整合GPS/BDS雙星系統之單頻精密單點定位研究

Abstract

本研究整合全球定位系統(Global Positioning System, GPS)及北斗衛星導航系統(Beidou Satellites Navigation System, BDS)進行雙星系單頻精密單點定位，並希望達到即時定位之目的。 定位誤差部分，使用UNB3m模型修正對流層誤差， 使用IGS提供的Ultra-Rapid精密星曆修正衛星軌道誤差與衛星時錶誤差，使用 IGS提供的全球電離層地圖修正電離層誤差，以及修正剩餘的微小誤差如地球固態潮汐(Solid Earth Tide)等。觀測量部分，使用了都普勒平滑偽距提升做為觀測量精度之方法，並與載波相位平滑偽距之定位結果比較。整合雙星系定位部分，使用了Helmert方差分量估計調整GPS與BDS的系統權重。 本研究比較了使用廣播星歷與使用精密星歷的定位結果，發現精密星曆在準度部分提昇，精度部分則與廣播星曆近乎相等。再測試都普勒平滑偽距與載波相位平滑偽距對於定位效果的提升，發現都普勒平滑偽距修正效果較好。最後比較GPS與BDS個別單星系定位與雙星系定位結果，在衛星觀測量穩定的情況下，雙星系定位平面精度部分由1.1∼1.4公尺下降至0.8公尺，高度部分則由1.4∼1.7公尺上升至1.9公尺，若單一衛星系統觀測量劇烈變動時，雙星系定位精度會受其影響，平面精度部分由1.3∼4.3公尺變為1.8公尺，高度部分則由2.0∼9.8公尺變為3.5公尺。

In this paper, we try to integrate the Global Positioning System (GPS) and Beidou Satellite Navigation System (BDS) single frequency precise point positioning, and achieve the purpose of real-time positioning. For modification errors, we use UNB3m model for correcting tropospheric delay, the Ultra-Rapid ephemeris provided by International GNSS Service (IGS) for correcting satellite orbit errors and satellite clock errors, the Global Ionosphere Map provided by IGS for correcting ionospheric errors, and we correct the small errors such as Earth Solid Tide, phase wind up and so on. For satellite observations, we use Doppler-smoothing of code pseudoranges to enhance the accuracy and precision of positioning, and compare the results of Doppler-smoothing of code pseudoranges with the results of carrier-smoothing of code pseudoranges. For integrating double satellite system, we use the Helmert variance component estimation to adjust the weightings of GPS and BDS. First, we compare the broadcast ephemeris with the precise ephemeris. The results indicate the precise ephemeris enhance the accuracy of positioning, but the positioning precision of the precise ephemeris is almost equal to the precision of positioning of broadcast ephemeris. Then, we compare Doppler-smoothing of code pseudoranges with carrier-smoothing of code pseudoranges. The results indicate Doppler smoothing pseudorange is better than carrier-smoothing of code pseudoranges. Lastly, we compare positioning results of individual single satellite system with positioning results of double satellite system. If the satellite observations are stable, the precision of positioning of the double satellite system would be better. The result indicates the horizontal precision of positioning changes from 1.1~1.4 meters to 0.8 meters, and the vertical precision of positioning changes from 1.4~1.7 meters to 1.9 meters. On the contrary, if the single satellite system observations changes drastically, the precision of positioning of the double satellite system would be worse. The result shows the horizontal precision of positioning changes from 1.3~4.3 meters to 1.8 meters, the vertical precision of positioning changes from 2.0~ 9.8 meters to 3.5 meters.