Progressive Channel Estimation for Single-Carrier Communications Aided by Reconfigurable Intelligent Surfaces

Cyclic-prefix single-carrier transmissions aided by a reconfigurable intelligent surface (RIS) can extract multipath diversity profiting from the cyclic delay diversity technique. However, due to the substantial number of unit elements an RIS can possess, the pilot block size can be extremely large, violating the requirement for low-latency communications. To solve this problem, in this letter, we present a progressive channel estimation method that transmits pilots and data alternately. As the number of transmitted pilot blocks increases, we can attain increasingly comprehensive channel state information via least-square estimation in the time domain, and hence, a higher multipath diversity gain. The normalized mean square error of the proposed channel estimator is analytically assessed via a novel closed-form expression. Our simulation results demonstrate the robustness of the proposed method over time-varying channels, outperforming a competing benchmark scheme.