Space-based navigation systems operating at single frequencies below 10 GHz require ionospheric information for correcting the signal delay or range error. In order to mitigate ionospheric errors as well as satellite clock and orbit errors especially in aircraft navigation, Space-Based Augmentation Systems (SBAS) such as WAAS and EGNOS have been established worldwide. In the current standard, the SBAS broadcasts vertical ionospheric delays at the ionospheric grid points (IGP) spaced by five degrees in latitude and longitude. The vertical delay is converted at user level to the required specific slant delay by using an obliquity factor called mapping function (MF) derived under the simplifying assumption of a thin-shell ionosphere fixed at 350 km height. In the present work we compared the performance of the thin-shell MF with a new MF approach derived based on multi-layer ionosphere assumption using data from a network of about 200 ground GNSS stations worldwide. We have found that using the new MF instead of the thin-shell MF the mean errors in slant delay computation can be reduced by more than 50% regardless of the user location and ionospheric conditions. Ionospheric scintillations are generally characterized via scintillation indices, calculated from amplitude and phase of the received GNSS signals. For many scintillation monitoring and mitigation applications, it is important to determine these indices accurately. Investigating appropriate data algorithms (here, data detrending) in deriving scintillation information for mitigation applications is the focus of this paper. Commonly, most GNSS receivers use a Butterworth filter with a fixed cutoff frequency of 0.1 Hz to remove low frequency trends from the data [Forte and Radicella 2002, Mushini, et al., 2012]. However, as shown in Forte and Radicella, 2002, inherent characteristics of ionospheric effects at different regions require different detrending settings. In this study, four detrending methods and effectiveness of each are examined using real data sets from high latitude and equatorial regions. Based on our results, it is observed that data detrending via wavelet-based filter can result in cleaner (less noisier) signal. In addition, correlation between computed amplitude and phase scintillation indices improves when wavelet filtering is used. Moreover, we present initial considerations for scintillation monitoring and mitigation via exploiting new GNSS signals to determine additional information. To examine real data, IF samples from scintillation events are post-processed using the GSNRxTM software receiver, developed by the Position, Location and Navigation (PLAN) group at the University of Calgary. This software receiver has the capability of processing GPS L1C/A and L2C signals. Scintillation parameters are calculated using the post-correlator in-phase (I) and quadra-phase (Q) components and carrier phase measurements, all obtained from the software receiver.


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    Title :

    GNSS Data Processing Investigations for Characterizing Ionospheric Scintillation


    Contributors:
    Najmafshar, M. (author) / Skone, S. (author) / Ghafoori, F. (author)


    Publication date :

    2014


    Size :

    13 Seiten, Bilder, Tabellen, Quellen


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English







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