UAB contributes to GERMINAL with its key expertise in the processing of LEO signals of opportunity (LEO-SOP)
The Signal Processing for Communications and Navigation (SPCOMNAV) research group at Universitat Autònoma de Barcelona (UAB), is leading the contribution on the processing of LEO signals of opportunity within the EUSPA-funded GERMINAL project. The ultimate goal is to use the signals received from some of the existing Low-Earth Orbit (LEO) satellites, in order to provide opportunistic positioning, and therefore become an alternate or backup solution to conventional Global Navigation Satellite Systems (GNSS).
Using LEO satellites for opportunistic and resilient positioning
The rapid deployment of large Low Earth Orbit (LEO) satellite constellations is creating a new and highly attractive opportunity for positioning, navigation, and timing (PNT) based on signals of opportunity. Unlike traditional GNSS satellites in medium Earth orbit, LEO satellites transmit significantly stronger signals, exhibit faster motion, and provide denser spatial coverage. These characteristics result in pronounced Doppler dynamics and improved signal visibility, which can be exploited to enhance positioning performance, particularly in environments where GNSS is unreliable, such as urban areas, indoors, or under intentional or unintentional interference.
Opportunistic LEO positioning is particularly relevant for resilient and complementary PNT solutions, as it leverages existing communication infrastructures without the need for dedicated navigation payloads. The core idea is to exploit the signals already transmitted by LEO satellites, despite the fact that they were designed and used for data communications, and extract meaningful information that could eventually be used to estimate the position of the user’s terminal.
Building on this concept, it has been shown that determining the user’s position is possible by exploiting either Doppler, carrier phase, or timing observables from existing LEO satellites. Interestingly, this approach can be extended to embrace multiple LEO constellations, thus providing resilient user positioning through multi-constellation diversity. This approach supports emerging use cases in which continuity and availability are critical, and positions opportunistic LEO positioning as a key enabler for hybrid PNT architectures that combine existing terrestrial and space-based systems.
In this line, SPCOMNAV’s work focuses on the processing and analysis of live LEO satellite signals for opportunistic positioning. We investigate signal-processing techniques to reliably extract Doppler and timing observables from heterogeneous LEO constellations such as Orbcomm, Iridium, and Starlink, and to assess their behavior under various propagation conditions. The results demonstrate the practical feasibility and strong potential of using real, in-orbit LEO transmissions as a complementary source of positioning information, paving the way toward unified user terminals that integrate multiple technologies including GNSS, LEO, and terrestrial systems such as 5G, as actually pursued in the GERMINAL project.
