GNSS researchers presented hundreds of papers at the 2023 Institute of Navigation (ION) GNSS+ conference, which took place Sept. 11-15, 2023, in Denver, Colorado, and virtually. The following four papers focused on ways to combat GNSS jamming and spoofing. The papers are available here.

GPS World will be attending this year’s ION conference in Denver, Colo., on Sept. 16-20.

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Optimal INS

The civil infrastructures behind safety-critical applications in aviation, maritime and terrestrial navigation rely heavily on global navigation satellite system (GNSS) signals. The civil GNSS signal structures are vulnerable to spoofing attacks, which can endanger public safety.

In this work, the authors introduced an optimal cumulative position-domain innovation (CPI) monitor to detect spoofing by accumulating tracking errors embedded in the spoofer’s signal. The authors also derived relationships between missed detection probability, tracking error magnitude and monitor run time to show that even with decimeter-level tracking error, the monitor can detect spoofing with a low probability of missed detection in less than 1 minute.

The team of researchers evaluated the performance of the CPI monitor for both white and time-correlated (colored) tracking errors. To compute protection levels and detect short-duration spoofing, researchers proposed a complementary solution separation (SS) monitor to implement in sequential, overlapping windows to compare the integrated INS/GNSS position solution against an inertial navigation system (INS) coasting solution. The INS-only coasting element allows the system to maintain positioning continuity after detection, albeit at lower accuracy, as the INS drifts.

The experimental results indicate that implementing a CPI monitor can dismiss the conjecture that INS-based spoofing detection is susceptible to slowly deviating counterfeit signals. It was found that if the duration of the spoofing event exceeds a minimum time defined by the variance and time constant of the tracking error, the spoofer’s target tracking error can be detected.

Birendra Kujur, Samer Khanafseh and Boris Pervan; “Optimal INS Monitor for GNSS Spoofer Tracking Error Detection.”

Space-Time Adaptive Processing

Antenna arrays and spatial processing techniques are among the most effective countermeasures against GNSS signal interference. In this paper, the authors propose a new array concept, space-time adaptive processing (STAP), that consists of spatially distributed subarrays small enough to fit inside the non-metallic parts of an automobile. The device is designed to be installed in bumpers or side mirrors.

During the experimental testing, the authors used beamforming algorithms for the array to perform against jammers in the GPS L5 and Galileo E5a bands. The authors composed a GNSS jamming scenario to compare conventional space adaptive processing (SAP) methods and the new STAP method using real-life measurements in a dynamic scenario. In this simulation, the car was rotated 360° throughout the complete measurement. The comparison between the received signal quality demonstrated an improvement for wideband signals.

The results demonstrate that the performance of the STAP was dependent on the number of taps analyzed in the testing simulation that included different fractional delays. Overall, the research showed STAP could outperform SAP implementation in applications requiring robust tracking, as it was able to process all satellites for an additional 12 seconds.

Marius Brachvogel, Michael Niestroj, Michael Meurer, Syed N. Hasnain, Ralf Stephan and Matthias A. Hein; “Space-Time Adaptive Processing as a Solution for Mitigating Interference Using Spatially-Distributed Antenna Arrays.”

Enabling RTK Positioning Under Jamming

New GNSS applications demand high position accuracy and resilience against radio frequency interference. Separately, these demands can be fulfilled by multi-antenna systems using spatial filtering and carrier-phase positioning algorithms, such as real-time kinematics (RTK), respectively. However, combining these approaches creates a severe issue: the spatial filtering induces a phase offset into the measured carrier phase leading to a loss of position accuracy.

This paper presents a new approach to compensate for the phase offset without knowing the antenna array radiation pattern or the direction of arrival of the signals. The proposed algorithm was tested in two different scenarios using an in-house software receiver in combination with the RTKlib — an open-source program package for GNSS positioning — that was used to estimate an RTK solution. In the first scenario, the signal power of a jammer from a constant direction of arrival (DoA) was raised stepwise. In the second scenario, a jammer with constant signal power was moved around the receiver antenna array. For both scenarios, the proposed algorithm was…