An Efficient and Easy-to-Implement Method for SLL Reduction in RIS-Aided Systems

Reconfigurable Intelligent Surfaces (RISs) are being considered as a potential technology for upcoming 6G cellular communication systems. RISs offer the capability to steer a wireless signal in a desired direction, thereby enhancing the overall performance of wireless systems in terms of coverage and spectral efficiency. However, the conventional methods of RIS beamforming result in significant inter-beam interference primarily caused by relatively high Side Lobe Levels (SLLs). In antenna beamforming, amplitude tapering has shown promising results in Multi-User Multiple-Input Multiple-Output (MU-MIMO) systems. Amplitude tapering allows for a notable reduction in inter-beam interference by decreasing SLLs, albeit at the expense of a reduction in the Main Lobe Level (MLL) and an increase in its width. In this paper we investigate the feasibility of utilizing this technique for RIS beamforming. In addition, we demonstrate the effectiveness of this technique through link-level simulations of a RIS-aided multi-user downlink system.