EGNOS Performances

EGNOS
Title	EGNOS Performances
Author(s)	GMV.
Level	Basic
Year of Publication	2011

EGNOS (European Geostationary Navigation Overlay Service) is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). EGNOS performances are usually described in terms of accuracy, integrity, availability and continuity.

EGNOS Performances Requirements

The performances required to EGNOS as per the EGNOS Mission Requirement Document are presented in the following table.

Service	Service Coverage	Accuracy (95%)		Integrity				Continuity	Availability
		Lateral	Vertical	HAL	VAL	TTA	Integrity Risk
Open Service	EU25 States (plus Norway and Switzerland) land masses	3m	4m	-	-	-	-	-	99%
SoL En-route and NPA	FIRs of ECAC 96	220m	-	556m	-	10s	1e-7/hour	1e-5/hour	99.9%
SoL APV-I	Land Masses of ECAC 96	16m	20m	40m	50m	6s	2e-7/150s	8e-6/15s	99%

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Typical Performances

The typical performances provided by EGNOS are presented in the next figures. For the computation, the day 7th February 2011, considered to be a representative day, has bee selected. The actual EGNOS messages have been taken from the EGNOS Message Server. The images have been generated with the eclayr tool.

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  Availability: The figure shows EGNOS availability map together with the iso-lines of availability compliance to APV-I service level availability requirements (i.e., HPL < 40 m and VPL < 50 m). The period of analysis corresponds to one day with the inner iso-line delimiting the user locations where a service level over 99% availability is achieved.

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  Continuity: The figure shows EGNOS continuity map together with the iso-lines of continuity risk compliance to APV-I service level. The continuity risk is computed as the probability of having a continuity event (Protection Levels bigger than Alarm Limits) during a period of 15 seconds provided that the service was available (Protection Levels smaller than Alarm Limits) at the start of the period. The inner iso-line, 1e-4, delimits the user locations which did not have a single continuity event during the analyzed day.

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  Accuracy: The figure shows EGNOS vertical accuracy map together with the iso-lines of 95% Vertical Position Error in metres. Users inside the inner iso-line had a vertical accuracy below 2 m (95%) for the analyzed day.

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  Integrity: The figure shows EGNOS vertical integrity margins as maximum Vertical Safety index map (maximum ratio between the vertical user error and the vertical user protection level). All values are under one meaning that no integrity failures at user level were observed.

Monitoring of EGNOS Performances

EGNOS performances are being monitored continuously by several entities, such as ESSP and ESA.

The EGNOS performance monitoring done by ESSP includes figures on achieved availability, continuity and integrity. In addition, it forecasts the performances in terms of availability and integrity.

The monitoring done by ESA is twofold. On the one hand, the messages, as broadcast by the EGNOS satellites, are analyzed to determine the status of several parameters, such as the GPS satellites which are augmented by EGNOS, the level of monitoring of the ionosphere over Europe or the achieved protection levels. On the other hand, ESA monitoring environment allows to select different reference stations and depicts the accuracy and integrity obtained for those sites.