Beam Alignment refers to the process of adjusting the direction of a transmitted or received beam to optimize its alignment with a target or counterpart. This is crucial in various technological applications, including wireless communications, optical systems, radar, and satellite communication, where precise alignment enhances performance and efficiency.

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Multi-user Beam Alignment for Millimeter Wave Systems in Multi-path Environments

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Directional transmission patterns (a.k.a. narrow beams) are the key to wireless communications in millimeter wave (mmWave) frequency bands which suffer from high path loss, severe shadowing, and intense blockage. In addition, the propagation channel in mmWave frequencies incorporates only a few number of spatial clusters requiring a procedure, called beam alignment (BA), to align the corresponding narrow beams with the angle of departure (AoD) of the channel clusters. In addition, BA enables beamforming gains to compensate path loss and shadowing or diversity gains to combat the blockage. Most of the prior analytical studies have considered strong simplifying assumptions such as i) having a single-user scenario and ii) having a single dominant path channel model for theoretical tractability. In this study, we relax such constraints and provide a theoretical framework to design and analyze optimized multiuser BA schemes in multi-path environments. Such BA schemes not only reduce the BA overhead and provide beamforming gains to compensate path loss and shadowing, but also provide diversity gains to mitigate the impact of blockage in practical mmWave systems.

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Robust Beam Tracking and Data Communication in Millimeter Wave Mobile Networks

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Millimeter-wave (mmWave) bands have shown the potential to enable high data rates for next generation mobile networks. In order to cope with high path loss and severe shadowing in mmWave frequencies, it is essential to employ massive antenna arrays and generate narrow transmission patterns (beams). When narrow beams are used, mobile user tracking is indispensable for reliable communication. In this paper, a joint beam tracking and data communication strategy is proposed in which, the base station (BS) increases the beamwidth during data transmission to compensate for location uncertainty caused by user mobility. In order to evade low beamforming gains due to widening the beam pattern, a probing scheme is proposed in which the BS transmits a number of probing packets to refine the estimation of angle of arrival based on the user feedback, which enables reliable data transmission through narrow beams again. In the proposed scheme, time is divided into similar frames each consisting of a probing phase followed by a data communication phase. A steady state analysis is provided based on which, the duration of data transmission and probing phases are optimized. Furthermore, the results are generalized to consider practical constraints such as minimum feasible beamwidth. Simulation results reveal that the proposed method outperforms well-known approaches such as optimized beam sweeping.

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