Optimal Authentication Staggering Groups for Chimera

Michael C. Esswein and Mark L. Psiaki

Abstract:	A periodic steady state covariance time history is developed to approximate the state covariance of a tightly coupled GPS/IMU estimation algorithm that assumes that all received measurements must first be authenticated by CHIps MEssage Robust Authentication (Chimera). Chimera is a Navigation Message Authentication (NMA) that is designed to authenticate incoming GPS signals through two methods referred to as the fast and slow channels. This paper uses a steady state approximation of the nonlinear estimator as a metric for evaluation in order to test different PRN combinations produced from a concept called authentication staggering. Analysis is done both locally, i.e., at a particular location on the Earth, and globally, i.e., at all locations on the Earth, for an instance in time. Analysis is also performed to consider the evolution of uncertainty through time and consider different grade Inertial Measurement Units (IMU). Results indicate significant improvement in uncertainty when considering authentication staggering in general, while also indicating that using the largest number of authentication groups possible is often preferred. Using this information, one can expect position uncertainty of 1-2 meters for a navigation grade IMU, and 10-45 meters for a tactical grade IMU.
Published in:	Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022) September 19 - 23, 2022 Hyatt Regency Denver Denver, Colorado
Pages:	3378 - 3392
Cite this article:	Esswein, Michael C., Psiaki, Mark L., "Optimal Authentication Staggering Groups for Chimera," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 3378-3392. https://doi.org/10.33012/2022.18440
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