GPS系統採用展頻技術有效地降低所需發射功率，但相對的微弱訊號極易在複雜環境下被屏蔽，以至在如都市、深山或室內環境之中，GPS往往無法提供連續的完整的定位服務。針對這個弱處，本篇論文援引具有強訊號、高動態的低軌道衛星作輔助定位。

進一步地，高動態直接造成接收訊號的都普勒頻移遠遠超出傳統接收機所保證能夠即時處理的範圍；另一方面，通常為商業系統的低軌道的擷取資訊也不易取得。回顧第一代全球導航系統TRANSIT，本篇論文嘗試以都普勒頻移取代偽距成為觀測量，以都普勒效應作為輔助方程來協作定位。本篇論文的目的在於開發利用低軌道衛星都普勒頻移作為GPS輔助的定位系統並研究其可行性。此系統結合GPS方面偽距資訊與低軌道衛星都普勒頻移資訊共同作定位解算，其包含兩個核心部分：對低軌道衛星的訊號處理，以及合併三角定位法與都普勒定位法作為創新的定位演算。

在此篇論文中，低軌道衛星波音公司的銥衛星通訊系統(IRIDIUM Network)為目標輔助系統，其物理架構與訊號結構、實地觀測以及針對都普勒頻移擷取的訊號處理皆有完整詳細的介紹與分析呈現。在合併定位演算法方面，首先介紹兩組原生演算法──三角定位及都普勒定位法；接著導出合併定位演算法並討論其所面臨的困境。在實現此輔助定位系統的驗證中，基於都市環境的假設作實驗設計並與傳統三角定位法作比較分析，得到不亞於原定位法的結果，證實以低軌道衛星合併都普勒定位法作GPS的輔助定位的可行性。

GPS adopts spreading spectrum technology, which effectively reduces the power consumption at the transmission, but the corresponding weak power signal can be blocked easily in challenging environments. In a city, near mountains or indoors, GPS cannot promise continuous positioning services at all. From this perspective, an LEO satellite communication system with stronger signal power and higher dynamics is introduced to aid the GPS positioning.

The wider Doppler shift range due to the high dynamics of LEO satellites causes enough trouble for the conventional GPS receiver that normal processing cannot guarantee on-time solutions for the positioning computation. On the other hand, acquisition information is not easy to obtain either. Inspired by TRANSIT, the first generation of satellite navigation system, in this thesis, the Doppler shift substitutes the pseudorange as the measurement, and the Doppler effect is applied for aiding in positioning. The main goal of this research is to develop an aiding positioning system using the Doppler shift of an LEO signal and to study its feasibility. The aiding positioning system, which combines the pseudorange information of the GPS system and the Doppler shift information of the LEO system for simultaneous calculation, includes two cores: the LEO signal processing and a combined positioning algorithm using the trilateration and Doppler positioning.

In the thesis, the IRIDIUM network, the satellite communication system of the Boeing Company, is the target LEO aiding positioning system. Its physical architecture, signal structure, local observation, worldwide availability analysis and signal processing are detailed in the content. In the algorithm, two original algorithms, the trilateration and the Doppler positioning, are firstly introduced, then the derivation of the combined positioning algorithm follows. In the confirmation and the demonstration of the developed aiding positioning system, the experiments are designed as in a city environment, and the results are compared to the conventional Trilateration-only positioning. The analysis shows the LEO aiding positioning system performance to be no worse than ordinary GPS positioning.

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