Angular-Based Hybrid Beamforming for Wideband THz Massive MIMO Systems: Mitigating Beam Split by Leveraging Angular Spread

TL;DR

The paper tackles beam split in wideband THz MIMO by introducing an angular-based hybrid beamforming (AB-HBF) framework that leverages coarse angular information and angular spread to design subcarrier-specific beams. By constructing an RF beamformer from a discretized angular dictionary aligned with AoD supports and applying a data-driven baseband precoder via SVD on the effective channel, the method broadens the effective beamwidth and reduces frequency-dependent misalignment without time-delay hardware. Key contributions include (i) an RF-stage angular dictionary for robust AoD coverage, (ii) a straightforward baseband precoding step that optimizes spectral efficiency, and (iii) demonstration that AB-HBF achieves near-unity array gain across subcarriers with performance close to fully digital precoding using far fewer RF chains. The approach provides a practical, scalable solution for mitigating beam split in next-generation wideband THz systems, with applicability to URA configurations and multi-antenna users. Overall, the work offers a cost-efficient path to maintain beam alignment and throughput in THz-wideband MIMO without resorting to hardware-intensive delay networks.

Abstract

Beam split is a critical challenge in wideband THz massive MIMO systems, arising from frequency-dependent beam misalignment that degrades communication performance, particularly in scenarios with narrow beamwidths and large arrays. This work proposes an angular-based hybrid beamforming framework that leverages angular spread to mitigate the beam split effect. Instead of relying on precise angular spread modeling, we utilize coarse angular information to guide the design of subcarrier-specific beams, effectively reducing misalignment across subcarriers. By broadening the effective beamwidth through angular spread, the proposed method enhances user coverage and alleviates beam split without requiring complex time-delay units or hardware-intensive solutions. Simulation results demonstrate that the proposed approach achieves significant improvements in spectral efficiency and beamforming accuracy while maintaining low computational and hardware complexity. This work provides a practical and efficient solution for addressing beam split in next-generation wideband THz communication systems.

Figures (8)

• Figure 1: System model of AB-HBF wideband massive MIMO.
• Figure 2: RF beamformer design for a $16 \times 16$ URA for different angular spreads of (a) 2° and (b) 10°.
• Figure 3: Normalized array gain of the RF beamformer for varying angular spreads.
• Figure 4: Comparison of normalized array gain between (a) narrowband conventional beamformer and (b) AB-HBF in a wideband THz massive MIMO system.
• Figure 5: Normalized array gain of the proposed AB-HBF scheme versus elevation and azimuth angles in a wideband THz massive MIMO system.