Satellite-based localization technologies are strategic opportunities in railway applications because they offer new possibilities of service and have advantages that current technologies relying mainly on infrastructures deployed along tracks cannot equal. GNSSs (Global Navigation Satellite Systems) can, in particular, offer localization services in ERTMS (European Rail Traffic Management System), the system developed within the European railway community to harmonize, at European scale, railway signalling and control/command systems. However, using GNSS in such safety applications is slowed down when trying to comply with railway standards. Indeed, demonstrations of RAMS properties (Reliability, Availability, Maintainability, Safety) are required on new solutions embedded in trains. They aim at verifying if all dependability (RAM) and safety aspects are controlled over the lifecycle of the solutions before using them operationally. No RAMS evaluation technique exists for systems based on signal propagation and subject to failures provoked by environment effects. The major challenge is so to develop proof methods that will give means to fulfil the railway certification process. In this article, we propose a procedure to work in that direction after having presented the advantages, the possibilities and the challenges to use GNSS in rail transportation. The procedure is based on experiments for the evaluation of RAMS properties related to satellite-based localization units. We apply the method to different position measurements obtained in several typical railway environments. The obtained results are discussed according to the dependability and safety points of view.

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Simulation-based evaluation of dependability and safety properties of satellite technologies for railway localization

GRAIL-2 is the evolution of the GRAIL project (GNSS introduction in the RAIL Sector), a project funded by the GSA (GNSS Supervisor Authority) with the aim of facilitating the introduction of GNSS (Galileo and EGNOS) in the Rail sector GRAIL-2 takes over it predecessor focusing on the development of a GNSS based Enhanced Odometer with high integrity and safety level in a context of High Speed Lines (HSL) The purpose of a GNSS based odometer is to integrate and/or replace the traditional odometric systems currently used in the ETCS environment (tachometers, INS, Doppler radar etc) GRAIL-2 inherits the know-how acquired by GRAIL improving the accuracy of the computed Position-Velocity-Acceleration solution by means of an advanced data fusion algorithm The safety level is guaranteed introducing RAIM and Protection Level computation algorithms The purpose of this paper is to describe the results obtained analyzing the preliminary data captured on the train

GNSS for Enhanced Odometry: The GRAIL-2 results

Global Navigation Satellite Systems (GNSS) are potentially applicable for various railway applications, especially the safety-related applications such as train localisation for the purpose of train control. In order to integrate GNSS for train localisation, a trustable stand-alone GNSS-based localisation unit should be developed. Then to comply with EN 50126 (reliability, availability, maintainability, and safety; RAMS) standards, the demonstration of GNSS quality of service (QoS) should be evaluated in consistent with RAMS. However there are currently no appropriate performance evaluation methods on GNSS for railway safety-related applications.
This dissertation identifies the required performance for train localisation in consideration of GNSS QoS and railway RAMS. The common and different properties of the performance are analysed in detail using consistent attribute hierarchy structures based on UML class diagram. Then formalised performance requirements are proposed quantitatively on four properties (accuracy, reliability, availability, and safety integrity). After that, the evaluation and verification methodologies are introduced. The evaluation methodology is using a reference measurement system for GNSS receiver measured train location accuracy identification, and a stochastic Petri net (SPN) model for GNSS receiver measured train location accuracy categorisation. The SPN model illustrates the GNSS receiver measured train locations into three states (up state, degraded state, and faulty state). Then the four proposed properties are allocated and estimated formally using the three states in the SPN model. The verification methodology is used to verify the GNSS receiver measured train location in real time based on a localisation unit. The GNSS receiver measured train locations are verified using hypothesis testing methods based on the accurate digital track map provided beforehand. Then train location estimation from the localisation unit is verified according to the mileage of the train. With the verified train location estimation from the localisation unit, the corresponding safety margin for each train location is calculated.
The data for evaluation and verification methodologies are collected from a test train running on a railway track in High Tatra Mountains. The results show an approach of the possible certification procedure for the GNSS receivers in railway safety-related applications.

GNSS for Train Localisation Performance Evaluation and Verification

A system includes a motion switch module, an energy storage module, a resistive module, and an interface. The motion switch module includes at least one motion activated switch that is movable between an open and a closed position responsive to movement of an axle to which the motion switch module is coupled. The energy storage module includes at least one energy storage element that discharges a stored charge responsive to a motion of the corresponding at least one motion activated switch from the open to the closed position. The resistive module includes least one resistive element that dissipates energy discharged by the corresponding at least one energy storage module. The interface is configured to provide information regarding a change in charge state of the at least one energy storage element, wherein the change in charge state corresponds to a movement of the vehicle.

Systems and methods for cold movement detection

Safety and reliability have always been concerns for railway transportation. Knowing the exact location of a train enables the railway system to react to an unusual situation for the safety of human lives and properties. Generally, the accuracy of localisation systems is related with their deployment and maintenance costs, which can be on the order of millions of dollars a year. Despite a lot of research efforts, existing localisation systems based on different technologies are still limited because most of them either require expensive infrastructure (ultrasound and laser), have high database maintenance, computational costs or accumulate errors (vision), offer limited coverage (GPS-dark regions, Wi-Fi, RFID) or provide low accuracy (audible sound). On the other hand, wireless sensor networks (WSNs) offer the potential for a cheap, reliable and accurate solutions for the train localisation system. This thesis proposes a WSN-based train localisation system, in which train location is estimated based on the information gathered through the communication between the anchor sensors deployed along the track and the gateway sensor installed on the train, such as anchor sensors’ geographic coordinates and the Received Signal Strength Indicator (RSSI). In the proposed system, timely anchor-gateway communication implies accurate localisation. How to guarantee effective communication between anchor sensors along the track and the gateway sensor on the train is a challenging problem for WSN-based train localisation. I propose a beacondriven sensors wake-up scheme (BWS) to address this problem. BWS allows each anchor sensor to run an asynchronous duty-cycling protocol to conserve energy and establishes an upper bound on the sleep time in one duty cycle to guarantee their timely wake-up once a train approaches. Simulation results show that the BWS scheme can timely wake up the anchor sensors at a very low energy consumption cost. To design an accurate scheme for train localisation, I conducted on-site experiments in an open field, a railway station and a tunnel, and the re-

Train Localisation using Wireless Sensor Networks

GRAIL is an FP6 project initially managed by the Galileo Joint Undertaking (GJU), but this year being managed by the GNSS Supervisory Authority (GSA) that has taken over from the GJU The title of the project, GNSS for RAIL, addresses the use of GNSS in all rail applications However, the number of railway applications where GNSS could be used is very large and so the focus of the project is on Safety-Critical applications and specifically on ETCS (European Train Control System), although other applications (like Asset Management, etc) are also investigated The first ETCS application to be addressed in the project is the use of GNSS in enhanced odometry In this configuration, GNSS-based location is used as substitute or complement to the current odometry sensors (tachometers, INS, Doppler Radar etc) It can, therefore, remain internal to the ETCS (as a part of the Odometry Macrofunction) In this configuration the GNSS system is composed only of a GNSS receiver, augmented, if needed, by local elements to achieve the required performances (in safety, for example) The expected improvements of this approach for ETCS are the overall improvement of Train Location accuracy and a reduction in safety margins and tolerances The presentation will address the common specifications agreed in GRAIL by all signalling suppliers and under review by ETCS rail operators, as well as the future trials in Spain

GNSS Introduction in the RAIL sector

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Alvaro Urech

Papers

GNSS Introduction in the RAIL sector

The GRAIL project: Galileo Localisation for the European Train Control System