QRD-Based Precoding Design for Multiuser Massive MIMO Null-Space Expansion

This article proposes a precoding weight suitable for null-space expansion (NSE) in multi-user massive multiple-input multiple-output (MU-mMIMO). NSE improves inter-user interference (IUI) suppression performance by steering multiple nulls for interfering user terminals (UTs). However, NSE faces challenges in effectively forming beams and nulls for IUI suppression, as well as in managing the computational complexity for precoding. We employ QR decomposition-based Gram-Schmidt orthogonalization (QRGSO) as a precoding algorithm suitable for NSE. Computer simulation demonstrates the superiority of the proposed scheme in terms of IUI suppression performance and computation complexity.