Design and analysis of a GPS tracking loop controller with Doppler effect compensation
Date Issued
2007
Date
2007
Author(s)
Chen, Yu-Jung
Abstract
This thesis starts by making a brief description about the Global Positioning System (GPS), and introduces how the signal processing task in GPS receivers is divided into sub-tasks and accomplished as a whole. Then, the tracking loop in the GPS signal processing sub-system is particularly addressed. Finally, a tracking loop controller is designed specifically for the signal processing purpose. In the tracking loop, a Doppler effect compensator is added first to suppress the Doppler effect on signals transmitting in the outer space. This makes it easier to deal with the signals subsequently, such as the phase shift of C/A code in the satellite signal. The step taken after Doppler compensation is to divide a signal into frames with different lengths, from 1 to 20 milliseconds, and to compute the correlation coefficients between frames and locally generated C/A code copies with different phase delays. In every computation result, the phase shift is recorded according to the highest absolute value of correlation coefficient, so that the trace of phase shift can be obtained, which represents phase changes as time passing. Based on the relationship between code phase shift and Doppler effect, the estimated value of Doppler effect can be counted by finding the least-square line from the code phase shift and time, and can be used in tracking loop for the next iteration. The thesis finishes with the analysis of noise margin using different frame lengths. After summarizing the relation between all six kinds of frame length and noise margin, an equation can be obtained to estimate one with the other. Besides, the total calculation effort with different frame length is discussed.
Subjects
GPS, tracking loop, frame length, noise margin, phase shift, Doppler Effect
Type
thesis
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