A Novel RIS Channel Model for 6G Wireless Communication Systems

In this paper, a novel three-dimensional (3D) geometry-based stochastic model (GBSM) for reconfigurable intelligent surface (RIS) assisted massive multiple-input multiple-out (MIMO) communication systems is proposed. The model includes a more general path loss model and a small-scale fading channel model that considers the RIS electromagnetic (EM) response and RIS polarization adjustment. In the path loss model, a method for generating large-scale parameters with height-dependent is proposed. In the small-scale fading model, four different propagation conditions are given to reflect the diverse link states among base station, RIS, and user equipment, depending on whether the sub-channel is line-of-sight (LOS) or non-line-of-sight (NLOS). Different from the conventional phase shift (PS) model, the RIS response matrix in the small-scale fading channel model can distinguish EM waves scattered from different directions. The accuracy of the proposed channel model is further verified by real channel measurements. The results can well guide the practical deployment of RIS in future sixth generation (6G) wireless communication systems.