Research On Scheduling Strategy And Real-time Performance Analysis Of Train Control Network

ABSTRACT:With the development of embedded technology and the field bus technology, modern train control system has developed from the direct centralized digital control system into a network-based distributed computer control system. When the fieldbus technology is introduced into the train control system, the system structure is simplified, reducing the cable connections, but as a result of the delays in communication and its uncertainty, it brings security and stability issues to the train control system. Therefore, it is important to study the real-time communication in network-based train control system.There are several kinds of train control network. According to the principles of classification of real-time scheduling, it can be divided into time-driven, the token type and priority-driven. The dissertation mainly researches on these three typical kinds of train control network, time-driven MVB network, the token type ARCNET network and priority-driven CAN network system,studies its methods and properties of real-time communication. The completion of the major innovative work and results obtained are as follows:1. The dissertation establishes the real-time communication information model, and analyzes the time-driven, the token-ring and the priority-driven principles of train control network, and provides the hierarchcal simulation models of the different media access control type train control network system.2. On the basis of analysis of different train control network system, the dissertation proposes that the real-time commucation scheduling layer can be added above data link layer. And gives two kinds of bandwidth allocation strategies: bandwidth reservation mode and bandwidth without reservation model. In the bandwidth reservation mode, general real-time scheduling algorithm can be used to scheduling the train control network communication. In the bandwidth without reservation mode, a special scheduling method for real-time communication in train control network is given.3. A method of reducing the size of schedule is researched. Typical periodic message scheduling algorithm uses LCM/HCF to determin the basic period and macro period in the generation of a typical periodic scheduling table. This involves great memorization problems when some periods are relatively prime. Then the dessetation researches on the theoretical conditions of reduction in the length of the periodic message scheduling table.4. On the bais of study of characteristic of static schedule algorithm and dynamic algorithm, the dissertation gives a novel timing scheduling algorithm. It can meet the flexibility commanding of schedule, and can reduce the run-time overload. In the train control network, there are two sorts of messages:real-time periodic and non-real-time sporadic. Real-time periodic messages are of crucial importance to train control network.Such as the control command and control decision-making needs of the device status information. It is easy to use an off-line static scheduler to manage it. This is full determinism and low run-time overhead. But it is operational inflexibility. The referred inflexibility is typical of static scheduling and its improvement calls the use of a different scheduler. One of the possible solutions is to use a dynamic scheduler that is constantly invoked to select the next message to be broadcast over the bus. In this case, it needs higher run-time overhead and an on-line schedul ability analyser to guarantee that all time constraints can be met. Based on the analysis of the performance of static and dynamic scheduling, it proposed the timing scheduler with mixed static/dynamic characteristics that allows achieving a reasonable compromise.5. Delay will be increase drastically when the concurrent events are increased using the typical event arbitration method. An optimized sporadic message arbitration algorithm based on event search is proposed. In the transport layer long non-periodic information will be divided into fixed-length packets for convenient transmission. So the message may be sent continuously during transmission. The typical event search altorithm did not consider this situation, so several times of event search is not needed. The proposed algorithm reduces the arbitration delay by memorying the search event.6. The bottom end-to-end communication delay of the different tain control networks in high speed trains is analyzed. On this basis, the influence factors of real-time performance are analyzed, respectively real-time scheduling algorithm, the amount of periodic and sporadic. It indicates that the proposed scheduling algorithm increasing the run-time overhead,but little effect on the end-to-end delay.when the periodic messages increases, the corresponding reduction in bandwidth of sporadic,it presents the curve of relationship between the different telegram increasing and the number of allowing concurrent events. When the sporadic bandwidth is constant, the sporadic arriving rate changed, the average arbitration delay is vary. It presents the relationship curve of average arbitration delay and arriving rate and the number of concurrent events.7. Train brake control system requires for high performance of real-time. On the study of train control network, it builds a train brake control network test and verification platform. It designes the emulation model of brake control unit, MVB interface module, ARCNET interface module and CAN interface module. It establishes a brake control subnet with CAN bus, vehicle network with MVB bus, train network with ARCNET. The run-time overload of proposed scheduling algorithm and the real-time performance is tested and analyzed in this platform.In the last part, on the basis of summary and analasis of the full dissertation,the dissertation points out the remaining problems that need of further study.