This paper describes the generation of "truth" satellite orbit and clock product for advanced receiver autonomous integrity monitoring (ARAIM) offline monitor. The ARAIM user algorithm, which includes fault detection and exclusion (FDE), is autonomously executed at the airborne receiver. To achieve specific integrity and continuity requirements, the real-time FDE process requires assertions on the signal-in-space (SIS) performance, in particular on satellite clock and orbit ephemeris error characteristics. This information is broadcast in the integrity support message (ISM). The offline ground monitor estimates precise GNSS satellite orbits and clocks which are utilized to validate the ISM. In contrast to other sophisticated orbit determination processes that focus on accuracy for performance, such as the one used by the international GNSS service (IGS), the proposed offline monitor (OFM) architecture is mainly intended for safety-critical aviation applications, in which integrity is of primary concern. This monitor employs a straightforward approach to estimate satellite orbit/clock using the existing satellite based augmentation system (SBAS) ground infrastructure. For prototyping purpose, twenty sparsely-distributed reference stations (RS) are selected from a worldwide network of IGS stations, and their publicly-available observation data is utilized. A parametric satellite orbital model is employed in the estimator, whose implementation is described in the paper. Initially, the GPS legacy orbit model is utilized to analyze the impact of different error sources on the estimation and to resolve numerical issues on the estimator. And we show that signal-in-space ranging error due to our product of satellite orbit and clocks are in the order of decimeter.
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