RIS-Aided Next-Generation High-Speed Train Communications: Challenges, Solutions, and Future Directions

High-speed train (HST) communication is a very challenging scenario in wireless communication systems due to its fast time-varying channels and significant penetration loss. Thanks to its low cost and smart channel reconfiguration ability, the reconfigurable intelligent surface (RIS) has been proposed as a promising technology to solve the aforementioned challenges cost effectively and achieve high spectral and energy efficiency in the next-generation HST communication systems. In this article, we first provide a novel RIS-aided HST wireless communication paradigm, including its main challenges and application scenarios. Furthermore, practical solutions are provided to realize efficient signal processing and resource management in the considered system. Finally, promising research directions of RIS-aided HST communication systems are pointed out to inspire further investigation in future work.