Demo: Frequency-Shifting RIS for Multi-User mmWave OFDMA

Abstract

Millimeter-wave (mmWave) networks suffer from two practical limitations: blockage often leaves clients in non-line-of-sight (NLoS) conditions, and client radios support much smaller instantaneous bandwidth than a base station. We demonstrate Mirage, a custom space-time-coded reconfigurable intelligent surface (RIS) that behaves as a directional mixer. The surface reflects signals arriving from different angular sectors with different, integer-subcarrier frequency shifts. Narrowband clients can therefore reuse one channel while a wideband gNodeB receives their signals in distinct frequency blocks. Our 39 GHz prototype combines a 16 × 8-element RIS and mmWave front ends. In the live demonstration, moving a narrowband user equipment (UE) changes the received frequency block without retuning the UE. Attendees can observe the transmitted and received OFDM grids, target and non-target constellations, and the effect of changing the RIS space-time code in real time.