Advanced RAIM, or ARAIM, extends and improves upon traditional RAIM algorithm to detect and mitigate independent, multiple, and correlated GPS signal faults. A key input to ARAIM is the assumed user range error caused by satellite imperfections such as clock and ephemeris errors. In analyses done to date, estimates of one-sigma nominal errors (URE) and one-sigma error bounds (URA) are treated as fixed, whereas in reality, they vary with the age of data (AoD) of the clock and ephemeris navigation data broadcast by each satellite. Today's GPS satellites are normally uploaded with new data every 24 hours, and as this data ages, it becomes less representative of the current satellite status. Thus, satellite errors tend to grow predictably with age of data. In this paper, ARAIM simulations for the future GPS III satellite constellation are conducted with AoD as a modeled parameter, and satellite errors are adjusted based upon it. AoD is computed from estimated upload times based on when each satellite passes over the GPS Master Control Segment (MCS) site at Schriever AFB in Colorado Springs, CO (i.e., one upload per satellite per day). The results of these simulations are similar to those obtained previously for GPS III satellites, which show a large performance improvement over today's mix of Block II satellites. Variations in performance are caused by the increase in URA with age of data beyond what was considered in previous results. In particular, locations near Colorado Springs have generally lower AoD and perform somewhat better than before, while locations far away have longer AoD and perform somewhat worse. In addition, simulations were run in which AoD was reduced by implementing three uploads per satellite per day and by providing an external source of navigation data such that AoD never exceeds 1 hour. One subcase also provides actual URA values instead of the conservative integers broadcast by the satellites. As expected, these changes further improve GPS III ARAIM performance. Locations with relatively long AoD tend to improve most when switching from one to three uploads per day, while locations with short AoD improve most with 1 hour AoD (externally provided) and knowledge of actual URA values.
GPS III Accuracy and Integrity Improvements using ARAIM with Shorter Age of Data
2014
11 Seiten, Bilder, Tabellen, 15 Quellen
Conference paper
Storage medium
English
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