Channel Estimation for Active RIS-Aided mmWave MIMO Systems

In this work, the problem of channel estimation is studied for active RIS-aided mmWave MIMO systems. By designing specific UE pilot sequences and RIS phase configurations, decoupling of the angles of departure (AODs) at the UE from the cascaded channel parameters is achieved, enabling separate estimation of the angles of arrival (AOAs) at the base station (BS), the AODs at the UE, and the cascaded channel parameters. To address the challenge of estimating the cascaded channel parameters, a low-complexity algorithm that decouples the 2D cascaded channel parameters is developed. Utilizing greedy algorithm principles, it transforms the estimation process into multiple 1D searches, significantly reducing computational complexity. Additionally, we apply the spatial alternating generalized expectation maximization algorithm for further refinement. Simulation results validate the effectiveness of the proposed estimation algorithm.