For the first time, position fixes in real time using signals from Galileo have been achieved with an open source software receiver. The milestone was achieved by a research team from the Statistical Inference Department at the Centre Tecnològic de Telecomunicacions de Catalunya (CTTC), which manages the development of the open source project GNSS-SDR.
Professional, full-featured receivers are expensive, and even in those cases the users have limited access (if any) to know exactly how position and time information were computed, CTTC said. In addition, these receivers exhibit very few upgrading capabilities. A software receiver allows all kind of modifications and inspections. “GNSS-SDR unleashes the full potential of the signals and, best of all, it is open and for free,” said Carles Fernández-Prades, GNSS-SDR project manager and Head of the Communications Systems Division at CTTC.
A GNSS software receiver is a computer program that performs all the signal processing from raw satellite signals to the computation of position, velocity and time, just as is done by the GPS chips that are embedded in smartphones and other devices with satellite-based positioning capabilities. The key difference relies on the great flexibility in the design, upgradability and the experimentation possibilities that the software version allows, in opposition to integrated circuits, true black boxes with inputs and outputs but with no accessible information about what is going on inside of them.
“With GNSS-SDR, researchers and technology enthusiasts can easily change the implementation of a certain functional block and assess the impact of that change on the whole receiver performance,” said Pau Closas, GNSS-SDR scientific advisor and Head of the Statistical Inference Department at CTTC. “This paves the way to innovative mass-market, industrial and scientific applications that could make use of Galileo signals but require non-standard features which are not present in mass-market receivers nor in costly professional equipment.”
The first Galileo-based positioning fix, obtained by Javier Arribas using a general purpose GNSS antenna and a RF front-end connected to a commodity PC running GNSS-SDR represents an important milestone in the research on GNSS receiver design. “Next steps will be devoted to provide outputs in standard formats that will allow the application of geodesic-grade tools for extremely precise positioning (on the order of centimeters) and higher degrees of reliability,” Arribas said.
GNSS-SDR is the first open source solution that offers this possibility, CTTC said. The source code released under the GNU General Public License (GPL) secures practical usability, inspection, and continuous improvement by the research community, allowing the discussion based on tangible code and the analysis of results obtained with real signals. The source code is complemented by a development ecosystem, consisting of a website, as well as a revision control system, instructions for users and developers, and communication tools.
With GNSS-SDR, researchers from CTTC (with the aid of an open community created around the project, such as the students participating in the Google Summer of Code program in 2012 and 2013 Luis Esteve, Mara Branzanti, Daniel Fehr and Marc Molina) are offering a tool that fosters the use of GPS and Galileo signals in unexpected new ways, making possible applications with unforeseen benefits in a wide range of fields, such as geodesy, robotics, unmanned vehicles and safety-related systems.