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Research on High-dynamic GPS Signal Simulation and Processing

Author: ZhuJiangHua
Tutor: BaoQiLian
School: Shanghai Jiaotong University
Course: Navigation,Guidance and Control
Keywords: Global Positioning System signal simulation High-dynamic Signal acquisition Signal tracking
CLC: P228.4
Type: Master's thesis
Year: 2011
Downloads: 268
Quote: 2
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Abstract

Global Position System is widely used in the past decades. There is a huge Doppler frequency shift and variation in carrier frequency in the high-dynamic environment because of relative velocity between the satellites and GPS receiver. The traditional acquisition and tracking system is not adaptive any more in this situation. This thesis researches on GPS navigation system in high dynamic environment, focusing on analyzing signal’s character and processing methods, with the purpose of supply the theoretic support for the study in high dynamic environment.First, it simply introduces the development of GPS receiver and research status of acquisition and tracking algorithms; then, it introduces the principles of acquisition and tracking , and analyses the signal character in high dynamic environment. The analysis result discovers that frequency searching range and correlation calculations will be enlarged as Doppler frequency shift in carrier frequency increase. At the same time, Doppler frequency shift can cause the tracking loop losing lock, consequently, user can not get the navigation data and receiver’s position.The thesis designs a high dynamic GPS Intermediate Frequency(IF) signal simulation software, it can simulate adjustable Carrier-to-Noise Ratio(CNR) signal when carrier is in all kinds of motion trajectory .After a detailed introduction on GPS system principle and signal structure, the thesis analyzes Doppler frequency shift react on upon GPS signal. Then, it deduced the GPS Intermediate Frequency (IF) signal mathematic model. The model contains many parameters such as Doppler frequency shift, C/A code and noise. The Doppler frequency shift can be calculated by authentic ephemeris and carrier’s motion trajectory. At last, a GPS intermediate frequency signal in high-dynamic environment is produced.Then, the thesis discusses the high-dynamic GPS IF signal acquisition and tracking on the basis of simulated signal. It finds that these acquisition parameters, such as data length, search step and search range, have great influences on acquisition performance by experiments. So the thesis proposes an INS aided acquisition method. The experiment shows that this method has much better performance in accuracy and rapidity than normal FFT search and serial search. The initial phase and frequency get from acquisition are use as the GPS signal tracking initial value. On the base of phase lock loop (PLL) theory, realize software implementation of the second-order, three-order. In consideration of influence of high dynamic environment, design an INS aided carrier tracking loop. The experiment demonstrated that these methods can reduce noise and improve sensitivity.This thesis analyzed and simulated GPS IF signal in high dynamic situation, and research on INS aided acquisition and tracking algorithm. A preliminary conclusion was drawn at the end of the thesis; this will provide a preliminary groundwork for GPS/INS supper tightly-coupled system in high dynamic environment.

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