Radio Resource And Mobility Management Of LTE-U In Urban Rail Transit System

In Communication Based Train Control(CBTC)systems,the information exchange between trains and wayside equipment is achieved through continuous bi-directional and large-capacity train-wayside wireless communication system to ensure accurate closed-loop control of the train.The train-wayside wireless communication system,as a subsystem of the CBTC systems,gives priority to CBTC signal services and carries various urban rail transit production services.Its performance would affect the safety and efficient operation of urban rail transit.In recent years,the LTE-based train-wayside wireless communication system,which is called the LTE-M system,provides communication services in the licensed band.However,the LTE-M system has limited spectrum resources,which can not meet the increasingly high throughput requirements of IMS(Image Monitoring System)service and PIS(Passenger Information System)service in urban rail transit system in the future.In order to solve the above problems,unlicensed spectrum resources are introduced to carry IMS and PIS services for urban rail transit in this thesis.LTE-U(LTE in Unlicensed),as a complementary technology to LTE,aggregates licensed and unlicensed spectrum radio resources.Therefore,the application of LTE-U system takes the advantage of the licensed band,while the usage of unlicensed spectrum resource of LTE-U can effectively alleviate the pressure of spectrum resource shortage.The application of LTE-U in urban rail transit train-wayside wireless communication system and its radio resource scheduling and mobility management algorithms are studied in this paper.The work of the thesis can be summarized as follows:(1)The special wireless communication environments between the train and wayside as well as the channel models in urban rail train-wayside communication system are introduced.The network structure of LTE-U train-wayside communication system is proposed,and the signaling processes are designed for the radio resource and mobility management in LTE-U system.(2)Due to the fact that the main working users of the unlicensed band are WLAN users,the coexistence mechanism of the LTE and WLAN systems in the unlicensed band is studied.Combined with the service characteristics of the urban rail transit system,a coexistence scenario of LTE-U train-wayside wireless communication and WLAN system in the unlicensed band is presented.In this paper,the ABS(Almost-Blank Subframes)collaboration strategy of the time domain sharing strategy is used to configure a certain number of blank subframes,where the LTE system is kept in silenced state and WLAN will transmit data in these blank subframes.(3)Considering the rapidly time-varying urban rail transit wireless communication environment and the coexistence of heterogeneous networks,in order to improve the satisfaction of users in the unlicensed band,a dynamic resource allocation algorithm based on Q-learning in the the operation scenarios of single and multi-train is proposed.Finally,the algorithm is compared with other static resource algorithms and coexistence methods through simulation experiments.The results show that the algorithm can improve the overall performance of users in the unlicensed band.(4)Considering the small coverage of the LTE-U system unlicensed band base station,the train will handover between cells frequently.Handover algorithm with CoMP based unlicensed bands is proposed.Then the influence of the algorithm on the performance index of the communication system is analyzed.Finally,the simulation results prove that the communication performance of the handover algorithm is better than the traditional handover algorithm.