Unified Channel Estimation for XL-RIS Assisted mmWave MU-MIMO Systems

Abstract

Channel estimation is one of the key challenges for the deployment of reconfigurable intelligent surface (RIS) assisted multiple-input multiple-output (MIMO) systems. In this paper, we study the channel estimation problem for extremely large-scale RIS (XL-RIS) assisted MU-MIMO systems with hybrid beamforming structures. For this system, we for the first time propose an unified channel estimation method that yields a notable estimation accuracy in the far-field BS-RIS and far-field RIS-User channels (in short, far-far field channels), and far-near field channels. Via experiments and complexity analysis, we verify the effectiveness of the proposed channel estimation method (named CLRA-JO).