- 學位論文
衛星導航接收機載波及展頻碼同步之設計與分析
Design and Analysis of Carrier and Code Synchronization for GNSS Receiver
摘要
現今所使用的全球導航衛星系統(GNSS)，以美國的全球定位系統(GPS)最讓人熟知。而歐洲聯盟也將自行開發下一代全球導航衛星系統，稱之為伽利略(Galileo)衛星定位系統。本論文將採低中頻接收機架構，可同時接收GPS及伽利略在E1頻帶的信號。本論文中將針對低中頻接收機，分析射頻前端複數濾波器所造成的非常數群延遲，及其對基頻信號處理的影響。 伽利略E1系統的展頻碼週期為4毫秒，其長度為GPS C/A碼的四倍。換言之，由於在擷取信號(Acquisition)階段，所需搜尋的碼相位個數變多，則需要較長的搜尋時間或更多的硬體來擷取信號。 在本論文中，所提出的方法以較少的硬件複雜度及較短的搜尋時間，來擷取衛星信號。此方法的基本概念，是修改展頻碼的結構和縮短展頻碼週期，以降低所需的運算複雜性。然而，將展頻碼縮短的代價是，修改過後的展頻碼正交性，將不會和原始展頻碼一樣好，而造成在最大相關增益的衰減。在所需的擷取信號時間大幅降低之下，對於性能的衰減是可以接受的。
並列摘要
The United State Global Positioning System (GPS) is the familiar Global Navigation Satellite System (GNSS). The European Union will develop its own next generation GNSS, called Galileo Positioning System. In the thesis, the Low-IF receiver architecture is adopted to receive GPS/Galileo E1 signal. In the thesis, the non-constant group delay of the RF front-end complex filter and the baseband signal processing effect is analyzed for low-IF receiver. Galileo E1 system has a code period of 4ms which is quadruple that of GPS C/A code. In other words, due to the large number of hypotheses in code phase at acquisition stage, a longer searching time or more hardware resource is required. In the thesis, the proposed method acquires these satellite signals with hardware complexity reduction. The underlying concept in the method is to modify the code structure and shorten the code period such that the acquisition complexity can be decreased. However, the computation reduction by code shortening is not for free. The orthogonality of the modified code will not be as good as the original code anymore---there is degradation of maximum correlation gain. In the most cases of this thesis, the performance degradation is acceptable when mean acquisition time is used as a performance metric.