to NLOS transition regions, 13 dB for indoor and 17 dB for outdoor. Abrupt changes of the strongest-component angle of arrival, up to 60 degrees over a few cm were observed. We also quantify path loss and root-mean square delay spread (RMS DS) for LOS, NLOS and mixed environments in an airport maintenance hangar. This hangar contains various aircraft, and multiple metallic objects whose positions changed over the measurement time. The maximum path loss exponent was 3.14 for these mixed environments. The RMS DS was a maximum of 16.23 ns in the NLOS region. Rotating the receiver antenna to capture the maximum-power signal from a reflecting object decreased the RMS DS by approximately 4 ns (25%). We observed a small minimum stationarity distance, i.e., six wavelengths in NLOS and a large minimum stationarity distance, approximately six hundred wavelengths in LOS.