Research On The Wireless Train-ground Communication Of PIS In Urban Rail Transit Based On LTE

With the accelerated process of urbanization, people have higher requirements for the safety, efficiency and service of urban rail transit, which makes the operations management philosophy change from the vehicle-centric model to the passenger-centric model. As a guide system for providing information services for passengers,Passenger Information System(PIS) plays a key role in promoting the quality of service and operational level for urban rail transit. At present, WLAN technologies based on IEEE802.11 g standard has been used in the wireless train-ground communication of PIS. The technology has many shortcomings, such as frequent handoff, more interference sources, can not meet the needs of HD and so on. However, with the vigorous development of urban rail transit, the higher requirements have been put forward for the train-ground communication technology. In terms of rate, time delay and mobility, Long Term Evolution(LTE) as a quasi 4G technology which to achieve a smooth transition of 3G to 4G, it is able to meet the bi-directional demand of the wireless train-ground communication of PIS. LTE becomes the development direction of next generation wireless network for urban rail transit. The dissertation aims at the wireless train-ground communication of PIS in urban rail transit based on LTE, and elaborates the problems and solutions of the wireless train-ground communication of PIS based on this technology.Firstly, the network structure, protocol structure and key technologies of LTE are introduced and analyzed. Meanwhile, the feasibility and superiority of LTE in the train-ground communication of PIS has been verified by comparing the theory and simulation results based on IEEE 802.11 g with that of LTE. Then, the composition and function of PIS have been further researched, and the requirements and key technologies of the wireless train-ground communication of PIS in 4G environment have been analyzed. The system architecture and network security deployment plan of the wireless train-ground communication of PIS based on LTE in urban rail transit have also been introduced.Secondly, aiming to the existing problems of handoff under the network environment of LTE for urban rail transit, a handoff scheme of vehicle terminal control has been proposed. The advantage of the scheme in handoff delay is verified by theory analysis. Moreover, the handoff performance has been simulated including failure probability and outage probability.Finally, the performance of wireless link using the mechanism of Hybrid Automatic Repeat Quest(HARQ) has been researched. As for the overlap region between two cells, the existing mechanism of HARQ cannot fully ensure the reliability of wireless link with the increasingly deteriorated quality of wireless link. An improved scheme to enhance the reliability of wireless link based on train position information has been proposed. The simulation results show that the link quality of wireless communication system based on LTE can be improved effectively when using the mechanism of HARQ, and the proposed scheme has much more advantages in enhancing the reliability of wireless link in overlapped areas.