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Session B5: Atmospheric Effects

Vector Tracking Algorithms Performances during Strong Equatorial Scintillation on Dynamic Platforms
Dongyang Xu, Colorado State University; Yu Morton, University of Colorado Boulder; Yu Jiao, Intel Corporation; Charles Rino, Rong Yang, University of Colorado Boulder
Location: Cypress
Alternate Number 4

The objective of this project is to evaluate the performance of a vector-based GNSS receiver on dynamic platforms while operating during strong equatorial scintillation.
Strong equatorial scintillation is known to pose challenges for receiver carrier tracking with its simultaneous fast phase changes and deep fading. In addition, [1] presented the GPS signal processing results from data collected in Ascension Island (7.9°S, 14.4°W), March 2013, revealing strong scintillation with S4 index over 0.75 simultaneously observed on 6 out of 11 GPS satellites in view. For stationary receivers used in applications such as ground-based atmosphere monitoring and environment remote sensing, open-loop-based algorithms utilizing the known receiver location for signal tracking has demonstrated improved robustness [2][3]. For applications on dynamic platforms such as aircrafts, such advantage does not apply. Moreover, the platform dynamics and the dynamic vibration-induced oscillator phase noise will further stress a scalar-based carrier tracking loop.
The vector-based structure, on the other hand, tracks the signal parameters of multiple satellites simultaneously in a vector form and can therefore benefit from the correlation between different channels on the platform dynamics and oscillator noise with improved robustness and accuracy [4]. However, in a vector-based structure, the tracking performance and the navigation performance are tightly correlated. Therefore a compromise has to be made between two conflicting needs: the need to make use of more satellites to achieve better geometry and hence more accurate navigation solutions, and the need to drop the satellites affected by severe scintillation from the tracking vector, so that the error experienced in these satellites do not contaminate the tracking of other satellites.
In this paper, the vector-based receiver will be implemented with a commonly used vector delay and frequency lock loop (VDFLL). The receiver performance will be evaluated under different satellite selection strategies during strong equatorial scintillation on a dynamic platform. In order to achieve this objective, it is necessary to have IF data of GNSS signals under this scenario. Although there is a lack of real scintillation data collected on dynamic platforms, the authors’ team recently developed a physics-based, data-driven simulator suitable to simulate such data [5]. The dynamic vibration-induced oscillator noise will also be incorporated into the simulator, in order to generate realistic scintillation signals received on a dynamic platform. Using this simulator, controlled scenarios of different platform dynamics, oscillator noise of different characteristics, and different configurations of scintillation satellites will be created to evaluate the VTL performances, in terms of loss-of-lock, and tracking and navigation accuracy. Based on this evaluation, insights can be obtained to help a vector-based receiver select satellites in order to achieve optimal tracking and navigation results.
References
[1]. Carroll, M. and Y. Morton, “Triple frequency GPS signal tracking during strong ionospheric scintillations over Ascension Island”, Proc. IEEE PLANS, 43 – 49, Monterey, CA, 2014.
[2]. Curran, J. T., M. Bavaro, J. Fortuny-Guasch and A. Morrison, “Developing an ionospheric scintillation monitoring receiver”, Inside GNSS, pp. 60-72, September/October, 2014.
[3]. Xu, D. and Y. Morton, "GPS carrier parameters characterization during strong equatorial ionospheric scintillation," Proc. ION ITM, Dana Point, CA, 2015.
[4]. Lashley, M., “Modeling and performance analysis of GPS vector tracking algorithms”, PhD Thesis, Auburn University, 2009.
[5]. Jiao Y., C. Rino, and Y. Morton, "Scintillation simulation on equatorial GPS signals for dynamic platforms," in Proc. ION GNSS+, Portland, OR, 2017.



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