Optimal Beamforming with Combined Channel and Path CSIT for Multi-cell Multi-User MIMO

We consider a combined form of partial CSIT (Channel State Information at the Transmitter(s) (Tx)), comprising both channel estimates (mean CSIT) and covariance CSIT. In particular multipath induced structured low rank covariances are considered that arise in Massive MIMO and mmWave settings. For the beamforming optimization, we first revisit Weighted Sum Rate (WSR) maximization with perfect CSIT and introduce yet another equivalent approach: Weighted Sum Unbiased MSE (WSUMSE). We then turn to the partial CSIT case where we consider Expected WSR (EWSR) maximization for which EWSUMSE turns out to be a better approximation compared to the existing EWSMSE approach. These approaches also allow an uplink/downlink duality interpretation for partial CSI.