Performance of Covariance-Aided CSI Acquisition with Non-Orthogonal Pilots in Massive MIMO

Abstract

With the final objective of analyzing the benefits of covariance-aided uplink multi-user channel state information (CSI) acquisition in massive MIMO systems, in this paper we compare the channel estimation mean-square error (MSE) for (i) conventional CSI acquisition, which does not assume any knowledge on the users’ individual spatial covariance matrices and uses orthogonal pilot sequences; and (ii) covariance-aided CSI acquisition, which exploits the individual covariance matrices (and especially their low rank) for channel estimation and possibly uses non-orthogonal pilot sequences. We apply a large- system analysis to the latter case and provide insights about how much the CSI acquisition process can be overloaded (in the sense of allowing estimating CSI with sufficient accuracy for more users than the number resource elements allocated for training) when a covariance-aided approach is adopted. This hints at potentially significant gains in the spectral efficiency of CSI acquisition in Massive MIMO.