Galileo Broadcast Ephemeris and Clock Errors, and Observed Fault Probabilities for ARAIM

The characterization of Clock and Ephemeris error of the Global Navigation Satellite Systems is a key element to validate the assumptions for the integrity analysis of GNSS Safety of Life (SoL) applications. Specifically, the performance metrics of SoL applications require the characterization of the nominal User Range Errors (UREs) as well as the knowledge of the probability of a satellite, Psat or a constellation fault, Pconst, i.e. when one or more satellites are not in the nominal mode. We will focus on Advanced Autonomous Integrity Monitoring (ARAIM). The present dissertation carries-out an end-to-end characterization and analysis of Galileo and GPS satellites for ARAIM. It involves two main targets. First, the characterization of Galileo and GPS broadcast ephemeris and clock errors, to determine the fault probabilities Psat and Pconst, and the determination on an upper bound of the nominal satellite ranging accuracy (?URA). Second, using these experimental results, to assess the performance of the ARAIM at user level. With regard to the first goal, the main contribution has been the extension of the algorithms already developed for GPS satellites to the Galileo constellation. This is not a straightforward task, as it requires to consider the particular features of Galileo data. This characterization involved the development and implementation of complex algorithms to consolidate broadcast navigation files from a huge set of individual receivers, and using these consolidated files, to develop automatic monitors to assess the nominal behaviour of the GNSS satellites and detect anomalous events. The methodology has been applied to more than 5 years of Galileo data (since Galileo Open Service was declared on 15 December 2016) and more than 10 years of GPS data. Thanks to this analysis the satellite orbit and clock faults have been identified, the probability of failure established and ?URA determined. The Not-to-Exceed (NTE) thresholds from Galileo commitments have been used to identify the satellite faults and to estimate the observed probabilities Psat and Pconst. Using the NTE = 39.78 m, when excluding the first six-month period of Galileo IS OS, the analysis over the last five-year window shows very promising results. Only two satellite faults have been found. These two faults over this five-year period result in a fault probability Psat=3.0 ? 10?6/sat, which is far below the 1 ? 10?5/sat commitment. Regarding to te second goal, the main contribution of this thesis has been the assessment of the global performance of the H-ARAIM based in the experimental results of previous characterization of Psat, Pconst and ?URA. The approach involves multi-constellation (Galileo and GPS) and single constellation (Galileo alone or GPS alone). The metric for H-ARAIM examinations the 99.5th percentile of availability for the Required Navigation Performance (RNP) with lateral accuracy of 0.1 (RNP-0.1). The results show almost 100% global coverage for all analysed configurations, except with single-frequency Galileo with E1 or E5, or Galileo plus GPS with E5 and L5. This is when the basic-constellation, with 24 satellites per constellation, or the optimistic constellation with 27 satellites, are used. With a degraded-constellation (23 satellites RNP-0.1 is only achieved with multi-constellation and dual frequency [Galileo E1/E5 plus GPS L1/L5]. The dissertation also includes a sensitivity analysis of ARAIM algorithm as a function of the Integrity Support Message (ISM).