Wireless data traffic is growing rapidly as the number of mobile devices increase and video contents become more popular. As 2.4\,GHz and 5\,GHz band communications only provide limited bandwidth, these frequency bands cannot support the demand of ultra-high data rate. Millimeter-wave (mmWave) communications promise massive available bandwidth to support the next generation of wireless communications (e.g. 5G and the next Wi-Fi standard) such as 60\,GHz band that offers 7\,GHz available bandwidth. This extremely high frequency (EHF) band not only provides large available bandwidth, but it also experiences more losses than in 2.4 GHz and 5\,GHz band communications. With such excessive path loss challenge, mmWave communications employ beamforming to compensate the losses. Switched beamforming, which is performed in the media access layer (MAC), is preferred due to its low computational complexity compared to adaptive beamforming. However, to avoid high beam training overhead, beam-searching algorithm in the MAC layer beamforming must be chosen appropriately.

Beam-searching protocol in IEEE 802.15.3c and IEEE 802.11ad, which exploit two-level of beam-searching, still can experience high training overhead if narrow beams are used. Therefore, hierarchical beam-searching algorithms are proposed to reduce training packet overhead. In our approach, hierarchical beam-searching approach with two beam candidates at each level of beam-searching is chosen to minimize the number of training packets. These beam candidates then transmit training packets giving signal quality information of each beam so that the best beam can be selected.

Some beamforming techniques have already been proposed to follow hierarchical beam-searching algorithm. However, the prior beamforming techniques do not consider non-isotropic array element beam pattern. As a result, the gain follows array element beam pattern where the gain weaken at the angle direction close to the end-fire direction following beam pattern of a single patch antenna element. In this thesis, we propose a beamforming technique that has uniform gain within the scanning coverage even with the non-isotropic element patterns. To the best our knowledge, our proposed beamforming is the first work that considers a realistic element beam pattern in mmWave communications. The proposed beamforming requires flexible antenna weight vectors (AWVs) and more antenna elements than IEEE 802.15.3c or discrete Fourier transform (DFT) based beamforming. Due to flexibility value of AWVs, the AWVs must be done in the digital domain. However, digital beamforming requires a large number of radio frequency (RF) chains. Therefore, hybrid beamforming is chosen to solve the problem. We show that we achieve uniform gains with reasonable complexity.