An Innovations Approach to False-Lock Mitigation for GPS/Galileo BOC Signals

F. Nunes, F. Sousa and J. Leitao

Abstract:	Binary offset carrier (BOC) modulation was considered for modernized military GPS and for the European Navigation System Galileo. Although it performs better than the conventional BPSK modulation, the BOC waveforms have autocorrelation functions with multiple peaks that lead to potential tracking ambiguities. In the paper we propose to minimize this problem with a bank of stochastic nonlinear filters that estimate the three components (phase, frequency and frequency-rate) of the state vector from the quadrature components of the incoming signal. The code discriminator is a weighted sum of code delays with the weights being nonlinear functions of the filters innovations. Two solutions are proposed and compared for the state vector estimation: a simplified Gaussian sums filter that propagates iteratively a single Gaussian mode and the extended Kalman filter. When compared to the early-late power discriminator the proposed algorithms are much less prone to lose tracking of the BOC autocorrelation main peak while allowing the receiver to cope with a broader range of code delay errors. Besides, the resulting receiver provides side information about the emitter/receiver trajectory dynamics (through the state vector estimates) and the quality of the received signals (through the innovations processes).
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:	2636 - 2644
Cite this article:	Nunes, F., Sousa, F., Leitao, J., "An Innovations Approach to False-Lock Mitigation for GPS/Galileo BOC Signals," 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. 2636-2644.
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