Study On Theory And Methods For Real-Time Of The Train Communication Network

With the rapid technical development of computer communication and network, intelligent computer, embedded microelectronics, fieldbus and fault diagnosis, the modern train control system has been developed from the central digital control system to distributed computer system which is based on networked control system on board. The train networked control system which is a typical real-time distributed control system can interconnect all the intelligent applications and special smart devices with various fieldbus technologies so as to exchange information and share the resource. TCN (train communication network) is the special network used within the control system. To be a standard platform for exchange information, IEC defined an international network specification named IEC61375-1 which comprises MVB(Multifunction Vehicle Bus) and WTB(Wired Train Bus). WTB is a kind of standard communication bus which was defined in TCN to connect vehicles in a train, while MVB is another kind of standard bus designed for interconnection equipment within a vehicle or within different vehicles in closed train sets. The use of TCN technology not only simplifies the structure of train networked control system but also achieves the real distributed train control by making complex control functions down to the different level.As an industrial control network in essence, train communication network can also be used as a specific fieldbus in train control application compared with the general communication network. From the view point of typical real-time distributed control network, real-time characteristic is very important for train communication network, which affects the performance of whole train control system. So many key problems relevant to the real time characteristic of train communication network are worth studying. It is expected that the modeling and analyzing of the real time communication scheduling as well as the real time characteristic will be achieved, and these results will provide some useful guidance for application.At the beginning of the dissertation, phytogeny of train communication network and its research status are presented, and existent real-time problem of train communication network is also indicated. In the body of the dissertation, on analyzing the real time scheduling theory and methods of fieldbus, the real time problem of train communication network is researched. The m ajor contributions in the dissertation can be described as follows:Real-time schedule process is one of the most important thing in the train communication network. As for the real-time schedule of periodic messages, it is the key problem that how to model for the communication process and which kind of real-time schedule time table could be set up. From the point of analyzing the basic communication scheduling mechanisms, the real-time schedule mechanism of MVB and WTB are further researched respectively. Firstly, the algorithms for constructing the real-time schedule table of MVB and WTB are introduced according to the characteristics of the periodic messages traffic. Secondly, the algorithm schedulability of periodic messages is proposed and the condition judging the validity of the schedule time table built is also given by analyzing the worst-case response time. Finally, the algorithms and methods proposed in this dissertation are validated by some programs, and the validity of the model built is showed by the example of application.The communication scheduling mechanism of sporadic messages and its response time characteristic can affect the real-time performance of train communication network. Based on quite different sporadic messages scheduling mechanism, the arbitration scheme based collision can be used to transfer MVB messages whereas WTB adopts the method of polling. The response time characteristic of sporadic communication on MVB and WTB is analyzed, and consequently the computation method to the worst-case response time is introduced. Moreover, the algorithms proposed in this dissertation are validated by some examples of application, and the validity about the response time of the sporadic messages is evaluated.To analyze the network performance is a basis for improvement and optimization of the network performance, and can be guaranteed to provide stable quality of network service. The method to calculate the real-time performance and other average characteristic parameters is introduced, and simulation based on these parameters is also made. The modeling and analysis of the average transmission delay are studied especially with queue by example of MVB. Then the methods to compute the average network performance such as utilization, transmission efficiency and throughput of train communication network are particularly studied. The validity of the model is validated by simulation. The simulation results point out the key cause which affects the train communication network performance, and it provides a good guidance for optimization the network performance.On analyzing the scheduling mechanism and whole performance of the train communication network, there are many problems which is relating to the improvement and optimization of the real time performance of train communication network are worth studying. To guarantee the real-time requirement of all messages, the constraint between the individual period and maximal logical ports of the sporadic messages is put forward. Then the SFS method based on process data slave frame stuffing is proposed, which improves the real-time performance of urgent sporadicmessages in train communication network.Finally, the future research works are discussed.