On the estimation of slow-fading coefficients for pilot contamination precoding

Massive multiple-input multiple-output (MIMO) has been actively studied for next generation wireless systems since it can provide high data rate and an improved energy efficiency in multiuser systems using large antenna arrays at base stations (BSs). While massive MIMO has various advantages, its perfor- mance is known to be limited by pilot contamination. To mitigate the intercell interference resulting from pilot contamination, pilot contamination precoding (PCP) was proposed for downlink transmissions. For PCP, slow-fading coefficients need to be estimated. In this paper, we study the estimation of slow-fading coefficients. We show that slow-fading coefficients cannot be estimated using the conventional uplink training. Thus, we have proposed amplitude modulated pilot sequences, which allow us to estimate slow-fading coefficients without requiring additional orthogonal pilot sequences.