mmWave beamforming techniques for future wireless communication applications

Recent years have witnessed an unprecedented growing demand on wireless data rates, which cannot be satisfied through traditional methods that increase the spectral efficiency of the available spectrum at sub-6GHz frequencies. Fortunately, the wide unlicensed swaths of the spectrum at millimeter-wave (mmWave) frequencies can solve the spectrum scarcity problem. However, mmWave frequencies have quasi-optical line of sight characteristics and high path loss propagation, making communication at extended ranges challenging. Adaptive steering of highly directional antenna beams can overcome the more significant path loss of signals at mmWave frequencies. Therefore, we present a novel 60GHz pattern reconfigurable antenna capable of steering its beams in both the azimuth and the elevation directions. The performance of this steerable antenna was evaluated via ray-tracing simulations of an urban city model. The proposed antenna outperforms a conventional omnidirectional antenna in terms of received power and delay spread characteristics. The narrow beams are a potential solution to the path loss, albeit they are vulnerable to the blockage that causes deep fading of the signal. Solving the indoor blockage problem is critical to effectively using the mmWave spectrum. Experimental results showed that switching to a wider beam with lower gain can partially restore or maintain a communicating link. Effective beam switching and coordinated beam steering can shorten deep fading, which is crucial for mmWave communication systems that are very susceptible to the spatial characteristics of the environment. Directional communication at mmWave frequencies requires the precise alignment of the transmitter and the receiver. Exhaustively scanning all directions to find the optimal link is a time-consuming process that renders directional communication impractical. Low latency beamforming using phased antenna arrays is the key to the practical deployment of the envisioned mmWave Gbps mobile networks. Thus, we used reconfigurable antennas in the sub-6GHz 5G new radio (NR) band to aid codebook-based beam selection in the mmWave band of the 5G-NR. We exploited the congruence between the spatial propagation signatures of signals at both mmWave and sub-6GHz frequencies to reduce the beam search space. The simulation results show a significant reduction in mmWave beam search overhead. We further introduced a novel direction of arrival (DoA) estimation technique using a single RF chain reconfigurable Alford loop antenna (RALA) at sub-6GHz frequencies to allow a rapid optimal beam selection process at mmWave frequencies. This thesis provides a measurement-based DoA estimation method, shows the reduced beam scanning overhead at mmWave frequencies, and designs an SDR-based test-bed for evaluating the proposed novel integrated system.