I. Introduction
With the popularity of applications in high-speed railways and highways, high-mobility environments attract great attention in the fifth generation (5 G) and beyond mobile communications, leading to many new challenges, such as fast time-varying channels, frequent handovers, and complex channel environments [1]. At the same time, it is an important ability of 5G and beyond networks to efficiently support ultra-reliable and low-latency communication (URLLC) services for autonomous driving and vehicle-to-everything (V2X) scenarios [2]. Providing stable, reliable, and fast data transmission service is also a crucial target in high-mobility wireless communications. As a most important component in achieving the above targets [3], dynamic multi-channel access (DMCA), should be greatly improved [4], since it can also effectively promote system throughputs [5].