Channel Tracking for RIS-Enabled Multi-User SIMO Systems in Time-Varying Wireless Channels

Estimation of channel state information, balancing accuracy and pilot overhead, is critical for Single-Input Multiple-Output communication (SIMO) systems empowered by the emerging technology of Reconfigurable Intelligent Surfaces (RISs). Due to the predominantly passive nature of the RIS, the reflected signals are coupled together, rendering the estimation of the multiple cascaded channels a challenging task. Additionally, the time-varying feature of most of the realistic wireless channels drives up the cost of real-time channel tracking significantly, especially when RISs with massive numbers of unit elements are deployed. In this paper, capitalizing on a PARAllel FACtor (PARAFAC) decomposition of the received signal model, we unfold the three-dimension signal into matrices and present a low complexity channel tracking framework for the uplink of RIS-enabled multi-user SIMO communication systems. The proposed algorithm incorporates a PARAFAC-based estimator together with the generalized approximate message passing technique, combining their advantages for reducing the computational complexity and pilot overhead of channel tracking, while maintaining improved accuracy. Our numerical results validate the feasibility and efficiency of the proposed channel tracking approach for various system parameters.