As of August, 2023, operational Galileo GNSS satellites, with some exceptions, have been updated and are now transmitting an improved I/NAV message. Users will see an enhancement in the Galileo E1 Open Service (OS) performance in terms of robustness and a significant reduction in time to first fix in challenging environments, with both unassisted and assisted GNSS. Backward compatibility is assured, with no impact on legacy receivers and low complexity implementation within OS receivers.
Galileo satellites broadcast different types of data in four navigation messages: the F/NAV and I/NAV navigation messages, a commercial navigation message (C/NAV) and a governmental navigation message (G/NAV). The latest upgrade comprises new features added to the I/NAV message, carried by the E1-B signal.
According to the EU Agency for the Space Program (EUSPA), the improved Galileo I/NAV signal now includes the Reed Solomon outer forward error correction (RS FEC2), enabling faster and more robust positioning. The RS FEC2 increases demodulation robustness at all times, enhancing sensitivity, while also improving overall time to retrieve clock and ephemeris data (CED) thanks to the broadcast of additional, redundant CED information. This allows the device to restore potentially corrupt data bits autonomously.
The reduced CED (RedCED) enables fast initial positioning, with lower than nominal accuracy, by decoding a single I/NAV word while waiting to receive the four I/NAV words carrying the full-precision CED. In combination, the new features allow users to obtain a rough first position much faster, while also significantly reducing the time required to obtain a first full-accuracy solution. The result is a much-reduced time to first fix, particularly when operating in difficult environments.
The improvements also benefit users working in assisted GNSS (A-GNSS) mode, through the new secondary synchronization pattern (SSP). In A-GNSS mode, when navigation data is received from non-GNSS channels, and when the receiver’s knowledge of the Galileo system time is affected by a relatively large error, clock uncertainty must be resolved quickly and reliably. With the I/NAV improvements, receivers can do this via the SSP feature, thus reducing TTFF in A-GNSS mode.
New I/NAV testing campaign
EUSPA is set to launch a testing campaign, open to receiver manufacturers, enabling participants to confirm the proper implementation and processing of the I/NAV improvements in their products. The tests will be conducted at the European Commission’s Joint Research Centre (JRC) in Ispra and at the European Space Agency facility in Noordwijk (ESA/ESTEC). Participants will be assigned to one of the two facilities depending on specific conditions and availability.