Mass-market Global Navigation Satellite System (GNSS) receivers offer a low-cost positioning solution for agricultural robotics, which are increasingly needed to address food insecurity and a shrinking, ageing agricultural workforce. While high end GNSS receivers have become mainstream on large, expensive farm machinery such as tractors, smaller agritech robotics have to be price-competitive and therefore rely on mass-market GNSS receivers and other low-cost sensors. Mass-market receivers can deliver centimetre-level accuracy for precision agriculture, but this is typically demonstrated in more ideal open-sky conditions. In practice, agriculture also includes more challenging environments that are not usually considered in mass-market receiver applications, such as covered structures. In particular, polytunnels create a complex propagation environment that makes it harder to achieve precise and accurate positioning using GNSS alone.

To the authors’ knowledge, this is the first study to jointly characterise detailed signal-level behaviour and standalone positioning performance for a mass-market dual-frequency GNSS receiver operating inside a polytunnel. The experimental methodology uses identical u-blox F9P receivers placed inside and outside an ETFE-covered polytunnel, operating concurrently, to provide an open-sky reference against the covered environment. We analyse signal level metrics including carrier-to-noise density ratio (C/N₀), code-minus-carrier (CMC) and cycle slips, alongside receiver standalone GNSS position solutions and pseudorange residuals. The analysis considers multiple constellations primarily looking at GPS L1/L5 and Galileo E1/E5a signals. We analyse signal level metrics including carrier-to-noise density ratio (C/N₀), code-minus-carrier (CMC) and cycle slips, alongside receiver standalone GNSS position solutions and pseudorange residuals. The analysis considers multiple constellations primarily looking at GPS L1/L5 and Galileo E1/E5a signals.

The results show that the polytunnel’s metal frame and structure lead to a modest but systematic reduction in L1/E1 C/N₀ relative to open-sky conditions and introduce short-delay multipath, as indicated by metre-level oscillations in the de-meaned CMC time series and corresponding increases in the pseudorange residuals reported by the receiver relative to the open-sky reference. L5/E5a signals remain closer to the open-sky reference and appear more resilient to multipath under the same conditions, while cycle slip events are concentrated on a small number of lower-elevation L1/E1 links, with the carrier phase remaining largely continuous and trackable. This degradation in signal quality leads to a reduction in the precision of the receiver’s position inside the polytunnel. Finally, we discuss what these findings mean for the design of GNSS and its integration in navigation for a polytunnel, whilst outlining practical ways to overcome these challenges induced by the polytunnel.

Global Navigation Satellite Systems (GNSS) and Satellite-Based Augmentation Systems (SBAS) are now widely used across various domains, ranging from automotive applications to safety-of-life services. Due to their rapid evolutions, constantly aiming to improve the accuracy and robustness of the PVT (Position, Velocity and Time) solutions offered, a continuous wave of application design, development, and updates are today experienced.

Open access to PVT algorithms is thus essential to accelerate application development and foster education. As proprietary algorithms embedded in industrial receivers limit experimentation and learning, the development of open-source alternatives such as GNSS-SDR and FGI-GSRx is invaluable. However, these solutions often present challenges in code comprehension and deployment across software and hardware platforms.

To address such challenges, the GRIPP system (GNSS/SBAS Receiver, Independent and Portable PVT) has been introduced at ENC 2025. Compatible with Galileo, GPS and EGNOS signals across multiple frequency bands, GRIPP combines portability, modularity, and ease of customization, enabling for junior engineers and students the opportunity to code by themselves a GNSS/SBAS receiver.

The hardware architecture integrates a Raspberry Pi (acting as the PVT computation unit and datastore), a Pocket SDR front-end device, and an L-band antenna. On the software side, GRIPP adopts a client-server architecture. The back-end server leverages Pocket SDR software to interface with the corresponding device and retrieve raw measurements and navigation bits, while PVT computation is managed through modular blocks, enabling easy reconfiguration and community-driven enhancements. A datastore complements the architecture, storing the different data flown down by the server, and being able to store correction messages that can be injected into the system.

This study presents the first release of GRIPP software, along with use cases and captured datasets demonstrating its potential as an accessible and educational platform. Finally, the updated release calendar and development roadmap for the coming year will be outlined, highlighting GRIPP role in lowering barriers to GNSS/SBAS technology research and development, fostering collaborative innovation.

The Galileo 2nd Generation (G2G) development phase is accelerating with the deployment of testing signals on first generation satellites. These signals, which include the E5a Quasi-Pilot (E5aQP) component, allow the experimentation of new features and services, which will be fully developed and matured with the G2G satellites. The E5aQP component has been developed to respond to the demand for low-complexity acquisition signals favorable for snapshot positioning and Internet-of-Things (IoT) devices. The format of the E5aQP signal has been disclosed in November 2025 in the latest version of the Galileo Interface Control Document (ICD) and consists in the repetition of a short Pseudo-Random Noise (PRN) sequence of 330 chips. The E5aQP signal is Binary Phase-Shift Keying (BPSK) modulated with a chipping rate equal to 5.115 Mchips/seconds. It is transmitted at the same centre frequency of the E5a components and is designed to aid the E5a acquisition by providing an efficient way for estimating the signal Doppler frequency. In this way, the search space for the E5a signal parameters is significantly reduced.
This paper describes the first results obtained by processing Galileo E5aQP signals collected from the satellites reconfigured for transmitting quasi-pilot components. E5a baseband In-phase/Quadrature (IQ) samples have been collected using a Software Defined Radio (SDR) front-end and processed with a custom SDR receiver developed in Python. Different acquisition schemes have tested and compared for the processing of the E5aQP component, which is currently data-less. An efficient parallel Fast Fourier Transform (FFT) acquisition engine has been developed. The algorithm exploits the short duration of the E5aQP signal, which is approximately 0.065 ms. After carrier wipe-off, the input samples are wrapped and accumulated in a data buffer of size equal to the E5aQP code duration. The accumulation accounts for the fact that the sample frequency and the code duration may not be commensurable. This operation significantly reduces the length of the data, which are correlated using a standard FFT-based approach with the E5aQP local code. While coherent integration can be extended arbitrarily though the data wrapping and accumulation process, correlation is performed only on a short data block corresponding to the E5aQP code duration. This approach is compared with standard approaches showing the opportunities brought by the structure of the current E5aQP signals. Figures of merits such as computational complexity and execution time are experimentally evaluated.
The paper also investigates different hand-over approaches for the acquisition of the E5a signals. More specifically, Doppler aiding from the E5aQP signal is implemented for the acquisition of the E5a pilot component. The search space of this component is significantly reduced and involves only the delay domain. Also in this case, different options are investigated including the use of a parallel search based on the FFT and a serial search limited to the code ambiguities left when the code delay of the E5aQP is known.
The paper provides a complete overview of the potentialities and limitations offered by the E5aQP signals transmitted by Galileo first generation satellites.