The reliance on global navigation satellite system (GNSS) has reached a level where interruptions caused by radio frequency interference (RFI) pose significant societal and economic consequences. Recent reports of jamming affecting low earth orbit (LEO) satellite constellations, such as Starlink (Waterman, 2025), further underline the growing need for space-based RFI monitoring and mitigation capabilities. Beyond navigation, GNSS signals have also been widely exploited in remote sensing applications through GNSS reflectometry (GNSS-R), a bistatic radar technique that utilizes reflected GNSS signals to infer geophysical parameters such as surface roughness, ocean state, and wind speed (Martin-Neira, 1993; Komjathy et al., 2000). Both GNSS RFI monitoring and GNSS-R rely on similar payload architectures and signal processing principles, enabling the development of a shared and configurable system. This paper presents the development and validation of a configurable software defined radio (SDR) payload for the Athene-1 small satellite mission (Bachmann et al., 2024). The payload architecture employs a zenith antenna for direct reception of GNSS signals, and a nadir-facing antenna for the acquisition of reflected GNSS signals or emissions from ground-based interference sources. The corresponding signal streams are processed independently within the digital signal processing (DSP) unit and recorded as time-tagged in- & quadrature-phase (IQ) data. To ensure robust pre-launch verification, a staged hardware-in-the-loop validation strategy is adopted, covering laboratory-based end-to-end testing, integration of flight-representative onboard DSP unit, and post-launch in-orbit validation. This approach enables systematic assessment of both the payload architecture and associated algorithms before in-orbit operations. The paper focuses on a representative pseudolite scenario emulating a spoofing test case. The defined key performance indicator (KPI)s evaluate the signal dynamics, Doppler consistency, and time-tag alignment between the zenith and nadir channels. Furthermore, practical limitations encountered during laboratory validation are discussed, and representative results are presented to demonstrate the capabilities of the proposed testbed.
Umesha et al. (Thu,) studied this question.