Post-Computing Analog Beams after User Selection in a Hybrid Beamforming System

We investigate the benefits of recomputing analog beams after users are selected in a Hybrid Beamforming (HBF) system. In the standard HBF procedure, each user selects an analog beam, the effective channels are computed, users are selected, and finally the digital precoder is computed. However, this means that the analog beams are picked for users in isolation, without consideration of the joint interference characteristics.A natural way to address this is for the analog beams to be recomputed after the user selection step, since then the interference for the simultaneously transmitting users is known. We study this scheme and demonstrate that for specific configurations of selected users, it can lead to significantly higher SINR and therefore system performance. However, we also show that in a full simulation, the gains are marginal. This is because the user selection step typically selects users that are far apart in beam space, and hence have the least interference. We view this as a positive result since it means that the extra effort involved in the beam recomputation step is not generally needed.