Experimental Evaluation for Multicell MIMO Systems with Downlink Interference Nulling

Interference nulling (IN) is a linear precoding technique for downlink multiuser multiple-input multiple-output (MU-MIMO) systems. With perfect channel knowledge at the transmitter, IN eliminates other users´ interference at each cell, thus improving the sum rate of the users in the system. To evaluate its suitability in a multicell setup, we have implemented the real-time system based on IN as well as on single-base-station closed-loop (SB-CL) precoding meeting the 3rd generation partnership project (3GPP) long term evolution (LTE)-Advanced system profile over a 20 MHz bandwidth. Our field trial in an indoor deployment of two operating base stations (BSs) and two mobile stations (MSs) shows that (1) if both MSs are located near the cell edge, IN outperforms SB-CL in terms of signal-to-interference-plus-noise-ratio (SINR) and sum throughput; (2) if two MSs are close to their respective serving BSs, IN is inferior to SB-CL. Thus, IN is more favorable for improving the transmission rate and quality of services for users near the cell-edge.