Info Multiuser transmission scheme in millimeter-wave systems assisted by an RIS subarray

Abstract

The deployment of reconfigurable intelligent surfaces (RISs) can enhance the coverage ability of millimeter wave (mmWave) communication systems.However, the typical strong line-of-sight (LoS) far-field propagation between a base station (BS) and an RIS reduces channel rank, thus affecting multiuser spatial multiplexing.To address this issue, we propose an RIS subarray-assisted mmWave multiuser transmission scheme.To increase channel rank, RIS is divided into multiple subarrays with adjustable spacing, and the channel is modeled using a hybrid spherical- and planar-wave model.To minimize interuser interference, the RIS subarrays are deployed in the discrete Fourier transform (DFT) direction of the BS antenna array.To maximize signal efficiency, the BS precoder, the RIS reflection coefficients, and the user’s combiner are jointly designed.Numerical simulations were conducted to verify the effectiveness of the proposed RIS subarray deployment strategy and the performance of the wireless transmission scheme.In a four-user equipment (UE) communication scenario in the mmWave band, the effective rank of the BS-RIS channel approaches full rank, and the spectral efficiency of each UE is improved by at least 3 bit/(s·Hz).