Over-the-Air Interference Suppression Using Reconfigurable Intelligent Surface With Discrete Reflection Coefficients (DRC) Design

The emergence of reconfigurable intelligent surfaces (RIS) provides a novel perspective on channel interference suppression to enable the interference signals to mutually cancel out over the air. However, mostly existing research on interference suppression using RIS is based on the assumption of continuous reflection coefficients (CRC), which is not feasible due to hardware limitations in the real world. This paper explores the efficacy of RIS in interference suppression over-the-air with discrete reflection coefficients (DRC). First, the paper formulates an interference suppression ratio (ISR) maximization problem to optimize the DRC and proposes an algorithm based on semidefinite relaxation to solve the ISR optimization problem. Then, the upper and lower boundaries of ISR under the proposed algorithm are derived to provide more insight into its performance. The simulation shows that interference channel gain can be suppressed by 32 dB to 40 dB under DRC limitations.