  Reconfigurable intelligent surface (RIS) is one of the most promising
technologies for 5G-Adv and 6G. It has the characteristics of low cost, low
complexity, and easy deployment, which provides a new opportunity to develop
intelligent high-speed railway communications. The typical applications of
RIS-assisted smart high-speed railway communications are introduced in detail,
including suppressing the Doppler shift effect, solving frequent handoff
problems, overcoming high penetration loss problems, and supporting
high-precision train positioning. The key technologies of RIS-assisted smart
high-speed railway communications are discussed in-depth, including channel
measurement and modeling, channel estimation and feedback, beamforming, network
architecture, and network deployment. It is believed that the combination of
the new intelligent high-speed railway infrastructure and the new
electromagnetic infrastructure built by RIS will bring broad industrial
prospects to the intelligent high-speed railway in the future.
