Recent developments in Positioning, Navigation, and Timing (PNT) sources offer a wealth of potential techniques to provide accuracy, robustness and reliability beyond traditional methods such as GNSS. 5G Terrestrial Network (TN) and Non-Terrestrial Networks (NTN), as well as LEO-PNT signals, can be used to test PNT receivers, in combination with real GNSS and LEO-SOP signals, the latter collected from a set of different communication satellite constellations. Hybrid receivers could leverage the capability to use all these signals simultaneously, or in specific combinations, to obtain high accuracy solutions, especially in difficult environments, such as urban areas, demonstrating the synergies that arise when these signals are used together. This paper is devoted to presenting the general structure of these solutions, giving some descriptions as to how all the data sources are integrated and providing a general overview of the design, development and testing activities, including some preliminary test results, for a GNSS+LEO-PNT+5G+LEO-SoP User Terminal prototype carried out over the course of the project.
This development is carried out in the context of the GERMINAL (Connectivity: Enabling next generation NAV/COM Hybrid Terminal) project, funded by the European Union through EUSPA, in the context of their Fundamental Elements Grants program. The aim of the project is to test a PNT solution combining GNSS (including Galileo E5 Quasi-Pilot signals and Galileo E1B OSNMA), LEO-PNT, 5G (TN and NTN signals) and LEO-SOP (with signals of four different constellations: Starlink, Iridium, Orbcomm, Globalstar). The terminal also has wireless communication capabilities, by using the 5G TN service, through which data can be transmitted. The consortium behind the development is made up of three Spanish organizations with GMV as the lead, IMDEA Networks (Instituto Madrileño de Estudios Avanzados) providing their 5G expertise and UAB (Universitat Autònoma de Barcelona) as LEO-SOP experts.
Many potential applications can be identified across industries such as Maritime, Rail, Road, Unmanned Aerial Vehicles (UAVs) or Location Based Systems (LBS). The combination of PNT sources proposed in this solution allows for remarkable performances in terms of accuracy, as multiple signals are used simultaneously. The use of signals in multiple different bands offers robustness against threats like jamming, spoofing, constellation shutdowns and more threats which can significantly impact Early Warning and Search and Rescue services. The performance can exceed that of conventional PNT solutions in different environments such as urban, given the availability of 5G service in this context.
At the time of writing, the Unified Hybrid Terminal is in the late development and integration stage. The paper presents the preliminary results that are sufficiently mature to be reported. All the blocks (related to each of the signals used) have been integrated and thoroughly tested, on an individual basis. The results that we are obtaining are mature, in line with what was proposed in initial design and specification phases. In general terms, tests are designed to analyse the performance of many different combinations of modules and the general performance of the Hybrid Terminal in different environments. The obtained test results include performance assessments.

The increasing prevalence of intentional and unintentional radio frequency interference (RFI), including jamming and spoofing, poses a significant threat to the reliability and integrity of Global Navigation Satellite Systems (GNSS). Traditional single-element antennas, with static radiation patterns, are not able to effectively suppress these threats without compromising signal availability. Multibeam antennas present a compelling solution to directional interference by enabling the formation of multiple, simultaneous beams in different directions. This architecture allows for comparably easy spatial filtering by spatially isolating interference sources while at the same time maintaining high-gain tracking of legitimate satellite signals, multibeam systems significantly enhance the resilience of GNSS receivers in contested environments.

This work presents the design, fabrication, and validation of a novel dual-frequency (L1/E1 and L5/E5), dual-polarization, multibeam lens antenna. The core component of the antenna is a partial maxwell fisheye lens (PMFL). This gradient-index lens geometry is ideal for multibeam applications as it inherently supports a wide field-of-view and wide-angle scanning with minimal beam degradation. Additionally, the PMFL exhibits a flat focal plane allowing the integration with planar feed arrays.
The lens is realized using a multi-material Fused Filament Fabrication (FFF) technique. This additive manufacturing approach allows for the precise realization of the complex refractive index profile required by the PMFL. High-Impact Polystyrene (HIPS) and ABS650 were strategically chosen as the constituent materials due to their distinct and stable dielectric properties. The desired spatially dependent refractive index of the lens is realized using a “Gyroid” pattern with spatially modulated volumetric infill.

To achieve the desired multibeam functionality, the PMFL is fed by a seven-element antenna array positioned in its focal plane. The array elements are designed to operate at both the L1/E1 and L5/E5a frequency bands and support both Right-Hand Circular Polarization (RHCP) and Left-Hand Circular Polarization (LHCP). This dual-polarization capability is essential for capturing the right hand circular polarized GNSS signals and enables polarization-based interference rejection strategies.

The performance of the fabricated prototype was validated in terms of the far-field radiation patterns of the individual antenna elements in the feed array. The prototype multibeam lens antenna achieves maximum realized gains of ~11dBi and ~10dBi in the L1/E1 and L5/E5 bands. The results confirm the successful realization of a low-cost, and highly functional multibeam antenna capable of supporting next-generation interference mitigation algorithms for robust GNSS positioning and multibeam capabilities for remote sensing applications.

Accurate and resilient timing is a foundational element of Positioning, Navigation, and Timing (PNT) services, underpinning critical infrastructures such as telecommunications, finance, power distribution, and transportation. While traditional timing systems rely primarily on satellite-based Global Navigation Satellite Systems (GNSS), these services remain vulnerable to interference, spoofing, and signal degradation. Quantum Time Transfer (QTT) has emerged as a promising technique to augment and extend existing PNT capabilities by providing ultra-precise, secure, and verifiable time dissemination over both optical fibre and free-space links.

For global-scale networks, space-deployed optical links are essential to enable intercontinental synchronisation and to extend high-accuracy timing services beyond terrestrial fibre networks. The recent surge of interest in optical ground stations—driven largely by developments in quantum communication and Quantum Key Distribution (QKD)—has led to significant advancements in optical terminal design, pointing and tracking systems, and adaptive optics. These same technological foundations can be leveraged for Quantum Time Transfer.

In this work, we explore the use of quantum communication infrastructure to define and optimise the requirements for Quantum Time Transfer systems. Building upon its ongoing efforts in developing optical ground stations for quantum communication, we show a detailed performance analysis of QTT implementations. This includes assessing timing precision under realistic link conditions, evaluating photon-level synchronization mechanisms, and identifying hardware and software parameters that most critically affect timing stability.

A key focus of the study is the relationship between optical link loss, environmental variability, and network resilience. Well-architected ground stations play a pivotal role in maintaining reliable operation under varying atmospheric and orbital conditions. By modelling and testing system architectures that integrate robust pointing and acquisition subsystems, high-efficiency optical transceivers, and precision clock interfaces, we aim to establish design principles that ensure both scalability and reliability across hybrid ground-to-space and fibre-based networks.

Ultimately, this work seeks to advance the understanding of how Quantum Time Transfer can complement and enhance the broader PNT ecosystem. Through leveraging existing investments in quantum communication technologies, particularly those developed for QKD, QTT offers a pathway toward a more accurate, secure, and resilient global timing infrastructure capable of meeting the demands of next-generation space and terrestrial networks.

There is no positioning or navigation without a Reference Frame. In its Hidden Risks report, the United Nations Global Geodetic Center of Excellence (UN-GGCE) highlights the critical dependencies of modern society on the Global Geodesy Supply Chain. This supply chain encompasses all components required to produce geodetic products, such as global geodetic reference frames that form the foundation of navigation.

The Navigation Support Office at the European Space Operations Centre (ESOC) is ESA’s centre of excellence for Geodesy and precise navigation and is responsible for providing the Geodetic Reference for ESA missions. It is furthermore leading the Galileo Geodetic Service Provider Consortium that delivers the Geodetic Reference for Galileo.

Although different entities operate numerous components of the Global Geodesy Supply Chain, enabling global interoperable navigation requires collaboration across multiple international stakeholders. As of today, these activities are coordinated on a best effort basis by the International Association of Geodesy (IAG) and its corresponding services.

To ensure the alignment of ESA’s Geodetic Reference to the international references such as the International Terrestrial Reference Frame (ITRF), the Navigation Support Office contributes to the IAG services by providing data, processing capabilities and expertise. ESA is contributing to all four space geodetic services, acting as Analysis Centre (AC) for the International GNSS Service (IGS), the International Laser Ranging Service (ILRS), the International Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Service (IDS), and as associated AC for the International Very Long Baseline Interferometry (VLBI) Service (IVS). In addition to the official role in these IAG services, ESA provides numerous products enabling navigation such as a backup product for the Earth Orientation Parameter predictions, or metadata necessary to perform precise orbit determination such as estimated phase centre offsets for all GNSS constellations.

The presentation will highlight the importance as well as the weaknesses of the Global Geodesy Supply Chain for navigation and positioning and therewith for institutions, industry and modern society. It will describe ESA’s contributions to strengthen the supply chain to enhance the reliability and integrity of the geodetic products. It will highlight the ongoing developments to improve resilience and accuracy required to serve modern society needs such as climate research. The presentation will also expand on ongoing activities towards the Moon describing the needs and the status of the ongoing developments.