Blind Pilot Decontamination

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 [1], 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.