Revisiting Beamforming Design for Stable Millimeter-Wave Communications Under Blockages

This study examines analog beamforming designs utilizing multi-panel arrays for millimeter-wave (mmWave) communication systems under stochastic path blockages where each panel is an integrated circuit that includes power amplifiers, a limited number of antenna elements, and the corresponding phase shifters. In existing commercial mmWave systems, analog beams are typically designed by leveraging all panels cooperatively to align with the line-of-sight (LoS) path, thereby maximizing array gain. Although this beam design is effective in static channels, it is highly susceptible to frequent link disconnections caused by sudden path blockages. To address this challenge, the present study revisits the design of analog beamforming and proposes a multi-beam approach using multi-panel arrays to enhance robustness to path blockages. To evaluate the performance of the multi-beam with multimodal directivity, a theoretical analysis of the outage probability of the spectral efficiency (SE) is conducted. To design the optimal multi-beam based on the derived outage probability, we formulate a panel allocation problem to determine the assignment of panels to specific paths, including both LoS and non-line-of-sight (NLoS) paths. Numerical simulations confirm that the optimal beam, at high target SE, comprises a single sharp beam aligned to the LoS path to maximize array gain, whereas the optimal beam at low target SE is a multi-beam aligned to both the LoS and NLoS paths to acquire spatial diversity. These results demonstrate that the proposed multi-beam design, which utilizes multiple paths, effectively enhances the stability of mmWave communications while ensuring a minimum required performance level.