MA-Aided Hierarchical Hybrid Beamforming for Multi-User Wideband Beam Squint Mitigation

TL;DR

This paper introduces a movable antenna architecture combined with hierarchical hybrid beamforming to mitigate beam squint in wideband near-field arrays, improving multi-user performance without complex TTD hardware.

Contribution

It proposes a novel MA-aided hierarchical hybrid beamforming architecture that reconfigures antenna tile positions to emulate TTD effects, enhancing broadband focusing and reducing beam squint.

Findings

Achieves up to 5% higher sum rate compared to fixed arrays.

Demonstrates robust beam squint suppression in simulations.

Maximum sum rate improvement exceeds 140%.

Abstract

In wideband near-field arrays, frequency-dependent array responses cause wavefronts at different frequencies to deviate from that at the center frequency, producing beam squint and degrading multi-user performance. True-time-delay (TTD) circuits can realign the frequency dependence but require large delay ranges and intricate calibration, limiting scalability. Another line of work explores one- and two-dimensional array geometries, including linear, circular, and concentric circular, that exhibit distinct broadband behaviors such as different beam-squint sensitivities and focusing characteristics. These observations motivate adapting the array layout to enable wideband-friendly focusing and enhance multi-user performance without TTD networks. We propose a movable antenna (MA) aided architecture based on hierarchical sub-connected hybrid beamforming (HSC-HBF) in which antennas are grouped into tiles and only the tile centers are repositioned, providing slow geometric degrees of freedom that emulate TTD-like broadband focusing while keeping hardware and optimization complexity low. We show that the steering vector is inherently frequency dependent and that reconfiguring tile locations improves broadband focusing. Simulations across wideband near-field scenarios demonstrate robust squint suppression and consistent gains over fixed-layout arrays, achieving up to 5\% higher sum rate, with the maximum improvement exceeding 140\%.