Adaptive Phase Shifters for Hybrid Beamforming in mmWave Systems

Full-array (FA) hybrid beamforming, integrating analog and digital components, is employed in millimeter wave (mmWave) systems to achieve directional signal transmission with enhanced gains. The main hardware challenge in this hybrid configuration resides in the analog segment, where each antenna at the transmitters and receivers is linked to an entire network of phase shifters (PSs). To address this, researchers have investigated sub-array (SA) hybrid designs that use fewer PSs to reduce hardware complexity; however, the number of PSs scales linearly with the number of antenna subarrays. This paper introduces innovative adaptive phase shifters (APSs) designed for hybrid beamforming that feature low hardware complexity and operate independently of the number of antenna arrays and radio frequency (RF) chains. The proposed APSs hybrid scheme is designed to achieve performance comparable to the FA iterative hybrid design while minimizing the number of required PSs. Specifically, the number of PSs can vary from two per RF chain to the entire network of PSs, allowing for a more efficient and high-performance design of hybrid systems. Furthermore, the full network of PSs per RF chain, corresponding to the total number of antenna elements, is reduced using modified K-means algorithms. Simulation results demonstrate that the spectral efficiency performance of APSs hybrid designs using only two PSs surpasses that of conventional FA hybrid design and SA hybrid design and exhibits similar performance to FA iterative hybrid designs with a smaller number of PSs. The proposed APSs hybrid design represents promising technology for 6G systems and beyond, owing to its innovative design with low hardware complexity and high-gain spectral efficiency.