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

Abstract

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 the low cost and smart channel reconfiguration ability, reconfigurable intelligent surface (RIS) has been proposed as a promising technology to solve the aforementioned challenges costeffectively and to 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. Then, we propose practical solutions are provided to realize efficient signal processing and resource management in the considered system. Finally, future directions of RIS-aided HST communication systems are pointed out to inspire further investigation in future work.

Two-Stage Multiarmed Bandit for Reconfigurable Intelligent Surface Aided Millimeter Wave Communications

“…Lately, RIS has drawn much consideration as an up-and-coming technology that can suit future wireless systems demands [ 18 ], i.e., 6G and beyond. Hence, RIS has promoted wireless applications such as RIS-aided wireless power transfer [ 19 ], RIS-aided mobile edge computing [ 20 ], RIS-aided physical layer security [ 21 , 22 ], RIS-aided UAV communications [ 23 , 24 ], and mobility and handover management for RIS-aided wireless communications in high-speed trains [ 25 ].…”

Physical Layer Enhancement for Next-Generation Railway Communication Systems

“…In [112], a twotime scale channel estimation framework was proposed to separately estimate the quasi-static BS-RIS channel on a larger time scale and the fast-varying RIS-UE/BS-UE channel on a shorter time scale. It is also mentioned in [113] that prior information such as location, direction, velocity and geometry information such as angles of departure (AoD) and angles of arrival (AoA) can be obtained from an external location information system, such as a global navigation satellite system (GNSS). Such information can be used to decrease the channel estimation complexity and reduce the training overhead.…”

“…In the HST scenario, based on statistical CSI, [129] proposed an IRS-assisted communication system model to relieve blockage issues in terms of the outage probability. In [113], [121], applying RIS for coverage extension, frequent handover reduction, blockage, and dead zone suppression in HST scenarios was thoroughly investigated. Two types of RIS deployments have been discussed: i) RIS deployed on one side of the rail track, for example, on a roadside advertising board as a reflective panel [113], [129].…”

“…In [113], [121], applying RIS for coverage extension, frequent handover reduction, blockage, and dead zone suppression in HST scenarios was thoroughly investigated. Two types of RIS deployments have been discussed: i) RIS deployed on one side of the rail track, for example, on a roadside advertising board as a reflective panel [113], [129]. ii) RIS deployed on top of train carriages.…”

“…As a result, when combined with RIS, distinct polarization states can be applied for signal refraction enhancement under different propagation circumstances and this technology seems to be promising when combined with polarization diversity transmission. An RIS deployment attached to the external surface of a train window to promote signal refraction was proposed in [113], [121]. If the RIS is active and dynamically configurable, additional beamforming can be applied to serve the UEs located at different positions inside the train.…”