Receiver Maximum Eigenmode Beamforming-Based Null-Space Expansion for Multiuser Massive MIMO

This paper verifies the performance improvement of multiuser massive multiple-input multiple-output (MIMO) null-space expansion (NSE) in time-varying environment incorporating receiver maximum eigenmode beamforming (MEB). Although multiuser MIMO can enhance spectral efficiency by multiplexing a number of user terminals in spatial domain, it has a critical issue of inter-user interference (IUI) caused by time-varying channels. NSE significantly improves IUI suppression capability by exploiting plentiful degree of freedom of huge number of antenna elements at the base station (BS) side. NSE contains the nature of channel prediction since it performs null-steering to IUI on the past and the present channel states. Its effectiveness has been clarified when each user has a single antenna so far. In this paper, considering the beamforming gain of the user terminal with multiple antenna elements, we elucidate the enhanced spatial multiplexing performance of MEB-based NSE compared with channel prediction-based approaches through computer simulation.