Over-the-Air Co-Channel Interference Neutralization: An Active Reconfigurable Intelligent Surface Approach

This paper advocates the use of reconfigurable intelligent surface (RIS) in an active manner to suppress the over-the-air co-channel interference. Different from the commonly used passive RIS, the active RIS reflects and amplifies the electromagnetic wave with phase shifts, enabling more flexible configuration of wireless propagation environment with respect to e.g., interference mitigation. In this paper, we consider a single-cell multiple-input single-output (MISO) channel with the presence of an unknown interferer, where an active RIS is placed to suppress such co-channel interference. Under such setting, we first propose an algorithm to minimize the normalized maximal interference, by which we identify the condition under which the co-channel interference can be perfectly mitigated. Then, we formulate an achievable rate maximization problem to design reflection coefficients, for which an iterative algorithm built upon fractional programming and the convex-concave procedure is proposed.