In high-speed railway communication (HSRC) systems, ensuring the continuity of on-going services is one of the toughest challenges, for the existence of influential factors such as frequent handoff event, short time window for handoff, and severe channel distortion, etc. In HSRC systems with limited resources, admission control (AC) is one of the most efficient methods to overcome this challenge and guarantee the requirement of service dropping probability (SDP). However, now it still lacks of recognized AC scheme that can be used in HSRC systems. In this paper, a novel AC scheme is proposed to HSRC systems, where resource reservation algorithm and resource preemption model are developed together to reduce the SDP.
First, the main reasons of on-going service dropping related to AC scheme are analyzed, which include frequent adjustment of services’ modulation-and-coding-scheme (MCS) and continual handoff events. Second, an adaptive resource reservation algorithm is proposed to optimize the amount of reserved bandwidth for ongoing services, where the effect of MCS change at physical-layer and the characteristics of HSRC are both taken into account. Third, considering the effect of resource preemption on on-going services, a resource preemption model is developed to further obtain the available bandwidth resources. Then, according to the above works, the AC scheme is proposed to optimize the SDP performance. Finally, simulation results are presented to demonstrate the effectiveness of the proposed AC scheme.