A Novel Iterative Hybrid Beamforming Design With Per-RF Chain Power Constraints in Massive MIMO OFDM Systems

One of representative strategies for hybrid analog-and-digital beamforming (HBF) in massive multiple-input multiple-output (MIMO) systems is the two-stage design, where radio frequency (RF) and baseband (BB) beamformers are optimized sequentially. However, the two-stage approach overlooks the impact of BB beamforming (BF) on RF BF design, resulting in loss of optimality of RF BF. To address this, we propose an iterative two-stage HBF design that considers the influence of BB BF on RF BF design. The BB BF is designed per subcarrier for orthogonal frequency division multiplexing (OFDM) systems and optimized under per-RF chain power constraints. Simulation results verify superiority of the proposed HBF design.