Experimental Verification of Null-Space Expansion for Multiuser Massive MIMO using Measured Channel State Information

This paper presents experimental results of our proposed null-space expansion scheme for multiuser massive MIMO in time varying channel. Multiuser MIMO transmission with proposed scheme can suppress inter-user interference (IUI) caused by outdated channel state information (CSI). The excess degrees of freedom (DoFs) of massive MIMO is exploited to perform additional null-steering using past estimated CSI. The signal-to-interference ratio (SIR) performance achieved by a null-space expansion scheme that uses measured CSI is experimentally evaluated through CSI measurements. It is confirmed that the proposed scheme shows SIR performance superior to the conventional channel prediction scheme. In addition, IUI can be stably suppressed even in high mobility environments by further increasing the null-space dimension.