The Study Of Mission Critical Communication Mechanism In The Scenario Of LTE-R

As a key enabling infrastructure in railway operation,mobile communication system guarantees the operational safety of railway.Voice dispatching service is of vital importance in the railway mobile communication system.In the current GSM-R system,voice dispatching service is built on the basis of the circuit domain of the network.With the rapid development of communication technology and the emerging new services in railway mobile communication,railway mobile communication system is undergoing a tremendous evolution from GSM-R towards LTE-R.Implementing the voice dispatch service in the full IP LTE system has become the focus of research in the industrialization and standardization of LTE-R.Taking into consideration the actual needs of railway trunking system,my paper is to propose an MCPTT implementation scheme for LTE-R based on the MCPTT mechanism for mission-critical communication tasks in public security area defined in 3GPP protocol.In this context,following aspects are studied in this paper.First,the technical principles,functional architecture and related communication protocols of the MCPTT mechanism are analyzed in depth.The detailed explanation for functional entities in the user layer and signaling control layer is given.Related protocols and interfaces are introduced.Having reviewed the principles of MCPTT for mission-critical communication,this paper proposes an MCPTT architecture for LTE-R according to the actual need of railway services.Procedures as well as their signaling realizations are designed for key functions including private call,group call and forced releasing.Original implementation approaches for location-based group call function,multi-priority and forced releasing function are put forward in this paper for the first time.For functions that are already defined by 3 GPP like private call setup and group call quitting,existing schemes are optimized to adapt to railway services.Based on MCPTT architecture,an LTE-R wagon-borne mobile terminal is designed and developed for voice dispatching service.Procedures and message fields are defined for different functions of call control module in LTE-R wagon-borne mobile terminal,including authentication,authorization,system configurations acquisition,private call,group call and location reporting.Finally,MCPTT server and SIP core are implemented in the LTE hardware platform of IRICT laboratory of Beijing Jiaotong University.Wired dispatching system FAS is then connected to the MCPTT server.MCPTT-based voice dispatching service is tested and verified on the platform.Experiments results proved the full functionality of call control module in LTE-R wagon-borne mobile terminal,as well as the feasibility of LTE-R voice dispatching service using MCPTT.