Group-Blind Detection for Uplink of Massive MIMO Systems

When paired with traditional channel estimation and detection, massive MIMO is severely affected by pilot contamination. While sticking to the traditional structure of the training phase, where orthogonal pilot sequences are reused in different cells, we propose a new group-blind detector that takes into account the presence of pilot contamination. Our detector uses the excess antennas to partially remove interference during the data transmission phase, thus outperforming conventional non-group-blind schemes. We derive asymptotic expressions for the SINR gain, and find that it depends on the number of cells and channel gains only. Implementing the group-blind detector requires an estimate of the aggregate out-of-cell channel covariance. We propose a simple scheme, referred to as method of silences, to obtain such estimate. Numerical results confirm our analysis in scenarios of practical interest, and show cases where a scheme as simple as the method of silences achieves a large fraction of the promised SINR gain over conventional detectors.