Fractional Pilot Reuse with Vertical Sectorization in Massive MIMO Systems

In this paper, we analyze the performance of the fractional pilot reuse (FPR) scheme with vertical sectorization in massive multiple-input multiple-output (MIMO) system. In this scheme, users are classified into the cell-center ones in inner vertical sector and the cell-edge ones in outer vertical sector 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 to avoid strong interference from adjacent sector 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 express the SINR to the 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. By using a proposed heuristic iterative algorithm, 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 FPR scheme.