GNSS mobile apps: Data outputs and Galileo

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29 November 2016
Galileo is an invaluable resource for mobile developers working on precise positioning applications.


With more signals and better accuracy, Galileo is an invaluable resource for mobile developers working on precise positioning applications. During the first Galileo Hackathon at the WhereCamp in Berlin, experts from the European Commission’s Joint Research Centre (JRC) shared how Galileo is boosting accuracy and making positioning applications more precise.

App-developers at the first GSA Hackathon in Berlin got a full technical briefing on the latest developments and opportunities for GNSS and Location Based Services (LBS) at Beuth Hochschule für Technik. The packed briefing session heard why the GSA wants the developer community to play with Galileo data, how it hopes to stimulate the community to use Galileo signals to enhance their applications and, therefore, bring the two closer together.

To give the users further insight on the various data outputs and capabilities of Galileo, and GNSS in general, Michele Bavaro of the European Commission’s Joint Research Centre (JRC) described his work in testing Galileo ready receiver hardware.

1st Galileo Hackathon - watch the video here

Testing hardware

Broadly, two main categories of GNSS receivers exist: professional precision receivers and mass-market (currently only single frequency) receivers. Professional receivers are used for applications requiring high-accuracy, typically at decimetre, centimetre and even millimetre level. The mass-market category includes the chipsets found in smartphones, tablets, sat-navs, trackers, cheap drones and wearable electronics.

Last year JRC was involved in the assessment of Galileo-compliance and also characterised the effects of interference for a total of seven precision receivers. More recently, JRC has worked closely with the GSA and assessed the availability and consistency of the Galileo observables on the BQ Aquaris X5 Plus smartphone.

In the video we can see the list of all GPS and all GALILEO satellites the device has in sight. We can see values such as the ID of the satellite, SNR (Signal to Noise Ratio), Elevation, and Azimuth. The flags show if the satellite is Used in Fix, whether that satellite provides the Almanac for the constellation and the Ephemeris.

“Galileo is different to the current GPS system,” Bavaro stated. “It has more signals and better accuracy: essentially I believe it is the future of navigation.” He showed the results of simulated and real world testing of combined GPS + Galileo signals in both static and mobile situations. All the receiver manufacturers had been extremely supportive during the testing.

Bavaro said that the residuals of the Galileo E1 signal were smaller than those of the equivalent GPS L1 signal and that the performance of the combined (GPS+Galileo) signals was always better in both nominal and interference testing scenarios. The accuracy in live mobile testing could only be partially assessed due to the limited number of Galileo satellites available at the time.

The results of the testing showed that Galileo support is mature in most precision professional receivers and, where it is not, manufacturers are ready to implement changes and improve their firmware. Chipsets for the mass-market mainly support Galileo as an adaptation of their legacy GPS technology, so the full potential benefits of the modernised Galileo Signal in Space (SIS) are not necessarily exploited. Those chipsets, unlike professional ones, are also required to maintain minimal battery power drain and have to rely on simplified front ends and antennas.

Galileo for smartphones

Smartphones and tablets are often connected to Internet, allowing them to fully explore web based Assisted GNSS (reducing their time to first fix (TTFF) to a few seconds). In other words the navigation information (on satellite orbits and clocks), which normally needs to be decoded from live SIS can be retrieved from the Internet instead, with a validity of several days. In addition the computational core of the GNSS receiver is a small piece of silicon Intellectual Property (IP) inside a System on Chip (SoC) which also integrates the application processor.

“The Galileo E1 Open Service (OS) signals are designed with an in-phase pair of data and pilot,” explained Bavaro. “The availability of a (data-less) pilot channel represents a unique asset for smartphones as it allows a level of processing gain, and therefore sensitivity, only bounded by the quality of the receiver's internal oscillator.”

Such oscillators have greatly improved in the last decade driven by the need for high data-rates on cellular networks (4G) and WiFi. From a 200 milliseconds signal snapshot a smartphone can derive a very precise, unambiguous ranging signal to Galileo satellites by leveraging the pilot codes. This is much harder to do with GPS signals.

The Galileo E1BC signals also overlap in frequency with GPS L1 thus they don't require additional radio frequency circuitry inside a GNSS chip, just more silicon for digital signal processing. The binary offset carrier (BOC) modulation used by Galileo is more robust compared to GPS in most modern receiver architectures and another obvious advantage of Galileo E1BC modulation is that it has three times higher accuracy than the legacy GPS.

Galileo uses longer codes compared to GPS, which makes the code synchronisation search longer and more difficult to perform for a receiver, but in turn the ranging has much larger ambiguity of 1200 km compared to 300 km for GPS. Again this greatly reduces the search space for all receivers.

Trends in GNSS

Bavaro identified the major trends in GNSS research as Protect, Toughen and Augment (PTA). There is a need to introduce rules to protect the valuable spectrum which is the basis for provision of position and time globally. In parallel GNSS vulnerabilities must be addressed, making satellite navigation more resilient to malicious attacks or involuntary-induced signal anomalies such as jamming and spoofing. And finally synergies with other technologies must be assessed that can increase availability and robustness.

Today everyone carries at least one GNSS receiver and the mass market needs ever increasing availability, accuracy and reliability. With the advent of drones and self-driving vehicles coexisting with humans’ personal space there is a requirement for even more accuracy, availability and reliability. This means there is a need for both an enhanced Signal in Space and the integrity service provided by EGNOS.

“Today satellite positioning is done by billions of people using signals designed 40 years ago as secondary channels for military users - GPS L1 C/A stands for ‘Coarse Acquisition’,” says Bavaro. “Europe has a unique opportunity to provide the new de-facto standard for GNSS. It is obvious that, if all the vulnerabilities are accounted for, it is time to start building user accuracy, availability and reliability on top of a modern PNT system, and Galileo may well be all or part of that system.”

“Galileo signals are inherently more accurate. The future for locations is based on accuracy, so Galileo is an answer,” he concluded. “Galileo was born to be compatible with GPS so it is also relatively cheap and easy to integrate with existing GNSS receiver technology.”

“Galileo signals are inherently more accurate. The future for location is based on accuracy.”

More information:
European Commission Joint Research Centre (JRC)

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Updated: Jan 16, 2017