Title: Potential Limitations of RAIM in Assured Navigation
Author(s): Jyh-Ching Juang
Published in: Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016)
September 12 - 16, 2016
Oregon Convention Center
Portland, Oregon
Pages: 180 - 185
Cite this article: Juang, Jyh-Ching, "Potential Limitations of RAIM in Assured Navigation," Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 180-185.
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Abstract: Robust and assured navigation has become an important issue in the multi-GNSS era in which a variety of satellite-based and ground-based navigation and assistance signals has enriched many location-based applications while, in the meantime, the user device may be subject to erroneous signals or even malicious attacks. In the range measurement and position determination domain, the user relies on a set of measurements with uncertain error characteristics for the determination of position, velocity, and time (PVT). Typically, the measurements are processed to provide PVT solution and to detect anomalies. The latter is performed based on the Receiver Autonomous Integrity Monitoring (RAIM) algorithm so that excessive position error can be protected. In the paper, potential limitations of RAIM for assured navigation are analyzed. The principle of RAIM is to verify the consistency of measurement equations. This does not mean that the position (or timing) error is well bounded. Indeed, in the presence of one failure (or spoofing), the position error exhibits a linear relationship with the test statistic. By considering the maximal slope between the estimated position error and test statistic, the protection level can be obtained given the noise characteristics, false alarm rate, and detection probability. When multiple satellites are subject to spoofing, the situation becomes more complicated. The paper establishes in a rigorous manner the upper bound of the ratio between the test statistic and estimated position error. It is pointed out that when there are n measurements and more than n-4 satellites are subject to spoofing, the position error can become unbounded even when the test statistic is very small. The paper further investigates the worst-case bias vector that renders the maximal position error without triggering the RAIM-based detection scheme. This analysis can serve as a hint for user to adjust the weighting in processing GNSS measurements.