Gradient Projection-Based Alternating Minimization Algorithm for Designing Hybrid Beamforming in Millimeter-Wave MIMO Systems

摘要

This letter considers the use of alternating minimization (AltMin) framework as the main design principle in determining the optimal weights of hybrid digital and analog beamforming in millimeter-wave massive multiple-input multiple-output systems. However, such framework experiences analog beamformer design problem because analog beamformers are normally constructed using phase shifters (PSs), which result in non-convex constraints, and known solutions suffer from high computational complexity. We address this issue by proposing a simple yet efficient gradient projection (GP)-based AltMin (GP-AltMin) algorithm for hybrid beamforming design problems. In addition, when quantized PSs are adopted, we propose non-uniform PSs on the basis of the Lloyd-Max algorithm for minimizing the performance loss caused by quantization. Simulation results demonstrate that the proposed GP-AltMin algorithm not only has lower complexity but can also achieve spectral efficiency, which is comparable with or higher than those of the state-of-the-art algorithms that use unquantized and low-resolution PSs.