On the Impact of Mutual Coupling on RIS-Assisted Channel Estimation

TL;DR

This paper quantitatively evaluates how mutual coupling affects channel estimation in RIS-assisted systems, revealing that element spacing and RIS size significantly influence estimation accuracy in practical scenarios.

Contribution

It provides a electromagnetics-compliant analysis of mutual coupling's impact on RIS channel estimation, highlighting when mutual coupling can be safely ignored.

Findings

Mutual coupling impact increases with RIS size and element proximity.

Ignoring mutual coupling can lead to significant estimation errors in dense RIS configurations.

Even with mutual coupling considered, tight element spacing degrades estimation performance.

Abstract

Amid the demand for densely integrated elements in techniques such as holographic reconfigurable intelligent surfaces (RISs), the mutual coupling effect has gained prominence. By performing a misspecified Cramer-Rao bound analysis within an electromagnetics-compliant communication model, this letter offers a quantitative evaluation of the impact of mutual coupling on RIS-assisted channel estimation. Our analysis provides insights into situations where mutual coupling can be disregarded safely. The analyses and numerical results reveal that within practical scenarios, closer integration of RIS elements or the enlargement of RIS size accentuates the impact of neglecting mutual coupling. In addition, even with mutual coupling-aware setups, excessively tight RIS element spacing can lead to substantial degradation in the channel estimation performance.