【作者】 杨崇哲；

【导师】 方旭明；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2011， 硕士

【摘要】 高速铁路的发展对地面高速移动环境下车地无线通信系统提出了更高的要求。受到理论和技术限制,现有的车地无线通信技术均无法解决未来350km/h以上高速列车中旅客的宽带移动通信需求。高速移动场景下的车地无线通信网络面临着频繁的越区切换、多普勒频移、信道快速变化等一系列的技术问题。本文主要解决其中的频繁越区切换问题。在高速铁路场景下,越区切换的成功率对行车安全有着至关重要的影响。对高速列车的越区切换而言,要求更短的切换时间和更高的切换成功率,以保证系统的可靠性和有效性,但现有的系统中较难实现。要解决高速铁路中越区切换的问题,关键是设计支持高移动性的切换机制,以减小切换的复杂度,从而提高切换成功率。本文分别采用分布式无线通信系统和中继站技术为高速移动环境下车地无线通信提出了相应的解决方案。主要的研究内容和贡献如下：第一,未来的无线通信网络结构趋向于Internet一样的网状结构,而不再是传统的分层树型结构,Mesh、Relay等现有分布式无线通信技术逐渐成为了未来无线通信技术的重要支撑。这类系统的特点在于利用大量的分布式天线单元在整个系统内提供高质量的、无缝的无线电信号覆盖。一方面通过合理地选择天线单元为不同的用户提供覆盖,并获得空间分集,提高系统容量以及用户的通信质量；另一方面通过采用灵活的切换方式,为移动用户提供可靠的高质量的通信链路。本文所设计的方案利用分布式无线通信系统为高速铁路提供无缝的无线电信号覆盖,利用多车载台通信系统设计了多车载台协作小区切换方法,以解决高速移动中越区切换的问题,减小切换的复杂度,提高切换的成功率。分析和仿真结果表明,该方案能够合适的提前切换,保证列车有足够的时间完成切换,从而提高切换成功率,并使系统容量提升50%。第二,目前我国所采用的高速铁路车地无线通信系统为GSM-R,并非分布式无线通信系统。因此本文基于分布式无线通信技术提出了一种共享中继辅助的切换机制以改善现有GSM-R系统的切换质量。该机制中共享中继可以改善相邻基站重叠区内来自目标基站信号的质量,减少由于信号波动导致的切换误判。分析和仿真结果表明,该机制将列车的切换的触发地点提前约500m,从而保证列车在重叠区内有足够的距离完成切换,并且由于信号质量的改善,减少了乒乓效应,将切换失败概率降低到了10-6,从而提高了切换成功率。更多还原

【Abstract】 In cellular wireless communication system, some problems are caused by users’ high-speed movement, such as over-frequent handover, Doppler frequency shift, and channel fast variation. For the wireless communication of high-speed railway, handover success rate critically impacts on the traffic safety. In order to ensure the system robustness and effectiveness, it requires shorter handover time and higher handover success rate, which cannot be achieved by the most current wireless communication systems. Therefore it has important significance to design new handover scheme to meet demand of the high-speed railway communication.Distributed wireless communication system and relay technology have been mainly studied in this thesis for high-speed railway communication. The author’s main research work and contributions are as follows:Firstly, distributed antenna technology, as one of the important next-generation wireless communication technologies, has aroused extensive attention. The technology has been applied in high-speed movement environment. Such system is characterized by using a large number of distributed antenna units along the railway to provide high-quality, seamless coverage of radio signals. On the one hand, different trains choose different antenna units to get access. The spatial diversity improves system capacity and Quality of Service (QoS). On the other hand, mobile trains take flexible handover manner to ensure reliable high-quality communications link when they move across two adjacent cells. This thesis proposes a novel handover scheme based on on-vehicle dual-antenna for high-speed railway distributed antenna system (DAS). On-board antennas which collaborate each other, are mounted on the top of high-speed train (the one is at the front-end and the other is at the rear-end). The proposed scheme utilizes distributed transceivers and centralized processing technology. The numerical analysis and simulation results show that the novel scheme can pre-trigger handover appropriately, guarantee the higher handover success rate, and increase the system throughput by around 50%. In addition, the scheme is feasible and easy to be implemented.Thirdly, at present, the wireless communication system for high-speed rail is GSM-R (GSM for Railway) system in China. This thesis proposes an enhanced handover scheme with shared-RS (shared-Relay Station) in GSM-R network to improve system handover performance. In the scheme, shared-RS improves the target BS signal quality in overlapping region, and the handover can be triggered in advance so that there is much longer distance for completing handover process when the train is traversing through the overlapping region. The analysis and simulation results show that the scheme can trigger handover appropriately in advance about 500m, eliminate ping-pong effect, reduce handover failure probability to 10-6, and thereby guarantee the higher successful handover probability.更多还原