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The Impact on the Positioning Accuracy of the Frequency Reference of a GPS Receiver |
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| Authors: | Ta-Kang Yeh Chieh-Hung Chen Guochang Xu Chuan-Sheng Wang Kwo-Hwa Chen |
| Institution: | 1. Department of Real Estate and Built Environment, National Taipei University, No. 151, Daxue Rd., Sanxia District, New Taipei City 237, Taiwan, ROC 2. Institute of Earth Sciences, Academia Sinica, No. 128, Academia Road, Section?2, Nankang, Taipei 115, Taiwan, ROC 3. Department of Geodesy and Remote Sensing, GeoForschungsZentrum Potsdam, Telegrafenberg A17, 14473, Potsdam, Germany |
| Abstract: | Despite the pervasive use of the global positioning system (GPS) as a positioning technology for its high efficiency and accuracy, several factors reduce its performance. This study examines to which extent the frequency offset and the frequency stability of the internal quartz oscillator or of an externally supplied rubidium oscillator have an influence. Observations were made at the Taiwan Ching Yun University (TCYU) tracking station, where a quartz oscillator and a rubidium oscillator were applied alternatively on a monthly basis throughout a 16-month period. Moreover, the accuracy of the local oscillator used in this study was calibrated by the National Standard Time and Frequency Laboratory, Taiwan. The frequency offset and frequency stability calculated via the remote method at the TCYU station were compared with values (uncertainty is 3.0E?13) measured directly at the National Standard Time and Frequency Laboratory, Taiwan. Analytical results show that the two methods vary by 1.4E?10 in terms of frequency offset and by 6.5E?12 in terms of frequency stability, demonstrating that the remote method can yield computational results almost as accurate as direct measurement. Positioning precision results also show that rubidium oscillator accuracy improved by 5, 11, and 15 % for short-, medium-, and long-baseline positioning, respectively, indicating that clock quality is more influential for long-baseline GPS relative positioning and that the frequency stability of a receiver clock is far more critical than the frequency offset. On the other hand, the positioning performance noted is essentially independent (max. 15 % change) of the reference frequency stability, which indeed differed by 4 orders of magnitude. |
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