Doppler Mitigation Method Aided by Reconfigurable Intelligent Surfaces for High-Speed Channels

Reconfigurable intelligent surface (RIS) is an attractive solution to smart radio environment, which has a promising potential to mitigate Doppler effect for mobile channels. In this letter, we present a Doppler mitigation method assisted by RIS for high-speed scenarios, including the design of transmission protocol and the phase control of RIS pattern. The transmission protocol is an enhanced version of a two-stage protocol. A two-phase training sequence is introduced in the first stage, to decouple the estimates of direct and cascaded channels and simplify the training matrix for LS estimation. Training overheads are reduced in the second stage to improve the data rate. In addition, the real-time control matrix of the RIS pattern is provided for Doppler mitigation. Numerical simulations show that the presented method can effectively mitigate Doppler shift, and improve the achievable rate to be 1.82-fold.