A Novel Channel Estimation Method for RIS Assisted Wireless Communication Systems

Channel estimation (CE) can be challenging in reconfigurable intelligent surface (RIS)-assisted wireless communication systems. On the one hand, the dimensionality of the cascaded base station-RIS-user equipment (BS-RIS-UE) channel is exceedingly large. On the other hand, the currently available RIS hardware cannot arbitrarily switch between the active (reflection with configurable phase) and deactivate (absorption) modes, thereby resulting in a perpetual coupling between the BS-RIS-UE channel and BS-UE channel. To address the challenges above, we introduce a novel CE method that leverages the spatial modulation capabilities of RIS. The proposed CE strategy is bifurcated into two distinct phases: the BS-UE CE and the RIS-UE CE. In the BS-UE CE phase, the RIS is strategically configured to steer the incoming signals from the UEs away from the BS. This maneuver significantly suppresses the signal through the cascaded BS-RIS-UE channel, allowing it to be effectively disregarded. Consequently, this facilitates a separate BS-UE CE process using the conventional least squares (LS) algorithm. Armed with the estimated BS-UE channels, the RIS-UE channels can then be readily estimated. Simulation results show that, compared to the existing CE schemes, the proposed CE method can improve the estimation accuracy and reduce the computational complexity.