Channel Estimation for RIS-Aided Multi-User mmWave Systems With Uniform Planar Arrays

In this paper, we adopt a three-stage based uplink channel estimation protocol with reduced pilot overhead for an reconfigurable intelligent surface (RIS)-aided multi-user (MU) millimeter wave (mmWave) communication system, in which both the base station (BS) and RIS are equipped uniform planar array (UPA). Specifically, Stage I, state information (CSI) of typical user is estimated. To address power leakage issue common angles-of-arrival (AoAs) stage, develop low-complexity one-dimensional search method. II, re-parameterized BS-RIS constructed estimated from I to estimate other users’ CSI. III, only rapidly varying gains need re-estimated. Furthermore, proposed method can be extended multi-antenna UPA-type users, by decomposing $J$ scatterers into estimating single-scatterer channels virtual single-antenna user. An orthogonal matching pursuit (OMP)-based angles-of-departure (AoDs) at users. Simulation results demonstrate that algorithm significantly achieves high accuracy, approaches genie-aided upper bound signal-to-noise ratio (SNR) regime.