## 1 Introduction  
Global Navigation Satellite System (GNSS) technology plays an important role in an ever-expanding range of safety, security, business, and policy critical applications. Moreover, many critical infrastructures, such as telecommunication networks, energy grids, stock markets, etc. rely, at least to some degree, on uninterrupted access to GNSS positioning, navigation, and timing services [1]. At the same time however, different threats have emerged which have the potential to degrade, disrupt, or completely deny these GNSS services without prior warning [2]. This paper focusses on the threat posed by Radio Frequency Interference (RFI) to the GNSS L1/E1 spectrum. RFI can be emitted either unintentionally, e.g., by commercial high-power transmitters, ultra-wideband radar, television, VHF, mobile satellite services, and personal electronic devices, or intentionally, e.g., by jammers and more sophisticated signal spoofing devices [2, 3]. Due to the proliferation of GNSS-based applications to almost every part of the globe it can be assumed that this phenomenon of RFI threat to GNSS is no longer seen as a local or regional problem, but rather requires an international perspective. To ensure GNSS is protected, there is now a need to also respond at an international level by ensuring that there is the following: (_i_) A common standard for real-world GNSS threat monitoring and reporting, and (_ii_) a global standard for assessing the performance of GNSS receivers and applications under threat. GNSS threat reporting standards would allow for compilation of real-world threats into a database that could be analyzed to develop GNSS receiver testing standards that ensure new applications are validated against the latest threats [4; 5; 6; 7]. Both these standards are currently missing across all civil application domains and, if implemented, could potentially open the field for wider adoption and success of GNSS in the higher value markets. The EU Horizon2020 research project STRIKE3 (Standardization of GNSS Threat reporting and Receiver testing through International Knowledge Exchange, Experimentation and Exploitation) is a European initiative that addresses the need to monitor, detect, and characterize GNSS threats and to propose standardized testing procedures to validate different categories of receivers against these threats [4; 5; 6; 7]. Importantly, STRIKE3 has deployed an international network of GNSS interference monitoring sites that monitor interference on a global scale and capture real-world threats for further analysis [8]. Utilizing thousands of threats collected from this network over a three-year period, STRIKE3 has developed a baseline set of typical real-world interference/jamming threats that can be used to assess performance of different categories of GNSS receivers. This baseline set, which is used in this paper to assess the performance of two categories of receivers, consists of five different threat signatures as follows: Wide swept frequency with fast repeat rate, multiple narrow band signals, triangular and triangular wave swept frequency, and tick swept frequency. Additional details about the behavior of these five threat signatures in the time and frequency domain and the criteria for their selection can be found in [9]. The STRIKE3 project also proposed standardized testing procedures for GNSS receivers, which make use of these threat signatures for receiver validation. Collectively, the above activities aim to improve mitigation and resilience of future GNSS receivers against real-world interference threats. An example of such an attempt has already been made in [3], where an adaptive interference mitigation technique was proposed to counteract unintentional Narrow-Band Interference (NBI) detected at one of the STRIKE3 monitoring sites.