Using EGNOS as a UTC time source for time distribution systems

Time distribution is a system in which a master clock is responsible for synchronising one or more slave receiver clocks. In this application, the master clock synchronises itself using the Universal Time Coordinated (UTC) time provided by EGNOS and redistributes this time to the slave clocks.

Advantages of using EGNOS

Here, EGNOS Network Time (ENT) is synchronised with the UTC time issued by the Paris Observatory (UTC(OP)) in order to synchronise the master clock.

Architecture:

The master clock consists of a GPS/EGNOS receiver linked to an application engine (a microcontroller) and an integrated or offset antenna. The antenna must have a clear 'line of sight' in order to pick up the GPS and EGNOS signals. The receiver transmits its data to the microcontroller via e serial link.

Figure: Architecture of a Time Distribution system 

Figure: Architecture of a Time Distribution system

Functions used

When the receiver uses the GPS and EGNOS data to calculate the PVT, the time calculated is ENT. To obtain UTC time, a correction model is used applying data from the EGNOS type-12 message.

Receiver constraints

In this application the receiver in native mode is not accepting the MT12 corrections sent by EGNOS, but it can nevertheless calculate a position, velocity, and time (PVT) solution using GPS data and EGNOS's fast, long-term and ionospheric corrections (MT2-5, 6, 18, 24 and 26). The receiver must be able to supply the complete EGNOS message to the master clock application. The UTC correction is performed in this application.

Implementation details

  • The microcontroller must initialise the receiver's parameters in accordance with the manufacturer documentation, so that it:
  • Can use EGNOS data;
  • Ignores the type 0 message, where necessary;
  • Excludes, if possible, the use of the geostationary satellite used for EGNOS testing (Artemis in 2008);
  • Issues the EGNOS message as well as the PVT solution.

Once this initialisation has been completed, the microcontroller has to accept the messages from the receiver and wait for it to issue a PVT solution that takes EGNOS into account (the protocols indicate whether the solution has been calculated with GPS alone or with a SBAS satellite, and an EGNOS message.

When the microcontroller has received the PVT solution and the EGNOS message, it must then extract the type 12 message and correct the UTC time.

The UTC time obtained can then be sent to the slave clocks, correcting where necessary any delays due to calculation or data transmission.

These operations are repeated according to the refresh period for the PVT solution sent by the receiver. In most cases this period is one second.

More sample applications

Precision farming with EGNOS

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Creating a time distribution system

 

Using EGNOS through the EDAS service

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Using EGNOS's integrity mechanisms

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