What is a RIS? 

Reconfigurable Intelligent Surfaces (RISs) have been envisioned to reduce the energy consumption and improve the spectral efficiency of wireless networks by artificially re-configuring the propagation environment of electromagnetic waves
 
RIS is a meta-surface that can reflect the radio signals in a programmed direction This approach could be used for NLOS deployments indoors, or in
shopping malls and outdoor dense urban areas.

In an outdoor dense urban environment, the RIS could be used to disseminate the signal in a similar way to sun rays reflecting off a mirror. The RIS could be integrated within a large-scale outdoor advertising panel or building’s exterior glass to minimise the deployment cost: no extra wiring and power would be required.