Channel Estimation and Beamforming Design for MF-RIS-Aided Communication Systems

TL;DR

This paper proposes a novel beamforming design for MF-RIS-assisted multi-user communication systems, improving channel estimation accuracy and reducing thermal noise effects through an LS estimator and optimized algorithms.

Contribution

It introduces a least squares channel estimator considering coupled beams and thermal noise, and an optimal beamforming design achieving the CRLB with an alternating optimization algorithm.

Findings

Effective reduction of thermal noise impact

Achieves CRLB in channel estimation

Improved beamforming performance

Abstract

In this letter, we study the beamforming design for channel estimation of multi-functional reconfigurable intelligent surface (MF-RIS)-aided multi-user communications that supports simultaneous signal reflection, refraction, and amplification. A least square (LS) based channel estimator is proposed for MF-RIS by considering both the coupled MF-RIS beams and the introduced thermal noise. With the discrete fourier transform (DFT)-matrix, the MF-RIS beamforming design problem is simplified under the proposed LS channel estimator. The optimal MF-RIS beamforming design that achieves the Cram\'er-Rao lower bound (CRLB) of channel estimator is obtained with the proposed alternating optimization algorithm. Simulation results demonstrate the effectiveness of the proposed beamforming design in reducing the impact of thermal noise.