Julie Beugin

Method for evaluating an extended Fault Tree to analyse the dependability of complex systems: Application to a satellite-based railway system

Evaluating dependability of complex systems requires the evolution of the system states over time to be analysed. The problem is to develop modelling approaches that take adequately the evolution of the different operating and failed states of the system components into account. The Fault Tree (FT) is a well-known method that efficiently analyse the failure causes of a system and serves for reliability and availability evaluations. As FT is not adapted to dynamic systems with repairable multi-state components, extensions of FT (eFT) have been developed. However efficient quantitative evaluation processes of eFT are missing. Petri nets have the advantage of allowing such evaluation but their construction is difficult to manage and their simulation performances are unsatisfactory. Therefore, we propose in this paper a new powerful process to analyse quantitatively eFT. This is based on the use of PN method, which relies on the failed states highlighted by the eFT, combined with a new analytical modelling approach for critical events that depend on time duration. The performances of the new process are demonstrated through a theoretical example of eFT and the practical use of the method is shown on a satellite-based railway system.

Modelling Communication Based Train Control System for Dependability Analysis of the LTE Communication Network in Train Control Application

The Communication Based Train Control (CBTC) systems today has generated immense interest in transport domain because of its ability to enhance safety and improve operational effectiveness. The current communication solutions for urban guided transport system that is based on the Wireless local area network (WLAN) becomes obsolete with a number of shortcomings in term of capacity and capability. Hence, the Long Term Evolution (LTE) is considered as a new solution for railway communication technology. Before widely deploying this new solution in railway industry, it must be evaluated and tested to ensure the desired performance level for CBTC system according to the railway safety standards. Therefore, it is necessary to propose a model of CBTC system that allows to consider the behaviours of the LTE communication network in real time. In this paper, we propose to use Petri nets for modelling CBTC system based on a LTE architecture. Using this model, preliminary dependability analysis for the data communication system based on the LTE technology is then performed.

Dependability evaluation of a GNSS and ECS based localisation unit for railway vehicles

Today, GNSS-based solutions (Global Navigation Satellite Systems) facilitate the implementation of the train localisation function on-board the vehicle. In the railway context, as a train has to travel different zones on its itinerary, multiple obstacles in these environments can cause different signal perturbations: multipaths, signal delays and masking phenomena that lead to negative consequences on the position accuracy. To reinforce the position quality, a localisation system, developed in the GaLoROI european Project and based on the combination of sensors such as a GNSS receiver and an Eddy Current Sensor, is studied. In this paper, we present a procedure and a model, which aims at evaluating the dependability of this system under local impacts of different railway environments. It allows us analysing complex behaviours of the sensor fusion component on the availability and accuracy of data provided by GNSS & ECS sub-systems and also to take into account the reliability parameters of hardware components.

Analytical approach for evaluating LTE communication errors in train control application

The current communication solutions train control application that is based on WLAN or GSM-R becomes obsolete with a number of shortcomings in term of capacity and capability. Hence, deploying a new dependability vehicular communication is recommended. In this context, the Long Term Evolution (LTE) technology is considered as a new solution for railway communication because of its ability to support multi-service traffic (voice, video, data). Before widely deploying this new solution in railway industry, it must be evaluated and tested to ensure the desired performance level for train control system (TCS) according to the railway safety standards. In order to overcome the high time execution and low accuracy of statistical evaluation for small probabilities, the analytical treatment is a a complementary approach to the simulation approach. Therefore, it is necessary to propose a new analytical approach for analysing and evaluating the communication error types of the LTE based TCS. It is also the goal of this paper. The results presented in the framework of this paper are prerequisites for the dependability analysis of the advanced TCS based on the LTE technology in further works.

Sensitivity assessment to analyse dependability of a multisensor localisation system based on GNSS

This paper proposes to use sensibility measures to analyse the dependability and safety of railway localisation systems based on GNSS. In such systems, train positions are determined by combining all available sources of localisation information. However, each source of data suffers from specific errors, which are inherent to the nature of the sensors and, which are difficult to manage with common dependability methods. The proposed evaluation method based on a sensitivity analysis aims at showing the influence of the variability of sensor parameters on the RAMS (Reliability, Availability, Maintainability and Safety) attributes. This implies (i) to identify characteristics of the different sensors that compose the system like features, behaviour and error model, and (ii) to make assumptions about the nature of position error on the output system (continuity, differentiability, etc...). This paper proposes a sensitivity computation method and interpretations related to a train positioning system. This can constitute a new approach in dependability analysis in GNSS-based systems with a low or nonexistent feedback.

Contribution to a terminology related to dependability for the qualification of an on-board satellite-based system

This paper aims at presenting the research work regarding the formalization of dependability-related localization attributes within the framework of the European project QualiSaR. The processing of natural language is used with the aim of creating a structure of dependability and safety-related terms for evaluating automated systems in general and satellite positioning performances more specifically. The attribute hierarchy developed is managed by the help of iglos, an NLP tool (Natural Language Processing). The standardization objective of this research work consists of making a proposal for an international standard, which describes satellite-based system quality criteria that is understandable by transportation communities.