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Session B5: Atmospheric Effects

Simulation and Tracking Algorithm Evaluation for Scintillation Signals on LEO Satellites Traveling Inside the Ionosphere
Dongyang Xu, Colorado State University; Yu Morton, University of Colorado Boulder; Yu Jiao, Intel Corporation; Charles Rino, University of Colorado Boulder
Location: Cypress

The objective of this project is to present robust GNSS receiver carrier tracking algorithms for receivers on board satellites traveling close to or inside ionosphere plasma irregularity structures. Recent studies show that the ESA’s Swarm satellites experienced total loss of GPS signals in areas known for frequent occurrence of ionosphere plasma irregularities. The phenomena of losing critical location information have been observed in other satellite missions. More robust receiver technologies are needed in order to improve the positioning capabilities for future low Earth orbit (LEO) satellite missions.
In order to achieve this objective, it is necessary to have IF data of GNSS signals under this scenario to facilitate the development and assessment of algorithms. Although there is a lack of real scintillation data collected on LEO satellites, the authors’ team recently developed a physics-based, data-driven simulator suitable to simulate such data [1]. The simulation results have shown that for LEO satellites travelling through or close to ionospheric bubbles over equatorial region, GNSS signals received by the LEO satellites experience simultaneous deep signal fading and carrier phase changes in the order of several tens of times faster than ground observed strong scintillation. Such highly disturbed signals posing a severe challenging for receiver carrier tracking [2], state-of-the-art processing algorithms such as vector tracking is not suitable to handle this challenging scenario. This is because for a satellite inside a plasma bubble, all GNSS satellite signals may experience scintillation effects which are uncorrelated between satellites and thereby greatly undermine the benefit of the vector based processing.
This paper presents an adaptive Kalman filter with Allan variance based scintillation modelling (AKF-ASM), which has been demonstrated to be robust in tracking scintillation signals on an aviation dynamic platform [3]. Based on the AKF framework presented in [4], this algorithm models the scintillation induced system noise based on the a priori information of the oscillator noise effects and the expected platform dynamics. The measurement noise model is based on the thermal noise and can be updated according to a high-rate real-time estimated C/N0. At every epoch, based on the system model and the updated measurement model, the steady-state Kalman gain is numerically solved and applied in the AKF tracking. The main update is the system noise modeling of phase scintillation in this AKF-ASM algorithm. This is achieved by treating the phase scintillation as oscillator noise and applying the equivalent Allan variance based modeling approach.
The performance of this algorithm will be evaluated using the simulated data with realistic scintillation effects for LEO satellites travelling through the ionospheric irregularity structures. A conventional phase lock loop (PLL) with different combinations of loop parameters will also be evaluated using the simulated data, in order to provide guidelines for the PLL parameter choice in GNSS receivers with more limited computational resource.
References
[1]. Y. Jiao, C. Rino, and Y. Morton,” Scintillation Simulation on Equatorial GPS Signals for Dynamic Platforms”, in Proceedings of ION GNSS+, 2017, Portland, OR.
[2] D. Xu, Y. Jiao, R. Yang, J. Wang, and Y. Morton, “Robust GNSS Receiver Carrier Tracking for Receivers on LEO Satellites Traveling inside Ionosphere Plasma Structures”, presentation of ION JNC, 2017, Dayton, OH.
[3]. D. Xu, Y. Morton, Y. Jiao, and C. Rino,” Robust GPS Carrier Tracking Algorithms during Strong Equatorial Scintillation for Dynamic Platforms”, in Proceedings of ION GNSS+, 2017, Portland, OR.
[4] R. Yang, K. V. Ling, E. K. Poh and Y. Morton, ”Generalized GNSS signal carrier tracking-- part I: modelling and analysis, ” Aerospace and Electronic Systems, IEEE Transactions on, vol. PP, no. 99, pp. 1-1, 2017.



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