Channel estimation and signal reconstruction for massive MIMO with non-orthogonal pilots

This paper analyzes the minimum mean square error (MMSE) channel estimation for a target terminal in a singlecell massive multiple-input multiple-output (MIMO) system with non-orthogonal pilots. To minimize the sum mean square error (SMSE) of all terminals, the correlation between the available pilot sequences should be as weak as possible. Based on this conclusion, when the pilot process is long enough, the orthogonal Procrustes principle (OPP) is proposed directly to reconstruct mutually orthogonal pilot sequences. When the pilot process is not long enough, the optimal pilot sequences are reconstructed through an additional block matrix method. If the number of base station (BS) antennas is high but finite, simulation results verify the effectiveness of the reconstructed pilot sequences in obtaining better system performance.