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.

The 3GPP 5G Non-Terrestrial Network (NTN) technology fundamentally relies on a Global Navigation Satellite System (GNSS) fix at the User Equipment (UE) to pre-compensate for user-link delay and Doppler shifts prior to any transmission, including the random-access procedure for the initial access. In GNSS-denied or interfered environments, this dependency triggers preamble collisions and connection dropouts, undermining satellite-based global connectivity. To address this vulnerability, this paper introduces a novel single-satellite positioning framework designed for higher-frequency (Ku/Ka-band) 5G NTN Very-Small-Aperture Terminal (VSAT) equipped with a phased-array antenna. The multi-step scheme derives an initial coarse position from Angle of Arrival (AoA) observables, extracts Frequency of Arrival (FoA) and Time of Arrival (ToA) measurements from Low Earth Orbit (LEO) downlink reference signals and hybridizes them within a Levenberg–Marquardt navigation filter. Systematic evaluations across static grids and realistic dynamic urban trajectories detail the incremental gains of transitioning from single-epoch AoA error minimization (J₀) to multi-epoch angular tracking (J₁), followed by the integration of Doppler (J₂) and ranging observables (J₃). Grounded in a realistic error budget, the proposed framework reduces initial positioning uncertainty from tens of kilometers down to a few kilometers. This level of positioning accuracy, combined with the GNSS-resilient features introduced in 3GPP Release 20 NR NTN specifications, enables robust initial access in compromised operational environments with minimal relaxation of 3GPP standards.