Inter-user interference suppression in time varying channel with null-space expansion for multiuser massive MIMO

This paper proposes a novel Inter-User Interference (IUI) suppression scheme in time varying channels with null-space expansion for multiuser massive MIMO systems. The channel time variation deteriorates the accuracy of the channel state information at the transmitter (CSIT) and causes IUI on multiuser MIMO downlink transmission. In massive MIMO, the degrees of freedom (DoFs) of the base station antenna array are generally used to obtain the beamforming gain and capacity enhancement. The proposed null-space expansion scheme exploits the excess DoFs to perform additional null-steering, which extend the null-space dimension and thus suppress the IUI caused by the time varying channel. Computer simulations show that the proposed scheme has superior IUI suppression performance to existing channel prediction scheme; our scheme can improve the SIR by over 50dB.