LAUSR

This paper proposes the efficient downlink channel state information (CSI) feedback scheme for reconfigurable intelligent surface (RIS) assisted multi-user multi-input multi-output (MU-MIMO) wireless communication systems. RIS is the state-of-the-art technology that is extensively researched as the solution to solve the problems derived from the sparse propagation environment of the millimeter wave (mmWave) communication systems. For optimal performance, the reliable downlink CSI for designing the phase shift value of the RIS reflective elements and the precoder for beamforming is necessary at the base station (BS). However, in the practical environment, the channel feedback problem occurs due to the large number of reflective elements constituting the RIS. In this paper, to alleviate this problem, compressive sensing (CS) based channel feedback scheme is proposed. By utilizing sparse nature of mmWave propagation environment, the downlink CSI is compressed with the small number of channel vector and the corresponding index is transferred to the BS. Then, the BS acquires downlink CSI by employing the recovery algorithm of CS. The simulation results show that the proposed channel feedback scheme achieves the improved performance compared to conventional scheme in multi-user and limited scattering environment.