Beam-Squint-Aware Channel Estimation for Dual-Wideband UPA-Type RIS-Aided Massive MIMO

This letter presents a novel beam-squint-aware (BSA) channel estimation method for uniform planar array (UPA)-type reconfigurable intelligent surface (RIS)-aided frequency- and spatial-wideband (dual-wideband) massive multiple-input multiple-output (MIMO) systems. The proposed scheme considers the angles of arrival (AoAs), angles of departure (AoDs), and propagation delays as slowly-varying, while treating the channel gains as fast-varying parameters. To estimate these parameters, we divide the estimation procedure into slow-time parameter estimation (ST-PE) and fast-time parameter estimation (FT-PE) modes. During the ST-PE mode, we propose a BSA periodogram for estimating the AoAs at the base station (BS), followed by a BSA orthogonal matching pursuit (OMP) algorithm for estimating the cascaded angles and delays. In the FT-PE mode, we propose a subspace-aware least squares (SA-LS) method to estimate the channel gains. Simulation results demonstrate the superiority of the proposed estimation methods in terms of root mean square error (RMSE) and achievable rate metrics when compared to state-of-the-art approaches.