Multi-constellation GNSS Receiver for Rail Applications

The main characteristics of GNSS-based Safety -of -Life (SoL) applications are the identification and possible recovery of failures that may come from the signals transmitted by constellations (failures, feared events), from the environment (ionosphere, troposphere, interference and multipath) or even from the receiver, in order to provide reliable navigation information to the user. In particular, railway scenarios represent a challenging environment, in terms of poor constellation visibility, frequent signal obscuration and various forms of multipath and interferences from nearby structures In this context, Thales Alenia Space Italia (TAS-I) put a great deal of effort in various technological solutions, with multi -frequency, multi -constellation receiver, to improve integrity, accuracy and continuity of the navigation solution: The integration of MEMS-based Inertial Measurement System (IMS) within the GNSS solution and Integrity Monitoring functionalities. SBAS information on the ranging measurement accuracy, properly integrated in the filtering process, enhancing the algorithm reliability and propagating protection level on filtered measurements. A new technique, namely Acquisition Speed -Up Engine (ACSE). It improves performance in term of acquisition time with respect to the serial -parallel architecture employing a different type of transformation, called Fast Fractional Fourier Transform (FFRFT) and reducing the large required effort for a fine FFT. Adaptive filtering techniques have been developed to detect and track interferer spectral components. This interference mitigation module is integrated into the GNSS engine FPGA (GALVANI) and interfaces directly the A\D conversion stage of RF module. A novel structure of correlator for multipath mitigation has been simulated and tested. The implementation and integration of these technological aspects in a single -board GNSS receiver platform is presented together with a summary of test results achieved in a real railway environment.