# Interference Monitoring from Low Earth Orbit: The OPS-SAT Experiment +
###### Abstract  
In the context of the Jammertest [2023], a collaborative experiment was carried out by the European Commission Joint Research Centre (JRC), the European Space Operations Centre of ESA (ESOC), the Norwegian Communication Authority, and the Norwegian Defense Research Establishment (FFI) to explore potential RF interference monitoring in the navigation GNSS band from LEO. The experiment utilizes the ESA OPS-SAT satellite and the possibility of transmitting a custom jamming signal pattern during the Jammertest event. The objective is to validate the feasibility of detecting and locating ground-generated jamming signals using SDR technology on-board LEO. The insight into the signal structure and location provides a unique chance to assess the performance and limitations of this approach in a real-world scenario. This paper presents the processing of raw RF data collected during the in-flight experiment, including the generation of frequency difference of arrival (FDOA) observables and emitter geolocation. Despite the constraints posed by onboard resources and mission limitations, this work offers a persuasive proof of concept and suggests new guidelines for implementing this technology on future LEO missions.  
RFI monitoring; interference localization; LEO satellite; software-defined radio; cross ambiguity function; frequency difference of arrival ()  
20258888008 tandem [3], new detection and localization techniques, and the availability of New Space hardware and software technologies.  
The OPS-SAT experiment aligns with this objective and provides an unprecedented in-flight demonstration of LEO-based RFI monitoring, even with nanosatellite low-cost technology and strict onboard resource constraints. In September 2023, the European Commission's Joint Research Centre (JRC), in collaboration with the European Space Operations Centre of ESA (ESOC), the Norwegian Communication Authority, and the Norwegian Defense Research Establishment (FFI), envisioned exploiting ESA's OPS-SAT LEO satellite and its onboard SDR (Software Defined Radio) [4] to conduct an experiment aimed at monitoring GNSS interference emissions generated on the ground. The concept originated from the unique opportunity presented by FFI to conduct experimentation during the Jammertest 2023 event [5]. This framework provides a one-of-a-kind chance to perform RFI tests in a controlled environment, replicating the necessary conditions to stimulate and validate RFI detection and localization from the OPS-SAT LEO satellite as it passes over the Norwegian Andeya site.  
In this paper, we present all aspects of the experiment, from the setup of ground-based emitted jamming signals to the OPS-SAT RF data acquisition, and we include raw I/Q sample processing for interference identification and localization. Our work contributes to the analysis of single-satellite RFI monitoring techniques, introducing novel and customized processing to address sparse measurements, low signal to noise ratios (SNRs), and hardware limitations. The presented results demonstrate that processing OPS-SAT I/Q data allows for the generation of cross-ambiguity-based FDOA measurements compatible with a coarse target localization in extremely challenging conditions. The paper is organized as follows. Section 2 details the experimentation settings, including the OPS-SAT platform's hardware capabilities, satellite operations, and on-ground jamming signal generation. Section 3 provides an analysis of in-flight RF data collection, including different spectrum data monitoring techniques. After this analysis, a cross-ambiguity function and FDOA-based localization technique is presented including its implementation for the OPS-SAT experiment's use case. The experiment results are finally presented in Section 5, together with the analysis of the encountered issues. Section 6 addresses the lessons learned and the opportunities for testing more advanced LEO-based RFI monitoring techniques.