Underdetermined AOA Estimation Using Non-Uniform Sub-Connected Hybrid Beamforming Systems

Abstract

Hybrid beamforming (HBF) is emerging as a key technology for future wireless networks, particularly in millimeter wave (mmWave) bands. In this paper, we present a non-uniform sub-connected hybrid beamforming (NSC-HBF) system that enables the implementation of the difference co-array for the underdetermined angle-of-arrival (AOA) estimation. We propose a broad beam synthesis technique to mitigate performance degradation caused by uneven analog combining gains. To further enhance estimation efficiency, we modified the co-array least mean squares (co-array LMS) method by directly solving the least-squares problem to determine the filter weights. The proposed method reduces computational complexity and eliminates iterative procedures for faster processing. Our numerical results demonstrate the pseudo-spectrum and detection performance for both pencil and broad beams, highlighting the importance of analog combining codebook design. Additionally, the proposed method achieves higher estimation accuracy compared to the co-array root-LMS.