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

High-speed railway (HSR) has demonstrated a tremendous growth worldwide, and currently is attaining a maximum velocity of 575 km/h. Such a high speed makes the mobile wireless communications a challenging task for HSR to sustain since the handover (HO) rate increases with speed which might result in a high loss of link connectivity. By employing a dedicated distributed antenna system (DAS) along with the two-hop network architecture for HSR wireless communications, this thesis aims to attain a high system capacity, a more transmission reliability, and consequently a superior mobile wireless communication quality-of-service (QoS) for commuters on HSR.

First, this thesis proposes a frequency switch (FSW) scheme to mitigate the persistent HO issue in conventional HSR wireless communication systems. The proposed scheme significantly alleviates the interruption time and the dense signalling overhead associated with the traditional HO process, providing a much more convenient scheme, i.e. fast and soft which suits the remote antenna unit (RAU) small coverage area and the train's high moving speed. Therefore, FSW scheme provides mobility robustness signalling process that guarantees a more successful frequency switch instead of HO, thereby, reduces the probability of a radio link failure (RLF) compared with HO process in traditional HSR systems.

Second, an enhanced fast predictive HO mechanism is proposed by starting the HO process earlier, when moving from one RAU coverage area to the next where these two RAUs are controlled by different central units (CUs). It shows that the proposed fast HO scheme achieves a lower HO command failure probability than the traditional HO. This leads to a lower HO failure probability which consequently can considerably enhance the end-users' quality-of-service (QoS) experience. Analytical results verify that the proposed schemes can improve the system performance substantially by delivering ultra-reliable low-latency communications.

Finally, with the aim of providing an ultra-reliable low-latency wireless communications, this thesis also proposes an onboard frequency switch scheme to further simplify our previously proposed FSW scheme.