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Session A7: Cooperative Space-Based Sources: Signals

Resiliency of Frequency Division BPSK Modulations Broadcast from LEO Satellites
Gina Staimer, Philip Dafesh and Daniel J Agress, The Aerospace Corporation
Location: Ballroom C
Alternate Number 1

Use of frequency division Binary Phase shift Keying (BPSK) (FDB) has been described previously as an approach to achieve a lightweight military navigation signal. As described in [1], the frequency diversity of FDB provides inherent diversity that may be used to provide improved jam resistance. When transmitted form a proliferated Low Earth Orbit (LEO) satellite constellation, such systems have challenges including shorter orbit periods (< 2 hrs) and shorter times in view (< 15 minutes for LEO compared to hours for GPS).
Recent analyses have suggested that the antijam benefit of Frequency Division Multiple Access (FDMA) approaches can only be realized when the number of satellites in view is 4 greater than the number of FDMA frequencies for navigation or equal to the number in view for acquisition [2]. To address this assumption and investigate the tradeoffs with LEO satellite constellations, this work investigates the resiliency of LEO satellite constellations with varying number of satellites in view across the globe.
The work assumes a receiver model incorporating a 17-state unscented Kalman filter operating with varying degrees of inertial sensor quality including commercial, industrial, tactical and navigation grades. For each sensor grade, inertial error terms including accelerometer bias, velocity random walk, gyro bias, and angular random walk are modeled to determine navigation performance. Measurements are made at a 1 sec updates for each sensor under consideration.
The model uses inertial sensors to perform dead reckoning in conjunction with multiple pseudorange measurements from the same satellite to enable both pseudorange and doppler based navigation from a single satellite to improve overall navigation resilience. The use of inertial sensors enables the receiver to navigate with multiple pseudoranges from the same satellite, even when the receiver is in motion.
The results compare the effectiveness of various jamming strategies in terms of accuracy degradation. The performance of FDB is shown as a function of the number of satellites in view, sensor accuracy and jammer tactics to illustrate the performance under different use cases.

[1] Philip A. Dafesh, “The Design of a Lightweight Military Navigation Signal,” ION JNC 2023
[2] John W. Betz, Alex P. Cerruti, Brady W. O’Hanlon, “Frequency-Division Binary Offset Carrier Military Acquisition (FBMA) Signal,” ION JNC 2022.
[2] Mr. Scott Minas, Dr. Madeleine Naudeau, Dr. Jon Anderson, “Military Lightweight SATNAV Study: Phase II,” ION JNC 2023.
[3] https://www.vectornav.com/resources/inertial-navigation-primer/theory-of-operation/theory-inertial.

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