A detection algorithm of frequency jumps for GNSS satellite clocks
As the frequency and time reference of space satellites, satellite clock has a direct influence on GNSS service performance. Any anomaly of the atomic clock behavior on board the satellites causes errors for user position. Therefore, it is necessary to detect clock anomaly. Frequency jumps are one of the most common anomalies in atomic clocks of on-board satellites, which appear due to space radiation, temperature change and other factors. In this paper, a detection algorithm of frequency jumps based on the batch least squares residues is proposed. Performance of the new algorithm is analyzed and verified by numerical simulation. The detection algorithm of frequency jumps for satellite clocks proposed in this paper is helpful to GNSS satellite clock autonomous integrity monitoring.
Application of the Dynamic Allan Variance for the Characterization of Space Clock Behavior
Due to their stability atomic clocks represent the core of navigation systems such as GPS and the future European Galileo system. To identify possible anomalies, it is fundamental to detect when the clock stability varies with time. The dynamic Allan variance (DAVAR) makes this monitoring process possible. We extend the DAVAR to the case of a time series with missing data, and we analyze the presence of periodic behaviors, two common phenomena in space clocks.
The Galileo Ground Segment Integrity Algorithms: Design and Performance
Galileo, the European Global Navigation Satellite System, will provide to its users highly accurate global positioning services and their associated integrity information. The element in charge of the computation of integrity messages within the Galileo Ground Mission Segment is the integrity processing facility (IPF), which is developed by GMV Aerospace and Defence. The main objective of this paper is twofold: to present the integrity algorithms implemented in the IPF and to show the achieved performance with the IPF software prototype, including aspects such as: implementation of the Galileo overbounding concept, impact of safety requirements on the algorithm design including the threat models for the so-called feared events, and finally the achieved performance with real GPS and simulated Galileo scenarios.