PROGRAMME OF THE
EUROPEAN UNIONGALILEO OPEN SERVICESERVICE DEFINITIONDOCUMENT (OS SDD)
Issue 1.3 | November 2023

#EUSpace

More information on the European Union is available on the Internet (http://europa.eu).
Luxembourg: Publications Office of the European Union, 2023
ISBN: 978-92-9206-074-9
doi: 10.2878/08361

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

TERMS AND CONDITIONS OF USE OF
THE GALILEO OPEN SERVICEThe Galileo OS, unless augmented by certified orotherwise legally approved dedicated systems
designed to this effect, has been designed and can only
be used for non-safety critical purposes, i.e. purposesthat have no impact on the safety of human life andwhere an underperformance in availability, continuity,
accuracy and/or integrity of the Galileo SIS could notcause any kind of direct or indirect personal damage,including bodily injuries or death.
Scope of Galileo OS Commitment
Although care has been taken in designing,
implementing and operating the system, as well as inproviding the OS, the OS is not meant to offer any
service guarantee to the users.
The minimum level of performance against which thesystem has been validated and is operated, as well as
data of actual performance of the OS are expressed inthis document in statistical values that are valid underassumptions described in the Galileo OS SDD. The
European Commission reserves the right to revise theGalileo OS SDD should these assumptions change orto reflect changes in performance during the
deployment of the Galileo infrastructure. This
commitment regarding the minimum level of
performance shall be without prejudice to thedisclaimer of liability below, measures potentiallyaffecting service availability that may be taken either by
the Security Accreditation Board, or according to theCouncil decision 2021/698/CSFP, or in the interests ofMember States' national security.
The European Union plans to take all necessary
measures for the foreseeable future to maintain or
exceed the minimum levels of the OS performancedescribed herein.
The minimum level of performance of the Galileo OS,
as specified in the Galileo OS SDD, is obtained under
the condition that the user equipment processes thehealth and status flags as described in section 2.3.1.3
and only uses signals declared "HEALTHY". The users
are also reminded that important notices (Notice
Advisory to Galileo Users – NAGUs and Service
Notices), which are published through the GNSS
Service Centre, must be considered when planning to
use the Galileo OS for any purpose.
User responsibilities
The user retains his responsibility to exercise a level ofcare appropriate with respect to the uses he intends tomake of the Galileo OS, taking into account theconsiderations outlined above.

The users are reminded that the timing and positioning
performance they will experience is also driven byother parameters outside the control of the Galileo OS
provider (e.g. signal propagation errors or user receiver
induced errors), which have to be pondered when
deciding to use the Galileo OS for a given purpose.
Before any use of the Galileo OS, users should study
this document in order to understand how they can use
the service, as well as to familiarise themselves withthe performance level and other aspects of the service
they can rely on, in particular the Annex C.4 for a morecomprehensive discussion of the relationships between
the Galileo OS performance and the end user Position
Velocity Time (PVT) performance expectations.
In case of doubt, the users and other parties should
contact the Galileo helpdesk (see section 1.6.4 forcontact details) and their user equipment manufacturer.
Disclaimer of liability
As the owner of the Galileo system, the European
Union - including any of its institutions, offices oragencies, such as the European Commission, theEuropean Union Agency for the Space Programme(EUSPA), and other entities acting on the basis of acontract or agreement with the European Union
involved in the Galileo OS service provision - does notoffer any warranties of any kind (whether expressed or
implied) with respect to the Open Service, including,but not limited to, the warranties regarding availability,
continuity, accuracy, integrity, reliability and fitness fora particular purpose or meeting the users'
requirements. No advice or information, whether oral or
written, obtained from the European Union - including
any of its institutions, offices or agencies, such as theEuropean Commission, the European Union Agency for
the Space Programme (EUSPA), and other entities
acting on the basis of a contract or agreement with theEuropean Union involved in the Galileo OS service
provision - shall create any such warranty.
By using the Galileo Open Service, the user accepts andagrees that the European Union - including any of its
institutions, offices or agencies, such as the European
Commission, the European Union Agency for the Space
Programme (EUSPA), and other entities acting on thebasis of a contract or agreement with the European
Union involved in the Galileo OS service provision shall not be held responsible or liable for any damages
resulting from the use of, misuse of, or the inability to
use the Galileo Open Service, including, but not limited
to, direct, indirect, special or consequential damages,
including, but not limited to, damages for interruptionof business, loss of profits, goodwill or other intangible
losses, other than in accordance with Article 340 of theTreaty on the Functioning of the European Union.

ii

DOCUMENT CHANGE RECORDREASON FOR CHANGE
First issue

ISSUE

REVISION

DATE

1

0

December 20161

1

May 2019

1

2

July 2021

1

3

July 2023

The text of various sections of the document has been
improved.
New parameters and respective Minimum Performance
Levels have been added, specifically the Availability of the
Position Dilution of Precision and the Availability of
Positioning and UTC Service. As a consequence, theMinimum Performance Level for the Availability ofRanging Service has been removed.
The text of various sections of the document has been
improved or updated.
Various MPL values have been improved.
The definition of the Ranging Rate Accuracy has been
added.
The definition and expected value of Galileo URA havebeen added.
Annex E structure has been updated.
Version aligned with Galileo Open Service - Enhanced
Services Update milestone.
Establishes new MPLs on metrics of particular relevancefor the Aviation Users Community: Ranging Accuracy at
higher confidence level, Range Rate Accuracy, Time
Determination Accuracy, Positioning Accuracy, URA, Psat,
Pconst.
Introduces the new Galileo Extended Operations Mode
(EOM), addressing increased usability and robustness ofService.

FOREWORD
This “Galileo - Open Service - Service Definition
Document” (Galileo OS SDD) defines the Minimum
Performance Levels (MPLs) of the Galileo Open
Service (OS).
The document will be updated in the future toreflect further changes and improvements of theGalileo Open Service, in particular during the
deployment of the Galileo system infrastructure,
until the Full Operational Capability (FOC) isachieved.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

TABLE OFCONTENTSSECTION 1: THE GALILEO OPEN SERVICE ...... 2
1.1

PURPOSE OF THE DOCUMENT ................. 2

1.2

SCOPE OF THE DOCUMENT ....................... 2

1.3

TERMS AND CONDITIONS OF USE .......... 3

1.4

ABBREVIATIONS AND ACRONYMS ........ 3

1.5

GALILEO OPEN SERVICE DEFINITION ..... 3
GALILEO OS RANGING SERVICE ............ 3

GALILEO OS POSITIONINGSERVICE .......................................................................... 4
GALILEO OS UTC TIME
DETERMINATION SERVICE ..................................... 4

1.6

GALILEO SYSTEM OVERVIEW ................... 4
GALILEO SPACE SEGMENT ...................... 4
GALILEO GROUND SEGMENT ................. 5
GALILEO SERVICE FACILITIES ................. 6

THE EUROPEAN GNSS SERVICECENTRE (GSC): GALILEO INTERFACEWITH USERS ................................................................. 7
GALILEO TIME AND GEODETIC
REFERENCE FRAMES ................................................ 8

SECTION 2: GALILEO OPEN SERVICE SISCHARACTERISTICS AND MINIMUM USAGE
ASSUMPTIONS ....................................................... 11
2.1 OS SIS INTERFACE CONTROLDOCUMENT REQUIREMENTS............................. 11
2.2 OVERVIEW OF OS SIS INTERFACE
CHARACTERISTICS ................................................ 11

POSITIONING ............................................................. 19
GALILEO OS AVAILABILITY ................... 20
GALILEO OS: EXTENDED
OPERATIONS MODE ............................................... 21

2.4 USAGE ASSUMPTIONS FOR OPENSERVICE PERFORMANCE .................................... 21
OS USER RECEIVERS ................................ 21
LIMITATIONS ON OS SIS STATUS ....... 22
EXCLUDED ERRORS ................................. 23

2.5 OPERATIONAL CAPABILITYEVOLUTION ............................................................... 23

SECTION 3: GALILEO OS MINIMUMPERFORMANCE LEVELS ...................................... 25
3.1

OVERVIEW...................................................... 25

3.2 GALILEO OS CONSTELLATION
DEFINITION ................................................................ 25
3.3

GALILEO OS ACCURACY .......................... 26

GALILEO SIS RANGING
ACCURACY MPL ....................................................... 27
GALILEO SIS RANGING ACCURACY
AT HIGHER PERCENTILES .................................... 28
GALILEO SIS RANGE RATE
ACCURACY MPL ....................................................... 28
GALILEO SIS UTC TIMEDISSEMINATION ACCURACY MPL.................... 28
GALILEO SIS UTC FREQUENCYDISSEMINATION ACCURACY MPL.................... 29
GALILEO UTC TIME DETERMINATION
ACCURACY ................................................................. 29
GALILEO OS POSITIONING
ACCURACY ................................................................. 29

3.4

GALILEO OS AVAILABILITY ..................... 30
GALILEO PER-SLOT AVAILABILITY .... 30

GALILEO OS SIS RF
CHARACTERISTICS ..................................................11

AVAILABILITY OF THE GALILEO UTC
TIME DISSEMINATION SERVICE......................... 30

GALILEO OS SIS NAV MESSAGE
CHARACTERISTICS ..................................................12

AVAILABILITY OF THE GALILEOPOSITION DILUTION OF PRECISION ................ 31

2.3 OVERVIEW OF GALILEO OSPERFORMANCE CHARACTERISTICS .............. 13

AVAILABILITY OF THE GALILEOPOSITIONING SERVICE .......................................... 31

GALILEO OS SIS STATUS.........................13

AVAILABILITY OF THE GALILEO UTC
TIME DETERMINATION SERVICE ....................... 32

GALILEO OS ACCURACY:RANGING SERVICE ...................................................18
GALILEO OS ACCURACY: TIMESERVICE ........................................................................18
GALILEO OS ACCURACY:

3.5

ADDITIONAL FUNCTIONALITY ............... 33

GALILEO OS COMPATIBILITY AND
INTEROPERABILITY WITH OTHER GNSS ...... 33

3.6

GALILEO SUPPORT FOR AVIATION ..... 34iv

3.7 PERFORMANCE LEVEL FOR THE
GNSS SERVICE CENTRE ....................................... 36
TIMELY PUBLICATION OF NAGUS .......36

D.1.2 LIMITATIONS .................................................. 53
D.1.3 GALILEO CONSTELLATION EXPECTEDEVOLUTION ................................................................ 53

ANNEX A: REFERENCE DOCUMENTS ............. 39

D.2 GALILEO SIS RANGING ACCURACY:EVOLUTION OF EXPECTED SISE ...................... 53

ANNEX B: ABBREVIATIONS
AND ACRONYMS ................................................... 41

D.3 EVOLUTION OF THE EXPECTEDAVAILABILITY OF GLOBAL PDOP .................... 53

ANNEX C: OS SIS BACKGROUNDINFORMATION AND PVT ACCURACYPERFORMANCE DRIVERS ................................... 43
C.1. INTRODUCTION .............................................. 43
C.1.1 SCOPE ................................................................43
C.1.2 LIMITATIONS ...................................................43

C.2. CONSTELLATION ............................................ 43
C.2.1 RELATIONSHIP WITH SECTION 3.2.......43

D.4. EVOLUTION OF THE EXPECTED GALILEO
OS POSITIONING PERFORMANCE ................... 54
D.4.1 EVOLUTION OF THE GALILEO OS
POSITIONING EXPECTED ACCURACY ............ 54
D.4.2 EVOLUTION OF THE GALILEO OS
POSITIONING EXPECTED AVAILABILITY ....... 54

D.5. ADDITONAL PERFORMANCEPARAMETERS ........................................................... 55
D.5.1 EXPECTED SIS RANGING ACCURACY
IN EXTENDED OPERATIONS MODE ................. 55

C.2.2 BASELINE 24-SLOT CONSTELLATIONCONFIGURATION ......................................................43

D.5.2 I/NAV IMPROVEMENTS............................ 55

C.3. SERVICE COVERAGE ..................................... 45
C.3.1 RELATIONSHIP WITH SECTION 3.2.......45

ANNEX E: DESCRIPTION OF ADVISORYNOTICES TO GALILEO .......................................... 58

C.3.2 PER-SATELLITE COVERAGE .....................45

E.1. LIST OF DEFINED NAGUS............................ 58

C.3.3 SERVICE VOLUME .........................................45

E.2. NAGU FORMAT ............................................... 62

C.4. ACCURACY ........................................................ 45

E.2.1 SPECIFIC NAGU ............................................. 62

C.4.1 RELATIONSHIP WITH SECTION 3.3.......45

E.2.2 GENERAL NAGU ............................................ 62

C.4.2 DEFINITION OF SIGNAL-IN-SPACERANGING ERROR ......................................................45

E.2.3 DESCRIPTION OF NAGU’S CONTENT... 62

D.5.3 ACCURACY OF ALMANAC ....................... 56

C.4.3 INSTANTANEOUS SISE PERFORMANCE
METRICS .......................................................................45
C.4.4 TIME DEPENDENCY ......................................47
C.4.5 UERE BUDGET ................................................49
C.4.6 USER TOTAL UNCERTAINTY IN UTC
TIME ESTIMATION ....................................................51
C.4.7 IONOSPHERIC DELAY MODEL FORGALILEO SINGLEFREQUENCY USERS ..............51
C.4.8 SINGLE-FREQUENCY GROUP DELAY
TIME CORRECTION ERRORS ................................51

C.5. INTEGRITY.......................................................... 51
C.6. CONTINUITY ..................................................... 51

ANNEX D: GALILEO OS PERFORMANCEEVOLUTION AND ADDITIONALPERFORMANCE PARAMETERS ........................ 53
D.1. INTRODUCTION .............................................. 53
D.1.1 SCOPE ................................................................53v

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

LIST OF FIGURES
Figure 1. High level scheme of the Galileo Ground
Segment Architecture............................................................. 6
Figure 2. Overall context of the GSC. ............................... 7
Figure 3. Signals transmitted by Galileo satellites. ...11
Figure 4. Example of decision tree for thedetermination of the status of broadcast SIS. ..............16
Figure 5. Graphical representation of the various
components of the total uncertainty in the estimationof the UTC Time......................................................................19
Figure 6. NAGU types ..........................................................36
Figure 7. SISE projection onto the line of sight for eachuser location.............................................................................46
Figure 8. Typical SISE vs. Prediction Time from ToE(all batches). For illustration only - Performance will
gradually improve over time toward the full system
deployment. .............................................................................48
Figure 9. Typical SISE vs. Prediction Time during
Extended Operations Mode. For illustration only. ......48
Figure 10. Graphical summary of the various types of
NAGUs. ......................................................................................58vi

LIST OF TABLES
Table 1. Reference Orbit Parameters. .............................. 5
Table 2. Mapping of Message types to Signal
Components .............................................................................12
Table 3. Signal Health Status Bit Values. .....................14
Table 4. Data Validity Status Bit Values. ......................14
Table 5. SISA index values relevant to the assessmentof the SIS Status. ....................................................................15
Table 6. Galileo Open Service SIS Status vs SIS Status
Flags ...........................................................................................17
Table 7. Summary of SIS flags to be checked by thedifferent Galileo OS users to compute the Status of
Signals-in-Space ....................................................................17

Table 26. Galileo URA for DF users. .............................. 35
Table 27. Galileo URA for SF users................................ 35
Table 28. Galileo probability of Single SIS fault........ 35
Table 29. Galileo probability of constellation SIS fault.
..................................................................................................... 36
Table 30. MPL of the Timely publication of NAGUs. 37
Table 31. Galileo Constellation Reference TechnicalParameters. ............................................................................. 43
Table 32. Galileo Constellation at FOC. Reference
Geometry at 2016/11/21 00:00:00 UTC....................... 44
Table 33. Typical UERE budget for Single Frequency
E1 – Rural Pedestrian (RP) User Environment (**). .. 49
Table 34. Typical UERE budget for Dual Frequency
E1/E5a – Rural Vehicle (RV) User Environment (**). 49
Table 35. Evolution of the Expected Availability of
Global PDOP. ......................................................................... 54

Table 8. Galileo Constellation Parameters (Ref. Epoch:
2016/11/21 00:00:00) – Reference constellation forthis OS SDD. ............................................................................26

Table 36. Evolution of the Expected Galileo OS
Positioning Performance in nominal configuration (inmetres, 95% values). ........................................................... 54

Table 9. Galileo SIS Ranging Accuracy MPL for any
satellite. .....................................................................................27

Table 37. Typical Galileo OS Positioning Service
Availability (global average) and expected evolution.
..................................................................................................... 54

Table 10. Galileo SIS Ranging Accuracy MPL over all
satellites. ...................................................................................27
Table 11. Galileo OS Ranging Accuracy performance
calculated at 99.9% percentile (on yearly basis). .......28
Table 12. Galileo OS Range Rate Accuracy
performance MPL. ..................................................................28
Table 13. Galileo SIS UTC Time Dissemination
Accuracy MPL. .........................................................................28
Table 14. Galileo SIS UTC Frequency Dissemination
Accuracy MPL. .........................................................................29
Table 15. Galileo OS Time Determination Accuracy
MPL at any user location .....................................................29
Table 16. Galileo OS Positioning Accuracy MPL ataverage user location............................................................29

Table 38. Galileo Extended Operations Mode
Expected SIS Ranging Accuracy ...................................... 55
Table 39. Time to CED (95%) in open sky
environment with perfect channel conditions ............ 56
Table 40. Typical RedCED Ranging Accuracy
Performance ............................................................................ 56
Table 41. Galileo almanac SIS Ranging Accuracy
typical values over all satellites, Global Average,
when almanac’s clock and ephemeris information isused............................................................................................ 56
Table 42. List of general NAGUs. ................................... 59
Table 43. List of specific NAGUs. .................................... 60
Table 44. List of obsolete NAGUs. ................................. 61

Table 17. Galileo OS Positioning Accuracy MPL atworst user location ................................................................29
Table 18. MPL of the Per-Slot Availability. ..................30
Table 19. MPL of the Availability of the Galileo OS
UTC Time Dissemination Service. ....................................30
Table 20. MPL of the Availability of the Galileo
Position Dilution Of Precision. ...........................................31
Table 21. MPL of the Availability of the Galileo
Positioning service, at average user location. ..............31
Table 22. MPL of the Availability of the Galileo
Positioning service, at worst user location. ...................32
Table 23. MPL of the Availability of the Galileo UTCTime Determination service, from any point in theservice coverage. ....................................................................33
Table 24. MPL of Galileo GST-GPS Time Offset
Determination Accuracy. .....................................................34
Table 25. MPL of Galileo GST-GPS Time Offset
Determination Availability. .................................................34

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

SECTION 1: THE GALILEO
OPEN SERVICE

The main document comprises the following sections:1)

The main purpose of this section is tointroduce the document, define the Galileo
Open Service and to provide a generaldescription of the Galileo system.
2)

Galileo is the European Global Navigation Satellite
System (EGNSS), under civil control, that provides
satellite positioning services to European citizens andworldwide.

In order for users to be able to benefit as early as
possible from the Galileo services, the Galileo Initial
Services provision phase started before the Galileo
core infrastructure was fully deployed, in 2016. Since
then, in parallel to the infrastructure deployment, theperformance of the Galileo Services has improved.
This Service Definition Document describes theGalileo Open Service provided at the time of its
publication. Future releases of this document may be
issued to properly take into account any further
evolution of the Galileo OS.

1.1 PURPOSE OF THE
DOCUMENT
The purpose of this Galileo Services - Open Service
Definition Document is to describe the characteristics
and performance of the Galileo OS provided throughthe Galileo OS SIS. The OS SDD presents the
Minimum Performance Levels (MPLs) targeted forsuch service and defines the conditions under whichsuch MPLs can be reached. This document addresses
all users of Galileo OS. The Galileo OS is provided freeof charge to all users.
This OS SDD consists of a main body and fiveannexes. It provides an overview of the EGNSS
programme as well as an overview of the OS SIS. It
then presents the MPLs for the OS. It concludes withthe relevant reference documents. The annexes
provide additional information on Galileo OS andabout the performance at FOC.

Galileo Open Service SIS Characteristics
and Minimum Usage Assumptions

This section includes a description of theGalileo SIS and the definition of theparameters used to identify the MPLs.

Galileo provides ranging signals on three different
frequencies, in two different frequency bands,
enabling single- and dual- frequency positioning forusers equipped with suitable receivers.
As one of the services offered by Galileo, the Galileo
Open Service (OS) enables free of charge, global
ranging, positioning and timing, by means of theGalileo OS Signal-In-Space (SIS).

The Galileo Open Service

3)

Galileo OS MPLs
This section provides the Galileo Services Open Service MPLs and describes additional
OS SIS functionality.

The following Annexes close the document:• Annex A: Reference Documents.
• Annex B: Abbreviations and Acronyms.
• Annex C: OS SIS Background Information and
PVT Accuracy Performance Drivers.
• Annex D: Galileo Open Service - Performance
Evolution.
• Annex E: Description of Notice Advisory to
Galileo Users.

1.2 SCOPE OF THE
DOCUMENT
This Galileo OS SDD applies to the Galileo OS asprovided at the time of its publication. This document
does not address Galileo restricted access signals
such as the E1A signal or the signals broadcast in theE6 band.
The OS SDD belongs to the series of Galileo
Programme Reference Documents published for the
benefits of Galileo users, to present and explain
various aspects of the EGNSS concerning Galileo OS.
The other Programme Reference Documents are:•

The European GNSS (Galileo) – Open Service –Signal In Space Interface Control Document(Annex A [1] (OS SIS ICD)).
By describing exhaustively the SIS, it specifies theinterface between the Galileo Space Segment
and the Galileo User Segment. It is addressed to
the whole Galileo OS user community.

2•The European GNSS (Galileo) – Open Service –Ionospheric Correction Algorithm for Galileo
Single-Frequency Users (Annex A [2]).
It describes in detail the reference algorithm to be
implemented by user receivers to compute theGalileo ionospheric corrections. It is addressed
mainly to Galileo OS receiver manufacturers.

All public Galileo Programme Reference Documents
are made available to users through the web portal of
the European GNSS Service Centre (http://www.gsceuropa.eu).

1.3 TERMS AND
CONDITIONS OF USE
The terms and conditions of use of the Galileo Open
Service are described at the beginning of thisdocument.

1.4 ABBREVIATIONS AND
ACRONYMS
Abbreviations and acronyms used in this document
are provided in Annex B.

1.5 GALILEO OPENSERVICE DEFINITIONThe Galileo Open Service is a free of charge global
ranging, positioning and timing service. Each Galileo
satellite transmits navigation signals (Signal-InSpace, SIS) in three frequency bands. The OS SIS,
broadcast on two out of these three bands, provide
access to the Galileo OS ranging, positioning andtiming services for users equipped with a Galileo OS
compatible receiver. The following services aresupported by Galileo OS SIS:•

Single-Frequency and Dual-Frequency Ranging,•

Single-Frequency
Positioning,•andDual-Frequency

UTC Time Determination.

Open Services are provided in either single-frequency(SF) or dual-frequency (DF) mode. In the case of SF
usage mode, the user equipment tracks and processes
the information provided by only one of the three OS

frequencies (see 2.2 for more details). The different
OS single-frequency usage modes are E5a (only), E5b(only) and E1 (only). In any SF usage mode, specificcompensations need to be applied: Broadcast Group
Delay (BGD), to compensate for specific satellite
systematic delays between the different frequencies,
and ionospheric compensation, to compensate foratmospheric delays of the signals. The respective
algorithms are specified in the Galileo OS SIS ICD(Annex A [1]) and in the Ionospheric Correction
Algorithm for Galileo Single-Frequency Users (Annex
A [2]).
In the case of DF usage mode, the user equipment
tracks and processes the information provided by twoof the three OS frequencies. The different OS dualfrequency usage modes are E1/E5a and E1/E5b. In
dual-frequency usage modes, BGD compensation is
not required, and the ionospheric delays are cancelledout by Galileo OS receivers, taking advantage of thedispersion property of the ionosphere, which renders
the resulting delay inversely proportional to thesquare of the signal frequency, allowing to implement"iono-free" linear combination of the ranging
observables collected on two different carriers.

GALILEO OS RANGINGSERVICE
Ranging allows users to continuously estimate theirdistance to the satellite. This measure is the core of
positioning services since the user's position and time
can be estimated using ranging measurements from(at least) four different satellites. GNSS ranging
services comprise a set of electromagnetic signals
transmitted by satellites and properly modulated tocarry the information, generated by an appropriate
ground infrastructure, needed by receivers to estimate
the user-to-satellite range.
The Galileo OS Ranging Service is provided in both SF
usage mode and DF usage mode.
DF usage mode is in general characterised by higher
accuracy of the range measurement. The use of two
frequencies permits in most cases a better
compensation of the disturbing effect of theionosphere on the SIS, thus providing better
performance to the end user.
The Galileo OS Ranging Service is interoperable withGPS ranging services and therefore it provides a direct
benefit to users who are able to exploit both Galileo
and GPS constellations, by increasing the number ofavailable signals-in-space.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

GALILEO OS POSITIONINGSERVICE
By combining the ranging measurements with thenavigation parameters delivered by the SIS, all users
equipped with a Galileo OS receiver who are locatedwithin the Service Volume of the Galileo OS (seeSection C3.3) are able to estimate their position andtime. The Positioning Service is provided in either
single-frequency or dual-frequency mode.

the navigation signals (i.e. the Galileo navigation
message) and broadcast to the users.
The Galileo system offers seven high-performanceservices worldwide:•

Open Service (OS): Galileo open and free of user
charge service set up for positioning and timing
services. The OS are the only services addressedin this document.

•

Open
Service
Navigation
Message
Authentication (OSNMA): provided by tags
allocated in the Navigation message carried by
E1-B SIS, allows user receivers to authenticate
the acquired navigation data that it uses toachieve position and time, allowing to distinguish
if the source of those parameters is genuinely
Galileo system or any malicious spoofing entity.

•

Public Regulated Service (PRS): Service
restricted to government-authorised users, forsensitive applications that require a high level ofservice continuity.

•

High Accuracy Service (HAS): A free accessservice complementing the OS, delivering highaccuracy data, enabling users to achieve submeter level positioning accuracy.

•

Commercial Authentication Service (CAS): A
service complementing the OS, providing acontrolled access and authentication function to
the users.

•

Search and Rescue Service (SAR): Europe's
contribution
to
COSPAS-SARSAT,
aninternational satellite-based search and rescue
distress alert detection system.

•

Emergency Warning Service (EWS): A
worldwide service to broadcast emergency
warnings linked to natural or man-madedisasters.

The Galileo OS Positioning Service, which is based on
the Galileo OS Ranging Service, is interoperable with
GPS positioning services. It therefore provides a direct
benefit to users who are able to exploit both Galileo
and GPS constellations, by increasing the number ofavailable satellites in view.

GALILEO OS UTC TIME
DETERMINATION SERVICE
GNSS satellites also broadcast data which allow
GNSS receivers to relate the GNSS time scale tointernational reference timescales. The precise atomic
clocks in the Galileo system allow delivery to users ofvery accurate timing data. The OS UTC Time
Determination Service provides Galileo users
worldwide with direct and accurate access to the
Universal Time Coordinated (UTC) reference. It
provides both the integer seconds offset between the
Galileo System Time (GST) and UTC (see also section
1.6.5.2) and the fractional GST-UTC difference at
nanosecond level. This allows users to time-stamp
their data in UTC or local time and to precisely
synchronise to UTC their clocks, which can be situatedat very different locations in the world.

1.6 GALILEO SYSTEMOVERVIEWThe Galileo system is composed of a Core
Infrastructure and a number of Service Facilities. The
Core Infrastructure, in turn, comprises a Space
Segment and a Ground Segment.
The Galileo Space Segment consists of a constellationof satellites transmitting navigation signals providinguser access to the Galileo services. The Galileo
Ground Segment consists of a ground infrastructure
providing the functionality to monitor and control thesatellite constellation and the generation and further
dissemination of the mission data that are included in

GALILEO SPACE SEGMENT
The Galileo Space Segment generates and transmits
the Galileo navigation signals as specified in the
Galileo OS SIS ICD (Annex A [1]).
The baseline Galileo constellation configuration isdefined as a 24/3/1 Walker constellation: 24 nominal
Medium Earth Orbit satellite slots are arranged in 3
orbital planes, with their ascending nodes uniformly
distributed at intervals of 120 degrees, inclined at 56
degrees with respect to the Equator. Each orbital
plane includes 8 satellite slots uniformly distributed
within the plane, i.e. at intervals of 45 degrees ofargument of latitude. The angular shift between

4

satellites in adjacent planes is 15 degrees. Satellites
In service in these slots are referred to as nominal
satellites. These nominal satellites contribute to theachievement of the service performance in this SDD.
The constellation may be complemented by Galileo
auxiliary satellites, which occupy orbital slots that are
not part of the baseline constellation and are notdefined a priori. Auxiliary satellites that are in thebaseline orbital planes may be repositioned to any
given nominal slot within its orbital plane, dependingon maintenance or service evolution needs. The
processing by Galileo receivers of healthy SIS
broadcast by auxiliary satellites is not required inorder to achieve the service performance presented inthis OS SDD, although their use results in an
improvement of the service performance.
Furthermore, the Galileo constellation may comprise:•

Not-in-service satellites, i.e. satellites that are
currently not providing Galileo services and are
not broadcasting a navigation SIS.

•

Decommissioned Satellites, i.e. satellites that areremoved from service permanently.

The constellation geometry repetition period
corresponding to the nominal orbital parameters isapproximately 10 sidereal days (corresponding to 17
orbital revolutions). This means that for any fixed
Galileo user, the local satellite geometry at a given
instant will repeat every 10 sidereal days,
approximately.

GALILEO GROUNDSEGMENTThe Galileo Ground Segment comprises both the
Ground Control Segment and the Ground Mission
Segment and it includes the following infrastructure:•

Two
Galileo
Control
Centres(GCC),
implementing ground control and ground mission
capabilities at each site.

•

A worldwide network of Galileo Sensor Stations(GSS), which collects and forwards Galileo SIS
measurements and data to the GCCs in real time.

•

A worldwide network of Galileo Uplink Stations(ULS), which distributes and uplinks the mission
data to the Galileo constellation.

•

A worldwide network of Telemetry, Tracking &Control stations (TTC stations), which collects
and forwards telemetry data generated by the
Galileo satellites, and distributes and uplinks thecontrol commands required to maintain the
Galileo satellites and constellation in nominal
operational conditions.

An overview of the Galileo Ground Segment isprovided in Figure 2, where only the Galileo Ground
Segment functionality related to the Open Service isincluded.
The Galileo Ground
functions required to:

Segment

implements

all

The main reference orbit parameters of the Galileo
constellation are specified in Table 1. The
constellation is further described in Annex C, while
the constellation that is operational at the time of
publication of this OS SDD is described in section 3.2.

•

Generate the Galileo mission support data (e.g.
satellite orbit and time synchronisation data,ionospheric correction model data and otherinformation transmitted in the navigation
signals).

The up-to-date status of the Galileo constellation isavailable through the European GNSS Service Centre(GSC) webpage1.

•

Perform the monitoring and control of all Galileo
system assets (both ground and space segment).

•

Interface with the Service Facilities (see section
1.6.3), entities that are not part of the Galileo core
infrastructure ground segment but neverthelesshave a role in the provision of the Galileo services
and are considered part of the Galileo System(e.g. Time Service Provider, Geodetic Reference
Service Provider, COSPAS - SARSAT mission
segment, European GNSS Service Centre).

Table 1. Reference Orbit Parameters.

REFERENCE ORBITPARAMETER

Constellation Type
Orbit semi-major axis, mOrbit eccentricity

NOMINAL VALUE

Walker 24/3/1
295998010Orbit inclination, deg

56.0

Argument of Perigee, deg

0.0

1 www.gsc-europa.eu/system-service-status/constellation-information

5

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Ground Control Segment
The Galileo Ground Control Segment (GCS) provides
a large range of functions to support the management
and control of the satellite constellation. The scope of
this functionality includes control and monitoring of
the satellites and payload, planning and automation
functions that allow safe and correct operations totake place, and the support of payload related
operations by means of TT&C links.

Ground Mission Segment
The Galileo Ground Mission Segment (GMS)
determines the navigation and timing data part of thenavigation messages and transmits it to the satellite
via its C-Band ground stations.
The GMS architecture consists of facilities deployed in
the 2 Galileo Control Centres (GCCs) plus ULS andGSS Stations deployed at remote sites located aroundthe world. The Ground Mission Segment includes theProcessing Chain, which is in charge of computing thedata to be broadcast in the Galileo navigation
messages.

GALILEO SERVICEFACILITIES

outside the perimeter of the Galileo Core
Infrastructure that support the provision of Galileo
services.
The service facilities contributing to the provision of
the Galileo OS are:•

The European GNSS Service Centre (GSC): GSC
is the interface between the Galileo user
community and the Galileo system (see section
1.6.4 for further information).

•

The Geodetic Reference Service Provider (GRSP):
This entity supports the GCC in realising theGalileo Terrestrial Reference Frame (GTRF),
consistently with the international Terrestrial
Reference Frame (ITRF).

•

The Time Service Provider (TSP): This entity
supports the GCC in the realisation of the Galileo
System Time (GST) and its alignment to the
Coordinated Universal Time (UTC).

•The Galileo Security Monitoring Centre (GSMC):
This facility is in charge of monitoring the systemsecurity.

An additional service facility, the Galileo ReferenceCentre (GRC), is responsible for monitoring andassessment of the performance of the Galileo
services, completely independently from the Galileo
core infrastructure and its operations.

The Galileo Service Facilities are elements locatedFigure 1. High level scheme of the Galileo Ground Segment Architecture.

6

THE EUROPEAN GNSSSERVICE CENTRE (GSC):GALILEO INTERFACE WITH
USERS
The European GNSS Service Centre (GSC), part of theEuropean GNSS infrastructure, provides the single
centralised ground interface between the Galileo user
communities and the Galileo system infrastructure
and operator, for the provision of specific services

beyond the SIS transmitted by the Galileo satellites. It
is accessible through its web portal www.gsceuropa.eu.
The GSC is conceived as a centre of expertise,knowledge sharing, custom performance assessment,
information dissemination and support to theprovision of value- added services enabled by the
Galileo services. To implement these objectives, the
GSC interfaces with the key elements of the Galileo
ground segment, as well as with external entities.
Figure 2 depicts the overall context of the GSC.

Galileo Service Facilities

2381048927
95672047876

Geodetic
Reference

Time Reference

Performance
Monitoring

Galileo Control
CentreEGNOS Service
CentreOther GNSS
Service Centres

GNSS Service Centre
GSMC* GNSS stands for 'Global navigation satellite system’

Figure 2. Overall context of the GSC.

GSC Functionality
The GSC has the task of interfacing with the user
communities across the entire value chain.
The GSC web portal is conceived as the one-stopshop providing ready access to key information foruser communities of Galileo OS, OSNMA, HighAccuracy and SAR services.

The functionality and services covered by the GSC are:•Helpdesk support:
For answering general queries and incident
notifications from users on Galileo SIS andspecific queries from Galileo receiver andapplication developers on the official Galileo user
documents. In addition, registered users can
subscribe to be informed in real time about
events affecting the Galileo services.

7

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023•

Information on Galileo system status:
Publication of Galileo almanacs and ephemeris
data, of constellation status and provision of
Galileo Service Notices.

•can be also found in the GSC web page, www.gsceuropa.eu, under “System Status”.
Specific MPLs apply for the timely publication of
NAGUs (see section 3.7.1).

Publication of notifications to users:
General information on the constellation andcurrent status of the different space vehicles are
published by means of Notice Advisory to Galileo
Users messages (NAGUs, see section 1.6.4.1.1),
which inform regularly about the system status.
Users have the possibility of subscribing to theautomatic notification of NAGUs via e-mail.

•

Reports on the Galileo Open Service navigation
key performance indicators and on the GSC
performance itself are also published for theusers' information.

•

Electronic
Library,
including
Programme
Reference
documentation
andgeneralinformation.

•

Support to GNSS developers, including the GNSS
Simulation and Testing infrastructure (GSTI).

•Interface with other GNSS Service Providers.

•

Galileo user satisfaction monitoring, including
customised performance assessment, reportingand forecasts for specific communities, andsupport to the Galileo services development foreach community or domain.

1.6.4.1.1

GALILEO TIME AND
GEODETIC REFERENCE
FRAMESThe Galileo system establishes its independent
terrestrial reference frame and system time scale. The
satellite positions and satellite clock offsets encodedin the navigation data are referenced to these Galileo
time and terrestrial internal references. Without
additional processing, the navigation solution
computed by a Galileo OS receiver (using themathematical algorithms described in the SIS-ICD)
provides the receiver's position and time offset
referenced to these internal references.
The Galileo system terrestrial and time references are:•

The instantaneous satellite positions derived
from the data provided in the OS SIS and using
the algorithm defined in the OS SIS ICD (Annex A[1]) are referenced to the GTRF. The GTRF is
specified to always be in line with theinternational terrestrial reference frame, as
defined by the international Earth Rotation andReference Systems Service (IERS). The GTRF
specification is provided in section 1.6.5.1.

Notifications To Users (NAGUS)

The GSC is responsible for the publication of Notice
Advisory to Galileo Users (NAGU) messages. NAGUs
are used to notify Galileo users about the SIS statusof all satellites in the Galileo constellation. Different
kinds of NAGUs are issued depending on the specific
event to be communicated, related to either changes
intheconstellation(commissioned
anddecommissioned satellites, for example) or to
occurrence and recovery of (planned and unplanned)
outages of SIS.
Examples of planned events that are anticipatedthrough the publication of a specific NAGU aresatellite manoeuvres and maintenance activities,
declaration of a satellite entering into service,
recovery from outages. Examples of unplanned
events that are notified through the publication of a
specific NAGU are satellite failure, information about
short outages already recovered, unscheduled
outages of SIS of an undefined duration.
The description of the structure and content of the
NAGUs is provided in Annex E. This information,
together with the list of active and archived NAGUs

Galileo Terrestrial Reference Frame (GTRF): theGalileo spatial reference frame•

Galileo System Time (GST): the Galileo time andfrequency reference
The instantaneous satellite clock parameters
derived from the data provided in the OS SIS andusing the algorithm defined in the OS SIS ICD(Annex A [1]) are referenced to the Galileo
System Time. The GST steered to TAI with anoffset of 19 seconds and the required parameters
to transform it to UTC are transmitted in thenavigation message, as explained in section
1.6.5.2.

Galileo Terrestrial Reference
Frame
The Galileo Terrestrial Reference Frame is theindependent realisation of the international
Terrestrial Reference System based on the estimatedcoordinates of each one of the Galileo Sensor Station(GSS) sites.

8

The determination of the GSS positions is based on
global free network adjustment and the precise
network solution thus obtained is aligned to theinternational Terrestrial Reference Frame. For thispurpose, a significant number of ITRF stations colocated or non- co-located with GSSs are part of the
network of stations operated by the GRSP.
The GTRF is a highly accurate realisation of the ITRS.
At any time, the alignment between the GTRF and thelatest physical realisation of the ITRF is such that thedifference between the ITRF and the GTRF
coordinates of the ITRF stations/markers used in therealisation of the GTRF is less than 3 cm (2σ).
The Galileo system uses the geodetic input
information to produce navigation data (e.g. satellite
ephemeris) referenced to the GTRF. Accordingly, theuser position coordinates derived from Galileo
position solutions are referenced to GTRF. Due to thegood alignment of GTRF to ITRF both reference
frames are understood to be equivalent in the frameof this document. The GTRF is regularly aligned if new
ITRF realisations are published.

rotation period).
The time synchronisation information disseminated in
the Galileo SIS (e.g. satellite clock offsets) is
referenced to GST. This information allows the Galileo
OS users to estimate their local time referenced to the
GST realisation computed by the OS receiver.
In order to better support timing applications basedon UTC, the Galileo OS data message includes
additional parameters which enable the Galileo OS
users to obtain a realisation of the UTC time by
applying a correction to the GST (further details areprovided in Annex C.4.6). These parameters provide a
prediction of GST-UTC based on UTC realisations
available at, currently, a minimum of 5 European
metrological institutes.

To obtain the position in any reference frame different
from ITRF, Galileo OS user equipment needs to apply
the appropriate valid transformation parameters
between the latest ITRF and the desired reference
frame. This transformation is under full control andresponsibility of the Galileo OS user.
Concerning the interoperability between GPS and
Galileo, the GPS terrestrial reference frame and the
GTRF are both realisations of the ITRF. Therefore, formost OS applications, a high level of interoperability
is provided between the spatial positions obtainedwith GPS and those obtained with Galileo, without
further activity by the user equipment.

Galileo System TimeThe Galileo System Time is a continuous timescale
based on the definition of the second (according to theinternational System of Units, SI) whose
origin/reference epoch GST(T0) is defined as 13
seconds before 1999-08-22 00:00:00 UTC. UTC is
the time scale endorsed by the 15th General
Conference of Weights and Measures for worldwide
time coordination and dissemination. It is theinternational time metrological standard and it ismaintained, coordinated and disseminated by the
BIPM.
UTC is defined as an atomic timescale (time interval isconsistent with the SI definition of the second), but
unlike GST, it is steered towards UT timescale (which
is not based on atomic standards but on the Earth9

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

SECTION 2:
GALILEO OPEN SERVICESIS CHARACTERISTICS
AND MINIMUM USAGE
ASSUMPTIONS

10SECTION 2: GALILEO
OPEN SERVICE SISCHARACTERISTICS
AND MINIMUM
USAGE
ASSUMPTIONSThis section starts with a short description, which isprovided for information purposes. The reference
document for details of the Galileo OS SIS Interface
characteristics is the OS SIS ICD (Annex A [1]).
In the event of conflict between the OS SIS interface
characteristics described in this document and the
ICD, the latter shall prevail.
A description is then provided of the different MPLs,
along with the minimum usage assumptions for theusers of the Galileo OS.

2.1 OS SIS INTERFACECONTROL DOCUMENTREQUIREMENTS
The OS SIS complies with the technical requirements
related to the interface between the Space Segment
and the OS receivers as established by the OS SISInterface Control Document (ICD) (Annex A [1]).

2.2 OVERVIEW OF OS SISINTERFACE
CHARACTERISTICSGALILEO OS SIS RF
CHARACTERISTICS
Galileo comprises several signals and codes within
the 1.1 to 1.6 GHz band, namely:•

E1 signal, centred at 1575.42 MHz;•E5a and E5b signals, at 1176.45 MHz and1207.14 MHz
respectively,
multiplexed
together through an AltBOC scheme andtransmitted at the E5 carrier frequency centred
at 1191.795 MHz;•E6 signal, centred at 1278.75 MHz.

A complete representation of the Galileo signal
baseline is provided in Figure 3.
The Galileo SF OS is provided by each of the threesignals: E1 E5a and E5b, whereas the Galileo DF OS
is provided by each of the following signal
combinations broadcast by the same satellite:•

E1 and E5a;•

E1 and E5b.

The E1 OS signal comprises a pair of components
modulated with the CBOC(6,1,1/11) scheme:•a data component (E1-B), carrying the I/NAV
navigation message (see section 2.2.2) with adata rate of 125 bps and a symbol rate (after
FEC)
of
250
sps,
modulatedwith
CBOC(6,1,1/11,+);•a data-less component (E1-C), modulated witha CB0C(6,1,1/11,-).

Figure 3. Signals transmitted by Galileo satellites.

11

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

The E5 signal is made of four components
multiplexed together through an AltBOC(15,10)
scheme:A pair of components on the E5a carrier:••a data component (E5a-I), carrying the F/NAV
navigation with a data rate of 25 bps and asymbol rate of 50 sps;
a data-less component (E5a-Q);

A pair of components on the E5b carrier:•a data component (E5b-I), carrying the I/NAV
navigation message with a data rate of 125 bps
and a symbol rate of 250 sps;•

a data-less component (E5b-Q).

All components of E5a and E5b are generated
coherently, which allows them to be processed
together for increased accuracy and redundancy,
when required.

GALILEO OS SIS NAVMESSAGECHARACTERISTICS
The Galileo OS provides two different message types(see Table 2): the F/NAV and the I/NAV navigation
messages.
Table 2. Mapping of Message types to Signal Components.

MESSAGE TYPECOMPONENT

F/NAV

E5a-I

I/NAV

E5b-I and E1-B

The complete navigation message data aretransmitted on each data component as a sequenceof frames. A frame is composed of several subframes, and a subframe in turn is composed of several
pages. The page is the basic structure for building thenavigation messages.
Each navigation message contains the necessary
parameters and status flags enabling the OS Users
to access the SF and DF positioning and timing
services. These include:•

the time parameters and clock corrections,needed to compute satellite clock offsets andtime conversions;•the ephemeris parameters, needed to computethe satellite payload antenna coordinates;•

the service parameters, with satellite signal
health status information;•

the ionospheric parameters model, needed forsingle-frequency receivers;•

the almanacs, allowing less precise computationof the position of all satellites in the constellation
to facilitate the initial acquisition of the signals by
the receiver.

The purpose, structure and content, with full details
concerning the Galileo OS SIS Navigation Messages
and their use can be found in the Galileo OS SIS ICD(Annex A [1]). Please take note for the need ofprocessing SIS health status flags following thespecification in Table 7, depending on implementing a
SF or DF solution.
In the context of this document, the term “navigation
message” refers to a sub-frame (50 seconds for
F/NAV and 30 seconds for I/NAV), which contains
ephemeris, clock and ionospheric corrections or SIS
status information, that is, Page Type 1 to 4 for the
F/NAV and Word Type 1 to 6 for the I/NAV, unlessotherwise specified.

THE CYCLIC REDUNDANCYCHECK (CRC) IN GALILEO
NAVIGATION MESSAGE
To detect corruption of the received data, a checksum
is used by the Galileo navigation message, employing
a CRC technique. The detailed description of thischecksum is provided in the OS SIS ICD (Annex A [1]).
The CRC is not used to indicate any problem atsatellite level, on the transmitter side. The CRC
checksum is related exclusively to the errorless
reception of the transmitted bits, i.e. to thetransmission channel, not to the correctness of thestructure or the contents of the message astransmitted by the Galileo system. The CRC within
the navigation message of Galileo is therefore not
involved in the definition of the SIS Status.
If the CRC checksum is not passed successfully, therespective data must be rejected and no
determination of the SIS Status is possible. Once anavigation message is received with a successful
CRC, the user can then proceed to the SIS Statusdetermination, as described in the next section, andeventually to the utilisation of such SIS.

12

2.3 OVERVIEW OFGALILEO OSPERFORMANCE
CHARACTERISTICS
The Galileo OS performance characteristics are thefollowing: Status, Accuracy and Availability.

GALILEO OS SIS STATUS
Users of the Galileo OS can obtain information about
the OS SIS Status, i.e. about the operational status of
the OS SIS broadcast by each one of the Galileo
satellites, through the signals themselves, whentransmitted.
The Galileo OS SIS Status can take one of thefollowing four values:•

Healthy•

Unhealthy•

Marginal•

Extended Operations Mode

The meaning of the four possible values of the SIS
Status is the following:•

SIS “Healthy”: The SIS is expected to meet the
MPL2.

•

SIS “Unhealthy”: The SIS is out of service orunder test.

•

SIS “Marginal”: The SIS is in neither of the two
previous states.

•

SIS “Extended Operations Mode”: The SIS is
expected to meet reduced ranging accuracy (seesection 2.3.6).

The Galileo OS MPLs reported in the Galileo OS SDD
refer exclusively to Healthy SIS, unless statedotherwise.
No MPL is defined for Unhealthy or Marginal SIS. Thisimplies that no SIS performance parameter isbounded in its error for SIS in a Marginal or Unhealthy
state. It is explicitly recommended not to use any SIS
flagged as Marginal or Unhealthy.

The Extended Operations Mode is a Galileo
operational mode characterized by a graduallydegrading accuracy with respect to the nominal
operational mode, in case the Galileo OS navigation
message generation function is interrupted for morethan 24 hours.
A navigation solution obtained with Galileo SIS is
expected to meet the MPLs reported in the Galileo
OS SDD only if receivers comply with theassumptions reported in section 2.4, including theuse of navigation parameters within their broadcast
period (see also section C.4.4).
It is noted that if the SIS broadcast by an auxiliary
satellite is flagged Healthy, such SIS complies withthe accuracy MPLs defined in this OS SDD and may
be used by Galileo users, without compromising
performance. The presence of healthy SIS broadcast
by auxiliary satellites always improves the Dilution ofPrecision, allowing users who are able to exploit
them to obtain a navigation solution with improved
accuracy and availability, especially in urban
environments.
Nonetheless, auxiliary satellites are not required tofulfil the OS SDD availability MPLs of the Galileo
constellation. This implies that their SIS might beflagged as Marginal or Unhealthy for a higher
percentage of time than the Galileo satellites
belonging to the baseline constellation, without
impacting the availability commitment. Moreover, themeasured availability of the auxiliary satellites is notconsidered in the availability calculations of theGalileo services.

SIS Status dissemination
The status of each Galileo signal involved in theprovision of OS is determined by the SIS Status
information embedded in the navigation message orby the presence of a specific “dummy message” that
may replace the standard one (see section 2.3.1.2).
Users are also notified off-line about the SIS status of
the satellites in the Galileo constellation through the
publication of the Notice Advisory to Galileo Users,by the GSC (see section 1.6.4).

Dummy navigation message
Dummy pages are defined in the Galileo OS SIS ICD(Annex A [1]) (Page/Word Types 63 for F/NAV and
I/NAV, respectively). Such dummy pages, if

This assertion does not apply to the Minimum Performance Level for the provision of the Galileo-GPS System
Time Offset (GGTO, see section 3.5.1.1). Healthy SIS can broadcast parameters that indicate a non-valid GGTO
(see (Annex A [1]) for more details about the dummy value of the GGTO parameters).
2

13

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

transmitted, replace all the sub-frames containing
ephemeris and clock corrections of the navigation
message, which is then defined as dummy navigation
message. A dummy navigation message indicates an
Unhealthy SIS. Therefore, as soon as a dummy page,i.e. Page/Word Types 63, is decoded by a receiver,
the respective SIS must be considered Unhealthy.
Once the transmission of the dummy message
terminates and normal transmission is recovered,users must follow the appropriate procedure to checkthe SIS Status, as described in the next sections,
before starting to reuse the SIS.
Note that in the case of Dual-Frequency (DF) users, adummy navigation message on either one of thefrequencies implies that the DF SIS is not Healthy(see also section 2.3.1.43).

SIS Status flags
The status of the Signal-In-Space is encoded within
the navigation message through three SIS Status
Flags:•The Signal Health Status (SHS) flag.

•

The Data Validity Status (DVS) flag.

•

The Signal-In-Space Accuracy (SISA) value.

Full details concerning the position of the Galileo SIS
Status flag within the Galileo SIS Navigation Message
can be found in the Galileo OS SIS ICD (Annex A [1]).
Signal Health Status (SHS)The SHS flag is contained in the navigation data andthe almanac messages of each Galileo OS signal (E1,
E5a or E5b). For E1 and E5b, the SHS flags areincluded in the I/NAV navigation data stream. For
E5a, the SHS flag is included in the F/NAV navigation
data stream.
The SHS flag to be used is the one broadcast in thenavigation data transmitted by the satellite whose
SIS is being used.
The SHS flags broadcast as part of the almanac data
are provided for convenience in support of satelliteacquisition but shall not be used operationally todetermine the SIS Status.
The SHS flag can be raised by the system at any
moment4. The SHS flags can take the values definedin the OS SIS ICD (Annex A [1]), which are recalled

for convenience in Table 3.
Table 3. Signal Health Status Bit Values.

SIGNALHEALTHSTATUS(SHS)DEFINITION

0Signal OK

1

Signal out of service

2
3

Signal will be out of service/
Extended operations mode5
Signal component currently in
Test

Data Validity Status (DVS)For each Galileo OS signal (E1, E5a or E5b), the DVS
flag is contained in the navigation data. For E1 andE5b, the DVS flags are included in the I/NAV
navigation data stream. For E5a, the DVS flag is
included in the F/NAV navigation data stream. The
flag can assume the values defined in the OS SIS ICD(Annex A [1]), which are recalled for convenience inTable 4.
The DVS can be triggered independent of navigation
message refresh and users shall expect that its value
can change at any time.
Table 4. Data Validity Status Bit Values.

DATA
VALIDITYSTATUS(DVS)
0
1

DEFINITION
Navigation data valid
Working without guarantee(WWG)

Signal-In-Space Accuracy (SISA)For E1 and E5b, the SISA index is contained in the
I/NAV navigation data stream. For E5a, the SISA
index is contained in the F/NAV navigation data
stream.
As described in the OS SIS ICD, the SISA is aprediction of the minimum standard deviation (1σ) of
the unbiased Gaussian distribution which overbounds the Signal–in–Space Error (SISE, see section
2.3.2.1) predictable distribution for all possible user
locations within the satellite coverage area. Suchprediction applies to ranging measurements obtained
from DF SIS combinations, hence Table 7 quotes
SISA(E1,E5a) and SISA(E1,E5b). The SISA parameter

The navigation message, specifically the I/NAV, transmitted on E1 and E5b, has been designed to include
another type of page: the Alert Pages (see OS SIS ICD, Annex A [1] for a detailed definition). The transmissionof Alert Pages is a capability that the Galileo system is currently not exploiting.
4
The Time To Alert between the occurrence of an event and the setting of the SHS is under definition.
5
For more details please see section 2.3.6 and Table 6.
3

14

can assume 255 values. Nevertheless, when the
SISA is used as one of the means for determining the
SIS Status, it must be considered as a binary indicator,
with its only meaningful values being “No Accuracy
Prediction Available” (that is NAPA, when
SISA=255) or “not NAPA” (when SISA≠255). Notethat those SISA values described in the OS SIS ICD(Annex A [1]) as Spare (from 126 to 254) are to beconsidered as “not NAPA”.
Note also that a fixed SISA value of 125 is used in
combination with the SHS flag set to 2, to notify that
the Galileo OS service is operating in Extended
Operations Mode (see Table 3 and Table 6). In
Extended Operations Mode the SISA flag must still
be considered as the same binary indicator as
mentioned above. Therefore, a raw SISA value of 125
during Extended Operations Mode is still to beconsidered as “not NAPA”, being not representativeof any sizing of the ranging error.
The SISA index values relevant to the assessment of
the SIS Status, as defined in the OS SIS ICD (Annex
A [1]), are recalled for convenience in Table 5.
Table 5. SISA index values relevant to the assessment of
the SIS Status.

SISA INDEX
255
0 … 254SISA VALUE
No Accuracy Prediction
Available (NAPA)
Not NAPA

that the navigation message has been properly
received, i.e. it has successfully passed the CRC check(see section 2.2.2.1).
The first condition to be fulfilled by the navigation
message in order for the user to proceed with thedetermination of the SIS Status is that it must not bea dummy message. As explained in section 2.3.1.2, incase of dummy message the respective SIS must be
considered Unhealthy.
If the message is not dummy, the user can proceedwith checking the other conditions to determine the
SIS Status as specified in Table 6. The order in which
the flags are checked by a receiver on receipt of anon-dummy navigation message is arbitrary and up
to the manufacturer. The value of each flag can beread (and taken into account) independently from thevalue of the other flags. An example of a possible
decision tree for the determination of the SIS Statusis provided in Figure 4.
As an example of receiver operations, in section
2.3.1.3 it is explained that DVS flag equal to WWG
implies that the respective SIS cannot be considered
Healthy but, depending on the value of the otherflags, only Marginal. This means that the SIS might
not meet the MPLs defined in this document. As soon
as receivers detect that the DVS value has been set
back to 0, and that, taking into account the otherrelevant flags, the SIS Status is back to Healthy, they
will have to retrieve the most recently broadcast
navigation data in order to use such SIS.

Mapping between SIS Status
Flags and SIS Status
The mapping between the values of the SIS Health
Status Flags, presented in section 2.3.1.3, and thefour values of the SIS Status is provided in Table 6. Inorder to determine the Status for a specific SIS
broadcast by a Galileo satellite, the user must ensure

15

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Figure 4. Example of decision tree for the determination of the status of broadcast SIS.6

Decision tree for user receivers able to interpret SHS = 2 as SIS in Extended Operations Mode (EOM). In thecase that EOM is activated, receivers implemented as per SDD issue 1.2 or earlier will consider the SIS as“marginal”.
6

16

Table 6. Galileo Open Service SIS Status vs SIS Status Flags.

MESSAGETYPE

SIS FLAGSSIS STATUS

DUMMY

SHS

DVS

SISA

Dummy
(not usable)

Yes

N/A

N/A

N/A

UnhealthyNo

1 = Out of Service

Any Value

Any Value

UnhealthyNo

3 = In Test

Any Value

Any Value

Marginal

No

0 = Signal OK
2 = Extended
Operations Mode7

Marginal

No

0 = Signal OK
2 = Extended
Operations Mode7

0 = Signal OK

Depending on the service to be used, SingleFrequency (SF) or Dual-Frequency (DF), Users will
have to check the value of the various flags on
different signals.
Table 7 shows the summary of the SIS Status Flags to

be checked by the different Galileo OS users for bothSF and DF services.
Furthermore, it is recalled that messages with Age of
Ephemeris beyond 4 hours are to be considered
expired and thus not usable.

7
8

E1
E5a

X

X

E1/
E5b

X

X

X

X

E5b
E1/
E5a

SISA(E1,E5b)X

E5bDVS

X

E5bHS

USERS

I/NAV

E1BDVS

F/NAV

E1BHS

Note also that the value of SIS Status flags applies tothe whole sub-frame they belong to. As an example,
the DVS flag in the I/NAV message is located in Word
Type 5 but its value is applicable also to the content
of the Word Type 1, 2, 3 and 4.

Table 7. Summary of SIS flags to be checked by thedifferent Galileo OS users to compute the Status of Signalsin-Space.

SISA(E1,E5a)This means that all parameters to be used by areceiver have to be retrieved after the SIS is (back to)
Healthy in order to ensure that the MPLs are expected
to be met.

(Not intended to be
representative of
ranging accuracy
when in EOM)raw value  255 =not “NAPA”

0 = “NDV”

E5aDVSNo

0 = “NDV”

E5aHS

Healthy

raw value 255 =“NAPA”
typical raw value =125(formerly “Will beout of Service” 8)

SINGLEFREQUENCYNo

Any Value

Any Value

2 = Extended
Operations Mode7

DUAL
FREQUENCY

ExtendedOperations Mode

1 = “WWG”

X

X

X

X

X

X

X

X

X

X

X

As interpreted by receivers applying OS SDD V1.3 and above, as well as OS SIS ICD V2.1.
As interpreted by receivers unable to construe EOM.

17

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

GALILEO OS ACCURACY:RANGING SERVICEThe Galileo OS Ranging Service Accuracy
performance is based on the following two
parameters:•

Galileo OS Ranging Accuracy.

•

Galileo OS Ranging Rate Accuracy.

for time periods during which the transmitted SIS was
healthy. Galileo OS Ranging Accuracy (and therefore
Galileo OS Ranging Accuracy over all satellites) areevaluated over all age of data (AOD9) values, i.e. the
SISE time series will consider the navigation message
at the age of data when it was observed. Expected
ranging accuracies for different values of AOD areprovided in Annex D.

Galileo OS Ranging Rate
Accuracy

Galileo OS Ranging Accuracy
The Galileo OS Ranging Accuracy is defined as astatistical measure of the Galileo SIS Ranging Error(SISE). SISE is defined as the combination of two error
contributions, originating from the instantaneous
difference between the true position and on-board
time offset of a Galileo satellite, and the related user
estimates obtained from broadcast OS navigation
message parameters. The estimation error in satellite
position coordinates is projected to the user-satellite
direction, while the estimation error in its clock offset
w.r.t. the Galileo System Time (GST) is converted tounits of length; then, the two contributions are added
together.
In the case of a SF user, an additional contribution
adds up to the SISE, consisting in the offset between
the true bias affecting its code range measurements,
and the estimate provided by the applicable broadcast
BGD parameter.
The SISE is the system contribution to the GNSS error
budgets to the User Equivalent Range Error (UERE),
and contains all effects originating from and/or
controlled by the Galileo system, while user local
effects as well as atmospheric effects and SIS
propagation effects (ionospheric/tropospheric) are notconsidered.
Since the instantaneous SISE depends on the usersatellite direction i.e. on the user position, the Global
Average SISE is defined as the root-mean-square of
the instantaneous SISE across the coverage area of
the Galileo satellite considered. In turn, theconstellation average of the instantaneous SISE isdefined as the root-mean square of the “global
average” as defined above, across the Galileo
constellation at a given time.
The Galileo OS Ranging Accuracy (respectively
Galileo OS Ranging Accuracy over all satellites) isdefined as the 95th and 99.9th percentile of the timeseries of the global average SISE (respectively of theconstellation average SISE). They are only measured
9

The Galileo SIS Ranging Rate Error (SISRE) is the first
derivative of the SISE (excluding discontinuities due tothe navigation message updates). It describes theerror on the rate of the SISE due to the satellite
navigation message ephemeris and clock errors. For
short time intervals, the SISRE is dominated by thestability of the Galileo on-board clocks. The Galileo
SIS Ranging Rate Accuracy at 95% Global Average foreach satellite is therefore derived from the stability ofthe on-board clock for a measurement time interval of
3 seconds.

GALILEO OS ACCURACY:TIME SERVICEThe Galileo OS provides means for users to determine
UTC by estimation of the GST-UTC difference using
the parameters transmitted in the Galileo OS SIS. Thisis done by first estimating the local offset from GST,
and secondly estimating the offset of GST withrespect to UTC applying the GST-to-UTC conversion
provided in the Galileo OS navigation data (see Annex
A [1]). The accuracy in the UTC estimation, which iscalled the Galileo OS UTC Time Determination
Accuracy, depends therefore on both the
instantaneous GST determination error and on theerror in the broadcast GST-UTC conversion
parameters. This second component is defined as theGalileo SIS UTC Time Dissemination Accuracy.
The Galileo OS UTC Time Dissemination Accuracy
performance is characterised by:•

Galileo SIS UTC Time Dissemination Accuracy.

•

Galileo SIS
Accuracy.

UTC

Frequency

Dissemination

As for all performance parameters included in the OS
SDD, the UTC Time Dissemination Accuracy and the
UTC Time Determination Accuracy do not include
effects that are not under the control of the Galileo

The Age of Data is the elapsed time since the generation of the navigation message data.

18

operator, such as user local contributions dependingon the receivers or due to atmospheric effects, whichhave to be accounted for to assess the total
uncertainty in the UTC estimation experienced by theuser. Figure 5 shows the various components of thetotal uncertainty in the estimation of the UTC Time.

Galileo SIS UTC Time
Dissemination Accuracy
Galileo SIS UTC Time Dissemination Accuracy is the
SIS component of the overall user’s UTC Time
Determination, which is driven by the accuracy of thebroadcast GST-UTC parameters.
Galileo SIS UTC Time Dissemination Accuracy isdefined as the 95th percentile of the broadcast GSTUTC conversion parameters error.

Galileo SIS UTC Frequency
Dissemination Accuracy
The Galileo SIS UTC Frequency Dissemination
Accuracy, defined on the basis of the derivative of theGalileo SIS UTC Time Dissemination Accuracy, is the
major contribution to the UTC frequency transfer
accuracy. Galileo SIS UTC Frequency Dissemination
Accuracy is defined as the 95 th percentile of the first
derivative of the broadcast GST-UTC conversion
parameters error, i.e. the normalised frequency offset
relative to UTC.

Galileo OS UTC Time
Determination Accuracy
UTC Time Determination Accuracy is defined as astatistical measure of the UTC Time Determination
error of a GNSS user. The accuracy of the UTC solution
experienced by the user, i.e. the Galileo UTC Time
Determination
Accuracy
dependsontheinstantaneous GST determination error and on theerror in the broadcast GST-UTC conversion
parameters.
The total UTC determination accuracy is obtained as
the root sum square of the GST determination
accuracy and the UTC time dissemination accuracy.

Figure 5. Graphical representation of the various components of the total uncertainty in the estimationof the UTC Time.

GALILEO OS ACCURACY:POSITIONING
Positioning Accuracy is defined as a statisticalmeasure of the positioning error of a GNSS user. The

positioning error consists of the difference between
the true user position vector in GTRF coordinates
and the solution obtained by the receiver. Such error
vector is commonly projected into a local
topocentric coordinate system to obtain horizontal
and vertical errors.

19

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Positioning accuracy depends both on themeasurement accuracy of the range observations
and on the geometry of the visible satellites (as e.g.
characterized by the Position Dilution of Precision).
The measurement accuracy is both impacted byerror sources that are under control of the GNSS
system (e.g. SISE and BGD) and by non-system
contributions to the UERE budget (e.g. residual
ionospheric and tropospheric delay compensation
error, multipath, receiver noise etc.).
The positioning accuracy MPL does not include
effects that are not under the control of the Galileo
system and is computed for both single and dual
frequencies as well as for the average and worst
user location. It is provided as a monthly value.

GALILEO OS AVAILABILITY
In the computation of all the Galileo OS availability
MPLs, both planned and unplanned outages areincluded. Outages comprise the time intervals when
SIS is not broadcast.
The availability performance of the Galileo OS
comprises:

Per-slot availability of OS SIS
Per-Slot Availability of OS SIS is defined as theaverage availability of Healthy SIS at any nominal
slot of the Galileo satellite constellation occupied bynominal satellites10. The Per-Slot Availability isprovided as normalised annual value.

Availability of the Galileo OS
UTC Time Dissemination
Service
The Availability of the Galileo OS UTC Time
Dissemination Service is computed at any user
location as the percentage of time when a user isprovided with a healthy SIS, either single-frequency(E1, E5a, E5b) or dual-frequency (E1/E5a, E1/E5b),
allowing UTC time estimation. The MPL for the
Availability of Galileo OS UTC Time Dissemination
Service is specified for the worst user location within
the service coverage (see section C3 for thedefinition of service coverage). It is provided as amonthly value.

Availability of the Galileo OS
Position Dilution of Precision(PDOP)The Availability of PDOP is computed at any user
location as the percentage of time at least 4 Galileo
satellites are visible, above a minimum elevation of
5 degrees, transmitting healthy SIS and with a
PDOP <= 6. The availability of global PDOP is
specified for the average user location within theservice coverage, i.e. computed as the average over
all user locations11. It is provided as a monthly value.

Availability of the Galileo OS
DF and SF Positioning
Service
The availability of PDOP (section 3.4.3) and the OS
SIS ranging accuracy (section 3.3.1) determine theavailability of Galileo OS DF and SF Positioning
Service. This MPL is provided as a monthly value.
At any user location, the availability of DF and SF
Positioning service for OS is computed as thepercentage of time that the DF and SF horizontal
and vertical positioning error is less than or equal toa specific threshold at 95%, considering only SIS
error contributions and only healthy Galileo SIS. The
MPL for availability of the Galileo positioning service
is specified both for the average user location (AUL)
within the service coverage area, i.e. computed as
the average over all user locations, and for the worst
user location (WUL) within the service coveragearea (see section C3 for the definition of service
coverage).

Availability of the Galileo OS
UTC Time Determination
Service
The Availability of UTC Time Determination service
for OS is computed at any user location as thepercentage of time that the UTC Time
Determination error is less than or equal to a specificthreshold at 95%, considering only SIS error
contributions and only healthy Galileo SIS, for users
at a known location. The MPL for the availability of

The Galileo constellation is currently under deployment. The up-to-date status of the Galileo constellation isavailable through the European GNSS Service Centre (GSC) webpage at https://www.gsc-europa.eu/systemservice-status/constellation-information
11
Expected values for the availability of the Galileo OS PDOP for WUL are provided in Annex D.
1020

Galileo UTC Time Determination Service is specified
for the average user location within the service
coverage (AUL), i.e. computed as the average over
all user locations within the service coverage (seesection C.3. for the definition of service coverage). It
is provided as a monthly value.

GALILEO OS: EXTENDED
OPERATIONS MODE
As mentioned already in section 2.3.2.1, the ranging
accuracy of Galileo OS service depends on theaccuracy of a series of parameters broadcast in the
Galileo Navigation Message, allowing to reconstruct
the orbit path and the on-board clock behaviour inthe forthcoming period. These predictions degrade
over time, constituting the need to continuously
calculate and uplink fresh navigation data to the
Galileo constellation, with an appropriate
frequency. In nominal conditions, the Galileo OS
Service has a 24 hour prediction window for thenavigation parameters broadcast in the Galileo
Navigation Message. For details, please refer toAnnex C.4.
In the exceptional case when these parameters
cannot be refreshed for more than 24 hours, theGalileo Extended Operations Mode provides longterm navigation data via the Galileo Navigation
Message. The mode allows for a SIS with gracefully
decaying ranging accuracy for up to 6 days. The
Galileo Extended Operations Mode is characterisedby the following:•

The transition to and from Extended Operations
Mode is seamless and transparent to the user;•

The Ranging Accuracy gradually degrades withrespect to the nominal operating mode;•

Users will be notified of the operational mode
via SIS and NAGU.

In addition to the above, it is to be noted that usersof receivers not able to exploit the capability
provided by the Extended Operations Mode, will
identify the SIS as Marginal. These receivers will
therefore assume that all errors are unbounded intheir size, as presented in section 2.3.1 for MarginalSIS.
The Extended Operations Mode Ranging Accuracy
is defined as the 95th percentile of the time seriesof the global average SISE. They are only measured
for time periods during which the transmitted SIS isin Extended Operations Mode. The typical value ofthe ranging accuracy for satellites in EOM isprovided in Annex C.4. No MPL is provided in thisversion of the OS SDD.

2.4 USAGEASSUMPTIONS FOR
OPEN SERVICEPERFORMANCEThe MPLs contained in this OS SDD are conditioned
upon certain assumptions regarding the use of the
OS SIS. Those assumptions are as follows.

OS USER RECEIVERS
This OS SDD assumes that the Galileo OS user
receiver complies with the technical requirements
related to the interface between the Space Segment
and Galileo OS receivers as established by the
Galileo OS SIS ICD (Annex A [1]). The use of aiding
sensors or systems is not considered.
For each frequency or pair of frequencies used, it isassumed that the user receiver is capable of tracking
the respective OS SIS (compliant to the SIS ICD(Annex A [1])) from all Galileo nominal satellites, inview above a masking angle of 5 degrees over the
local horizon, and with the receiver operating within
the Galileo Service Volume (as defined in sectionC3.3). The user has unobstructed visibility of the sky
above this mask angle. As detailed in section 2.4.3,
any error source related to the user receiver is notaccounted for in the definition of the MPL. It is also
assumed that the user receiver uses, as described in
section 5.1 of the OS SIS ICD (Annex A [1]), up-todate ephemeris and clock data for all satellites.
More specifically, receivers must retrieve the valuesof navigation parameters relevant to the type ofnavigation solution to be computed from the mostrecent navigation data set broadcast on a Healthy
SIS by the Galileo system after the start of thecurrent receiver operation. The performance
resulting from the usage of any other set ofparameters, including reduced clock and ephemeris
data, is not expected to meet the MPL.
The navigation solution is expected to meet the
MPLs only if receivers do not use navigation
parameters beyond their broadcast period (seeC.4.4 for further details).
User receivers do not need to make use of the SIS
broadcast by auxiliary satellites in order to achieve
the navigation performance presented in the OS

21

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

SDD, however they may use them to achieve better
performance.
It is underlined that Galileo receivers, like mostGNSS
receivers,
canincreasenavigation
performance by implementing fault detection andisolation algorithms, for example by using
algorithms based on the consistency of redundant
pseudorange observations (such as ReceiverAutonomous
Integrity
Monitoring(RAIM)
algorithms).

Usage of parameters
identified by an Issue of
Data
As defined in the OS SIS ICD, (Annex A [1]), thenavigation parameters are disseminated in data
batches, each identified by an Issue of Data (IOD)
value. The identification of each batch by an IOD
value enables:•

the users to distinguish the data in different
batches received from each satellite;•

the user receiver to compute the full batch ofdata even if it misses some pages or starts
receiving the data somewhere during thetransmission.

Two independent IODs are defined for:•the ephemeris, satellite
parameters and SISA;•

the almanac.

clock

correction

To compute position and clock corrections, receivers
must use, for each satellite, IOD-tagged parameters
corresponding to the same IOD Value. Moreover,these parameters must be retrieved from the mostrecent navigation data set broadcast on a Healthy
SIS by the Galileo satellite after the start of thecurrent receiver operation. These are the two
conditions regarding the IOD-tagged parameters
under which the navigation solution is expected tomeet the MPL. The utilisation of parameters
identified by different IOD Values from a single
satellite is not recommended and the resulting
performance is not expected to meet the MPL.
Galileo satellites are not expected to all transmit thesame IOD. For positioning, users can combine SIS
from different satellites with different IOD Values
provided that the navigation parameters derived
from each satellite are tagged by a unique IOD
Value.

12

It is relevant to note that IOD Values are notnecessarily incremented in steps of one and that an
IOD with higher value does not necessarily meanthat it tags more recent data. The only valid
comparison between IOD Values is whether they
are equal or not.
Concerning the parameters not tagged by an IOD,
i.e. the BGD, the ionospheric corrections, the GSTUTC and GST-GPS conversion parameters, the DVS
and the SHS flags, as stated in section 2.4.1,
receivers must retrieve their values (for thoseparameters relevant to the type of navigation
solution to be computed12) from the most recent
navigation data set broadcast on a Healthy SIS by
the Galileo system after the start of the current
receiver operation. This is the condition regarding
the parameters not tagged by an IOD under which
the navigation solution is expected to meet the MPL.
The satellite specific parameters (BGD, DVS, SHS)
have to be obtained separately from each satellite
and for each frequency while system parameters(ionospheric corrections, GST-UTC and GST-GPS
conversion parameters) can be obtained from any
Healthy SIS.

LIMITATIONS ON OS SISSTATUSThis OS SDD assumes that a Galileo receiver will
only use OS SIS whose Status is indicated as
Healthy. This OS SDD explicitly assumes that a
Galileo receiver will not make use of an OS SIS
whose health status is indicated as either Marginalor Unhealthy. Please consider that, as per Table 6,
the special combination SHS=2, DVS=0, SISA=125
indicates that Galileo system enabled the Extended
Operations Mode: in this case, SIS may be utilised(by enabled receivers), but it is only expected tomeet a reduced ranging accuracy.

Priority of broadcast OS SIS
Health Status information
As described in section 2.3.1, for each Galileo OS
signal (E1, E5a, E5b), SHS, DVS and SISA are flags
contained in the navigation data messages andconfigured by Galileo system to allow obtaining the
SIS Status, thus its usability. As detailed in Annex A[1]:•

I/NAV message contains SIS health status flags
applicable for SF E1, E5b, and for DF E1-E5a,
E1-E5b. SISA(E1,E5b) is included in Type 3

As an example, DF users do not need to retrieve ionospheric parameters.

22•

word, SHS and DVS flags are included in theType 5 word;

segment, reaches its full operational capability(FOC).

F/NAV message carries SIS health status flags
applicable for SF E5a and for DF E1-E5a. All
SISA (E1,E5a), SHS and DVS flags are includedin the Type 1 word.

The MPLs included in the current version of the
document have been derived taking into account thecurrent Galileo system deployment status. Future
updates of the MPLs may be considered for
subsequent versions of the OS SDD, as the Galileo
system evolves over time.

These are the flags that should be used on routinely
basis for determining the SIS Status.
Additionally, these flags are also included in thecorresponding almanac messages for indicative
purposes. This allows focusing the search ofsatellites during initial acquisition on satellites witha healthy signal. In cases of conflict, the value in theType 5 words of the I/Nav and the Type 1 words ofthe F/Nav message streams must be used, in linewith section 2.3.1.3.

Information about the current Galileo system statusis available to users through the European GNSS
Service Centre (GSC) webpage (see section 1.6.4).

EXCLUDED ERRORSThe MPLs reported in section 3 of this OS SDD do
not take into account any error source that is notunder direct control of the Galileo system.
Specifically excluded errors comprise those due tothe effects of:•

Signal distortion caused by ionospheric and/or
tropospheric propagation effects.

•

Residual
receivercompensation errors.

ionospheric

delay

•

Residual
receivercompensation errors.

tropospheric

delay

•

Receiver noise (including received signal power
and interference power) and resolution.

•

Receiver hardware/software faults.

•

Multipath and receiver multipath mitigation.

•

User antenna effects.

•

Receiver operator error.

2.5 OPERATIONALCAPABILITYEVOLUTION
The entry into the service provision phase of theGalileo OS took place before the Galileo core
infrastructure is fully deployed. As a consequence,an evolution of the performance is expected as thesystem, including both space segment and ground

23

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

SECTION 3:
GALILEO OS
MINIMUMPERFORMANCELEVELS

24

SECTION 3: GALILEO OS
MINIMUMPERFORMANCELEVELS
3.1 OVERVIEWThis section specifies the Galileo OS performance interms of Minimum Performance Levels (MPLs)
defined for the set of performance parametersdescribed in section 2. In addition, it provides further
specifications about the constellation applicable atthe time of the publication of the document and theservice coverage, and lists the potential conditions
and constraints that are applicable for service
provision.
For all MPLs, all Ages of Data (within the maximum
nominal broadcast period of a healthy navigation
messagedataset)observed
duringthemeasurement time interval are considered.
The navigation solution is expected to meet the OS
MPLs only if the usage assumptions for OS asprovided in section 2.4 and specifically those related
to the OS user receiver in section 2.4.1 are fulfilled.
The Galileo OS MPLs do not include any
contribution that is not under the control of theGalileo system. In particular, tropospheric,ionospheric, and receiver noise contributions orinterference are not included in the specifications(see also section 2.4.3).

3.2 GALILEO OS
CONSTELLATION
DEFINITIONThe Galileo constellation considered as reference inthe preparation of this OS SDD is reported in Table 8
and comprises 22 operational satellites. The
baseline Galileo constellation configuration is
described in section 1.6.1 and in Annex C.
The Galileo constellation is currently under
deployment. The up-to-date status of the Galileo
constellation, including auxiliary satellites, isavailable through the European GNSS Service
Centre (GSC) webpage13. All events related to the
Galileo Space Segment are communicated to users
through the Notice Advisories to Galileo Users(NAGUs) provided by the GSC (see section
1.6.4.1.1).
The correspondence between satellite plane andslot and Space Vehicle identifier (SVID) is also
reported on the GSC webpage.
The availability MPLs presented in this document
only consider nominal satellites as defined in
section 1.6.1, and listed under the section “Nominal
Satellites” in the table “Reference Constellation
Orbital and Technical Parameters” available on the
GSC web site. The possible contribution of any
auxiliary satellites broadcasting healthy SIS is notaccounted for.

13 www.gsc-europa.eu/system-service-status/constellation-information

25

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Table 8. Galileo Constellation Parameters (Ref. Epoch: 2016/11/21 00:00:00) – Reference constellation for this OS SDD.

POSITION

SEMI-MAJOR
AXIS

ECCENTRICITINCLINATIONY

RAAN

ARG. PERIGEEMEANANOMALY

deg

deg

deg

deg

Plane

Slot

km

A

1

29599.801056.0317.6320

180.153A

329599.801056.0317.6320270.153A

429599.801056.0317.6320315.153A

529599.801056.0317.632

0

0.153

A

6

29599.801056.0317.632045.153A

729599.801056.0317.632090.153A

829599.801056.0317.6320135.153B

129599.801056.077.632

0

195.153B

229599.801056.077.6320240.153B

329599.801056.077.6320285.153B

429599.801056.077.6320330.153B

529599.801056.077.632015.153B

629599.801056.077.632060.153B

729599.801056.077.6320105.153B

829599.801056.077.6320150.153C

129599.801056.0

197.6320210.153C

229599.801056.0

197.6320

255.153C

329599.801056.0

197.6320300.153C

429599.801056.0

197.6320345.153C

629599.801056.0

197.632075.153C

729599.801056.0

197.6320120.153C

829599.801056.0

197.6320165.153

Percentiles;

3.3 GALILEO OS
ACCURACY••

Galileo SIS UTC Time Dissemination Accuracy;

This section provides the MPLs of the accuracy of
the Galileo OS. The following MPLs define the OS
performance in accuracy:•

Galileo SIS UTC Frequency Dissemination
Accuracy;•

Galileo OS UTC Time Determination Accuracy.

For ranging services:•

Galileo SIS Ranging Accuracy for any satellite;•

Galileo SIS Ranging Accuracy over all satellites;•

Galileo SIS Ranging Accuracy at higher

Galileo SIS Range Rate Accuracy for any
satellite.

For timing services:

For positioning Service:•

Galileo OS Positioning Accuracy.

The associated MPLs for the availability of services
are defined in section 3.4.

26

GALILEO SIS RANGING
ACCURACY MPL
The Galileo OS SIS Ranging Accuracy MPL for any
satellite as defined in 2.3.2.1, is specified in Table 9.
The Galileo OS SIS Ranging Accuracy MPL over all
satellites as defined in 2.3.2.1, is specified inTable 10.

Table 10. Galileo SIS Ranging Accuracy MPL over all
satellites.

GALILEO SISRANGING
ACCURACY MPLOVER ALLSATELLITESTable 9. Galileo SIS Ranging Accuracy MPL for any
satellite.

GALILEO SISRANGING
ACCURACY MPL
FOR ANYSATELLITE

CONDITIONS AND
CONSTRAINTS• Calculated over a periodof 30 days

For each SF:• ≤ 2m (95%), overall AODs• Calculated over a periodof 30 days

• For any healthy OS SIS

For each SF:• ≤ 7m (95%)
globalaverage, overall AODs

above a minimum
elevation angle of 5
degrees• Including Broadcast

Group Delay errors
when operating in SF• Propagation and user

contributions excluded• Neglecting single

CONDITIONS AND
CONSTRAINTS• 95th percentile of thetime series of
constellation average
Galileo SIS Ranging
Accuracy (computed as
the rms of theinstantaneous global
average SISE)• Calculated over a periodof 30 days
• 95th percentile of the

For each DF
combination:• ≤ 2m (95%), overall AODs

time series of
constellation average
Galileo SIS Ranging
Accuracy (computed as
the rms of theinstantaneous global
average SISE)

frequency ionosphericdelay model errors14• Calculated over a period

For each DF
combination:• ≤ 7m (95%)
globalaverage, overall AODs

of 30 days

• For any healthy OS SIS

above a minimum
elevation angle of 5
degrees• Propagation and user

contributions excluded

14

Note that although parameters for the correction of the ionospheric effect for SF users are broadcast by the
Galileo OS SIS, the single-frequency ionospheric delay model errors are not accounted for in the MPL, just likeany contribution to the MPL due to propagation that is not under control of the Galileo operator. This is valid
throughout the document.

27

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

GALILEO SIS RANGING
ACCURACY AT HIGHERPERCENTILESThe Galileo OS SIS Ranging Accuracy at 99.9th
percentile for any satellite as defined in 2.3.2.1, is
specified in Table 11.
Table 11. Galileo OS Ranging Accuracy performance
calculated at 99.9% percentile (on yearly basis).

GALILEO SISRANGING
ACCURACY AT
99.9th Percentile

CONDITIONS AND
CONSTRAINTSGALILEO SIS RANGE RATE
ACCURACY MPL
The Galileo OS Range Rate Accuracy as defined in
section 2.3.2.2 is provided in Table 12.
Table 12. Galileo OS Range Rate Accuracy performance
MPL.

GALILEO SIS RANGE
RATE
ACCURACY MPL
FOR ANY SATELLITECONDITIONS AND
CONSTRAINTS• Calculated over a

period of 30 days
• For any healthy OS

SIS• Calculated over a periodof 1 year• Over All AOD• For any healthy OS SISFor E1 and E5a SF
SIS :• ≤ 20 m (99.9%),
Worst User
Location• ≤ 10 m (99.9%),
Global Average

above a minimum
elevation angle of 5
degrees• Neglecting

discontinuities due tonavigation message
updates• Propagation and user

frequency ionosphericdelay model errors15• Calculated over a period• ≤ 10 m (99.9%),
Global Averageinterval at any AoD

frequency ionosphericdelay model errors

Group Delay errors when
operating in SF• Neglecting single• ≤ 20 m (99.9%),
Worst User
Location• over any 3 second• Neglecting single-• Including Broadcast

contributions excluded

For E1-E5a DF
combination:

For each SF and DF
combination:● ≤ 0.005 m/s, at any
AODof 1 year• over all AOD• For any healthy OS SIS

above a minimum
elevation angle of 5
degrees

GALILEO SIS UTC TIMEDISSEMINATION
ACCURACY MPL
The Galileo OS SIS UTC Time Dissemination
Accuracy MPL is specified in Table 13.
Table 13. Galileo SIS UTC Time Dissemination Accuracy
MPL.

GALILEO SIS UTCTIMEDISSEMINATION
ACCURACY MPL• Propagation and user

contributions excluded

CONDITIONS AND
CONSTRAINTS• For any healthy OS SIS

For each SF and DF
combination:• < 30ns (95%) overall AODs• At any user location• Calculated over a

period of 30 days
• Propagation and user

contributions excluded.

15

Note that although parameters for the correction of the ionospheric effect for SF users are broadcast by the
Galileo OS SIS, the single-frequency ionospheric delay model errors are not accounted for in the MPL, just likeany contribution to the MPL due to propagation that is not under control of the Galileo operator. This is valid
throughout the document.

28

GALILEO SIS UTC
FREQUENCYDISSEMINATION
ACCURACY MPLThe OS Galileo SIS UTC Frequency Dissemination
Accuracy MPL is specified in Table 14.
Table 14. Galileo SIS UTC Frequency Dissemination
Accuracy MPL.

GALILEO SISUTC FREQUENCYDISSEMINATION
ACCURACY MPL

For each SF and
DF combination:• < 3E-13( 95%)
over all AODs

GALILEO OS POSITIONING
ACCURACY
The OS Galileo OS Positioning Accuracy MPLs are
specified in Table 16 and Table 17.
Table 16. Galileo OS Positioning Accuracy MPL ataverage user location.

GALILEO OS
POSITIONING
ACCURACY AT
AVERAGE USER
LOCATION• Position solution is available

CONDITIONS AND
CONSTRAINTS• Calculated over a period of

30 days• For any healthy OS SIS

For each SF:• At any user location• ≤ 5m (95%)
horizontalerror• ≤ 8m (95%)
vertical error• Calculated over a periodof 30 days

• Propagation and user

GALILEO UTC TIME
DETERMINATION
ACCURACY
The Galileo UTC Time Determination Accuracy MPL
is specified in Table 15.
Table 15. Galileo OS Time Determination Accuracy MPL
at any user location.

CONDITIONS AND
CONSTRAINTS• Propagation and user

contributions excluded

For each DF
combination:• ≤ 5m (95%)
horizontalerror• ≤ 8m (95%)
vertical error• Position solution is available• Calculated over a period of

30 days• Propagation and user

contributions excluded

Table 17. Galileo OS Positioning Accuracy MPL at worst
user location.

GALILEO OS
POSITIONING
ACCURACY AT
WORST USER
LOCATION

CONDITIONS AND
CONSTRAINTS• Position solution is available• At any user location• Calculated over a period of

30 days• For users at a known

location• ≤ 30 ns ( 95%)
over all AODs

Delay errors when operatingin SF

ionospheric delay model
errors• Time solution is available

For each SF and
DF combination:• Including Broadcast Group• Neglecting single frequency

contributions excluded

GALILEO UTC
TIME
DETERMINATION
ACCURACY

CONDITIONS AND
CONSTRAINTS• From any point in theservice coverage Including
Broadcast Group Delayerrors when operating inSF• Propagation and user

contributions excluded• Neglecting single

frequency ionosphericdelay model errors• Calculated over a period of 30

days

For each SF:• ≤ 10m (95%)
horizontalerror• ≤ 16m (95%)
vertical error• Including Broadcast Group

Delay errors when operating
in SF• Propagation and user

contributions excluded• Neglecting single frequency

ionospheric delay model
errorsFor each DF
combination:• Position solution is• ≤ 10m (95%)
horizontalerror• ≤ 16m (95%)
vertical error• Calculated over a period ofavailable
30 days• Propagation and user

contributions excluded

29

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

3.4 GALILEO OS
AVAILABILITY
This section provides the MPLs associated with the
OS availability. The availability MPLs provided inthis section correspond to the current Galileo
deployment configuration status, and includes only
nominal satellites, i.e. it does not include auxiliary
satellites.
The following availability MPLs currently define OSavailability performance:•

Per-Slot Availability.

•

Availability of the Galileo OS UTC Time
Dissemination Service.

•

Availability of the Galileo OS position dilutionof precision (PDOP).

•

Availability of the Galileo OS Positioning
Service.
Availability of the Galileo OS UTC Time
Determination Service.

•

GALILEO PER-SLOT
AVAILABILITYThe OS MPL for the Per-Slot Availability is specified
in Table 18.

MPL OF THE PERSLOT AVAILABILITY
For each DF
combination:• ≥ 92% probability

that a nominal
orbital slot in the
Galileoconstellation16 is
occupied by aGalileo satellite
transmitting thehealthy DF SIS
combination

For each SF:• ≥ 92% probability

that a nominal
orbital slot in the
Galileoconstellation16 is
occupied by aGalileo satellite
transmitting thehealthy SF SIS

16

CONDITIONS AND
CONSTRAINTS• Calculated as anaverage of theavailability of the SF
SIS over all nominal
orbital slots in the
Galileo satellite
constellation16,
normalised annual• Including planned andunplanned outages• Calculated as anaverage of theavailability of the DF
SIS combination over
all nominal orbitalslots in the Galileo
satellite
constellation16,
normalised annually• Including planned andunplanned outages

AVAILABILITY OF THE
GALILEO UTC TIMEDISSEMINATION SERVICEThe OS MPL for the Availability of the Galileo UTCTime Dissemination Service is specified in Table 19.
Table 19. MPL of the Availability of the Galileo OS
UTC Time Dissemination Service.

MPL OF THE
AVAILABILITY OF
THE GALILEO OS
UTC TIME
DISSEMINATIONSERVICE

CONDITIONS AND
CONSTRAINTS• Calculated over a period of

Table 18. MPL of the Per-Slot Availability.

MPL OF THE PERSLOT AVAILABILITY

CONDITIONS AND
CONSTRAINTS

For each SF:• ≥ 95% of time auser is provided
at least one
healthy SF SIS

30 days• Above a minimum elevation

angle of 5 degrees• From any point in the service

coverage• Including planned andunplanned outages
For each DF
combination:• Calculated over a period of

30 days• Above a minimum elevation• ≥ 95% of time auser is provided
at least one
healthy DF SIS
combination

angle of 5 degrees• From any point in the service

coverage• Including planned andunplanned outages

The Galileo Space Segment is currently under deployment. At any time, the Galileo constellation to be taken
as reference is the one published by the GSC (https://www.gsc-europa.eu/system-servicestatus/constellation-information). Since the deployment of the Galileo constellation has not been completed
at the time of publication of this document, constellation maintenance and replenishment during this phasewill be covered by continuation of the satellite deployment plan.

30

AVAILABILITY OF THE
GALILEO POSITIONDILUTION OF PRECISIONThe OS MPL for the Availability of the Galileo
Position Dilution of Precision is specified in Table 20.
Table 20. MPL of the Availability of the Galileo Position
Dilution Of Precision.

MPL OF THE
AVAILABILITY OF
THE POSITIONDILUTION OF
PRECISION

CONDITIONS AND
CONSTRAINTS• With a Position Dilution

For each SF and DF
combination:• ≥ 90% at

average user
locationof Precision less than orequal to 6

• At least 4 satellites inTable 21. MPL of the Availability of the Galileo
Positioning service, at average user location.
MPL OF THE
AVAILABILITY OF THEPOSITIONINGSERVICEaccuracy better than 7.5 m (95%)• With a vertical positioning

accuracy better than 15 m (95%)

of 30 days

• At least 4 satellites in view above• Including planned and

For each SF:• With a Position Dilution• ≥ 90% at• At least 4 satellites in

CONDITIONS AND CONSTRAINTS• With a horizontal positioning• Calculated over a periodof Precision less than orequal to 6

• ≥ 87% at worst
user location

The performance of the OS SIS Ranging Accuracy
over all satellites (section 3.3.1) and of the
Availability of the OS PDOP (section 3.4.3) support
the MPL for the Availability of the Galileo
Positioning Accuracy for OS. This MPL is specified inTable 21, at average user location, and in Table 22, atworst user location.

view above a minimum
elevation angle of 5
degrees

unplanned outages

For each SF and DF
combination:

AVAILABILITY OF THE
GALILEO POSITIONINGSERVICEa minimum elevation of 5 degrees• Calculated over a period of 30

averageuser
locationview above a minimum
elevation angle of 5
degreesdays• Including planned and unplanned

outages• Including Broadcast Group Delayerrors when operating in SF• Propagation and user

contributions excluded• Calculated over a period• Neglecting single frequencyof 30 days

ionospheric delay model errors17• Including planned and• With a horizontal positioning

unplanned outages

accuracy better than 7.5 m (95%)• With a vertical positioning

For each DF:• ≥ 90% at

averageuser
locationaccuracy better than 15 m (95%)• At least 4 satellites in view abovea minimum elevation of 5 degrees• Calculated over a period of 30

days• Including planned and unplanned

outages• Propagation and user

contributions excluded

17

Note that although parameters for the correction of the ionospheric effect for SF users are broadcast by the
Galileo OS SIS, the single frequency ionospheric delay model errors are not accounted for.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Table 22. MPL of the Availability of the Galileo
Positioning service, at worst user location.

MPL OF THE
AVAILABILITY
OF THEPOSITIONINGSERVICE

CONDITIONS AND
CONSTRAINTS• With a horizontal

positioning accuracy better
than 7.5 m (95%)• With a vertical positioning

accuracy better than 15 m
(95%)

• At least 4 satellites in view

For each SF:• ≥ 87% atworst user
locationabove a minimum elevationof 5 degrees

AVAILABILITY OF THE
GALILEO UTC TIME
DETERMINATION SERVICEThe OS MPL for the Availability of the Galileo UTCTime Determination service derives from the MPL
defined for the OS SIS Ranging Accuracy over all
satellites (3.3.1), from the MPL defined for the
Galileo SIS UTC Time Dissemination Accuracy(3.3.4), and from the MPL for the Availability of theGalileo UTC Time Dissemination Service (3.4.2).
These three MPLs result in an MPL for the
Availability of the Galileo UTC Time Determination
service as specified in Table 23, from any point in theservice coverage area.

• Calculated over a period of

30 days• Including planned andunplanned outages• Including Broadcast Group

Delay errors when operating
in SF• Propagation and user

contributions excluded• Neglecting single frequency

ionospheric delay model
errors18• With a horizontal

positioning accuracy better
than 7.5 m (95%)• With a vertical positioning

For each DF:• ≥ 87% atworst user
locationaccuracy better than 15 m
(95%)

• At least 4 satellites in view

above a minimum elevationof 5 degrees• Calculated over a period of

30 days• Including planned andunplanned outages• Propagation and user

contributions excluded

18

Note that although parameters for the correction of the ionospheric effect for SF users are broadcast by the
Galileo OS SIS, the single frequency ionospheric delay model errors are not accounted for.

32

Table 23. MPL of the Availability of the Galileo UTC Time
Determination service, from any point in the service
coverage.

MPL OF THE
AVAILABILITY OF
THE UTC TIME
DETERMINATIONSERVICE

3.5 ADDITIONALFUNCTIONALITY

CONDITIONS AND
CONSTRAINTSGALILEO OS
COMPATIBILITY AND
INTEROPERABILITY WITH
OTHER GNSS

• With UTC Time

Determination accuracy
better than 31 ns (95%)• At least 1 satellite in view

above a minimum elevationof 5 degrees• For users at a known location• From any point in the service

coverage

For each SF:• Calculated over a period of• ≥ 95%• Including planned and

30 days

unplanned outages• Including Broadcast Group

Delay errors when operating
in SF• Propagation and user

contributions excluded• Neglecting single frequency

The Galileo OS is compatible, i.e. operates on no
harmful interference basis, with the other GNSS
services, such as GPS, GLONASS and Beidou
services. One of the main drivers of the Galileo
system design has been its interoperability withother GNSS. In the GNSS context, interoperability
should be understood as the capability for user
equipment to exploit available navigation signals ofdifferent GNSS and to produce a combined solutionthat generally exhibits performance benefits (e.g.
better accuracy, higher availability) with respect tothe standalone system solution.
The design of the Galileo system has addressedinteroperability from different perspectives:•

The Galileo frequency bands have been
allocated in the Radio Navigation Satellite
Services (RNSS) part of the spectrum. The OS
carrier frequencies (in particular E1, and E5a)and their modulation characteristics simplify
the combined use of Galileo with otherconstellations (GPS, GLONASS, and Beidou).

•

The Galileo terrestrial and time reference
systems have been defined and arecontinuously aligned to the corresponding
international terrestrial and time reference
systems, ITRF and UTC, respectively (seesections 1.6.5.1 and 1.6.5.2.

ionospheric delay model
errors19• With UTC Time

Determination accuracy
better than 31 ns (95%)• At least 1 satellite in view

above a minimum elevationof 5 degrees

For each DF:• For users at a known location• From any point in the service• ≥ 95%coverage• Calculated over a period of

30 days• Including planned andunplanned outages

Furthermore, Galileo implements additionalfeatures in order to support an enhanced level ofinteroperability with GPS, as explained in the next
section.

• Propagation and user

contributions excluded

19

Note that although parameters for the correction of the ionospheric effect for SF users are broadcast by the
Galileo OS SIS, the single frequency ionospheric delay model errors are not accounted for.

33

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

Galileo System Time to GPS
Time Offset
Galileo System Time (GST) (see section 1.6.5.2) andGPS time are two independent continuous
timescales steered respectively to UTC(k) andUTC(USNO). Although the coherence of all UTC
realisations inherently provides a high degree ofinteroperability between Galileo and GPS, theactual physical realisations are independent, hence
Galileo and GPS system times are different and thisdifference is variable with time.
This inconsistency between Galileo and GPS timereferences can be solved either by autonomous
calculation in the user equipment or by provision ofsystem time offsets by any of the participating
GNSS.
For autonomous calculation in the user equipment,
an additional unknown parameter is introduced into
the positioning system of equations for the a priori
unknown time difference between the systems. In
solving the set of equations, the time difference isalso inherently resolved. The disadvantage of thisapproach is that at least one additional line-of-sightmeasurement is required for solving the set of
equations. Effectively, at least one available satelliteof the combined visible constellation is dedicated tosolving for the time difference.
The Galileo system provides the “Galileo to GPS
Time Offset” (GGTO) as part of its navigation
message. The MPLs for the GGTO parameter arepresented in section 3.5.1.2.

Galileo OS GST to GPS Time
Offset determination
performance
The accuracy in determination of the GST-GPS timeoffset is defined as the 95th percentile of thedifference between the GST versus GPS time ascomputed using the Galileo navigation message andthe true GGTO, averaged over one day. True GGTO
is the GST-GPS Time offset as observed through the
SIS of the two systems.
The availability of determination of the GST-GPS
time offset is defined as the global average
percentage of time that the GGTO is broadcast on
one or more healthy SIS receivable from a nominal
satellite above a minimum elevation angle of 5
degrees from any point in the service coverage(including both planned and unplanned outages).

The GGTO determination accuracy for the OS is
specified in Table 24. The respective GGTO
determination availability is specified in Table 25.
Table 24. MPL of Galileo GST-GPS Time Offset
Determination Accuracy.

MPL OF GALILEO GSTGPS TIME OFFSET
DETERMINATION
ACCURACY

CONDITIONS AND
CONSTRAINTS

Any OS SIS:

• For any healthy OS• < 20 ns (95%)• Calculated over adifference between
the broadcast GGTO
and the true GGTO,
averaged daily

SIS

period of 30 days

• Propagation and user

contributions
excluded

Table 25. MPL of Galileo GST-GPS Time Offset
Determination Availability.

MPL OF GALILEO
GST-GPS TIMEOFFSET
DETERMINATIONAVAILABILITY

CONDITIONS AND
CONSTRAINTS• Above a minimum

Any SIS OS:• ≥ 95% of time that auser is provided a valid
GGTO on at least one
healthy SIS

elevation angle of 5
degrees• From any point in theservice coverage• Calculated over a periodof 30 days

• including planned andunplanned outages

3.6 GALILEO SUPPORTFOR AVIATION
In order to support the use of Galileo Open Service
for aviation use cases, certain additional
performance parameters are required. MPL’s forseveral of these parameters are provided here: theGalileo User Range Accuracy (URA), the probabilityof constellation fault (Pconst) and the probability of asingle signal in space fault (Psat).

34

GALILEO USER RANGE
ACCURACY
Galileo URA for DF users, σURA,DF (and respectively
for SF user, σURA,SF) is defined as the standard
deviation of a normal distribution which overbounds
the actual distribution of dual frequency(respectively, single frequency) SIS range errors up
to the probability Psat. Galileo σURA,DF is specified inTable 26. Galileo σURA,SF is specified in Table 27.
Galileo σURA,DF applies to any user location and to ahealthy SIS dual-frequency combination E1/E5a,while σURA,SF applies to any user location and to ahealthy SIS single-frequency user (E1 or E5a).
Table 26. Galileo URA for DF users.

GALILEO URA FOR
DUAL FREQUENCY
USERS

CONDITIONS AND
CONSTRAINTS• At any user location

For E1-E5a DF
combination:
σURA,DF ≤ 6 m• Applicable to a healthy
OS DF SIS
combination• Propagation and user
contributions
excluded

Table 27. Galileo URA for SF users.

GALILEO URA FORSINGLE FREQUENCY
USERS

CONDITIONS AND
CONSTRAINTS• At any user location

For E1 and E5a SF SIS:
σURA,SF ≤ 7.5 m• Applicable tohealthyOS SIS• Propagation and user
contributions
excluded

Psat. BGD residual errors are the remaining
errors after applying Galileo BGD corrections
broadcast in the navigation message.

The values presented in Table 27 provide upperbounds of Galileo URA. Galileo plans to provide
dynamic values through the SIS as part of the future
Galileo Integrity Support Message (ISM).

PROBABILITY OF SIS FAULT(Psat)
Psat is the probability that the instantaneous ranging
signal error of a healthy Galileo satellite (excluding
atmospheric and receiver errors) exceeds k times theGalileo user range accuracy (Galileo URA).

Galileo URA in Psat definition corresponds to σURA,DFor to σURA,SF for dual-frequency or single-frequency
users, respectively.
The factor k is the number of standard deviations
from the mean corresponding to a probability of Psat
in a normal distribution. The factor k is 4.17,
corresponding to the maximum Psat value, 3×10-5,
specified in Table 28.

Psat applies at any given time and at any location in

the satellite visibility area to both single frequency
and dual frequency users. This faulty situation could
be caused, for example, by erroneous satellite
navigation data or anomalous satellite payload
events.
Table 28. Galileo probability of Single SIS fault.

GALILEOPROBABILITY
OF SINGLE SIS
FAULT• SISE > k × Galileo URA (factor

k is 4.17 for Psat 3·10–5)• At any location in the

Galileo σURA,SF considers the Galileo σBGD and can bederived from the following expression:
2
2
2
2
𝜎URA,
SF = 𝜎URA, DF + 𝛾𝑓 ∙ 𝜎BGD

where:
𝛾𝑓 represents the frequency inflation factor equal
22
to 𝑓𝐸1/𝑓𝐸5𝑎
for E5a users and to 1 for E1 users;
Galileo σBGD is defined as the standard deviation ofa zero-mean normal distribution which
overbounds the actual distribution of BGD
residual errors such that the probability ofunbounded errors is negligible with respect to

CONDITIONS AND
CONSTRAINTS

respective visibility areas of theaffected satellites
Psat ≤ 3x10–5• Applicable to both OS single

frequency users (E1 and E5a)and dual frequency users (E1E5a combination), starting fromhealthy supporting signals• Propagation and user

contributions excluded

35

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

PROBABILITY OF
CONSTELLATION FAULT(Pconst)Pconst is the probability that the instantaneous
ranging signal error of two or more healthy Galileo
satellites (excluding atmospheric and receiver
errors) exceeds k times the Galileo URA due to acommon failure.

Galileo URA in Pconst definition corresponds to
σURA,DF or to σURA,SF for dual-frequency or singlefrequency users, respectively.
The factor k is 4.17, corresponding to the maximum
Psat value, 3×10-5, specified in Table 28.

Pconst applies at any given time and at any locationin the respective visibility areas of the affectedsatellites to both single-frequency and dualfrequency users. One example of this kind of event
would be the broadcast by multiple satellites ofincorrect navigation data due to a common cause
originating at the GNSS’ ground segment.
The maximum value of the Galileo Pconst is reported
in Table 29.
Table 29. Galileo probability of constellation SIS fault.

GALILEOPROBABILITY OF
CONSTELLATION SIS FAULTCONDITIONS AND
CONSTRAINTS• SISE > k × Galileo URA(factor k being 4.17) for two
or more satellites due to acommon failure.

3.7 PERFORMANCELEVEL FOR THE GNSSSERVICE CENTRE
As described in section 1.6.4, the GSC acts as the
single interface for help and support between the
Galileo OS user community and the Galileo systeminfrastructure and operator. It is responsible, among
other tasks, for reporting on the status of the service
through the dissemination of NAGUs and forproviding helpdesk service to the users.
These two services by the GSC are part of theoverall service provided by Galileo to its users andare subject to MPLs.
The GSC performance is characterised by the Timely
publication of NAGUs.

TIMELY PUBLICATION OF
NAGUS
The Timely publication of NAGUs refers to the timeintervals within which Galileo NAGUs are
published, before any planned event or after any
unplanned event.
The MPL for the Timely publication of NAGUs for
the OS is specified in Table 30 and further clarified in
Annex E.
The description of the structure and content of the
NAGUs is provided in Annex E.

• At any location in thePconst ≤ 2x10-4

respective visibility areas of
the affected satellites

SERVICEAVAILABILITY

PLANNED• Applicable to both OS

single frequency users (E1and E5a) and dual
frequency users (E1/E5a
combination), starting fromhealthy supporting signals

NAGU
GENERALUNPLANNED• Propagation and user

contributions excluded
Figure 6. NAGU types.

36

Table 30. MPL of the Timely publication of NAGUs.

MPL OF THE TIMELYPUBLICATION OF
NAGUS

CONDITIONS AND
CONSTRAINTS

Planned events affecting
the service• ≥ 48 hours before theservice is affected

Unplanned eventsaffecting the service• ≤ 15 hours after the

event affecting theservice is detected

Service availability
events• ≤ 15 hours after the

event affecting theservice is detected

General events to be
notified before theiroccurrence (more details
in Annex E):• ≥ 48 hours before theoccurrence of theevent to which they
refer

General events to be
notified after theiroccurrence (more details
in Annex E):• ≤ 30 hours after theoccurrence of theevent to which theyrefer

• Including GENERAL(NOTICE), GENERAL(LEAP SECOND),
GENERAL (TIMING
PLN_OUTAGE)• All other types of

GENERAL NAGUs,
including also
GENERAL (NOTICE),CANCEL, RESCH and
EXTNS NAGUs

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

38

ANNEX A: REFERENCE DOCUMENTS
This section identifies the documents explicitly referenced in this Open Service - Service Definition Document.

REFERENCE

TITLE

ISSUE

[1]

European GNSS (Galileo) Open Service Signal-In-SpaceInterface Control Document (OS SIS ICD).

The most up-to-date issue.
(Available on the web page of the
GNSS Service Centre)[2]

Ionospheric Correction Algorithm for Galileo Single
Frequency Users.

Issue 1.2, European Union,
September 2016. (Available on
the web page of the GNSS
Service Centre)

39

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

ANNEX B:ABBREVIATIONS
AND ACRONYMS

40

ANNEX B: ABBREVIATIONS AND ACRONYMS
AltBOC

Alternative BOC modulation

IERS

International Earth Rotation and Reference Systems
ServiceAOD

Age of Data

IOD

Issue of Data

AOE

Age of Ephemeris

ITRF

International Terrestrial Reference Frame

ARAIM

Advanced Receiver Autonomous Integrity Monitoring

MPL

Minimum Performance Level

AUL

Average User Location

NAGU

Notice Advisory to Galileo Users

BGD

Broadcast Group Delay

NAPA

No Accuracy Prediction Available

BIPM

International Bureau of Weights and Measures

NDV

Navigation Data Valid

BOC

Binary Offset Carrier modulation

OS

Open Service

CAS

Commercial Authentication Service

PconstProbability of Constellation Fault

CBOC

Composite BOC modulation

PDOP

Position DOP

CED

Clock and Ephemeris Data

PRS

Public Regulated Service

CIRS

Celestial Intermediate Reference System

Psat

Probability of SIS Fault

CRC

Cyclic Redundancy Check

PVT

Position, Time, and Velocity

DF

Dual-Frequency

RAAN

Right Ascension of the Ascending Node

DOP

Dilution Of Precision

RAIM

Receiver Autonomous Integrity Monitoring

DVS

Data Validity Status

RF

Radio Frequency

EGNSS

European GNSSRNSSRadio Navigation Satellite Services

EOM

Extended Operations Mode

SAR

Search And Rescue

EU

European Union

SBAS

Satellite-Based Augmentation System

EUSPA

European Union Agency for the Space Programme

SDD

Service Definition Document

F/NAV

Navigation Message broadcast on Galileo E5a signal

SF

Single-Frequency

FEC

Forward Error Correction

SHS

Signal Health Status

FOC

Full Operational Capability

SIS

Signal In Space

GBAS

Ground-Based Augmentation SystemSISA

SIS Accuracy

GCC

Galileo Control Centre

SISE

SIS Ranging Error

GCS

Ground Control Segment

SV

Space Vehicle

GDOP

Geometric Dilution Of Precision

SVID

Space Vehicle Identifier

GGTO

Galileo-GPS Time Offset

TAIInternational Atomic Time

GLONASS Globalnaya Navigatsionnaya Sputnikovaya Sistema

TDOP

Time Dilution Of Precision

GMS

Ground Mission Segment

TTDOP Time Transfer Dilution Of Precision

GNSS

Global Navigation Satellite System

TTFF

Time to First Fix

GPS

Global Positioning System

TOE

Time of Ephemeris

GRC

Galileo Reference Centre

TE

Time Error

GRSP

Geodetic Reference Service Provider

TSP

Time Service Provider

GSC

European GNSS Service Centre

TTC

Telemetry, Tracking, and Commanding

GSMC

Galileo Security Monitoring Centre

UEE

User Equipment Error

GSS

Galileo Sensor Station

UERE

User Equivalent Range Error

GST

Galileo System Time

ULS

Galileo Uplink Station

GTRF

Galileo Terrestrial Reference Frame

URA

User Ranging Accuracy

HAS

High Accuracy Service

USNO

United States Naval Observatory

HDOP

Horizontal Dilution Of PrecisionUTC

Coordinated Universal Time

I/NAV

Navigation message broadcast on Galileo E5b and E1
signals

VDOP

Vertical Dilution Of Precision

ICD

Interface Control Document

WUL

Worst User Location

WWG

Working Without Guarantee

41

ANNEX C:
OS SIS BACKGROUNDINFORMATION
AND PVT ACCURACYPERFORMANCE DRIVERS

42

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

ANNEX C: OS SISBACKGROUNDINFORMATION AND
PVT ACCURACYPERFORMANCEDRIVERS
C.1. INTRODUCTION
C.1.1 SCOPE
This Annex comprises additional backgroundinformation and details regarding the Galileo OS SIS
performance parameters.

C.1.2 LIMITATIONS
The information in this Annex is provided
exclusively for reference and does not in any way
affect the MPLs presented in section 3 of this OS
SDD.

nominal Medium Earth Orbit satellite slots arearranged in 3 orbital planes, with their ascending
nodes uniformly distributed at intervals of 120
degrees, inclined at 56 degrees with respect to theEquator.
Each orbital plane includes 8 satellite slots
uniformly distributed within the plane, i.e. atintervals of 45 degrees of argument of latitude. The
angular shift between satellites in two adjacentplanes is 15 degrees. Satellites In service in theseslots are referred to as nominal satellites.
The constellation is complemented by auxiliary
satellites that can be repositioned to any given slot
in the same plane depending on maintenance orservice evolution needs.
The reference constellation geometry of the 24- slot
Galileo constellation is defined in Table 1. The
Keplerian parameters are given in Celestial
Intermediate Reference System (CIRS) frame20.
Table 32 shows a snapshot of the reference orbit at

the reference epoch 2016/11/21 00:00:00 UTC. The
reference RAAN, argument of perigee and Mean
Anomaly are dynamic parameters, while the others
are static. To calculate values for other epochs,
users are advised to use a linear extrapolation for
the RAAN, argument of perigee and the Mean
Anomaly with the temporal rates shown in Table 31.
Table 31. Galileo Constellation Reference TechnicalParameters.

REFERENCE
PARAMETER RATES

SLOTS

C.2.1 RELATIONSHIP WITH SECTION
3.2

𝑑 𝑅𝐴𝐴𝑁𝑑𝑡-0.02764398 deg/day

Section 3.2 of this document provides the Galileo
constellation operational configuration at the timeof the publication of this document. In the next
section, information is provided on the baseline
Galileo constellation expected at FOC.

𝑑 𝐴𝑟𝑔. 𝑝𝑒𝑟𝑖𝑔𝑒𝑒
𝑑𝑡0.00000000 deg/day

𝑑 𝑀𝑒𝑎𝑛 𝑎𝑛𝑜𝑚𝑎𝑙𝑦
𝑑𝑡

613.72253566 deg/day

C.2. CONSTELLATION

C.2.2 BASELINE 24-SLOT
CONSTELLATIONCONFIGURATIONThe baseline Galileo constellation configuration isdefined as a 24/3/1 Walker constellation: 24
20

The CIRS is a geocentric coordinate system based on the current position of the Celestial Intermediate Pole. In this system,
the right ascension is calculated along the Celestial Intermediate Equator from the Celestial Intermediate Origin, a point close
to the vernal equinox. The exact definition can be found in the Nomenclature for Fundamental Astronomy Glossary edited by
the International Astronomical Union.

43

Table 32. Galileo Constellation at FOC. Reference Geometry at 2016/11/21 00:00:00 UTC.

POSITION

SEMI-MAJOR
AXIS

RAAN

ARGUMENT
OF PERIGEEMEANANOMALY

deg

deg

deg

deg

ECCENTRICITY INCLINATION

Plane

Slot

Km

A

1

29599.801

056

317.6320

180.153A

229599.801

056

317.6320225.153A

329599.801

056

317.6320270.153A

429599.801

056

317.6320315.153A

529599.801

056

317.632

0

0.153

A

6

29599.801

056

317.632045.153A

729599.801

056

317.632090.153A

829599.801

056

317.6320135.153B

129599.801

05677.632

0

195.153B

229599.801

05677.6320240.153B

329599.801

05677.6320285.153B

429599.801

05677.6320330.153B

529599.801

05677.632015.153B

629599.801

05677.632060.153B

729599.801

05677.6320105.153B

829599.801

0

56

77632

0

150.153C

129599.801

056

197.6320210.153C

229599.801

056

197.6320

255.153C

329599.801

056

197.6320300.153C

429599.801

056

197.6320345.153C

529599.801

056

197.632030.153C

629599.801

056

197.632075.153C

729599.801

056

197.6320120.153C

829599.801

056

197.6320165.153

44

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

C.3. SERVICE COVERAGE

C.4. ACCURACY

C.3.1 RELATIONSHIP WITH SECTION
3.2

C.4.1 RELATIONSHIP WITH SECTION
3.3

This section of the Annex provides further information
regarding the service coverage, particularly withrespect to the coverage from each Galileo satellite.

To complement the information provided in section
3.3 of the document, this part of Annex C provides
further details about several aspects concerning thedefinition of the SISE accuracy and its behaviour intime. In addition, insight is provided about how toestimate the error in position and time experienced by
Galileo users, through the definition of the User
Equivalent Range Error and of the Position Dilution Of
Precision.

C.3.2 PER-SATELLITE COVERAGE
C.3.2.1. MASKING ANGLESThe Galileo OS SIS ICD (Annex A [1]) defines theminimum power levels of Galileo signals above a 5
degree elevation angle. However, this definition does
not recommend or impose any specific minimum user
masking angle.
The Galileo user masking angle is a function of various
factors: the SIS ICD defined minimum user-received
power levels, the specific signals tracked, the Galileo
user receiver antenna gain patterns for eachfrequency, the receiver front-end sensitivity at eachfrequency, and the particular usage objective, as wellas other signal environment and user receiver related
factors.
For the scope of the assessments in this SDD a typicalminimum user elevation angle of 5 degrees has beenused. Other user needs might mandate different
minimum elevation angles.

C.3.2.2. SATELLITE FOOTPRINT
The footprint of a satellite is defined as the fraction of
the surface of the Earth that is illuminated by signals
from that particular satellite. The footprint of eachsatellite occupying a slot in the baseline 24-slot
constellation covers under purely geometrical aspects
approximately 39% of the Earth's surface at 0 degrees
minimum user elevation angle. However, the footprintarea is reduced by the consideration of user elevation
masking angle. With a 5-degree user masking angle,
the satellite's footprint is reduced to roughly one-thirdof the Earth's surface (35%).

C.3.3 SERVICE VOLUME
The terrestrial service volume defines the region on
and around Earth in which the Galileo services areprovided. The terrestrial service volume is defined as
the region extending from the surface of the Earth up
to an altitude of 30.48 km above the surface of the
Earth.

C.4.2 DEFINITION OF SIGNAL-INSPACE RANGING ERRORThe Signal in Space Ranging Error (SISE) is defined as
the difference of the satellite position and time as
broadcast by the navigation message and the true
satellite position and time, projected on the usersatellite direction. The SISE incorporates Galileo
system contribution to the User Equivalent Range
Error (UERE). Its statistics constitute the Ranging
Accuracy MPLs. The following section illustrates the
SISE performance metrics used for the Galileo system
performance verification.

C.4.3 INSTANTANEOUS SISEPERFORMANCE METRICS
The instantaneous SISE is computed as the difference
between the predicted satellite position and time,
based on the broadcast navigation message, with aposteriori precise clock and orbit estimations.
The SISE inside the satellite footprint is typicallycharacterised either as a Global Average or as the
SISE at the Worst User Location (WUL).
The Global Average SISE can be determined in twoways, numerically on a grid or analytically.

C.4.3.1. NUMERICAL DERIVATIONThe Global Average SISE can be evaluated bycomputing the instantaneous SISE at grid points
evenly distributed over the satellite service area.
The global average can be computed as the RMS of
the instantaneous SISE values at all grid points in thevisibility footprint of the satellite at each time step.
The number of grid points in the satellite footprint is45

typically a few hundreds to thousand points. To
compute statistics of the Global Average SISE atypical time interval between step is of the order of 5
minutes.

Location, typically occurs at the edge of the visibility
cone, as shown in Figure 7.

The maximum error, i.e. the SISE at the Worst User
Prediction error projected onto the line of sight for each user
location on the grid map

Figure 7. SISE projection onto the line of sight for each user location.

C.4.3.2. ANALYTICAL DERIVATION
The instantaneous global average SISE value can bederived analytically from the Galileo satellite'salong-track (A), cross-track (C) and radial (R) orbit
error components and its total SIS clock prediction
error (CLK) by means of the following
approximation formula21:

Eq. (1)𝑆𝐼𝑆𝐸𝐺𝑙𝑜𝑏𝑎𝑙𝐴𝑣𝑒𝑟𝑎𝑔𝑒 (𝑡) = √0.96910 ∙ 𝑅(𝑡)2 + 𝐶𝐿𝐾(𝑡)2 + 0.01545 ∙ (𝐴(𝑡)2 + 𝐶(𝑡)2 ) + 1.96881 ∙ 𝐶𝐿𝐾(𝑡) ∙ 𝑅(𝑡)The following convention has been considered forclock and orbit components:•

All errors are computed as the broadcast value
minus the precise reference value.

•

Radial direction: from the satellite towards the
Earth centre.

•

Cross direction: direction perpendicular to theorbital plane aligned with the cross product of21

the radius and velocity.
•

Along direction: perpendicular to the radius in
the orbital plane, positive in the same semi-planeof the velocity.

The coefficients provided in Eq. (1) are valid when an elevation masking angle of 5 degrees is applied by the
Galileo receivers.

46

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

C.4.4 TIME DEPENDENCY
C.4.4.1. SISE EVOLUTION WITH UPLOADSAS A FUNCTION OF TIMEThe Galileo system uploads 8 batches of navigation
data at a time (see the Galileo OS SIS ICD (Annex A[1]) for more details).
These 8 batches share the same generation time (i.e.,
propagation start time) and cover consecutive
applicability intervals with a 3h offset in the time ofephemeris (toe). Each batch spans a period of 4 hours,
and each of the first 7 batches stored onboard istransmitted over a period of 3 hours, before switching
to the next batch (unless refreshed by a subsequent
upload).
Dissemination of the navigation message is acompromise between upload frequency andnavigation data accuracy. A high upload frequency
ensures a low age of data (better orbit and clock
prediction accuracy) but also requires more frequent
decoding of the message by users. The navigation
dataset upload frequency is a parameter defined by
the operator and as such can be changed according
to operational needs, while maintaining the service
performance according to the MPLs.
The Age of Ephemeris (AOE) is the time elapsed
between the reference Toe (set at the beginning of

22each batch) and the time of usage of the ephemeris
by a receiver. The age of ephemeris can be checkedby the users22.
The Age of Data (AOD) is the elapsed time between
the generation of a navigation message by the
Ground Segment and its usage at user level. Aging of
the data (characterised by AOD) impacts the accuracyof the orbit and clock models. The accuracy of theirprediction inevitably degrades with higher ages.
Considering the 8 batches sequencing logic
described before, the maximum possible AOD of
healthy SIS is 25 hours.
Figure 8 illustrates the SISE evolution as a function of
the age of ephemeris and typical and maximum ageof data service envelops.

The typical service envelope is given by the lower
bound illustrated in Figure 8. For operations beyond
the typical Age of Data, the message error could
grow within the area defined as maximum. The
system targets operations in the typical service
envelope.23
As explained before, a given dataset of navigation
parameters is not expected to be broadcast for morethan 3 hours. Ranging accuracy decreases more
quickly after an age of ephemeris of 3 hours (seeFigure 8). No use should be made of navigation data
beyond their expiration at AOE=4 hours.

The following procedure can be used to estimate the age of ephemeris as prediction time from the referenceTime of Ephemeris (t-toe). Applying this algorithm, users are able to compare the age of the navigation
parameters they have available with the maximum nominal broadcast period of a healthy navigation message
data set. The Age of Ephemeris tk is defined as follows (see also Annex A [1]):tk = t - toe
wheret is the time of usage of the navigation message by the receiver in GST time [s] based on the broadcast
Time Of Week (TOW), defined as the number of seconds that have occurred since the transition fromthe previous week, ranging from 0 to 604799 seconds and reset to zero at the end of each week (00:00
Sunday).
toe is the Time of Ephemeris in GST time [s] (as for t ranging from 0 to 604799 seconds), as broadcast by
the navigation message.

If a receiver wishes to check whether the age of ephemeris of a certain set of navigation data is within a certain
time interval VT it will have to evaluate the following inequality:
0 ≤ tk ≤ VT
Note that, as explained in Annex A [1], note to Table 58, tk is the actual total time difference between the
broadcast GST and the Time of Ephemeris accounting for the possible beginning or end of week crossover. To
take this into account, if tk is greater than 302400 second, 604800 seconds must be subtracted from tk. If t k isless than -302400 seconds, 604800 seconds must be added to tk.
This approach is also valid to estimate the age of almanacs, replacing the t0e with t0a.
23
For information, during year 2020, Galileo operated in the typical service envelope. For 99% of the time.

47

Figure 8. Typical SISE vs. Prediction Time from ToE (all batches). For illustration only - Performance will gradually improveover time toward the full system deployment.

Figure 9. Typical SISE vs. Prediction Time during Extended Operations Mode. For illustration only.

As specified in section 2.4.1 the Galileo OS MPLs
are expected to be met only if the navigation
solution is computed by a receiver employing
Healthy SIS and using the navigation parameters
retrieved from the most recent navigation data set
broadcast by the Galileo system after the start of thecurrent receiver operation. The utilisation by areceiver of navigation parameters stored during
previous receiver operations implies that thenavigation performance that can be achieved is notexpected to meet the MPL. Furthermore, given theway the DVS and SHS flags can be triggered, anavigation data set within the maximum nominal
broadcast period of a healthy navigation message
data set but not retrieved from the currently
broadcast SIS might lead to the use of non-Healthy
signals: the use of an old navigation data set stored
in the memory of the receiver instead of the mostrecent data set transmitted by Galileo is at the user's
own risk.
Concerning the GST-UTC conversion parameters, inthe current system configuration they are updated
daily (although this may change in future

48

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

configurations). With respect to the almanacs, theirrefresh rate is the same as for the navigation data.

Under this assumption, the resulting UERE is thestandard deviation of the pseudorange error
distribution:

C.4.4.2. SISE EVOLUTION IN EXTENDED
OPERATIONS MODE
As mentioned in section 2.3.6, in the exceptionalcase when the Galileo orbit and clock parameters
cannot be refreshed for more than 24 hours, theGalileo Extended Operations Mode can provide longterm navigation data via the Galileo Navigation
Message. This mode allows for a SIS with gracefully
decaying ranging accuracy for up to 6 additionaldays.
The typical service envelope of the Extended
Operation Mode is dependent on several factors,
including clock type, but it is characterised by agraceful degradation of the SIS Ranging Accuracy.
Figure 9 illustrates this degradation of the SISE as afunction of time up to the maximum period of the
Extended Operation mode.

C.4.5 UERE BUDGETThe User Equivalent Ranging Error (UERE)
quantifies the distribution that describes thepseudorange errors of a specific set of user receivermeasurements. The UERE includes the following
contributions:••

Signal-In-Space Range Error (SISE). The
Signal- In-Space Range Error is the satellite-touser range error due to satellite signal
generation and navigation message clock andephemeris errors, which is a function of timeand user location within the satellite coverage
area.
User Equipment Error (UEE). The User
Equipment Error is the satellite-to-user range
error due to all residual error contributions in
the range domain that are not under the directcontrol of the GNSS system.

The UERE breakdown into SISE and UEE
distributions is important in order to differentiate
between the contributions under control of thesystem and those arising from factors not controlled
by the Galileo system, and to compare their relative
effect on the overall pseudorange Error.
The true characteristics of SISE and UEE
distributions are not necessarily Gaussian. However,both SISE and UEE can be considered sufficiently
close to unbiased, uncorrelated Gaussian
distributions, and hence SISE and UEE are
expressed by means of their standard deviations.

𝑈𝐸𝑅𝐸 = √𝑆𝐼𝑆𝐸 2 + 𝑈𝐸𝐸 2

Eq. (2)C.4.5.1. TYPICAL UERE BUDGETS
Table 33 and Table 34 show typical UERE budgets innominal operations for single frequency ruralpedestrian and dual frequency rural vehicle users,
respectively. (Note that these two typical error
budgets are based on different environmental
assumptions and dynamics that explain the
differences in the receiver dependent values).
These UERE budgets are shown for illustration
purpose only, in particular for those contributions
related to the receiver.
Table 33. Typical UERE budget for Single Frequency E1 –Rural Pedestrian (RP) User Environment (**).

ERROR SOURCE[METERS]

Signal in Space Ranging Error(SISE) (*)

0.67

Residual ionospheric error

6 (5°)–3 (90°)

Residual Tropospheric error

1.35 (5°)–0.14 (90°)

Thermal noise, Interference,
Multipath

0.69 (5°)–0.63 (90°)

Satellite BGD error

0.30

Code-Carrier ionospheric
divergence error

0.30

Total (1σ error)

6.24 (5°)–3.17 (90°)

Table 34. Typical UERE budget for Dual Frequency
E1/E5a –Rural Vehicle (RV) User Environment (**).

ERROR SOURCE[METERS]

Signal In Space Ranging Error(SISE) (*)

0.67

Residual Ionospheric error

0.08 (5°)–0.03 (90°)

Residual Tropospheric error

1.35 (5°)–0.14 (90°)

Thermal noise, Interference,
Multipath

0.50 (5°)–0.23 (90°)

Satellite BGD error

0.0

Code-Carrier Ionospheric
divergence error

0.0

Total (1σ error)

1.59 (5°)–0.72 (90°)(*) The values of the Galileo SISE, for each satellite49and for the constellation are reported in the Open
Service Quarterly Performance Reports, publishedquarterly and made available for download from the
GSC website.
(**) Typical range of elevation-dependent error
sources are provided.

C.4.5.2. DEFINITION OF DILUTION OF
PRECISION
The relative user-tracked transmitter geometry at agiven point in time defines the mapping functionthat relates the UERE to a PVT error distribution.
The parameter that provides the relation between
the error contributions in the range domain and in
the position and time domains is called the “Dilution
Of Precision” (DOP).
Denote as
𝑥 𝑖 , 𝑦 𝑖 , 𝑧 𝑖 the ECEF Cartesian
coordinates of the i-th satellite in view of the user,and 𝑥𝑢 , 𝑦𝑢 , 𝑧𝑢 its guessed position, to be
iteratively refined by solving navigation equations.
Let r be the relative geometric distance between theestimated user position and satellite one. Let us
further define:coordinates and time and, in particular, behave as
amplification factors.
Assuming that all ranging measurement errors are
Gaussian, zero mean and characterised by thestandard deviation 𝜎𝑈𝐸𝑅𝐸 , it is easy to demonstratethat the 3D positioning error would have a standard
deviation 𝜎𝑁𝑆𝐸 equal to:

Eq. (5)𝜎𝑁𝑆𝐸 = 𝑃𝐷𝑂𝑃 ⋅ 𝜎𝑈𝐸𝑅𝐸

where:𝑃𝐷𝑂𝑃 = √𝐷(1,1) + 𝐷(2,2) + 𝐷(3,3)

is known as “Position Dilution Of Precision” (PDOP)
factor.
Similarly, the error in the determination of 𝑐 ⋅ 𝑑𝑇, 𝑑𝑇
being the time offset of receiver clock w.r.t. Galileo
System Time, would have a standard deviation 𝜎𝑐⋅𝑑𝑇
given by:Eq. (7)𝜎𝑐⋅𝑑𝑇 = 𝑇𝐷𝑂𝑃 ⋅ 𝜎𝑈𝐸𝑅𝐸

with:

Eq. (8)𝑇𝐷𝑂𝑃 = √𝐷(4,4)
𝑤 (𝑖) −𝑤𝑢

(𝑖)

𝑎𝑤 =

𝑟

, w = x, y, z , 𝑖 =

1,2, … , 𝑚,

the components of unit vectors from the position of
the receiver to satellite i.
The following “design matrix” contains thecoefficients of the linear system of equations whichis to be solved by user:

𝐻=

𝑎(1)
𝑥

𝑎(1)
𝑦

𝑎(1)
𝑧

1

𝑎(2)
𝑥

𝑎(2)
𝑦

𝑎(2)
𝑧

1

𝑎(3)
𝑥

𝑎(3)
𝑦

𝑎(3)
𝑧

(𝑚)

𝑎(𝑚)
𝑎(𝑚)
𝑦
𝑧

⋯

[𝑎𝑥

⋯

⋯

1
⋯
1]

,

𝑫 = (𝑯𝑇 𝑯)−1

named “Time Dilution Of Precision” (TDOP) factor.
Given that there is a specific interest in themagnitude of positioning errors projected in local
topocentric coordinates, which means respectively
horizontal (HPE) and vertical (VPE) positioning error
components at user location, it is worth to introduce
the coordinate transform matrix:−S𝜆−C𝜆 ∙ S𝜑𝑺=[C𝜆 ∙ C𝜑0

C𝜆−S𝜆 ∙ S𝜑S𝜆 ∙ C𝜑
0

0
C𝜑
S𝜑
0

0
0
]
0
1

Eq. (9)where:

Eq. (3)S𝜆 = sin(𝜆) , C𝜆 = cos(𝜆)S𝜑 = sin(𝜑) , C𝜑 = cos(𝜑)The solution by least-squares implies to obtain thepseudo-inverse of 𝑯:
𝑫 ⋅ 𝑯𝑇Eq. (6)

Eq. (4)

Diagonal elements of matrix 𝑫 provide an indicationof how the ranging measurement errors areconverted into errors in the computation of user

𝜆 , 𝜑 being user geodetic coordinates (longitude andlatitude).
Let us define:̃ = 𝑺 ⋅ 𝑫 ⋅ 𝑺𝑇
𝑫

Eq. (10)so that:

𝜎𝐻𝑃𝐸 = 𝐻𝐷𝑂𝑃 ⋅ 𝜎𝑈𝐸𝑅𝐸

Eq. (11)𝜎𝑉𝑃𝐸 = 𝑉𝐷𝑂𝑃 ⋅ 𝜎𝑈𝐸𝑅𝐸

Eq. (12)50

GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

where:

̃ (1,1) + 𝐷
̃ (2,2)𝐻𝐷𝑂𝑃 = √𝐷̃ (3,3)𝑉𝐷𝑂𝑃 = √𝐷equationEq. (13)
Eq. (14)are respectively the Horizontal Dilution Of Precision(HDOP) and Vertical Dilution Of Precision (VDOP)
factors.
Note that 𝑺 is orthogonal and normal, so that:

𝑃𝐷𝑂𝑃 = √𝐻𝐷𝑂𝑃2 + 𝑉𝐷𝑂𝑃 2

Eq. (15)

It is also possible to consider an overall Geometric
Dilution Of Precision (GDOP) factor provided by:

𝐺𝐷𝑂𝑃 = √𝑃𝐷𝑂𝑃2 + 𝑇𝐷𝑂𝑃 2

Eq. (16)

In the special case of users interested in thedetermination of time, having “a priori knowledge”
of their coordinates, the solution of Navigation
equations foresees a single unknown, which is 𝑐 ⋅𝑑𝑇, so that an additional factor needs be considered,named Time Transfer DOP (TTDOP):
𝜎𝑐⋅𝑑𝑇 = 𝑇𝑇𝐷𝑂𝑃 ⋅ 𝜎𝑈𝐸𝑅𝐸

Eq. (17)𝑇𝑇𝐷𝑂𝑃 = √1⁄𝑛𝑆𝑉

Eq. (18)

Because the DOP depends exclusively on therelative geometry between user equipment and thetracked satellites, it is completely deterministic andpredictable under certain assumptions, namely:••

Knowledge of the approximate user andtransmitter locations at the desired time in the
future.
The user's sky visibility conditions or masking
angle above the horizon.

C.4.6 USER TOTAL UNCERTAINTY IN
UTC TIME ESTIMATION
Table 23 shows the Availability of the Galileo UTCTime Determination Accuracy, i.e., the system only
component to the overall uncertainty in the UTC
time estimation performed by users.
As introduced in section 2.3.3.1, non-system
contributions should also be considered in theestimation of the overall user UTC time transfer
accuracy. This can be achieved using the following

𝑈𝑈𝑇𝐶𝐸 = √(𝑈𝐸𝑅𝐸∙𝑇(𝑇)𝐷𝑂𝑃 2𝑐

Eq.

) + 𝑈𝑇𝐶𝐷𝐸 2(19)where:•

UUTCE = User UTC SIS Error (rms)•

T(T)DOP = Time (Transfer) Dilution ofPrecision• UTCDE = UTC SIS dissemination error(system only contribution).

C.4.7 IONOSPHERIC DELAY MODELFOR GALILEO SINGLEFREQUENCY USERS
The ionospheric delay model for Galileo singlefrequency users is the NeQuick model described in(Annex A [2]). The Galileo navigation message
includes several parameters that are used byreceivers implementing the NeQuick model tocompute the ionospheric effect in order to be able toapply the corresponding corrections.

C.4.8 SINGLE-FREQUENCY GROUPDELAY TIME CORRECTIONERRORSA single-frequency user receiver must apply the
Broadcast Group Delay (BGD) corrections to the SV
clock following the equations described in the
Galileo OS SIS ICD (Annex A [1]). Errors in the BGDvalues affect the SISE experienced by the singlefrequency users.
As an example, the UERE budget illustrated for the
single-frequency E1 - Rural Pedestrian (RP) in
Table 36 also includes a typical BGD error
contribution.

C.5. INTEGRITY
The characterisation of Galileo service in terms ofintegrity is an on-going activity. This section will be
developed in future issues of the document.

C.6. CONTINUITY
The characterisation of Galileo service in terms ofcontinuity is an on-going activity. This section will
be developed in future issues of the document.

51

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

ANNEX D: GALILEO OSPERFORMANCEEVOLUTION AND
ADDITIONALPERFORMANCEPARAMETERS
D.1. INTRODUCTION
D.1.1 SCOPE
The main body of this Galileo OS SDD focuses on the
MPLs provided by the Galileo OS at the time of
publication. This annex provides complementary
information about the expected performance levels
and their evolution during deployment of the system
and until its completion at FOC as well as the typicalvalues of additional performance parameters. The
expected values of each performance parameter areprovided in this Annex as a function of the number ofoperational satellites in the Galileo baseline
constellation. The values of the performanceparameters reported in this Annex for the reference
constellation described in Section 3.2 are typical
expected values.

D.1.2 LIMITATIONS
The information in this Annex is provided exclusively
for reference and does not in any way affect the MPLs
presented in section 3 of this OS SDD.

D.1.3 GALILEO CONSTELLATIONEXPECTED EVOLUTIONIn Table 8, the status of the Galileo constellationconsidered as reference in the preparation of this OS
SDD is provided. The evolution of the expectedvalues of the performance parameters presented in
the following sections assumes two deployment
stages with respectively 22 and 24 operational
satellites. Details of the final constellation of 24
satellites can be found in section C.2.

D.2 GALILEO SIS RANGING
ACCURACY: EVOLUTION OF
EXPECTED SISE
As explained in section 2.3.2.1, the Galileo OS
Ranging Accuracy is defined as a statistic of theGalileo SIS Ranging Error (SISE), which is the SIS
portion of the GNSS error budgets to the user
equivalent range error (UERE) and comprises all
effects originating from and/or controlled by the
Galileo system while user local effects andatmospheric effects (ionospheric/tropospheric) are
not included. The Galileo SISE is driven by the errorof the broadcast ephemeris and clock correction
parameters. The accuracy in the estimation of thesevalues depends mainly on the number ofobservables, i.e. ranging measures, available to thealgorithms implemented in the Ground Segment thatcomputes such values. For this reason, the increaseof the number of operational satellites in a GNSS
constellation implies an improvement of thedetermination of the broadcast ephemeris and clock
correction parameters and therefore of the SIS
ranging accuracy until a certain number ofoperational satellites is reached. Further satellites
will result in an increased availability of the services
provided, but not in a further improvement of theranging accuracy of individual satellites.
The Galileo constellation has already reached thissituation, with an expected typical ranging accuracy
below 1 metre, for any service (see also Figure 8).

D.3 EVOLUTION OF THE
EXPECTED AVAILABILITY OF
GLOBAL PDOP
In this section, values are provided for the evolutionof the expected Availability of Global PDOP, as afunction of the number of operational healthysatellites (see Table 35). The Availability of PDOP iscomputed at any user location as the percentage oftime at least 4 Galileo satellites, transmitting healthy
SIS, are in view above a minimum elevation angle of
5 degrees, and with a threshold of PDOP ≤ 6 to
identify sufficiently good local geometries. The
Availability of Global PDOP is specified for the
average user location (AUL) within the service
coverage, i.e. computed as the average over all user
locations (see section C3.3 for the definition ofservice coverage) and for the worst user location(WUL).

53

Table 35. Evolution of the Expected Availability of Global
PDOP.

NUMBER OF SATELLITESPDOP ≤ 6
24
AUL

Table 36. Evolution of the Expected Galileo OS Positioning
Performance in nominal configuration (in metres, 95%
values).

Spatialstatistics

DF

99.78%
AUL

WUL

SF

99.78%

D.4. EVOLUTION OF THE
EXPECTED GALILEO OS
POSITIONINGPERFORMANCEThis section of Annex D presents how the expected
positioning performance of the Galileo OS will evolvewith the deployment of the system until the FOC isreached.

D.4.1 EVOLUTION OF THE GALILEO
OS POSITIONING EXPECTED
ACCURACY
As explained in Annex C, the Galileo system, thesignal propagation channel and the user equipment
all contribute to the positioning accuracy experienced
by the Galileo users. Although in the main part of thisdocument all contributions to the performance ofGalileo that are not under control of the system are
not considered, in this Annex such contributions are
considered so that it is possible to indicate the global
average positioning performance and WUL
performance that a Galileo only user can expect toexperience. Specifically, Table 37 presents theevolution of the horizontal and vertical expected
position accuracy for the Galileo OS Positioning
versus the number of operational healthy satellites,
using the UERE values shown in Table 33 andTable 34. The values provided, which take into
account the constraint of geometrical PDOP≤6,
represent accuracy users would expect if they would
measure their position over one complete
constellation repeat cycle, from the worst user
location and from the average user location.

NUMBER OF
SATELLITESSERVICE

DF
WUL
SF

22

24

H

1.8

1.5

V

2.9

2.6

H

8.7

7.6

V

14.0

12.8

H

1.9

1.7

V

3.3

3.0

H

9.5

8.2

V

16.2

15.0

D.4.2 EVOLUTION OF THE GALILEO
OS POSITIONING EXPECTEDAVAILABILITY
Full deployment of the Galileo system will also imply
an increase of the OS Positioning Service Availability.
The Availability of DF and SF Positioning for OS iscomputed at any user location as the percentage oftime with a DF and respectively SF positioning error
less than or equal to a specific value, considering only
healthy Galileo SIS from satellites above a minimum
elevation angle of 5 degrees. The Availability of DF
and SF Positioning are provided as monthly values.
Table 37 presents the typical Availability of DF and
SF Positioning for OS and its expected evolution
versus the number of operational healthy satellites.
The values provided are global average values (i.e.
computed as the average over all user locations, seesection C3.3 for the definition of service coverage).
Table 37. Typical Galileo OS Positioning Service
Availability (global average) and expected evolution.

NUMBER OF
SATELLITESSERVICEMode

Horizontal
Accuracy(95%)

VerticalAccuracy
(95%)

22

24

DF

≤ 4m

≤ 8m

95%

99.5%

SF

≤ 15m

≤ 35m

94%

99.5%

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

D.5. ADDITONAL PERFORMANCEPARAMETERS
This section of Annex D presents additional
performance parameters to those described in themain body of the document. The aim is to provide afurther insight in the performance of the Galileo
service, beyond the parameters for which the MPLs
apply.
These parameters, therefore, are provided
exclusively for reference and their values do notconstitute any MPL expected to be met by any
service.
For the characterisation of the expected performanceof these parameters, only nominal satellites are
considered. This expected performance applies toany Healthy SIS broadcast by any Galileo satellite in
nominal or auxiliary slots.

D.5.1 EXPECTED SIS RANGING
ACCURACY IN EXTENDED
OPERATIONS MODE
The Extended Operations Mode is a Galileo
operational mode that is activated in case thenavigation message generation function isinterrupted for more than 24 hours. The extended
mode is characterized by a gradually decreasing
ranging accuracy, that is reflected in Annex C.4.4.2.
The Galileo Extended Operations Mode Expected SIS
Ranging Accuracy performance is specified in Table
38. Note that the SISA during Extended Operations
Mode is fixed at a value of 125, as noted in section
2.3.1.3. This SISA is not a performance indicator of
the SIS while in this mode.

Table 38. Galileo Extended Operations Mode Expected
SIS Ranging Accuracy.

GALILEO EXTENDED OPERATIONS MODE
EXPECTED SIS RANGING ACCURACY
MODE
For each SF

For each DF

EXPECTED SISRANGING ACCURACY• ≤ 50 m, global
average (95%), for up to
6 days of Extended
Operations Mode• ≤ 50 m, global

average (95%), for up
to 6 days of Extended
Operations Mode

D.5.2I/NAV IMPROVEMENTS
The Galileo Programme is committed to continuous
improvement of the Galileo Open Service. With
I/NAV improvements Galileo enables for the users
the possibility to considerably boost theirperformance in terms of robustness and Time To FirstFix (TTFF). In this context, ‘robustness’ includes thecapability of the navigation message to enable a fastreconstruction of the Galileo System Time (GST).
Additionally, as the time to receive clock corrections
and ephemeris data is a major contribution to theTime To First Fix in many conditions, a reduction ofthis time supports in general all applications that
require reception of this data from navigation signals.
Please refer to the Galileo OS SIS ICD (Annex A [1])for more information on all of the I/NAV features inthis section.
The Reduced Clock and Ephemeris Data (RedCED)
and the Reed Solomon Forward Error Correction (RSFEC2) enable receivers to reduce the time to first fix(TTFF) by reducing the time to CED.
The RedCED is a compact set of ephemeris and clock
minus radial error correction information, transmitted
within one single I/NAV word and with a reduced
accuracy with respect to the ephemeris. Receivers
can use these reduced-precision parameters tocompute an initial position fix in case a full ephemerisand clock correction set has not yet been received,
see Galileo SIS ICD for more details.
The improvements also include the broadcast ofadditional Reed Solomon Clock and Ephemeris Data
(RS-CED) coded by the RS FEC2. The set of 4 RSCED I/NAV words provide redundant information on
top of the CED I/NAV words. The full precision CED

55

data can now be re-constructed after the successful
demodulation of any four different I/NAV words. This
improves demodulation robustness but also
improves the time to CED.
In combination, these improvements allow for afaster time to a reduced CED, but also to a full
precision CED, compared to the regular subframelayout.
Lastly, the Secondary Synchronisation Patternprovides information within the I/NAV message toallow for the reconstruction of the Galileo systemtime as long as s coarse synchronisation is alreadyavailable. This improvement targets applications
working in assisted mode, i.e. where navigation data
is received from other channels.
The tables below typical performance improvements
to be expected for a user implementing RedCED and
Rs FEC2.
Table 39 shows the improvement of the Time to

Reduced CED and the Time to full precision CED incomparison to using the nominal subframe layout inan ideal environment, open sky with perfect channel
conditions. Table 40 shows the typical Ranging
Accuracy performance in the intermediate stage,using RedCED.

D.5.3 ACCURACY OF ALMANAC
As explained in the OS SIS ICD (Annex A [1]), thealmanac is a reduced-precision subset of the clockand ephemeris parameters and predicted SIS healthstatus of the satellites in orbit.
The scope of the almanac is to indicate the positionof all the satellites in the constellation with a reduced
accuracy in order to facilitate the Galileo signal
acquisition24.
In Table 41, the typical Galileo OS Ranging Accuracy
95% is provided in case only the clock and ephemeris
information retrieved from the Galileo almanac isused, instead of the information from the broadcast
navigation message. The typical values using 12 hour
old and 24 hour old almanac information areprovided.
Table 41. Galileo almanac SIS Ranging Accuracy typicalvalues over all satellites, Global Average, when almanac’s
clock and ephemeris information is used.

GALILEO ALMANACSIS RANGING
ACCURACY
TYPICAL VALUEOVER ALLSATELLITESTable 39. Time to CED (95%) in open sky environment
with perfect channel conditions.

Time to CED
Reduced accuracy
(95%)
I/NAV
Nominalsubframe
LayoutI/NAV

Reduced CED& ReedSolomon–NominalAccuracy
32 s

16 s

• Calculated over a

For each SF:• ≤ 860 m, at 12hours• ≤ 1400 m, at 24
hours
Global Average

22 s

Table 40. Typical RedCED Ranging Accuracy Performance.

Spatialstatistics

RedCED Ranging Accuracy (95%)

AUL

6m

WUL

12 m

CONDITIONS AND
CONSTRAINTS

For each DF
combination:• ≤ 860 m, at 12hours• ≤ 1400 m, at 24
hours
Global Average

period of 30 days
• Average, over theconstellation, of theGalileo SIS Ranging
Accuracy (95%) of each
Healthy SIS• Using almanac’s clockand ephemeris
information• Calculated over a
period of 30 days
• Average, over theconstellation, of theGalileo SIS Ranging
Accuracy (95%) of each
Healthy SIS• Using almanac’s clockand ephemeris
information

Auxiliary satellites might not have their associated almanac broadcast by the Galileo SIS. The user can referto the GSC web page for updated information about the Galileo constellation.
24

56

2)

Unplanned NAGU: all activities/events thathave an impact on the Service (i.e., SiS OFF or
SIS not healthy) and/or the performance levels
that have not been scheduled and could not be
foreseen in advance, before their occurrence.
The aim of unplanned NAGUs is to inform users
about the activity/event within a reasonable
time, after their occurrence.

3)

Service Availability NAGU: all events related to
the restoration of service provision, following
the end of a planned outage or the recovery ofan unplanned outage.

4)

General NAGU: all activities performed on the
Galileo system, or any occurring events, that
potentially or substantially have an impact on
the SiS and/or on the performance levels, which
would not be already covered by a planned or an
unplanned NAGU. It is to be noted that General
NAGUs can be related to both planned andunplanned events.

ANNEX E: DESCRIPTION OF
ADVISORY NOTICES TOGALILEO
NAGUs (Notice Advisory to Galileo Users) are used
to notify Galileo users about the SIS status of all
satellites in the Galileo constellation. Different
categories of NAGUs are issued depending on thespecific event to be communicated,
The information provided here, together with the listof active and archived NAGUs can be also found in
the GSC web page, www.gsc-europa.eu, under“System Status”.

E.1. LIST OF DEFINED NAGUS
The following four categories of NAGUs exist:
1)

Planned NAGU: all activities/events that havebeen scheduled and that could potentially havean impact on the SiS and/or the performancelevels. Planned NAGUs aim to inform users
about the activity/event with a reasonableadvance notice, ahead of their occurrence.

Table 42 and Table 43 provide the detail of each kindof NAGU. The NAGUs in Table 44 are obsolete andwill no longer be published, however they are listed
below for consistency with the NAGU archive
available at GSC.
Figure 10 presents graphically a summary of thevarious types of NAGUs with their timeline.

Figure 10. Graphical summary of the various types of NAGUs.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023
Table 42. List of general NAGUs.

NAGU TYPE(ABBREVIATION)

NAGU TYPE

NAGU DESCRIPTIONGENERAL(NOTICE)

General notice

General notifications such as announcing the IOV campaign, Service
validations,announcement of Service declarations, introduction of services, IOC, FOC,
etc.

GENERAL(LAUNCH)

LaunchNotification of the satellite launch.

GENERAL (LEAPSECOND)

Leap second

Notification of a leap second adjustment affecting UTC time scale,following the related announcement by IERS.

GENERAL(TIMING
PLN_OUTAGE)

Planned outage
timing services

Notification of a planned operation entailing an outage of timing related
services, consisting of GGTO and UTC determination capabilities at userlevel.

GENERAL(TIMING USABLE)

Availability oftiming services

Notification of availability of timing services following the end of a planned
operation/ recovery of an unplanned outage with impact related only totiming services.

GENERAL(TIMING CANCEL)

Cancellation ofplanned outage
timing services

Cancellation of published general NAGU notification for a planned
operation entailing an outage only affecting the timing services.

GENERAL(TIMING RESCH)

Reschedule ofplanned outage
timing services

Provision of new start/end times for published general NAGU notification
for a planned operation entailing an outage only affecting the timing
services.

GENERAL(TIMING EXTNS)Extension ofplanned outage
timing services

Provision of new end time for published planned NAGU entailing an
outage only affecting the timing services.

GENERAL(TIMINGUNP_UNUFN)

Unplanned outage
timing services

This general NAGU provides notification of an unplanned outage relatedwith timing services.

GENERAL(TIMING
UNP_SHTRCVR)

Short term outage
timing services

This general NAGU provides notification of short term timing services
outage that have been recovered before a NAGU could be published.

59

Table 43. List of specific NAGUs.

NAGU TYPE(ABBREVIATION)

NAGU TYPE

NAGU DESCRIPTION

PLN_MANV

Plannedmanoeuvre

Planned activity affecting the attitude and/or orbit (e.g., satellite relocation
to a new slot). It includes the planned outage start time and end time.

PLN_OUTAGE

Planned outage

Planned activity, in space or ground segment, that can potentially cause an
outage of the broadcast satellite Signal in Space. It includes the planned
outage start time and end time.

CANCEL

Cancellation

Cancellation of published NAGUs.

RESCHReschedule

Provision of new start/end times for an already published NAGU of the“PLANNED” category.

EXTNS

Extension

Provision of new end time for an already published NAGU of the“PLANNED” category, or notification of the planned outage end time for a
published NAGU of the “UNPLANNED” category (UNP_UNUFN).

DECOMMSNG

Satellite
decommissioned

Beginning of decommissioning phase. The end time for the nominal
provision of service is specified.

EOM_STARTStart of the
ExtendedOperation Mode

Start time of the Galileo Extended Operation Mode is communicatedthrough this NAGU.

EOM_END

End of the
ExtendedOperation Mode

Upon recovery of the nominal operation mode, this NAGU is issued tocommunicate the end time of the Galileo Extended Operation Mode.

UNP_UNUFN

Unavailable until
further notice

Unscheduled outage of the broadcast satellite Signal in Space,characterised by an undefined duration.

UNP_SHTRCVR

Short term outage
recovered

Outage events that have been already recovered, before a dedicated
NAGU could be published to notify their occurrence.
Satellite enters its active service provision, contributing to the constellation
service delivery.

USABINIT

Satellite first time
usableIt is used for satellites that enter their service provision for the first time,
indicating that the space vehicle is providing a Signal In Space in line withthe applicable OS SIS ICD, as well as the published OS SDD and therelated service performance commitment.
It includes also the type of clock being used to drive the navigation
payload.

USABLE

Usable for service
provision

The satellite restarts transmitting healthy Signal in Space, concluding aplanned outage period or the recovery after an unplanned outage.
It includes also a reminder about the exact outage start time, along withthe precise outage end time.
It includes also the type of clock being used to drive the navigation
payload.
This NAGU type is also used following Service Declaration, in order torecall the list of space vehicles that are expected to broadcast a Signal inSpace aligned with the applicable OS SDD during the specified service
provision phase.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023
The following NAGU types are obsolete and will no longer be published, however they are listed below forconsistency with the NAGU archive available at GSC.
Table 44. List of obsolete NAGUs.

NAGU TYPE(ABBREVIATION)AVAILINIT

NAGU TYPE

Satellite firsttime available

NAGU DESCRIPTION

The satellite is for first time providing healthy SIS following completionof satellite in-orbit commissioning activities.
The type of clock being used to drive the navigation payload is also
indicated.
Satellite is not yet contributing to service provision.

AVAILABLE

Available fortesting

Satellite available for testing purposes. This NAGU type was used prior
to the Initial Services Declaration. As of 15th of December, 2016, the
OS Initial Services Declaration has taken place and USABLE NAGU will
be published instead of AVAILABLE NAGU.

61

E.2. NAGU FORMATDATE GENERATED(UTC):

YYYY-MM-DD hh:mm

NAGU TYPE:

Specific NAGUs template (for Planned,
Unplanned and Service Availability notices);

AS PER GENERAL NAGU
DEFINITION

NAGU NUMBER:YYYYNNN

General NAGUs template (for General notices).

NAGU SUBJECT:FREE TEXT

The format of NAGUs issued to Galileo users
through the European GNSS Service Centre web
portal follows two possible templates:••

NOTICE ADVISORY TO
YYYYNNNGALILEO USERS (NAGU)

These NAGU templates are described in the next
sections and can be downloaded from the European
GNSS Service Centre web portal.

NAGU REFERENCED TO: YYYYRRR OR N/A

E.2.1 SPECIFIC NAGU

END DATE EVENT (UTC): YYYY-MM-DD hh:mm OR
N/A OR UNTIL FURTHERNOTICE

Specific NAGUs follow the format below:
NOTICE ADVISORY TO
GALILEO USERS(NAGU)YYYYNNNDATE GENERATED(UTC):

YYYY-MM-DD hh:mm

NAGU TYPE:

AS PER NAGU DEFINITION

NAGU NUMBER:YYYYNNN

NAGU SUBJECT:

AS PER NAGU TEMPLATENAGU REFERENCEDTO:YYYYRRR OR N/A

START DATE EVENT(UTC):

YYYY-MM-DD hh:mm

END DATE EVENT(UTC):

YYYY-MM-DD hh:mm OR
N/A

SATELLITE AFFECTED:SATELLITE_NAMESPACE VEHICLE ID:

SVID

SIGNAL(S) AFFECTED:

E1, E5a, E5b, E6-B, E6-C
OR ALL

EVENT DESCRIPTION:

AS PER NAGU TEMPLATE

START DATE EVENT(UTC):

YYYY-MM-DD hh:mm

SATELLITE AFFECTED:SATELLITE_NAME OR ALL

EVENT DESCRIPTION:

AS PER GENERAL NAGUTEMPLATE

E.2.3 DESCRIPTION OF NAGU’SCONTENTThe fields used within the specific and general
NAGUs are defined as follows:

1) HEADER: The first line of the text fieldrefers to the title “NOTICE ADVISORY TO
GALILEO USERS” (NAGU), followed by the
NAGU number in the format YYYYNNN,
where:

2)

E.2.2 GENERAL NAGU
General NAGUs follow a simplified version of theformat used for specific NAGUs, providing
additional flexibility on the definition of the subject(e.g. launch, validation campaigns, status flags, etc.):3)•

YYYY: Gregorian year;•

NNN: sequential number of the
NAGU, starting with 001 on the 1stof January every year andincrementing by 1 for eachsubsequent NAGU.

DATE GENERATED (UTC): The date when
the NAGU is generated on the GSC web
portal, in UTC time scale with format YYYYMM-DD hh:mm, where:•

YYYY: Gregorian year;•

MM: number of the month from 112 in sequence starting with 1 being
January, and finishing with 12 being
December;•

DD: day within the Gregorianmonth;•

hh: hour in the 24 hour format;•

mm: minute.

NAGU TYPE: The different NAGU types as
defined in Annex E.2.

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GALILEO - OPEN SERVICE - SERVICE DEFINITION DOCUMENT, ISSUE 1.3, 2023

4)

NAGU NUMBER: Reference to the NAGU
number in the format YYYYNNN (asdefined in the Header field).

5)

NAGU SUBJECT: The subject of the NAGU
summarizing the information provided in
the “Event Description”. The text to be
used in the subject is defined by the
template of each NAGU. For GENERAL
NAGU, this is a free text description.

6)

NAGU REFERENCED TO: If the current
NAGU refers to a previous NAGU, thisfield contains the referenced NAGU
number in the format YYYYRRR, where:•

YYYY: Gregorian year when the
NAGU was issued;•

RRR: issue number of the NAGU forthat year.

Otherwise, the field contains N/A (notapplicable) when there is no reference toa previous NAGU.
7)START DATE EVENT (UTC): The startdate of the event notified by the NAGU, in
UTC time scale with format YYYY-MM-DD
hh:mm.

8)

END DATE EVENT (UTC): The end date of
the event notified by the NAGU, in UTC
time scale with format YYYY-MM-DD
hh:mm, or defined as Not Applicable ordefined as Until Further Notice.

9)

SATELLITE AFFECTED: The name of thesatellite affected (GSAT, Galileo
SATellite). For GENERAL NAGU, this fieldcontains ALL to indicate that all satellites
are affected.

10) SPACE VEHICLE ID: The Space Vehicle ID(SVID) of the satellite affected. This field
is not present in the GENERAL NAGU.
11) SIGNAL(S) AFFECTED: The signal(s)affected by the satellite indicated in the
NAGU. The signals affected can be one or
a combination of the following: E1, E5a,E5b, E6-B, E6-C or ALL. Partial
outage/availability of the signals is
indicated in the NAGU subject if ALL
signals are not affected. This field is notpresent in the GENERAL NAGU.
12) EVENT DESCRIPTION: The event
description following the templates
defined for each NAGU.

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TS-02-23-184-EN-N

LINKING SPACE TO USER NEEDS
www.euspa.europa.eu@EU4Space@EU4Space
EUSPA@space4eu
EUSPA