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Session A7: Cooperative Space-Based Sources: Signals

GNSS Interference and Carrier Doppler Manipulation Assessment of Proliferated-LEO (pLEO) Waveforms Using On-orbit Data Collection and Channel Emulator
Taehwan Kim, Brent Bateman, Christian Cavalier, Nicholas Spens, Northrop Grumman Mission Systems
Location: Ballroom C
Date/Time: Tuesday, Jun. 4, 4:45 p.m.

Northrop Grumman Mission Systems (NGMS) conducted an on-orbit data collection and analysis campaign to assess the time-and-space dependent interference potential variation from the pLEO constellation to the legacy GNSS terrestrial service volume signals beyond the Spectral Separation Coefficient (SSC) method for static average behavior. To address the reduced allowable initial-acquisition dwell-time associated with faster LEO Doppler, range, and rate changes, NGMS has also been investigating pLEO carrier frequency Doppler manipulation for lower cost Time-to-First-Fix (TTFF) for high dynamics platforms using a composite form of Chirp Spread Spectrum (CSS).
To avoid direct L-band transmission while introducing realistic LEO higher carrier frequency Doppler and broader received power swing than the MEO GNSS, NGMS worked with commercial data collection providers for on-orbit RF recordings of ground-transmitted pLEO waveforms in ISM S- and C-bands compliant with the transmitted power limitations of the applicable FCC regulations. NGMS has also completed a preliminary evaluation of commercially available LEO channel simulation hardware (HW) to simulate real-world channel Doppler, delay, and attenuation of transmitted RF signals.
In this paper, Northrop Grumman presents the on-orbit data collection campaign findings, followed by HW Channel Emulator testing that compensated for some of the previously unknown challenges and limitations of real-time on-orbit data collection. First, the acquisition performances of 1, 2, and 4 MHz Gold codes as potential Pseudo-Random Noise (PRN) candidates of the Offset Binary Phase Shift Keying (OBPSK) in nominal C/N0, MEO-level moderate Doppler and code phase rate are presented as the baseline. Then, the nominal condition performances are compared with narrow-band Up-Down Chirp (UDC) with OBPSK bandwidths, Double-Chirp-sub-carrier Modulated Binary Offset Carrier, BOC(10,5), as either pilot or data channel components, and Dual-channel Composite UDC, designed preliminarily for high-dynamics Doppler manipulation. Iterative analyses of these signals under more challenging LEO C/N0, Doppler, and code phase rates are compared to the nominal MEO-like environments. The Doppler manipulation capability of Dual-Channel Composite UDC in poor C/N0 conditions is also demonstrated.

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