University of Teramo
In this paper, the authors analyze the behavior of the downlink of a cellular network as the number of its base station antennas tends to infinity. In this case, additive noise vanishes. Nonetheless, the fact that multiple users in different cells transmit non-orthogonal pilot sequences results in the contamination of their channel estimates. As a consequence, base stations transmit beamforming vectors containing components that point towards users in other cells, causing interference that persists even as the number of transmit antennas grows.