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Estimation of Channel Correlation for Massive MIMO Signal Transmission

Conventional channel estimation schemes may require for the use of orthogonal pilot signals for each antenna in frequency-division duplex (FDD) wireless systems. It is a very challenging issue to get channel information with an affordable signaling overhead in massive multi-input multi-output (m-MIMO) FDD transmission environments. The signaling overhead for the channel estimation can be reduced by exploiting the downlink channel correlation matrix (DCCM) of m-MIMO channel. With the use of DCCM, the channel information can be estimated using a reduced number of pilot signals. However, the accuracy of DCCM may seriously affect the estimation performance. In this paper, we consider the estimation of DCCM in m-MIMO transmission environments. Since the distance between a base station and a user is much larger than that between antennas, a set of antenna pairs of equal distance may experience similar spatial correlation due to the far-field effect. We consider the estimation of DCCM by averaging the correlation of these antenna pairs without reception of a large number of pilot signals, significantly reducing the pilot signaling overhead. We also consider the improvement of estimated DCCM by dropping out inaccurate correlation terms. Finally, we verify the proposed scheme by computer simulation.