Ultra-Low-Cost Hybrid Beamforming: A New Static-Connection Architecture with Sparse Phase-Shifter Sharing

2026-07-02

AI Summary

This work addresses the high hardware cost and control complexity of conventional subarray-based hybrid beamforming architectures, which require a dedicated phase shifter per antenna. To overcome this limitation, the authors propose a static sparse phase shifter sharing architecture that formulates the phase shifter–antenna connectivity optimization as an antenna grouping problem. By employing a fixed connection matrix, phase shifters are shared within subarrays, while adaptive phase tuning combined with digital precoding preserves dynamic beamforming capability. Theoretical analysis reveals the key mechanism for retaining analog-domain degrees of freedom under static sparse connectivity, thereby avoiding deep nulls and grating lobe degradation. Efficient grouping algorithms are developed for single- and multi-RF-chain scenarios, respectively, including a QoS-driven majorization-minimization (QoS-MM) approach. The proposed architecture achieves 37.5% and 62.5% reductions in phase shifter count while maintaining beamforming performance close to that of fully connected architectures.

Abstract

Hybrid beamforming is a promising solution for high-frequency multi-antenna wireless systems, but its implementation is constrained by the cost and complexity of analog phase-shifter (PS) networks. Although sub-connected architectures simplify the analog network, their conventional realization still requires a dedicated PS for each antenna, causing considerable layout area, wiring, calibration, and control overheads. To address this issue, this paper proposes a novel static-connection architecture with sparse PSs for ultra-low-cost sub-connected hybrid beamforming, where antennas within each sub-array share a PS through an optimized fixed PS-to-antenna connection matrix. The proposed architecture preserves static connections while enabling dynamic beam control via adaptive PS phase-shift adjustments and digital precoding. For the single-radio-frequency (RF)-chain scenario, the sparse-PS connection design is transformed into an antenna-grouping problem, with analytically characterized structural properties and an efficient algorithm. For the multi-RF-chain scenario, we develop a quality-of-service (QoS)-majorization-minimization (MM) algorithm to handle the mixed discrete-continuous optimization problem. Numerical results demonstrate that the proposed architecture reduces the PS count while preserving most beamforming capability of the traditional full-PS sub-connected architecture. In particular, the proposed design achieves PS-count reductions of 37.5% and 62.5% in single-RF-chain and multi-RF-chain systems, respectively, while avoiding deep-null and grating-lobe degradations associated with deterministic connection schemes. These results provide engineering insights into static sparse-PS sharing: the key to hardware-efficient hybrid beamforming is not merely reducing the PS count, but also preserving essential analog-domain degrees of freedom through optimized PS connection topologies.

Problem

• hybrid beamforming
• phase-shifter
• sub-connected architecture
• hardware cost
• analog beamforming

Innovation

• hybrid beamforming
• sparse phase-shifter sharing
• static-connection architecture
• sub-connected architecture
• hardware efficiency