  A reconfigurable intelligent surface (RIS) can shape the radio propagation by
passively changing the directions of impinging electromagnetic waves. The
optimal control of the RIS requires perfect channel state information (CSI) of
all the links connecting the base station (BS) and the mobile station (MS) via
the RIS. Thereby the channel (parameter) estimation at the BS/MS and the
related message feedback mechanism are needed. In this paper, we adopt a
two-stage channel estimation scheme for the RIS-aided millimeter wave (mmWave)
MIMO channels using an iterative reweighted method to sequentially estimate the
channel parameters. We evaluate the average spectrum efficiency (SE) and the
RIS beamforming gain of the proposed scheme and demonstrate that it achieves
high-resolution estimation with the average SE comparable to that with perfect
CSI.
