Switch-Based Hybrid Beamforming Transceiver Design for Wideband Communications With Beam Squint

Hybrid beamforming (HBF) transceiver architectures based on frequency-independent phase shifters (PSs) are sensitive to phases and physical directions, resulting in limited capability to compensate for the detrimental effects of the beam squint. Motivated by the fact that switches are phase-independent and more power/cost efficient than PSs, we consider the switch-based HBF (SW-HBF) for wideband large-scale multiple-input multiple-output systems in this paper. We first derive a closed-form expression of the beam squint ratio unveiling that the severity of beam squint linearly increases with the number of antennas, the antenna spacing distance, and the fractional bandwidth. We then focus on the SW-HBF designs to maximize the spectral efficiency (SE) in both single-user (SU) and multiuser (MU) systems. The formulated problems in both cases exhibit intractable non-convex and mixed-integer challenges. To address them, for the SU case, by combining the tabu search (TS) method and projected gradient ascend (PGA), we propose an efficient heuristic PGA-TS algorithm to design analog beamformers while the digital ones admit closed-form solutions. For the MU case, we develop a two-step algorithm based on fractional programming and the PGA-TS method. Simulation results show that the proposed SW-HBF schemes are efficient and can outperform PS-based HBF architectures in terms of both SE and energy efficiency in wideband systems.