Mitigating Pilot Contamination in Massive MIMO Using Cell Size Reduction

In this paper, we provide a novel solution to mitigate pilot contamination in massive MIMO technology. In the proposed approach, we consider seven copilot cells of the first layer of interfering cells of a cellular network. We derive and formulate the worst-case signal-to-interference power ratio (SIR) of a typical user in both downlink and uplink of a pilot contaminated cell. Based on the formulated SIR and other considerations of the system, the total pilot sequence length, the reliability of channel estimation within the cell, the spectral and energy efficiencies are derived and formulated in downlink. The user's transmit power and the achievable sum rate are also derived and formulated in uplink. Our results show that when the cell size is reduced the pilot contamination is significantly mitigated and hence the system performance is improved.