GPS∕Galileo單頻即時動態定位效能分析

A Feasibility Study of GPS/Galileo Single-frequency RTK Positioning

GPS 即時動態定位（Real-Time Kinematic, RTK）是目前最廣泛被應用在測量工程中的衛星定位技術，相較於傳統雙頻 RTK，單頻接收儀的週波值解算效率明顯較差，使得實務應用仍有困難。然而在不久的未來情況將有所改變，歐洲的導航衛星系統 Galileo 於2013年即將加入運作，預期將有更強的衛星幾何及觀測數量以加速單頻 RTK 的解算效率，更重要的是單頻接收儀在儀器價格上將有其優勢，因此是極具潛力的 RTK 設備。為降低基線距離限制，研究中將配合台灣 e-GPS 系統之虛擬參考站（Virtual Reference Station, VRS）技術進行 RTK，藉由整天 24小時真實單頻接收儀觀測量與模擬產生的 GPS/Galileo 觀測量來驗證單頻 RTK之效能。實驗將 RTK 系統分成三種組合：（1）GPS/Galileo 雙系統單頻：L1/E1；（ 2） GPS 單系統雙頻： L1/L2；（ 3） GPS 單系統單頻： L1。成果顯示出未來的GPS/Galileo 整合系統單頻 RTK 週波值解算效益將是最高，不僅優於現行的 GPS單、雙頻，在定位精度方面也顯示整合系統單頻 RTK 之3-D RMS 為三種系統中最好。隨著多系統 GNSS 時代的到來，研究成果指出未來使用 GPS/Galileo 單頻接收儀施測之效益與精度將會超越傳統的 GPS 雙頻接收儀，配合現行 e-GPS 系統，將是台灣 RTK 使用者最有效、最經濟之定位模式。 Real-Time Kinematic (RTK) positioning is the most widely used GNSS technique insurveying engineering. The single-frequency receivers have the cost advantage, butsingle-frequency RTK lacks enough measurements for quick and reliable carrier phaseambiguity resolution. This situation is about to change. The European Galileoconstellation is scheduled to be completed by 2013 and it will be interoperable with theexisting GPS system. This combined system (GPS/Galileo) will provide twice as manysatellites as today’s GPS, and thus it should substantially promote the application ofsingle-frequency RTK. This research is aiming at exploring future single-frequency RTKperformance associated with the GPS/Galileo combined system and Taiwan e-GPS system, as compared with today’s GPS dual-frequency RTK. The performance of integerphase ambiguity resolution was assessed with 24-h actual GPS data and simulatedGPS/Galileo data in three different scenarios: (1) single-frequency GPS/Galileo (GPSL1/Galileo E1), (2) dual-frequency GPS (GPS L1/L2), and (3) single-frequency GPS(GPS L1). Comparison results show that, among the three scenarios, the best ambiguityresolution performance is achieved with single-frequency GPS/Galileo and also have thebest 3-D RMS. This indicates that the future dual-system RTK can be practically builtwith low-cost single-frequency receivers. It should have a great impact on manyengineering applications.

Real-Time Kinematic (RTK) positioning is the most widely used GNSS technique insurveying engineering. The single-frequency receivers have the cost advantage, butsingle-frequency RTK lacks enough measurements for quick and reliable carrier phaseambiguity resolution. This situation is about to change. The European Galileoconstellation is scheduled to be completed by 2013 and it will be interoperable with theexisting GPS system. This combined system (GPS/Galileo) will provide twice as manysatellites as today’s GPS, and thus it should substantially promote the application ofsingle-frequency RTK. This research is aiming at exploring future single-frequency RTKperformance associated with the GPS/Galileo combined system and Taiwan e-GPS system,as compared with today’s GPS dual-frequency RTK. The performance of integerphase ambiguity resolution was assessed with 24-h actual GPS data and simulatedGPS/Galileo data in three different scenarios: (1) single-frequency GPS/Galileo (GPSL1/Galileo E1), (2) dual-frequency GPS (GPS L1/L2), and (3) single-frequency GPS(GPS L1). Comparison results show that, among the three scenarios, the best ambiguityresolution performance is achieved with single-frequency GPS/Galileo and also have thebest 3-D RMS. This indicates that the future dual-system RTK can be practically builtwith low-cost single-frequency receivers. It should have a great impact on manyengineering applications.