Multi-constellation GNSS Receiver for Rail Applications

A. Ferrario, L. Marradi, P. Iacone, A. Galimberti

Abstract:	With the entry into service of the Safety of Life (SoL) service of EGNOS, with the completion of the In-Orbit Validation (IOV) phase and launch of Full-Operational Capability (FOC) phases of Galileo and with the planned evolution of the new GPS civil signals (L2C and L5), the area of Multi-constellation GNSS receivers for Safety of Life (SoL) applications is evolving fast. The main characteristics of the user receivers for SoL application is the capability to identify and possibly overcome failures or anomalies that may come from the GNSS constellations (orbit or clock failures), from the transmitted signals (message, codes), from the environment (ionosphere, troposphere, interference, multipath) or even from the receiver itself, to provide a reliable navigation information. In particular, railway scenarios represent a challenging environment, in terms of multipath, interferences, and signal availability continuity. Urban zones are generally characterized by poor constellation visibility and unfavorable relative geometries (e.g. high buildings, galleries), which lead to frequent signal obscuration and various form of multipath. Nearby railway infrastructures are also responsible of signal reflection, degradation and interferences. In some cases, notably in a context of High Speed Lines (HSL), also dynamic stresses must be taken in account. In this context, TAS-I put a great deal of effort in various technological solutions, within multi-frequency, multi-constellation programmable single-board receiver, to provide robustness against signal degradations and losses. The accuracy and the continuity of the navigation solution are strongly improved by integration of Inertial Measurement Systems (IMS) within GNSS, by means of advanced data fusion techniques. Including acceleration measurements, the Receiver Autonomous Integrity Monitoring (RAIM) capability is greatly extended, by means of algorithms performing coherency analysis on measurements of different nature. SBAS provides considerable advantages in this sense. In addition to Signal In Space SIS integrity service itself, SBAS provides information on the ranging measurement accuracy. These estimations, properly integrated in the filtering process, enhance the algorithm reliability and make possible to propagate protection level on filtered measurements. In general, in order to reduce impacts of signal losses, acquisition and re-acquisition process has been enhanced. New techniques have been simulated, namely Acquisition Speed-Up Engine (ACSE), able to overcome the heavy disadvantages of the currently used acquisition algorithms, such as the low precision of the Parallel Code Search (PCS) or Parallel Frequency Search (PFS), the complexity of the Kalman and Viterbi approaches and the large FFT required for a fine Doppler search in the customary serial parallel architecture. The basic idea of ACSE is to modify the serial-parallel architecture employing a different type of transformation, called Fast Fractional Fourier Transform (FFRFT). Against Radio-Frequency Interferences, adaptive filtering techniques have been developed to detect and track disturbing spectral components. This interference mitigation module is integrated into GNSS engine GALVANI FPGA and interfaces directly the A\D conversion stage of RF module. Finally, a novel structure of multipath canceller has been simulated and tested specifically addressing the rail domain. This paper will describe implementation of all these technological aspects in a single-board receiver platform and it will present a summary of test results of a receiver prototype, achieved in a typical real railway environment.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2840 - 2851
Cite this article:	Ferrario, A., Marradi, L., Iacone, P., Galimberti, A., "Multi-constellation GNSS Receiver for Rail Applications," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 2840-2851.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In