An Efficient Channel Training Protocol for Channel Estimation in Double RIS-AIDED MIMO Systems

In this paper, we consider a double-Ris (D-RIS)-aided flat-fading MIMO system and propose an interference-free channel training and estimation protocol, where the two single-reflection links and the one double-reflection link are estimated separately. Specifically, by using the proposed training protocol, the signal measurements of a particular reflection link can be extracted interference-free from measurements of other reflection links. Therefore, the MIMO channels involved in a particular reflection link can be estimated interference-free from the extracted measurements using, e.g., a known state-of-the-art method. Simulation results are provided showing the effectiveness of the proposed channel training protocol.