| The mobile communication system is one of the key infrastructures of the railway.It carries tasks such as railway dispatching command,train operation control,fault warning,danger notice,and emergency rescue.At present,the evolution of GSM-R to the next-generation mobile communication system of railway LTE-R is on the upward trend,aiming at making full use of the advantages of large bandwidth,high data rate and low transmission delay for the development of railway mobile Internet,Internet of Things and smart railway.This will realize broadband,software-definable ubiquitous coverage of IP-based mobile communication networks,and carry various services such as voice call,instant data,images transmission,video session,and control information delivery in order to further ensure railway transportation security,improve operational efficiency,and service quality.Therefore,the well-defined LTE-R system architecture and the design of the railway-specific communication service scheme are inevitable.To reach this goal,this article has done the following work:Firstly,by researching on the 3GPP LTE,IMS,MCx series protocols,the MCx-based LTE-R basic logic architecture and protocol architecture scheme can be proposed in accordance to the LTE-R system and functional requirements specifications with the referenccce to the public network LTE architecture and business model.Details of its requirements,functions,and protocol reference points will be explained.After that,we focus on solving three key issues in the implementation of railway-specific communication services of LTE-R.Firstly,by studying on the LTE-R service scenarios and requirements,the group call service function is realized based on the GSM-R existing services and the 3GPP-defined services,and its procedure is designed using the timing diagram and the SDL diagram.Meanwhile the problem of priority of business applications in LTE-R is optimized,and the member-based and location-based group call schemes are proposed and realized using structured programming diagrams.Then,in order to implement LTE-R service,the design of the LTE-R numbering plan is necessary to solve the routing problem of the service,with the sufficiency and backward compatibility of the numbering resources guaranteed.Finally,through the analysis of networking architecture of the LTE-R application layer and related service roaming strategy,the service registration and routing scheme in the roaming scenario are designed to provide theoretical support for the global implementation of the service,which will be especially adopted in the train movements along multiple bureaus.Finally,the development and implementation of the server-side group call service module are carried out based on the design of the LTE-R architecture and services.In order to complete the function of the group call,the group call release,the floor control,and the location reporting in accordance with the user,the device,and the service configuration in the LTE-R numbering plan,architecture design and process signaling definition of the service module are completed.At the same time,based on the LTE-R system and functional requirements,the function and performance evaluation system of the application is proposed.The system architecture,service procedure,numbering plan,and system function and performance are tested in the test environment of the LTE-R Beijing-Shenyang section.The test results verify the consistency between the realization of MCx services and the LTE-R functional requirements.The system architecture and the performance of the call establishment delay,end-to-end voice transmission delay,and voice preemption delay are evaluated to confirm the effectiveness of the system design. |
