I/NAV improvements are now available to all Galileo Open Service users

The Galileo OS has been upgraded with three new features added to its I/NAV message, one of the four message types broadcast by Galileo satellites. Collectively referred to simply as I/NAV improvements, these features are now available to all Galileo Open Service users.

Starting on 12 August 2023, the gradual process of upgrading the operational Galileo FOC constellation satellites has been finalized, and the I/NAV improvements are openly accessible through the I/NAV message carried by the E1-B signal.

In simple terms, in case you have experienced delays when turning on your GNSS device, the I/NAV improvements can reduce them significantly. Let’s have a look at the features more in detail.

The Reed Solomon Outer Forward Error Correction (RS FEC2) increases demodulation robustness at all times and therefore enhances the sensitivity. It also improves the overall time to retrieve Clock and Ephemeris Data (time to CED) thanks to the broadcast of additional, redundant CED information, while allowing for the device to restore potentially corrupted data bits autonomously.

The Reduced Clock and Ephemeris Data (RedCED) allows for a fast-initial positioning, albeit with lower than nominal accuracy, by decoding one single I/NAV word, while waiting to receive the four I/NAV words carrying the full-precision CED.

The combination of these two features allows not only to obtain a first coarse position solution much faster (RedCED), but also to reduce significantly the time required to obtain a first full accuracy solution (RS FEC2). This translates into a much-reduced Time to First Fix (TTFF) for the OS users, particularly when operating in harsh environments.

The improvements also benefit applications working in assisted GNSS (A-GNSS) mode, through the Secondary Synchronisation Pattern (SSP). In A-GNSS mode, when navigation data is received from non-GNSS channels and the receiver’s knowledge of the Galileo System Time is affected by a relatively large error, typically in the order of a few seconds, the clock uncertainty must be resolved quickly and stably.

With the I/NAV improvements, receivers will be able to do this via the new SSP feature, thus reducing the TTFF also in A-GNSS mode.

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