High Beamforming Gain Precoding Weight Design Scheme with Null-Space Expansion for Multiuser Massive MIMO in Time-Varying Channels

This paper improves the conventional null-space expansion (NSE) method, which can significantly suppress inter-user interference (IUI) caused by the time-varying channel in multiuser massive MIMO system. NSE method can suppress IUI by using past estimated channel state information (CSI) to steer many nulls at the transmitter side. However, it consumes some of the degrees of freedom (DoFs), and therefore the desired signal gain deteriorates. The proposed method predicts time-varying channels based on the autoregressive (AR) model and can obtain superior desired signal gain by beamforming to the predicted time-varying channel. Computer simulation shows that the proposed method has the same interference suppression capability as conventional methods, and the improvement of the desired signal gain is achieved.