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Implementation of a software-defined GPS receiver using the technique for tracking weak signals
|Authors: ||Chih-Hung Chen|
|Contributors: ||NTOU:Department of Communications Navigation and Control Engineering|
GPS software receiver;Phase lock loop;Delay lock loop;C/A codes
|Issue Date: ||2011-06-22T08:47:06Z
|Abstract: ||在傳統的GPS接收機裡，通常是使用硬體架構來實現射頻與基頻兩大部分，但近年來隨著電腦速度快速的發展，軟體無線電（SDR）逐漸成為GPS發展的趨勢。相較於硬體不易改變其架構，使用軟體結構來取代基頻部份，好處為可程式性、彈性佳、及低成本，如此便可廣泛利用在民間的GPS接收機。在本論文中，我們將針對訊號的擷取與追蹤相關原理作說明，並且使用MATLAB做進一步的模擬與驗證。 另外本論文還提到追蹤微弱訊號的方法，當訊號受到雜訊干擾等因素變差時，會增加定位的誤差量；此時若把時延鎖相迴路的輸出加以修正，便能夠減少定位誤差，對於在室內GPS定位或在訊號不佳的環境下是非常有用的。最後，本論文將全部的GPS訊號處理以及定位功能加以實現，並且整合成一個完整的軟體式GPS接收機雛形件。|
In a traditional GPS receiver, the hardware structure is adopted to accomplish two main parts including RF frond-end and baseband. Because the clock rate of computer is becoming faster for the past few years, the software define radio(SDR), i.e. radio which uses a lot of software algorithm, has became a trend of GPS development. In compared with hardware structure, which is not easy to be modified, a basebase of receiver that utilizes software structure has many advantages such as programmability, flexibility, and low cost etc, so that it can be extensively used in civil GPS receivers. In this thesis, GPS acquisition and tracking algorithms are developed at first, which is then followed by simulation and verification using MATLAB program. Furthermore, in this thesis, we also provide a signal processing method which is capable of tracking weak signal. When a signal is interfered by noises, positioning errors may be increased. Hence, if the output of the delay lock loop can be further modified, the positioning error can be reduced, which is very useful for indoor GPS positioning or the case that the quality of the signal is poor. Finally, we will sum up all the function blocks of GPS positioning (including signal processing and navigation processing) to realize a prototype GPS software receiver.
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