Reminder: Join us on Monday, April 21 at 2 PM EDT for a complimentary webinar with Sharbel Kozhaya, Ph.D. candidate at The Ohio State University, as he discusses his research on "Unveiling Starlink for PNT." Register now at info.ion.org/webinar This paper can be downloaded for free on our open access website at https://lnkd.in/e2s-zSMD This paper provides a comprehensive theoretical and experimental description of how to exploit Starlink low Earth orbit (LEO) satellites for positioning, navigation, and timing (PNT). First, the paper reveals for the first time, the full Starlink orthogonal frequency division multiplexing (OFDM) beacon, which spans the whole time-frequency resource grid. This description of the beacon is achieved through blind beacon estimation, which shows that the Starlink sequences published in the literature only comprise 0.66% of Starlink’s full OFDM. Exploiting this full OFDM beacon is shown to increase the receiver’s process gain by nearly 18 dB compared to only using signals published in the literature. This process gain, in turn, unlocks higher effective SNR at the receiver’s correlator output, enabling reliable acquisition and tracking in low SNR regimes imposed by using low-gain antennas. Second, the paper studies and compares the maximum achievable received carrier-to-noise density ratio (C/N0) for different reception scenarios. Third, the paper shows the first experimental results of navigation observables extracted using OFDM signals transmitted by Starlink satellites, namely the carrier phase, Doppler shift, and code phase. The paper provides the most comprehensive Starlink signal collection from 2021 through 2024 and analyzes the quality of pilot-tone versus OFDM-based observables. Results show that step-like corrections sometimes contaminate all the OFDM-based navigation observables from Starlink satellites, rendering their raw integration a challenge for precise positioning. Fourth, the paper shows how corrections made to the OFDM carrier frequency offset (CFO) can be estimated on-the-fly with a good degree of fidelity within the tracking loop of the software-defined receiver. Unlike the CFO corrections, the estimation of code phase corrections is shown to be intractable, rendering pseudoranges from Starlink signals not suitable for reliable positioning. Moreover, the tracked OFDM carrier phase revealed excessive slips due to the employed communication scheme. Finally, the paper demonstrates the first positioning solution that uses OFDM-based Doppler shift exclusively. Four positioning frameworks are formulated and assessed: (i) pilot tone-based Doppler shift tracking that exhibits no sign of contamination from the OFDM-related corrections, (ii) OFDM-based Doppler shift with uncorrected CFOs, (iii) OFDM-based Doppler shift with corrected CFOs that are estimated on-the-fly, and (iv) OFDM-based Doppler shift with corrected CFOs that are estimated using the knowledge of an assumed...
