Multi-Constellation Blind Beacon Estimation, Doppler Tracking, and Opportunistic Positioning with OneWeb, Starlink, Iridium NEXT, and Orbcomm LEO Satellites

A novel blind spectral approach is proposed for blind beacon estimation, Doppler tracking, and opportunistic positioning with unknown low Earth orbit (LEO) satellite signals. The framework is agnostic to the modulation and multiple access scheme adopted by LEO satellites. First, an analytical derivation of the received signal frequency spectrum is presented, which accounts for the highly dynamic channel between the LEO satellite and a terrestrial receiver. Second, a frequency domain-based blind Doppler discriminator is proposed. Third, a Kalman filter (KF)-based Doppler tracking algorithm is developed. Fourth, a blind beacon estimation framework for LEO satellites is proposed and its convergence properties are studied. Simulation results are presented showing successful beacon estimation and Doppler tracking of Starlink LEO satellites transmitting 5G orthogonal division multiple access (OFDM) signals. Experimental results are presented demonstrating the efficacy of the proposed framework on multi-constellation LEO satellites, namely OneWeb, Starlink, Orbcomm, and Iridium NEXT. Despite adopting different modulation and multiple access transmission schemes, the proposed framework is capable of successfully estimating the beacon and tracking the Doppler, in a blind fashion, of 8 LEO satellites (2 OneWeb, 4 Starlink, 1 Iridium NEXT, and 1 Orbcomm) over a period of about 560 seconds with Hz-level accuracy. The produced Doppler measurements were fused through a nonlinear least-squares estimator to localize a stationary receiver to an unprecedented level of accuracy. Starting with an initial estimate about 3,600 km away, a final three-dimensional (3-D) position error of 5.8 m and 2-D position error of 5.1 m was achieved. Aside from achieving this unprecedented accuracy, these results represent the first successful opportunistic tracking of unknown OneWeb LEO signals and their exploitation for positioning.