RIS Beams & MIMO (Primer)

Concept

A Reconfigurable Intelligent Surface (RIS) applies per-element phases \(\theta_{n}\) to reflect incident waves. The effective scalar channel (TX \(\rightarrow\) RIS \(\rightarrow\) UE) is: \(h_\text{eff} = \sum_{n=1}^{N} h_{\mathrm{RIS}\to \mathrm{UE},n}\, e^{j \theta_n}\, h_{\mathrm{TX}\to \mathrm{RIS},n}\)

RIS and MIMO