摘要
基于时分-长期演进(Time Division-Long Term Evolution,TD-LTE)的高速铁路宽带无线通信系统可以提供语音通信、数据通信、互联网业务、公共信息查询和列车视频图像监控业务。由于高铁列车运行速度比较快,当列车时速达到350公里/小时,10公里的基站间距,用户终端(User Equipment,UE)从一个基站移动到另外一个基站的时间在100秒左右,导致每100秒将发生一次切换,小区的频繁切换容易引起网络连接的断开和掉话,导致网络的性能下降。
论文介绍高速铁路时分-长期演进(TD-LTE)系统切换算法的研究,主要工作包括以下四部分：
第一部分研究时分-长期演进(TD-LTE)系统物理层参考信号接收功率(Reference Signal Received Power,RSRP)和参考信号接收质量(Reference Signal Received Quality,RSRQ)的测量。首先研究了时分-长期演进(TD-LTE)系统的参考信号的产生,其次介绍时分-长期演进(TD-LTE)系统物理层仿真链路平台搭建,分析仿真链路平台中一些模块算法实现的瓶颈；再次通过参考信号接收功率(RSRP)和参考信号接收质量(RSRQ)测量算法的介绍来说明链路仿真是如何实现参考信号接收功率(RSRP)和参考信号接收质量(RSRQ)的测量；最后通过MATLAB物理层链路级仿真平台对比不同测量带宽和用户终端(UE)的移动速度对参考信号接收功率(RSRP)和参考信号接收质量(RSRQ)测量结果的影响。
第二部分研究基于高速铁路环境的时分-长期演进(TD-LTE)系统A3事件触发切换算法的优化。通过对常规的A3事件切换判决准则的研究,提供了两种基于用户终端(UE)速度的A3事件触发切换判决准则的优化算法。然后,介绍时分-长期演进(TD-LTE)系统级仿真平台的搭建,最后,系统级仿真证明提出的两种优化的切换算法有效提高了切换成功率。
第三部分研究高速铁路环境基于地理位置信息的时分-长期演进(TD-LTE)系统切换算法和基于目标小区预承载的时分-长期演进(TD-LTE)系统切换算法。分析了常规的基于A3事件触发切换判决准则的不足,提出了一种基于用户终端(UE)地理位置的切换判决算法方法和一种基于目标小区预承载的切换判决算法。这两种算法能够改进系统切换性能,减少无线链路失效(RLF)的发生概率,同时消除乒乓切换(PPHO)的发生。并且对长期演进(TD-LTE)系统的信令流程图进行了优化。系统级仿真证明这两种技术方案能够明显提高切换成功率,并且可以缩小切换带的覆盖长度,有利于降低小区边缘的信号干扰,提高信号传输质量。
第四部分研究高速铁路环境时分-长期演进(TD-LTE)系统的软切换算法。总结前面几种硬切换机制的缺陷,针对高速铁路时分-长期演进(TD-LTE)系统专网的特点,提出时分-长期演进(TD-LTE)系统的软切换算法。并且重新设计了支持软切换算法的长期演进(TD-LTE)系统的信令流程图。系统级仿真结果证明该算法可以较好地解决切换过程的掉话、断路现象,降低切换失败率。
Broadband wireless communication system based on TD-LTE (Time Division-Long Term Evolution) system in high-speed railway can significantly provide the voice communication, data communication, internet traffic, public information inquiry and train video monitoring traffic. The velocity of train is350km/h and the distance is10kilometers between the two cells. The high-speed train runs so fast that the user equipment (UE) will take about100seconds to pass from one cell to the neighboring cell, which leads to handover in the period of almost every100minutes. Thus will cause serious wireless communication network disconnection and call drops and result in the decline of the network performance at the same time.
This thesis focuses on the research about the handover algorithm of TD-LTE system in high-speed railway environment, which is composed of four parts, it is as follows:
The first part of the thesis concentrates on the research about the measurement of TD-LTE physics layer Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ). Firstly, the generation of reference signal is studied for TD-LTE system. Secondly, the establishment of physics layer link level simulation platform is introduced for TD-LTE system and the bottle-neck of some modules algorithms feasibility is analyzed in the link level simulation platform. The thirdly, the simulation platform measures RSRP and RSRQ is introduced by the measurement algorithm of RSRP and RSRQ. At last, the measurement results of RSRP and RSRQ are analyzed under the different measurement bandwidth and the velocity of the user equipment (UE) via the simulation platform of the physics layer developed by MATLAB software.
The second part of the thesis describes the research on the optimization of event A3triggering handover algorithm based on TD-LTE system in high-speed railway scenario. Firstly, the analysis are represented about two kinds of event A3handover judgment criteria based on the velocity of the UE, which is compared to common event A3handover judgment criteria. Then the establishment of TD-LTE system level simulation platform is introduced. At last the simulation result shows the feasibility of two kinds of optimized handover algorithms, which improve handover success rate significantly.
The third part of the thesis mainly focuses on two kinds of handover algorithms of TD-LTE system based on GPS information and pre-bearer procedure of target eNodeB in high-speed railway scenario. Aiming at the deficiency of the common event A3handover judgment criteria mechanism, two kinds of novel handover judgment algorithms based on position information of the UE and pre-bearer mechanism of target eNodeB is proposed. These algorithms could improve system handover performance and reduce the possibility of Radio Link Failure (RLF) and eliminate the deficiency of Ping-Pong Handover (PPHO) at the same time. And the signalling flow chart of TD-LTE system has been optimized. System level simulation results represents both handover algorithms could greatly improve the success rate of handover and shorten the coverage of handover area while system level simulation demonstrates that in overcoming inter-cell interference and improving signal transmission quality, both algorithms are also proved to be effective.
The fourth part of the thesis mainly studies Soft Handover (SHO) algorithm of TD-LTE system under the high-speed railway scenario. Summarizing the aforementioned the deficiencys of several Hard Handover (HHO)-mechanisms, a SHO algorithm of TD-LTE system is proposed according to the characteristics of high-speed railway special network of TD-LTE. Moreover the signalling flow chart of TD-LTE system has been redesigned to support the soft handover of TD-LTE system.The system level simulation demonstrates that this algorithm could solve the deficiencies of call drop and communication interrupt better during the whole handover procedure and reduce handover failure rate.
引文
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