全球導航衛星系統(Global Navigation Satellite Systems, GNSS)可提供全球衛星、地面參考站、使用者設備相對於全球的分佈位置，故其對於測量與製圖技術的進步與發展有著重大的影響改變。本研究擬利用自行研發的GNSS模擬器，針對未來GPS (Global Positioning system)及Galileo整合式系統，提供台灣地區包含衛星可視數量、Dilution Of Precision (DOP)值、可靠度等性能指標，針對空間分佈、時間分佈及對遮蔽效應的敏感度等模式進行深入評估分析。

GNSS的系統誤差模型決定模擬系統的精度，故本研究針對電離層、對流層、軌道誤差等系統誤差，發展符合台灣地區的誤差模式。利用衛星與使用者的坐標位置與相關資訊，吾人可計算兩者間的真實距離與載波相位，同時搭配上述各GNSS觀測量系統誤差模型及加入模擬的軌道誤差、對流層誤差、電離層誤差等系統誤差以產生模擬觀測量。最後吾人可利用模擬的觀測量及含整數週波未定值之載波相位進行後續多系統聯合解算演算法設計及結果計算分析用。

實驗結果顯示，整合雙系統的發展比起過去單一GPS或Galileo系統具備可視衛星數量的增加、DOP值的下降、內可靠度與外可靠度值的降低等優勢，故預期未來聯合雙系統必然較現行GPS大幅提升執行效能與定位精度。當然，未來多系統多頻率的GNSS除了性能提升的課題值得持續探討外，多系統整合所衍生出系統互操作性及相容性之課題，亦值得未來相關領域研究活動之關注。

Global Navigation Satellite Systems (GNSS) can provide the positions of satellites, reference stations and user receivers globally. It will have significant impact on the development of surveying and mapping technologies. Based on the compatibility of the navigation signals between modernized Global Positioning system (GPS) and Galileo, this study aims at exploiting the performances of each system and GPS/Galileo integrated system in Taiwan region, respectively. Therefore, a GNSS software simulator is developed in this study. The performance indices satellite visibility, dilution of precision (DOP) values and reliability are analyzed in terms of their temporal variations, spatial variations and sensitivities to signal obstruction.

The correctness of simulated GNSS measurements used for further relay on the systematic error models of GNSS implemented in the software simulator. Therefore, the error models including ionospheric and tropospheric delays as well as orbital errors are investigated to fit the scope of Taiwan region. Given the positions of GNSS satellites and user, the simulated pseudoranges and carrier phase measurements can be obtained with the addition GNSS systematic error models and integer ambiguity for further use.

The preliminary results presented in this sutdy indicate the improvement for the GPS/Galileo integrated constellation in terms of the visible satellites in comparison with GPS or Galileo individually. In addition, the averaged DOP values and reliability of the dual system are improved for the standalone GPS and Galileo scenario. Most importantly, using GPS/Galileo system provides sufficient availability for positioning in extreme masking environment, where positioning with GPS or Galileo is currently very difficult. Consequently, all the performance indices given in this study strongly indicate the benefits of future GPS/Galileo integrated positioning. On the other hand, the remaining issues concerning the compatibility and interoperability between GPS and Galileo should be investigated continuously to develop effective algorithms accommodating their measurements in the future study.

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