EGNOS improves the performance and reliability of GPS today, and of Galileo in the future.
EGNOS increases the accuracy of the GPS satellite navigation signals. It provides information on the level of confidence a user can have about the positioning and timing provided by the GPS satellites, a concept known in the business as ‘integrity’. In addition, EGNOS provides information on the continuity of the GPS signals (the system’s ability to function without interruption) and its availability (the percentage of time during which the signals fulfil the accuracy, integrity and continuity criteria).
How does EGNOS help you?
EGNOS enables users with an EGNOS-compatible GPS receiver to:
- improve the accuracy of their location to about one metre;
- access integrity data which validate the signals transmitted by GNSS satellites along with alerts in near real time (less than six seconds) of any shortcomings in the reliability of the positioning signals;
- benefit from accurate and reliable synchronisation with Universal Time Coordinated (UTC).
One of the main advantages of EGNOS is the improved accuracy in relation to a position solely calculated using GPS. EGNOS broadcasts differential corrections to GPS satellite orbits, clocks and the Earth’s ionosphere, which can affect the signal.
EGNOS provides a horizontal accuracy better than three metres and a vertical accuracy better than four metres.
Another important EGNOS benefit is the integrity information it delivers. GPS alone does not provide such information. EGNOS broadcasts an integrity signal, giving users the information they need to calculate a confidence interval, and alerting them when a GPS satellite malfunctions and is not to be used for an application, especially where safety is a factor.
The data produced and transmitted by EGNOS includes information on GPS satellite orbits, clock errors and estimates of errors due to the Earth’s ionosphere.
Synchronisation with UTC
The EGNOS system uses a system time known as EGNOS Network Time (ENT), which is linked to Universal Time Coordinated (UTC). All the differential corrections broadcast by EGNOS are referenced according to ENT.
Thus, the time obtained by the user when he/she calculates his/her position using EGNOS data is also referenced in ENT, not to the GPS clock. In addition, EGNOS also broadcasts a specific message containing several parameters allowing the receiver to estimate a UTC. The user then has a precise, reliable time directly synchronised with UTC. The accuracy obtained through EGNOS relative to UTC is less than 50 nanoseconds.
UTC is a timescale which serves as an international reference time. It is close to Universal Time (UT), which is directly linked to the Earth’s rotation and differs from International Atomic Time (TAI) by an integral number of seconds.