FFT Based DPD Localization Using LEO Signal without Signal Tracking

Kaito Kobayashi, Anji Fukuhara, Nobuaki Kubo, Ryohei Takahashi, Shoichiro Adachi, Sergi Granell Escalfet

Peer Reviewed

Abstract:	Low Earth Orbit Positioning, Navigation, and Timing (LEO-PNT) is being explored as a backup localization method for Global Navigation Satellite System (GNSS). Among various LEO-PNT approaches, we propose a Signals of Opportunity (SoOP) localization method that utilizes signals with unknown structures. Communication signals from LEO satellites are typically high-power and can be directly analyzed from SDR-acquired IQ data but signal structure is not opened. Leveraging this advantage, we estimate Doppler shift variations by applying FFT and computing cross-correlations between FFT results of multiple packets. These frequency measurements are noisy compared with when signal was tracked. Therefore, we tried to compare measured and theoretical doppler shift profiles and then estimate receiver position using grid search base Direct Point Determination (DPD) approach. We simulated three types of downlink messages and evaluated positioning accuracy using three satellites. The best positioning accuracy achieved in the simulation was 14 km, while some results exhibited errors exceeding 100 km. This variation is attributed to satellite–receiver geometry, and we propose a satellite selection strategy to select the satellite which can output best positioning accuracy using first rough localization and DOP (Dilution of Precision) calculation. This study could clear the issues to solve, including mitigation of TLE-based orbit errors and requirement of evaluation using real signal.
Published in:	Proceedings of the 2026 International Technical Meeting of The Institute of Navigation January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	51 - 59
Cite this article:	Kobayashi, Kaito, Fukuhara, Anji, Kubo, Nobuaki, Takahashi, Ryohei, Adachi, Shoichiro, Escalfet, Sergi Granell, "FFT Based DPD Localization Using LEO Signal without Signal Tracking," Proceedings of the 2026 International Technical Meeting of The Institute of Navigation, Anaheim, California, January 2026, pp. 51-59. https://doi.org/10.33012/2026.20525
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In