Selective transmission and channel estimation in massive MIMO systems

Massive MIMO systems have got extraordinary spectral efficiency using a large number of base station antennas, but it is in the challenge of pilot contamination using the aligned pilots.To address this issue, a selective transmission is proposed using time-shifted pilots with cell grouping, where the strong interfering users in downlink transmission cells are temporally stopped during the pilots transmission in uplink cells.Based on the spatial characteristics of physical channel models, the strong interfering users are selected to minimize the inter-cell interference and the cell grouping is designed to have less temporally stopped users within a smaller area.Furthermore, a Kalman estima-tor is proposed to reduce the unexpected effect of residual interferences in channel estimation, which exploits both the spatial-time correlation of channels and the share of the interference information. The numerical results show that our scheme significantly improves the channel estimation accuracy and the data rates.