Development and analysis of a Train-centric Distance Measurement System by means of Colored Petri Nets.
Dissertation, Technische Universität Braunschweig, Institut für Verkehrssicherheit und Automatisierungstechnik, 2018.
Based on the technology trends, the train control system should weaken the proportion of ground facilities, and give trains more individual initiative than in the past. As a result, the safety and flexibility of the train control system can be further improved. In this thesis, an enhanced movement authority system is proposed, which combines advantages of the train-centric communication with current movement authority mechanisms. To obtain the necessary train distance interval data, the onboard equipment and a new train-to-train distance measurement system (TTDMS) are applied as normal and backup strategies, respectively. While different location technologies have been used to collect data for trains, the development and validation of new systems remain challenges. In this thesis, formal approaches are presented for developing and verifying TTDMS. To assist the system development, the Colored Petri nets (CPNs) are used to formalize and evaluate the system structure and its behavior. Based on the CPN model, the system structure is validated. Additionally, a procedure is proposed to generate a Code Architecture from the formal model. The system performance is assessed in detection range and accuracy. Therefore both mathematical simulation and practical measurements validation are implemented. The results indicate that the system is feasible to carry out distance measurements both in metropolitan and railway lines, and the formal approaches are reusable to develop and verify other systems. As the target object, TTDMS is based on a spread-spectrum technology to accomplish distance measurement. The measurement is carried out by applying Time of Arrival (TOA) to calculate the distance between two trains, and requires no synchronized time source of transmission. It can calculate the time difference by using the autocorrelation of Pseudo Random Noise (PRN) code. Different from existing systems in air and maritime transport, this system does not require any other localization unit, except for communication architecture. To guarantee a system can operate as designed, it needs to be validated before its application. Only when system behaviors have been validated other relative performances' evaluations make sense. Based on the unambiguous definition of formal methods, TTDMS can be described much clearer by using formal methods instead of executable codes.