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    New receiver bias calculation for total electron content (TEC) in Bangkok, Thailand
    (2018-07-02)
    Tongkasem, Napat
    ;
    Supnithi, Pornchai
    ;
    Phakphisut, Watid
    Ionospheric delay is an important parameter which affects the positioning accuracy of Global Navigation Satellite System (GNSS). It can be analyzed from the total electron content (TEC) in the signal propagation path, computed from the code and carrier phase of at least dual-frequency GNSS signals. Although TEC models have previously been developed by several models including the Global Ionospheric Map (GIM), International Reference Ionosphere (IRI) and Klobuchar model for equatorial region, the estimation of TEC may not be as accurate as in other regions due to relatively fewer research studies as well as unique ionospheric characteristics at these latitudes. Generally, computed slant TECs need to be adjusted for satellite and receiver biases, the latter is dependent upon receivers and receiver location. Therefore, this study proposed the new receiver bias calculation algorithm which can deal with these problems including cycle slips, outlier data, and missing data. In particular, the TEC is computed from code pseudo range only, while the receiver bias is computed from both code and carrier phase together with the elevation angle restriction above 60 degrees (to reduce the cycle slip issue). To verify the proposed algorithm, TEC values at KMIT station (latitude = 13.73<sup>o</sup>, longitude = 100.77<sup>o</sup>), located in an equatorial region, in 2016 are estimated during 4 seasons. The TEC results are with those of International GNSS Service (latitude = 13.74<sup>o</sup>, longitude = 100.5<sup>o</sup>) and the global ionospheric map (at grid position: latitude = 13.7<sup>o</sup>, longitude = 100<sup>o</sup>) based on the Root Mean Square (RMS) error. The results evidently demonstrated that the averages of RMS are 20.60% and 10.99% for GIM and IGS, respectively.
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    Estimation of the single GPS-receiver bias using the gradient descent algorithm
    (2016-09-06)
    Chiablaem, Athiwat
    ;
    Supnithi, Pornchai
    ;
    Klinngam, Somjai
    ;
    Panachart, Chaiwat
    ;
    Saekow, Apithep
    The ionospheric Total Electron Content (TEC) can be obtained from processing measurements of the dual-frequency Global Positioning System (GPS) receiver. The main sources of errors in the TEC calculation are satellite and receiver biases. In this paper, we apply the gradient descent algorithm on the receiver bias estimation. The TEC is derived from measurements at 12 dual-frequency GPS stations in Thailand. The criterion of receiver bias estimation is based on the minimum sum of the vertical TEC (VTEC) standard deviation method. The results show that the maximum receiver bias value is approximately 3.69 ns at UDON station, while the minimum value is -5.91 ns at SRTN station. The accuracy of the receiver biases from this algorithm is compared with the reference method. The maximum percentage deviation is about 7.5% at SRTN station. The percentage deviation of the minimum sum of the VTEC between the reference method and the proposed method from all stations are less than 0.05%. Thus, the proposed algorithm is a viable option to estimate the receiver bias.