Downlink training scheme for massive MIMO systems

A novel downlink training scheme is proposed for time-division duplex massive MIMO systems. Different from conventional solutions, including the cell-specific reference signal in LTE, the UE-specific reference signal in LTE-A and the commonly used method without the downlink training sequence, the cell-specific demodulation reference signal is proposed by utilising the inherent asymptotic orthogonality, which is shared by all users within one cell and used for the estimation of effective channel coefficients. The training overhead is reduced and the downlink spectral efficiency can be improved considerably.