A Train Integrity Solution based on GNSS Double-Difference Approach

Nowadays, the train integrity function is assured by track circuits deployed along the line. This approach is safe but has several limitations since if any part of a track is occupied, that entire track circuit must be assumed as occupied and if the track circuits are made shorter to increase the traffic capacity, additional costs are incurred. In the European Rail Track Management System (ERTMS-ETCS) Level 3 trains must be able to localize and to monitor their integrity by themselves without the track circuits. This scenario makes it possible to optimize the capacity of the lines and to further reduce the operational costs by eliminating most of the track circuits... In this paper, we investigate the capability of the Global Navigation Satellite Systems (GNSS) to perform the integrity function in the perspective of the deployment of the ERTMS-ETCS L3 platform. The reference architecture is based on a pair of GNSS train Location Determination Systems (LDS) respectively located at the rear and the front-side of the train and connected each other by a radio link. A novel train integrity estimation solution that exploits a GNSS Double-Difference approach, has been developed for its advantages to mitigate most of the iono, tropo, clocks hazards caused by the GNSS signals. The Protection level and the Hazard Misleading Informations rates are derived by taking into account the safety requirements SIL-4 (Safety Integrity Level 4) of the ERTMS-ETCS system. The simulations have been performed by assuming a 2500 m train length; they confirm the validity of the proposed approach and pave the way for a seamless introduction of the GNSS into the ERTMS-ETCS L3 by replacing the fixed track circuits with virtual track circuits of variable size, and without affecting the safety requirements.