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Session A6a: Augmentation Services, Integrity, and Authentication 2

TESLA Chimera Discrete Event Simulation for GPS Authentication
James Gillis and Rachel Allen, The Aerospace Corporation
Date/Time: Friday, Sep. 20, 2:35 p.m.

TESLA Chimera Discrete Event Simulation for GPS Authentication
James Gillis and Rachel Allen
The Aerospace Corporation
TESLA Chimera is a key element of the planned Navigation Technology Satellite – 3 (NTS-3) experiment. On 15 January 2021, the President of the United States signed Space Policy Directive 7 (SPD-7), which directs the Secretary of Transportation to develop and validate requirements for both data and signal authentication of civil GPS and its wide area augmentations. The NTS-3 experiment, managed by the Air Force Research Lab (AFRL), supports this objective with the inclusion of a modified Chimera protocol in its emulation of the L1C modernized signal and navigation data (CNAV-2). As defined in the interface specification IS-AGT-101, this modified Chimera concept includes a TESLA key chain that reduces the broadcast rate of digital signatures. This approach makes more efficient use of the limited CNAV-2 throughput.
This paper presents a discrete event study that estimates the time to authentication performance of the NTS-3 TESLA Chimera concept. The study consists of three elements: a constellation simulation, a user equipment simulation, and user analysis post processing. The constellation simulation produces Earth-Centered Earth-Fixed (ECEF) states and authentication messages for a virtual 32-satellite Global Positioning System (GPS) constellation. These simulated messages are simple tokens containing ephemeris and message type. Radio frequency signals and detailed navigation data are not simulated. With these ECEF states, the user equipment simulation applies a Bernoulli trial approach to generate statistics for successful and unsuccessful authentications, assuming the TESLA Chimera scheme. The simulation consists of 40,000 runs of 200 batches on a high-performance computer, simulating 40,000 stationary users evenly distributed across the earth. With these user equipment simulation results, the user analysis post processing applies R, Tidyverse, and Apache Arrow open-source packages to obtain the reported authentication statistics.
The discrete event simulation shows that the proposed TESLA Chimera concept is a viable approach to civil GPS authentication. The analysis determines total successful authentications/validations and total failures and time between authentications/validations. Timing results show that this TESLA Chimera concept could meet PNT requirements of civil GPS users. This paper proposes additional post processing analysis studies to evaluate the TESLA Chimera authentication performance at extreme latitudes or longitudes. The goal of this presented analysis is to explore options on coupling channels for multi-channel TESLA Chimera.

Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL-2024-1115.



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