Pilot contamination mitigation by fractional pilot reuse with threshold optimization in massive MIMO systems

In this paper, we propose a fractional pilot reuse (FPR) scheme to mitigate pilot contamination in massive multiple-input multiple-output (MIMO) system. In FPR, users are classified into the cell-center and the cell-edge ones according to their signal-to-interference-plus-noise ratios (SINRs) at the receiver side. Then, the cell-edge users with low SINRs in different cells use different pilots or orthogonal pilots to avoid strong interference from adjacent cells while the cell-center users with high SINRs in different cells reuse the same pilots to improve the pilot efficiency. In order to identify the cell-center users and the cell-edge ones, we first approximate the SINR as a function of the distance between the user and the base station (BS) and then find the relationship between the network throughput and the distance threshold. The optimal distance threshold is found to maximize the network throughput. The analytical and simulation results demonstrate advantages of the proposed scheme compared with the conventional schemes.