Zeenat Afroze

Date of Award

Summer 2023

Document Type

Open Access Dissertation


Electrical Engineering

First Advisor

David W. Matolak


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. This technology can be used in many sectors: aviation, vehicles, public transportation, robotics, autonomous factories, etc. Yet mmWave communication systems suffer from some propagation challenges, including large free space path loss (PL), large penetration loss, and large diffraction loss. Hence, it is vital to quantify these and other channel effects to ensure link reliability. Most mmWave systems will employ directional antennas to enable acceptable link distances. In many settings this will require directional receiver antennas to rotate in azimuth to capture the strongest received signal in non-line-of-sight (NLOS) regions. Although terrestrial mmWave communication systems are advancing steadily, mmWave communication system applications in aviation and airport settings are still in their infancy. As commercial aviation is experiencing rapid growth, mmWave bands can be used for short range applications within airport areas, which can support a large robust data transfer. For this reason, research on mmWave wireless channel characterization for the aviation environments is a nascent area of study. In this dissertation, we present our measurement results for the 90 GHz band for two different types of settings: non-aviation public areas (indoor hallways and outdoor streets), and aviation settings (an airport maintenance hangar and airport baggage claim areas). We address line-of-sight (LOS), NLOS, mixed LOS/NLOS, and LOS-to-NLOS transitions settings, and provide channel statistics and models based upon extensive measurements using a 500 MHz bandwidth chirp signal. For all measurements, the transmitter (Tx) was fixed and the receiver (Rx) was moved. Emulating what an operational mmwave system will do, the Rx antenna was rotated to obtain maximum received power when the Rx was partially or fully obstructed. The multi path components (MPCs) measured allow us to compute the most common measure of dispersion, root mean-square delay spread (RMS-DS), as well as the spatial PDP correlation coefficient, used to assess stastical stationarity. We corroborated our results with geometric analysis and ray-tracing simulations.

For non-aviation environments, we estimated parameters for the close-in free space reference distance PL model using both simulated (ray-tracing software) and measured data. PL exponents are 1.6 for outdoor and 1.8 for indoors, smaller than for free space because of waveguiding. We observed rapid PL changes in the LOS to NLOS transition regions, 15 dB/ 20 cm for indoor and 15 dB/ 10 cm for outdoor. Abrupt changes of the strongest-component angle of arrival (AoA), up to 60 degrees over a few cm were also observed. Very small stationarity distances, as small as six wavelengths, were found in NLOS settings. For our second environment type, aviation settings, we measured 90 GHz channel characteristics in the Jim Hamilton L.B. Owens Airport (CUB), Columbia, SC, USA, and Columbia Metropolitan Airport (CAE), West Columbia, SC, USA. At CUB, we measured in an atypical environment, the airport maintenance hangar. This crowded environment contained multiple aircraft, metallic objects, and other obstacles, whose positions moved throughout the day; thus we characterized this setting as a mixed LOS/NLOS environment. For this mixed setting the pathloss exponents exceed that for free space, with a maximum of 3.14. As the Rx is surounded by several rich reflectors, the range of AoA at CUB is larger than 1040 , larger than in typical office environments. We also quantified the RMS DS, finding a maximum value of 24 ns for the NLOS case. The minimum stationarity distance for both LOS and NLOS settings at CUB maintenance hangar is 0.5 m. Aviation-setting measurements were also conducted at CAE baggage area for LOS, mixed, and LOS to NLOS transition settings. The CI model PL exponent is close to the free space PL exponent, as expected in this open setting. A relatively large RMS DS was observed in both LOS and NLOS settings: 20.5 ns for LOS and 23 ns for NLOS. The maximum LOS RMS DS in aviation environments is approximately double that of our non-aviation scenarios. These results will be of use to mmWave network designers in this unique aviation application.