Hybrid beamforming (HBF) structures have been recently proposed as one of the solutions to reduce cost and energy consumption of fully-digital multi-user MIMO systems in the millimeter-wave range. However, most of the initial references on HBF design assume frequency-flat single-carrier MIMO systems. Their extension to the frequency-selective multi-carrier MIMO-OFDM case is, in general, not a straightforward task, especially in partially-connected architectures. In this paper, we propose a new HBF design approach for multi-user massive MIMO-OFDM systems. Simulation results reveal that the proposed solution achieves a comparable performance to the benchmark methods in the fully-connected case, while significantly outperforming them in case of partially-connected architectures.

Hybrid beamforming; millimeter-wave; multi-user MIMO-OFDM