Null-Space Expansion for Multiuser Massive MIMO Inter-User Interference Suppression in Time Varying Channels

Abstract

This paper proposes a null-space expansion scheme for multiuser massive MIMO transmission in order to suppress inter-user interference (IUI) triggered by the temporal variation of the channel. The downlink multiuser MIMO channel capacity of time varying channels is severely degraded since IUI must be suppressed at the transmitter side by using past estimated channel state information at the transmitter side (CSIT). Massive MIMO has emerged as one of the most promising technologies for further capacity enhancement by increasing the number of base station (BS) antenna elements. Exploiting the excess degrees of freedom (DoFs) inherent in massive MIMO, a BS with the proposed IUI suppression scheme performs multiple null-steering for each UE (User Equipment) antenna element, which expands the null-space dimension. Computer simulations show that the proposed scheme has superior IUI suppression performance to the existing channel prediction scheme in time varying channels.