Improvement Of A High-Grade GNSS Receiver Robustness Against Ionospheric Scintillations Using A Kalman Filter Tracking Scheme
Résumé
The aim of this paper is to present the performance improvements introduced by different tracking loop architectures in ionospheric scintillation's environments. Ionospheric scintillation may cause deep and frequent SIS (Signal In Space) amplitude fading and phase variations resulting in degraded received GNSS (Global Navigation Satellite Systems) signals. GNSS services availability, integrity and continuity might be reduced during severe scintillation phenomena, especially in certain areas (geomagnetic equator and polar regions are notable examples).Current Thales Alenia Space-Italy receiver architecture for ground reference stations foresees the usage of a 3rd order Phase Locked Loop (PLL) to track the phase and frequency variations of the incoming signal. The target of this analysis is to identify and implement the best promising tracking loop architecture, in order to minimize the channel tracking loss probability, linked to the occurrence of Loss-of-Lock (LoL) events, and the discontinuities in carrier phase output, named Cycle Slip (CS) phenomenon. After a literature review the analysis has been focused on techniques that result the most appropriate for reference stations or ionospheric monitoring receivers.In order to emulate realistic conditions, at different ionospheric scintillation intensities, complex time series pre-generated with GISM model [8] have been processed and used in the simulator.The best performing tracking loop architecture is then object of further analysis and comparison, in terms of robustness and performance, involving a more reliable semi-analytic model extended also to Delay Lock Loop (DLL). This architecture is finally implemented and tested in a real HW receiver.Finally, performances are presented in terms of different figures of merit, such as Root Mean Square Error (RMSE) of frequency and phase, LoL and CS frequencies of occurrence.