Revisiting Doppler positioning performance with LEO satellites

Recently, the Doppler shifts from Low Earth Orbit (LEO) satellites have been used to augment GNSS and provide navigation services. We propose a Doppler-only point-solution algorithm for GNSS-like navigation systems operated in LEO. The proposed algorithm can simultaneously estimate the receiver clock drift, position and velocity. Then, we analyze the main error sources in Doppler positioning. To achieve the meter-level positioning accuracy, the satellite position and velocity errors should be within several meters and several centimeters per second, respectively. The ionospheric delay rates of C-band signal will cause about 1 m error in Doppler positioning, which can be eliminated using the ionosphere-free combination. The Doppler positioning accuracy will deteriorate sharply by dozens of meters if there are no corrections for the tropospheric errors. Subsequently, we analyze the Doppler positioning performance. The undifferenced Doppler positioning accuracy is at meter level, which is comparable with the pseudorange-based positioning in GNSS. To ensure convergence in the LEO-based Doppler positioning, the initial receiver position error should be less than 300 km when the satellites orbit is at an altitude of 550 km.