J. Marais

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

by J. Marais and Julie Beugin

Reliability Engineering & System Safety, 2015

ABSTRACT Evaluating dependability of complex systems requires the evolution of the system states ... more ABSTRACT 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 reparable 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 a 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 approach are demonstrated through a theoretical example of eFT and the practical use of the method is shown on a satellite-based railway system.

Land Mobile GNSS Availability and Multipath Evaluation Tool

by Marc Heddebaut, J. Marais, and M. Berbineau

IEEE Transactions on Vehicular Technology, 2005

System) in land transportation systems are already extensively deployed and will certainly contin... more System) in land transportation systems are already extensively deployed and will certainly continue to grow especially in the framework of Intelligent Transport Systems. However, one of the best-known drawbacks of such a system is the lack of satellite visibility in dense urban areas as well as in some specific embedded railway environments. This restricts considerably GNSS use for extended safety related applications. In this paper, a new tool is proposed to predict the availability of a satellite constellation from the point of view of the land transportation user. Knowing the trajectory of a land vehicle, the tool predicts the number of satellites which will be received and produces a safety criterion able to qualify the GNSS localization result. A first version of the tool, already in operation, merges an image processing approach providing the knowledge of the land environment, and the output of a satellite tracking program predicting satellite positions in the sky. This allows us to determine, using a simple optical approach, the number of satellites received in line-of-sight or blocked, with regard to the nearby environment of the receiving antenna. Results obtained in railway as well as in road environments show that satellite signals received by multipath are often used by GNSS receivers in the localization process. Thus, propagation characteristics of the satellite signals in an urban canyon configuration were characterized to determine when a signal received by multipath is used by the receiver or not. A criterion related to the satellite elevation is defined to improve the overall performance of the predictive tool. Comparisons with real measurements are commented on. Both simulations and measurements are very similar.

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Caractérisation et Structure 3D de l'environnement urbain pour une position GNSS plus précise

by J. Marais and Sebastien Ambellouis

ABSTRACT Cette communication est le second volet de la présentation des résultats obtenus dans le... more ABSTRACT Cette communication est le second volet de la présentation des résultats obtenus dans le cadre du projet CAPLOC dont les objectifs sont : de développer un système capable d&#39;extraire et de modéliser des connaissances sur l&#39;environnement traversé par le mobile à partir d&#39;une perception vidéo afin d&#39;inférer les caractéristiques du canal de propagation entre les satellites et l&#39;antenne du récepteur ; - de proposer des techniques d&#39;estimation plus précise de la position du mobile à partir de ces nouvelles connaissances.

Caractérisation et Structure 3D de l'environnement urbain pour une position GNSS plus précise

by J. Marais and Sebastien Ambellouis

ABSTRACT Cette communication est le second volet de la présentation des résultats obtenus dans le... more ABSTRACT Cette communication est le second volet de la présentation des résultats obtenus dans le cadre du projet CAPLOC dont les objectifs sont : de développer un système capable d&#39;extraire et de modéliser des connaissances sur l&#39;environnement traversé par le mobile à partir d&#39;une perception vidéo afin d&#39;inférer les caractéristiques du canal de propagation entre les satellites et l&#39;antenne du récepteur ; - de proposer des techniques d&#39;estimation plus précise de la position du mobile à partir de ces nouvelles connaissances.

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

by J. Marais and Julie Beugin

Reliability Engineering & System Safety, 2015

ABSTRACT Evaluating dependability of complex systems requires the evolution of the system states ... more ABSTRACT 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 reparable 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 a 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 approach are demonstrated through a theoretical example of eFT and the practical use of the method is shown on a satellite-based railway system.

Contribution to a Terminology Related to Dependability for the Qualification of an On-Board Satellite-Based System

by J. Marais and Julie Beugin

ICTIS 2013, 2013

Application des principes de la sûreté de fonctionnement à l'évaluation du service de localisation par satellites dans le domaine ferroviaire

by J. Marais and Julie Beugin

Recherche - Transports - Sécurité, 2008

Studies on DPM for the density estimation of pseudorange noises and evaluations on real data

IEEE/ION Position, Location and Navigation Symposium, 2010

GNSS localization is accurate in clear environment where the pseudorange noise distributions are ... more GNSS localization is accurate in clear environment where the pseudorange noise distributions are assumed white- Gaussian. But in constricted environment, e.g. dense urban environment, because of the signal reflections on the surrounding obstacles, this assumption cannot be used and accuracy and continuity of service of GNSS receivers are strongly degraded. To enhance the localization performances, we propose to use Dirichlet

Communiquer, Naviguer, Surveiller Dans Les Transports Terrestres: Recontre Des Doctorants Du Leost: Journbee Du 4 Fbevrier 2003 [Communication, Navigation and Control in Ground Transport: Proceedings of the Leost Laboratory Doctoral Students 2003 Workshop]

Simulating GNSS Position Accuracy using Non-line of Sight Reflected Signals

ABSTRACT This paper describes the development and use of a simulation tool, called QualiSIM. This... more ABSTRACT This paper describes the development and use of a simulation tool, called QualiSIM. This tool simulates GNSS-based position accuracy under various operational and environmental conditions, in particular in environments with large amounts of signal reflections. The signal reflections are implemented using the geometric path length the signal travels when it gets reflected from the surrounding buildings. Environmental influences on GNSS-based positioning are obstacles, such as buildings along streets which can lead to blocking and reflection of satellite signals. Examples of operational conditions are atmospheric effects and changes in the satellite geometry. The tool has been developed to work either with Galileo or GPS or with both satellite constellations. Since Galileo is only preoperational, the simulator is based on the nominal 27 satellite Galileo constellation. Further, the simulator uses: atmospheric models to simulate the effect on satellite signals through Earth’s atmosphere, designs of representative environments e.g. urban and rural scenarios, and a method to simulate reflection of satellite signals within the close environment of the GNSS (Global Navigation Satellite System) antenna. The simulator thus models: the signal path from satellite to receiver, satellite availability, the extended pseudoranges caused by signal reflection, and the position accuracy based on a least squares adjustment of the extended pseudoranges. In order to handle temporal and spatial variations of the different errors sources in GNSSbased positioning, the simulator has been developed for observing variations in position accuracy over time, along a given test trajectory, at different latitudes, and with different azimuths of the environment around the receiver. The environments used by the simulator could be typical representative scenarios such as, a narrow city street, a t-cross or mountain landscape. The choice of not using specific streets or cities has been made in order to keep the simulator open for every kind of environment. In this paper a simulation example is illustrated and shows the possibilities for visualisation of a narrow street with buildings on each side over a simulation time period of 24 hours. The impact of using reflected satellites in the position domain is significant. The DOP values are in general lower, but the error ellipses can be up to 8 times larger and furthermore deviate in shape.

Weighting models for GPS Pseudorange observations for land transportation in urban canyons

Use of image processing to assess GPS satellite availability along a railway line

Communiquer, Naviguer, Surveiller Dans Les Transports Terrestres

Quantify and improve GNSS quality of service in land transportation by using image processing

ABSTRACT Most of the Intelligent Transport Systems rely on GNSS positioning information. Unfortun... more ABSTRACT Most of the Intelligent Transport Systems rely on GNSS positioning information. Unfortunately, most of their uses occur in dense urban areas where signal propagation is degraded by surrounding obstacles because of the reception of NLOS (Non Line-Of-Sight) signals. Since the end of the 90’s, as a research institute concerned by transport applications, the LEOST team of IFSTTAR pursues research on the impact of the surroundings of a GNSS antenna on the receiver’s performances and in particular on NLOS cases when the direct path is not present or it is undetectable due to its low power compared to the rest of path. NLOS detection and mitigation remains an open research problem that can be studied from different angles: at signal processing level, at observable level and at PVT level. First works of LEOST have dealt to the development of a satellite availability prediction tool based on image processing already (PREDISSAT) for guided transport modes. Then, in collaboration with the Ecole Centrale of Lille, signal processing techniques have been developed to model the evolution of the satellite states of reception versus time and propose pseudo-range error models linked to the different states and in particular the NLOS case where reflected signal can be received without a direct ray. Recent activities are performed in the context of the CAPLOC research project. The main objective of CAPLOC, in collaboration with the Technical University of Belfort Montbéliard, is to provide an innovative tool for the positioning function, relying on satellite-based technologies, GPS and EGNOS, and mitigating the difficulties linked to the constricted environment of reception. In the same way than users of 3D models, our goal is to compare satellite positions to obstacles in order to detect satellite states of reception. Our approach relies on video records of the environments. This paper presents how the images sequences provided by several cameras installed on the roof of the vehicle allow characterizing GNSS performance and gives a quick overview of how they are used for accuracy enhancement in the CAPLOC project.

<title>A hybrid and adaptive segmentation method using color and texture information</title>

Image Processing: Machine Vision Applications III, 2010

This paper presents a new image segmentation method based on the combination of texture and color... more This paper presents a new image segmentation method based on the combination of texture and color informations. The method first computes the morphological color and texture gradients. The color gradient is analyzed taking into account the different color spaces. The texture gradient is computed using the luminance component of the HSL color space. The texture gradient procedure is achieved using

Localisation De Mobiles Terrestres Par Satellites. Mise en Œuvre D'Outils Permettant L'Analyse De L'Influence Des Conditions De Propagation et Des Effets De Masques Sur La Disponibilite Du Service Offert

GNSS Urban Localization Enhencement using Dirichlet Process Mixture Modelling

Satellite propagation path model along a railway track for GNSS applications

IEEE 60th Vehicular Technology Conference, 2004. VTC2004-Fall. 2004, 2004

The applications of GNSS (Global Navigation Satellite System) services are continuously growing i... more The applications of GNSS (Global Navigation Satellite System) services are continuously growing in the field of transport. However, the choice of the system for a given application is directly guided by its availability and the availability of most satellite-based localization processes of terrestrial mobiles is considerably degraded in transport environments because of significant masking effects. In these environments, the availability

Gnss performance enhancement in urban environment based on pseudo-range error model

2008 IEEE/ION Position, Location and Navigation Symposium, 2008

... Environment Based on Pseudo-range Error Model N. Viandier, DF Nahimana, J. Marais INRETS/LEOS... more

Advanced signal processing techniques for multipath mitigation in land transportation environment

13th International IEEE Conference on Intelligent Transportation Systems, 2010

GNSS (Global Navigation Satellite Systems) are today the core of all new ITS applications and req... more GNSS (Global Navigation Satellite Systems) are today the core of all new ITS applications and require increasing accuracy in particular in dense urban areas where complex localization scenarios become more and more frequent as the number of users evolves. In order to reduce inaccuracy caused by the obstacles around the receiver's antenna, a solution lies in developing new filtering algorithms. These algorithms will take into account both the variation of the noise distribution over time and the reception environment. This paper intends to be a synthesis of our investigations conducted both theoretically and experimentally since 2006. They have been performed by cooperation between Ecole Centrale of Lille and the INRETS-LEOST lab. Results show the achieved performances of each of the proposed algorithms.

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