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Adaptive interference suppression filter for GNSS receivers
Interference detection on the frontlines: Battling GNSS jamming and spoofing
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Adaptive interference suppression filter for GNSS receivers
Interferers disrupt GNSS signals and prevent pseudorange measurement calculation, which in turn affects the positioning engine, resulting in degradation of the positioning, navigation, and timing (PNT) solution.
To increase the accuracy and reliability of the estimated position, GNSS transmit signals via more than one system of satellites known as constellations, as well as in both lower and upper regions of the L-Band spectrum. This redundancy in available signals helps maintain positioning when some of the satellite signals are affected by interference.
Although most modern GNSS receivers support multi-constellation, multi-frequency operation, interferers can jam multiple constellations sharing the same GNSS signal band simultaneously. Also, despite the inherent processing gain of the GNSS receiver through spread spectrum modulation, interferers can be several orders of magnitude stronger than the GNSS signal. This limits the benefit of using conventional radio frequency (RF) analog bandpass and digital notch filters to suppress interferers due to their limited out-of-band frequency attenuation.
Jammers can also generate multiple narrowband interferers around the GNSS signal, or the interferer can vary over time, reducing the efficacy of conventional notch filtering. Therefore, to maintain positioning accuracy in a harsh jamming environment, the effect of these narrowband interferers must be mitigated automatically in the signal processing chain of a GNSS receiver.
The CN0 improvement and phase noise reduction with the adaptive filter are impressive and result in much less error in the pseudorange and accumulated Doppler range measurement. By utilising NovAtel’s advanced interference detection technology, the adaptive filter has the potential to track and mitigate narrowband, continuous wave interferers automatically, leading to a precise PNT solution in harsh jamming environments.
What you will learn
Written by Santosh Nath, GNSS tracking engineer at Hexagon’s Autonomous Solutions Business Area, this article presents an adaptive filter to suppress narrowband interferers automatically without any user input. The adaptive filter uses NovAtel’s ITK technology to detect the presence of a jammer and then track a single narrowband interferer, multiple tones of narrowband interferers simultaneously, as well as a time-varying interferer. At each tracked interferer’s frequency location, the filter automatically places a notch, thus effectively suppressing these interferers.
Adaptive interference suppression filter implementation for interference mitigation.
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