Mueller, Ralf R. (Dept Electronics & Telecommunications, Norwegian University of Science & Technology, 7491 Trondheim, Norway)
Vehkaperae, Mikko (Dept Signal Processing & Acoustics, Aalto University, 02150 Espoo, Finland)
Cottatellucci, Laura (Institute Eurecom, 450 route des Chappes, 06410 Biot, France)
We propose a nonlinear channel estimation method based on a subspace projection that is suitable for asymmetric antenna array systems. We show that the so-called pilot contamination problem reported in , is an artefact of (inappropriate) linear channel estimation and does not occur in cellular systems with power-controlled handoff when the channel estimation method proposed in this paper is used. We intuitively explain our result by establishing an isomorphism between a massive MIMO system and a spread-spectrum system with unknown signature sequences.