Forward signaling strategies for MU-MIMO downlink transmission

In this work we consider a multi-user multiple-input-multiple-output downlink system with linear precoding at the base station (BS). Both, BS and user equipments (UEs) employ multiple antennas, where the number of parallel data streams exceeds the number of UE antennas. Hence, inter-stream interference cannot be handled at the UE side only. For that purpose linear precoding is employed at the BS side. In order to maximize the achievable user rate, it can be beneficial to shift a part of the interference suppression to the UE side, where knowledge of the precoded channel is required for receive filtering, successive interference cancellation and coherent detection. For making the precoded channel available at the UEs, we investigate the strategies of precoded reference signals (PRS) and precoded channel forwarding (PCF). The performances is compared w.r.t the effective rate, which combines the achievable rate for payload data as well as the loss for signaling the precoded channel. We found that PRS outperforms PCF as soon as the channel is only imperfectly available at the BS side.