Topology Analysis Of WSNs In Monitoring Of High-speed Railways

In recent years, the high-speed trains and railways have been rapidly developed in our country, which brings great convenience and comfort for people’s travel. However, it’s worth noting that the safety of high-speed trains operating has gradually attracted people’s attention. Nowadays, the cable networks are still widely used to monitor environment of stations and high-speed trains operating. It is generally known that the monitoring systems based on the traditional wireline networks have some obvious disadvantages such as high cost, routing restrictions, bad scalability and flexibility. Thus the systems can hardly meet the demands that the scales of high-speed railways are rapidly growing. It is necessary for the railway industry to seek the monitoring networks with more efficience, lower cost and wider coverage, which is developing toward information, high-speed and safety.Wireless sensor networks are characterized by low-power, self-organization, and high reliability, which have become the newly developed industry and a research hot spot of general scholars today. Due to the particularity of the high-speed and operating environment of high-speed trains, the application of wireless sensor networks in monitoring of high-speed railways is rare or immature and the existing routing protocols of wireless sensor networks for monitoring of high-speed railways are seldom. The optimization problem of node deployment and topologies are investigated for the monitoring of high-speed railways based on wireless sensor networks in this thesis.For the selection of nodes type in the monitoring of high-speed railways based on wireless sensor networks, the thesis analyses specific factors of security threats to operating of high-speed trains and regards these threats as the main objects of wireless sensor networks monitoring. Considering the linear structure of nodes deployed along the railway, the deployment strategy is proposed by use of Lagrange multiplier method in the conditions that the length of monitoring area and the number of nodes are given, which aims at minimizing total energy consumption of nodes. Due to the higher requirements of high-speed trains for monitoring networks, the real-time, robustness and lifetime of linear wireless sensor networks based on a sink node are investigated in two typical topologies which are based on the minimum and maximum distance transmission. In the topology of maximum distance transmission, the thesis proposes a group-based data transmission mechanism. Results of theoretical analysis and relevant experiments show that the proposed mechanism brings better performances of real-time and robustness for the topology based on maximum distance transmission. In addition, changes in the spacing and number of nodes lead to different effects on the network lifetime of two topologies.Considering the actual demands of high-speed trains for the monitoring networks, the monitoring model based on multiple sink nodes is proposed, at the same time, the proposed model resolves the problem of unbalanced load of nodes in linear wireless sensor networks. For the practical deployment of nodes along railways, namely, only the length of monitoring area is given and the number of nodes is unknown, the deployment condition of nodes based on optimal spacing is derived in the thesis. The proposed strategy of deployment obtains the optimal network lifetime and total energy consumption and the desired results are verified by some relevant experiments.