Channel Estimation for Reconfigurable Intelligent Surface-Assisted Wireless Communications Considering Doppler Effect

In wireless systems aided by reconfigurable intelligent surfaces (RISs), channel state information (CSI) plays a pivotal role in achieving the performance gain of RISs. In this letter, we propose a novel Doppler shift adjustment (DSA) method to improve CSI estimation accuracy in the presence of motions at the communication ends for RIS-assisted systems. Specifically, the estimated channel frequency response is transformed into the time domain to facilitate phase shift adjustment, which is then converted back to the frequency domain. The proposed DSA necessitates only one more symbol which incurs negligible extra overhead compared with the large number of symbols originally required for channel estimation. Further, low-complexity channel estimation and DSA schemes are designed for approximately single-path scenarios applicable to millimeter-wave and terahertz systems. Simulation results demonstrate the effectiveness of the proposed DSA and channel estimation methods.