The engineering team behind the signal technology underpinning Europe’s Galileo satellite navigation system has reached the final of this year’s European Inventor Award, run by the European Patent Office.
The team is led by Spanish engineer José Ángel Ávila Rodríguez – now part of ESA’s Galileo team – and his French colleague Laurent Lestarquit from France’s CNES space agency.
The team also includes German Günter Hein, formerly head of the department studying the evolution of EGNOS and Galileo for ESA, as well as Belgian Engineer Lionel Ries, now in ESA’s technical directorate, as well as French CNES engineer Jean-Luc Issler.
The engineers, who had previously worked together as members of the multinational Galileo Signal Task Force, came up with a pair of innovative signal modulation techniques to pack multiple Galileo signals together, simultaneously serving different sets of users while boosting signal performance and robustness. Both innovations have been adopted by Galileo and are in use today.
The first technique, called Alternative Binary Offset Carrier modulation, or ‘AltBOC’ for short, combines four signals into one large one, resulting in the widest bandwidth navigation signal ever transmitted. Two of these signals are sitting on the one carrier, namely E5a, while the other two are on E5b.
“AltBOC is a way of transmitting four components in a very wide bandwidth signal, using a single radio frequency chain on the satellite in an intelligent way, where originally two chains would have been needed to transmit in two separate frequency bands (E5a and E5b),” explains José Ángel, now ESA’s Global Navigation Satellite System Evolution Signal and Security Principal engineer for Galileo.
“The result is a frequency-rich signal that fundamentally improves positioning performance and robustness.
“AltBOC is interoperable with GPS in E5a/L5 and allows receiver manufacturers to process it as one very large signal – extending over the whole E5a and E5b range – or as two separate signals, one at each frequency carrier (E5a or E5b).
“AltBOC serves open service users in general. Moreover, when used in its full performance mode (E5a+E5b), it also facilitates geodetic and precision scientific applications such as gradual tectonic motion, or the use of accurate positioning on Earth – including proposed ‘reflectometry’ missions to make altimetry measurements from satnav signals reflected from Earth’s surface.
“But the application of AltBOC could go beyond the current use by providing accurate positioning to satellites in space thanks to its unique bandwidth characteristics.”
The second modulation method, known as Composite Binary Offset Carrier, or ‘CBOC’, results in a signal for use by the mass market, also possessing both a narrowband and a wideband component.
“For the best possible positioning performance, a satnav receiver needs to process the two parts of CBOC together, which is already today a reality for some applications thanks to the user advanced technology development of past years, and will certainly become the standard in the future,” adds José.
“At the same time, we needed a signal that would work with lower-end receivers today, such as those in smartphones and using narrow bandwidth front-ends. Those receivers are only using the narrowband component of CBOC for the moment.
“The current GPS system is using signals designed many years ago, back in the 1960s, and still does a good job of meeting today’s user needs, so we wanted to accomplish something similar with CBOC. This is a signal that already flies today and will be flying for another 20 years or more, so the availability of the wideband component helps future-proof it, offering manufacturers a means of extending receiver performance over time for mass market applications.
“The other requirement CBOC had to fulfil is to be interoperable with GPS in E1/L1, allowing receivers to use both sets of signals on a seamless basis – letting them see twice as many satellites at once.
“The Chinese are now planning to use a comparable ‘CBOC’ solution for the Beidou satellites, so the Galileo E1 Open Signal is really set to become the new standard for mass market applications. ”
Established a decade ago, the Galileo Signal Task Force was made up of experts from ESA and EU Member States, tasked with designing signals that would fulfil Galileo’s various technical, political, programmatic and security needs.
Today, the resulting signals are everyday reality, transmitted first by Galileo’s prototype GIOVE satellites from 2005, and operationally by the 18-satellite Galileo constellation from 15 December last year – with the full constellation due to be completed at the decade’s end.
“One of the nicest surprises is that the actual transmitted signals have more than met our expectations,” concludes José. “And we’ve seen a growing number of applications making use of the full CBOC signal. Scientists too are really making use of AltBOC – for altimetry and reflectometry in particular – to exploit it as fully as possible.”
The winners of the 12th European Inventor Award will be known on 15 June at the Arsenale di Venezia in Venice, Italy.
European Inventor Award 2017
Invention: Radio signals for better satellite navigation