Comparison of Traditional Tracking Loops and Vector Based Tracking Loops for Weak GPS Signals

Matthew Lashley and David M. Bevly

Abstract:	In this paper, a variant of the Vector Delay/Frequency Lock Loop (VDFLL) algorithm is introduced for the GPS L1 civilian signal. The VDFLL algorithm uses a single Extended Kalman Filter (EKF) to simultaneously track the GPS signals and determine the user’s navigation states. The states of the EKF are the user’s position, velocity, acceleration, clock bias, and clock drift. The carrier frequency and Pseudo-Random Noise (PRN) code phase for each satellite are predicted based on the states of the EKF. Unlike traditional approaches, the VDFLL algorithm does not use Delay Lock Loops (DLL’s) or Costas Loops to track the GPS signals. The VDFLL algorithm has the ability to track weak GPS signals and rapidly reacquire blocked signals. The performance of the VDFLL is compared to that of a high end commercial receiver in an environment with dense foliage and rapidly fluctuating signal levels. The experimental results show that the VDFLL outperforms the commercial receiver and provides continuous coverage in GPS challenged environment.
Published in:	Proceedings of the 2008 National Technical Meeting of The Institute of Navigation January 28 - 30, 2008 The Catamaran Resort Hotel San Diego, CA
Pages:	310 - 316
Cite this article:	Lashley, Matthew, Bevly, David M., "Comparison of Traditional Tracking Loops and Vector Based Tracking Loops for Weak GPS Signals," Proceedings of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 310-316.
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