Evaluation of Mitigation Methods Against Commercial-off-the-shelf (COTS) Privacy Protection Devices (PPDs)
J. Rossouw van der Merwe, Alexander Rügamer, Fabio Garzia, Fraunhofer IIS, Germany; Jan Wendel, Airbus Defence and Space GmbH, Germany; Wolfgang Felber, Fraunhofer IIS, Germany
Privacy protection devices (PPDs) are cheap commercial-off-the-shelf (COTS) jammers used to interfere purposefully with global navigation satellite system (GNSS) receivers. Although these devices are considered illegal to use in most countries, they can still be purchased easily and cheaply over the internet; therefore making such devices a common threat to GNSS receivers. There have been incidents where such interferences have caused major disruptions, albeit unintentionally. The design of mitigation methods to negate the effects of these interferences, are required for reliable GNSS receivers.
A number of mitigation methods against interferences have been developed. The performance and resource requirements of these methods vary, and depend on the type of interfering signal to be mitigated. The aim of this paper is to evaluate the mitigation methods against actual PPD signals, such that a good understanding of the benefits and drawbacks of the signals in real-world scenarios can be gained. PPDs tend to use a-symmetric linear chirp signals, hence chirp-mitigation methods will considered in this paper. These interference mitigation methods include adaptive notch filtering, narrow-band (NB) pulse blanking (PB), filter bank pulse blanking (FBPB), and frequency domain adaptive filtering (FDAF).
Three COTS PPDs with varying cost are acquired and used as interferences sources. The waveforms of the signals are recorded, analyzed and the theoretical disruption without mitigation is determined. The recorded signals are added to recordings of GNSS signals to and evaluated using a SDR based mitigation and GNSS receiver. This allows repeatable and controllable analysis of the same scenario for different mitigation methods. Next, a controlled laboratory experiment with the PPDs and GNSS signals is done such that the signal combining is done with the radio frequency (RF) signals. The mitigation methods are compared in software (simulative and repeatable) and in a laboratory setup (quasi-repeatable with receiver effects included). However, the impact on a potential hardware implementation will be assessed.
The difference of the receiver estimated C/N0 will be used as the metric to evaluate the performance of the mitigation method, as this is a measure of the GNSS tacking capability after mitigation has been applied. For the setups, the L1 band will be considered. A BPSK(1) signal and a BOCc(15, 2.5) will be analyzed, as the performance of the mitigation methods and the interference rejection of the correlators are also a function of the GNSS signal under evaluation.