On superimposed pilot for channel estimation in massive MIMO uplink

In this paper, we consider the uplink (UL) of multiuser multi-cell massive MIMO systems, and present a transmission-efficient channel estimation technique by using time-superimposed (TS) pilots, where pilots are superimposed onto data symbols in time domain. In large-antenna regime, we mathematically characterize the UL achievable rate of massive MIMO as a closed-form expression. Concerning the asymptotic case, we show that the UL achievable rate is a monotonically increasing function of pilot power, and also depends on the time allocation between pilot and data. Theoretical analysis and simulation results demonstrate the superiority of the proposed design in comparison with both the conventional TS and time-multiplexed pilots.