Weighted Sum Rate Maximization for Hybrid Beamforming Design in Multi-Cell Massive MIMO OFDM Systems

In this paper, we look at hybrid beamforming (HBF) for the MIMO Interfering Broadcast Channel (IBC), i.e. the Multi-Input Multi-Output (MIMO) Multi-User (MU) Multi-Cell downlink channel, in an orthogonal frequency-division multiplexing (OFDM) system. While most of the existing works on wideband hybrid systems focus on single-user systems and a few on multi-user single-cell systems, we consider HBF design for OFDM systems in the case of multi-cell. We look at the maximization of weighted sum rate (WSR) using minorization and alternating optimization, the main advantage of which compared to the Weighted Sum Mean Squared Error (WSMSE) based methods is it's faster convergence to a local optimum and user streams selection. Through Simulation results, we show that the proposed deterministic annealing based approach for phase shifter constrained analog BF performs significantly better than state of the art Weighted Sum Mean Squared Error (WSMSE) or WSR based solutions in a wideband OFDM setting. We show that the optimal analog BF can be frequency flat and also provide an analysis of the minimum number of RF chains required to obtain fully digital performance.