【作者】 杨柳；

【导师】 钟章队；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2016， 硕士

【摘要】 随着移动通信系统的发展,数字信号交换和传输的速率不断提高,时钟信号的频率偏差所产生的影响也越发明显,因此移动通信网络尤其是无线接入网对于时钟同步都有了更高的要求。我国铁路移动通信系统主要采用GSM-R (GSM for Railway)系统承载各类行车相关业务,由于GSM-R网络规模越来越大,网络在实际运行过程中时常会遇到由于时钟同步问题引发的故障和网络性能劣化,出现掉话、传输误码、切换失败等情况。然而时钟同步重要性在很长一段时间内并没有得到充分的认识,时钟同步技术的研究在铁路方面也不够深入和彻底。目前,铁路移动通信系统无线接入网的频偏分析大多集中在多普勒频移上,很少涉及到基站参考时钟频率偏差而引起移动台和基站上下行载波频率偏差的研究；时钟频率偏差对网络性能的影响也没有得到充分的验证,同时也缺乏完善有效的测试方法。针对以上这种情况,本论文的主要工作和具体贡献如下：(1)基于GSM-R网络各网元间时钟同步的实现方式,分析时钟信号从核心网传递至无线接入网过程中产生频率偏差的原因,研究时钟频偏对无线接入网性能和业务服务质量(Quality of Service, QoS)指标的影响。(2)基于参考时钟存在偏差的情况,分析频偏在无线接入网传递过程中各节点,包括基站时钟、上下行载波、多普勒频移的频率及相对频率偏差情况,并建立参考时钟频偏对各个节点频率及相对频率偏差影响的函数关系。(3)利用以上函数关系,针对GSM-R 900MHz系统,定量分析无线接入网中各节点由于参考时钟频偏造成的频率变化情况。(4)在实验室搭建实验环境,建立测试方案,通过向参考时钟添加频率偏差的方式测试频偏对GSM-R基站下行载波频率、电路交换数据业务(Circuit Switch Data, CSD) QoS以及切换成功率的影响。更多还原

【Abstract】 With the development of the mobile communication system, the digital signal is switched and transmitted at a higher rate. The effect of the frequency offset of the clock signal is more and more obvious. The mobile communication network, especially the radio access network, has a higher requirement for the clock synchronization.In China, GSM-R is mainly used in railway mobile communication system to carry all kinds of services related to train operation. As the scale of GSM-R network is getting larger, due to the fault and network performance degradation caused by clock synchronization problem, some occasions like call dropout, transmission error and switch failure often happen in the actual operation. However, in a long period of time, the importance of clock synchronization has not been fully recognized and the research on clock synchronization technology in the railway is not enough and thorough either.At present, the analysis of frequency offset in wireless access network for railway mobile communication system are mostly concentrated in the research of Doppler frequency shift, which rarely involves the uplink and downlink carrier, the Doppler frequency shift relative offset between MS and base station caused by the relative frequency offset of base station reference clock. The impact of clock frequency offset on the performance of the network has not been fully verified, and it also lack of effective testing methods. In view of the above situation, the main contributions of this paper are as follows:(1) Based on the realization of clock synchronization for radio access network, the factors of frequency deviation of clock signal which is transmitted from the core network to the radio access network are analyzed, and the effect of wireless access network performance and QoS parameters because of frequency deviation are researched.(2) When the reference clock frequency offset exists, the frequency and the relative frequency of base station clock, uplink and downlink carrier, and Doppler frequency shift are researched during frequency offset transmitted in the wireless access network. Meanwhile we also establish the functional relationship of relative frequency offset between reference clock and each node.(3) Using the function above, we quantitatively analyze the frequency variation due to the frequency offset of each node in the GSM-R 900MHz system.(4) The test environment is set up in the laboratory, and the influence of frequency offset for base station downlink carrier frequency, the QoS of CSD service are tested by adding frequency offset to the reference clock frequency.更多还原