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Author: search.filters.author.Panachart, Chaiwat

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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.
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    Improvement of GPS positioning accuracy when utilizing Klobuchar model with ionospheric conditions in Thailand
    (2016-09-06)
    Jongsintawee, Sutat
    ;
    Runraengwajiake, Sarawoot
    ;
    Supnithi, Pornchai
    ;
    Panachart, Chaiwat
    In global positioning system (GPS) is now widely implemented in the smartphones since the GPS receiver module is integrated in a single chip of CPU. However, over billion of smartphones are based on the single-frequency (L1: 1,575.42 MHz) GPS receiver. Since the positioning error of single-frequency GPS receiver is mainly caused by the atmospheric, especially the ionospheric delay. The Klobuchar model is well-known model which was developed to compensate for ionospheric delay and is currently used for civilian single-frequency GPS receiver. The coefficients of the model are daily broadcast in the GPS satellite navigation message for worldwide users. The remaining errors due to the unique local ionospheric characteristics can cause significant position errors. In this work, we compute the ionospheric delay which obtained Klobuchar model at 3 stations in Thailand: Chiang Mai, KMITL and Surat Thani on 4<sup>th</sup> September, 2012. The maximum ionospheric delay is 9.9417 meter during day time, while the minimum ionospheric delay is 1.5033 meter during night time. The Klobuchar model can reduce the 95% horizontal errors by more than 34% at Chiang Mai station when we compensate the pseudorange with estimated ionospheric delay.