Real-time Communication Techniques Of Train Communication Network Based On Switched Ethernet

As rail transportation technologies evolving towards convenience, comfortableness and intelligence, the control and diagnosis techniques become more and more advanced and train control data are also increasing fast in volume. Current train communication network solutions cannot meet the demand of fast increasing data transmission.Switched Ethernet, known for its high transmission rate, low cost and certainty, has become a potential solution of future train communication networks. The main prerequisite for Switched Ethernet being applied to train communication networks is the issue of improving the real-time performance, which is the main focus of this dissertation.The upper limit delays for WTB+MVB networks and Ethernet-based train communication networks specified in IEC61375has selected as the low-standard and high-standard criteria, respectively, in this dissertation. Based on the criteria, whether or not the maximum and average end-to-end delays satisfy the real-time requirement is evaluated.Focusing on the three main factors determining real-time performance, including topology, switch nodes and terminals, communication techniques to improve real-time performance and evaluation methods are discussed. The main research accomplishments include:1. Quantitative analysis of upper limit of delays and in-time reliability in train communication networks based on Switched Ethernet is conducted. First a train communication network topology with redundancy is designed according to specifications in IEC61375. Then the maximum end-to-end delay is verified to satisfy the low-standard delay criteria proposed in the dissertation. Through theoretical analysis and simulation experiments, practical methods to improve real-time performance satisfying high-standard delay criteria are proposed. At the end, the binary decision diagram based on edge expansion is proposed to analyze in-time reliability of the network. Through theoretical analysis and simulation experiments, the proposed network topology is proven to possess a high degree of in-time reliability.2. The optimal dispatching mapping from terminals to switches based on relative delay is researched. Firstly, the objective function of dispatching from train terminals to switches based on relative delay variance is proposed. Theoretical analysis and simulation results confirm that the objective function can reduce the transmission delay of equipment effectively. Then from the perspective of expanding search domains, further equipment dispatching improvement based on Hybrid Cross Genetic Algorithm, or HCGA, is proposed. The algorithm is confirmed to be able to speed up convergence rate, and improve both the best and the average fitness values.3. A two-tier queues scheduling algorithm for switch nodes is proposed. First, after using IEEE802.1P to map the three kinds of train data, i.e., real-time cycle data, real-time aperiodic data and non-real-time data, to three priority queues, the two-tier queues scheduling algorithm is proposed. The first tier of priority-timeframe scheduling scheme solves the problem of priority scheduling sequence while the second tier minimum deadline scheduling scheme applies minimum deadline priority scheduling scheme to data in every real-time queue. In this way, the transmission of real-time data is guaranteed to be interference-free from non-real-time data, while making sure that real-time cycle data and real-time aperiodic data may transmit at the same time and that real-time cycle data with a smaller deadline could be sent with higher priority. Based on the two-tier queues scheduling, this paper proposes to use G/D/1queuing theory to analyze average end-to-end delay and get the result that the average delay of the network satisfies the high-standard delay criteria.4. Two bandwidth allocation schemes based on time division multiple access (TDMA) are researched. First, the time division model based on data type is researched. An improved version of the Dijkstra algorithm is proposed to design the real-time cycle data scheduling table in Switched Ethernet. Simulation experiments confirm that this algorithm can lead to smaller delivery time of real-time cycle compared to the RM algorithm and scenarios where the link resources are restrained and avoiding traffic congestion in switches are taken into consideration of its implementation. And then an experimental network based on the RTNET protocol is established, confirming that the TDMA based bandwidth allocation scheme could achieve smaller network delay than Ethernet+TCP/IP protocols. The restrictions of this method and principles of time division are then summarized.5. An experiment platform for train network controlling based on Switched Ethernet is established. Through two of the main nodes in the network, i.e. the train electronic control system and the PIS-CCTV integrated control system, end-to-end delay experiment of vehicle-level and train-level data is conducted and network usages under different real-time performance criteria are given.. Finally, problems for further research are presented on the basis of summary and consideration of the dissertation.