鎖相迴路應用於GPS定位系統之研究

Abstract

在全球衛星定位系統中，需要接收衛星傳遞之訊號用以做定位使用，由於在傳遞訊號時衛星與接收端之相對運動以及發射至接收訊號之時間，都會造成訊號的頻率偏移以及訊號延遲的狀況，造成我們必須準確的鎖定訊號之頻率與其時間延遲才有辦法順利得到定位所需資訊，因此我們利用鎖相迴路來完成此工作。 本論文首先為了分析鎖相迴路所能鎖定之頻率範圍，利用極限環方法來找出在不同的控制器下所能鎖定之狀況，以及藉由系統轉移函數來分析如何設計系統參數。由於希望將鎖相迴路之分析結果應用於軟體GPS追蹤系統，首先分析追蹤系統中之迴圈，並且為了符合GPS所需之離散系統，將設計參數方法從連續系統轉換至離散系統，最後應用於GPS追蹤系統。 此外為了將GPS系統應用於火箭，除分析衛星運動之外，也分析衛星運動與火箭之速度與加速度對於衛星傳輸訊號之影響，在火箭速度10馬赫時都卜勒頻率範圍為±21kHz，另外在火箭加速度10G時造成都卜勒頻率改變量可達515.58Hz/s，最後藉由模擬找出不同的火箭移動狀況下所需要之系統共振頻率。 本論文利用Matlab軟體編譯GPS追蹤系統之演算法，並且利用分析出之設計方法來設計系統參數，除了驗證演算法之可用性外，同時也觀察模擬結果是否符合所設計之規格。最後為了改善GPS追蹤迴圈，提出藉由改變迴圈運作方式來改善系統響應性能，並以模擬驗證。

In Global Positioning Systems, we need to receive the signal transited by satellite for positioning. Because of the relative motion between satellite and receiver and transit time, it will cause the frequency shift and time-delay of the signal. We must lock the frequency and time-delay of the signal precisely for acquiring the information for positioning. So we need to reach the goal by using Phase Locked Loop. This paper majors in the analysis of the frequency range which can be locked by Phase-Locked Loop, using limit cycle to understand the locking situation of different controllers, and designing system parameters by transfer function of the PLL system. Because we hope to implement the analysis result of Phase-Locked Loop to software-defined GPS tracking system, we analyze the loops of tracking system and utilize the parameters designed method to tracking system. Besides, in order to implement the GPS system to rocket, we analyze the satellite motion, and the effect between satellite motion, rocket speed, rocket acceleration and the satellite transmit signal. The range of the Doppler frequency is about ±21kHz when rocket speed reach 10Ma,and the change of the Doppler frequency will reach 515.57Hz/s when rocket acceleration reach 10G. Finally, we will use simulation to find the system nature frequency which is needed by different rocket moving situations. This paper using Matlab to compile the algorithm of software-defined GPS tracking system,and utilizing the designed method to design system parameters. We not only verify the feasibility of the algorithm, but also observe if the simulation results fit the designed specifications. Finally, in order to improve GPS tracking systems, the method of changing the tracking loop is proposed in this paper, and will verified by simulation.