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Session A2: Cooperative Space-Based Sources: Experimentation

Ranging and Navigation Experimentation for Novel GPS Waveforms
Charles Connors, Kojo Zilevu, Mike Tinston, Enrico Mattei, Afsayh Saquib, Expedition Technology, Inc.
Location: Room 1-3
Date/Time: Monday, Jun. 3, 11:50 a.m.

A GPS system is comprised of a space, control, and user segment. The space segment is the constellation of transmitting satellites, the control segment is the system for monitoring and managing the satellites, and the user segment is the GPS receivers. Due to the space segment's nature, development tends to be limited, slow moving, and costly while processing gains and advances are routinely found in the user segment. This dichotomy lends itself to the potential for significant advances in the space segment. We have developed a novel GPS waveform that is agile and resistant to interference. We believe this represents the next frontier in GPS processing gains particularly in contested environments. It is important to note that development and testing of such a waveform is non-trivial due to the infrastructure requirements. In this work, we will discuss our novel GPS waveform, test architecture and SDR implementation that has facilitated its development, and experimentation to validate its performance through GPS test events.
We are developing a new class of learned PNT waveforms that combine a machine learning approach with an adaptive layer to enable waveforms that can operate in the presence of dynamic jamming. In the development of these novel waveforms, we have progressed from software simulation to hardware implementation. In hardware, we began waveform testing with a cabled loopback experiment on a single SDR. We then scaled to test ranging performance OTA with a single transmitter. To test the ranging performance, we completed a week of ranging experimentation at a GPS test event. We were able to consistently validate a ranging solution at distances up to 2km. We have now scaled our experimentation to test the navigation performance utilizing three ground-based transmitters and a mobile receiver. We tested this configuration in an adversarial environment where we demonstrated the ability to navigate on a 2D plane via latitude and longitude with high accuracy for a short-range scenario. For our next set of experiments, we will be attending a GPS test event for a 2D navigation experiment with ranges up to 7km as seen in Figure 1. We hope to characterize the navigation performance across range, interference type and magnitude. This small-scale navigation experiment will serve as a proof-of-concept demonstration that will lead to an eventual system with reprogrammable transmitters in orbit allowing for an in-theater ability to sense the RF environment and adapt to it. The on-orbit transmitters can be an additional payload on future GPS spacecraft as well as signals from commercial constellations such as the TrustPoint LEO constellation.
In this talk, we will briefly describe our novel waveform and hardware test apparatus before a discussion of ranging and navigation experiments performed in contested field environments. If applicable, we will discuss preliminary results from our long-range navigation tests.
Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL-2024-0456



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