Search

To protect civilian Global Positioning System (GPS) users from spoofing, the Air Force Research Lab has developed the chips-message robust authentication (Chimera) signal enhancement for the GPS L1C signal. With Chimera, standalone receivers that only have access to the GPS signal will be able to authenticate their received measurements once every 3 min, whereas users with access to an out-of-band source will be able to perform authentication once every 1.5 or 6 s. However, moving receivers typically rely on much faster real-time GPS update rates of 1-20 Hz. In this work, we design a spoofing-resilient filter framework that provides continuous and secure state estimation between Chimera authentication times. By leveraging self-contained sensors on-board the vehicle, such as an inertial measurement unit or wheel encoder, as well as the periodic Chimera authentication, our proposed filter determines how much to rely on the received unauthenticated GPS measurements for state estimation. In this respect, our filter relies more extensively on GPS measurements in order to improve real-time navigation performance and reduce localization errors when GPS signals are authentic, while successfully mitigating spoofing-induced errors during an experienced attack. We experimentally validate our proposed spoofing-resilient filter in a simulated test environment for a ground vehicle model with access to the 3-min Chimera channel, under various simulated spoofing attack scenarios. To the best of the authors' knowledge, this is the first adaptive filter proposed for Chimera that continuously leverages real-time GPS measurements in a spoofing-resilient manner. [ABSTRACT FROM AUTHOR]

To protect civilian global positioning system (GPS) users from spoofing attacks, the U.S. Air Force Research Lab has proposed the chips-message robust authentication (Chimera) enhancement for the L1C signal. In particular, the Chimera fast channel allows users to authenticate the received GPS signal once every 1.5 or 6 s, depending on the out-of-band source utilized for receiving the fast channel marker keys. However, for many moving receiver applications, receivers often use much higher GPS measurement rates, at 5-20 Hz. In this work, we derive a stochastic reachability (SR)-based detector to perform continuous GPS signal verification and state estimation between Chimera authentications. Our SR detector validates the received GPS measurement against any self-contained sensor, such as an inertial measurement unit, in the presence of bounded biases in the sensor error distributions. We demonstrate via Monte Carlo simulations that our detector satisfies a user-defined false alarm requirement during nominal conditions, while successfully detecting a simulated spoofing attack. We further demonstrate that our SR state estimation filter successfully bounds the true state during both authentic and spoofed conditions. [ABSTRACT FROM AUTHOR]