Seamless Mobility Under a Dedicated Distributed Antenna System for High-Speed Rail Networks

High-speed railway (HSR) has demonstrated tremendous growth worldwide, and is currently attaining a maximum velocity of 575 km/h. Such a high speed makes mobile wireless communications extremely challenging for HSR since the handover (HO) rate increases with speed, resulting in a high call dropping probability. By employing a dedicated distributed antenna system (DAS) along with the two-hop network architecture, in this paper, we propose a frequency switch (FSW) scheme to mitigate the persistent HO issue in conventional HSR wireless communication systems. The proposed scheme significantly alleviates interruption time associated with the traditional HO process, providing an effective scheme when the train moves across small cells covered by remote antenna units (RAUs) belonging to the same central unit (CU). In order to further reduce the HO command failure probability, an enhanced fast predictive HO mechanism is proposed by starting the HO process in advance, when the train moves from one RAU to the next one controlled by the adjacent CU. Analytical results show that compared to the traditional HO scheme, the proposed schemes can improve the system performance substantially by delivering ultra-reliable low-latency communications with a reduced HO/FSW rate.