Contamination by Idle RIS in Cellular Systems - Impacts and Solutions

Reconfigurable intelligent surface (RIS) is a promising technology to enhance the coverage and cover the areas under blockage. However, the efficient utilization of RIS resources during idle periods remain a challenge. The conventional RIS configuration inadvertently leads to signal reflection even during the idle periods, resulting in potential signal degradation and interference that can impede the direct and/or neighboring communication links. Due to hardware limitations, it is practically impossible for the RIS to completely absorb the unwanted signal, resulting in minimal reflection amplitude. Therefore, this paper presents the innovative operational mode called “scatter mode” for the RIS, a concept that intelligently controls the RIS behaviour during idle period by scattering incident signals in all spatial directions. By mitigating unnecessary signal reflections and reducing interference, the scatter mode enhances signal quality and network reliability. To realize the proposed scatter mode, two solutions are proposed, namely “random phase selection” and “sub-RIS”. With random phase selection and sub-RIS, the minimum interference is reduced by 12 dB and 25 dB compared to optimized phase to reflect. Finally, the signalling flow and procedure to seamlessly integrate the proposed configuration into the existing RIS deployment strategies and its practical implications are shown.