Pilot Decontamination for Cell-Edge Users in Multi-Cell Massive MIMO Based on Spatial Filter

Massive MIMO has been viewed as one of the most promising techniques for 5G communications. However, its potential is highly confined by the so called pilot contamination issue. For cell-edge users, this problem is particularly critical, because their signals might be overwhelmed by their peers in adjacent cells. In this paper, we propose an innovative pilot decontamination method based on spatial filter, which can greatly improve the channel estimation accuracy for cell-edge users. There are two phases in the proposed method: pilot transmission phase and idle phase. During the first phase, users transmit pilot sequences to BS, and the BS employs matched filter to obtain channel estimation, which contains both desired signal and pilot contamination. In the second phase, all users in the target cell stay silent for one symbol period, and the BS receives signal from adjacent cells. Then, fast Fourier transform can be employed to analyze the spatial spectrums of received signals in these two phases. By comparing these two spectrums, pilot contamination components can be identified, and a spatial filter can be constructed to eliminate them. Both theoretical analysis and simulation results are presented to justify the efficacy of the proposed method.