Revisiting End-to-End Communication Model for Realistic Reconfigurable Intelligent Surfaces

The Reconfigurable Intelligent Surface (RIS), a planar intelligent structure made of a large number of reflecting elements, is a potential smart radio technology that enables the intelligent construction of reconfigurable wireless environments. More precisely, each element of the RIS changes the reflection of the incident signal according to its own set of specifications. As a result, wireless environment becomes smart based on multiple design goals. The radio map of RIS assisted environment can be generated using end-to-end (E2E) analytical communication model reported in literature where all unit cells of RIS are assumed as metallic cylindrical thin wires and the mutual coupling effects of them are calculated analytically. While such simplistic analytical modelling applies only to simple structures and is based on several assumptions, the more accurate full wave computational electromagnetic (EM) modelling has its own limitations and drawbacks like computational complexity and storage requirements. In order to study the realistic RIS assisted wireless environment, we employ a hybrid approach where the effective impedance of unit cells are calculated using full wave EM simulation and are employed in the analytical E2E communication model. We also investigated the influence of a) the placement of RISs, b) the number of RIS reflecting elements, and c) multi-RIS environments using both analytical and hybrid approaches. It is shown that the proposed approach can be leveraged for efficient modeling, analysis, and optimization of RIS-assisted communications.