Adaptive Blanking as an Innovative Signal Enhancer for GNSS Receivers

Francis Soualle and Mathieu Cattenoz

Peer Reviewed

Abstract: Signal blanking, which consists in setting to zero samples whose power exceeds a specific threshold, is a common signal processing technique used to mitigate strong pulsed interferences in the context of Global Navigation Satellite System (GNSS) applications. In this paper, a way to take benefit from the signal blanking to improve the Signal-to-Noise Ratio (SNR) in a pulse-free environment is presented and validated. The analysis of a refined closed-form expression for the SNR has been firstly performed to interpret each constitutive contribution. This has yielded to isolate one specific term responsible for most of the SNR degradations, caused by a symmetry bias in the distribution of the blanked signal. Once this term discarded, the updated analytical expression has shown that blanking can actually significantly augment the SNR in an interference-free context. From those derivations, a “smart adaptive blanking scheme” has been developed. This innovative concept consists in introducing two thresholds (one positive and one negative) for comparison with the received samples. Those thresholds are offset at each sample epoch by the expected value of the tracked signal buried into the noise. As an example, it has been shown that for blanking thresholds set at noise level, the SNR improvement could reach up to 3.5 dB, whereas a reduction of 7 dB would be obtained with a conventional blanking scheme. Those assessments have been also confirmed by Monte Carlo simulations. Based on those encouraging results, an implementation of the smart adaptive blanker to a Delay Lock Loop has been proposed. The validation has been conducted successively with synthetic and real RF samples processed by an in-house Software Defined Receiver modified for this purpose. These first experimentations covering static and dynamic scenarios have confirmed SNR improvements, equivalent to several dB, and this even in harsh environments (e.g. at low elevations with multipath and shadowing).
Published in: Proceedings of the 2017 International Technical Meeting of The Institute of Navigation
January 30 - 2, 2017
Hyatt Regency Monterey
Monterey, California
Pages: 1302 - 1315
Cite this article: Soualle, Francis, Cattenoz, Mathieu, "Adaptive Blanking as an Innovative Signal Enhancer for GNSS Receivers," Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 1302-1315.
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