Modeling and Optimization of Reconfigurable Intelligent Surfaces in Propagation Environments with Scattering Objects

The reconfigurable intelligent surface (RIS) is an emerging technology that changes how wireless networks are perceived, therefore its potential benefits and applications are currently under intense research and investigation. In this letter, we focus on electromagnetically consistent models for RISs, by departing from a recently proposed model based on mutually coupled loaded wire dipoles. While existing related research focuses on free-space wireless channels or ignore the interactions between the RIS and the scattering objects present in the propagation environment, we introduce an RIS-aided channel model that is applicable to more realistic scenarios, which include the presence of scattering objects that are modeled as loaded wire dipoles. By adjusting the parameters of the wire dipoles and the loads, the properties of general natural and engineered material objects can be modeled. We introduce a provably convergent and efficient iterative algorithm that jointly optimizes the RIS and base station configurations to maximize the system sum-rate. Extensive numerical results show the net performance improvement provided by the proposed method compared with existing optimization algorithms.