Pilot decontamination in multi-cell massive MIMO systems

Abstract

In this paper, the performance of massive multiple-input-multiple-output (M-MIMO) with an infinite number of the base station (BS) antennas is studied. The performance of such systems is only limited by the pilot contamination, which is a negative effect of reusing uplink pilot sequences in the neighboring cells. The channel estimates obtained in the presence of pilot contamination is contaminated, which results in inter-cell interference in the downlink data transmission. This paper shows the severity of pilot contamination in the multi-cell scenario and proposes the implementation of distinct orthogonal variable spreading factor code at each BS to mitigate the pilot contamination in the time-division duplex (TDD) multi-cell M-MIMO systems. The performance of the uplink and downlink sum rates of the proposed scheme is compared with those of the time-shifted pilot scheme for an infinite number of BS antennas. The simulation results show that the proposed scheme outperformed time-shifted pilot scheme, which shows the effectiveness and validity of the proposed scheme.