Massive MIMO with clustered pilot contamination precoding

In this paper, a practical approach to pilot contamination precoding (PCP) for massive MIMO is proposed through a joint clustering and pilot reuse scheme. We also introduce power scaling to enforce per-base station (BS) power constraints. We consider a massive MIMO system, where uncoordinated conventional beamforming is implemented in each cell. PCP acts as outer linear precoding prior to conventional beamforming through a cooperative transmission scheme with 3 base stations (BSs) involved. We partition each cell into 3 sectors and assign pilot sequences in a suitable way in order to perform PCP. In order to characterize performance and avoid time-consuming simulations, we employ large system analysis and random matrix theory. Numerical results show that the superiority of the clustered PCP is marginal for the moderate number of transmit antennas, but it becomes more significant in a massive MIMO mode. In addition, depending on user location, some users may experience a two-fold increased spectral efficiency after applying clustered PCP in the massive MIMO mode.