Derivation of Dependability Targets for Train Born Localisation.
ROSAS Safety Days, September 2019 2019. ROSAS Safety Days.
With the availability of powerful satellite positioning systems, their use for train tracking in rail transportation is getting closer and closer while promising multiple benefits. For safety-related localisation tasks, their realization must meet several requirements, resulting as well from advanced operational behavior, as accuracy and from legal requirements as dependability including safety, security and availability. In this context the terminology of dependability properties will be outlined, also in order to be not confused by the different terminology of the aerospace and railway domains.
As railway operation must guarantee a certain safety level, e.g. as safe or better than actual transportation, safety design targets must be derived. For this purpose, special approaches have been applied, to fulfil safe operations for a lot of use cases for railway operational processes and tasks.
Since the availability of satellite signals in rail transport is not always guaranteed , e.g. due to shadowing in tunnels or stations, or subject to unwanted or intended disturbances, e.g. through multipath propagation or jamming and spoofing, a vehicle-based location can be achieved only in conjunction with other sensors and a map reference to provide a high level of dependability.
This results in a functional architecture of a redundant multi-sensor system in which the impermissible deviations can be detected by fault detections, but the parameterization of the thresholds are related to the required accuracy, safety and availability values. The analytical context and its quantification for fulfilling a given safety integrity level (SIL, THR) by the m-of-n redundancy concept of the multi-sensor configuration and the component parameter design will be presented. In addition, the necessary procedures for determining the required features and parameters of reliability (RAMS) as well as the accuracy of the satellite receiver are explained.