Generalized Impedance Model of Wireless Links Assisted by Reconfigurable Intelligent Surfaces

We devise an end-to-end (E2E) communication channel model that describes the performance of reconfigurable intelligent surface (RIS)-assisted MIMO wireless links. The model borrows the impedance (interaction) matrix formalism from the method of moments (MoM) and provides a physics-based communication model. In configurations where the transmit and receive antenna arrays are distant from the RIS beyond a wavelength, a reduced model provides accurate results for arbitrary RIS unit cell geometry. Importantly, the simplified model configures as a cascaded channel transfer matrix whose mathematical structure is compliant with widely accepted, but less accurate, system-level RIS models. A numerical validation of the communication model is presented for the design of binary RIS structures with scatterers of canonical geometry. Attained results are consistent with path-loss models adopted in communication system design and have been validated with full-wave simulations. Our results shows that the applicability of communication models based on mutual impedance matrices is not restricted to canonical minimum scattering RIS unit cells.