Indoor and Outdoor 90 GHz LOS-to-NLOS Channel Transition Characteristics

Millimeter wave (mmWave) communication systems can offer unprecedented amounts of spectrum and multi-Gigabit-per-second (Gbps) data rates. Directional antennas are typically used to ensure adequate link range, and in non-line-of-sight (NLOS) regions, transceivers must often "search" in the angular domain for a signal of significant strength. This paper presents millimeter-wave propagation measurement results for both outdoor and indoor office scenarios at 90 GHz, focusing on LOS-to-NLOS transitions. Our results are based upon measurements using a 500-MHz bandwidth chirp signal. We first estimate propagation path loss, and model this using a single-frequency close-in (CI) free space reference distance model. Pathloss exponents are less than that for free space path: 1.6 for outdoor and 1.8 for indoors. The channel transitions can present some of the most challenging conditions to link reliability: large ranges and rapid rates of change of the strongest multipath component angle of arrival (AoA), root mean-square delay spread, and stationarity distance. We found abrupt path loss changes of over 13 dB for indoor and 17 dB for outdoor scenarios, and abrupt changes of the strongest-component AoA of up to 60 degrees over receiver travel distances of a few cm.