  Reconfigurable intelligent surface (RIS) has been widely discussed as new
technology to improve wireless communication performance. Based on the unique
design of RIS, its elements can reflect, refract, absorb, or focus the incoming
waves toward any desired direction. These functionalities turned out to be a
major solution to overcome millimeter-wave (mmWave)'s high propagation
conditions including path attenuation and blockage. However, channel estimation
in RIS-aided communication is still a major concern due to the passive nature
of RIS elements, and estimation overhead that arises with multiple-input
multiple-output (MIMO) system. As a consequence, user tracking has not been
analyzed yet. This paper is the first work that addresses channel estimation,
beamforming, and user tracking under practical mmWave RIS-MIMO systems. By
providing the mathematical relation of RIS design with a MIMO system, a
three-stage framework is presented. Starting with estimating the channel
between a base station (BS) and RIS using hierarchical beam searching, followed
by estimating the channel between RIS and user using an iterative resolution
algorithm. Lastly, a popular tracking algorithm is employed to track channel
parameters between the RIS and the user. System analysis demonstrates the
robustness and the effectiveness of the proposed framework in real-time
scenarios.
