Directional Interference Reduction for 5G Massive MIMO Systems Using Codebook Subset Restriction

Interference management of 5G base stations (BSs) is indispensable for spectrum sharing with other communication systems, e.g., fixed satellite service. Notably, massive multi-input multi-output (mMIMO) systems form high-gain beams, causing larger interference with other systems. This study focuses on the interference mitigation for codebook-based 5G mMIMO systems and proposes a novel nullforming approach based on a codebook subset restriction (CBSR) mechanism. A BS determines a subset of 2D discrete Fourier transform (DFT) beams from the Type-I codebook defined in 5G, where the BS exploits the orthogonality of the DFT beams to form a horizontal or vertical null in a target direction. Then, the use of unselected beams is restricted. Results show that the proposed scheme can successfully form horizontal or vertical nulls only by using the CBSR framework in 5G. The interference reduction performance achieved using the proposed horizontal and vertical nullforming is over 16.7 dB and 14.1 dB, respectively, regardless of the target direction.