RIS-aided OTFS Modulation in High-Doppler Channels

Two research topics, namely, reconfigurable intelligent surfaces (RIS) and orthogonal time frequency space (OTFS) modulation, have drawn significant interest in recent wireless research. While RIS technology can aid communication by favorably controlling the electromagnetic wave propagation towards the receiver, OTFS modulation can offer robust performance in high-Doppler channels. Both RIS and OTFS are envisioned to be promising technologies for 6G and beyond. This paper investigates a RIS-aided OTFS system. A novel and useful contribution in this paper is the detailed derivation of the end-to-end delay-Doppler (DD) domain input-output relation of a RIS-aided OTFS system, which can serve as a basic system model that can aid the investigation of efficient transceiver techniques/algorithms, performance evaluation, and implementation. We consider maximization of the Frobenius norm of the effective end-to-end DD channel matrix of the RIS-aided OTFS system to choose the phase vector at the RIS. Our simulation results show that RIS-aided OTFS performs significantly better compared to RIS-aided OFDM.