Research On Link Transmission Optimization Technology Of Lte System In High Speed Railway

High-speed railway transportation in China is growing rapidly due to its energy conservation, environmental protection, convenience, safety, reliability, and many other advantages. Railway wireless communication system is one of the key subsystems to high-speed railway construction. It is urgent for the system to upgrade in order to satisfy the new demands of broadband railway communication. International Union of Railways has recommended that current widely deployed GSM-R (GSM for Railway) should be evolved to LTE-R (LTE for Railway) smoothly. As a fourth generation mobile communication system standard, LTE system, which is with mature technology, has been deployed with a large-scale for commercial use. However, LTE system mainly aims at the traditional public cellular communication. It can’t satisfy the special requirements of high-speed railway communication systems directly.There are many special features in high-speed railway scene such as cell linear coverage, fast moving terminal, and rapid varying channel. All these may challenge the reliability of wireless link transmission. In addition, the train control information, which is carried by communication systems, requires extremely high reliability and safety. Therefore, the study of optimization techniques to improve the reliability of LTE link transmission, is of great significance for high-speed railway.In this thesis, optimization schemes are proposed for the LTE high-speed railway reliable link transmission system in two aspects. The one is adaptive modulation and coding, and the other is location management. The main research directions and contributions of this thesis are as follows:First, it is found that, the performance of the traditional link adaptive technology depends on the accuracy of the terminal feedback channel information, indirectly affected by channel estimation error and the terminal processing speed and other factors. The problems of LTE adaptive modulation and coding techniques in the high-speed railway scene are analyzed, and the quantitative assessment is made on the block error rate caused by the terminal CQI feedback delay. Moreover, an optimized adaptive modulation and coding scheme based on the radio environment map is proposed. Analysis and simulation results show that the proposed scheme can reduce false MCS judgment due to the feedback delay as well as the block error rate of system, meanwhile, improve the LTE link transmission reliability in high-speed railway scene.Second, mobility management function is the important foundation of cellular mobile communication system. It is necessary to design and optimize mobility management function for particular scene such as railway. LTE location management technologies and signaling flows are analyzed, It points out the inapplicability of traditional location management scheme under the railway chain network scenarios. For reducing the signaling congestion, a theoretical optimization model of tracking area update and paging signaling overhead is built, which provides the optimal probability distribution of tracking area list under particular paging-signaling threshold. The high-speed railway tracking area list scheme is proposed which could help to simplify location management function and improve system reliability.