EGNOS SoL by ESA

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SafetyofLife

Service DefinitionDocument

European Commission

Directorate-General for Enterprise and Industry

Ref : EGN-SDD SoL, V1.0


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Document Change Record

Revision Date Summary of Changes

1.0 02/03/2011 First release of the document

Approved by Date

Paul Verhoef, European GNSS Programme Manager 02/03/2011


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i European Union 2011Document subject to terms of use and disclaimers p. 4 - 6EGNOS SoL SDD, Issue 1.0, February 2011

Table of Contents

1. Executive Summary ................................................................................................................. 1

2. Introduction .............................................................................................................................. 3

2.1. Purpose And Scope Of The Document ............................................................................................. 3

2.2. Egnos SoL Service Description ........................................................................................................4

2.3. Terms And Conditions Of EGNOS SoL Service Use, Including Liability .......................................4

2.3.1. Scope Of The EGNOS Safety of Life Service Commitment...........................................................4

2.3.2. Who Can Use The EGNOS SoL Service? ..................................................................................... 4

2.3.3. Obligations Of The Users To Exercise Due Care ........................................................................... 5

2.4. Reference Documents ........................................................................................................................6

3. Description Of The Egnos System And Egnos SoL Service Provision Environment ....... 7

3.1. High Level Description Of The EGNOS Technical Framework .......................................................7

3.1.1. Satellite Navigation Concept ..........................................................................................................73.1.2. Errors Affecting User Positioning ...................................................................................................7

3.1.3. Objective of EGNOS ......................................................................................................................8

3.1.4. GPS Overview ................................................................................................................................9

3.1.4.1. GPS Services .......................................................................................................................................... 9

3.1.4.2. GPS Architecture .................................................................................................................................... 9

3.1.5. EGNOS Overview ..........................................................................................................................9

3.1.5.1. EGNOS Services .................................................................................................................................... 9

3.1.5.2. EGNOS: One SBAS Amongst Others ................................................................................................... 11

3.1.5.3. EGNOS Architecture ............................................................................................................................. 11

3.2. EGNOS Organisational Framework ................................................................................................15

3.2.1. Bodies Involved in the EGNOS Programme and Service Delivery ..............................................15

3.2.2. How to get Information on EGNOS and EGNOS Applications or Contact the Service Provider ..15

4. EGNOS SIS ............................................................................................................................. 17

4.1. EGNOS SIS Interface Characteristics .............................................................................................17

4.1.1. EGNOS SIS RF Characteristics ...................................................................................................17

4.1.2. EGNOS SIS Message Characteristics ......................................................................................... 17

4.2. EGNOS Time and Geodetic Reference Frames ............................................................................. 18

4.2.1. EGNOS Terrestrial Reference Frame ETRF 23 ........................................................................ 18

4.2.2. EGNOS Network Time: ENT GPS Time Consistency ............................................................... 19

4.3. EGNOS SIS Performance in the Range Domain ............................................................................ 20

4.3.1. Accuracy in the Range Domain....................................................................................................20

4.3.2. Integrity in the Range Domain......................................................................................................21

5. EGNOS Receivers .................................................................................................................. 23

5.1. EGNOS Receivers For Aviation .......................................................................................................23

5.2. Receiver & Avionics Certification ...................................................................................................23

6. EGNOS SoL Service Performance ........................................................................................ 25

6.1. EGNOS SoL Service Description and Characteristics .................................................................. 256.2. EGNOS SoL Service Performance Requirements ......................................................................... 25


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6.3. EGNOS SoL Minimum Service Performance Characteristics ......................................................26

6.3.1. NPA - Non Precision Approach .................................................................................................... 27

6.3.1.1. Accuracy ...............................................................................................................................................27

6.3.1.2. Integrity .................................................................................................................................................27

6.3.1.3. Availability .............................................................................................................................................27

6.3.1.4. Continuity .............................................................................................................................................28

6.3.2. APV-I - Approach with Vertical Guidance .................................................................................... 29

6.3.2.1. Accuracy ...............................................................................................................................................29

6.3.2.2. Integrity .................................................................................................................................................29

6.3.2.3. Availability ............................................................................................................................................29

6.3.2.4. Continuity ..............................................................................................................................................30

6.4. EGNOS SoL Service Limitations .....................................................................................................31

Appendix A. EGNOS SoL Service Performance Observed During the Independent Performance

Assessment used for EGNOS v.2.2-EXT ............................................................. 33

Appendix A.1 Data ................................................................................................................................33

Appendix A.2 EGNOS SIS Availability ................................................................................................34Appendix A.3 Accuracy ........................................................................................................................34

Appendix A.4 Availability .....................................................................................................................36

Appendix A.5 Continuity ......................................................................................................................37

Appendix B. EGNOS SoL Service Accuracy ............................................................................. 41

Appendix C. EGNOS integrity concept ..................................................................................... 43

Appendix D. Definitions .............................................................................................................. 47

Appendix E. Acronyms ............................................................................................................... 51


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List of Figures

Figure 1. Existing and planned SBAS systems .......................................................................................... 11

Figure 2. EGNOS architecture ...................................................................................................................12

Figure 3. EGNOS RIMS sites .....................................................................................................................13

Figure 4. ENT GPS time offset evolution (Period Feb 2008 - March 2010) ...............................................19

Figure 5. EGNOS service area used for SREW computation .................................................................... 20

Figure 6. EGNOS NPA availability ..............................................................................................................27

Figure 7. EGNOS NPA continuity ...............................................................................................................28

Figure 8. EGNOS APV-1 availability........................................................................................................... 29

Figure 9. EGNOS APV I continuity .............................................................................................................30

Figure 10. Network of monitoring stations .................................................................................................... 33

Figure 11. EGNOS SIS availability ...............................................................................................................34

Figure 12. Horizontal position error histogram for PRN124 (logarithmic plot) ..............................................35

Figure 13. Vertical position error histogram for PRN124 (logarithmic plot) ..................................................35

Figure 14. Horizontal position error map for PRN124 .................................................................................. 35

Figure 15. Vertical position error map for PRN124.......................................................................................35

Figure 16. EGNOS combined availability for PRN120-PRN124 ..................................................................36

Figure 17. Compliance to the 99% Availability reference baseline ............................................................... 37

Figure 18. EGNOS combined continuity for PRN120-PRN124 .................................................................... 38

Figure 19. Continuity Compliance to the 10-4 reference ............................................................................... 38

Figure 20. Continuity Compliance to the 510-4 reference...........................................................................38

Figure 21. APV-I accuracy expected from EGNOS ...................................................................................... 41

Figure 22. Possible situations when navigating with EGNOS ...................................................................... 45

Figure 23. ECAC service volume .................................................................................................................49

Figure 24. ECAC landmasses ......................................................................................................................50


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List of Tables

Table 1. Reference documents ...................................................................................................................6

Table 2. GEOs used by EGNOS ...............................................................................................................12

Table 3. Where to find information about EGNOS ....................................................................................16

Table 4. EGNOS SIS transmitted MTs ......................................................................................................18

Table 5. Typical EGNOS and GPS stand-alone SIS UERE ...................................................................... 21

Table 6. EGNOS equipment operational classes......................................................................................23

Table 7. Existing ETSOs and hardware requirements for SBAS operations ............................................24

Table 8. SoL service performance requirements (ICAO). .........................................................................26

Table 9. EGNOS SoL Service performance values ..................................................................................26

Table 10. Approach with vertical guidance accuracy .................................................................................. 29

Table 11. EGNOS SoL service limitations .................................................................................................. 32

Table 12. Accuracy performance summary (Position error)........................................................................34

Table 13. RTCA MOPS C&D terminology differences for navigation mode ................................................48


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1. Executive Summary

The European Geostationary Navigation Overlay Service (EGNOS) provides an

augmentation signal to the Global Positioning System (GPS) Standard PositioningService (SPS). Presently, EGNOS augments GPS using the L1 (1575.42 MHz) Coarse/Acquisition (C/A) civilian signal function by providing correction data and integrityinformation for improving positioning and navigation services over Europe.

The EGNOS Safety of Life (SoL) Service is provided openly and is freely accessiblewithout any direct charge and is tailored to safety-critical transport applications invarious domains, in particular for aviation applications. The service is thus compliantwith the aviation APV-I (Approach with Vertical Guidance) requirements , as defined byICAO in Annex 10, but may support also applications in other SoL domains. The use ofthe EGNOS SoL Service may require specific authorisation by the relevant authorities

in the application sectors concerned.

This version of the EGNOS SoL Service Definition Document (EGNOS SoL SDD) isintended to give information on the EGNOS SoL Service, which is mainly designed foraviation users.

The document describes the EGNOS system architecture and Signal-In-Space (SIS)characteristics, the SoL service performance achieved with the current EGNOSSystem Release (ESR) V2.2ext and provides in addition information on the establishedtechnical and organisational framework, at European level, for the provision of thisservice. It is intended to be of use for Air Navigation Service Providers (ANSPs),receiver manufacturers, equipment integrators, airlines, operators, GNSS applicationdevelopers and the final users of the EGNOS SoL Service.

The document includes also high level information on GNSS concepts, the GPSService, the EGNOS System/Services, the EGNOS Management structure and EGNOSinterfaces with users, as well as the minimum performance of the EGNOS SoL Service.The observed performance of the EGNOS SoL Service over a specified period is alsogiven in appendices A and B.

This document is not intended to address EGNOS Open Service (OS) performance.Information about the EGNOS OS is available in a separate document called theEGNOS Service Definition Document Open Service (EGNOS SDD OS - [RD-6]).

This document will be updated in the future as required in order to reflect any changesto the EGNOS SoL Service.


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2. Introduction

2.1. Purpose And Scope Of The Document

The EGNOS SoL SDD presents the characteristics of the service offered to users byEGNOS by highlighting the positioning performance currently available to suitablyequipped users using both the GPS SPS broadcast signal and the EGNOS augmentationsignals.

The minimum level of performance of the EGNOS SoL Service as specified in theEGNOS SoL SDD is obtained under the condition that compliance is ensured with:

the main GPS SPS SIS characteristics and performance defined in the GPSICD [RD-4], in SBAS MOPS appendix B [RD-2] and in GPS SPS PerformanceStandard [RD-3] and;

the receiver characteristics as described in chapters 3 and 4.

The EGNOS SoL SDD comprises 6 main sections:

the first section is an executive summary of the document

the second section (Introduction) defines the scope of the document and therelevant reference documents, and clarifies with the terms and conditions ofEGNOS SoL Service use, including liability, and its intended life time;

the third section (Description of the EGNOS system and EGNOS SoL serviceprovision environment) gives a brief description of the Satellite Navigation

concept and the technical and organisational framework for EGNOS serviceprovision;

the fourth section (EGNOS SIS) introduces the EGNOS SIS characteristicsand performance in the range domain;

the fifth section (EGNOS Receivers) briefly presents the certification contextfor aviation receivers.

the sixth section (EGNOS SoL Service Performance) describes the positioningService offered to users by the EGNOS SoL Service and the minimumperformance in the positioning domain;

the document also includes information concerning the EGNOS performancecollected during the pre-operational life of the EGNOS system (Appendix A),the expected accuracy (Appendix B) and the integrity concept used in EGNOS(Appendix C).

Finally, definitions and the list of acronyms used in the document can be foundin Appendix D and Appendix E, respectively.

While the EGNOS performance reported in section 4.3 and 6 represents the minimumperformance that can be expected when using the EGNOS SoL Service, the performancereported in Appendix A shows the performance of the SoL Service as it can typically be

observed in reality.This document does not address the Open Service (OS) [RD-6] and the CommercialData Distribution Service (CDDS) that are described in separate dedicated Service


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Definition Documents. The CDDS SDD will be published at the time of entry intooperation of this service.

2.2. Egnos SoL Service Description

The EGNOS SoL Service consists of signals for timing and positioning intended for

most transport applications in different domains. Nevertheless, navigation operationsbased on the EGNOS SoL Service may require a specific authorisation, issued by therelevant authority, unless the authority, or applicable regulation, establishes that nosuch authorisation is required.

The SoL service is based on integrity data provided through the EGNOS satellitesignals.

The main objective of the EGNOS SoL service is to support civil aviation operationsdown to LPV (Localiser Performance with Vertical guidance) minima. Therefore theservice is compliant with aviation APV-I (Approach with Vertical Guidance) requirementsdefined in the ICAO Standard and Recommended Practices (SARPs) for SBAS [RD-1].

However, the SoL Service is also intended to support applications in a wide range ofother domains such as maritime, railways and road.

The EGNOS SoL Service is available from the 2nd March 2011 and is intended to beprovided for a minimum period of 20 years with at least a six-year advance notice incase of significant changes to the service provided, in compliance to ICAO SARPS[RD-1].

2.3. Terms And Conditions Of EGNOS SoL Service Use, IncludingLiability

2.3.1. Scope Of The EGNOS Safety of Life Service Commitment

The EGNOS Safety of Life service (further EGNOS SoL Service) comprises theprovision of an augmentation signal to the Global Positioning System (GPS) StandardPositioning Service (SPS) with the specific committed performance and subject to theservice limitations described here in the EGNOS SoL Service Definition Document(further EGNOS SoL SDD).

Only minimum performance characteristics are included in the commitment eventhough the users can usually experience a better performance. These characteristicsare expressed in statistical values under given assumptions.

2.3.2. Who Can Use The EGNOS SoL Service?

In general, the EGNOS SoL Service is intended for most transport applications indifferent domains where lives could be endangered if the performance of the navigationsystem is degraded below specific accuracy limits without giving notice in the specifiedtime to alert. This requires that the relevant authority of the particular transport domaindetermines specific requirements for the navigation service based on the needs of thatdomain, as well as certification procedures if necessary. In addition, the navigationoperations based on the EGNOS SoL Service may require a specific authorisation,issued by the relevant authority, unless the authority, or applicable regulation, establishesthat no such authorisation is required.

At the date of EGNOS SoL SDD publication, only the aviation domain has specificservice requirements, as well as certification and individual authorisation proceduresdeveloped and implemented.


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Therefore, from the date of EGNOS SoL SDD publication the EGNOS SoL Service isonly offered for use in aviation, for all phases offlight within the corresponding EGNOSSoL Service area, to aviation users (further Aviation Users) namely:

airspace users, as defined in the Single European Sky framework Regulation1,equipped with an EGNOS certified receiver and located within the appropriate

EGNOS SoL Service area corresponding to the phase offl

ight in which theEGNOS SoL Service is used (as described in the EGNOS SoL SDD);

certified Air Navigation Service Providers having signed a working agreementwith ESSP SAS that is valid at the moment of the use of the EGNOS SoLService.

2.3.3. Obligations Of The Users To Exercise Due Care

EGNOS is a complex technical system and the users also have certain obligations toexercise due care in using the EGNOS SoL Service. Before any use of the EGNOSSoL Service, all users should study the EGNOS SoL SDD (available on the ESSP

SAS website http://www.essp-sas.eu/ ) in order to understand if and how they can usethe service, as well as to familiarise themselves with the performance level and otheraspects of the service they can rely on.

In case of doubt the users and other parties should contact the ESSP SAS helpdeskat [email protected]. Aviation Users may also contact their NationalSupervisory Authority.

- DISCLAIMER OF LIABILITY -

The European Union, as owner of EGNOS, and ESSP SAS, as EGNOS services

provider, disclaim all warranties of any kind (whether express or implied) to any party,other than Aviation Users specified under 2.3.2 above, and/or for any other use ofthe EGNOS SoL Service including, but not limited to, availability, continuity, accuracy,integrity, reliability and fitness for a particular purpose or user requirements.

By using the EGNOS SoL Service, the user agrees that the European Union and ESSPSAS shall not be held liable for any indirect or consequential loss or damage, such asloss of profits, business, contracts, anticipated savings, goodwill or revenue, resultingfrom the use, misuse, or inability to use the EGNOS SoL Service.

Furthermore, no party shall be entitled to any claim against ESSP SAS and/or theEuropean Union if the damage is the result, or the consequence, of one of the following

events:

Use of EGNOS SoL Service beyond the conditions and limitations of use setforth in the EGNOS SoL SDD, or

Use of equipment or receivers which are

not fully compliant to MOPS (Minimum Operational Performance Standardsfor Global Positioning System/Wide Area Augmentation System AirborneEquipment) or

not certified or approved by the relevant competent authority or

malfunctioning, or

1 Regulation (EC) No 549/2004 of the European Parliament and of the Council of 10th March 2004 laying down the

framework for the creation of the single European sky (the framework Regulation).


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Use of the EGNOS SoL Service when a test message is broadcast (a MessageType 0 or a Message Type 0/2), or

Use of the EGNOS SoL Service without required authorisation, or

In case of a Force Majeure event.

2.4. Reference Documents

Reference

Document

Document Title

RD-1ICAO Annex10 Volume I (Radio Navigation Aids) 6th Edition July 2006 amendment85

RD-2 RTCA MOPS DO 229 (Revisions C or D)

RD-3GPS Standard Positioning Service Performance Standard 30th September 2008 4thEdition

RD-4IS GPS 200 Revision D NAVSTAR GPS Space Segment / Navigation User Interface

7th

December 2004RD-5 GNSS Manual ICAO Doc 9849 1st Edition 2005

RD-6

EGNOS Service Definition Document Open Service, Ref : EGN-SDD OS V1.1 30th October 2009

http://ec.europa.eu/enterprise/policies/satnav/egnos/files/egnos-service-definition-document-open-service-v1.1-30-10-2009_en.pdf

http://www.essp-sas.eu/docs/printed_documents/egnos_sdd_os_v1_1_30_10_2009_print.pdf

RD-7Regulation (EC) No 683/2008 OF THE EUROPEAN PARLIAMENT AND OF THECOUNCIL of 9th July 2008 on the further implementation of the European satellitenavigation programmes (EGNOS and Galileo)

RD-8 EC/ESA/CNES User Guide for EGNOS Application Developers Ed. 1.1 30th July 2009

Table 1. Reference documents


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3. Description Of The Egnos System And

Egnos SoL Service Provision Environment

3.1. High Level Description Of The EGNOS Technical Framework

3.1.1. Satellite Navigation Concept

Satellite Navigation is a technique whereby mobile and static users can determine theirposition based on the measurement of the distance (range) between a number of orbitingsatellites and the user receiver. Each satellite of the constellation broadcasts periodicsignals that can be used by the user equipment to precisely determine the propagationtime between the satellite signal transmission and the satellite signal reception by thereceiver. This propagation time can easily be converted into a distance since, at a firstapproximation, the signals travel in space at a constant speed (the speed of light). Eachsatellite also continuously broadcasts all information (so-called ephemeris) necessaryto determine the exact position of the satellite at any point in time.

Knowing the spacecraft position and the distance from that particular satellite, the userposition is known to be somewhere on the surface of an imaginary sphere with a radiusequal to that distance. If the position of and distance to a second satellite is known, theuser/aircraft must be located somewhere on the circumference, where the two spheresintersect. With a third and fourth satellite, the location of the user can be inferred.

A GNSS receiver processes the individual satellite range measurements and combinesthem to compute an estimate of the user position (latitude, longitude, altitude, and user

clock bias) in a given geographical coordinate reference frame2.

3.1.2. Errors Affecting User Positioning

As explained in the previous section, the estimation of the satellite-to-user range isbased on the measurement of the propagation time of the signal. A number of errorsources affect the accuracy of these measurements:

Satellite clocks: any error in the synchronisation of the different satellite clocks willhave a direct effect on the range measurement accuracy. These errors are similarfor all users able to view a given satellite.

Signal distortions: any failure affecting the shape of the broadcast signal may havean impact on the propagation time determination in the user receiver.

Satellite position errors: if the spacecraft orbits are not properly determined bythe systems ground segment, the user will not be able to precisely establish thespacecraft location at any given point in time. This will introduce an error whencomputing the user position. The size of the error affecting the range measurementsdepends on the users location.

Ionospheric effects: The Ionosphere is an ionized layer of the atmosphere locateda few hundred kilometres above the surface of the Earth. When transiting throughthe ionosphere, the satellite navigation signals are perturbed, resulting in range

2 Based on this principle (called triangulation), the location of a receiver could theoretically be determined using the

distances from only 3 points (satellites). However, in reality, the determination of a location requires in addition an

estimate of the unknown receiver clock bias. This necessitates an additional (4 th) range measurement.


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measurement errors. The size of the error will depend on the level of solar activity(peaks in the solar activity occur on approximately an 11 year cycle) and on thesatellite elevation above the horizon. For a low elevation satellite (5 above thehorizon), the error affecting the measurement is about 3 times larger than the erroraffecting a satellite seen at the zenith.

Tropospheric effects: The troposphere is the lower part of the atmosphere wheremost weather phenomena take place. The signal propagation in this region will beaffected by specific atmospheric conditions (e.g. temperature, humidity) and willresult in range measurement errors. The size of the error will also depend on thesatellite elevation above the horizon. For a low elevation satellite (5 above thehorizon), the error affecting the measurement is about 10 times larger than the erroraffecting a satellite seen at the zenith.

Reflections: When propagating towards the user receiver, navigation signals areprone to reflections from the ground or nearby objects (buildings, vehicles...). Thesereflected signals combine with the direct signals and introduce a bias in the rangemeasurements made by the user receiver, denoted as multipath error.

Thermal noise, Interference and User receiver design: the navigation signalshave an extremely low power level when they reach the user receiver. The rangemeasurements made by the receiver will therefore be affected by ambient noiseand interfering signals, and the accuracy of such measurements will depend on thequality of the user receiver design.

When trying to characterise the overall range measurement errors, all error sourcesdescribed above are aggregated and a unique parameter is used called the UserEquivalent Range Error (UERE). The UERE is an estimate of the uncertainty affectingthe range measurements for a given satellite.

When computing its position the user receiver combines the range measurements fromthe different satellites in view. Through this process, the individual errors affecting eachrange measurement are combined which results in an aggregate error in the positiondomain. The statistical relationship between the average range domain error and theposition error is given by a factor that depends on the satellite geometry; this factor isnamed DOP (Dilution Of Precision).

3.1.3. Objective of EGNOS

Satellite navigation systems are designed to provide a positioning and timing serviceover vast geographical areas (typically continental or global coverage) with high

accuracy performance. However, a number of events (either internal to the systemelements or external, due to environmental conditions) may lead to positioning errorsthat are in excess of the typically observed navigation errors. For a large variety ofusers, such errors will not be noticed or may have a marginal effect on the intendedapplication. However, for safety critical applications, such errors may directly impactthe safety of operations, therefore there is an absolute need to compensate and/orcorrect for such errors, or to warn the user in due time when such errors occur andcannot be corrected. For this reason, augmentation systems have been designed toimprove the performance of existing global constellations.

EGNOS is a Satellite Based Augmentation System (SBAS). SBAS systems are designed

to augment the navigation system constellation by broadcasting additional signalsfrom geostationary (GEO) satellites; they provide differential correction messages andintegrity data for the satellites which are in the view of a network of monitoring stations.


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It increases the accuracy and the confidence a user can have in the satellite navigationpositioning solution extending the field of satellite navigation to support more demandingapplications. Today, EGNOS augments GPS signals.

3.1.4. GPS Overview

3.1.4.1. GPS ServicesThe GPS is a space-based radio-navigation system owned by the United StatesGovernment (USG) and operated by the United States Air Force (USAF). GPS providespositioning and timing services to military and civilian users on a continuous worldwidebasis. Two GPS services are provided: the Precise Positioning Service (PPS), availableprimarily to the armed forces of the United States and its allies, and the StandardPositioning Service (SPS) open to civil users (further information on SPS SIS or PPSSIS can be found on the web site of the National Executive Committee for Space-Based Positioning Navigation and Timing (PNT), (http://pnt.gov/public/docs). The GPSSignal In Space characteristics are defined in the GPS ICD [RD-4]

The GPS SPS performance characteristics are defined in the GPS SPS PerformanceStandards (GPS SPS PS) [RD-3].

3.1.4.2. GPS Architecture

In order to provide its services, the GPS system comprises three segments: the Control,Space, and User Segment. The Space and Control segments are briefly describedbelow.

The Space Segment comprises a satellite constellation. The GPS baseline constellationcomprises 24 slots in 6 orbital planes with four slots in each plane. The baseline satellitesoccupy these slots. Any surplus GPS satellites that exist in orbit occupy other locations

in the orbital planes. The nominal semi-major axis of the orbital plane is 26,559.7 Km.The signals broadcast by the GPS satellites are in the Lband carriers: L1 (1575.42MHz) and L2 (1227.6 MHz). Each Satellite broadcasts a pseudo-random noise (PRN)ranging signal on the L1 carriers.

The Operational Control System (OCS) includes four major subsystems: a MasterControl Station, a backup Master Control Station, a network of four Ground Antennas,and a network of globally-distributed Monitoring Stations. The Master Control Stationis located at Schriver Air Force Base, Colorado, and is operated on a continuous basis(i.e. 24 hours per day, 7 days a week, all year); it is the central control node for the GPSsatellite constellation and is responsible for all aspects of the constellation command

and control.

3.1.5. EGNOS Overview

3.1.5.1. EGNOS Services

EGNOS provides corrections and integrity information to GPS signals covering a broadarea centred over Europe.

EGNOS will provide three services:

The Open Service (OS), freely available to any user;

The Safety of Life (SoL) Service, that will provide the most stringent level ofsignal-in-space performance to all Safety of Life user communities;


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The Commercial Data Distribution Service (CDDS) for customers who requireenhanced performance for commercial and professional use.

OS

The main objective of the EGNOS Open Service is to improve the achievable positioningaccuracy by correcting several error sources affecting the GPS signals as described in

section 3.1.2. The corrections transmitted by EGNOS contribute to mitigate the rangingerror sources related to satellite clocks, satellite position and ionospheric effects. Theother error sources (tropospheric effects, multipath and user receiver contributions) arelocal effects that cannot be corrected by a global augmentation system. Finally, EGNOScan also detect distortions affecting the signals transmitted by GPS and prevent usersfrom tracking unhealthy or misleading signals.

The Open Service has been available since 1st October 2009, and the correspondingSDD [RD-6] can be found at:

http://www.essp-sas.eu/docs/printed_documents/egnos_sdd_os_v1_1_30_10_2009_print.pdf

SoL Service

The main objective of the EGNOS SoL service is to support civil aviation operationsdown to LPV minima. At this stage, a detailed performance characterisation has beenconducted only against the requirements expressed by civil aviation but the EGNOSSoL service might also be used in a wide range of other application domains (e.g.Maritime, Railways, Road) in the future. In order to provide the SoL Service, theEGNOS system has been designed so that the EGNOS SIS is compliant to the ICAOSARPs for SBAS [RD-1].

The detailed performance of the EGNOS SoL service is described in this document

(EGNOS SoL SDD). The EGNOS SoL Service is available from the 2nd March 2011.Commercial Data Distribution Service (CDDS)

EGNOS CDDS will provide authorised customers (e.g. added-value applicationproviders) the following EGNOS products for commercial distribution:

all EGNOS augmentation messages in real time (including satellite clock andephemeris corrections, propagation corrections and integrity information in theSBAS format);

Raw data from the Ranging and Integrity Monitoring Stations (RIMSs) in realtime (including satellite high precision pseudorange measurements);

Application Providers will be able to connect to the EGNOS Data Server, and exploitthe EGNOS products, offering added-value services3 to final customers.

The EGNOS Commercial Data Distribution Service is planned to be provided on thebasis of agreements between the EGNOS Service Provider and its customers.

A dedicated Service Definition Document will be published for the CDDS when theservice is declared available4.

3 Examples of potential applications that could be provided are: provision of EGNOS information in the RTCM

format; EGNOS pseudolites; provision of EGNOS services through RDS, DAB, Internet; accurate ionosphericdelay/TEC maps; provision of RIMS data; provision of performance data (e.g. XPL availability maps, GIVE maps,

etc.); provision of EGNOS message files.

4 In order to gather user requirements for the final CDDS, an initial service called EGNOS Data Access Service

(EDAS) is being provided by EC (http://www.gsa.europa.eu/go/egnos/edas).


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3.1.5.2. EGNOS: One SBAS Amongst Others

EGNOS is part of a multimodal interregional SBAS service, able to support awide spectrum of applications in many different user communities, such as aviation,maritime, rail, road, agriculture. Similar SBAS systems, designed according to thesame standard (i.e. SARPs [RD1]), have already been commissioned by the US

(Wide Area Augmentation System WAAS) and Japan (MSAS). Implementation ofanalogous systems is being investigated in other regions of the world (e.g. GAGAN inIndia and SDCM in Russia). The worldwide existing and planned SBAS systems areshown in Figure 1.

For additional information on WAAS, the reader is invited to visit the FAA website:http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/

navservices/gnss/

MSAS

SDCM

GAGANWAAS

EGNOS

In addition, most of these systems have plans to extend their service areas toneighbouring regions, thus paving the way for near global SBAS coverage.

3.1.5.3. EGNOS Architecture

The EGNOS functional architecture is shown in Figure 2.In order to provide its services to users equipped with appropriate receivers, the EGNOSsystem comprises two main segments: the Space Segment, and the Ground Segment.

Figure 1. Existing and planned SBAS systems


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EGNOS Space Segment

The EGNOS Space Segment comprises 3 GEO satellites broadcasting corrections andintegrity information for GPS satellites in the L1 frequency band (1575,42 MHz). At thedate of publication the 3 GEOs used by EGNOS are:

GEO Name PRN Number Orbital Slot

INMARSAT AOR-E PRN 120 15.5 W

INMARSAT IOR-W PRN 126 25.0 E

ARTEMIS PRN 124 21.5 E

This space segment configuration provides a high level of redundancy over the whole

service area in case of a geostationary satellite link failure. The EGNOS operationsare handled in such a way that, at any point in time, typically two of the three GEOsbroadcast an operational signal. Since it is only necessary to track a single GEOsatellite link to benefit from the EGNOS SoL, this secures a switching capability in caseof interruption and ensures a high level of continuity of service.

It is intended that the EGNOS space segment will be replenished over time in order tomaintain a similar level of redundancy. The exact orbital location of future satellites mayvary, though this will not impact the service offered to users. Similarly, different PRNcode numbers may be assigned to future GEOs. However, all SBAS user receiversare designed to automatically detect and use any code in a pre-allocated set reserved

for SBAS. Such evolutions will therefore be transparent for end users and will notnecessitate any human intervention or change of receiving equipment.

GEO

SpaceSegment

NLES

MCCGroundSegment

UserSegment

RIMS

GPS

EWAN (EGNOS Wide Area Network)

PACF

ASQF

Performance Assessment andCheck-out Facility

Application Specific QualificationFacility

MissionControlCentres

NavigationLand EarthStations

Ranging &IntegrityMonitoringStations

Figure 2. EGNOS architecture

Table 2. GEOs used by EGNOS


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EGNOS Ground Segment

The EGNOS Ground Segment comprises a network of Ranging Integrity MonitoringStations (RIMS), four Mission Control Centres (MCC), six Navigation Land EarthStations (NLES), and the EGNOS Wide Area Network (EWAN) which provides thecommunication network for all the components of the ground segment. Two additional

facilities are also deployed as part of the ground segment to support system operationsand service provision, namely the Performance Assessment and Checkout Facility(PACF) and the Application Specific Qualification Facility (ASQF), which are operatedby the EGNOS Service Provider (ESSP SAS).

RIMS

The main function of the RIMS is to collect measurements from GPS satellites andto transmit these raw data every second to the Central Processing Facilities (CPF)of each MCC. The initial configuration includes 34 RIMS sites located over a widegeographical area.

In order to improve the performance of the EGNOS system and enlarge the area wherethe EGNOS services can be used, an extension of the monitoring network is expectedsoon which will see the deployment of additional RIMS in La Palma, (Spain), Athens(Greece) and Alexandria (Egypt). A further extension is also planned in a slightly longertimeframe that should improve the EGNOS performance in the southern parts of theservice area. Figure 3 shows the geographical distribution of the RIMS already inoperation and the RIMS current under deployment.

CPF

The Central Processing Facility (CPF) is a module of the Mission Control Centres thatuses the data received from the network of RIMS stations to:

Elaborate clock corrections for each GPS satellite in view of the network ofRIMS stations. These corrections are valid throughout the geostationarybroadcast area (i.e. wherever the EGNOS signal is received).

Elaborate ephemeris corrections to improve the accuracy of spacecraftorbital positions. In principle, these corrections are also valid throughout thegeostationary broadcast area. However, due to the geographical distribution of

JME

EGIRKK

MON

KOU

ALY

HBK

DJAMADCNRLPI

NOU

TRD

GVLLAP

GLG

AUS

CTN

FUC

SWA

PAR

TLS

SCZ ATH

GOL

ROM

ZUR

LAN

BRN WRS

SOF

ALB

CIA

BUR

SDC

TORLSB

MLG

PDM

ACR

CRK

LYR

TRO

KIR

RIMS in operation

MCC

NLES

RIMS deployed,awaiting integration

Figure 3. EGNOS RIMS sites


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the EGNOS ground monitoring network, the accuracy of these corrections willdegrade when moving away from the core service area.

Elaborate a model for ionospheric errors over the EGNOS service area in orderto compensate for ionospheric perturbations to the navigation signals.

This function requires a dense network of monitoring stations. For this reason,

the ionospheric model broadcast by EGNOS is not available for the wholegeostationary broadcast area but is only provided for a region centred overEurope.

These three sets of corrections are then broadcast to users to improve positioningaccuracy.

In addition, the CPF estimates the residual errors that can be expected by the usersonce they have applied the set of corrections broadcast by EGNOS. These residualerrors are characterised by two parameters:

User Differential Range Error: this is an estimate of the residual range error

after the application of clock and ephemeris error correction for a given GPSsatellite.

Grid Ionospheric Vertical Error: this is an estimate of the vertical residual errorafter application of the ionospheric corrections for a given geographical gridpoint.

These two parameters can be used to determine an aggregate error bounded by thehorizontal and vertical position errors. Such information is of special interest for Safetyof Life users but may also be beneficial to other communities needing to know theuncertainty in the position determined by the user receiver. More details on the EGNOSintegrity concept can be found in Appendix C.

Finally, the CPF includes a large number of monitoring functions designed to detectany anomaly in GPS and in the EGNOS system itself and is able to warn users within avery short timeframe (less than 6 sec) in case of an error exceeding a certain threshold.These monitoring functions are tailored to the Safety Of Life functions and will not befurther detailed in this document.

NLES

The messages elaborated by the CPF at the Master MCC5 are transmitted to theNLESs. The NLESs (two for each GEO for redundancy purposes) transmit the EGNOSmessage received by the CPF to the GEO satellites for broadcast to users and to

ensure the synchronisation with the GPS signal.

CCF

The EGNOS system is controlled through a Central Control Facility (CCF) located ineach of the Mission Control Centres. These facilities are manned on a 24/7 basis inorder to ensure permanent service monitoring and control.

5 EGNOS has 4 MCC located in Italy, Germany, United Kingdom and Spain, amongst which the role of Master

rotates.


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3.2. EGNOS Organisational Framework

3.2.1. Bodies Involved in the EGNOS Programme and Service Delivery

The European Union is the owner of the EGNOS system. The European Commission isin charge of the overall EGNOS programme management and as such, is responsible

for taking decisions regarding the system exploitation and evolutions.The European Space Agency (ESA) led the technical development of the EGNOSsystem in the past and is now mandated by the European Commission to play the roleof a design and procurement agent for system evolutions.

The European Satellite Services Provider (ESSP) SAS is a company established by anumber of major European Air Navigation Service Providers. The founding membersof ESSP are the Air Navigation Service Providers of France (DGAC/DSNA), Germany(DFS), Italy (ENAV SpA), Portugal (NAV-EP), Spain (AENA), Switzerland (Skyguide)and the United Kingdom (NATS). The EGNOS service provider has its headquartersand operations centre in Toulouse (France), and its service provision centre in Madrid

(Spain).

ESSP SAS as EGNOS service provider will also generate EGNOS Notice To Airmen(NOTAM) proposals to the appropriate Aeronautical Information Service providerswithin Europe that should validate and distribute the final Official EGNOS NOTAM.

3.2.2. How to get Information on EGNOS and EGNOS Applications or Contact theService Provider

A number of websites and e-mail addresses are made available by the EuropeanCommission, the European Space Agency, the EGNOS Service Provider and otherorganisations to provide detailed information on the EGNOS programme, the systemstatus and system performance, as well as a number of useful tools. The table belowlists the main sources of information about EGNOS.

Information about Organisation Web address

EGNOS Programme EC http://ec.europa.eu/enterprise/policies/satnav/index_en.htm

EGNOS System aspects ESA http://www.esa.int/esaNA/egnos.html

Official reporting of the EGNOSStatus and Performance

ESSP http://www.essp-sas.eu

EGNOS User Support website ESSP http://egnos-user-support.essp-sas.eu/

EGNOS Helpdesk ESSP [email protected]

EGNOS general information andEGNOS applications

EC/GSA www.egnos-portal.eu

EASA Functional Mailbox (Servicedifficulties or malfunctions relatedto certified EGNOS compatiblereceivers)

EASA [email protected]

EDAS GSA/EC/ ESSP http://www.gsa.europa.eu/go/egnos/edas

EGNOS SoL SDD readers are also invited to refer to the GPS SPS PS [RD-3] andEASA European Technical Standard Order (ETSO)-145/146 for details of both thefundamental GPS SPS service and EGNOS receiver equipment. EGNOS also meetsthe ICAO Annex 10, Standards and Recommended Practices (SARPs) for Global

Table 3. Where to find information about EGNOS


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Navigation Satellite System (GNSS) Satellite Based Augmentation System (SBAS)except for the continuity requirements where some waivers exist as detailed in section6.3.1.4 for NPA and in section 6.3.2.4 for APV-I.


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4. EGNOS SIS

4.1. EGNOS SIS Interface Characteristics

The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS[RD-1]. This section provides an overview of the EGNOS SIS interface characteristics,related to carrier and modulation radio frequency (section 4.1.1) and structure, protocoland content of the EGNOS message (section 4.1.2).

4.1.1. EGNOS SIS RF Characteristics

The EGNOS GEO satellites transmit right-hand circularly polarised (RHCP) signals inthe L band at 1575.42 MHz (L1). The broadcast signal is a combination of a 1023-bitPRN navigation code of the GPS family and a 250 bits per second navigation datamessage carrying the corrections and integrity data elaborated by the EGNOS groundsegment.

The EGNOS SIS is such that, at all unobstructed locations near ground level fromwhich the satellite is observed at an elevation angle of 5 degrees or higher, the level ofthe received RF signal at the output of a 3dBi linearly polarised antenna is within therange of 161 dBW to 153 dBW for all antenna orientations orthogonal to the directionof propagation.

It is intended that future geostationary satellites used for EGNOS replenishment willbroadcast higher minimum signal power levels in order to improve the acquisition andtracking performance of the user receiver.

4.1.2. EGNOS SIS Message Characteristics

The EGNOS SIS Navigation Data is composed of a number of different Message Types(MT) as defined in the SBAS standard. Table 4 below reports the MTs that are used byEGNOS and their purpose.

Message

Type

Contents Purpose

0 Dont Use (SBAS test mode)Discard any ranging, corrections and integrity data fromthat PRN signal. Used also during system testing.

1 PRN Mask

Indicates the slots for GPS and GEO satellites provided

data

2-5 Fast corrections Range corrections and accuracy

6 Integrity information Accuracy for all satellites in one message

7 Fast correction degradation factorInformation about the degradation of the fast termcorrections

96 GEO ranging function parameters EGNOS satellites orbite information (ephemeris)

10 Degradation parametersInformation about the degradation of the long termcorrections

12SBAS network Time/UTC offsetparameters

Parameters for synchronisation of SBAS Network timewith UTC

6 MT 9 is broadcast with some information about the orbital position of the broadcasting GEO satellite. At this

stage, the EGNOS system does not support the GEO Ranging function which is described in ICAO SARPs as an

option. This is indicated by a special bit coding of the Health and Status parameter broadcast in MT 17.


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Message

Type

Contents Purpose

17 GEO satellite almanacs GEO Almanacs

18 Ionospheric grid point masksIndicates for which geographical point ionophericcorrection data is provided

24 Mixed fast/long-term satellite errorcorrections

Fast-term error corrections for up to six satellites andlong-term satellite error correction for one satellite in onemessage.

25Long-term satellite errorcorrections

Corrections for satellite ephemeris and clock errors forup to two satellites

26 Ionospheric delay corrections Vertical delays/accuracy at given geographical points

27 EGNOS service message Defines the geographic region of the service

63 Null message Filler message if no other message is available

The format and detailed information on the content of the listed MTs and their use atSBAS receiver level are given in ICAO SARPs [RD-1] and RTCA SBAS MOPS [RD-2].

4.2. EGNOS Time and Geodetic Reference Frames

Strictly speaking, the time and position information that are derived by an SBASreceiver that applies the EGNOS corrections are not referenced to the GPS Timeand the WGS84 reference systems as defined in the GPS Interface Specification.Specifically, the position coordinates and time information are referenced to separatereference systems established by the EGNOS system, namely the EGNOS NetworkTime (ENT) timescale and the EGNOS Terrestrial Reference Frame (ETRF). However,these specific EGNOS reference systems are maintained closely aligned to their GPScounterparts and, for the vast majority of users, the difference between these two time/terrestrial reference frames is negligible.

4.2.1. EGNOS Terrestrial Reference Frame ETRF 23

The EGNOS service was initially designed to fulfil the requirements of the aviation usercommunity as specified in the ICAO SBAS SARPS. This reference established theGPS Terrestrial Reference Frame, WGS84, as the terrestrial reference to be adoptedby the civil aviation community.

The ETRF is an independent realisation of the International Terrestrial Reference Frame

(ITRF) which is a geocentric system of coordinates tied to the surface of the Earthand in which the unit distance is consistent with the SI7 definition of the metre. TheITRF system is maintained by the International Earth Rotation and Reference SystemsService (IERS)8 and is the standard terrestrial reference system used in geodesy andEarth research.

In order to define the ETRF, the ITRF coordinates and velocities of the RIMS antennasare estimated using space geodesy techniques based on GPS data. Precise GPSephemeris and clock corrections produced by the International GNSS Service (IGS)9are used to filter the GPS data collected over several days at each RIMS site and toderive the antenna coordinates and velocities with geodetic quality. This process is

7 Information on the International System of Units (SI) can be obtained from http://www.bipm.org/en/si/

8 Information on IERS can be obtained from http://www.iers.org/

9 Information on IGS can be obtained from http://igscb.jpl.nasa.gov/

Table 4. EGNOS SIS transmitted MTs


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repeated periodically (at least once per year) in order to mitigate the degradation of theETRF accuracy caused by the relative drift between the two reference frames.

Both ETRF and WGS84 are closely aligned to ITRF and new releases of ETRF andWGS84 are issued periodically to ensure that the level of consistency with ITRF ismaintained at a level of a few centimetres. This means that, for the vast majority of

applications, it can be considered that the positions computed by an EGNOS receiverare referenced to WGS84 and can be used with maps or geographical databases inWGS84.

4.2.2. EGNOS Network Time: ENT GPS Time Consistency

The time reference used by EGNOS to perform the synchronisation of the RIMS clocksis the EGNOS Network Time (ENT). The ENT timescale is an atomic timescale whichrelies on a group of atomic clocks deployed at the EGNOS RIMS sites. The EGNOSCPFs compute the ENT in real time, using a mathematical model which processestiming data collected from a subset of the RIMS clocks.

The ENT is continuously steered towards GPS Time (GPST) by the EGNOS systemand the relative consistency between the two timescales is maintained at the level oftens of nanoseconds as observed in Figure 4.

All satellite clock corrections computed by the EGNOS ground segment and transmittedto the EGNOS users are referenced to the ENT timescale.

Despite the high level of consistency between the ENT and GPST timescales,EGNOS users are advised not to combine uncorrected GPS measurements (i.e. thosereferenced to GPST) and GPS measurements which have been corrected using EGNOSparameters (i.e. those referenced to ENT), when computing a navigation solution.Indeed, this approach might noticeably degrade the accuracy of the solution (by up to10 to 20 metres). EGNOS users who want to combine GPS measurements referencedto different timescales should account for an additional unknown corresponding to thetime offset between the two time references in the receiver navigation models.

10 Courtesy of CNES

12

10

8

6

4

2

0

29/01/2008

29/02/2008

29/03/2008

29/04/2008

29/05/2008

29/06/2008

29/07/2008

29/08/2008

29/09/2008

29/10/2008

29/11/2008

29/12/2008

29/01/2009

28/02/2009

29/03/2009

29/04/2009

29/05/2009

29/06/2009

29/07/2009

29/08/2009

29/09/2009

29/10/2009

29/11/2009

29/12/2009

29/01/2010

28/02/2010

29/03/2010

ENT-GPST(ns)

Figure 4. ENT GPS time offset evolution (Period Feb 2008 - March 2010)10


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4.3. EGNOS SIS Performance in the Range Domain

4.3.1. Accuracy in the Range Domain

The accuracy performance is characterised by two parameters, representingrespectively the performance of the time and orbit determination process, and the

ionospheric modelling process: the Satellite Residual Error for the Worst user location (SREW) in the relevant

service area11, representing the residual range error due to the ephemeris andclock errors once EGNOS corrections are applied

The Grid Ionospheric Vertical Delay (GIVD) which represents the residual rangeerror due to ionospheric delay after applying the EGNOS ionospheric correction ateach of the grid points predefined in the MOPS [RD-2].

Table 5 provides the comparison of the pseudorange error budget when using theEGNOS SoL Service and GPS stand-alone to correct for clock, ephemeris andionospheric errors.

11 The relevant service area is defined as the intersection of the EGNOS service area (Figure 5) and the monitored

GPS satellite footprint which is different tothe NPA and APV-I service areas defined in sections 6.3.1 and 6.3.2

respectively.

-40

20

30

40

50

60

70

-30 -20 -10 0 10 20 30 40

Figure 5. EGNOS service area used for SREW computation


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Error sources (1) GPS - Error Size (m) EGNOS - Error Size (m)

GPS SREW 4.012 2.3

Ionosphere (UIVD error) 2.0 to 5.013 0.5

Troposphere (vertical) 0.1 0.1

GPS Receiver noise 0.5 0.5

GPS Multipath (45 elevation) 0.2 0.2

GPS UERE 5 elevation 7.4 to 15.6 4.2 (after EGNOS corrections)

GPS UERE 90 elevation 4.5 to 6.4 2.4 (after EGNOS corrections)

Note 1: The shaded parameters in the EGNOS columns are provided for information

only and give an idea of the overall range accuracy performance that can be expected

when using the EGNOS SoL Service in a clear sky environment with high-end receiver

equipment properly accounting for tropospheric effects. Only the SREW and User

Ionospheric Vertical Delay (UIVD) parameters do not depend on the type and brand of

receiver.

Note 2: Please note that the values in the GPS column are provided for information only

and that the actual applicable UERE budget can be found in GPS SPS PS [RD-3]. In

case where there are discrepancies between Table 5 and [RD-3], the latter shall prevail.

As stated above, the EGNOS SREW and UIVD values in Table 5 relate to the worstuser location inside the service area and are calculated with conservative models.EGNOS SIS Users will usually experience better performance.

4.3.2. Integrity in the Range Domain

As the SREW and GIVD range accuracy parameters cannot be monitored in real time,the EGNOS system provides an estimation of the statistical distribution (i.e. standarddeviation) which bounds the real SREW and GIVD. The two integrity parametersprovided by EGNOS are the User Differential Range Error (UDRE) and the GridIonospheric Vertical Error (GIVE). The UDRE characterises the SREW parameter whilethe GIVE characterises the GIVD.

For the integrity in the range domain, the range error should be bounded by a thresholdbased on the UDRE and GIVE parameters. For each pseudorange, the range errorshould be less than 5.33 times the estimated standard deviation ( 5.33 where isRange error and is the computed SBAS Range error estimate standard deviation).

The metrics used for analysis in the range domain aim at demonstrating that the UDREand the GIVE parameters bound respectively the pseudorange errors at the worst userlocation (SREW) and the Grid Ionospheric vertical delay (GIVD). In other words, inorder for UDRE and GIVE to bound properly the true range error in the measurements,it should be ensured that 5.33UDRE> SREWand 5.33GIVE> GIVD.

EGNOS is designed in such a way that the SoL service ensures that the satellitecorrection error and Ionospheric error are bounded with a probability of 99.99999%.The observed maximum values for SREW/UDRE and GIVD/GIVE are both around 3.

More details on the EGNOS integrity concept can be found in Appendix C.

12 GPS Standard Positioning Service Performance Standard [RD-3].

13 This is the typical range of ionospheric residual errors after application of the baseline Klobuchar model broadcast

by GPS for mid-latitude regions.

Table 5. Typical EGNOS and GPS stand-alone SIS UERE


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5. EGNOS Receivers

5.1. EGNOS Receivers For Aviation

Since the SBAS standards have been initially derived to meet the stringent navigationperformance requirements applicable to civil aviation approach and landing operations,the reference SBAS receiver standards have been also developed by the civil aviationcommunity. These standards are called SBAS Minimum Operational PerformanceStandards (MOPS) and are published by the Radio Technical Commission forAeronautics (RTCA) under the reference DO-229 [RD2]. This receiver standard hasbeen designed by and for the aviation community and therefore supports both horizontaland vertical navigation and implements a large number of features aimed at ensuringthe integrity of the derived position.

This standard identifies different classes of user receivers depending on the intendedoperations. The following table summarises the main characteristics of the EGNOSequipment operational classes:

Operational Class Phases of Flight

Class 1Oceanic and domestic en route, terminal, approach (LNAV), and departureoperation

Class 2Oceanic and domestic en route, terminal, approach (LNAV, LNAV/VNAV),and departure operation

Class 3Oceanic and domestic en route, terminal, approach (LNAV, LNAV/VNAV,LP, LPV), and departure operation

Class 4 Equipment that supports only the final approach segment operation

For EGNOS, the minimum performance levels are defined for two specific types ofoperations and assume equipage with a class 1 receiver (for operations down to NPA)or class 3 receiver for LPV operations.

For non-aviation SoL users, alternative EGNOS message processing may beimplemented, deviating from the DO-229 MOPS standard. However, the EGNOSsystem performance has not been characterised for such a receiver configuration andtherefore the performance experienced by such receivers is likely to deviate from that

described in the SoL SDD.

5.2. Receiver & Avionics Certification

According to the intended operation, EASA material providing implementing guidance andAccepted Means of Compliance (AMCs) is available. The AMCs include airworthinesscriteria such as equipment qualification and functional criteria, airworthiness compliancefor installation, as well as operational criteria.

The equipment qualification recommended in the AMCs refers to ETSO certifiedequipment. An ETSO certified piece of hardware (receiver, antenna, etc) has beendemonstrated to have been designed, tested and manufactured in compliance with the

applicable standards. It is recalled that the ETSO approval process is just a way thatthe equipment manufacturer chooses to demonstrate compliance with the standards; itis not the unique method. Therefore it is possible to find non-ETSO certified equipment

Table 6. EGNOS equipment operational classes


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that is fully compliant with the standards and that is certified for use by the competentNSA.

It should also be considered that ETSO certificates refer only to the equipment itself(avionics and related hardware) and not the installation within the aircraft. The user/operator should follow the guidance provided in the applicable AMC in order to seek

approval for the avionics installation.The following table lists the existing ETSOs related to the hardware required for SBASoperations:

ETSO Hardware Required for SBAS Operations

ETSO-C144 Airborne Global Positioning System Antenna

ETSO-C145Airborne Navigation Sensors Using the Global Positioning System (GPS)Augmented by the Wide Area Augmentation System (WAAS)

ETSO-C146Stand-alone airborne navigation equipment using the Global positioning system(GPS) augmented by the wide area augmentation system (WAAS)

Table 7. Existing ETSOs and hardware requirements for SBAS operations


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6. EGNOS SoL Service Performance

6.1. EGNOS SoL Service Description and Characteristics

The EGNOS SoL Service is available from the 2nd March 2011

It consists of signals for timing and positioning, provided openly which are freelyaccessible and without any direct charge. In the case of aviation, the use of EGNOSSoL Service is subjected to the subscription of specific Working Agreements betweenESSP and ANSPs as required by the EC Single European Sky regulation. The EGNOSWorking Agreement is intended to cover both contractual and technical elementsrequired by ANSPs to publish EGNOS based procedures.

The EGNOS SoL Service is accessible to any user equipped with an EGNOS receiveras described in Section 5 within the EGNOS SoL Service area as defined in Section

6.3. The minimum performance reported in this section is the performance that canbe experienced when using receiving equipment compliant with RTCA MOPS DO229Class 3 specifications as described in section 5.1. It also assumes GPS characteristics/performance as mentioned in section 2.1 and a clear sky environment with no obstaclemasking satellite visibility at angles greater than 5 above the local horizontal plane.

At the time of publication of this document there are two GEOs in operation mode,while the third is in test mode, therefore broadcasting Message Type 0. The two GEOsin Operation for the SoL Service are identified as PRN 120 (INMARSAT AOR-E) andPRN 124 (ARTEMIS). The configuration of the GEO in operation does not changefrequently but possible updates are nevertheless reported on the EGNOS Service

Provider website.This service is compliant with the aviation NPA (Non Precision Approach) and APV-I(Approach with Vertical Guidance) requirements, except for specific deviations notedwithin Section 6.3 but is also intended to support applications in other SoL domains.

The minimum performance figures shown in this section tend to be more conservativethan the observed figures presented in Appendix A, as those in Section 6 take intoaccount a number of abnormal system states or non-typical environmental conditionsthat can statistically be expected to occur during the lifetime of the system. Thesetwo types of characterisation are considered to provide valuable and complementaryinsights into EGNOS service performance for receiver manufacturers, for GNSS

application developers and for end users of the EGNOS SoL Service.

The performance reported in this document is the one that can be obtained with theversion of EGNOS currently in operation (ESR v2.2ext). It is the objective that futureESRs will deliver, as a minimum, an equivalent level of performance. Any evolution ofthe minimum performance levels will be reflected in formal revisions of the EGNOS SoLSDD.

6.2. EGNOS SoL Service Performance Requirements

The EGNOS system has been designed to support different types of civil aviation

operations. Requirements for each type of operation have been issued by ICAO andare summarised in the following table:


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Typical

Operation

Horizontal

Accuracy

(95%)

Vertical

Accuracy

(95%)

Integrity Time-

To-Alert

(TTA)

Horizontal

Alert Limit

(HAL)

Vertical

Alert

Limit

(VAL)

Continuity Availability

En-route (oceanic/ continental lowdensity)

3.7 km

(2.0 NM)

(Note 6)

N/A 1 - 1x10-7/h 5 min 7.4 km

(4 NM)

N/A 1 - 1x10-4/h

to 1 - 1x10-8/h

0.99 to

0.99999

En-route(continental)

3.7 km

(2 NM)

N/A

En-route, Terminal 0.74 km

(0.4 NM)

N/A 1 - 1x10-7/h 15 s 1.85 km

(1 NM)

N/A 1 - 1x10-4/h

to 1 - 1x10-8/h

0.99 to

0.99999

Initial approach,Intermediateapproach, Non-precision approach(NPA), Departure

220 m

(720 ft)

N/A 1 - 1x10-7/h 10 s 556 m

(0.3 NM)

N/A 1 - 1x10-4/h

to 1 - 1x10-8/h

0.99 to

0.99999

Approachoperations withvertical guidance(APV-I)

16.0 m

(52 ft)

20 m

(66 ft)

1 - 2x10-7

in any

approach

10 s 40 m

(130 ft)

50 m

(164 ft)

1 - 8x10-6/15 s 0.99 to

0.99999

6.3. EGNOS SoL Minimum Service Performance Characteristics

The EGNOS SoL minimum performance characteristics are described below foraccuracy, integrity, availability and continuity. This minimum performance is conservativesince it has been derived to take account of a number of degraded conditions orabnormal environmental conditions that could be experienced throughout the lifetimeof the system. Users can usually experience a better performance as reported inAppendix A and Appendix B.

EGNOS SoL Service performance meets aviation requirements, as described in section6.2.

Parameter Performance Comment

Accuracy

VerticalAccuracy

4 meters (95% percentile)

Accuracy maps areincluded in Appendix B

Accuracy values at givenlocations are available athttp://www.essp-sas.eu

HorizontalAccuracy 3 meters (95% percentile)

Accuracy maps areincluded in Appendix B

Accuracy values at givenlocations are available athttp://www.essp-sas.eu

IntegrityIntegrity Risk 2x10-7/approach

Time To Alert Less than 6 seconds

Availability Availability99.9% for NPA in all the ECAC

99% for APV-I in most ECAC

See sections 6.3.1.3 and6.3.2.3

Continuity Continuity

For NPA:


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6.3.1. NPA - Non Precision Approach14

The performance commitment for NPA covers other less stringent phases of flight (enroute, terminal or other RNPs) using EGNOS only for lateral guidance.

6.3.1.1. Accuracy

The EGNOS accuracy is compliant with the accuracy requirements specifi

ed in Table 8for NPA inside the availability service area defined in Section 6.3.1.3.

6.3.1.2. Integrity

The EGNOS integrity is compliant with the integrity requirements specified in Table 8for NPA.

6.3.1.3. Availability

The following figure provides the minimum availability performance that can be expectedfrom EGNOS for NPA. The area in red is where the 99.9% availability requirement ismet. These values correspond to the expected average performance measured by

a fault-free receiver using all SV in view over a period of one month, using all theoperational EGNOS GEOs.

14 Even if it is recommended by RTCA MOPS 229 to use ionospheric corrections if they are available, the NPA

performance results provided in this document consider that the ionospheric correction applied for this navigation

mode is the GPS model, which represents a conservative approach.

-4020

30

40

50

60

70

-30 -20 -10 0 10 20 30 40

Longitude

SL2 Availability

Latitude

99.9%

99%

Figure 6. EGNOS NPA availability


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6.3.1.4. Continuity

The following figure provides the commitment on the continuity that can be expectedfrom EGNOS for NPA. These values correspond to the expected average performancemeasured by a fault-free receiver using all SV in view over a period of one month, usingall the operational EGNOS GEOs.

The minimum continuity risk performance is less than 2.510-4 per hour in most of ECAC

96 Flight Information Regions (FIRs). There are however some regions in the ECAC96 FIRs where the risk rises up to 2.510-3 per hour. Such a minimum performanceis not strictly compliant to ICAO requirements for NPA as described in Table 8. Thesevalues are however considered as sufficient to start the EGNOS use in civil aviation.Indeed, ICAO SARPs include interpretative material stating that when the continuityperformance objective is not achieved by a given system, it is still possible to allowapproaches based on the given system. In this case, local air navigation authoritiesshall define, if necessary, measures to mitigate the risks of an operational nature16.

15 In order to observe the minimum NPA continuity performance shown in the map (2.510-4), at least 6 months of

data needs to be evaluated due to the discrete nature of discontinuity events.

16

Annex 10, Volume 1 of the Chicago Convention, Attachment D, 3.4.3.4: For those areas where the systemdesign does not meet the average continuity risk specified in the SARPs, it is still possible to publish procedures.

However, specific operational mitigations should be put in place to cope with the reduced continuity expected.

For example, flight planning may not be authorised based on GNSS navigation means with such a high average

continuity risk.

25

30

35

45

55

65

40

50

60

70

-20 -10 0 10 20 30 40

Longitude

SL2 Continuity

Latitude

2.5x10-4/h

5.0x10-4/h

1.0x10-3/h2.5x10

-3

/h

Figure 7. EGNOS NPA continuity15


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6.3.2. APV-I - Approach with Vertical Guidance

6.3.2.1. Accuracy

Accuracy Definition Value

HorizontalCorresponds to a 95% confidence bound of the bi-dimensional position

error17 in the horizontal local plane for the worst user location3m

VerticalCorresponds to a 95% confidence bound of the unidimensional unsigned

position error17 in the local vertical axis for the worst user location4m

The EGNOS system is therefore compliant with the accuracy requirements specified inTable 8 for APV-I inside the availability service area defined in Section 6.3.2.3.

6.3.2.2. Integrity

The EGNOS integrity is compliant with the integrity requirements specified in Table 8for APV-I.

6.3.2.3. Availability

Figure 8 shows the minimum availability performance that can be expected fromEGNOS for APV-I. The area in orange represents the area where the 99% availability

17 As for the case of range errors, the horizontal and vertical positioning accuracies correspond to a composition

of residual errors from different sources (EGNOS ground and space segments, local environment and user

segment). The assumptions taken on residual error sources beyond the control of EGNOS (e.g. tropospheric

effects, receiver noise and multipath) are similar to the ones described in section 4.3.

25

30

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45

55

65

40

50

60

70

-20 -10 0 10 20 30 40

Longitude

APV-I Availability

Latitude

99%

98%

95%

90%

Table 10. Approach with vertical guidance accuracy

Figure 8. EGNOS APV-I availability


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requirement is met and other colours represent other availability requirements (yellow -98%, green - 95% and blue - 90%). These values correspond to the expected minimumperformance measured by a fault-free receiver using all Space Vehicles (SV) in view,when averaging over a period of one month, using all the operational EGNOS GEOs.

6.3.2.4. Continuity

The followingfi

gure provides the minimum continuity performance that can beexpected from EGNOS for APV-I. These values correspond to the expected minimumperformance measured by a fault-free receiver using all SVs in view, when averagingover a period of one month, using all the operational EGNOS GEOs.

The minimum continuity risk performance is less than 10-4 in any 15 seconds in corepart of ECAC landmass, and less than 510-4 in any 15 seconds in most of ECAClandmass. There are however some regions with a risk of over 10-3 in any 15 seconds.Such a minimum performance is not strictly compliant to ICAO requirements forAPV-I as described in Table 8 (810-6 in any 15 seconds). These values are howeverconsidered as sufficient to start the EGNOS use in civil aviation. Indeed, ICAO SARPsinclude interpretative material stating that when the continuity performance objectiveis not achieved by a given system, it is still possible to allow approaches based on thegiven system. In this case, local air navigation authorities shall define, if necessary,measures to mitigate the risks of an operational nature18.

25

30

35

45

55

65

40

50

60

70

-20 -10 0 10 20 30 40

Longitude

APV-I Continuity

Latitude

1.0x10 -4/15s

5.0x10-4/15s

1.0x10 -3/15s

18 Annex 10 of the Chicago Convention, Attachment D, 3.4.3.4: For those areas where the system design does

not meet the average continuity risk specified in the SARPs, it is still possible to publish procedures. However,

specific operational mitigations should be put in place to cope with the reduced continuity expected. For example,

flight planning may not be authorised based on GNSS navigation means with such a high average continuity risk.

Figure 9. EGNOS APV-I continuity


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6.4. EGNOS SoL Service Limitations

In the vast majority of cases, the EGNOS SoL Service will be available and will provideperformance in line with or beyond the minimum performance levels described inthe previous sections of this document (section 6.3.1 for NPA and section 6.3.2 forAPV-I). However, in a limited number of situations, users may experience non-nominal

navigation performance levels. The most common causes for such abnormal behaviourare listed below.

Root Cause Most Likely Symptoms

Broadcasting delays

As explained in section 3.1.5.3, one of thefunctions of EGNOS is to elaborate a model of theionosphere and to broadcast this model to usersso that they can correct the related errors. Whenusing the SBAS standard, the reception of all theparameters that are necessary to build such amodel may take up to 5 minutes to be received,

depending on the receiver. Therefore, the fullpositioning accuracy may not be reached as soonas the receiver is turned on.

EGNOS SoL Service not immediately available

The receiver does not immediately use EGNOS tocompute a navigation solution and therefore theposition accuracy improvement is not available untila few minutes after the receiver is turned on.

EGNOS signal blockage

The EGNOS signals are broadcast by twogeostationary satellites. This ensures somelevel of redundancy in case a satellite link islost due to shadowing by a close obstacle (e.g.terrain, buildings, foliage, aircraft manoeuvres,fuselage). When moving North to high latitudes,the geostationary satellites are seen lower on theusers horizon and therefore are more susceptibleto masking.

Degraded position accuracy after some time

The effect of losing the EGNOS signal (on b

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