Vector tracking loop design for GPS receivers

Üzel, Deniz
This study describes the design of a modern GPS receiver architecture based on vector tracking loops. Since the traditional tracking loops process the signals independently, there is no information exchange between channels. Due to that fact, aiding of weaker signals in the presence of relatively strong signals is impossible. On the other hand, vector tracking loops simultaneously process the signals from all visible channels. Therefore, they are able to perform better than the traditional tracking loops in degraded signal environments where carrier to noise ratio is significantly low. In this thesis, a review of GPS receivers and satellite constellation is firstly presented. Then, the implementation details of traditional tracking loops and Vector Delay/Frequency Lock Loop (VDFLL) algorithm, which is a common type of the vector tracking architectures, are discussed. In addition, a modified version of VDFLL, which has a navigation filter with less number of states, is proposed. The mentioned algorithms are implemented in MATLAB environment. The performances of these algorithms are compared by using a Spirent GPS signal simulator. These performance comparison results indicate that the vector tracking algorithms have improved signal tracking capabilities in low carrier to noise ratio environments. Besides the superiority of the vector tracking algorithms, it is also shown that the modified version of VDFLL algorithm may be an alternative to original VDFLL with the advantage of lower computational load and almost similar performance in degraded signal environments. These algorithms can be used to track GPS signals in challenging GPS signal environments such as urban canyons and indoor areas.


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Citation Formats
D. Üzel, “Vector tracking loop design for GPS receivers,” M.S. - Master of Science, Middle East Technical University, 2016.