Extended Kalman Filter-Based Tracking of Weak GPS Signals under High Dynamic Conditions

Nesreen I. Ziedan and James L. Garrison

Abstract:	This paper develops GPS receiver algorithms designed to work with weak signals, and under high dynamic conditions. The first one is an acquisition algorithm that is suitable for environments in which the receiver is moving with a high acceleration, and produces approximate code delay, Doppler shift and Doppler rate. The second algorithm provides fine Doppler shift and rate estimates, needed to initialize the tracking module. The third one is a code tracking algorithm based on Extended Kalman Filter (EKF) approaches. It implements a second order filter, and adjusts the coherent/incoherent integration times, and the early/late separation, based upon the signal condition and the correctly decoded data. The fourth one is a carrier tracking algorithm, which is also based on the EKF, and implements a square root filter to circumvent numerical errors associated with the EKF. It also has the capability of adjusting the integration time. The last one utilizes the structure of the navigation message to enable its decoding even for signals with theoretical Bit Error Rate that does not allow for such detection. These algorithms are demonstrated using simulated GPS C/A code signals, and TCXO clocks. The results have shown their ability to work with signals having a Doppler rate over 300 Hz/sec, and with power as low as 15 dB-Hz.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	20 - 31
Cite this article:	Ziedan, Nesreen I., Garrison, James L., "Extended Kalman Filter-Based Tracking of Weak GPS Signals under High Dynamic Conditions," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 20-31.
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