Global Navigation Satellite Systems (GNSS) for vehicle navigation and timing are widely relied upon by many users in a variety of different sectors such as transit, financial, military, and many others. There are a number of ways for an agent to purposefully degrade a GNSS user's navigation performance. One such attack is a spoofing attack where the agent transmits signals with the same signal structure as GNSS signals, but they are modified to produce an incorrect navigation solution. Resiliency to these attacks is important for GNSS navigation. Two methods for GNSS resiliency are explored in this dissertation. The first method uses a Controlled Reception Pattern Antenna and receiver in order to obtain direction of arrival estimates of all visible signals and their computed pseudoranges. Two contributions were produced for this method. The first contribution is an optimization of a DoA cost metric that use DoA estimates along with known GNSS ephemerides to distinguish authentic signals from spoofed signals. The second contribution of this work is a combined DoA/pseudorange cost metric to improve the classification of authentic signals from spoofed signals as well as improve its robustness to multi-transmitter spoofing attacks. The second method uses a method known as Chimera, which involves authenticating the civilian L1C GPS signal using a digital signature in the navigation message and punctures in the spreading code. This method can be used to distinguish authentic and spoofed signals, however, a delay between the time the signal is tracked by the receiver and the time when it can be determined authentic is inherent in Chimera and degrades navigation performance. This delay can range from 2 seconds to 3 minutes. Four additional contributions have been made in support of Chimera. The first Chimera contribution is the design and evaluation of a navigation system for Chimera using a tightly coupled GPS/INS extended SRIF that accounts for the Chimera authentication delays. The second Chimera contribution is an investigation into staggering of the authentication times of the GPS satellites in order to improve navigation results. The third Chimera contribution is the development of a RMS or maximum steady-state position error metric to compare the accuracy achieved by different authentication group designs when used in conjunction with the previously discussed filter from the first Chimera contribution. The fourth Chimera contribution investigates different authentication group designs to find groups that will produce low value metrics. These investigations included local authentication group optimization, synthesizing a global design using local designs, and the effects of time and IMU grade. Each of these contributions has a significant impact on improving either the resilience of a GPS receiver to spoofing or the navigation accuracy of a GPS receiver that is inherently resilient to spoofing. / Doctor of Philosophy / Global Positioning System (GPS) navigation and timing plays a pivotal role in a variety of different sectors such as transit, financial, military, and many others. There have been instances where a signal is purposefully generated to look similar to a GPS signal in order to mislead a GPS user of their true position, velocity, and timing. This type of attack is known as a spoofing attack. This dissertation discusses two methods to identify these spoofed signals so that they are not used to disrupt nominal navigation and timing. The first method uses multiple GPS antennas to determine the direction of all visible signals. This dissertation provides an algorithm to distinguish the authentic GPS signals from the spoofed signals using the determined signal directions. The second method is for the GPS satellites to watermark the GPS signal they transmit, using modern encryption techniques, to be able to authenticate incoming signals. This method, however, produces a delay between when the signal is received by a GPS user and when it can be deemed authentic. This delay is a problem for navigation. This dissertation develops techniques for dealing with this delay by incorporating an Inertial Measurement Unit (IMU). This dissertation also proposes the idea to stagger the time that the digital signature, which is needed for signal verification, is sent from different GPS satellites. Lastly, this dissertation investigates how different staggered groupings of GPS satellites improve navigation performance and provides a metric for quantifying the navigation performance of different groupings. Overall, the dissertation's contributions to the first method improve the resilience of a receiver to spoofing attacks while the contributions to the second method improve navigation performance of an inherently resilient method.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/116631 |
| Date | 03 November 2023 |
| Creators | Esswein, Michael Craig |
| Contributors | Aerospace and Ocean Engineering, Psiaki, Mark L., Joerger, Mathieu, Scales, Wayne A., Woolsey, Craig A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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