Artificial Fast Fading from Reconfigurable Surfaces Enables Ultra-Reliable Communications

Reconfigurable intelligent surfaces (RISs) have been shown to be able to assist wireless communications in various
scenarios by either increasing the received signal powers or neutralizing destructive signal parts such as interference. In
order to tune the RIS elements, information about the component channels to and from the RIS are required. In this work, we let the RIS operate without channel state information and show that the outage probability of an RIS-assisted mmWave link can be significantly improved by choosing random phases. Furthermore, we show that the zero-outage capacity of the RIS-assisted link is positive. This enables robust ultra-reliable communications without the need for accurate channel estimation and feedback.