Time Reversal in RIS-Aided Environments

Emerging technological trends present unique requirements for future wireless communication systems, particularly in terms of energy efficiency, capacity, and scalability. Time reversal (TR) is a pre-coding technique that is envisioned to facilitate these stringent requirements in frequency selective environments due to its ability in providing spatial and temporal focusing of energy. With the introduction of reconfigurable intelligent surfaces (RISs) presenting an additional design aspect in the wireless systems, we develop a framework for the design and analysis of TR in RIS aided environments. Moreover, we investigate the system performance in terms of bit error rate and effective diversity order under several RIS reflection coefficient configuration strategies. We showcase that TR is able to exploit multi-path diversity in RIS supported frequency selective channels. Additionally, we demonstrate that configuring the RIS to maximize the aperture gain at the strongest attainable tap yields a performance comparable to that of an optimally configured RIS, due to the limited degrees of freedom at the RIS.