臺灣博碩士論文加值系統

全球定位系統(GPS)是結合了CDMA通訊系統的編碼及三角定位法組成的精確定位系統。本論文提出GPS接收機設計之演算法於在微弱GPS訊號下之搜尋與鎖定。微弱的GPS訊號在搜尋的過程中會發生很多問題，諸如運算時間過長，脫鎖的發生機率增加。若接收機所在的環境具有較大的都卜勒頻移(Doppler shift)，在處理訊號的積分時間內，其中心頻率會改變。在這種環境下，傳統的搜尋方法將會抓取不到訊號。在本論文中，我們設計出一名稱為「新型延遲碼補償演算法」的方法來解決訊號中心頻率會改變的問題。除此之外，我們使用兩種搜尋的方式並比較其成果，分別是傳統式搜尋法及快速傳立葉搜尋法。我們也討論了搜尋自相關函數(auto-correlation)上之峰值發生位置的演算法，以期提昇系統的搜尋效率。為了使系統的模擬更有效率，每一個子系統皆模擬在個人電腦上。此演算法是針對可在室內運作的GPS接收機，所以模擬的GPS信號强度只有-155dBm Watt (-185 dB Watt)，相當於室外訊號強度的一千分之一。使用這些演算法之後，整個系統的處理增益(Processing Gain)可以提昇約10個 dB。此演算法雖需輔助訊號的幫忙，但能確實有效的在信號微弱且具有較大都卜勒頻移(Doppler Shift)之環境使用。

GPS is the system combined CDMA code and trilateration method to get precision positioning system. The main goal of this thesis is design and analysis of GPS receivers on acquisition and tracking of weak signals. Acquisition of weak GPS signals has some problems, such as long operation time and the probability of cycle slip will be increased. If the signals have large Doppler shift, the central frequency of signals will be changed in the integration period. When the situation happens, using the original acquisition process will get nothing. Here a new method called code delay compensation algorithm is designed. The algorithm can help the receiver to solve the problem. Besides these, two acquisition schemes will be compared, namely conventional and Fast Fourier Transform (FFT). And peak finding algorithm used on autocorrelation function will be discussed. The expectancy of the algorithm is increasing the acquisition efficiency. In order to simulate the whole system in an efficient way, all functions are simulated in the personal computer. The receiver is designed to use in indoor environment, so the power of the simulated GPS signal is only -155dBm Watt (-185 dB Watt). The power is equal to one thousandth of outdoor signal. Using the algorithm, whole system’s processing gain can be increased about 10dB. Although the algorithm is needed the aiding signal, it can catch the GPS signal correctly in the badly environment such as weak signal, strong noise and large Doppler shift.

Abstract…………………………………………………………………………..i
Contents…………………………………………………………………………iii
List of Tables…………………………………………………………………...vii
List of Figures…………………………………………………………………viii
1 Introduction…………………………………………………………………1
1.1 Motivation……………………………………………………………..1
1.2 Scope of Research……………………………………………………..3
1.2.1 Acquisition of Weak Signals……………………………………..3
1.2.2 System Architecture……………………………………………...4
1.3 Thesis Organization…………………………………………………....4
2 Global Positioning System (GPS) Receiver Description…………………....7
2.1 GPS Signal Specification………………………………………………7
2.2 C/A Code and Its Properties……………………………………………9
2.2.1 Verify the C/A Code Generator…………………………………...11
2.3 GPS Receiver Architecture…………………………………………...14
2.4 GPS Signal Power Levels…………………………………………….16
2.4.1 Signal Path Loss and Transmit Antenna Gain…………………16
2.4.2 Received Signal Power and Antenna Gain…………………….18
2.4.3 Noise Analysis…………………………………………………20
2.5 The Difference Between Standard GPS Receiver and High Sensitivity Receiver…………………………………………………...21
2.5.1 Acquisition……………………………………………………..21
2.5.2 Indoor GPS Hardware Processing Approach…………………..25
3 Acquisition of GPS Signal…………………………………………………29
3.1 Conventional Acquisition Method……………………………………30
3.1.1 Sampling Rate Problem.……………………………………….32
3.1.2 Approximation of Envelopes………………………………......33
3.1.3 Acquisition in Time Domain…………………………...….…..34
3.2 Acquisition in Frequency Domain…………….……………………...37
3.2.1 FFT Search Algorithm…………………………………………38
3.2.2 FFT Size…………….………………………..………………...39
3.3 Finding Peak Value on Autocorrelation Function……………....…….43
3.3.1 Peak Finding Algorithm………….…………………….………44
3.3.2 Simulation of Peak Finding Algorithm………………………..46
3.3.3 Deciding Integration Time Algorithm………………...……….48
4 New GPS Code Delay Compensation Algorithm for Weak Signal Acquisition………………………………………………….……….……..51
4.1 Math Formula………………………………………….……………..52
4.2 Block Diagram and C/A Code FFT Table……...……………………..54
4.3 Simulation Results………………………….………….……………..55
4.3.1 Clock Offset…………………………………….………………55
4.3.2 Simulation .………………………………………….………….57
4.4 Processing Gain ……………………………………..……………….59
4.4.1 Fixed Integration Time ………………………………...……….59
4.4.2 Different Integration Time and Different Signal Power…….......61
4.4.3 Processing Gain of Large Doppler Shift Signal………..……….64
5 Tracking of GPS Signal……………………………..…………………......71
5.1 Phase-Locked Loops…………………………….……………………72
5.1.1 Phase-Locked Loops Basics……..…………………………….72
5.1.2 Analysis of the Phase-Locked Loop…………………………...74
5.1.3 Transform from Continuous Time to Discrete Time Systems…76
5.2 Carrier Tracking Loop…………………………..……………………78
5.3 Code Tracking Loop…………………………….……………………79
5.4 Costas Phase-Locked Loop………………………...…………………80
5.5 Doppler Frequency Shift…………….………….…………………….82
5.5.1 Average Rate of Change of the Doppler Frequency…...………84
5.5.2 Maximum Rate of Change of the Doppler Frequency...………85
5.6 Simulation Results……………………………………………………86
5.6.1 Tracking Result…...……………………………………………86
5.6.2 RMS Tracking Error…...………………………………………88
6 Conclusions and Future Work………………….……………………...…...93
6.1 Concluding Remarks………………………………………………….93
6.2 Future Works…………………………………………………..……...94
Bibliography………………………………………….…………………….......95

[1]F. Van Diggelen and C. Abraham: “Indoor GPS Technology”, CTIA Wireless-Agenda, Dallas, May 2001.
[2]F. Van Diggelen: “Indoor GPS Theory & Implementation”: IEEE Position, Location & Navigation Symposium, vol.31, no.1, pp.240-247, 2002.
[3]E. D. Kaplan: “Understanding GPS: Principles and Application”, Artech House, London, 1996.
[4]P. Misra and P. Enge, “Global Positioning System: Signals, Measurements and Performances”, Ganga-Jamuna Press, Lincoln, 2001.
[5]S. Haykin, “Neural networks”, Prentice Hall, New Jersey, 1999.
[6]J. B. Y. Tsui: “Fundamentals of Global Positioning System Receivers, a Software Approach”, John Wiley & Sons, Canada, 2000.
[7]M. S. Braasch, and A. J. Van Dierendonck, ”GPS Receiver Architecture and Measurement”, Proc. of the IEEE., vol.87, no.1, pp. 48-64, Jan. 1999.
[8]R. Taylor and J. Sennott, “Navigation System and Method”, United States Patent 4445118, NASA, Filed May 22, 1981.
[9]Moeglein & Krasner, “An Introduction to Snaptrack Server-Aided GPS”,. Proceedings of the Institute of Navigation conference, ION-GPS 1998.
[10]M. S. Grewal, L. R. Weill and A. P. Andrews, “Global Positioning Systems, Inertial Navigation and Integration”, John Wiley & Sons Inc., 2001.
[11]H. L. Van Trees, “Detection, Estimation, and Modulation Theory, Part 1”, John Wiley & Sons Inc., 2001
[12]M. Djebbouri and D. Djebbouri: “Fast GPS Satellite Signal Acquisition”, Electronics Letters.com, no.1/10/2003
[13]D. R. Stephens: “Phase-Locked Loops for Wireless Communications: Digital and Analog Implementation”, Prentice Hall, Kluwer Academic, 1998.
[14]A. J. Van Dierendonck, P. Fenton, and T. Ford, “Theory and Performance of Narrow Correlator Spacing in a GPS Receiver,” Navigation: J. Inst. Navigation, vol. 39, no. 3, pp. 265–283, Fall 1992.
[15]A. J. Van Dierendonck, “GPS Receivers,” in Global Positioning System: Theory and Application, vol. I, B. W. Parkinson and J. J. Spilker, Jr., Eds. Washington, DC: American Institute of Aeronautics and Astronautics, 1996, ch. 8, pp. 329–407.
[16]P. Ward, “Satellite Signal Acquisition and Tracking,” in Understanding GPS: Principles and Applications, E. Kaplan, Ed. Boston: Artech House, 1996, ch. 5, pp. 119–208.
[17]P. Misra, B. P. Burke, and M. M. Pratt, “GPS Performance in Navigation,” in Proc. of IEEE, vol. 87, no.1, pp. 65–85, January 1999.
[18]J.Guo, X.Hu and B.Vucetic, “Performance of a Digital Code Tracking Loop for DSSS Systems in the Presence of Doppler Shift”, in Proc. Commun. of IEE, vol. 150, no.3, pp.202-206, June 2003.
[19]楊志偉, “Development and Simulation of L5 GPS Baseband Processor”, 國立台灣大學電機工程研究所碩士論文,2003.
[20]B. W. Parkinson, and Jr. J. J. Spilker: “Global Positioning System: Theory and Applications”, AAAI, USA, 1996.
[21]R. L. Peterson, R. E. Ziemer and D. E. Borth, “Introduction to Spread Spectrum Communications”, Prentice Hall International, New York, 1985.
[22]R. E. Best, “Phase-Locked Loops, Theory, Design and Applications” Mc-Graw-Hill, Inc., 1993.