Low-Complexity Beamforming Design for Green Near-Field Communications in 6G Ultra-Massive Multiple-Input-Multiple-Output

The ultra-massive multiple-input-multiple-output (UM-MIMO) is envisioned to be an integral part of future sixth-generation (6G) communication networks to meet the ever-increasing demand for higher data rates. However, the excessive energy consumption of UM-MIMO’s massive radio frequency chains and performance degradation due to beam misalignment pose critical challenges. This paper investigates low-complexity beamforming optimizations with UM-MIMO for green near-field (NF) wireless communications. We first propose an adjustable orientation discontinuous reception (A-ODRX) mechanism merging the beam alignment state into long DRX cycles to reduce power consumption while preserving beamforming capabilities enabled by UM-MIMO’s large aperture. The A-ODRX mechanism demonstrates provable robustness against beam misalignments through theoretical derivations. We designed a phase extraction zero-forcing (PE-ZF) aided hybrid beamforming architecture tailored for NF channels’ spherical waveform effects to further overcome hardware constraints. Simulation results demonstrate that the proposed low-complexity beamforming design for the green NF wireless communication method outperforms benchmarks in terms of energy efficiency, achievable sum rate, rate scaling with users, resilience to NF mobility, and beamforming gain.