Real-Time Environment and Sensors Simulator for Rail Applications

P. D'Angelo, S. Gómez de Agüero, D. De Castro, A. Fernández, J. Diez, A. Albanese, L. Foglia

Abstract:	In this paper, a real-time software developed for demonstrating the benefits of GNSS introduction in rail sector is described. It has been developed by DEIMOS Space in the frame of GRAIL contract, lead by Ineco/Tifsa, for the GNSS Supervisory Authority (GSA). Potential application of GNSS technology as an enhanced ETCS/ERTMS (European Train Control System/European Railway Traffic Management System) applications provider has been studied analysing the results of laboratory and on-site tests. In this context, the GESS (GRAIL Environment and Sensor Simulator) has been a key element for testing the User Terminal and studying the overall sensors system before the on-train test campaign. The main objectives of the achievement of a common specification for the GNSS subsystem, agreed by all involved parties, has been completed by focusing on two particular applications: the Enhanced Odometry application and the Enhanced ETCS applications (absolute positioning, train awakening and train integrity). The GESS simulates the trajectory and attitude of train’s head and tail cabins and the measurements generated by the on board sensors. The system includes two GNSS receivers, one on train’s head and the other on tail, an Inertial Measurement Unit (IMU), an odometer, and simulation of the ERMTS balises (enhanced odometry). It also defines the generic platform that could be used for the analysis of any other application of a GNSS system; in fact, any other sensor can be easily introduced in the overall model. The software runs on a standard PC with a Linux-based real-time operative system and has the same interfaces of the real sensors. The models of GNSS receiver and the other sensors have been implemented in Matlab/Simulink environment. The real-time simulator development has been divided into three main activities: the definition and implementation of the Simulink model, the communication protocol, and the real time algorithms. Using the autocoding tool provided by Real–Time Workshop, the Simulink model is completely coded in C and integrated in the RTAI (Real Time Application Interface for Linux) real-time operative system, which has been chosen following specific project requirements. In order to provide the suitable input/output (I/O) interfaces required to simulate the real sensors, a PCI board with eight RS232 ports has been integrated into the system. A specific software driver has been developed for this multiport board to meet the necessary real-time constraints. For all the sensors connection a specific communication protocol has been implemented. A complete database, composed of different configuration data-files storing the parameters of sensor models and I/O interfaces, has been defined. In addition to the real-time output, it is possible to perform offline analysis of the simulated data thanks to the ad hoc simulator tools. The software is available in three main configurations depending on the foreseen laboratory tests. The first is the complete configuration, in which all components of the reference scheme are simulated; the second and third are partial configurations, in which some parts of the complete configuration are removed and substituted by hardware elements. In all three of them there is a control shell that provides communication between the autocoded Simulink models and I/O interface. All these configurations have been verified and validated in the CEDEX (Centro de Estudios y Experimentación de Obras Públicas) certified laboratory. Train trajectory and attitude are obtained from the train track and the train along track position, velocity, and acceleration. The train track is stored in a file using standard Universal Transverse Mercator (UTM) coordinates, while the along track position, velocity and acceleration can be computed through interpolation of configurable profiles or can be directly received as external input. The GNSS receiver model has been built to be fully configurable: it can be used for generic GNSS multisystem simulation including GPS, EGNOS and Galileo, that are the systems taken into account in the GRAIL project. Space, Ground and User segments are modelled for constellation simulation, navigation message evaluation and raw data generation. The orbital state is obtained through analytical propagation of initial ephemeris considering gravitational perturbation due to Earth’s oblateness and third body effect (Sun and Moon). The clock state is obtained using a very detailed model that defines the clock error offset and drift as the result of deterministic and stochastic components. Navigation message is generated through the satellites orbital and clock state estimation reproducing the main ground segment processes. The raw data, pseudorange and carrier phase, are evaluated computing the geometrical range, the range errors and the range correction for each allocated satellite. All the measurements provided by the sensors are sent to the GRAIL User Terminal (UT) that elaborates them: it generates and then transmits through PROFIBUS (Process Field Bus) I/F the messages for the on board ETCS. The GRAIL-UT is an integrated Navigation/Communication user terminal demonstrator developed by Thales Alenia Space in the frame of GRAIL program. The definition of the GNSS-based UT architecture for rail applications has been the output of a process considering different needs, technical solutions and approaches. The UT architecture is consistent with the current deployment process of ERTMS/ETCS in Europe for the integration of GNSS into control and command applications. In conclusion, the GESS has been one of the most important elements for the design of a GNSS-based UT prototype, able to draw conclusions on common specifications for both the Enhanced Odometry and Enhanced ETCS applications in both real line and laboratory environments. Furthermore it defines a platform for development of different application simulations.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2724 - 2731
Cite this article:	D'Angelo, P., de Agüero, S. Gómez, De Castro, D., Fernández, A., Diez, J., Albanese, A., Foglia, L., "Real-Time Environment and Sensors Simulator for Rail Applications," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2724-2731.
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