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Methods and Tools for the Certification of GALILEO Localisation for Railway Applications

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Methods and Tools for the Certification of GALILEO Localisation for Railway Applications Methods and Tools for the Certification of GALILEO Localisation for Railway Applications Jan Poliak1, Juliette Marais2, Frank Hänsel1, Uwe Becker1, Eckehard Schnieder1 1Institute for Traffic Safety and Automation Engineering (iVA), Technical University of Braunschweig, 2Transport Electronics and Signal Processing laboratory, French National Institute for Transport and Safety Research (INRETS-LEOST) Abstract Positioning information is used in many railway typical applications: for track, fleet or wagon management as well as for level crossings and many others. Today, this function is provided by track side equipments. However, in the context of European harmonisation but also for saving costs (in particular to help low density traffic lines survive) GNSS (Global Navigation Satellite Systems) seems to fulfil some of the railway localisation requirements – or at least can be one of the bricks of a localisation system. In order to introduce this technology, many applications have been developed over the last few years in this sector and supported by European Commission and national programs. They integrate and use available as well as innovative technologies with the main focus on satellite based positioning (GPS and EGNOS already available, GLONASS and Galileo under re- deployment and development). But this introduction will not be possible without any validation of the performances. The basic idea that will be developed in this paper consists of developing generic reference measurement platforms for the evaluation and validation of applications in the transportation sector. The upcoming European satellite based localisation system Galileo will provide five different services with different performances and characteristics that will be suitable for different ranges of applications. These services will be: Open Services, Safety of Life Services, Commercial Services, Public Regulated Service and Rescue Service. The Safety of Life Service is the key service for most safety related applications due to its guaranteed characteristics of integrity, availability and accuracy. For the concrete validation or testing of applications and services, it is expedient to conclude simulation tests with an evaluation of the real system [4]. For this evaluation, the environmental conditions of the real operation have to be met as good as possible (or sensible) to make the results significant. For this, adequate reference platforms have to be set up and used. These platforms have to offer a very accurate positioning system independent from the positioning systems under test (here independent form satellite based localisation). In this paper, we will first introduce what kind of applications can benefit from Galileo before presenting a methodology devoted to validate the performances in the particular railway environment. An experimental platform is developed that will be presented in the last part, before conclusions. Introduction: GNSS and Railways The Context Most of the positioning functions in railways today rely on track side equipments: balises, track circuits or transponders, and other odometry methods [7]. These sensors are efficient, but offer mainly discrete positioning and lead to high maintenance costs (especially on low density lines compared with the often very low revenue on these tracks). Moreover, historically and technically, railway networks differ from one country to another on infrastructure, energy (Electrification 25, 15, 3, 1.5 KV and 750 V), rolling stock, maintenance and exploitation rules, as well as control-command systems and signalling. This is obviously also the case for positioning functions. In Europe in particular, the cross-border interoperability became a major problem for train circulation. The ETCS (European Train Control System) aims to solve it by defining a standard on European level. The first level of its development relies on track-mounted Eurobalises, augmented by odometry. However, some railways regard them as too costly. First experimental lines GNSS based localisation will be the low density traffic lines, which represent more than 110 000 km single lines in all Europe (approximately 50% of all lines). Indeed, lots of such lines in Europe are threatened of closing for economical reasons. In Germany, for example, 5199 km lines have been close in the last 16 years (approximately 10% of the total track length). GNSS solutions are today expected to reduce or eliminate the need for infrastructure by offering a worldwide solution that is independent of the trackside elements. Challenges During the last years, initiatives have been funded by European Commission, ESA and GJU as well as by national research programs in order to evaluate GNSS-based applications in railways. First operational solutions focus on non safety critical applications with relaxed requirements. This is the case of the SNCF locomotives tracking and tracing system or the DB Cargo initiative for wagon survey. Safety critical applications are today still subject of research and experimentation. The projects APOLO [1], GADEROS [6], LOCOPROL [10] have opened the way, the GRAIL consortium is currently working on availability and maturity of different “service enablers” (appropriate standards, availability of user terminal, economic and regulatory aspects, awareness, etc) [2]. It aims to propose a strategy, consistent with the current deployment process of ERTMS/ETCS in Europe. The issues to deal with for a good introduction of GNSS in railways are various. We can mention: • The interoperability of GNSS with ERTMS/ERTCS is mandatory in order not to define new standards resulting in the need of new investments. • Of course, performances will have to reach the specific requirements. • Some railways are uncomfortable about relying on outside parties. In particular, the certification process will have to be understood and acceptable compared to the railway certification usages. For all these reasons, the validation stage will be an important step that will demonstrate the expected GNSS performance in the real railway environment. This will be the purpose of the contents of this paper. Validation Methodology At next, the first approach to the methodology will be shown. Figure 1 shows the workflow in which the GALILEO receiver will be considered as a “black box”. The performance of the typical GALILEO receiver will be characterised based on GALILEO specifications and existing documents. EN 50126 EN 50129 EN 50128 Figure 1: Requirements relation between transport application types and GNSS In a first step, this paper will deal with general definitions and general requirements [11]. The main task will be first to describe each feature of quality: accuracy, integrity, continuity, availability [3]. Each of these features of quality has to be defined and described (using a formal language if necessary) [5], so that everybody can agree on the definition. Indeed, discussions between representatives of different transport modes make quickly appear the languages and interpretations different (Figure 2). In particular, the goal is to make them understandable for every transport mode community and make transposable the specification definitions to the transport. In the next steps, the work will define performance requirements for application classes. Each class will represent a certain level of accuracy, integrity, availability independently of the application. The railway applications will then be associated to the different classes previously defined. From this classification, different evaluations can be done according to the appropriate class using some simulation or “real life” tests, as shown in an example in Figure 2. Figure 2: Schematic representation of the validation process Requirements will be summarised based on existing documents from the specification of the GALILEO system. Some other identified documents are: the report of the GNSS rail user forum (2000), LOCOPROL reports, UIC working group reports. The GRAIL project has already presented some first results [2], classifying some applications function of integrity and accuracy. A state of the art on standards will be begun and if necessary, a standardised classification could be proposed (see also Figure 3). A necessary step will be to specify a standardised course and predefined trajectory for each class previously defined (comparable to the “EuroCycle” for fuel consumption). Some examples of applications will be chosen, related to safety. Scenarios will be defined and described that will be used in a second phase of work in order to validate the GNSS answer to these particular requirements. The validation process will then be applied on these examples, based on experimental use of both CaRail and PREDISSAT tools (which are described in the next section), which will be combined in order to validate the scenarios for the selected applications. The performance of a GNSS receiver will be analysed based on a reference trajectory and the knowledge of the reception environment. Train protection Trackman warning < 1 < 1 s Track protection Maintenance Reliability Time to Alarm Alarm Time to Tilting technology GSM-R Train integrity Communikation Power supply Dispatching 1s < Alarm < 10 s < 10 1s < Alarm Standstill detection Infrastructure inspection Tracking and Tracing (track, catenary wire) Passenger Panthograph information lowering > 10 s 10 km 1 km 100 m 10 m 1 m 10 cm 1 cm Discrete Continous Accuracy Figure 3: Railway applications function of reliability and accuracy requirements Approaches
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