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Session B5a: LEO-PNT: Concepts, Systems and Use Cases

Statistical Analysis of an Improved Clock Model for Opportunistic LEO Navigation
Angel Slavov, Ferran Valdes Crespi, Sebastian Durst, Peter Knott, Fraunhofer FHR
Location: Grand Ballroom ABC
Date/Time: Thursday, May. 1, 11:26 a.m.

Within the context of alternative positioning, navigation and timing (A-PNT), the employed reference clock stability directly impacts the achievable time synchronisation and thus positioning accuracy and velocity estimation. This paper analyses the impact of clock instability when the clock is subjected to various effects while carried onboard a satellite on low Earth orbit (LEO) or on receiver on the ground. Two categories of relativistic effects are considered: time dilation and gravitational redshift. Their influence was evaluated using the orbital parameters from the Starlink 2090 satellite. More precisely, the achievable accuracies are examined when using an oven-controlled oscillator (OCXO) and a temperature-controlled oscillator (TCXO) on the satellite and on the ground, respectively. To address the corresponding platform dynamic effects on either clock, two different clock models are proposed: one for the clock on the satellite and one for the clock on the ground. For either clock type, clock drift and clock bias are modelled as zero-mean Gaussian random variables. A Monte Carlo simulation with 20000 iterations is performed to estimate the fluctuations around the mean value. The number of iterations indicates the expected number of LEO satellites, respectively clocks, in orbit due to the LEO mega-constellations. The simulation results allow us to estimate the velocity and position errors caused by each clock mounted on a LEO satellite. The outcomes show that the more stable OCXO manifests less position and velocity deviations compared to the TCXO. The influence only of the gravitational effects was estimated to have a sub-metre position deviation from the true position.
Index Terms—LEO, positioning, opportunistic navigation, timing

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