I. Introduction
With the rapid development of the High-Speed Railway (HSR) all over the world, HSR is becoming one of the dominant ways for people to travel. For example, the business mileage of HSR in China already reached 29,000 km by the end of 2018, and is expected to increase 8.06% every year [1]. With more and more people traveling via HSR, the amount of time they will spend on trips indicates a huge demand for network services.