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Performance Budget File

Version: 3.1

Printed by: GALA_Administrator

Printed on: 08 December 2000

Generated from DOORS 5.0

Contents

1 4INTRODUCTION

1.1 4Scope of the document1.2 5Organization of the document

2 7REFERENCES

2.1 7Definitions2.1.1 7Accuracy (NSE(95%))2.1.2 7Integrity

2.1.2.1 7Integrity Risk2.1.2.2 7Alarm limit2.1.2.3 7System Time to Alert2.1.2.4 8(Horizontal-vertical) Protection level

2.1.3 8Continuity Of Service2.1.4 8Availability of service

2.2 8Acronyms2.3 8Reference document

3 10GALILEO constellation Performance definitions andassumptions

3.1 10Constellation geometry assumptions3.2 10Satellite RAMS figures3.3 12Orbit and synchronisation residual error

4 13GALILEO Navigation performance Allocation

4.1 13Overall Approach4.2 14Galileo Mission Requirements4.3 16Architecture Identification

4.4 17Allocation with other sytems4.5 18Accuracy4.6 18Global Navigation Function Only services

4.6.1 18Performance Allocation for OAS-G1 & 24.6.2 19Integrity Performance Allocation for SAS-G/En Route4.6.3 23Continuity Performance Allocation for SAS-G/En Route4.6.4 24Availability Performance Allocation for SAS-G/En Route

4.7 25Global Navigation Function + Global Integrity Function4.7.1 25Integrity Performance Allocation for CAS1-G

4.7.1.1 25GIC and RAIM allocation4.7.1.1.1 26Option 1: Serial Allocation4.7.1.1.2 26Option 2: Parallel Allocation4.7.1.1.3 28User Integrity Risk Allocation tree

4.7.1.2 30Integrity Risk Allocation within Global component4.7.1.3 32Time To Alarm Allocation

4.7.2 34Integrity Performance Allocation for CAS1-GS 4.7.3 35Integrity Performance Allocation for SAS/NPA4.7.4 36Integrity Performance Allocation for SAS-G/Cat 14.7.5 39Integrity Performance Allocation for SAS-GS/Cat14.7.6 39Integrity Performance Allocation for GAS-G4.7.7 40Integrity performance allocation for GAS-GS service4.7.8 41Continuity Performance Allocation for CAS1-G4.7.9 42Continuity performance allocation for CAS1-GS service

4.7.10 43Continuity Performance Allocation for SAS-G/NPA4.7.11 45Continuity Performance Allocation for SAS-G/Cat14.7.12 47Continuity Performance Allocation for SAS-GS/Cat14.7.13 47Continuity Performance Allocation for GAS-G4.7.14 48Continuity Performance Allocation for GAS-GS4.7.15 48Availability Performance Allocation for CAS1-G service4.7.16 50Availability Performance Allocation for CAS1-GS service

Contents i

4.7.17 51Availability Performance Allocation for SAS-G/NPAservice

4.7.18 52Availability Performance Allocation for SAS-G/Cat1service

4.7.19 52Availability Performance Allocation for SAS-GS/Cat1service

4.7.20 53Availability Performance Allocation for GAS-G service4.7.21 54Availability Performance Allocation for GAS-GS service

4.8 54Global Navigation Function + Regional IntegrityFunction

4.8.1 54SAS-R service provision4.8.2 56Integrity Performance Allocation for SAS-R service4.8.3 58Integrity performance allocation for SAS-RM service 4.8.4 58Continuity Performance Allocation for SAS-R4.8.5 61Continuity performance allocation for SAS-RM4.8.6 61Availability Performance Allocation for SAS-R 4.8.7 63Availability performance allocation for SAS-RM service4.8.8 64EGNOS service provision

4.9 64Global Navigation functions + Local functions4.9.1 65Integrity Performance Allocation for CAS1-L14.9.2 68Integrity performance allocation for SAS-L service 4.9.3 68Integrity performance allocation for GAS-L service 4.9.4 69Continuity Performance Allocation for CAS1-L service4.9.5 70Continuity Performance Allocation for SAS-L service4.9.6 70Continuity Performance Allocation for GAS-L service4.9.7 71Availability Performance Allocation for CAS1-L service4.9.8 72Availability Performance Allocation for SAS-L service4.9.9 73Availability Performance Allocation for SAS-L service4.10 73From Mission to System Requirements

5 77UERE budget

5.1 77Scenario definition 5.1.1 77System Specific Parameters

5.1.1.1 77Galileo services5.1.1.2 78System Architecture

5.1.2 79User Specific Parameters 5.1.3 80Signal Structure Hypothesis

5.2 81Dual L band frequency UERE with SAS/GAS receiverassumption

5.2.1 81UERE budget error in GLOBAL5.2.1.1 81Signal to Noise ratio

5.2.1.1.1 81Signal power5.2.1.1.2 83User antenna gain5.2.1.1.3 84Receiver Thermal Noise5.2.1.1.4 85Galileo Cross Interference5.2.1.1.5 86External Interference5.2.1.1.6 88Signal to Noise Ratio

5.2.1.2 89Receiver Budget Error5.2.1.2.1 89Code Tracking Error5.2.1.2.2 91Multipath Budget Error 5.2.1.2.3 93Global Receiver Budget Error

5.2.1.3 94Tropospheric Residual Error5.2.1.4 96Total UERE after Dual Frequency Processing

5.2.1.4.1 97UERE with high multipath5.2.1.4.2 99UERE with low multipath

5.3 100Dual L band frequency UERE with OAS/CAS1 receiverassumption

5.3.1 100UERE budget error in GLOBAL5.3.1.1 100Multipath Budget Error 5.3.1.2 102Total UERE after Dual Frequency Processing

Contents ii

5.3.1.2.1 102Total UERE with high multipath5.3.1.2.2 104Total UERE with low multipath

5.4 105Single L band frequency UERE with OAS/CAS1 receiverassumptions

5.4.1 105Residual Ionospheric Error5.4.2 107Total UERE

5.5 108Single C band frequency UERE with SAS/GAS receiverassumptions

5.5.1 108UERE in Global5.5.1.1 108Multipath Budget Error5.5.1.2 109Ionospheric Budget Error5.5.1.3 110Total Budget Error

5.6 112UERE in Local5.6.1 112L band UERE budget with SAS/GAS receiver

assumptions5.6.1.1 112Receiver Budget Error

5.6.1.1.1 112Code measurements5.6.1.2 112Troposphere Budget Error5.6.1.3 114Ionosphere Budget Error5.6.1.4 115Total Budget Error

5.6.1.4.1 115Local UERE with high multipath5.6.1.4.2 116Local UERE with low multipath

5.6.2 117L band UERE budget with OAS/CAS1 receiverassumptions

5.6.2.1 118UERE in local with high multipath5.6.2.2 119UERE in local with low multipath

5.6.3 120C band UERE budget with SAS/GAS receiverassumptions

5.6.3.1 120UERE budget with high multipath5.6.3.2 122UERE budget with low multipath

5.7 122UERE Recapitulative

5.7.1 123GLOBAL UERE5.7.1.1 123High multipath5.7.1.2 124Low multipath

5.7.2 125LOCAL UERE5.7.2.1 125High multipath5.7.2.2 126Low multipath

6 128Performance budget

6.1 128Baseline simulations assumptions6.1.1 128Space segment6.1.2 128Receiver Assumptions

6.1.2.1 128Number of channels6.1.2.2 128Masking Angle6.1.2.3 128Navigation Algorithm6.1.2.4 129RAIM availability algorithm6.1.2.5 129GIC availability algorithm6.1.2.6 129RAIM GIC combination6.1.2.7 129Integrity allocation

6.1.3 129Ground Segment6.1.4 129Simulation assumptions

6.1.4.1 129Area6.1.4.2 130Simulation duration6.1.4.3 130Time sampling6.1.4.4 130Latitude sampling6.1.4.5 130Longitude sampling6.1.4.6 130Failures

6.1.5 130UERE budget6.1.6 130Urban Canyon Characterization

6.2 132Continuity preliminary assessment6.2.1 132SAS-G/NPA

Contents iii

6.2.2 138SAS-G/Cat16.3 138Availability assessment

6.3.1 139OAS Service 6.3.1.1 139OAS-G16.3.1.2 141OAS-G2

6.3.2 143CAS1 service6.3.2.1 143CAS1-G

6.3.2.1.1 143Accuracy performance6.3.2.1.2 143Integrity performance

6.3.2.2 146CAS1-L6.3.2.2.1 146Accuracy performance6.3.2.2.2 148Integrity performance

6.3.3 150SAS and GAS Services6.3.3.1 150SAS-G/En route


6.3.3.2 154SAS-G/NPA6.3.3.2.1 154Accuracy performance6.3.3.2.2 154Integrity performance

6.3.3.3 156SAS-G/Cat1 and GAS-G6.3.3.3.1 157Accuracy performance6.3.3.3.2 159Integrity performance

6.3.3.4 162SAS-R6.3.3.5 162SAS-L and GAS-L


6.3.4 167Sensitivity analysis6.3.4.1 167Sensitivity to the multipath error budget6.3.4.2 171Sensitivity to the user mask angle6.3.4.3 175Sensitivity to the horizontal / vertical allocation of the

integrity risk

6.3.4.4 178Sensitivity to the vertical alarm limit value6.3.4.5 180Sensitivity to the vertical accuracy requirement value

7 182Performance with External system

7.1 182Global Positioning System (GPS+)7.1.1 182Assumptions

7.1.1.1 182Constellation parameter7.1.1.1.1 182GPS constellation parameter

7.1.1.2 183UERE7.1.2 184Combined Galileo/GPS Navigation Performance

7.1.2.1 184Performance of GPS only7.1.2.2 186Baseline Availability of Service for combined use of GPS

and Galileo7.1.2.2.1 186OAS-GS7.1.2.2.2 188CAS1-GS

7.1.2.2.2.1 188Accuracy performance7.1.2.2.2.2 190Integrity performance

7.1.2.2.3 192SAS-GS/Cat1 and GAS-GS7.1.2.2.3.1 192Accuracy performance7.1.2.2.3.2 194Integrity performance

7.1.2.2.4 196SAS-RM7.1.2.3 200Sensitivity analysis of the availability for combined use of

Galileo and GPS7.1.2.3.1 200OAS-GS

7.1.2.3.1.1 200Sensitivity to the multipath level7.1.2.3.1.2 202Sensitivity to the requirement

7.1.2.3.2 203CAS1-GS7.1.2.3.2.1 204Sensitivity to the multipath level7.1.2.3.2.2 206Sensitivity to the requirement

7.1.2.3.3 210SAS-GS and GAS-GS

Contents iv

7.1.2.3.3.1 210Sensitivity to the multipath level and the user maskangle

7.1.2.3.3.2 212Sensitivity to the requirement7.2 214Loran C/ Eurofix

7.2.1 214Introduction7.2.2 215Loran C performance assumption7.2.3 216Combined Galileo/Loran C expected performance.

7.2.3.1 216Performance Allocation7.2.3.2 216Availability Performance in Urban canyon7.2.3.3 217Outage Characterization

7.2.3.3.1 217Mean number of satellites in visibility7.2.3.3.2 219satellites availability 7.2.3.3.3 221Horizontal Accuracy availability statistics

7.2.3.4 222Conclusion7.3 223Hybridization with other system

8 224Synthesis : Availability compliance matrix forGALILEO and Galileo+GPS services

9 227Conclusion And Open Points

9.1 227Open points and recommendation9.1.1 227Local effects characterization

9.1.1.1 227Multipath contribution in UERE budget9.1.1.2 227Multiple and single failure due to local effects 9.1.1.3 228Masking angle and Interference mask

9.1.2 228Allocation assumptions9.1.2.1 228RAMS analysis9.1.2.2 228Clock stability9.1.2.3 229Network reliability9.1.2.4 229Up-link capabilities with dynamic antennas

9.1.3 229Integrity concept

9.1.3.1 229Feasibility of the GIC concept9.1.3.2 230Integrity performance concept

9.1.4 230Model limitations9.1.4.1 230Integrity modeling9.1.4.2 230Availability modeling9.1.4.3 231Other sensor/ system simulation

9.2 231Conclusion

Contents v

DD-036 Page 1 of 232 Printed 08 December 2000

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DD-036-1

DD-036-2

DD-036-3


DOCUMENT PRODUCTION

DOCUMENT DISTRIBUTION

From Stephane LANNELONGUE

Project Acronym GALA

Project Name Galileo Overall Architecture Definition

Title Performance Budget File

Issue 3.1

Reference GALA-ASPI-DD036

Date 08/12/00

Pages number 225

File GALA-ASPI-DD036v3.doc

Issue 3.1

Classification PU

WBS D34

Contract GALA-ASPI

Emitting Entity ALCATEL SPACE INDUSTRIES

Type of Document A

Status -

Template Name gala_aspi.dot (V1)

DOCUMENT ENDPAPER

Written by Responsibility - Company Date Signature

S. LANNELONGUEH. DELFOUR

ASPIASPI

Verified by


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28

ID

DD-036-3663


JM PIEPLU ASPI

Approved

A. MASSON ASPI

CHANGE RECORDS

ISSUE DATE § : CHANGE RECORD AUTHOR

1A 03/03/00 First issue F AIGLE

1.1 05/05/00 MTR versionAll sections changed

S LANNELONGUE

2.0 20/07/00 PM4 versionAll sections changedConsolidation of the UEREProvision of performance allocation[Simulation results provided at MTR removedbecause no longer applicable]

S LANNELONGUE

2.1 31/07/00 Adjustment of mission requirementsparameter with DD09Alignment with DD31 for the performanceallocation

S. LANNELONGUE

3.a 10/08/00 Working version including final version ofPerformance allocation and UERE budget

S. LANNELONGUE

3.b 10/11/00 Working version.Addition of chapter 6 and 7 for performanceassessmentAddition of System requirement derivationmethod

H. DELFOURS. LANNELONGUE

3.0 20/11/00 Final version delivered for Final ReviewInclusion of comments coming from GALAinternal review process

H. DELFOURS. LANNELONGUE


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DD-036-6


3.1 08/12/00 Migration to DOORS JL DAMIDAUX

TABLE OF CONTENTS

INDEX OF TABLES

INDEX OF FIGURES


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DD-036-7

DD-036-8

DD-036-9

DD-036-10

DD-036-11

DD-036-12

DD-036-13

DD-036-14

DD-036-15

DD-036-16

DD-036-17

DD-036-18

DD-036-19

DD-036-20

DD-036-21


1 INTRODUCTION

1.1 Scope of the document

This document is the output of the work package 3.4 of GALA dealing with Galileo architecture performance assessment.

The main objective of this work package is to assess the feasibility of the required navigation system performance by means ofsimulations for the proposed architecture. The performance considered are:

- accuracy

- integrity

- continuity

- availability

First, mission requirements are allocated to the different component of Galileo which are namely:

- The global component

- The regional component

- The local component

- And the user terminal

Some of the services are planned to be provided with GPS. For such service an allocation of performance which is, in this case,closer to an a priori estimation of GPS is also provided.

Next, the UERE computations is detailed. Different class of users (or different class of services) are considered: OAS (OpenAccess Service), CAS1 (Control Access Service level 1) , CAS2/SAS (Safety critical service), CAS2/GAS (Governmental service).


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DD-036-22

DD-036-23

DD-036-24

DD-036-25

DD-036-26

DD-036-27

DD-036-28

DD-036-29

DD-036-30

DD-036-31


In a third step performance of Galileo with respect to the mission requirements is assessed. The performance are computed withhigh level models (global models to evaluate the system and to have sensitivity analyses rather than models of the actualalgorithms or functions, since many of them are not yet defined or stabilized). Assessment of the performance withhybridization and other systems is also performed. The other systems identified to be hybridized with Galileo components areGPS, Loran C and GNSS 1. GLONASS is not yet included since the future of this system within Galileo architecture dependsheavily of international negotiation.

One important thing to point out is that the detail design of the different component is not the task of GALA. Therefore, thisdocument does not pretend to make compliance statement between the Galileo architecture and the Galileo missionrequirements. On the contrary, the definition of the Galileo mission requirements is the task of GALA. Therefore, thisdocument aims at assessing the feasibility of the requirements making reasonable assumptions on the architecture in order toconsolidate them.

A first cost estimation shows that, as far as performance is concerned, the most critical component is the space segment. Therefore, the performance assessment part of this document will focus on the constellation performance. At the end, it is surethat the ground segment design will have a great impact on the final performance. However the cost of the system is drivenmainly by the constellation. Therefore for assessing feasibility, the ground segment will be assumed compliant to allocatedperformance requirements.

1.2 Organization of the document

This document aims at managing all information concerning Galileo final performance. It presents the performance budgetsand justifications associated to each service levels. It shall include trace-ability of the mission requirements to system andsubsystem requirements, a preliminary performance allocation and margins, justification of the compliance levels (experiments,analyses and simulation results).

The main outcomes of this document are

- [Chapter 4] Allocation of the top mission requirements to the different component of the system (global, regional, local,receiver, signal).

- [Chapter 5] UERE budget for different classes of user (OAS, CAS1, SAS and GAS)

- [Chapter 6] Performance assessment for Galileo only services

- [Chapter 7] Performance assessment of Galileo combined with other system such as GPS and Loran C


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69

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DD-036-32

DD-036-33


- [Chapter 8] Galileo architecture “Compliance” to Mission Performance requirement

- [Chapter 9] Open points, recommendation and conclusion


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DD-036-34

DD-036-35

DD-036-36

DD-036-37

DD-036-38

DD-036-39

DD-036-40

DD-036-41

DD-036-42

DD-036-43

DD-036-44

DD-036-45

DD-036-46


2 REFERENCES

2.1 Definitions

Performance parameters are defined in the Definition document of GALA [RD-09]. The relevant ones for performanceestimation are recalled here after.

2.1.1 Accuracy (NSE(95%))

This is the value that bounds the “instantaneous” position error at a specific location and a specific time with a probability of kpercent not to be exceeded. This definition is usable as an accuracy definition. The NSE (Navigation System Error) will bespecified at 95 percent confidence level. This NSE parameter is the one used to declare at every space-time point the availabilityof the positioning service with required accuracy.

2.1.2 Integrity

2.1.2.1 Integrity Risk

This is the probability during the period of operation that an error, whatever is the source, might result in a computed positionerror exceeding a maximum allowed value, called Alarm Limit, and the user be not informed within the specific time to alarm.

2.1.2.2 Alarm limit

This is the maximum allowable error in the user position solution before an alarm is to be raised within the specific time toalarm. This alarm limit is dependent on the considered operation, and each user is responsible for determining its own integrityin regard of this limit for a given operation following the information provided by GALILEO SIS (Signal In Space). In thisdocument, we will refer to this definition by HAL (Horizontal Alarm Limit) and VAL (Vertical Alarm Limit), and XAL standingfor HAL or VAL.

2.1.2.3 System Time to Alert

The System time to alert is defined as the time starting when an alarm condition occurs to the time that the alarm is displayed atthe user interface. Time to detect the alarm condition is included as a component of this requirement.

Industry considers that start event of an alarm condition is the beginning of a sampling period, in the monitoring stationreceiver, during which an erroneous pseudo range will be received.


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DD-036-47

DD-036-48

DD-036-49

DD-036-50

DD-036-51

DD-036-52

DD-036-53

DD-036-54

DD-036-55

DD-036-56


2.1.2.4 (Horizontal-vertical) Protection level

This is the value computed by the user receiver which estimates the confidence bound on the actual Navigation System Errorusing data transmitted by the Galileo ground mission segment signal (e.g. SISA, differential corrections accuracy, …) and/orpre-determined bounds. The user integrity monitoring function is available when the protection level is computable and is lessthan the alarm limit. In this document, we will refer to this definition by HPL (Horizontal Protection Level) and VPL (VerticalProtection Level), and XPL standing for HPL or VPL.

The XPL value varies with the confidence required. This confidence is expressed in terms of false alarm and miss detectionprobabilities. Those parameters are sized according to the probability of failure of the system and the integrity risk required.

2.1.3 Continuity Of Service

Continuity of Navigation Service is defined as the probability that the accuracy and integrity requirements will be supported bythe Navigation System over the time interval applicable for a particular operation within the coverage area given that they aresupported at the beginning of the operation and that they are predicated to be supported all along the operation duration.Satellite outages predicted at least 48 hours in advance of the outage do not contribute to loss of continuity. This assumes thatan adequate notice is provided to the users. For civil Aviation this service is referred to as NOTAM (Notice to Airmen).

2.1.4 Availability of service

Availability of the Navigation Service is the probability that the Positioning service and the Integrity monitoring service areavailable and provide the required accuracy, integrity and continuity performances . The service will be declared available whenaccuracy and integrity requirements In practice, for integrity, we compute the availability of the UIM function (e.g. XPLavailability) are met at the beginning of an operation and are estimated to be met during all the operation period (= continuityrequirement).

2.2 Acronyms

See document Performance definition GALA-ASPI-DD092

2.3 Reference document

[RD-01] GALILEO Mission Requirements GALA-ASPI-DD108

[RD-02] GALILEO System Requirements GALA-ASPI-DD107


Index ID Performance Budget File

[RD-03] Global component requirements GALA-ALS-DD31

[RD-04] Regional component requirements GALA-ALS-DD32

[RD-05] Local component requirements GALA-DSS-DD33

[RD-06] Galileo Constellation trade-offs GALA-ASPI-DD12

[RD-07] Galileo Integrity Trade-off GALA-ASPI-DD13

[RD-08] Galileo Architecture Baseline Definition GALA-ASPI-DD027.

[RD-09] GALA Performance Definition GALA-ASPI-DD092

[RD-10] GALA Architecture justification GALA-DSS-DD030

[RD-11] Use of Other Systems GALA-SC75-DD015

[RD-12] Use of Other Sensors GALA-SEXTANT-DD016

[RD-13] Galileo system and segments justification file GNSS2-P2-sys-501Issue 2B

[RD-14] MOPS for GPS/Wide Area Augmentation System Airborne Equipment,RTCA

[RD-15] Signal Design and Transmission Performance Study for GNSS

[RD-16] Global Positioning System, Theory and Application, James J. Spilker.

[RD-17] A modernization deployment strategy to meet military and civil needs,ION-GPS 1999, Nashville

[RD-18] FAA's plan for the future use of GPS, Sandhoo, Biggs, ION-GPS 1999,Nashville

[RD-19] MASPS (Draft) for local augmentation, RTCA


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DD-036-76

DD-036-77

DD-036-78

DD-036-79

DD-036-80

DD-036-81

DD-036-82

DD-036-96

DD-036-97

DD-036-98


3 GALILEO constellation Performance definitions and assumptions

3.1 Constellation geometry assumptions

Several options were considered for the constellation architecture:

- The 30 MEOs (Medium Earth Orbit) constellation

- The 27 MEOs + 3 active spares

- The 24 MEOs and 3 GEOs (Geo-stationary) constellation (3 GEO for regional service, for GLOBAL service 8 GEOs arenecessary)

The goal of this work package is not to compare those constellations. Optimization of the constellation orbital parameters is theresponsibility of GalileoSat study and furthermore within GALA project, WP2.2.1 (Constellation trades-off) is in charge ofcomparing constellation performance. The objective of this WP is to assess requirements feasibility. Therefore only the baselineconstellation is included in the scope of this work package. Due to the fact that the 27/3/1 constellation appears to be morerobust to satellite failures comparing to the 30/3/0, it has been selected as baseline in GalileoSat study. Therefore thisconstellation is used for performance estimation for the final version of this document. The orbital parameters of thisconstellation are gathered in the Table 1:

Table 1: Constellation parameters

Walker constellation 27/3/1

Altitude 23616 km

Inclination 56°

Eccentricity 0

3.2 Satellite RAMS figures

Preliminary results about satellites failures were provided during the Comparative System Study phase 2 (CSS2). Thoseconclusions are present in the justification file [RD-013] and are recalled here after. They will be used in the frame of GALA inorder to assess the Galileo performance. However, let us remind that it is not the role of GALA to define accurately the satellitereliability. The goal of this document is more to take reasonable assumptions to check that the performance requirements puton Galileo global component are feasible. The RAMS figure taken into account are detailed in the following Table:


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DD-036-117

DD-036-118

DD-036-119

DD-036-120

DD-036-121

DD-036-122

DD-036-145


MEO GEO

Manoeuvres MTBM = 365 daysMTTR = 3 hours

MTBM = 15 daysMTTR = 8 hours

Short termfailures

MTBF = 625 daysMTTR = 72 hours

Long term failures MTTR = 7 days (in-orbit spares)MTBF = 22.9 years

MTTR = 5 months (on-ground spares)MTBF = 22.9 years

MTTR= Mean Time To Repair, MTBF= Mean Time Between Failure

Table 2: Constellation RAMS figure

The following assumptions are used to compute the probability of state of the constellation:

In orbit spare available to cope for long terms failure

Maneuver what ever is the state of the constellation

By processing the above figures of satellite failures with a Markov process, the following state probabilities of the constellationcan be computed. Those probability have been computed considering that the satellite has a reliability law that follows anexponential curve.

Table 3: Probability of State of the Constellation

Number of satellites operational Probability of state

27 0.844

26 0.136

25 0.017

24 2.10E-03

23 2.41E-04

22 2.65E-05


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148

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DD-036-146

DD-036-147

DD-036-148

DD-036-149


3.3 Orbit and synchronisation residual error

The trade off concerning the determination of orbit and clock characteristics of Galileo satellites has been addressed in theComparative System Study [RD-013]. For this investigation, which consider the different influence of H-maser and RAFS(Rubidium) clocks stability, it has been implemented an accurate algorithm for the Allan Variance clock model .

These analyses demonstrate that is possible to have a contribution to UERE below 1m up to 3 hours (RAFS case at ρ<0).Choosing an adequate uploading frequency for clocks corrections the URE value can reach about 0.65m. Obviously a betterbehavior versus the uploading frequency can be reached by using the H-maser clock.

This parameter had to be provided by GalileoSat to GALA. The value of 65 cm for the clock and Ephemeris budget has beenconfirmed by ESA during the GalileoSat PM2 (June 2000) and will be used in this document.


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DD-036-150

DD-036-151

DD-036-152

DD-036-154

DD-036-155


4 GALILEO Navigation performance Allocation

4.1 Overall Approach

Navigation service levels are defined in [RD-01] for each type of service, namely OAS, CAS1, SAS and GAS. As shown on thefollowing graph, those Galileo mission requirements were deduced from the user requirements. They include also services withother systems such as GPS and Loran C or hybridization. From those mission requirements, the performance have to beallocated to the Galileo system, the Galileo receiver and to the other sensors. The performance allocated to the Galileo systemand the receiver will be turned into requirements. For the other sensors, it will be managed through interface definition andperformance assumptions.

Figure 1: Performance Requirement Tree

Other systems

Galileo Mission Requirements WP 2

Performance allocation

Globalcomponent

WP 3.4

Galileo System Requirements

WP 3.4

ReceiverRequirements

Performance allocation

Regionalcomponent

Localcomponent

OtherSensors

From this allocation requirements will be provided to the global, regional and local component, the signal and the user terminal.


Index

154

155

156

ID

DD-036-187

DD-036-188

DD-036-189…


Table 4: Performance Requirement Trace-ability within GALA deliverables

Global Regional Local User Terminal SignalGlobal Services

a a aGlobal + Regional

Services a a a aGlobal + local

Services a a a

DD31 DD32 DD33 MOPS SIS-ICD

4.2 Galileo Mission Requirements

The Galileo Mission Requirements extracted from [RD-01] are detailed above:


Index ID

…DD-036-189


Accuracy Integrity

Position(NSE 95%)

Serv

ice

Leve

l

Oth

er S

yste

m

Num

ber o

fFr

eque

ncie

s

Cove

rage

(lat

)

Mas

king

Ang

le(°

)

Hor. Vert.

Velo

city

Tim

ing

Cont

inui

ty ri

sk

Risk

TTA

Hor.

Alar

mLi

mit

Vert.

Ala

rmLi

mit

Avai

labi

lity

OAS-G1 No 1 90S/90N 10 16m 36m(30m up to 75°)

50cm/s 0.1s NA NA NA NA 99%

OAS-G2 No 2 90S/90N 10 7m 15m(12m up to 75°)


OAS-GS GPS 2+2 90S/90N 10 4m 10m(8m up to 75°)


CAS1-G No 2 90S/90N 10 7m 15m(12m up to 75°)

20cm/s

10 to 20 ns static100ns dynamic

2.10-4/ hour5s outage 2.10-7/ hour 10s 20m 45m

(35m up to 75°) 99%

CAS1-GS GPS 2+2 90S/90N 10 4m 10m(8m up to 75°) NA


2.10-4/ hour5s outage 2.10-7/ hour 10s 13m 32m

(25m up to 75°) 99%

CAS1-L1 No 2 local in90S/90N 10 0.8m 1.2m

(1m up to 75°) NA10 to 20 ns static100ns dynamic

2.10-4/ hour1s outage 2.10-7/ hour 1s 2m 3.5m 99%

CAS1-L2 No 2 local in90S/90N 10 0.8m 1.2m

(1m up to 75°) NA10 to 20 ns static100ns dynamic

2.10-4/ hour5s outage 2.10-7/ hour 10s

tbc 2m 3.5m 99%

CAS1-L3 No 3 local in90S/90N 10 tbd tbd tbd Tbd tbd tbd tbd tbd tbd tbd

SAS-Gen route No 2 90S/90N 10 100

m NA 20cm/s


2.10-4/ hour10s outage 2.10-7/ hour 15s 556m NA 99%

SAS-GNPA No 2 90S/90N 10 100

m NA 20cm/s


2.10-5/ hour5s outage 2.10-7/ hour 10s 556m NA 99.9%

SAS-GCAT1 No 2 90S/90N 10 6m 6m 20cm/

s10 to 20 ns static100ns dynamic

10-5/ 15s1s outage

3.510-7/150s 6s 11m 15m 99%

SAS-GSCAT1 GPS 2+2 90S/90N 10 3m 4m 20cm/


10-5/ 15s1s outage

3.510-7/150s 6s 8m 10m 99.9%

SAS-RCAT1 No 2 local in

90S/90N 10 6m 6m 20cm/s


10-5/ 15s1s outage

3.510-7/150s 6s 11m 15m 99%

SAS-RMGPS

+ GNSS12+2 Regional –

GNSS1 10 3m 4m 20cm/s


10-5/ 15s1s outage

3.510-7/150s 6s 8m 10m 99.9%

SAS-L No 2 local in90S/90N 10 1m 1.5m 20cm/


5*10-6/ 15s1s outage

2*10-9/150s 1s 3m 5.5m 99.9%

GAS-G No 2 90S/90N 10 6m 6m 20cm/s


10-5/ 15s1s outage

3.510-7/150s 6s 11m 15m 99%

GAS-GS GPS 2+2 90S/90N 10 3m 4m 20cm/s


10-5/ 15s1s outage

3.510-7/150s 6s 8m 10m 99.9%

GAS-L No 2 local in90S/90N 10 1m 1.5m 20cm/


5*10-6/ 15s1s outage

2*10-9/150s 1s 3m 5.5m 99.9%

EGNOS-2GPS

+GNSS11 Regional

GNSS1 5° 100m - - 20 ns 2.10-5/ hour 2*10-7/ hour 10s 556m - 99.9%

EGNOS-3AGPS

+GNSS11 Europe 5° 7.7m 7.7m - 20 ns 10-6/ 150s 3.5*10-7/

150s 6s 20m 20m 95%

EGNOS-3BGPS

+GLO+GNSS1

1 Europe 5° 4m 4m - 20ns 10-6/ 150s 3.5*10-7/150s 6s 10m 10m 95%

EGNOS-3CGPS

+GNSS12 Regional

GNSS1 5° 7.7m 7.7m - 20ns 10-6/ 150s 3.5*10-7/150s 6s 20m 20m 99%


Index

157

158

159

160

161

162

163

164

ID

DD-036-201

DD-036-202

DD-036-203

DD-036-204

DD-036-205

DD-036-206

DD-036-207

DD-036-208


4.3 Architecture Identification

The goal of this chapter is to allocate the top-system requirements to the different functions of the system. The differentfunctions necessary to provide the different services are:

- The global navigation function

- The global integrity function

- The regional integrity function

- The local functions

- The receiver

The allocation of performance is made according to the system components used to provide the service. Among all the servicessome of them are provided with the same combination of components. Therefore for those services the way to perform allocationbetween components will be similar even thought the final allocate requirements might be different. From allocation point ofview, it is wise to differentiate four cases for Galileo only services:

Global Navigation Function

OAS-G1 [Accuracy only]

OAS-G2 [Accuracy only]

OAS-GS (+GPS) [Accuracy only]

SAS-G/En Route [Accuracy, Integrity and Continuity]

Global Navigation function and Global Integrity function

CAS1-G [Accuracy, Integrity and Continuity]

CAS1-GS (+GPS) [Accuracy, Integrity and Continuity]

SAS-G/NPA [Accuracy, Integrity and Continuity]

SAS-G/Cat1 [Accuracy, Integrity and Continuity]

SAS-GS [Accuracy, Integrity and Continuity]

GAS-G [Accuracy, Integrity and Continuity]


Index

188

189

190

191

192

193

194

ID

DD-036-234

DD-036-235

DD-036-236

DD-036-237

DD-036-239

DD-036-240

DD-036-241


GAS-GS (+GPS) [Accuracy, Integrity and Continuity]

Global Navigation Function and Regional Integrity function

SAS-R [Accuracy, Integrity and Continuity]

SAS-RM (+GPS) [Accuracy, Integrity and Continuity]

EGNOS 2 [Accuracy, Integrity and Continuity]

EGNOS 3A [Accuracy, Integrity and Continuity]

EGNOS 3B [Accuracy, Integrity and Continuity]

EGNOS 3C [Accuracy, Integrity and Continuity]

Global Navigation function and Local functions

CAS1-L1/2/3 [Accuracy, Integrity and Continuity]

SAS-L [Accuracy, Integrity and Continuity]

4.4 Allocation with other sytems

The other system that are candidates to be integrated with Galileo are GPS and Loran C (and UMTS). Those systems arealready in place and cannot be significantly modified in terms of performance to fulfill all the Galileo needs.

- For GPS, the system has been working for 20 years already. Its current performances are well known and some informationon the expected performance in 2010 are available.

- For Loran C, the system is also already working. Although Europe can improve Loran C zone of coverage if it appears that itprovides a real added value to Galileo, it will be difficult to improve the accuracy performance of Loran C.

Therefore the services defined with Galileo and other systems will have two different situations according to external systemsconsidered.

For systems such as Loran C or UMTS final performances will depend on expected performance of those systems andperformances expected from Galileo only. This means that, when the two systems are added “independently”:

- No specific requirements on the other systems should come from the services defined with Galileo and other systems. Theperformance estimation will be based on minimum performances expected from those other systems and the services will beprovided with the right level of quality only if the other systems are consistent with the assumptions made.


Index

195

196

197

198

199

200

201

202

ID

DD-036-242

DD-036-243

DD-036-244

DD-036-245

DD-036-246

DD-036-247

DD-036-248

DD-036-249


- No specific requirements on the Galileo system should come from the services defined with Galileo and other systems

For GPS, the situation is different. GPS and Galileo are not independent anymore since the Galileo system is required toprovide GPS integrity. Therefore the performance for the provision of this integrity service have to be specified. In that sensethe Galileo + GPS that requires GPS integrity will imply requirements on the system and demands as well an allocation. Forthose services the GPS assumptions that shall be taken into account for Galileo system design shall be clearly stated.

4.5 Accuracy

Accuracy allocation between the receiver and the SIS is made through the computation of the UERE (User Equivalent RangeError). A budget is allocated for the error that are receiver specific such as thermal noise, interference and multipath. Thoseerror budget are added to the ones that are more SIS specific such as clock and ephemeris error, ionospheric error ortropospheric error. The UERE computation is detailed in the following part of the document (Chapter 4).

4.6 Global Navigation Function Only services

4.6.1 Performance Allocation for OAS-G1 & 2

The OAS-G (1&2) services do not include any guaranty of service on integrity or continuity performance. Therefore, theallocation between elements has only to be done for the availability of accuracy of the service. The availability of accuracy is thepercentage of time for which the accuracy required is achieved. The following trees shows a preliminary allocation between thedifferent elements of the global component. Indeed for such a service, since it is only provided by the global component, does notimply any specific requirements in terms of performance on the Regional or Local components. The availability are even onlyallocated to the SIS. The target for OAS is mass market, it means people that want to buy cheap receiver. Furthermore,although specifying a SIS availability makes sense, for the receiver parameter such as MTBF and especially MTTR are left toreceiver manufacturer and service provider.

Within the SIS, the availability is split between the ranging function and the communication function. A first apportionment isto put the lack of availability due to navigation message out of date negligible comparing to the lack of availability due satellitegeometry which is much more demanding. However these are only preliminary results. This is not the task of GALA to allocatethe performance between the elements of a same component. Concerning the constellation availability, it appears not possibleto go deeper in the allocation with this kind of approach. Indeed, the geometry availability will be the average of the availabilityobtained with different failure scenarios weighted by the probability of occurrence of those scenarios. Therefore only a Globalnumber can be specified. The impact of one failure has to be traded off with the constellation design and the robustness ofGalileo satellites.


Index

203

204

205

206

207

ID

DD-036-250

DD-036-251

DD-036-253

DD-036-254

DD-036-255


RQ-Gl The global navigation function shall be able to support an OAS-G1 service with an availability of 99%.

RQ-Gl The global navigation function shall be able to support an OAS-G2 service with an availability of 99%.

Figure 2: Availability Allocation Tree for OAS-G1/2Availability of Accuracy

0.99

RxNot included in Perf budget

SIS0.99

Nav messageout of date

0.999

OSS

OSPF

GWAN

ULS

GeometryHNSE<Accuracy limit

0.99

SatelliteFault-free

1 failure 2 failures 3 failures

Fault freeAvailability

1 failurestate probability

2 failuresAvailability

3 failureAvailability

1 failureavailability

2 failuresstate probability

Fault freestate probability

3 failuresstate probability

Global

Global

4.6.2 Integrity Performance Allocation for SAS-G/En Route

For some of the services no GIC is available to fulfill the integrity requirements. For OAS services the consequences are notimportant since no integrity requirements are officially specified for integrity. However, for a SAS-G to be used for safetycritical application in a global basis, RAIM has to be used to insure the system integrity.


Index

208

209

210

211

212

213

214

215

216

217

ID

DD-036-256

DD-036-257

DD-036-258

DD-036-259

DD-036-260

DD-036-261

DD-036-262

DD-036-263

DD-036-265

DD-036-266


The budget is first split between the SIS and the receiver. Within the SIS two situations occur. The nominal case where thereare no error on the pseudo-range. This one is the most probable and its probability of occurrence is close to 1. The secondsituation is when a single failure arises on one measurement without warning from the SIS. When no GIC is present theprobability of occurrence of this event is not negligible and has to be taken into account. On the contrary when GIC is present,the space segment is closely monitored by a ground segment that will generate flags as soon as a failure occurs on one satellite.Therefore the probability of undetected failure remains low. Without GIC, failure shall be detected by the RAIM.

The final integrity risk will then depend from :

- the Probability of occurrence of a failure

- the Miss detection probability of the RAIM

In order to get a clear idea of the final user integrity risk, a thorough identification of the failure mode has to be done. Once thisinformation is available, it will be possible to tune the performance of integrity risk mitigation techniques and conclude on thefinal system performance in terms of integrity and availability. Since, until now neither the failure mode nor their probabilityof occurrence are clearly identified, assumptions relying on what has been observed with the other radio navigation systemshave been taken.

First, two integrity macro failure mode are selected:

- Misleading information due to satellite failure

- Misleading information due to local effects

For the first failure mode, no specific data is available for Galileo. This is not surprising since this kind of parameter is usuallyassessed with measurement campaigns and detailed RAMS analysis. Nevertheless some information are available for GPS. According to the WAAS-MOPS [RD-014], the hazardous failure rate for one GPS satellite among 24 is 10-4/h. The same valuewill be used for Galileo.

For local effects, information dealing with occurrence probability are not available even for GPS. Therefore the conservativestrategy selected is the following. Since no information is available in local effects and in order not to neglect one failure modecomparing to the other, the value selected for satellite failure mode is selected for local effects as well.


Index

218

219

220

221

222

223

224

225

ID

DD-036-267

DD-036-268

DD-036-269

DD-036-270

DD-036-271

DD-036-272

DD-036-273

DD-036-274


Once the integrity risk due to one failure is specified using a top-down approach from the user needs and that the failure modesare identified, the RAIM can be tuned to meet the requirements. For SAS-G service the RAIM miss detection is specified at 2.5

10-4.

The third cases mentioned in the allocation tree is the probability that the user is confronted to a multiple failure configuration. It means that several range measurement are corrupted. Multiple failure can arise from the combination of two independent

single failures. In that case, if the probability of having one failure is assumed equal to 10-4/h the probability to have two is

equal to 10-8/h. This probability is of the same order of magnitude of the risk budget for fault free and single failure cases.

However, although the RAIM is designed for single failure cases, its detection performances is not null for multiple failure

cases. Assuming a RAIM miss detection probability of 10-2 is enough for the risk due to multiple failure being negligible.

However, another source of multiple failure is the common mode of failure (i.e: one event may cause a failure on severalsatellites). Typically, an error in the ephemeris determination will have an impact on several satellites. Therefore theprobability of event of common failure mode has to be specified. In order not to impact the total integrity risk, the specification

for multiple SIS HMI has been selected equal 10-8/h which is equal to the same order of magnitude of the multiple failuresevents caused by independent single failures combination

Depending of the user situation the integrity risk can be allocated differently on the horizontal and vertical component. In thecase that both components matter, the risk will be allocated part on the vertical and part on the horizontal component. Forusers such as civil aviation, one dimension is always favored (horizontal for En Route, vertical for Cat 1) and all the risk isallocated to it. For SAS-G/En route, no requirement is identified in horizontal, therefore all the risk is allocated to the verticalperformance.

RQ-Gl The probability that the global navigation function sends a hazardous misleading information to theSAS-G/En Route user though the SIS affecting a single satellite shall be less than 1E-4/h.

RQ-Gl The probability that the global navigation function sends a hazardous misleading information to theSAS-G/En Route user though the SIS affecting a several satellites shall be less than 1E-8/h.

RQ-Rx The integrity risk due to the SAS-G/En Route user segment shall be less than 1E-7/h. User integrity risk covers theprobability of the user segment to generate on its own a misleading information due to hardware or software. Integrity riskdue to RAIM algorithm performance is not included in the integrity risk user segment budget.


Index

226

227

228

ID

DD-036-275

DD-036-276

DD-036-277


The TTA specified for the SAS-G/En Route service is equal to 15 seconds. However the service tolerate a 10 seconds outagewithout service interruption. Therefore 5 seconds remain left for integrity determination using RAIM. The RAIM specified inthe MOPS/RTCA ([RD-014]) and that has been selected in GALA as well is a snapshot algorithm. Therefore the performanceare defined assuming only one measurement. Therefore removing the contribution of the receiver the TTA allocated to theglobal navigation function cannot be less than 1 second. Therefore the TTA allocation between the global navigation functionand the receiver is as follows:

RQ-Sg The signal structure shall allows to provide a pseudo-range measurement at least every second.

RQ-Rx In case of a failure detectable by RAIM, the period between the instant when a faulty pseudo-range is used in thenavigation solution and the instant that an alarm is displayed to the user shall not exceed 4 seconds.


Index

229

230

231

ID

DD-036-279

DD-036-280

DD-036-281


Figure 3: Integrity Allocation Tree for SAS-G/En Route service

Rx Integrity Risk

User Integrity Risk2E-7/h

Fault-free Integrity Risk

5E-8/h

XNSE>XPLin nominal case

5E-8/h

Fault-Free stateProbability

≈ 1

1E-7/h

Single failure Integrity Risk

5E-8/h

XNSE>XPLwith one failure

≈ 1

Undetected single failure probability

5E-8/h

Multiple failure Integrity Risk

Negligible

Single SIS failure2E-4/h

RAIM miss detection

2.5E-4

Single SIS due to localeffect1E-4/h

Single SIS due tosatellite failure

1E-4/h

Probability UnknownGPS figure extracted

from MOPS

or

or

and and

and

GLOBAL

Independent failure mode

1E-8/h(estimation)

Common failure mode

1E-8/h

HMI on data message

RAIM≈1E-2

Multiple failureProbability

2E-8/h

and

GLOBAL

4.6.3 Continuity Performance Allocation for SAS-G/En Route

The continuity risk is allocated between the receiver, the geometric performance of the constellation and the RAIM false alarm. The budget on the RAIM false alarm is 10-5/h for SAS-G/En Route service which is similar to the MOPS requirements for EnRoute phase of flight. The number of independent samples in one hour is assumed equal to 10. Therefore the RAIM false alarm

probability is selected at 10-6 per independent samples. As for the miss detection this budget has to be split into two budgets,one for horizontal and one for vertical dimension.


Index

232

233

234

235

236

237

ID

DD-036-282

DD-036-283

DD-036-285

DD-036-286

DD-036-287

DD-036-288


RQ-Gl The probability to loose the SAS-G/En Route service because of a failure on the Global navigation function shall be lessthan 5E-5/h. (The interruption due to RAIM false alarm are not covered by this budget).

RQ-Rx The probability of failure of the SAS-G/En Route user segment shall be less than 2E-4/h

Figure 4: Continuity Allocation in Global for SAS-G/En Route

SIS1E-4/h

XPL>XAL9E-5/h

Loss of Continuitydue to Satellite

Failure5E-5/h

Loss of Continuitydue to Local Effects

(Interference/Masking)4E-5/h

RAIMfalse alarm

1E-5/h

Receiver1E-4/h

Continuity Risk2E-4/h

or

or

or

Global

4.6.4 Availability Performance Allocation for SAS-G/En Route

For the same reasons mentioned above for OAS service the receiver is not included in the availability performance budget. Theavailability required is in fact the SIS availability. It is again split between the navigation function and the communicationfunction. The criteria to declare the system available is that the protection level computed with RAIM is to be less than thealarm limit.

RQ-Gl The unavailability of the SIS SAS-G/En Route service due to the global navigation function shall be less than 1E-2. The availability includes availability of:


Index

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

ID

DD-036-289

DD-036-290

DD-036-291

DD-036-292

DD-036-293

DD-036-294

DD-036-295

DD-036-296

DD-036-297

DD-036-298

DD-036-299

DD-036-300

DD-036-301

DD-036-302

DD-036-303

DD-036-304

DD-036-305


- Accuracy at 95%, 100m horizontal

- Integrity provided by RAIM in for a HPL of 556m with 2.5E-4 miss detection probability and 1E-6 false alarm probability

- Continuity with a continuity risk less than 5E-5/h

4.7 Global Navigation Function + Global Integrity Function

4.7.1 Integrity Performance Allocation for CAS1-G

4.7.1.1 GIC and RAIM allocation

The CAS1 users have at their disposal at system level two barriers that they can use to set their final integrity risk: the GIC(Galileo Integrity Channel) and the RAIM (Receiver Autonomous Integrity Monitoring). Those two techniques have differentfeatures:

- GIC

- Able to detect and isolate multiple satellites failure

- Less demanding in terms of availability

- Unable to detect local effects

- RAIM

- Able to detect local effects

- Able to detect single satellite failure.

- Detection capacity very demanding in terms of availability

- Failure isolation possible but much too demanding in terms of availability

- Performance against multiple failure not very well characterized


Index

255

256

257

258

259

260

261

262

ID

DD-036-306

DD-036-307

DD-036-308

DD-036-310

DD-036-311

DD-036-315

DD-036-316

DD-036-317


As mentioned for the SAS-G service the weak point on performance allocation trees at this stage of the study is theidentification of the failure mode with their probability of occurrence. In the case that both local and satellite failure have asame probability of occurrence equal to 10-4/h, two options concerning GIC and RAIM allocation are identified. In the twooptions the shall have a “GIC and RAIM” integrity algorithm available for integrity.

4.7.1.1.1 Option 1: Serial Allocation

In that option, as showed in the following figure, the two barriers that are GIC and RAIM are placed in series. However, sincethe assumptions made were to have the same probability of occurrence on local effects and satellite failures, this option is notrelevant. Indeed, since the RAIM has to detect local effects, its miss detection probability cannot be reduced significantly, evenif the GIC allows to detect part of satellite failures.

Figure 5: Serial GIC/RAIM AllocationSIS failure due to local effects

1E-4/h

SIS failure dueto satellite failure

1E-4/h

GIC miss detection

1E-3

RAIMmiss detection

1E-3


or

For this combination to be relevant, two assumptions should be made:- Probability of occurrence of local effects is much lower than the probability of occurrence due to satellite failure

And- The detection performance of GIC and RAIM are not correlated ( i.e: the integrity events not detected by the RAIM aredifferent from the ones not detected by the GIC).

Although those two assumptions might be true, there are far to be proven at the moment. Therefore it does not appear safe atthis stage of the project to go on with a serial approach

4.7.1.1.2 Option 2: Parallel Allocation

In that option, the two barrier that are GIC and RAIM are placed in parallel in the integrity tree. RAIM is in charge to detectlocal effects and GIC has to detect satellite failures.


Index

263

264

265

266

267

268

269

270

271

272

ID

DD-036-318

DD-036-320

DD-036-321

DD-036-322

DD-036-323

DD-036-324

DD-036-325

DD-036-326

DD-036-327

DD-036-328


Figure 6: Parallel GIC/RAIM AllocationSIS failure due to local effects

1E-4/h

SIS failure dueto satellite failure

1E-4/h

GIC miss detection

1E-3

RAIMmiss detection

1E-3


or

From performance point of view this option has two advantages:

- It allows to provide specification on GIC independently from the ones put on RAIM.

- The user integrity risk is conservative since RAIM will also anyway impact the risk due to satellite failures.

Since this option appears much safer in the risk estimation it is the one selected for the GIC/RAIM allocation.

However, in that situation, if the local effect probability is estimated similar to the satellite failure probability, the missdetection and false alarm probability put on the RAIM will be quite stringent. Therefore the final service availability will betotally driven by the RAIM availability. Since the RAIM is very demanding in terms of availability, meeting the requirementsas they are expressed in the mission requirements with Galileo RAIM only will be impossible except by doubling the number ofGalileo satellites. In order to relax RAIM requirements , what could be done is, instead of splitting 50/50 the budget on localeffects and satellite failure as it is done in Figure 6, to allocate the main part of the total user integrity risk on the local effects. But this would improve marginally the situation. It would two effects:

- The miss RAIM probability will be multiplied by two. This would have a marginal impact from RAIM availability since RAIMavailability depends also from false alarm requirements. To really improve RAIM availability, detection performance should berelaxed of a factor of 10.

- The GIC requirement will be made more stringent of a factor of 10. This appears not wise since real GIC potentialperformance are not fully characterized.

Therefore local effects will have to be dealt partly:


Index

273

274

275

276

277

278

279

280

281

ID

DD-036-329

DD-036-330

DD-036-331

DD-036-332

DD-036-333

DD-036-334

DD-036-335

DD-036-336

DD-036-337


- With receiver detection techniques for multipath and interference. This will have as impact to decrease the probability ofoccurrence of local effects at RAIM input

- And with RAIM but augmented with other system (GPS, GLONASS…) or other sensors (INS, baro-altimeter or clocks).

Therefore the specifications put on RAIM on the following sections will be assumed to be fulfilled by combining the twotechniques mentioned above.

Furthermore since RAIM/AAIM performance will most likely depend much more from the type of hybridization used than theconstellation performance itself, no RAIM specifications will be put on the global component. The strategy will be to assesswhat is available in terms of RAIM performance from the constellation and to see what is missing in terms of on boardaugmentation to fulfill the requirements for local effect detection. For trace-ability of the requirements, the RAIM specificationwill nevertheless remain as NCDP (Non Critical Design Parameter) on the global component.

4.7.1.1.3 User Integrity Risk Allocation tree

The risk at user level is first allocated between the SIS and the receiver. Risk on the receiver does not include RAIM. RAIM isan algorithm specified at system level. Therefore, although it is implemented in the receiver, its performance depends on theSIS. Receiver integrity risk includes all the HMI (hazardous misleading information) generated by a malfunction of thehardware or software. Nevertheless, although such requirements might be achievable with enough redundancy it will make thereceiver very expensive. Although it might not be a problem for SAS users, it will certainly be for CAS1 users. Nevertheless,according to user need in integrity requirements, the receiver specification can be relaxed. The important point from the SISside is to make sure that the user is provided with a SIS that can allow him to reach a 10-7/h integrity risk.

On the SIS the risk is split into three categories:

- Fault-Free: This is the user risk when the system is working nominally. This risk is not zero since normal distribution areassumed to model the errors. Therefore there is always a risk to be out of the protection level without having any failure on thesystem.

- Risk due to a single SIS failure: This is the user risk when a failure arise on one SIS. The probability that a failure on the SISwill lead to a position error exceeding the specified alarm limit is estimated to 1. Therefore the risk in this situation will bemainly driven by the probability of having a undetected (by GIC or RAIM) single failure at user level.


Index

282

283

284

285

ID

DD-036-338

DD-036-340

DD-036-341

DD-036-342


- Risk due to multiple SIS failure The situation is the same as for single failure integrity risk. Furthermore, since theprobability of having multiple failure is already low, the probability of having undetected multiple failures appears negligiblecomparing to other source of integrity risk.

Figure 7: Integrity performance allocation at system level for CAS1-G serviceUser Integrity Risk

2E-7/h

Fault-free Integrity Risk

5E-8/h

XNSE>XPLin nominal case

5E-8/h


≈ 1

Rx Integrity Risk1E-7/h

Single failure Integrity Risk

5E-8/h


≈ 1


5E-8/h


Negligible

XNSE>XPLwith multiple

Failure

Undetected multiplefailure probability

1E-10/h

RAIM miss detection

2.5E-4

Single SIS due to localeffect

1E-4/h

Undetected Globalsingle SIS by GIC

2.5E-8/h

Global Single SIS

1E-4/h

GIC single failure miss detection

2.5 E-4

Multiple SISdue to local

Effect1E-8/h

Multiple SIS failureincluding an undetected

satellite failurenegligible

Global multiple SIS

GIC multiple failure miss detection

Undetected Localsingle SIS by RAIM

2.5E-8/h

and and

and and

and

or

or

or

and

GIC/RAIM

RAIMmiss detection

1E-2

≈ 1

and

This tree allows to deduct the performance that shall be assessed from the global component designer in order to fulfill theglobal user integrity risk requirement. In the next part, this performance will be allocated on the different functions of theglobal component.

RQ-Rx The integrity risk due to the CAS1-G user segment shall be less than 1E-7/h. User integrity risk covers the probabilityof the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithm performance is notincluded in the integrity risk user segment budget.


Index

286

287

288

289

290

291

292

293

ID

DD-036-343

DD-036-344

DD-036-345

DD-036-346

DD-036-347

DD-036-348

DD-036-349

DD-036-351…


4.7.1.2 Integrity Risk Allocation within Global component

The risk due to a single failure, as explained before for the RAIM, depends on two parameters:

- The probability to have a failure

- The probability of miss detection of this failure

The first parameters depends from the satellites and control segment but also from the orbito & synchro component of themission segment. Indeed this failure mode includes also the eventuality of the broadcast of a corrupted SISA to the users.

The second parts concerns the ability of the ground segment monitoring to detect an event and broadcast a alarm to the userwithin the TTA required. This function is split between the detection function and transmission function. The detectioncomponent includes the monitoring station and the integrity processing facility algorithms. The transmission componentsincludes the chain from the integrity processing facility to the user.

It has to be pointed out that the elements mentioned in this figure are the ones currently identified in GALA architecture. However, the requirements expressed in this document are relatively independent from the architecture considered. Therequirements are put on functions and not on elements.

Figure 8: Integrity Risk Allocation between elements of the Global component


Index

294

295

ID

…DD-036-351

DD-036-352

DD-036-353



2.5E-8/h

Global Single SIS

1E-4/h


1.5E-4

Invalid SISA At SV output

1E-5/h

Corruption of valid SISA in SIS

1E-8/h

Satellite not monitored not flaggedNegligible

Miss transmissionof Alert within TTA

1.5E-4

SatelliteFailure1E-4/h

Miss Detectionwithin T1*

1E-4

Transmission failurewithin T2*

5E-5

Transmissionfrom IPF to GUI

2E-5

Transmission fromGUI to Satellite

2E-5

Integrity message loss due to biterror rate

1E-5Transmission delay

Data corruption

Transmission delay

Data corruption

*T1=Allocated budget for detectionT2=Allocated budget for transmissionTTA=T1+T2

GLOBALand

oror

or

or

or or

or

From this tree, it is possible to identify requirements for the navigation message robustness:

- Among the 10s TTA, 1 second is assumed allocated to the message. The structure of the message is also assumed synchronouswith frames of 1 second. Therefore if the alarm message is lost or not decoded correctly the TTA cannot be met. The probabilitytolerated for this kind of event is 10-5. Therefore the probability to loose an integrity message shall be less than 10-5. The lossof a message can come either of incoherence detected but not corrected in the message by the CRC or from an error in themessage not detected by the CRC. At first sight the probability of the second event appears very remote comparing to the firstone.


Index

296

297

298

299

300

301

ID

DD-036-354

DD-036-355

DD-036-356

DD-036-357

DD-036-358

DD-036-359


- The integrity flags provide information on the correctness of the SISA. SISA provides information on the correctness on orbitosynchro parameters. In order to ensure integrity it is very important for those parameters to be coherent with one another. Therefore the probability to have an HMI generated by the message on SISA and orbito synchro parameters has to be veryremote. The integrity risk allocated to this event is estimated at 10-8/h

It is also important to keep in mind that signal design is not a task that is in the scope of the global component designer. Therefore, since the bit error rate impacts the integrity risk as described above, the integrity risk requirements of 1.5E-8/h thathas to be fulfilled by the global components assuming a loss of message due to bit error rate of 1E-5. This figure is a necessaryinput for the Global component design has to be provided by GALA. This is done through the Signal In Space ICD. That is puton the global component designer to be used as inputs. For specification purpose, it may be wise to allocate performance to theglobal component assuming a “fault-free” SIS. In that case the specification would be as follow:

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the CAS1-G userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 1.5E-8/h.

4.7.1.3 Time To Alarm Allocation

The following graph shows an apportionment between the system and the receiver for the time to alarm:


Index

302

303

304

305

306

307

ID

DD-036-361

DD-036-362

DD-036-363

DD-036-364

DD-036-365

DD-036-366


Figure 9: Time To Alarm allocation for CAS1-G service

GMS GPF GUI ULS

MEO

User

Integrity Event

0.8s5.2s without message loss (Up to 9.2s with message losses)

Global

Alarm

For CAS1 the TTA requirements coming from user needs is equal to 10 seconds. However since other services demand a 6second TTA, the Galileo infrastructure will have to be able to provide 6 seconds TTA to users. Therefore, the requirementsallocated to the global component will be in line with a 6 seconds time to alarm. The other part of the budget is allocated to thesignal. It means that the alarm will be repeated at least five times and that the user can afford to loose 4 message withoutrisking to miss it or to jeopardize the 10s TTA performance.

RQ-Gl The TTA allocated to global component of the integrity function for CAS1-G service is equal to 5.2 seconds. It includesthe time to detect the misleading information and transmit it to the receiver antenna in nominal conditions (ie without loss ofmessage).

RQ-Rx The time elapsed between the moment when an alarm arrives at the CAS1-G receiver and the alarm is displayed to theuser shall not exceed 0.8s

RQ-Sg When an integrity alarm is sent to the user, it shall be available in the message for 5 seconds. The loss of an integrityalarm message due to bit error rate on CAS1-G service shall not exceed 1E-5

RQ-Sg The probability that the an HMI is generated within the CAS1-G navigation message due to bit error rate shall be lessthan 10-8/h


Index

308

309

310

311

312

313

314

315

316

ID

DD-036-367

DD-036-368

DD-036-369

DD-036-370

DD-036-371

DD-036-372

DD-036-373

DD-036-374

DD-036-375


4.7.2 Integrity Performance Allocation for CAS1-GS

As mentioned above, the parameter that is specified to the global component is the probability of undetected failure. Thisparameter depends of the satellite failure probability and the detection performance of the ground segment. Since, in globalthe space and mission segment are in charge of one entity , it is up to it to allocate the performance on those two functions. However, in the case that Galileo has to provide integrity for GPS, the situation is different. Since GPS constellation is notunder Galileo control, it may be necessary to go one step further in the allocation and starting from an estimation of the GPSfailure rate probability, derive a requirement for failure detection performance.

Providing GPS integrity may have a major impact on the ground segment dimensioning:

- First, if the number of satellite is doubled, the failure rate is doubled as well, and then to keep the same integrity risk got withGalileo only, the ground segment should have performance assessment that are better. This is mainly due to the fact that thetarget in terms of alarm limit for the services including GPS are smaller than the one considered for service provided by Galileoonly.

- Next, in order to detect failure on the system, ground monitoring may not be the only answer. Many checks can beimplemented on board, and then the risk could be allocated between on-board test on-ground test. With GPS satellite, thisapproach is no longer possible to consider. Therefore all the detection performance have to be put on the ground segment.

For the time being, The same logic that has been used to deduct CAS1-G requirements will be used for CAS1-GS requirements. Bit this kind of requirements will have to be completed by the assumptions that shall take into account the designer on the GPSconstellation. Those information are indispensable since the Galileo designer does not control GPS performance.

For this service and all the ones that will be provided by with GPS, the navigation function is supported by Galileo and GPSspace segment.

RQ-Rx The integrity risk due to the CAS1-GS user segment shall be less than 1E-7/h. User integrity risk covers the probabilityof the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithm performance is notincluded in the integrity risk user segment budget.

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the CAS1-GS userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 1.5E-8/h.


Index

317

318

319

320

321

322

323

324

325

326

327

ID

DD-036-376

DD-036-377

DD-036-378

DD-036-379

DD-036-380

DD-036-381

DD-036-382

DD-036-383

DD-036-384

DD-036-385

DD-036-386


RQ-Gl The TTA allocated to global component of the integrity function for CAS1-GS service is equal to 5.2 seconds. It includesthe time to detect the misleading information and transmit it to the receiver antenna in nominal conditions (ie without loss ofmessage).

RQ-Rx The time elapsed between the moment when an alarm arrives at the CAS1-GS receiver and the alarm is displayed tothe user shall not exceed 0.8s

RQ-Sg When an integrity alarm is sent to the user, it shall be available in the message for 1 seconds. The loss of an integrityalarm message due to bit error rate on CAS1-GS service shall not exceed 1E-5

RQ-Sg The probability that the an HMI is generated within the CAS1-GS navigation message due to bit error rate shall be lessthan 10-8/h

4.7.3 Integrity Performance Allocation for SAS/NPA

At system level the integrity tree used to allocate the risk between GIC and RAIM for SAS-G/NPA service is quite similar to theone used for CAS1-G. This is due to the fact that the overall architecture used for those two services is similar. The same logichas been used to deduct CAS1-G requirements:

RQ-Rx The integrity risk due to the SAS-G/NPA user segment shall be less than 1E-7/h. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget.

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the SAS-G/NPA userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 1.5E-8/h.

RQ-Gl The TTA allocated to global component of the integrity function for SAS-G/NPA service is equal to 5.2 seconds. Itincludes the time to detect the misleading information and transmit it to the receiver antenna in nominal conditions (ie withoutloss of message).

RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-G/NPA receiver and the alarm is displayed tothe user shall not exceed 0.8s

RQ-Sg When an integrity alarm is sent to the user, it shall be available in the message for 1 seconds. The loss of an integrityalarm message due to bit error rate on SAS-G/NPA service shall not exceed 1E-5


Index

328

329

330

331

332

333

334

ID

DD-036-387

DD-036-388

DD-036-389

DD-036-390

DD-036-391

DD-036-392

DD-036-394…


RQ-Sg The probability that the an HMI is generated within the SAS-G/NPA navigation message due to bit error rate shall beless than 10-8/h

4.7.4 Integrity Performance Allocation for SAS-G/Cat 1

At system level the integrity tree used to allocate the risk between GIC and RAIM for SAS-G/Cat 1 service is quite similar to theone used for CAS1-G. This is due to the fact that the overall architecture used for those two services is similar.

However, one important point is that the two services do not have the same requirements. Therefore, the integrityrequirements allocated on the different components may be different for the two services. For the global component that are thesame ones for the two services, the requirements should as far as possible remain the same. In the case that they weredifferent, only the most stringent would be applicable.

The probability of occurrence of local events or satellite failures has been kept similar to the one used for global services. Thefollowing trees show how the integrity risk is allocated first at system level between GIC and RAIM and next within the Galileoglobal component.

As far as time to alarm is concerned the requirements for SAS-G/Cat1 service is equal to 6 seconds. Therefore the allocation tothe global component is kept equal to 5.2 without loss of message. The allocation to receiver is kept equal to 0.8s. Concerningthe signal, the time allocated is reduced from 5 to 1 second. Therefore the alarm does not need to be repeated several times.

Figure 10: Integrity performance allocation at system level for SAS-G/Cat1 service


Index

335

336

ID

…DD-036-394

DD-036-395

DD-036-397…


User Integrity Risk3.5E-7/150s

Fault-free Integrity Risk1E-7/150s

VNSE>VPLin nominal case

1E-7/150s


≈ 1

Rx Integrity Risk1.5E-7/150s

Single failure Integrity Risk1E-7/150s


≈ 1


1E-7/150s


Negligible

XNSE>XPLwith multiple

failure

Undetected multiplefailure probability

RAIM miss detection

1.25E-2

Single SIS due to localeffect

4E-6/150s1E-4/h


5E-8/150s

Global Single SIS

4 10-6/150s1E-4/h


1.25E-2

Multiple SISdue to local

effect Undetected Globalmultiple SIS by GIC

Global multiple SIS

GIC multiple failure miss detection

Undetected Localsingle SIS by RAIM

5E-8/150s

and

or

oror

and and

and and

and

RQ-Rx The integrity risk due to the SAS-G/Cat1 user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget.

Figure 11: Integrity risk allocation within the Galileo global component for SAS-G/Cat1


Index

337

338

339

ID

…DD-036-397

DD-036-398

DD-036-399

DD-036-400



5E-8/150s

Global Single SIS

4E-6/150s


7.5E-3

Invalid SISA At SV output4E-8/150s



7.5E-3

Satellitefailure

4E-6/150s


5E-3

Transmission failurewithin T2*2.5E10-3


1E-3

Transmission fromGUI to User

1E-3

Integrity message loss due to bit error

rate5E-4

Transmission delay

Data corruption

Transmission delay

Data corruption


Corruption of validSISA in SIS2E-8/150s

and

or

or

or

oror

Global

As for CAS1-G service, those trees allow to deduct the following requirements on the global component, the receiver and thesignal:

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the SAS-G/Cat1 userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 3E-8/150s. This figuresassumes a loss of message probability due to bit error rate of 5E-4.

RQ-Gl The TTA allocated to global integrity function for SAS-G/Cat1 service is equal to 5.2 seconds. It includes the time todetect the misleading information and transmit it to the receiver antenna.


Index

340

341

342

343

344

345

346

347

348

349

350

351

ID

DD-036-401

DD-036-402

DD-036-403

DD-036-404

DD-036-405

DD-036-406

DD-036-407

DD-036-408

DD-036-409

DD-036-410

DD-036-411

DD-036-412


RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-G/Cat1 receiver and the alarm is displayed tothe user shall not exceed 0.8s

RQ-Sg The loss of an integrity alarm message due to bit error rate on SAS-G/Cat1 service shall not exceed 5E-4.

RQ-Sg The probability that a HMI is generated within the SAS-G/Cat1 navigation message due to bit error rate shall be lessthan 2 10-8/150s

4.7.5 Integrity Performance Allocation for SAS-GS/Cat1

RQ-Rx The integrity risk due to the SAS-GS/CAT1 user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget.

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the SAS-GS/CAT1user without that the global integrity function sends a warning within the TTA allocated shall be less than 3E-8/150s. Thisfigures assumes a loss of message probability due to bit error rate of 5E-4.

RQ-Gl The TTA allocated to global integrity function for SAS-GS/CAT1 service is equal to 5.2 seconds. It includes the time todetect the misleading information and transmit it to the receiver antenna.

RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-GS/CAT1 receiver and the alarm is displayedto the user shall not exceed 0.8s

RQ-Sg The loss of an integrity alarm message due to bit error rate on SAS-GS/CAT1 service shall not exceed 5E-4.

RQ-Sg The probability that a HMI is generated within the SAS-GS/CAT1 navigation message due to bit error rate shall be lessthan 2 10-8/150s

4.7.6 Integrity Performance Allocation for GAS-G

The way to allocate integrity risk performance is for GAS-G service is very similar to the one used for SAS-G/Cat1. Since therequirements in terms of integrity risk are exactly the same the allocation trees are also identical. It allows to deduct thefollowing requirements:


Index

352

353

354

355

356

357

358

359

360

361

362

363

ID

DD-036-413

DD-036-414

DD-036-415

DD-036-416

DD-036-417

DD-036-418

DD-036-419

DD-036-420

DD-036-421

DD-036-422

DD-036-423

DD-036-424


RQ-Rx The integrity risk due to the GAS-G user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget.

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the GAS-G userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 3E-8/150s. This figuresassumes a loss of message probability due to bit error rate of 5E-4.

RQ-Gl The TTA allocated to global integrity function for GAS-G service is equal to 5.2 seconds. It includes the time to detectthe misleading information and transmit it to the receiver antenna.

RQ-Rx The time elapsed between the moment when an alarm arrives at the GAS-G receiver and the alarm is displayed to theuser shall not exceed 0.8s

RQ-Sg The loss of an integrity alarm message due to bit error rate on GAS-G service shall not exceed 5E-4.

RQ-Sg The probability that a HMI is generated within the GAS-G navigation message due to bit error rate shall be less than 210-8/150s

4.7.7 Integrity performance allocation for GAS-GS service

RQ-Rx The integrity risk due to the GAS-GS user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget.

RQ-Gl The probability that the global navigation function sends an hazardous misleading information to the GAS-GS userwithout that the global integrity function sends a warning within the TTA allocated shall be less than 3E-8/150s. This figuresassumes a loss of message probability due to bit error rate of 5E-4.

RQ-Gl The TTA allocated to global integrity function for GAS-GS service is equal to 5.2 seconds. It includes the time to detectthe misleading information and transmit it to the receiver antenna.

RQ-Rx The time elapsed between the moment when an alarm arrives at the GAS-GS receiver and the alarm is displayed to theuser shall not exceed 0.8s

RQ-Sg The loss of an integrity alarm message due to bit error rate on GAS-GS service shall not exceed 5E-4.


Index

364

365

366

367

368

369

370

371

372

373

374

375

ID

DD-036-425

DD-036-426

DD-036-427

DD-036-428

DD-036-429

DD-036-430

DD-036-431

DD-036-432

DD-036-433

DD-036-434

DD-036-435

DD-036-436


RQ-Sg The probability that a HMI is generated within the GAS-GS navigation message due to bit error rate shall be less than2 10-8/150s

4.7.8 Continuity Performance Allocation for CAS1-G

CAS1-G service has a continuity requirement. However, although the service is provided on a global basis by the globalcomponent, the mission requirements cannot be directly applied as system requirements. Even once the receiver contributionhas been removed, there are several parameters that are not in the scope of the global component and that impacts thecontinuity performance of the system. For instance, all that is dealing with local effects and signal performance should beremoved from the performance budget specified to the Global component.

The following tree represents the allocation of continuity risk between the different function of the system. The first step is toallocate between the receiver and the SIS.

The first arm on the SIS part is an allocation on the geometry. A degradation of the geometry during an approach can be due toa loss of one or several satellites. The rest of the budget is allocated to the RAIM false alarm and the loss of integrity function.

The continuity risk allocation induces a specification on the bit error rate. On this topic, it is interesting to note in the missionrequirements that an interruption of 5 seconds is allowed without interruption of service. Therefore, to loose continuity, theuser has to miss 5 messages in a row. Therefore, the message shall be designed in a way that the probability to miss 5 messagesconsecutively is less than 1E-6/h.

This allocation tree allows to deduct the following requirement on the global system component that provides CAS1-G service. This global component includes the navigation function and the global Galileo integrity channel.

RQ-Gl The probability to loose the CAS1-G the global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 3.5E-6/h

RQ-Gl The probability to loose the CAS1-G global integrity function because of the loss of data flow within the global integrityfunction shall be less than 4E-5/h

RQ-Gl The probability to loose the CAS1-G global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 1E-6/h

RQ-Rx The probability to loose the CAS1-G service because of a failure in the user terminal shall be less than 1E-4/h

RQ-Sg The probability to loose the CAS1-G service because of a loss of message shall be less than 1E-6/h


Index

376

377

378

ID

DD-036-438

DD-036-439

DD-036-440


Figure 12: Continuity performance allocation for CAS1-G service

SIS1E-4/h

XPL>XAL4E-5/h

Loss of continuity

due toSatelliteFailure4E-6/h

Loss of continuity

due toGIC false

alarm3E-5/h

Los of continuitydue satellites not monitored

1E-6/h

Loss of IMS data

RAIM false alarm1E-5/h

Loss of Ground Integrity function

5E-5/h

No satellites broadcasting integrity above 25 degrees

Elevation angle1E-6/h

Loss ofsatellite

Data flow1E-5/h

Loss of IntegrityData from IPF

to GUI2E-5h

Loss of IntegrityData from GUI

to Satellite2E-5/h

No reception linkwith any satellites

broadcasting integrity 9E-6/h

Loss of continuitydue to a loss of message

error rate1E-6/h

Local effectsMasking/Interference

9E-6/h

Receiver1E-4/h


Local Effects(Interference

/Masking)5E-6/h

or

or

or

Global

Global

or

or

or

4.7.9 Continuity performance allocation for CAS1-GS service

RQ-Gl The probability to loose the CAS1-GS the global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 3.5E-6/h


Index

379

380

381

382

383

384

385

386

387

388

ID

DD-036-441

DD-036-442

DD-036-443

DD-036-444

DD-036-445

DD-036-446

DD-036-447

DD-036-448

DD-036-449

DD-036-452…


RQ-Gl The probability to loose the CAS1-GS global integrity function because of the loss of data flow within the globalintegrity function shall be less than 4E-5/h

RQ-Gl The probability to loose the CAS1-GS global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 1E-6/h

RQ-Rx The probability to loose the CAS1-GS service because of a failure in the user terminal shall be less than 1E-4/h

RQ-Sg The probability to loose the CAS1-GS service because of a loss of message shall be less than 1E-6/h

4.7.10 Continuity Performance Allocation for SAS-G/NPA

The SAS-G/NPA is the one among the Galileo services that has the strongest continuity requirements. This parameter will bedimensioning for the Galileo infra-structure design. However this requirements has to be interpreted in the right way becausethe service level required in terms of accuracy and integrity (HPL and TTA) is quite loose comparing to the others such as(SAS-G/Cat 1). Therefore the allocation on the different budget will be different. The following tree shows how the SAS-G/NPAcontinuity risk is allocated to the different system component:

Two main differences can be identified:

- The budget allocated to the geometry is much lower to the one allocated to the continuity of the integrity link. Since the HPLvalue is much larger than the expected performance of the system, an interruption of the service due to the degradation appearsvery remote.

- The budget allocated to the signal robustness is also much lower than the one allocated to the infrastructure. Indeed, since theTTA for this service is equal to 10 seconds, loss of messages do not threaten service continuity. Therefore, even that low, thisrequirement on the signal will most likely not be design critical.

Figure 13: Continuity allocation requirements for SAS-G/NPA


Index

389

390

391

ID

…DD-036-452

DD-036-453

DD-036-454

DD-036-455


SIS1E-5/h

XPL>XAL1E-7/h

Loss of continuity


Loss of continuity

due toGIC false

alarm5E-8/h


1E-8/h

Loss of IMS data



8E-6/h



Loss ofsatellite

Data flow2E-6/h


to GUI3E-6h


to Satellite3E-6/h


broadcasting integrity 2E-6/h


error rate1E-8/h


2E-6/h

Receiver1E-5/h



/Masking)3E-8/h

or

or

or

Global

Global

or

or

or

RQ-Gl The probability to loose the SAS-G/NPA global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 1E-7/h.

RQ-Gl The probability to loose the SAS-G/NPA global integrity function because of the loss of data flow within the globalintegrity function shall be less than 3E-6/h

RQ-Gl The probability to loose the SAS-G/NPA global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 1E-8/h.


Index

392

393

394

395

ID

DD-036-456

DD-036-457

DD-036-458

DD-036-459


RQ-Rx The probability to use the SAS-G/NPA service because of a failure in the user terminal shall be less than 1E-5/h

RQ-Sg The probability to use the SAS-G/NPA service because of a loss of message shall be less than 1E-8/h

4.7.11 Continuity Performance Allocation for SAS-G/Cat1

The allocation for SAS-G/Cat1 has been following the same logic than for CAS1-G


Index

396

397

ID

DD-036-461

DD-036-462


Figure 14: Continuity allocation requirements for SAS-G/Cat1

SIS8E-6/15s

XPL>XAL3E-6/15s

Loss of continuity

due toSatelliteFailure

4E-7/15s

Loss of continuity

due toGIC false

alarm2E-6/15s


1E-7/15s

Loss of IMS data

RAIM false alarm1E-6/15s2.4E-4/h


4E-6/15s


Elevation angle4E-7/15s

Loss ofsatellite

Data flow2E-6/15s


to GUI1E-6/15s


to Satellite1E-6/15s


broadcasting integrity

1.9E-6/15s


error rate1E-7/15s


15E-7/15s

Receiver2E-6/15s

Continuity Risk1E-5/15s


/Masking)5E-7/15s

or

or

or

Global

Global

For the RAIM specification, the false alarm probability is no longer expressed per hour but per 15s. Therefore, for this servicethe time between independent samples is estimated at 15s. This means that the RAIM false alarm probability for SAS-G/Cat1is equal to 1E-6 per independent samples.


Index

398

399

400

401

402

403

404

405

406

407

408

409

410

ID

DD-036-463

DD-036-464

DD-036-465

DD-036-466

DD-036-467

DD-036-468

DD-036-469

DD-036-470

DD-036-471

DD-036-472

DD-036-473

DD-036-474

DD-036-475


For the loss of continuity due to bit error rate the situation comparing to CAS1-G and SAS-G/NPA is different. Indeed the TTAfor the SAS-G/Cat1 service is equal to 6 seconds comparing to 10s for the other services. Therefore, the TTA budget allocated tothe signal is equal to 1 second instead of 4. However, as shown in the integrity risk allocation tree, if the probability to loose amessage is less than 5 10-4, the loss of one message does not threaten the user integrity. Therefore loosing one message is notevent that will interrupt the service. Otherwise, the requirement on the loss of message would be equal to 6 10-9 which isbarely compatible with what is possible to do. However, the loss of two messages will lead to a non continuity event.

RQ-Gl The probability to loose the SAS-G/Cat1 global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 2.5E-7/15s.

RQ-Gl The probability to loose the SAS-G/Cat1 global integrity function because of the loss of data flow within the globalintegrity function shall be less than 2E-6/15s

RQ-Gl The probability to loose the SAS-G/Cat1 global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 4E-7/15s.

RQ-Rx The probability to use the SAS-G/Cat1 service because of a failure in the user terminal shall be less than 2E-6/15s

RQ-Sg The probability to use the SAS-G/Cat1 service because of a loss of message shall be less than 1E-7/15s

4.7.12 Continuity Performance Allocation for SAS-GS/Cat1

RQ-Gl The probability to loose the SAS-GS/Cat1 global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 2.5E-7/15s.

RQ-Gl The probability to loose the SAS-GS/Cat1 global integrity function because of the loss of data flow within the globalintegrity function shall be less than 2E-6/15s

RQ-Gl The probability to loose the SAS-GS/Cat1 global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 4E-7/15s.

RQ-Rx The probability to use the SAS-GS/Cat1 service because of a failure in the user terminal shall be less than 2E-6/15s

RQ-Sg The probability to use the SAS-GS/Cat1 service because of a loss of message shall be less than 1E-7/15s

4.7.13 Continuity Performance Allocation for GAS-G


Index

411

412

413

414

415

416

417

418

419

420

421

422

423

424

ID

DD-036-476

DD-036-477

DD-036-478

DD-036-479

DD-036-480

DD-036-481

DD-036-482

DD-036-483

DD-036-484

DD-036-485

DD-036-486

DD-036-487

DD-036-488

DD-036-489


The allocation for GAS-G are identical to the one made for SAS-G/Cat1.

RQ-Gl The probability to loose the GAS-G global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 2.5E-7/15s.

RQ-Gl The probability to loose the GAS-G global integrity function because of the loss of data flow within the global integrityfunction shall be less than 2E-6/15s

RQ-Gl The probability to loose the GAS-G global integrity function because of the fact that the user has no longer any satellitesabove 25 degrees elevation angle broadcasting integrity shall be less than 4E-7/15s.

RQ-Rx The probability to use the GAS-G service because of a failure in the user terminal shall be less than 2E-6/15s

RQ-Sg The probability to use the GAS-G service because of a loss of message shall be less than 1E-7/15s

4.7.14 Continuity Performance Allocation for GAS-GS

RQ-Gl The probability to loose the GAS-GS global navigation function because of a failure or a malfunction on the globalnavigation or integrity function shall be less 2.5E-7/15s.

RQ-Gl The probability to loose the GAS-GS global integrity function because of the loss of data flow within the global integrityfunction shall be less than 2E-6/15s

RQ-Gl The probability to loose the GAS-GS global integrity function because of the fact that the user has no longer anysatellites above 25 degrees elevation angle broadcasting integrity shall be less than 4E-7/15s.

RQ-Rx The probability to use the GAS-GS service because of a failure in the user terminal shall be less than 2E-6/15s

RQ-Sg The probability to use the GAS-GS service because of a loss of message shall be less than 1E-7/15s

4.7.15 Availability Performance Allocation for CAS1-G service

Availability is representative of a long term reliability of the system. Therefore an availability tree will put only requirementson the physic entity that provided the function and not on the function itself. The following tree shows how the systemavailability is allocated between the elements of the global component. However those figures are provided only for informationsince it is not the task of GALA to provide such information.


Index

425

426

427

428

429

430

431

432

433

434

435

ID

DD-036-490

DD-036-491

DD-036-492

DD-036-493

DD-036-494

DD-036-495

DD-036-496

DD-036-497

DD-036-498

DD-036-499

DD-036-501…


RQ-Gl The unavailability of the SIS CAS1-G service due to the global navigation function has to be less than 9E-3. Thisincludes the unavailability of:

- Accuracy in horizontal and vertical

- Integrity provided by RAIM/AAIM in horizontal and vertical with 1.25E-4 (NCDP) miss detection probability on eachdimension and 5E-6 (NCDP)false alarm probability on each dimension

- Integrity provided by GIC

- GIC protection level (fault free case) protecting the end user with a risk of 2.5E-8/h on each dimension smaller than the alarmlimit .

- Continuity risk of 4E-6/h

RQ-Gl The unavailability of the SIS CAS1-G service due to the global integrity function has to be less than 1E-3. Thisincludes the unavailability of:

- two MEO satellites broadcasting integrity information

- with a continuity risk of 4E-5/h

False alarm probability requirements are deducted from continuity performance allocation whereas miss detection performancerequirement are deducted from the integrity performance allocation.

Figure 15: Availability Allocation for CAS1-G service


Index

436

437

438

ID

…DD-036-501

DD-036-502

DD-036-503

DD-036-504


Unavailability1E-2

ReceiverNot included in Perf budget

SIS1E-2


1E-3

GeometryXPL<Alarm limit

8E-3

Integritychannel not available

1E-3

N Satellitesfailure

N satellite failureAvailability

N satellite failurestate probability

N satelliteSatellite Failure

N Satellite not monitored

IMS failure

Transmission IMS-IPF failure

Integrity messagebroadcast

unavailability5E-4

Integrity messagegeneration

unavailability5E-4

IPF to GUItransmissionunavailability

GUI to USERtransmission unavailability

OSS

OSPF

GWAN

ULS

GLOBAL

or

or

4.7.16 Availability Performance Allocation for CAS1-GS service

RQ-Gl The unavailability of the SIS CAS1-GS service due to the global navigation function has to be less than 9E-3. Thisincludes the unavailability of:



Index

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

ID

DD-036-505

DD-036-506

DD-036-507

DD-036-508

DD-036-509

DD-036-510

DD-036-511

DD-036-512

DD-036-513

DD-036-514

DD-036-515

DD-036-516

DD-036-517

DD-036-518

DD-036-519


- Integrity provided by RAIM/AAIM in horizontal and vertical with 1.25E-4 (NCDP) miss detection probability on eachdimension and 5E-6 (NCDP)false alarm probability on each dimension


- GIC protection level (fault free case) protecting the end user with a risk of 2.5E-8/h on each dimension smaller than the alarmlimit .

- Continuity risk of 4E-6/h

RQ-Gl The unavailability of the SIS CAS1-GS service due to the global integrity function has to be less than 1E-3. Thisincludes the unavailability of



4.7.17 Availability Performance Allocation for SAS-G/NPA service

Using the same approach than for CAS1-G service the following requirements on the global component are derived:

RQ-Gl The unavailability of the SIS SAS-G/NPA service due to the global navigation function has to be less than 9E-4. Thisincludes the unavailability of:


- Integrity provided by RAIM/AAIM in vertical with 2.5E-4 (NCDP) miss detection probability on each dimension and 2E-7(NCDP) false alarm probability on each dimension


- GIC protection level (fault free case) protecting the end user with a risk of 5E-8/h on each dimension smaller than the alarmlimit .

- With a continuity risk of 1E-8/h


Index

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

ID

DD-036-520

DD-036-521

DD-036-522

DD-036-523

DD-036-524

DD-036-525

DD-036-526

DD-036-527

DD-036-528

DD-036-529

DD-036-530

DD-036-531

DD-036-532

DD-036-533

DD-036-534

DD-036-535


RQ-Gl The unavailability of the SIS SAS-G/NPA service due to the global integrity function has to be less than 1E-4. Thisincludes the unavailability of:



4.7.18 Availability Performance Allocation for SAS-G/Cat1 service

The strategy to deduct availability requirements is the same as the one explained above for CAS1-G.

RQ-Gl The unavailability of the SIS SAS-G/Cat1 service due to the global navigation function has to be less than 9E-3. Thisincludes the unavailability of:


- Integrity provided by RAIM/AAIM in horizontal and vertical with 6.25E-3 (NCDP) miss detection probability on eachdimension and 5E-7 (NCDP) false alarm probability on each dimension


- GIC protection level (fault free case) protecting the end user with a risk of 5E-8/150s on each dimension smaller than thealarm limit .

- And a continuity risk lower than 4E-7/15s

RQ-Gl The unavailability of the SIS SAS-G/Cat1 service due to the global integrity function has to be less than 1E-3. Thisincludes the unavailability of:


- with an continuity risk of 2.4E-6/15s

4.7.19 Availability Performance Allocation for SAS-GS/Cat1 service

RQ-Gl The unavailability of the SIS SAS-GS/Cat1 service due to the global navigation function has to be less than 9E-4. Thisincludes the unavailability of:


Index

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

ID

DD-036-536

DD-036-537

DD-036-538

DD-036-539

DD-036-540

DD-036-541

DD-036-542

DD-036-543

DD-036-544

DD-036-545

DD-036-546

DD-036-547

DD-036-548

DD-036-549

DD-036-550

DD-036-551







RQ-Gl The unavailability of the SIS SAS-GS/Cat1 service due to the global integrity function has to be less than 1E-4. Thisincludes the unavailability of



4.7.20 Availability Performance Allocation for GAS-G service


RQ-Gl The unavailability of the SIS GAS-G service due to the global navigation function has to be less than 9E-3. Thisincludes the unavailability of:







Index

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

501

ID

DD-036-552

DD-036-553

DD-036-554

DD-036-555

DD-036-556

DD-036-557

DD-036-558

DD-036-559

DD-036-560

DD-036-561

DD-036-562

DD-036-563

DD-036-564

DD-036-565

DD-036-566

DD-036-567


RQ-Gl The unavailability of the SIS GAS-G service due to the global integrity function has to be less than 1E-3. This includesthe unavailability of:



4.7.21 Availability Performance Allocation for GAS-GS service


RQ-Gl The unavailability of the SIS GAS-GS service due to the global navigation function has to be less than 9E-4. Thisincludes the unavailability of:






RQ-Gl The unavailability of the SIS GAS-GS service due to the global integrity function has to be less than 1E-3. Thisincludes the unavailability of



4.8 Global Navigation Function + Regional Integrity Function

4.8.1 SAS-R service provision


Index

502

503

504

ID

DD-036-568

DD-036-569

DD-036-571


The SAS-R service provides to the region a way to handle integrity information on their own zone. Therefore the region cantake responsibility for what happens on its zone of coverage. As far as performance are concerned, SAS-R service is equivalentto SAS-G/Cat1. Since the SAS-G/Cat1 global service is provided by Europe, there is no need to have a regional component onEurope to provide SAS-R service. On the other hand, for regions outside Europe, even if there is an world wide infra-structureallowing to get SAS-R like performance, the deployment of a regional component is necessary. This regional component willallow the region to have complete control on the integrity information broadcast on the region

The difference between SAS-G/Cat1 and SAS-R is that the integrity function is now mainly insured by the region. ForSAS-G/Cat1 service the allocation was stopped at high level since the same entity (ESA/GalileoSat) is responsible of thedevelopment of all the elements supporting the integrity function. For regional service, the situation is different. Thecollection of information, the integrity determination and part of integrity dissemination is supported by the regionalcomponent. The broadcast of the information is supported by the global component. Outside Europe, navigation and integrityfunction are not under the same entity responsibility. Therefore, it is necessary to go a step forward in the allocation in order toclearly specify the contribution of the regional and global component to the navigation and integrity function.

Figure 16: SAS-R service provision

SAS REGIONALCOMPONENT




SAS REGIONAL COMPONENT

SAS REGIONAL COMPONENT

SAS GLOBAL COMPONENTSAS GLOBAL COMPONENT

SAS-R EuropeSAS-R Region 1 SAS-R Region 2 SAS-R Region 3


Index

505

506

507

508

ID

DD-036-572

DD-036-573

DD-036-575

DD-036-576


4.8.2 Integrity Performance Allocation for SAS-R service

The following tree details the risk allocation between the global and regional component of the system.

Figure 17: Integrity Risk Allocation for SAS-R serviceUndetected Globalsingle SIS by GIC

5E-8/150s

Global Single SIS

4E-6/150s


7.5E-3

Invalid SISA At SV output4E-8/150s



7.5E-3

Satellitefailure

4E-6/150s


5E-3

Transmission failurewithin T2*2.5E10-3


1E-3

Transmission fromGUI to User

1E-3

Integrity message loss due to bit error

rate5E-4

Transmission delay

Data corruption

Transmission delay

Data corruption


Global

Regional Global

and

or or

or

or

oror

Corruption of validSISA in SIS2E-8/150s

The 6 seconds time to alarm requirement is allocated as follows between the different components of the system. The system issupposed synchronous. The RUI, GUI and ULF are assumed to be in the same facility which is the ULS (up-link station).


Index

509

510

511

512

513

514

ID

DD-036-578

DD-036-579

DD-036-580

DD-036-581

DD-036-582

DD-036-583


Figure 18: Time To Alarm Allocation for SAS-R service

RMF RPF RUI GUI ULF

MEO

User

Integrity Event

Global

0.8s

Alarm

1.3s0.8s

1s0.2s

0.1s0.05s

Regional

0.1s0.06s

0.1s0.12s

0.25s

1.12s

3.45s 1.75s

ULS

6s without loss of message

Those diagrams rely on the assumptions that the integrity information from regions are collected at GUI level and broadcast bythe MEOs satellites.

RQ-Gl The probability that the SAS-R global navigation function sends a misleading information to the user shall be less than4E-6/150s.

RQ-Gl In the case that the SAS-R regional component sends an alarm, the probability that the SAS-R global component doesnot disseminate this alarm to the end user within 1.75 seconds shall be less than 1.5E-3.

RQ-Rg In the case that a misleading information is sent to the user by the SAS-R global navigation function, the probabilitythat the SAS-R regional component does not send a warning to the SAS-R global component within 3.45 seconds shall be lessthan 6E-3.

RQ-Rx The integrity risk due to the SAS-R user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget


Index

515

516

517

518

519

520

521

522

523

524

525

526

527

ID

DD-036-584

DD-036-585

DD-036-586

DD-036-587

DD-036-588

DD-036-589

DD-036-590

DD-036-591

DD-036-592

DD-036-593

DD-036-594

DD-036-595

DD-036-596


RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-R receiver and the alarm is displayed to theuser shall not exceed 0.8s

RQ-Sg The probability to loose an integrity message due to bit error rate on the SAS-R signal in space shall be less than 5E-4.

RQ-Sg The probability that the an HMI is generated within the SAS-R navigation message due to bit error rate shall be lessthan 2 10-8/150s

4.8.3 Integrity performance allocation for SAS-RM service

RQ-Gl The probability that the SAS-RM global navigation function sends a misleading information to the user shall be less than 4E-6/150s.

RQ-Gl In the case that the SAS-RM regional component sends an alarm, the probability that the SAS-RM global componentdoes not disseminate this alarm to the end user within 1.75 seconds shall be less than 1.5E-3.

RQ-Rg In the case that a misleading information is sent to the user by the SAS-RM global navigation function, the probabilitythat the SAS-RM regional component does not send a warning to the SAS-RM global component within 3.45 seconds shall beless than 6E-3.

RQ-Rx The integrity risk due to the SAS-RM user segment shall be less than 1.5E-7/150s. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to RAIM algorithmperformance is not included in the integrity risk user segment budget

RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-RM receiver and the alarm is displayed to theuser shall not exceed 0.8s

RQ-Sg The probability to loose an integrity message due to bit error rate on the SAS-RM signal in space shall be less than5E-4.

RQ-Sg The probability that the an HMI is generated within the SAS-RM navigation message due to bit error rate shall be lessthan 2 10-8/150s

4.8.4 Continuity Performance Allocation for SAS-R

The following tree represents the allocation of continuity risk between the system components. The first step is to allocatebetween the receiver and the SIS.


Index

528

529

ID

DD-036-597

DD-036-598


The first arm on the SIS part is an allocation on the geometry. A degradation of the geometry during an approach can be due toa loss of one or several satellites. The rest of the budget is allocated to the RAIM false alarm and the loss of integrity function. Concerning the RAIM false alarm, it is interesting to note that the specification if again much less stringent than for RAIM usedon global basis. This will improve the RAIM availability performance.

The loss of the integrity function can be due to loss of global or regional component. Therefore, the tree is developed until thedistinction between specifications on global and regional components can be identified.


Index

530

531

ID

DD-036-600

DD-036-601


Figure 19: Continuity Risk Allocation on System Component

SIS8E-6/15s

XPL>XAL3E-6/15s

Loss of continuity

due toSatelliteFailure

4E-7/15s

Loss of continuity

due toGIC false

alarm2E-6/15s


1E-7/15s

Loss of IMS data

RAIM false alarm1E-6/15s2.4E-4/h


4E-6/15s


Elevation angle4E-7/15s

Loss ofsatellite

Data flow2E-6/15s


to GUI1E-6/15s


to Satellite1E-6/15s


broadcasting integrity 19E-7/15s


error rate1E-7/15s


15E-7/15s

Receiver2E-6/15s

Continuity Risk1E-5/15s


/Masking)5E-7/15s

or

or

or

Regional

Global

RQ-Gl The probability to loose the SAS-R global navigation function because of a failure or a malfunction on the globalnavigation function shall be less 4E-7/15s.


Index

532

533

534

535

536

537

538

539

540

541

542

543

544

545

ID

DD-036-602

DD-036-603

DD-036-604

DD-036-605

DD-036-606

DD-036-607

DD-036-608

DD-036-609

DD-036-610

DD-036-611

DD-036-612

DD-036-613

DD-036-614

DD-036-615


RQ-Gl The probability to loose the SAS-R integrity function because of the interruption of the data flow within the globalcomponent shall be less than 1.4E-6/15s

RQ-Rg The probability to loose the SAS-R global navigation function due to a failure or a malfunction of the regionalcomponent shall be less d 2.1E-6/15s

RQ-Rg The probability to loose the SAS-R integrity function because of the interruption of integrity information provision bythe regional component shall be less than 1E-6/15s

RQ-Rx The probability of failure of the SAS-R user segment shall not exceed 2E-6/15s

RQ-Sg The probability to loose the SAS-R service because of a loss of message shall be less than 1E-7/15s

4.8.5 Continuity performance allocation for SAS-RM

RQ-Gl The probability to loose the SAS-RM global navigation function because of a failure or a malfunction on the globalnavigation function shall be less 4E-7/15s.

RQ-Gl The probability to loose the SAS-RM integrity function because of the interruption of the data flow within the globalcomponent shall be less than 1.4E-6/15s

RQ-Rg The probability to loose the SAS-RM global navigation function due to a failure or a malfunction of the regionalcomponent shall be less d 2.1E-6/15s

RQ-Rg The probability to loose the SAS-RM integrity function because of the interruption of integrity information provision bythe regional component shall be less than 1E-6/15s

RQ-Rx The probability of failure of the SAS-RM user segment shall not exceed 2E-6/15s

RQ-Sg The probability to loose the SAS-RM service because of a loss of message shall be less than 1E-7/15s

4.8.6 Availability Performance Allocation for SAS-R

As for the other services and still because it appears difficult to specify a MTTR (Mean Time To Repair) for a receiver, thereceiver is nor included in the availability performance budget. Therefore the availability is split between the navigationfunction and the integrity function.


Index

546

547

548

549

550

551

552

553

554

555

556

557

ID

DD-036-616

DD-036-617

DD-036-618

DD-036-619

DD-036-620

DD-036-621

DD-036-622

DD-036-623

DD-036-624

DD-036-625

DD-036-626

DD-036-628…


For the unavailability due to a lack of geometry, it is difficult to split the allocation between global and regional. Indeed, bothcomponents impact this budget. The loss of one satellite can be due either to a satellite failure or to the fact that the satellite isno longer monitored. This second event will come from the loss of a IMS from the IPF point of view (i.e.: loss of a IMS or loss ofthe link IMS-IPF). One solution is to make sure in the design of the regional component that the impact of a loss of one orseveral IMS is negligible on the global system availability.

RQ-Gl The unavailability of the SIS SAS-R service due to global navigation function shall be less than 9E-3. This includesthe availability of:




- GIC protection level (fault free case) protecting the end user with a risk of 5E-8/150s on each dimension smaller than thealarm limit

- Continuity with a continuity risk of 4E-7/15s

RQ-Gl The unavailability of the SAS-R integrity broadcast function insured by the global segment shall not be less than 2E-4. To be available this function shall provide:

- Two MEO’s above 25 degrees broadcasting integrity

- With a continuity risk of 1E-6/15s

RQ-Rg The unavailability of the SAS-R integrity determination and dissemination function insured by the regional component shall be less than 8E-4 with a continuity risk of 1E-6/15s

Figure 20: Availability Allocation between Global and Regional component for SAS-R


Index

558

559

560

561

ID

…DD-036-628

DD-036-629

DD-036-630

DD-036-631

DD-036-632


Unavailability1E-2

ReceiverNot included in Perf budget

SIS1E-2


1E-3

GeometryXPL<Alarm limit

8E-3Integrity

channel not available1E-3

Loss ofN satellites

N satellite lossAvailability

N satellite lossstate probability

N satelliteSatellite Failure

Integrity messagebroadcast

failure5E-4

Integrity messagegeneration failure

5E-4

IPF to GUItransmission

failure3E-4

GUI to USERtransmission

failure2E-4

OSS

OSPF

GWAN

ULS

N Satellite not monitored

Negligible

IMS failure

Transmission IMS-IPF failure

4.8.7 Availability performance allocation for SAS-RM service

RQ-Gl The unavailability of the SIS SAS-RM service due to global navigation function shall be less than 9E-4. This includesthe availability of:




Index

562

563

564

565

566

567

568

569

570

571

572

ID

DD-036-633

DD-036-634

DD-036-635

DD-036-636

DD-036-637

DD-036-638

DD-036-639

DD-036-640

DD-036-641

DD-036-642

DD-036-643



- GIC protection level (fault free case) protecting the end user with a risk of 5E-8/150s on each dimension smaller than thealarm limit


RQ-Gl The unavailability of the SAS-RM integrity broadcast function insured by the global segment shall not be less than2E-5. To be available this function shall provide

- Two MEO’s above 25 degrees broadcasting integrity

- With a continuity risk of 1E-6/15s

RQ-Rg The unavailability of the SAS-R integrity determination and dissemination function insured by the regional component shall be less than 8E-5 with a continuity risk of 1E-6/15s

4.8.8 EGNOS service provision

Regional European service such as SAS-R or SAS-RM are provided by the Galileo global component. Since the globalcomponent is under European responsibility, there is no need to set up a regional infrastructure for responsibility and liabilitypurpose. However, through the integration of EGNOS, Galileo provides additional specific regional services on ECAC (EGNOS1/2/3A/3B/3C). The allocation for those services is already available in the design document of EGNOS and will not be recalledin this document.

4.9 Global Navigation functions + Local functions

Five services use the global together with a local component: CAS1-L1/2/3, SAS-L and GAS-L. For local services the line is clearbetween global and local component. The global component impacts only the geometry. For the UERE and the integrityfunction, it is mainly driven by the local components. Generally, what can be said is that it appears difficult at this stage tomake an allocation between global and local since the architecture from one local component to the other might be very different[RD-010]. It depends whether, pseudolite, local corrections, interference detectors are used. The allocation may also be changedaccording to the fact that the local corrections are broadcast by a local communication link or though the MEO’s (CAS1-L2). Nevertheless, it makes sense to assume that the local service will provide the same type of basic function that have beenidentified in the other services, Global or Regional.


Index

573

574

575

576

577

578

579

580

581

582

583

584

585

ID

DD-036-644

DD-036-645

DD-036-646

DD-036-647

DD-036-648

DD-036-649

DD-036-650

DD-036-651

DD-036-652

DD-036-653

DD-036-654

DD-036-655

DD-036-657…


Those function are:

- Navigation function

- Correction and integrity determination function

- Correction and integrity broadcast function

The following trees give a preliminary allocation for integrity, continuity and availability between local and global component.

4.9.1 Integrity Performance Allocation for CAS1-L1

As for the local architecture, the way to derive local integrity to the end user is not totally defined yet. In order to make apreliminary performance apportionment on the local component, the protocol described in the MASP (Minimum requirementsfor receiver to be used in local differential conditions for civil aviation procedures [RD-019]). It can be summarized as follows:

The local station sends to the user:

- Differential correction

- UDRE like parameter allowing the user to compute a protection level under the assumption that the system is fault free(assumption H0)

- Bias parameters that allow the user to compute protection levels assuming a failure on one receiver among all present in thelocal station (assumption H1).

The final user protection is the largest among the ones computed. Therefore the system is designed to cope with one receiverfailure. A satellite failure does not induce an integrity risk for a local service as long as the differential corrections are updatedwithin the TTA (each second). Therefore the events that could threaten the user integrity are more than one undetectedreceiver failure in the local station or a failure in the data broadcast.

Figure 21: Integrity Risk Allocation between global and local component for CAS1-L1


Index ID

…DD-036-657


Total SystemIntegrity risk

2E-7/h

Receiver1E-7/h

SIS1E-7/h

XNSE>XPLunder H0 and H1

5E-8/h

XNSE>XPLunder H0

XNSE>XPLunder H1

Integrity failure due to other source than H0 and H1

5E-8/h

Undetected failure frommore than 1 reference Rx

Erroneous correctionsent to the user

Undetected localevents by RAIM

or

orCorrection

and integritydetermination

3E-8/h

Correction and integrity

broadcast2E-8/h

Local


Index

586

587

588

589

590

591

ID

DD-036-658

DD-036-659

DD-036-660

DD-036-661

DD-036-663

DD-036-664


As usual the budget is first split between receiver and SIS. Here, the same comment made is CAS1 global service can berepeated. The integrity risk allocation put on the receiver appears very stringent for a service that is not safety criticaloriented.

The budget SIS is split between two components. The first case is a kind of “fault free” situation. It includes the situation forwhich the system has been designed. Those situation include the “fault-free state” (H0) and the “single reference receiverfailure state” (H1). Two protection levels are computed at user level [RD-07] to protect him in those two situations.

The second part of the SIS risk budget is allocated to the generation and transmission of the differential corrections. Those twofunctions are normally performed by the local component’ at least for SAS. However, in GALA the possibility of broadcasting thelocal information through the MEO’s for CAS1-L2 has been mentioned. In this case the part of the risk allocated to the localcomponent should be put on the transmission link. In that case, if integrity is really required for this kind of service, therequirement induces by local services on the global component will be more stringent than the ones coming from global andregional services. CAS1 bit error rate will be also impacted.

As far as TTA is concerned the following allocation can be made:

Figure 22: Time To Alert Allocation for CAS1-L1 service

Integrity Event

Pseudo-rangemeasurement

User TerminalLocal Rx

Corrupted pseudo-range

Alarm reception

TTA=1s

AlarmDisplayed

1s 0.5s0.5s

The following requirements can be deduced from the preceding performance allocation tree.


Index

592

593

594

595

596

597

598

599

600

601

602

ID

DD-036-665

DD-036-666

DD-036-667

DD-036-668

DD-036-669

DD-036-670

DD-036-671

DD-036-672

DD-036-673

DD-036-674

DD-036-675


RQ-Lc The probability that local correction and integrity determination function generates an hazardous misleadinginformation due to a event not covered by H0 and H1 state without being corrected within the 0.5 second shall be less than5E-8/h for CAS1-L1 service.

RQ-Rx The integrity risk due to the user segment shall be less than 1E-7/h for CAS1-L1 service. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to potential use of RAIMalgorithm performance is not included in the integrity risk

RQ-Rx The time elapsed between the moment when an alarm arrives at the CAS1-L1 receiver and the alarm is displayed to theuser shall not exceed 0.5s

4.9.2 Integrity performance allocation for SAS-L service

The SAS-L requirements are deducted using the same strategy as the one used for CAS1-L1

RQ-Lc The probability that local correction and integrity determination function generates an hazardous misleadinginformation due to a event not covered by H0 and H1 state without being corrected within 1 second shall be less than5E-10/150s for SAS-L service

RQ-Rx The integrity risk due to the user segment shall be less than 1E-9/150s for SAS-L service. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to potential use of RAIMalgorithm performance is not included in the integrity risk

RQ-Rx The time elapsed between the moment when an alarm arrives at the SAS-L receiver and the alarm is displayed to theuser shall not exceed 0.5s

4.9.3 Integrity performance allocation for GAS-L service

The GAS-L mission requirements are similar to the SAS-L ones. Therefore the requirements allocated to the local station andthe user equipment are identical.

RQ-Rg The probability that local correction and integrity determination function generates an hazardous misleadinginformation due to a event not covered by H0 and H1 state without being corrected within the 0.5s shall be less than 5E-10/150sfor GAS-L service


Index

603

604

605

606

ID

DD-036-676

DD-036-677

DD-036-678

DD-036-680


RQ-Rx The integrity risk due to the user segment shall be less than 1E-9/150s for GAS-L service. User integrity risk covers theprobability of the user segment to generate on its own a misleading information. Integrity risk due to potential use of RAIMalgorithm performance is not included in the integrity risk

RQ-Rx The time elapsed between the moment when an alarm arrives at the GAS-L receiver and the alarm is displayed to theuser shall not exceed 0.5s

4.9.4 Continuity Performance Allocation for CAS1-L service

Figure 23: Continuity risk allocation between global and local component for CAS1-L service

SIS1E-4/h

XPL>XAL5E-5/h

RAIMfalse alarm

1E-5/h

Loss of correction and Integrity data

4E-5/h

Receiver1E-4/h


Satellite failure1E-5/h

APL failure2E-5/h

Correction and Integrity transmission failure

2E-5/h

Correction and Integrity determination failure

2E-5/h

Local effects on reference station1E-5/h

Reference RxFailure1E-5/h

Local effects1E-5/h

VHF failure1E-5/h

LocalGlobal

Local effects(Masking/Interference)2E-5/h

LocalLocal


Index

607

608

609

610

611

612

613

614

615

616

617

618

619

620

ID

DD-036-681

DD-036-682

DD-036-683

DD-036-684

DD-036-685

DD-036-686

DD-036-687

DD-036-688

DD-036-689

DD-036-690

DD-036-691

DD-036-692

DD-036-693

DD-036-694


For the risk allocated to the geometry, the same problem that arose in regional service to allocate the budget between failed andnot monitored satellite arises again. Geometry is impacted both by the global component through the satellites and the localcomponent through the pseudo-lites.

The rest of the risk is allocated to the generation and transmission of the differential correction data.

RQ-Rx The probability of failure of the user segment shall not exceed 1E-7/h for CAS1-L1 service

RQ-Lc The loss of the navigation function due to a failure or malfunction of the local component shall not exceed 2E-5/h forCAS1-L1 service (navigation function is impacted part by the satellites and part by the pseudolites)

RQ-Lc The loss of the CAS1-L1 correction and integrity determination function due to a failure on the local component shallnot exceed 1E-5/h.

RQ-Lc The loss of the CAS1-L1 correction and integrity dissemination function due to a failure on the local component shallnot exceed 1E-5/h.

4.9.5 Continuity Performance Allocation for SAS-L service

The architecture and requirements for GAS-L service are identical than the ones defined for SAS-L service. Therefore Theprevious requirements allow to deduct the system GAS-L service requirements.

RQ-Rx The probability of failure of the user segment shall not exceed 1E-6/15s for SAS-L service

RQ-Lc The loss of the navigation function due to a failure or malfunction of the local component shall not exceed 5E-7/15s forSAS-L service (navigation function is impacted part by the satellites and part by the pseudolites)

RQ-Lc The loss of the SAS-L correction and integrity determination function due to a failure on the local component shall notexceed 2E-6/15s.

RQ-Lc The loss of the SAS-L correction and integrity dissemination function due to a failure on the local component shall notexceed 2E-6/15s.

4.9.6 Continuity Performance Allocation for GAS-L service

The architecture and requirements for GAS-L service are identical than the ones defined for SAS-L service. Therefore Theprevious requirements allow to deduct the system GAS-L service requirements.


Index

621

622

623

624

625

626

627

628

629

630

631

632

ID

DD-036-695

DD-036-696

DD-036-697

DD-036-698

DD-036-699

DD-036-700

DD-036-701

DD-036-702

DD-036-703

DD-036-704

DD-036-705

DD-036-707…


RQ-Rx The probability of failure of the user segment shall not exceed 1E-6/15s for GAS-L service

RQ-Lc The loss of the navigation function due to a failure or malfunction of the local component shall not exceed 5E-7/15s forGAS-L service (navigation function is impacted part by the satellites and part by the pseudolites)

RQ-Lc The loss of the GAS-L correction and integrity determination function due to a failure on the local component shall notexceed 2E-6/15s.

RQ-Lc The loss of the GAS-L correction and integrity dissemination function due to a failure on the local component shall notexceed 2E-6/15s.

4.9.7 Availability Performance Allocation for CAS1-L service

The following tree allocates the system unavailability between global and local component. As mentioned before and as detailedin the following figure, the availability requirement allocation allows to deduct requirement on the global component and thelocal component.

RQ-Gl The unavailability of the CAS1-L1 navigation function shall be less than 9E-3. This includes the availability of:


- Integrity: protection level sized for a risk of 2.5E-8/h on each dimension

- Continuity less than 1E5/h

RQ-Lc The unavailability of the CAS1-L1 correction and integrity determination and dissemination function service shall bemore than 1E-3 with a continuity less than 2E-5/h.

Figure 24: Unavailability allocation between Local and Global component for CAS1-L service


Index

633

634

635

636

637

ID

…DD-036-707

DD-036-708

DD-036-709

DD-036-710

DD-036-711

DD-036-712


SIS1E-2

XPL>XAL9E-3

Loss of correction and Integrity data

1E-3

ReceiverNot included in the Perf Budget

Unavailability1E-2

Satellite failure

APL failure

Correction and Integrity transmission failure

3E-7/15s

Correction and Integrity determination unavailability

2E-7/15s

LocalGlobal

Local

4.9.8 Availability Performance Allocation for SAS-L service

The availability performance allocation for SAS-L service are done in the same way used for CAS1-L service at the differencethat SAS-L includes continuity requirements.

RQ-Gl The unavailability of the SAS-L navigation function shall be less than 9E-4. This includes the availability of:


- Integrity: protection level sized for a risk of 2.5E-10/150s on each dimension


Index

638

639

640

641

642

643

644

645

646

647

648

649

650

651

652

653

ID

DD-036-713

DD-036-714

DD-036-715

DD-036-716

DD-036-717

DD-036-718

DD-036-719

DD-036-720

DD-036-721

DD-036-722

DD-036-723

DD-036-724

DD-036-725

DD-036-726

DD-036-727

DD-036-728



RQ-Lc The unavailability of the SAS-L correction and integrity determination and dissemination function service shall be morethan 1E-4 with a continuity risk of 4E-6/15s .

4.9.9 Availability Performance Allocation for SAS-L service

The availability performance allocation for GAS-L service is done in the same way used for SAS-L service.

RQ-Gl The unavailability of the GAS-L navigation function shall be less than 9E-4. This includes the availability of:


- Integrity: protection level sized for a risk of 2.5E-10/150s on each dimension


RQ-Lc The unavailability of the GAS-L correction and integrity determination and dissemination function service shall bemore than 1E-4 with a continuity risk of 4E-6/15s .

4.10 From Mission to System Requirements

Mission performance requirements is the performance that the user can expect from the "total" system. It means that thisperformance includes all the components that have an impact on the final user performance which are namely:

- Galileo SIS

- Galileo Receiver

- Potential other systems

- Potential other sensors

The first step to identify the system requirements is obviously to determine what element is in the system and which one is not. As a generic rule, we can say that the elements that will be "physically" deployed by "Galileo industry" belong to the system andthe others do not. Following this strategy and as shown in the next document, the elements belonging to the system are:


Index

654

655

656

657

658

659

660

661

ID

DD-036-729

DD-036-730

DD-036-731

DD-036-732

DD-036-733

DD-036-734

DD-036-735

DD-036-737…


- The Galileo global component (GalileoSat + signal)

- The regional components outside Europe

- The local component

One thing that is under discussion is whether or not, components that will be developed outside Europe belong to the system. As far as cost in concerned, it is clear that all that is not European shall be excluded of the system. However, technicallyspeaking, the regional component is part of the global system. Since Galileo is a system that is designed globally, all thecontributions even not European should be included in it (as it is done for GNSS1). For cost matters, it will be more accurate tospeak about the European contribution to Galileo instead of the Galileo cost.

Therefore, now that what is included in the system is identified the second step is to specify it. At this point two options areavailable

The first one is to allocate the mission requirements between the system and the other components ( typically, the receiver) andto use what is allocated to the system as the specification.

The second one is to specify the system using the same figure as in the mission requirements but also giving as input what hasbeen allocated to component outside the system (option 2 in ppt file)

Figure 25: Option for System Requirements Formalization


Index

662

663

664

665

666

667

668

ID

…DD-036-737

DD-036-738

DD-036-739

DD-036-740

DD-036-742

DD-036-744

DD-036-745

DD-036-746


Mission requirements2 10-7/h

System 10-7/h

Receiver10-7/h

System requirements

System requirements: The probability that Galileo system combined with a typical receiver generates an Hazardous

Misleading Information shall be less than 2 10-7/hAND

The probability that a typical receiver generates anHMI is equal to

10-7/h

+

Mission requirements2 10-7/h

System10-7/h

Receiver10-7/h

System Rqts

System requirements: The probability that Galileo system generates an Hazardous Misleading Information shall be less

than 10-7/h

It is clear that the first option is preferable, but in order to be able to do that, the contribution of the system and the othercomponents to the total performance shall be as independent as possible. To see the problem let's have a look at two examples:

- SAS/Cat1 integrity risk requirements.

This risk is allocated between the SIS (system) and the Receiver in a simple arithmetic way:

Mission Rqt (3.5 10-7/150s)= SIS Rqt (2 10-7/150s) + Rx Rqt (1.5 10-7/150s)

In that case it is easy to select the option 1 and to specify directly 2 10-7/150s on the system.

- Accuracy requirement : 6 meter vertical

For this parameter it is already much more difficult to totally isolate the performance of the different components. Indeed the UERE budget depends from the system (clock, orbito) and the receiver (tracking...). It is not possible to allocate 4meters to the system and 2 to the receiver. In that situation we have to select the option 2, that is to say:


Index

669

670

671

672

673

674

675

676

677

678

679

ID

DD-036-747

DD-036-748

DD-036-749

DD-036-750

DD-036-751

DD-036-752

DD-036-753

DD-036-754

DD-036-755

DD-036-756

DD-036-757


1- To specify 6 meters vertical accuracy to the system

2- And providing the system with the assumed receiver performance to be used as inputs.

Therefore for Galileo system requirements, it is proposed to use the same approach as in the SARPS where the concept of"Fault-Free" receiver is adopted. This receiver is defined having neither continuity nor integrity failures but is characterizedwith a specific UERE budget and a specific contribution to the TTA.

Therefore the Galileo System requirements should include:

- A table equivalent to the one used in the mission requirements, but with the receiver contribution to the integrity risk andcontinuity risk removed. It should be clearly said that those performances have to be met with a fault free receiver. ANNEX Ashows an example of what could be the mission requirements. In this example the receiver is assumed having neithercontinuity and integrity budget nor TTA contribution.

- A definition for each service of the fault-free receiver

- Rx UERE (See §4)

- TTA allocation (See §3)

- Continuity and integrity risk allocation

- For the services including other system, the performance assumption made for those external system shall be also clearlyidentify in the document to be used as inputs (in the same way as the fault free receiver) by the system designers. In particularthe assumptions made for GPS need to be present in the document.)

The goal of the chapter was to propose a way to characterize the Galileo system requirements. However the official derivationof the mission requirements is out of the scope of this work package. The objective is to provide inputs to the [RD-02]. It is upto this document to provide the Galileo System requirements.


Index

680

681

682

683

684

685

686

687

688

689

690

691

692

693

694

695

ID

DD-036-758

DD-036-759

DD-036-760

DD-036-761

DD-036-762

DD-036-763

DD-036-764

DD-036-765

DD-036-766

DD-036-767

DD-036-768

DD-036-769

DD-036-770

DD-036-771

DD-036-772

DD-036-773


5 UERE budget

5.1 Scenario definition

Parameters impacting on the UERE can be split into two categories:

System specific parameters: Signal Structure and System Architecture

User specific parameters: User Environment, User Dynamics,…

5.1.1 System Specific Parameters

5.1.1.1 Galileo services

According to the current specification, Galileo satellite payload will broadcast different kind of service with different securitylevels [RD-010]:

- Open Access Service OAS

- Control Access Service level 1 CAS1

- Control Access Service level 2

- Safety critical CAS2/SAS

- Governmental Application CAS2/GAS

OAS service is broadcast on two frequencies in order to allow ionosphere dual frequency correction. However, dual frequencywill make the user receiver more complicated and more costly. Furthermore, dual frequency processing may not be well suitedto for strong multipath environment. For those two reasons it appears wise to define an OAS mono-frequency service.

OAS and CAS1 have the same signal structure. The two services differ only in the content of the data message. CAS1 shallbroadcast integrity information whereas OAS shall not. Therefore, as far as UERE is concerned, those two services areequivalent and are not treated separately.

The services CAS2 includes two sub-services, the SAS and GAS. The signal for those two services having different features,they are treated separately.


Index

696

697

698

699

700

701

702

703

704

705

706

707

708

ID

DD-036-774

DD-036-775

DD-036-777

DD-036-778

DD-036-779

DD-036-780

DD-036-781

DD-036-782

DD-036-783

DD-036-784

DD-036-785

DD-036-786

DD-036-787


5.1.1.2 System Architecture

The Galileo system includes a Global, Regional and Local component. According to the architecture selected by the user, theUERE will be different. On the current baseline, the mission of the regional component in only to compute and provideintegrity information. Indeed, since no intentional degradation is performed (no SA) and Galileo offers the possibility toperform dual frequency measurement to cancel errors due to ionosphere, regional correction would not bring any performanceimprovement. The only service that would benefit from regional ionospheric correction is the OAS single frequency service. However, it would not appear wise to develop a heavy and costly station network for the users that will not pay for the system. However, in order to reduce the ionospheric error for this kind of user, Galileo will broadcast ionospheric correction based on aKlobuchar like model on a Global basis.

In local two types of UERE can de identify. The first one is the one obtained on code measurement corrected by local differentialinformation. This can be done in real time. The second one is the one based on a direct carrier phase measurement (kinematicsmode). This second technique is more time demanding (TTFF/ Time to reacquire ) and is not applicable to high dynamicapplication. However, this time demand is decreased with the number of carriers available. For OAS/CAS1 service, since threecarriers are available, carrier phase measurements are possible in real time using TCAR technique.

On conclusion, as far as the system is concerned, 8 specific cases are identified for UERE estimation:

- OAS/CAS1

- Global

- Single frequency case 1

- Dual frequency case 2

- Local

- Local Differential case 3

- TCAR case 4

- SAS

- Global case 5


Index

709

710

711

712

713

714

715

716

717

718

719

720

721

722

723

724

725

726

ID

DD-036-788

DD-036-789

DD-036-790

DD-036-791

DD-036-792

DD-036-793

DD-036-794

DD-036-795

DD-036-796

DD-036-797

DD-036-798

DD-036-799

DD-036-800

DD-036-801

DD-036-802

DD-036-803

DD-036-804

DD-036-805


- Local case 6

- GAS

- Global case 7

- Local case 8

5.1.2 User Specific Parameters

Parameters impacting the UERE at user level are:

- Ionosphere mitigation technique: Single or Dual frequency

- Multipath environment: High or Low

- User dynamic: Static or Dynamic

- Interference environment: High or Low

To be exhaustive, an UERE should be provided for the combination of all the cases. However to limit the scope of theinvestigation, the strategy selected is the following. For each service a specific scenario is define in order to assess theperformances:

- Reference scenario for OAS single frequency service:

- Low User dynamic

- Urban environment

- Reference scenario for OAS/CAS1 dual frequency service:

- Medium User dynamic

- Urban environment


Index

727

728

729

730

731

732

733

734

735

736

737

738

ID

DD-036-806

DD-036-807

DD-036-808

DD-036-809

DD-036-810

DD-036-811

DD-036-812

DD-036-813

DD-036-814

DD-036-815

DD-036-816

DD-036-817


- Reference scenario for SAS service:

- High User dynamic

- Open environment

For all the scenario considered, the level of interference will be considered low. A preliminary maximum power tolerable on theGalileo signal band low enough not to degrade the navigation performance is provided. This budget will be consolidated in theGALA work package dealing with security aspects.

As far as multipath is concerned, the approach will be the following. Since multipath is very application dependant it is verydifficult to have a model representative of all the environment that the user may be confronted to. Therefore, for each service,performance will be first assessed with a low multipath level. “Low” means that the level of multipath is low enough not todegrade the UERE budget due to other contributors such as orbito&synchro, ionosphere, ect …

In a second step performance will be estimated including a budget for multipath. This budget will be computed using empiricalmodel (EGNOS like) and shall be interpreted as an allocation on the total budget for degradation affordable due to multipath. This budget can also be considered representing a “high” multipath scenario. Indeed, even if the budget does not appear veryhigh for one specific satellite, assuming that this kind of budget impacts all the satellites in sight makeS it very penalizing interms of navigation performance.

5.1.3 Signal Structure Hypothesis

The frequency mapping on Galileo Signal In Space is not totally define yet. At MTR seven scenarios were still considered. Eachscenario was based on different possible outcomes of international negotiations. Indeed, Galileo frequency will be very differentdepending from the fact that Europe decides to have an agreement with USA or Russia. After the WRC 2000 held in June inIstanbul, only two scenarios out of the seven were retained. At PM5, three were still under considerations.

At system performance level, following in real time the evolution of the signal task is not possible. Therefore a most robustapproach is necessary. As it is shown on this document the performance in terms of UERE as far as the signal is concerneddepend of the following parameters:

- L band or C band

- Single or Dual (or Triple) frequency in L band

- Narrow band or wide band on the different frequency


Index

739

740

741

742

743

744

745

746

747

748

749

750

751

ID

DD-036-818

DD-036-819

DD-036-820

DD-036-821

DD-036-822

DD-036-823

DD-036-824

DD-036-825

DD-036-827

DD-036-828

DD-036-829

DD-036-830

DD-036-831


- User terminal assumptions for each service

- Carrier power

The PM4 baseline scenario that will be referred as “working scenario” in the document allowed to cover the following cases:

- Single frequency in L band

- Single frequency in C band

- Dual frequency in L band with a narrow band and a wide band signal with CAS1 Receiver (6s integration time)

- Dual frequency in L band with a narrow band and a wide band signal with SAS/GAS Receiver (30s integration time)

Those cases allow to cover all the scenarios that are present in the three baselines still under considerations in GALA. Ofcourse some discrepancies may appear between the cases considered in the working scenario and the baselines (due to slightdifferences in chip rate, bit rate, … ), but those differences would remain minor and would not affect at all the validity of theworking scenario used for performance assessment.

5.2 Dual L band frequency UERE with SAS/GAS receiver assumption

5.2.1 UERE budget error in GLOBAL

5.2.1.1 Signal to Noise ratio

5.2.1.1.1 Signal power

The signal specification includes the minimum power available on ground with a 0 dBi antenna. For the carriers used for SASthis minimum power is equal to –155 dBw for E1 and –152 dBw for E5. However E5 contains two signals: a narrow band signalat 1.023 Mchips/s and a wide band signal at 10.23 Mchips/s. The total power on E5 will be therefore split on those two signals. Since the way to split the power is not totally defined yet, the assumptions used in this document will be to have half of thepower on each signals. As far as UERE performances are concerned, only the wide band signal is relevant, the narrow bandsignal being used mainly for acquisition.


Index

752

753

754

755

756

ID

DD-036-832

DD-036-833

DD-036-835

DD-036-836

DD-036-838…


Another parameter that can degrade the power available is the use of a pilot and data channel. In this case the power availablein total has to be split between the two signals. Currently the way to split the power is under study. However, the degradationof power at user level will only occur if the user is in such environment that he is not able to track the data channel. In nominalenvironment, the user should be able to track the pilot and the data channel and then recombine both. Therefore, the full poweris assumed available to perform ranging measurement. The validity of this assumption is detailed in WP4.1 that deals withuser terminal performance

Therefore the SAS signal on E5 will be considered as having a chip rate of 10.23 Mchips/s and a minimum power equal to –155dBw. This minimum power shall be available for all the elevation angle from 5 to 90 degrees. In order to provide such a servicenavigation satellite payload includes shaped antennas with a higher gain on the foresight to compensate for the slant rangebetween center of coverage and the hedge of coverage. However, those antennas are not perfect and to insure a minimumpower at 5 and 90 degrees elevation angle the power available at other elevation angle is higher. As an example the followingfigure shows the minimum signal level according to the elevation angle for GPS with a 3 dBi antenna.

Figure 26: GPS-ICD power specification

-160,5

-160

-159,5

-159

-158,5

-158

-157,5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Po

wer

leve

l (3d

Bi a

nte

nn

a)

Therefore it makes sense to assume the Galileo signal power will have the same behavior. The power available on ground witha 0 dBi antenna considered for SAS carriers are shown in the following graph:

Figure 27: Galileo E1 and E5 carrier power


Index

757

758

759

763

764

ID

…DD-036-838

DD-036-839

DD-036-840

DD-036-851

DD-036-852

DD-036-854…


-155,5

-155

-154,5

-154

-153,5

-153

-152,5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Po

wer

leve

l (0d

Bi a

nte

nn

a)

5.2.1.1.2 User antenna gain

The antenna used at user level is typically a narrow aperture antenna with a wide beam. The maximum gain may vary from4.5 to 7 dB according to the antenna type. For this study, the same typical radiation pattern that was used in the ComparativeSystem Study phase 2 [RD-013] is taken into account. The characteristic of the antenna gain are the followings:

Table 5: User antenna gain characteristics

Maximum Gain +4.5 dB

Mean Gain 2.8 dB

Minimum Gain - 4 dB

The detail of the user radiation pattern are shown on the following graph:

Figure 28: User antenna radiation pattern


Index

765

766

767

ID

…DD-036-854

DD-036-855

DD-036-856

DD-036-858


- 5

- 4

- 3

- 2

- 1

0

1

2

3

4

5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

E l e v a t i o n ( ° )

Rec

eive

an

ten

na

gai

n (

dB

)

5.2.1.1.3 Receiver Thermal Noise

The receiver antenna output is fed to a transmission line and band-pass filter and then to a Low Noise Amplifier as shown inthe following figure [RD-016]:

Figure 29: Receiver amplification chain configuration

Band-pass Filter LNA

Antenna

Galileo signals

Ampli 1


Index

768

769

770

771

772

773

774

775

776

777

778

779

780

781

ID

DD-036-859

DD-036-860

DD-036-861

DD-036-862

DD-036-863

DD-036-864

DD-036-865

DD-036-866

DD-036-867

DD-036-868

DD-036-869

DD-036-870

DD-036-871

DD-036-872


The amplifier placed after the LNA do not have any effect on the signal to noise ratio since they amplify in the same way theuseful signal and the noise. The receiver noise power density is computed with the two following formulas:

)(10log100 equTKN ⋅⋅=

RA

equ TLT

LL

TT +⋅−+= 0)1(

with: No = Receiver thermal noise floor

K = Boltzman cte (1.38 10-23 W/K-Hz)

Tequ = Receiver thermal noise temperature

TA = Antenna noise temperature

L = Transmission losses

To = Ambient temperature of the transmission line

Tr = LNA noise temperature.

A typically value usually selected for the antenna noise temperature is 130 °K. The losses are assumed negligible since the LNAshall be closed to the antenna. Nevertheless, although the impact of the losses are negligible on the noise floor, they attenuatethe carrier power. This effect will be taken into account in the final C/No computation. The LNA noise figure is assumed equalto 2.5 dB which is equivalent to a LNA temperature of 225 °K.

Therefore the thermal noise floor due to the receiver hardware is equal to –203 dBW/Hz

5.2.1.1.4 Galileo Cross Interference

Galileo system will use CDMA (Code Division Multiple Access). This technique allows the satellites to broadcast their signal onthe same frequency without cross-talk. However, the immunity between signals is not perfect and some cross interferenceremain. The model used for assessing cross interference level is extracted from [RD-016] and follows the following formula.


Index

782

783

784

785

786

787

788

792

793

ID

DD-036-873

DD-036-874

DD-036-875

DD-036-876

DD-036-877

DD-036-878

DD-036-901

DD-036-902

DD-036-903


( )c

scross f

PMN ⋅−⋅= 1

32

With Ncross = Noise component due to cross interference

M = Number of Galileo Satellite in sight

Ps = Power of one interfering signal at antenna output

fc = Chip rate

The main limitations of such a model is that the code is not ideal, and with quasi-stationary phenomena the impact could bestronger. It can be assumed however that the code is long enough to be considered as ideal. This will be refined after havingrefined the code length of the signal structure. The factor 2/3 is valid for square signal. In the case that the PRN is filtered aton lobe this parameter can raise up to 0.8. According to the baseline, the total satellite number in the constellation is 30. Therefore, the number of satellite in sight of one user is supposed not to exceed 15 satellites. According to Figure 27 themaximum power on ground with a 0 dBi antenna is -153.4 dBw. The satellites are considered spread on all the azimuth,therefore the power unbalance due to the antenna is selected at the mean gain which is 2.8 dB. However, cross interference aresubject to a 2 dB losses in the receiver. Therefore the noise power due to cross interference for each frequency is detailed in thefollowing table.

Table 6: Cross Interference Power

Carrier Max PowerLevel

Mean AntennaGain

Rx losses Chip rate Cross interferingpower

E1 -153.4 dBw +2.8 dB 2 dB 2.046 MHz -205 dBw/Hz

E5 -153.4 dBw +2.8 dB 2 dB 10.23 MHz -212 dBw/Hz

5.2.1.1.5 External Interference

The signal to noise ratio is also affected by external interference. This depends obviously of the characteristics of theelectromagnetic environment of the user. This environment is quite difficult to identify because it is different for all users.


Index

794

795

796

797

798

799

800

801

802

803

804

ID

DD-036-904

DD-036-905

DD-036-906

DD-036-907

DD-036-908

DD-036-909

DD-036-910

DD-036-911

DD-036-912

DD-036-913

DD-036-914


For Galileo one main issue in terms of frequency band allocation is the presence of radar and DME in E6 and E5 bandwidth. However those radar are seen only from high altitudes. Typically, ground users and low altitude users will not suffer this kindof interference. Therefore in terms of performance we have two cases.

The user is at high altitude and is subject to interference. This degrades the performance, but since the performance requiredat this altitude is quite relax, the interference should not be significantly. The main objective will be to keep tracking thesignal. This is why a narrow band signal less subject to interference has been added on E5.

At low altitude, the user does not see the interference due to radar and DME. Therefore he can track the wide band signalwithout specific problems and get a better accuracy.

The strategy to account for external interference in the UERE budget will be to define a maximum level of interference underwhich the performance should be met. This level will play in GALA study the same role as the MOPS-RTCA mask for civilaviation users. The model used to assess the noise component due to interference is the following [RD-016]:

cI f

JN =

with: NI = Noise component due to external interference

J = Jammer Power at antenna output

fc = Chip rate

The main limitations of such a model is that the code is not ideal, and with quasi-stationarity phenomena the impact could bestronger. It can be assumed however that the code is long enough to be considered as ideal. This will be refined after havingrefined the code length of the signal structure.

The only application that has a clear baseline for interference is Civil Aviation. This baseline specifies the maximum level ofinterference under which the user segment may have to operate.

For tone interference the maximum interference level in band level is equal to –120 dBm. However this value assumes the useof a 1023 bits 1 MHz code. Galileo will use more robust signal structure. Therefore the external interference power will bespecified at the input of the loop which means that the jammer assumed will be different for each signal option.


Index

805

806

810

811

812

816

817

ID

DD-036-915

DD-036-935

DD-036-936

DD-036-937

DD-036-957

DD-036-958

DD-036-960…


In the case of the current GPS signal structure with a jammer of –120 dBm with an antenna gain of 4.5 dB (worst case) , theexternal interfering power is computed at -205.6 dBw/Hz. This figure will be taken for all the signal structure.

Table 7: External Interference Power Level

Carrier Jammerpower

Mean AntennaGain

Chip rate External interferingpower

E1 -147 dBw +4.5 dB 2.046 MHz -205.6 dBw/Hz

E5 -134 dBw +4.5 dB 10.23 MHz -205.6 dBw/Hz

5.2.1.1.6 Signal to Noise Ratio

Taking into account the thermal noise, the noise due to cross-interference and the noise due to external interference, the globalnoise floor for each SAS frequency is equal to:

Table 8: Noise Floor

Carrier ThermalNoise

Cross interferencecomponent

External Interferencecomponent

Noise FloordBw/Hz

E1 -203 -205 -205.6 -199.6

E5 -203 -212 -205.6 -200.7

A budget of 2 dB is allocated to the receiver for the losses due to the sampler, feeder and correlator. This allows to derive thesignal to noise ratio for each carriers. The results are shown on the following graph:

Figure 30: C/No for E1 and E5


Index

818

819

820

821

822

823

824

ID

…DD-036-960

DD-036-961

DD-036-962

DD-036-963

DD-036-964

DD-036-965

DD-036-966

DD-036-967


36

38

40

42

44

46

48

50

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elv angle

C/N

o in

dB

w/h

z

E1E5

5.2.1.2 Receiver Budget Error

5.2.1.2.1 Code Tracking Error

The tracking error depends of the kind of DLL used in the receiver. For a non coherent Delay Lock Loop, the tracking error atone sigma is equal to the following formula [RD-016]:

(m)

+⋅=

00

21

2 NCB

NCB

k FIccRx λσ

with: σRx : Tracking error at one sigma in meter

λc : Code wavelength


Index

825

826

827

828

829

830

831

832

833

834

ID

DD-036-968

DD-036-969

DD-036-970

DD-036-971

DD-036-972

DD-036-973

DD-036-974

DD-036-975

DD-036-976

DD-036-978…


Bc : Code loop bandwidth

K : Factor taking into account the signal wave shape (=1 for a square signal can

reach 0.75 for a QPN signal

BFI : Pre-detection Bandwidth

C/No : Carrier to Noise Ratio including thermal noise, cross and external

interference

However, this formula is the Cramer-Rao bound of the pseudo-range accuracy; it means that such a value will be achieved only ifstatistical properties of signal and noise fit closely with the theoretical ones, and that the used estimator is the optimal one(according maximum likelihood approach). Therefore a margin of at least 50% needs to be integrated to take into accountreceiver technological discrepancies.

As specified in the chapter 5.1 the user is assumed dynamic. However, main of the receivers use PLL aiding to cope withdynamic. Therefore the loop bandwidth selected is the same that would have been selected for a static/low dynamic user, that isto say 2 Hz. The pre-detection bandwidth is directly linked to the symbol rate. The pre-detection bandwidth is thereforeselected at 330 Hz for E5 and 300 Hz for E1.

Considering those assumptions the tracking error due to thermal noise, cross-interference and external interference is shown onthe following graph:

Figure 31: Code Tracking Error on E1 and E5


Index

835

836

837

838

839

840

841

ID

…DD-036-978

DD-036-979

DD-036-980

DD-036-981

DD-036-982

DD-036-983

DD-036-984

DD-036-985


0

0,5

1

1,5

2

2,5

3

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elv Angle

Err

or

at 1

sig

ma

in m

E1E5

Due to a chip rate 5 times higher, the range measurement on E5 is much better the one available on E1.

5.2.1.2.2 Multipath Budget Error

The tracking loop measurement error do not depend only from the signal to noise ratio. Reflections of the navigation signal onobstacles (buildings, water, air-plane wings) disturb the carrier loop tracking. This phenomena is called multipath. This kind oferror is very difficult to model since it very much environment dependant. The difference can be quite high according to the userapplication. Furthermore, the type of technique implemented in the user receiver to mitigate the multipath has also a greatimpact on the residual error. According to the king of multipath to deal with, narrow correlation and carrier smoothing canreduce the residual error.

The key parameter that drives the multipath error at user level are:

- The number of reflections

- The attenuation of the reflection comparing to the direct path

- The delay of the reflection comparing to the direct path


Index

842

843

844

845

846

847

848

849

850

851

ID

DD-036-986

DD-036-987

DD-036-988

DD-036-989

DD-036-990

DD-036-991

DD-036-992

DD-036-993

DD-036-994

DD-036-996…


- The difference of frequency between the reflection and direct path

The objective of this chapter is to define a model that aims at representing a mean multipath error. Of course, since it is verymuch environment dependant, according to the application, the error might be much higher than the model prediction. However, considering the worst case in the UERE budget would be too conservative. The system shall not be designed takinginto account the worst cases users, otherwise, it would be totally oversized.

The model selected is the one used in EGNOS. The multipath error at 1 sigma varies according to the elevation angle accordingto the following formula:

( ))tan(

45

θσ

σ°

= mpmp

with: σmp = Multipath budget error at 45 degrees

= Elevation Angle

For the EGNOS 3B service level the budget at 45 degrees for GPS is selected at 0.25 m. GPS signals have a chip rate of 1.023Mchips/s. Since Galileo signals have different chip rates and multipath error is strongly dependant of the chip rate, as a rule ofthumb, the multipath budget for Galileo will be linearly sized according to the chip rate. However, it has to be pointed out thatthis budget is achieved in EGNOS by using 30s integration time carrier smoothing to mitigate the multipath. EGNOS is asystem designed for civil aviation. Since the reference scenario for SAS/GAS is a landing aircraft, it makes sense to keep thesame assumptions in terms of integration time.

Taking account those assumptions, the multipath UERE budget after carrier smoothing for SAS/GAS is shown on thefollowing graph:

Figure 32: Multipath Error budget for E1 and E5


Index

852

853

854

ID

…DD-036-996

DD-036-997

DD-036-998

DD-036-1000…


0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation angle in degrees

Err

or

in m

at

1 si

gm

a

E1E5

5.2.1.2.3 Global Receiver Budget Error

The receiver budget error includes errors due to the thermal noise, interference (external and internal) and multipath. Theprevious section described how those budget error are affecting the code tracking. However, a technique available to improvethe range measurement error is to filter the code with the carrier phase measurements. This technique has been already takeninto account when defining the multipath budget. However carrier smoothing will improve the receiver performance in terms ofnoise error as well. The carrier smoothing integration time for SAS is selected to 30 seconds. It is interesting to point out thatsince the GAS is considered as a governmental SAS, the assumptions on the receiver are similar for the two services.

Figure 33: Receiver Budget Error at 1 sigma including Thermal Noise, Interference and Multipath, smoothed with the carrier(30s integration time)


Index

855

856

857

858

859

860

ID

…DD-036-1000

DD-036-1001

DD-036-1002

DD-036-1003

DD-036-1004

DD-036-1005

DD-036-1006


0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elv angle

Err

or

at 1

sig

ma

in m

E1E5

5.2.1.3 Tropospheric Residual Error

The cross of the troposphere induces some disturbance on the navigation signals. Troposphere effects include attenuation anddelay. The attenuation is typically below 0.5 dB which is negligible in the link budget. On the other hand the delay can varyfrom 2 to 25 meters and has to be corrected. As simplified model relying on ray tracing gives the athmospheric delay includingthe dry and wet component according to the elevation angle [RD-016].

)(012.0)sin(

47.2m

Ed tropo +

=

with: dTropo = Delay due to the troposphere

E = Elevation Angle


Index

861

862

863

864

865

ID

DD-036-1007

DD-036-1008

DD-036-1009

DD-036-1011

DD-036-1012


The dry component which represents 90% of the total delay is something quite easy to predict. This not the case for the wetcomponent. In order to compensate the wet component measures of temperature and humidity are necessary. In ComparativeSystem Study, the accuracy of this model was assumed equal to 4% of the tropospheric delay. However this assumes that thedry component is removed and external sensors are used to correct half of the wet component delay. This will induce complexity(interface, extra sensor, additional software) and cost at receiver and cannot be taken for granted without further trade-off.Therefore the accuracy of the model is estimated at 10% and the residual tropospheric error at one sigma is equal to:

)(1.0*012.0)sin(

47.2m

Etropo +=σ

with: σTropo = Residual error due to the troposphere at 1 sigma

Figure 34: Residual error due to the troposphere at 1 sigma

0

0,5

1

1,5

2

2,5

3

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elv Angle in degree

Err

or

at 1

sig

ma

in m

The tropospheric delay is also quite dependant from the temperature, pressure and humidity as explained in the RTCA-MOPS[RD-014]. Nevertheless the correction accuracy are quite independent of those phenomena and the tropospheric error accordingto the elevation angle showed above is quite close to the one detailed in the MOPS for all conditions.


Index

866

867

868

869

870

871

872

873

874

875

876

877

878

ID

DD-036-1013

DD-036-1014

DD-036-1015

DD-036-1016

DD-036-1017

DD-036-1018

DD-036-1019

DD-036-1020

DD-036-1021

DD-036-1022

DD-036-1023

DD-036-1024

DD-036-1025


5.2.1.4 Total UERE after Dual Frequency Processing

When two signals are emitted by the satellite on two different carriers, it is possible to remove the error due to ionosphere bycombining measurements from the two carriers. The ionospheric delay on the first carrier can be expressed with the followingformula:

22

21

22

212

1

ffff

ionofree −−

=ρρ

ρ

With ρ1 = Pseudorange on carrier 1.

ρ2 = Pseudorange on carrier 2.

ρionofree = Pseudorange after ionopheric correction.

f1 = Frequency of carrier 1

f2 = frequency of carrier 2

The standard deviation of the ionospheric delay estimator is equal to:

( )222

21

22

42

21

41

ff

ffionofree

−

+=

σσσ

With σ1 = Standard deviation of ρ1 measurement

σ2 = Standard deviation of ρ2 measurement

The tropospheric error on each frequency are assumed correlated. Therefore it is not amplified by the processing of themeasurement on both frequency for correction of the ionospheric delay.


Index

879

880

881

882

883

884

885

886

887

888

ID

DD-036-1026

DD-036-1027

DD-036-1028

DD-036-1029

DD-036-1030

DD-036-1031

DD-036-1032

DD-036-1033

DD-036-1034

DD-036-1036…


The clock and ephemeris error is also not frequency dependant. Therefore it is not altered by the dual frequency processing. The budget for clock and Ephemeris error is equal to 0.65 m at 1 sigma.

Therefore the pseudorange error at one sigma is equal to:

( ) ectropoRxRx

psdff

ff+++

−

+= 22

222

21

22

42

21

41 σσ

σσσ

With σ1 = Rx budget Error on Carrier 1

σ2 = Rx budget Error on Carrier 2

σtropo = Tropospheric budget error

σc+e = Clock and Ephemeris Budget Error

5.2.1.4.1 UERE with high multipath

The total UERE for SAS service taking into account pessimistic assumptions for multipath is detailed on the following graph and table:

Figure 35: Total UERE with high multipath


Index

889

ID

…DD-036-1036

DD-036-1163


00.5

11.5

22.5

33.5

44.5

5

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

tropo

Tot Rx

clock+ephem

Tot UERE

Tot UERE+10%

Table 9: UERE with high multipath

Elv Receiver Tot Rx Tropo Clock+Eph

Total Total+10%margin

E1 E5 (Dual freq)

5 1,47 0,29 3,45 2,49 0,65 4,31 4,74

10 0,76 0,15 1,78 1,33 0,65 2,31 2,55

15 0,51 0,10 1,20 0,91 0,65 1,64 1,81

20 0,38 0,07 0,89 0,70 0,65 1,31 1,44

25 0,31 0,06 0,73 0,57 0,65 1,13 1,24

30 0,26 0,05 0,62 0,48 0,65 1,02 1,12

40 0,20 0,03 0,47 0,38 0,65 0,88 0,97

50 0,16 0,03 0,38 0,32 0,65 0,82 0,90

60 0,14 0,02 0,32 0,28 0,65 0,78 0,86


Index

904

905

906

907

ID

DD-036-1164

DD-036-1165

DD-036-1167

DD-036-1295


70 0,13 0,02 0,31 0,26 0,65 0,76 0,84

80 0,13 0,02 0,30 0,25 0,65 0,76 0,83

90 0,12 0,02 0,29 0,24 0,65 0,75 0,83

5.2.1.4.2 UERE with low multipath

In low multipath environment, the impact of multipath on the error budget is considered as negligible comparing to the othercomponents:

Figure 36: Total UERE with low multipath

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

5 15 25 35 45 55 65 75 85

Elevation Angle in m

Err

or

at 1

sig

ma

in m

RxTropoClock+EphemTotalTot+10%

Table 10: UERE with low multipath

Elv Receiver Tot Rx Tropo Clock budget TOTAL

Total+10%

E1 E5

5 0,34 0,06 0,81 2,49 0,65 2,70 2,97

10 0,27 0,05 0,63 1,33 0,65 1,61 1,77


Index

922

923

924

925

926

927

ID

DD-036-1296

DD-036-1297

DD-036-1298

DD-036-1299

DD-036-1300

DD-036-1301


15 0,21 0,04 0,49 0,91 0,65 1,22 1,35

20 0,16 0,03 0,38 0,70 0,65 1,03 1,13

25 0,16 0,03 0,36 0,57 0,65 0,94 1,03

30 0,15 0,03 0,35 0,48 0,65 0,88 0,97

40 0,13 0,02 0,31 0,38 0,65 0,81 0,89

50 0,12 0,02 0,29 0,32 0,65 0,78 0,86

60 0,12 0,02 0,28 0,28 0,65 0,76 0,84

70 0,12 0,02 0,29 0,26 0,65 0,76 0,83

80 0,12 0,02 0,29 0,25 0,65 0,75 0,83

90 0,12 0,02 0,29 0,24 0,65 0,75 0,83

5.3 Dual L band frequency UERE with OAS/CAS1 receiver assumption

5.3.1 UERE budget error in GLOBAL

The detail UERE computation are available in ANNEX C. Only the relevant difference comparing to the previous scenario aredescribe in this chapter.

One main difference is the difference of the integration time used for carrier smoothing. For SAS/GAS the user is assumedbeing in the open and can afford to filter the signal during a 30s period. However, since the CAS1 (OAS) user is assumedmoving within the urban environment, the time will most likely not be able to filter on a long period. Therefore the filteringtime is reduced down to 6 seconds.

5.3.1.1 Multipath Budget Error

The OAS/CAS1 user is assumed moving in urban environment. However, since no model is available to model this kind of error,the strategy for CAS1 will be to use the same empirical model as used for SAS to define a requirement for multipath budgeterror. The model aims at representing a mean multipath error. Of course, since it is very much environment dependant,according to the application, the error might be much higher than the model prediction. However, considering the worst case inthe UERE budget would be too conservative. The system shall not be designed taking into account the worst cases users,otherwise, it would be totally oversized.


Index

928

929

930

931

932

933

934

935

936

ID

DD-036-1302

DD-036-1303

DD-036-1304

DD-036-1305

DD-036-1306

DD-036-1307

DD-036-1308

DD-036-1309

DD-036-1311…


The empirical model selected is the one used in EGNOS. The multipath error at 1 sigma varies according to the elevation angleaccording to the following formula:

( ))tan(

45

θ

σσ

°= mp

mp

with: σmp = Multipath budget error at 45 degrees

= Elevation Angle

For the EGNOS 3B service level the budget at 45 degrees for GPS is selected at 0.25 m. GPS signals have a chip rate of 1.023Mchips/s. Since Galileo signals have different chip rates and multipath error is strongly dependant of the chip rate, as a rule ofthumb, the multipath budget for Galileo will be linearly sized according to the chip rate. However, it has to be pointed out thatthis budget is in EGNOS by using 30s integration time carrier smoothing to mitigate the multipath. This time may beaffordable for users in a open environment without obstacle such as civil aviation users. However for users moving in a urbanenvironment this time seems to long. Therefore, a more realistic integration time of 6 seconds is selected. Therefore, in orderto compensate for the 30s carrier smoothing, the multipath budget is multiplied by Sqrt(5).

Taking account those assumptions, the multipath UERE budget after carrier smoothing for OAS/CAS1 is shown on thefollowing graph:

Figure 37: Multipath Error budget E2 and E6


Index

937

938

939

940

ID

…DD-036-1311

DD-036-1312

DD-036-1313

DD-036-1314

DD-036-1316…


0

0,5

1

1,5

2

2,5

3

3,5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

at 1

sig

ma

in m

E2E6

5.3.1.2 Total UERE after Dual Frequency Processing

The total UERE is detailed on the following graph and table:

5.3.1.2.1 Total UERE with high multipath

Figure 38: UERE with high multipat


Index

941

ID

…DD-036-1316

DD-036-1443


0

2

4

6

8

10

12

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

TropoRxClock+EphemTotalTot+10%

Table 11: Dual Frequency UERE with high multipath

Elv Rx budget Rx Total Budget Tropo Clock budget TOTAL

Total + 10%margin

E2 E6 (Dual frequency)

5 3,30 0,33 10,06 2,49 0,65 10,39 11,43

10 1,71 0,17 5,22 1,33 0,65 5,43 5,97

15 1,16 0,11 3,54 0,91 0,65 3,72 4,09

20 0,86 0,08 2,63 0,70 0,65 2,80 3,08

25 0,71 0,07 2,16 0,57 0,65 2,33 2,56

30 0,61 0,06 1,85 0,48 0,65 2,02 2,22

40 0,46 0,04 1,41 0,38 0,65 1,60 1,76

50 0,38 0,04 1,16 0,32 0,65 1,37 1,50

60 0,33 0,03 1,01 0,28 0,65 1,23 1,36


Index

956

957

972

ID

DD-036-1444

DD-036-1571

DD-036-1573…


70 0,32 0,03 0,96 0,26 0,65 1,19 1,31

80 0,31 0,03 0,94 0,25 0,65 1,17 1,29

90 0,30 0,03 0,92 0,24 0,65 1,15 1,27

5.3.1.2.2 Total UERE with low multipath

Table 12: UERE budget with low multipath

Elv Rx budget Tot Rx Tropo Clock+Eph

Total Total+10%margin

E2 E6 Dual frequ

5 0,77 0,08 2,34 2,49 0,65 3,48 3,83

10 0,60 0,06 1,82 1,33 0,65 2,34 2,58

15 0,47 0,04 1,43 0,91 0,65 1,82 2,00

20 0,36 0,03 1,10 0,70 0,65 1,46 1,60

25 0,35 0,03 1,06 0,57 0,65 1,36 1,50

30 0,33 0,03 1,01 0,48 0,65 1,30 1,43

40 0,30 0,03 0,90 0,38 0,65 1,17 1,29

50 0,27 0,02 0,84 0,32 0,65 1,11 1,22

60 0,26 0,02 0,80 0,28 0,65 1,07 1,18

70 0,27 0,02 0,83 0,26 0,65 1,09 1,20

80 0,28 0,02 0,85 0,25 0,65 1,10 1,21

90 0,28 0,02 0,84 0,24 0,65 1,09 1,20

Figure 39: UERE with low multipath


Index

973

974

975

976

977

978

979

980

ID

…DD-036-1573

DD-036-1574

DD-036-1577

DD-036-1578

DD-036-1579

DD-036-1580

DD-036-1581

DD-036-1582

DD-036-1583


0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5 15 25 35 45 55 65 75 85

Elv angle in degrees

Err

or

in m

at

1 si

gm

a

TropoRxClock+EphemTotalTotal+10%

5.4 Single L band frequency UERE with OAS/CAS1 receiver assumptions

5.4.1 Residual Ionospheric Error

The ionospheric delay depends from the TEC (Total Electron Content) and the frequency of the carrier according the followingformula:

)()(*3.40

2 mEFf

TECdiono ×=

with: diono

= Ionospheric delay in m

TEC = Total Electron Content

F(.) = Obliquity factor [RD-016]

f = Carrier frequency


Index

981

982

983

984

985

986

987

988

ID

DD-036-1584

DD-036-1585

DD-036-1586

DD-036-1587

DD-036-1588

DD-036-1589

DD-036-1590

DD-036-1592


The use of a Klobuchar like model allows to correct the ionospheric error of 50%. Therefore the residual ionospheric error isequal to:

)(5.0)(*3.40

2 mEFf

TECiono ××=σ

with: σiono = Ionospheric delay in m

TEC = Total Electron Content

F(.) = Obliquity factor

f = Carrier frequency

A mean value of 30 1016 is selected for the TEC. The ionospheric error taking into account the above assumptions is detailed onthe following graph for each OAS+CAS1 carrier:

Figure 40: Ionospheric residual Error in mono frequency mode

0

2

4

6

8

10

12

14

16

18

20

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

at 1

sig

ma

in m

E2E6


Index

989

990

991

992

993

994

995

ID

DD-036-1593

DD-036-1594

DD-036-1595

DD-036-1596

DD-036-1597

DD-036-1599

DD-036-1713


5.4.2 Total UERE

The carrier selected for the single frequency service is E2. This choice is done for two reasons:

The chip rate is lower than on E6, therefore the receiver will be simpler and cheaper

Although the error due to the receiver is higher on this frequency comparing to E6, the UERE is much better thanks to aionospheric residual error lower.

The following graph shows the UERE for a mono frequency service:

Figure 41: UERE for E2 single frequency service

0

2

4

6

8

10

12

14

16

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

Tot UERETot+10%

Table 13: Single frequency service UERE

ElevationAngle

Rx budget Tropo Clockbudget

iono Total Total+10%margin


Index

1010

1011

1012

1013

1014

1015

ID

DD-036-1714

DD-036-1715

DD-036-1716

DD-036-1717

DD-036-1718

DD-036-1719


5 3,30 2,49 0,65 11,74 12,47 13,71

10 1,71 1,33 0,65 9,24 9,51 10,46

15 1,16 0,91 0,65 7,47 7,64 8,40

20 0,86 0,70 0,65 6,21 6,34 6,97

25 0,71 0,57 0,65 5,30 5,41 5,95

30 0,61 0,48 0,65 4,62 4,73 5,21

40 0,46 0,38 0,65 3,73 3,83 4,21

50 0,38 0,32 0,65 3,18 3,28 3,61

60 0,33 0,28 0,65 2,84 2,95 3,24

70 0,32 0,26 0,65 2,63 2,74 3,01

80 0,31 0,25 0,65 2,52 2,63 2,89

90 0,30 0,24 0,65 2,48 2,59 2,85

5.5 Single C band frequency UERE with SAS/GAS receiver assumptions

The assumptions to compute the UERE budgets are mainly the same than for SAS/GAS dual frequency service. The detailUERE computation are available in ANNEX C. Only the relevant difference are described in this chapter.

One main difference is the difference of the integration time used for carrier smoothing. For SAS/GAS L band dual frequencyservice the user is assumed being in the open and can afford to filter the signal during a 30s period. For C band, since the noiseis not amplified with dual frequency processing, 10 seconds integration time appear enough to reach the same performance.

5.5.1 UERE in Global

5.5.1.1 Multipath Budget Error

Multipath error for has been computed using the same assumptions used for the other services. The following graph shows themultipath budget at 1 sigma after filtering. However in that case the integration time of carrier smoothing is selected to 10seconds. In order to compensate the fact that carrier smoothing filtering time is 10s instead of 30s, the budget in amplified of afactor 1.7 (sqrt(3)).


Index

1016

1017

1018

1019

1020

ID

DD-036-1721

DD-036-1722

DD-036-1723

DD-036-1724

DD-036-1726…


Figure 42: Multipath Error

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

at 1

sig

ma

in m

5.5.1.2 Ionospheric Budget Error

This service includes only one frequency on C band. Therefore, no dual frequency processing is possible to get rid of the delaydue to the ionosphere. However, since the ionospheric error at C band is very much reduced compared to L band twofrequencies are not indispensable. Nevertheless, as for L band mono frequency mode, a model of the ionosphere could be used toreduce the error due to ionosphere. However since the efficiency of this kind of model is very poor in C band comparing to Lband (10% improvement in C band comparing to 50% in L band) and since the ionopheric error is no longer a driver in the totalbudget error, no ionospheric model will be used.

The ionospheric error taking into account the same assumptions used for L band is detailed on the following graph:

Figure 43: Residual Ionospheric Error


Index

1021

1022

1023

ID

…DD-036-1726

DD-036-1727

DD-036-1728

DD-036-1730…


0

0,5

1

1,5

2

2,5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elv angle

Err

or

at 1

sig

ma

in m

5.5.1.3 Total Budget Error

Taking into account all the budgets detailed above and by adding the clock and ephemeris error budget ( 0.65 m at 1 sigma), theUERE budget for C band service is detailed on the following graph:

Figure 44: UERE in global with high multipath


Index

1024

ID

…DD-036-1730

DD-036-1844


0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5 15 25 35 45 55 65 75 85

Elv Angle

Err

or

at 1

sig

ma

in m Rx

TropoClock+EphIonoTotalTot+10%

Table 14: UERE in Global with high multipath

ElvAng

User Rx Tropo Iono Clock+Ephem Total Total + 10%margin

5 0,71 2,49 2,28 0,65 3,50 3,85

10 0,40 1,33 1,78 0,65 2,35 2,59

15 0,29 0,91 1,44 0,65 1,85 2,03

20 0,21 0,70 1,20 0,65 1,55 1,70

25 0,19 0,57 1,02 0,65 1,35 1,49

30 0,17 0,48 0,90 0,65 1,22 1,34

40 0,14 0,38 0,72 0,65 1,05 1,16

50 0,13 0,32 0,62 0,65 0,96 1,05

60 0,12 0,28 0,54 0,65 0,90 0,99


Index

1039

1040

1041

1042

1043

1044

1045

1046

1047

1048

1049

ID

DD-036-1845

DD-036-1846

DD-036-1847

DD-036-1848

DD-036-1849

DD-036-1850

DD-036-1851

DD-036-1852

DD-036-1853

DD-036-1854

DD-036-1855


70 0,12 0,26 0,50 0,65 0,87 0,96

80 0,12 0,25 0,48 0,65 0,86 0,94

90 0,12 0,24 0,48 0,65 0,85 0,94

Since the service is single frequency, multipath does not have a great impact on the final UERE budget. Therefore the budgetswith and without multipath are similar.

5.6 UERE in Local

5.6.1 L band UERE budget with SAS/GAS receiver assumptions

5.6.1.1 Receiver Budget Error

5.6.1.1.1 Code measurements

In local only one frequency is used. Therefore the receiver budget error is the one that has been computed for E5 in global. Inlocal the fact to use only one frequency allows to take fully advantage of the high chip rate present on E5 (10.23 MHz). InGlobal it was not the case since, because of the dual frequency processing, all the noise was mainly due to E1 that had a chiprate much lower (2.046 MHz).

However, it is also necessary to take into account the budget error of the receiver placed in the local station. The only differencecomparing to the user receiver comes from the multipath. The user receiver error for SAS/GAS in local has been computedusing the same assumptions used for SAS/GAS in global.

For the reference station receiver error, the assumptions are mainly identical to the ones made for the user except for themultipath budget. Indeed, since the reference receiver is not moving, it is not possible to filter out the error due to multipath. That is why in EGNOS 3A, the multipath budget for the reference station (RIMS) is different from the one used for the usersegment. The model in inverse tangent is still applicable , however the value for GPS is increased from 0.25 to 0.5 meters. ForGalileo SAS, the multipath at 45 degrees after filtering for the reference receiver is:

σmp=0.25 m for E1 (2.046 Mc/s)

σmp=0.05 m for E5 (10.23 Mc/s)

5.6.1.2 Troposphere Budget Error


Index

1050

1051

1052

1053

1054

1055

1056

ID

DD-036-1856

DD-036-1857

DD-036-1858

DD-036-1859

DD-036-1860

DD-036-1861

DD-036-1862


In local the delay due to the troposphere is corrected using the information broadcast by the reference station. The accuracy ofthis correction depends of the distance between the user and the station. The dependency between this distance and thetropospheric residual error is assumed with the following model:

RVtropo ∆⋅⋅= −6102σ

With: σVtropo= Vertical tropospheric residual Error at 1 sigma (m)

∆R = Distance between the station and the user in m.

This residual error depends from the distance between the station and the receiver but also from the elevation angle. Thisdependance is expressed with the following formula :

)sin(EVtropo

Tropo

σσ =

For a baseline of 10 km between the station and the user the vertical tropospheric residual error is equal to 0.02 m. Theresidual tropospheric error in local is detailed in the following graph :


Index

1057

1058

1059

1060

1061

1062

1063

ID

DD-036-1864

DD-036-1865

DD-036-1866

DD-036-1867

DD-036-1868

DD-036-1869

DD-036-1870


Figure 45: Tropospheric error in local

0

0,05

0,1

0,15

0,2

0,25

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

in m

at

1 si

gm

aTropo

5.6.1.3 Ionosphere Budget Error

In local the delay due to the ionosphere is also corrected using the information broadcast by the reference station. The accuracyof this correction depends of the distance between the user and the station. The dependency between this distance and theionosphere residual error is similar to the one used for the ionosphere (extracted from [RD-016]):

RViono ∆⋅⋅= −6102σ

With: σiono = Vertical Ionosphere residual Error at 1 sigma (m)

∆R = Distance between the station and the user in km.

This residual error depends also from the elevation angle though the obliquity factor. For a baseline of 10 km between thestation and the user the ionosphere residual error is equal to 0.02 m.


Index

1064

1065

1066

1067

1068

ID

DD-036-1872

DD-036-1873

DD-036-1874

DD-036-1875

DD-036-1989


Figure 46: Ionospheric Error in local at 10 km

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,1

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

at 1

sig

ma

in m

Iono

5.6.1.4 Total Budget Error

5.6.1.4.1 Local UERE with high multipath

The total budget error taking into account all the budgets in local in detailed in the following graph:

Table 15: UERE in Local with high multipath

Elv User Rx Station Rx Tropo Iono Total Total+10%margin

5 0,29 0,57 0,23 0,09 0,69 0,76

10 0,15 0,29 0,12 0,07 0,35 0,38

15 0,10 0,19 0,08 0,06 0,23 0,26

20 0,07 0,14 0,06 0,05 0,17 0,19

25 0,06 0,11 0,05 0,04 0,14 0,15

30 0,05 0,09 0,04 0,04 0,11 0,13


Index

1083

1084

1085

ID

DD-036-1991

DD-036-1992

DD-036-2106


40 0,03 0,06 0,03 0,03 0,08 0,09

50 0,03 0,04 0,03 0,03 0,06 0,07

60 0,02 0,03 0,02 0,02 0,05 0,06

70 0,02 0,02 0,02 0,02 0,04 0,05

80 0,02 0,02 0,02 0,02 0,04 0,04

90 0,02 0,02 0,02 0,02 0,04 0,04

Figure 47: UERE in local with high multipath

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

User RxStat RxTot RxTotal UERETot UERE +10%

5.6.1.4.2 Local UERE with low multipath

Table 16: UERE in Local with low multipath

Elv Rx Station User Rx Tropo Iono Total Total+10%

5 0,06 0,06 0,23 0,09 0,26 0,29


Index

1100

1101

ID

DD-036-2108

DD-036-2109


10 0,05 0,05 0,12 0,07 0,15 0,17

15 0,04 0,04 0,08 0,06 0,11 0,12

20 0,03 0,03 0,06 0,05 0,09 0,10

25 0,03 0,03 0,05 0,04 0,07 0,08

30 0,03 0,02 0,04 0,04 0,07 0,07

40 0,02 0,02 0,03 0,03 0,05 0,06

50 0,02 0,02 0,03 0,03 0,05 0,05

60 0,02 0,02 0,02 0,02 0,04 0,05

70 0,02 0,02 0,02 0,02 0,04 0,05

80 0,02 0,02 0,02 0,02 0,04 0,05

90 0,02 0,02 0,02 0,02 0,04 0,05

Figure 48: UERE with low multipath

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

5 10 15 20 25 30 40 50 60 70 80 90

Elv angle in degree

Err

or

at 1

sig

ma

in m Rx station

Rx UserTropoIonoTotalTot+10%

5.6.2 L band UERE budget with OAS/CAS1 receiver assumptions


Index

1102

1103

1104

1105

ID

DD-036-2110

DD-036-2111

DD-036-2113

DD-036-2227


In local, the ranging function is done using E6 only. The total budget error taking into account all the budgets in local indetailed in the following graphs:

5.6.2.1 UERE in local with high multipath

Figure 49: UERE in Local with high multipath

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Tot RxTropoIonoTotal UERETot+10%

Table 17: UERE for in local with high multipath

Elv User Rx Station Rx Tropo Iono Total Total +10%margin

E6 E6

5 0,33 0,64 0,23 0,09 0,76 0,84

10 0,17 0,32 0,12 0,07 0,39 0,42

15 0,11 0,21 0,08 0,06 0,26 0,28

20 0,08 0,15 0,06 0,05 0,19 0,21

25 0,07 0,12 0,05 0,04 0,15 0,17


Index

1120

1121

1122

ID

DD-036-2228

DD-036-2230

DD-036-2344


30 0,06 0,10 0,04 0,04 0,13 0,14

40 0,04 0,07 0,03 0,03 0,09 0,10

50 0,04 0,05 0,03 0,03 0,07 0,08

60 0,03 0,03 0,02 0,02 0,06 0,06

70 0,03 0,02 0,02 0,02 0,05 0,05

80 0,03 0,01 0,02 0,02 0,04 0,05

90 0,03 0,01 0,02 0,02 0,04 0,04

5.6.2.2 UERE in local with low multipath

Figure 50: UERE in Local with low multipath

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

5 15 25 35 45 55 65 75 85

Elevation Angle in degrees

Err

or

at 1

sig

ma

in m Station Rx

User Rx

Tropo

Iono

Total

Tot+10%

Table 18: UERE in local with low multipath

Elev. Station Rx User Rx Tropo Ionosphere Total Total+10%


Index

1137

1138

1139

1140

ID

DD-036-2345

DD-036-2346

DD-036-2347

DD-036-2349…


5 0,04 0,09 0,23 0,09 0,26 0,29

10 0,03 0,06 0,12 0,07 0,15 0,17

15 0,02 0,05 0,08 0,06 0,11 0,12

20 0,01 0,04 0,06 0,05 0,09 0,09

25 0,01 0,03 0,05 0,04 0,07 0,08

30 0,01 0,03 0,04 0,04 0,06 0,07

40 0,01 0,03 0,03 0,03 0,05 0,06

50 0,01 0,03 0,03 0,03 0,05 0,05

60 0,01 0,03 0,02 0,02 0,04 0,05

70 0,01 0,03 0,02 0,02 0,04 0,04

80 0,01 0,03 0,02 0,02 0,04 0,04

90 0,01 0,03 0,02 0,02 0,04 0,04

5.6.3 C band UERE budget with SAS/GAS receiver assumptions

5.6.3.1 UERE budget with high multipath

The ranging in local is done on the only GAS carrier available that is in C band. The total budget error taking into account allthe budgets in local in detailed in the following graph:

Figure 51: Total UERE in Local with high multipath


Index

1141

ID

…DD-036-2349

DD-036-2463


0

0,2

0,4

0,6

0,8

1

1,2

1,4

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

Tot RxTropoIonoTotalTot+10%

Table 19: UERE in Local with high multipath

ElvAng

User Rx StatRx

Tropo Iono Total Total + 10%margin

5 0,71 0,74 0,23 0,09 1,06 1,16

10 0,40 0,39 0,12 0,07 0,58 0,63

15 0,29 0,26 0,08 0,06 0,40 0,44

20 0,21 0,19 0,06 0,05 0,30 0,33

25 0,19 0,16 0,05 0,04 0,25 0,28

30 0,17 0,14 0,04 0,04 0,22 0,25

40 0,14 0,10 0,03 0,03 0,18 0,20

50 0,13 0,09 0,03 0,03 0,16 0,17

60 0,12 0,07 0,02 0,02 0,14 0,16


Index

1156

1157

1171

1172

1173

1174

1175

ID

DD-036-2464

DD-036-2583

DD-036-2584

DD-036-2585

DD-036-2586

DD-036-2587

DD-036-2588


70 0,12 0,07 0,02 0,02 0,14 0,16

80 0,12 0,07 0,02 0,02 0,14 0,16

90 0,12 0,07 0,02 0,02 0,14 0,15

5.6.3.2 UERE budget with low multipath

Table 20: UERE in Local with low multipath

ElevAngle

Rx budget Rx Station TotalRx

Tropo Ionosphere Total Total+margin

5 0,36 0,21 0,42 0,23 0,09 0,49 0,54

10 0,27 0,16 0,31 0,12 0,07 0,34 0,38

15 0,21 0,12 0,24 0,08 0,06 0,26 0,28

20 0,16 0,09 0,18 0,06 0,05 0,20 0,22

25 0,15 0,09 0,17 0,05 0,04 0,18 0,20

30 0,14 0,08 0,17 0,04 0,04 0,17 0,19

40 0,13 0,07 0,15 0,03 0,03 0,15 0,17

50 0,12 0,07 0,14 0,03 0,03 0,14 0,15

60 0,11 0,06 0,13 0,02 0,02 0,13 0,15

70 0,12 0,07 0,13 0,02 0,02 0,14 0,15

80 0,12 0,07 0,14 0,02 0,02 0,14 0,15

90 0,12 0,07 0,14 0,02 0,02 0,14 0,15

5.7 UERE Recapitulative

Considering the following service mapping which is in coherence with the three scenarios under consideration, the UEREbudget for each service are detailed here after.

OAS single frequency: L band with narrow band signal

OAS dual frequency: Two L band frequencies with a narrow and wide band signal


Index

1176

1177

1178

1179

1180

1181

1182

ID

DD-036-2589

DD-036-2590

DD-036-2591

DD-036-2592

DD-036-2593

DD-036-2595

DD-036-2681


SAS: Two L band frequencies with a narrow and wide band signal

GAS: Two L band frequencies with a narrow and wide band signal

5.7.1 GLOBAL UERE

5.7.1.1 High multipath

The following table sum up the UERE computed for OAS, CAS1, SAS and GAS in Global.

Figure 52: Galileo Global UERE with high multipath

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

5 15 25 35 45 55 65 75 85

Elv Angle

Err

or

at 1

sig

ma

in m

OAS monoOAS+CAS1SAS/GASC band

Table 21: Galileo Global UERE with high multipath

Elv OAS mono OAS+CAS1 SAS/GAS C band

5 13,71 11,43 4,74 3,85

10 10,46 5,97 2,55 2,59


Index

1195

1196

1208

ID

DD-036-2682

DD-036-2750

DD-036-2752…


15 8,40 4,09 1,81 2,03

20 6,97 3,08 1,44 1,70

25 5,95 2,56 1,24 1,49

30 5,21 2,22 1,12 1,34

50 3,61 1,50 0,90 1,05

70 3,01 1,31 0,84 0,96

90 2,85 1,27 0,83 0,94

5.7.1.2 Low multipath

Table 22: Galileo Global UERE with low multipath

ElevationAngle

OAS/CAS1 SAS/GAS C band

5 3,01 2,97 3,80

10 1,91 1,77 2,57

15 1,47 1,35 2,02

20 1,20 1,13 1,69

25 1,11 1,03 1,48

30 1,05 0,97 1,34

50 0,91 0,86 1,05

70 0,89 0,83 0,96

90 0,89 0,83 0,94

Figure 53: Galileo Global UERE with low multipath


Index

1209

1210

1211

1212

ID

…DD-036-2752

DD-036-2753

DD-036-2754

DD-036-2755

DD-036-2817


0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

4,00

5 15 25 35 45 55 65 75 85

Elv angle

Err

or

in m

at

1 si

gm

a

OAS+CAS1SAS/GASC band

5.7.2 LOCAL UERE

5.7.2.1 High multipath

The following table sum up the UERE computed for OAS, CAS1, SAS and GAS in Local.

Table 23: Galileo UERE in Local with high multipath

UERE in LOCAL OAS+CAS1 SAS/GAS C band

5 0,84 0,76 1,16

10 0,42 0,38 0,63

15 0,28 0,26 0,44

20 0,21 0,19 0,33

30 0,14 0,13 0,25

50 0,08 0,07 0,17


Index

1223

1224

1225

ID

DD-036-2818

DD-036-2820

DD-036-2876


70 0,05 0,05 0,16

90 0,04 0,04 0,15

Figure 54: Galileo UERE in Local

0

0,2

0,4

0,6

0,8

1

1,2

1,4

5 15 25 35 45 55 65 75 85

Elevation Angle

Err

or

at 1

sig

ma

in m

OAS+CAS1SAS/GASC band

5.7.2.2 Low multipath

Table 24: Galileo UERE in Local with low multipath

Elevation Angle OAS+CAS1 SAS/GAS C band

5 0,25 0,29 0,54

10 0,14 0,17 0,38

15 0,10 0,12 0,28

20 0,08 0,10 0,22

30 0,06 0,07 0,19

50 0,04 0,05 0,15


Index

1235

ID

DD-036-2878


70 0,03 0,05 0,15

90 0,03 0,05 0,15

Figure 55: Galileo UERE in Local with low multipath

0,00

0,10

0,20

0,30

0,40

0,50

0,60

5 15 25 35 45 55 65 75 85

Elv angle in degrees

Err

or

at 1

sig

ma

in m

OAS+CAS1

SAS/GAS

C band


Index

1236

1237

1238

1239

1240

1241

1242

1243

1244

1245

1246

1247

ID

DD-036-2879

DD-036-2880

DD-036-2881

DD-036-2882

DD-036-2883

DD-036-2884

DD-036-2885

DD-036-2886

DD-036-2887

DD-036-2888

DD-036-2889

DD-036-2890


6 Performance budget

6.1 Baseline simulations assumptions

In the following paragraphs, baseline simulation assumptions are described. For sensitivity analysis presented in §6.3.4,changed parameters will be detailed in corresponding paragraphs.

6.1.1 Space segment

The Galileo constellation taken into account in the following simulations is the Walker constellation described in §3.1, that is tosay a 27/3/1 constellation + 3 spares in orbit.

However, for simulation purposes, it is considered :

- Only the 27 nominal satellites (the spares are not taken into account for the performance computations)

- The failure parameters introduced as simulation inputs are representative of in-orbit spares only (MTTR=7 days), which is alittle optimistic because once the spare of a given plane has been used to replace a failed satellite, if a second failure happens inthe same plane, the MTTR becomes equal to 5 months (on-ground spare).

6.1.2 Receiver Assumptions

6.1.2.1 Number of channels

The receiver is assumed having an all-in-view capability

6.1.2.2 Masking Angle

The receiver masking angle used as a baseline for all services is 10°.

6.1.2.3 Navigation Algorithm

The receiver is assumed having a weighted least square algorithm to compute the navigation position


Index

1248

1249

1250

1251

1252

1253

1254

1255

ID

DD-036-2891

DD-036-2892

DD-036-2893

DD-036-2895

DD-036-2896

DD-036-2897

DD-036-2898

DD-036-2899


6.1.2.4 RAIM availability algorithm

The receiver is assumed having a RAIM algorithm as described in the paper “Weighted RAIM for Precision Approach”, (ION95)to compute the RAIM alarm and RAIM protection levels.

6.1.2.5 GIC availability algorithm

The receiver is assumed having a GIC algorithm similar to the one described in the GALA-ASPI-DD13 deliverable dealing with“Integrity trades-off”.

6.1.2.6 RAIM GIC combination

RAIM GIC combination : For SAS-G/En route service, the user implements a RAIM only algorithm so he computes theprotection levels with the RAIM algorithm, and these protection levels have to be less than the alarm limits to declare theintegrity function available.For all other services which provides the user with integrity, although both GIC and RAIM protection levels should be computedand be less than the alarm limits, for reasons expressed in §4.7.1.1, a GIC only algorithm will be tested in the simulations.

6.1.2.7 Integrity allocation

In line with the description made in §3, when both horizontal and vertical requirements are defined, the integrity risk will beallocated equally on both dimensions, whereas, when only one requirement is defined either on horizontal or on verticaldimension, all the integrity risk is allocated to this dimension.

6.1.3 Ground Segment

The Galileo ground segment is not simulated.

6.1.4 Simulation assumptions

6.1.4.1 Area

To limit the number of receivers, simulations have not been run on the whole globe. An area representative of the performance worldwide has been selected (longitude between 30°W and 90°E, latitude between 0° and 90°N), taking into account particularproperties of the constellation.


Index

1256

1257

1258

1259

1260

1261

1262

1263

1264

ID

DD-036-2900

DD-036-2901

DD-036-2902

DD-036-2903

DD-036-2904

DD-036-2905

DD-036-2906

DD-036-2907

DD-036-2908


6.1.4.2 Simulation duration

The simulation has been run on a period of 1 day

6.1.4.3 Time sampling

300 seconds

6.1.4.4 Latitude sampling

5 degrees

6.1.4.5 Longitude sampling

15 degrees

6.1.4.6 Failures

Up to 3 failures among visible satellites

6.1.5 UERE budget

The UERE budgets used for the simulations are those given in §4. The baseline budgets used are those corresponding to highlevel of multipath. Sensitivity analysis to this level is nevertheless included in §6.3.4 showing the performances achieved with alower level of multipath corresponding to UERE budget also given in §4.

In addition, an important assumption on the UERE budget to be used in the protection level computations is that it is computedby considering that the estimation of ephemeris and clock errors results in an over bounding of SISA wrt SISE of 30%. Thisfigure comes from EGNOS experience in such algorithms design.

6.1.6 Urban Canyon Characterization


Index

1265

1266

1267

1268

ID

DD-036-2909

DD-036-2911

DD-036-2912

DD-036-2914…


One point of big interest in GALA is the performance of the system in urban environment. One option to assess thoseperformance is to use a high masking angle. However pitting a high masking angle on all the azimuth is very demanding forthe constellation, and furthermore it is not at all representative of a urban environment. The alternative to this problem is toassess the performance using the concept of urban canyon. The urban canyon is supposed to be representative of what a user isconfronted to when he is in a street. It means that he has a clear visibility in one direction (low masking angle) and highobstacles in the cross direction (high masking angle)

Figure 56: Urban Canyon scenario

Road Width

BuildingHeight

The resulting masking angle for different building height (H) and road-half width (h) are shown in the following figure:

Figure 57: Masking Angle Profile in Urban Canyon


Index

1269

1270

1271

1272

ID

…DD-036-2914

DD-036-2915

DD-036-2916

DD-036-2917

DD-036-2918


0

10

20

30

40

50

60

70

80

90

-90

-75

-60

-45

-30

-15 0 15 30 45 60 75 90

Azimuth in degree

Ele

vati

on

in d

egre

e

H=25m/h=5m

H=15m/h=10m

H=10m/h=15m

6.2 Continuity preliminary assessment

The continuity risk due to space segment failures has been preliminarily assessed for SAS-G/NPA and SAS-G/Cat1 services.

Indeed, SAS-G/NPA has the most constraining continuity requirement (2 10-5

/h) but, since the alarm limit is quite wide, thesystem can be considered as robust to 2 or even more failures and the stringency of the continuity risk requirements is

attenuated. On the contrary, for SAS-G/Cat 1, the continuity requirements (10-5/15s) are relaxed, but the alarm limits are quiteclose to the performance achievable with all the satellites. Therefore, it is interesting to provide a first estimation of thecontinuity risk due to space segment failures for these two services.

6.2.1 SAS-G/NPA

For this service, given that the alarm limit is very high compared to typical values of HPL reachable (cf. §6.3.3.2.2), the fearedevent designated by “XPL>XAL” in the continuity tree of §4.7.10 is nearly equivalent to “less than 4 satellite ranging signalsavailable”.


Index

1273

1274

1275

1276

ID

DD-036-2919

DD-036-2920

DD-036-2921

DD-036-2923…


This assumption has been used to assess the continuity risk corresponding to “XPL>XAL” event due to space segment failures.This risk has been then computed as follows :

( ) ( )

=−= ∑−=

−

G/NPA-SASfor 1h :duration operation : MTBF

1satellites visibleofnumber : V

with 1 short term4

op

V

Vj

jop

jVop

Vj

t

ttCrisk λλλ

This analysis has been made for the worst user location on the studied area, that is to say where the average number of visiblesatellites is the smallest. The following map shows this user (located at 15°E, 40°N) :

Figure 58 : Average number of visible Galileo satellites


Index

1277

ID

…DD-036-2923

DD-036-2924


For this identified user, the continuity risk due to space segment failures has been computed for each time step of thesimulation as function of the instantaneous number of visible satellites, as described by the last equation. The result isrepresented on the following figure :


Index

1278

ID

DD-036-2927…


Figure 59 : Continuity risk per hour associated with the number of visible satellites


Index ID

…DD-036-2927


Number of satellites visible from user (15°E, 40°N)

0

2

4

6

8

10

12

0 50 100 150 200 250 300 350

time step

nu

mb

er o

f vi

sib

le s

atel

lites

Continuity risk per hour corresponding to "less than 4 ranging signals available" due to satellite failures for user (15°E, 40°N)

-30

-25

-20

-15

-10

-5

00 50 100 150 200 250 300 350

time step

Co

nti

nu

ity

risk

(10

xx/h

)


Index

1279

1280

1281

ID

DD-036-2928

DD-036-2929

DD-036-2930


From this figure, it can be checked that the continuity risk decreases when the number of visible satellites increases. Moreover,it can be noticed that this decrease it very rapid : for example, if the number of visible satellites increases from 6 to 7, the

continuity risk is decreased from about 10-7/h to about 10-11/h.

It can be concluded also that this result is globally in line with the overall continuity requirement of this service, even ifallocation made in §4.7.10 has to be a little adjusted as follows :

Figure 59-1 : Continuity risk

SIS1E-5/h

XPL>XAL1E-6/h

Loss ofcontinuity


Loss ofcontinuity

due toGIC false

alarm5E-7/h

Los of continuitydue satellitesnot monitored

1E-7/h

Loss of IMSdata


Loss ofGround Integrity function

7E-6/h

No satellites broadcastingintegrity above 25 degrees


Loss ofsatellite

Data flow2E-6/h


to GUI2.5E-6h


to Satellite2.5E-6/h


broadcastingintegrity2E-6/h


error rate1E-8/h


2E-6/h

Receiver1E-5/h



/Masking)3E-7/h

or

or

or

Global

Global

or

or

or


Index

1282

1283

1284

1285

1286

1287

1288

1289

1290

1291

1292

1293

1294

ID

DD-036-2931

DD-036-2932

DD-036-2933

DD-036-2934

DD-036-2935

DD-036-2936

DD-036-2937

DD-036-2938

DD-036-2939

DD-036-2940

DD-036-2941

DD-036-2942

DD-036-2943


With these adjustments, the continuity risk computed in this paragraph seems indeed in line with the corresponding allocation(yellow box).

6.2.2 SAS-G/Cat1

For this service, the assumptions made in the last paragraph are no more valid given that the margins between achievedperformances and requirements are much more reduced.

So in this case, two different assumptions can be considered :

- One satellite failure among the visible satellites is sufficient to loose the service

- Or the service is still available for the single failure cases, and becomes unavailable for 2 satellite failures.

The following equation is used to compute the continuity risk corresponding to each assumption :

( ) ( )

=−= ∑

=

−

service theloose tofailures ofnumber minimal :n

G/NPA-SASfor 1h :duration operation :

MTBF1

satellites visibleofnumber : V

with 1

min

short term

minop

V

nj

jop

jVop

Vj

tttCrisk

λλλ

This leads to continuity risks of about :

- 10-5/15s for the first assumption

- 10-11/15s for the second assumption

So probably, the final figure is between these two results. It shows that allocation made in §4.7.11 for this continuity risk source

(4 10-7/15s) may reveal as difficult to fulfill. This will have to be studied in further details in the next phases of the project.

6.3 Availability assessment


Index

1295

1296

1297

1298

1299

1300

1301

ID

DD-036-2944

DD-036-2945

DD-036-2946

DD-036-2947

DD-036-2948

DD-036-2949

DD-036-2951…


6.3.1 OAS Service

6.3.1.1 OAS-G1

This part is aimed at assessing the availability of accuracy of a single frequency receiver using OAS service in nominalconditions, that is to say with a masking equal to 10° in all the directions. Accuracy requirements taken into account are:

- HNSEreq=16m

- VNSEreq=36m

The availability simulated is presented on the following figure :

Figure 60 : Accuracy availability for OAS-G1


Index

1302

1303

ID

…DD-036-2951

DD-036-2952

DD-036-2953


It can be concluded that availability performances achieved for OAS-G1 service seem compliant with the requirements. Theavailability is indeed greater than 99.4% on the whole studied zone, with a significant part of the area above 99.7%.

The following figures show the average accuracy (HNSE and VNSE) distributions in the case with no satellite failures.


Index

1305

1306

1307

1308

1309

1310

1311

ID

DD-036-2959

DD-036-2960

DD-036-2961

DD-036-2962

DD-036-2963

DD-036-2964

DD-036-2966…


Figure 61 : Average HNSE distribution forOAS-G1

Figure 62 : : Average VNSE distribution forOAS-G1

It appears that margins with respect to requirements are quite good in the case with no satellite failure, specially on the verticalaccuracy (average VNSE is less than 23m on the whole studied zone and requirement is equal to 36m).

6.3.1.2 OAS-G2

In this part, the availability of accuracy of a dual frequency receiver using OAS service in nominal conditions (masking equal to10° in all the directions) is assessed. Accuracy requirements taken into account are those detailed in §4.2 :

- HNSEreq=7m

- VNSEreq=15m


Figure 63 : Accuracy availability for OAS-G2


Index

1312

1313

ID

…DD-036-2966

DD-036-2967

DD-036-2968


It can be concluded that availability performances achieved for OAS-G2 service seem compliant with the requirements. Theavailability is indeed greater than 99.4% on the whole studied zone, with a significant part of the area above 99.7%.



Index

1315

1316

1317

1318

1319

1320

1321

1322

ID

DD-036-2973

DD-036-2974

DD-036-2975

DD-036-2976

DD-036-2977

DD-036-2978

DD-036-2979

DD-036-2980


Figure 64 : Average HNSE distribution forOAS-G2

Figure 65 : Average VNSE distribution forOAS-G2

For OAS-G2, margins with respect to requirements seem quite good when no satellite failures are considered. What can benoticed also, is that the average HNSE is much more uniform on the zone than the average VNSE.

6.3.2 CAS1 service

6.3.2.1 CAS1-G

6.3.2.1.1 Accuracy performance

The CAS1-G accuracy performance is the same as the one obtained for OAS-G2 service (cf. §6.3.1.2) because same UERE, sameother parameters and same requirements are used.

6.3.2.1.2 Integrity performance

The CAS1-G service provides its users with integrity information.


Index

1323

1324

1325

1326

ID

DD-036-2981

DD-036-2982

DD-036-2983

DD-036-2984


So this paragraph is aimed at assessing the availability of integrity for CAS1-G service on a zone representative of Galileoperformances. Alarm limits requirements taken into account are those detailed in §4.2 :

- HAL=20m

- VAL=45m

The integrity availability simulated is presented on the following figure :


Index

1327

1328

1329

ID

DD-036-2986

DD-036-2987

DD-036-2988


Figure 66 : Integrity availability for CAS1-G

This shows that integrity availability performances achieved for CAS1-G service seem compliant with the requirements (99%).The availability is indeed greater than 99.4% on the whole studied zone, with a significant part of the area above 99.7%.

The following figures show the average protection levels (HPL and VPL) distributions in the case with no satellite failures.


Index

1331

1332

1333

1334

1335

1336

1337

ID

DD-036-2993

DD-036-2994

DD-036-2995

DD-036-2996

DD-036-2997

DD-036-2998

DD-036-2999


Figure 67 : Average HPL distribution for CAS1-G Figure 68 : Average VPL distribution for CAS1-G

It appears that margins with respect to requirements seem quite good when no satellite failures are considered (averageHPL<12m and average VPL<32m whereas requirements are equal to 20m and 45m). What can be noticed also, is that theaverage HPL is much more uniform on the zone than the average VPL.

6.3.2.2 CAS1-L


This part describes the availability of accuracy of CAS1-L user. Accuracy requirements taken into account are those detailed in§4.2 :

- HNSEreq

=0.8m

- VNSEreq=1.2m



Index

1338

1339

1340

ID

DD-036-3001

DD-036-3002

DD-036-3003


Figure 69 : Accuracy availability for CAS1-L

It can be concluded that availability performances achieved for CAS1-L service are compliant with the requirements (99%) andare even much better. The availability is indeed greater than 99.96% on the whole studied zone.



Index

1342

1343

1344

1345

1346

1347

1348

1349

ID

DD-036-3008

DD-036-3009

DD-036-3010

DD-036-3011

DD-036-3012

DD-036-3013

DD-036-3014

DD-036-3016…


Figure 70 : Average HNSE distribution forCAS1-L

Figure 71 : Average VNSE distribution forCAS1-L

In these figures, important margins with respect to requirements that could already be foreseen from the average accuracyavailability obtained in Figure 69 are confirmed.


The CAS1-L service provides its users with integrity information.

The availability of integrity for this service on a zone representative of Galileo performances is here assessed. Alarm limitsrequirements taken into account are those detailed in §4.2 :

- HAL=2m

- VAL=3.5m


Figure 72 : Integrity availability for CAS1-L


Index

1350

1351

ID

…DD-036-3016

DD-036-3017

DD-036-3018


This figure shows that availability performances achieved for CAS1-L service are compliant with the requirements (99%) andeven much better. The availability is indeed greater than 99.96% on the whole studied zone.

The following figures show the average protection levels (HPL and VPL) distributions in the case with no satellite failures. Theyconfirm the important margins with respect to requirements that could already be foreseen from the average UIM availabilityobtained in Figure 72.


Index

1353

1354

1355

1356

1357

1358

1359

1360

ID

DD-036-3023

DD-036-3024

DD-036-3025

DD-036-3026

DD-036-3027

DD-036-3028

DD-036-3029

DD-036-3031…


Figure 73 : Average HPL distribution for CAS1-L Figure 74 : Average VPL distribution for CAS1-L

6.3.3 SAS and GAS Services

6.3.3.1 SAS-G/En route


The availability of accuracy of SAS-G/En Route user is assessed in this. Accuracy requirements taken into account are thosedetailed in §4.2 :

- HNSEreq=100m

- VNSEreq=NA


Figure 75 : Accuracy availability for SAS-G/En Route


Index

1361

1362

ID

…DD-036-3031

DD-036-3032

DD-036-3033


It can be concluded that accuracy availability performances achieved for SAS-G/En Route service are compliant with therequirements (99%) and even better. From these good results, it could be thought that from the space segment point of view, therequirements are oversized, but the results of the preliminary continuity assessment (cf. 6.2) show that the constellationconsidered allows to barely fulfill the requirements.

The following figures show the average horizontal accuracy (HNSE) distribution in the case with no satellite failures.


Index

1364

1365

1366

1367

1368

1369

1370

ID

DD-036-3037

DD-036-3038

DD-036-3039

DD-036-3040

DD-036-3041

DD-036-3042

DD-036-3043


Figure 76 : Average HNSE distribution forSAS-G/En Route

From this figure, important margin with respect to requirement that could already be foreseen from the average accuracyavailability obtained in Figure 75 is confirmed (maximal value of average HNSE reached on the zone is equal to 2.54m whereasrequirement is equal to 100m). This result is not surprising given that SAS-G signal (and so UERE budget) is dimensioned forproviding Cat1 performances.


The SAS-G/En Route service provides its users with integrity information, using a RAIM algorithm.

So this paragraph studies the availability of integrity for SAS-G/En Route service on a zone representative of Galileoperformances. Alarm limits requirements taken into account are those detailed in §4.2 :

- HAL=556m

- VAL=NA



Index

1371

1372

ID

DD-036-3045

DD-036-3046


Figure 77 : Integrity availability for SAS-G/En Route

This shows that UIM availability performances achieved for SAS-G/En Route service are compliant with the requirements (99%)and even better. The availability is indeed greater than 99.9% on the whole studied zone. It should be noted however, that theseresults have been obtained with space segment failure assumptions that must be considered as a little optimistic (MTTR equalto the in-orbit spares figure), which effect could be very important on the RAIM availability.


Index

1373

1375

1376

1377

1378

1379

1380

1381

ID

DD-036-3047

DD-036-3051

DD-036-3052

DD-036-3053

DD-036-3054

DD-036-3055

DD-036-3056

DD-036-3057


The following figures show the average horizontal protection levels (HPL) distribution in the case with no satellite failures.

Figure 78 : Average HPL distribution forSAS-G/En Route

The important margin with respect to requirement that could already be foreseen from the average integrity availabilityobtained in Figure 77 is confirmed here (maximal value of average HPL reached on the zone is equal to 13.91m whereasrequirement is equal to 556m).

6.3.3.2 SAS-G/NPA


As requirements are the same as for SAS-G/En route (except for the availability that must be greater than 99.9%) and otherparameters are also the same, refer to §6.3.3.1.1 for the accuracy performance analysis.

From this paragraph, it can be concluded that the system is compliant to the accuracy requirements as accuracy availability isgreater than 99.9% on the whole studied zone.


The SAS-G/NPA service provides its users with integrity information.


Index

1382

1383

ID

DD-036-3058

DD-036-3060


Corresponding requirements are the same as for SAS-G/En Route but have to be met with an availability of 99.9% (in place of99% for SAS-G/En Route). This leads to the use of a GIC algorithm because, although RAIM availability is above 99.9% onFigure 77, this has been achieved with optimistic satellites failures assumptions (in orbit spares always considered), which isdeterminant for RAIM availability. The integrity availability simulated is presented on the following figure :

Figure 79 : Integrity availability for SAS-G/NPA


Index

1384

1385

1387

1388

1389

ID

DD-036-3061

DD-036-3062

DD-036-3066

DD-036-3067

DD-036-3068


It can be concluded from this map that integrity availability performances achieved for SAS-G/NPA service are compliant withthe requirements (99.9%) and even better. However, it must be noted that accuracy of the simulation (only up to 3 satellitesfailures among visible satellites are considered) is not sufficient to allow a more precise characterization (above 99.9%) of theavailability figures. In addition, from these good results, it could be thought that from the space segment point of view, therequirements are oversized, but the results of the preliminary continuity assessment (cf. 6.2) show that the constellationconsidered allows to barely fulfill the requirements.

The following figure shows the average horizontal protection level (HPL) distribution in the case with no satellite failures.

Figure 80 : Average HPL distribution forSAS-G/NPA

This confirms important margin with respect to requirement that could already be foreseen from the average integrityavailability obtained in Figure 79 (maximal value of average HPL reached on the zone is equal to 6.78m whereas requirement isequal to 556m). This result is not surprising given that SAS-G signal (and so UERE budget) is dimensioned for providing Cat1performances.

6.3.3.3 SAS-G/Cat1 and GAS-G

As all parameters defining SAS-G/Cat1 and GAS-G services are the same, only one simulation has been made. The differencebetween these two services is indeed at the level of control access management.


Index

1390

1391

1392

1393

1394

1395

ID

DD-036-3069

DD-036-3070

DD-036-3071

DD-036-3072

DD-036-3073

DD-036-3075…



This part is aimed at assessing the availability of accuracy of SAS-G/Cat1 and GAS-G users. Accuracy requirements taken intoaccount are those detailed in §4.2 :

- HNSEreq=6m

- VNSEreq=6m

The accuracy availability simulated is presented on the following figure :

Figure 81 : Accuracy availability for SAS-G/Cat1 and GAS-G


Index ID

…DD-036-3075


From this figure, it can be deduced the zone whereaccuracy availability is greater than 99% (cf.Figure 82). This zone is not equal to the wholestudied area, so the system is partially compliantto the accuracy requirements of SAS-G/ Cat1 andGAS-G. The regions where the requirements arenot met with sufficient availability are :

Figure 82 : Accuracy service area for SAS-G/Cat1and GAS-G



• A latitude band situated above 85°N.• Some regions located between 10°N and25°N latitude.

The following figures show the average accuracy(HNSE and VNSE) distributions in the case withno satellite failures.

Figure 83 : Average HNSE distribution forSAS-G/Cat1 and GAS-G

Figure 84 : Average VNSE distribution forSAS-G/Cat1 and GAS-G


Index

1398

1399

1400

1401

1402

1403

1404

1405

ID

DD-036-3084

DD-036-3085

DD-036-3086

DD-036-3087

DD-036-3088

DD-036-3089

DD-036-3090

DD-036-3091…


It appears that the margin between average HNSE and the corresponding requirement seems correct (maximum value ofaverage HNSE is 2.54m wrt a requirement of 6m) whereas the margin between average VNSE and required vertical accuracy isvery reduced with respect to results obtained for the other services (maximal average value reached is 5.24m wrt a requirementof 6m also). This certainly explains the availability holes observed on Figure 82.


The SAS-G/Cat1 and GAS-G services provide their users with integrity information.

So this paragraph presents the availability of integrity for SAS-G/Cat1 and GAS-G services on a zone representative of Galileoperformances. Alarm limits requirements taken into account are those detailed in §4.2 :

HAL=11m

VAL=15m

The integrity availability simulated is illustrated by the following figure :


Index

1406

1407

1408

ID

…DD-036-3091

DD-036-3092

DD-036-3093

DD-036-3094


Figure 85 : Integrity availability for SAS-G/Cat1 and GAS-G

It appears that integrity availability performances achieved for SAS-G/Cat1 and GAS-G services seem very poor. Theavailability is indeed greater than 99% only for some users located on a latitude band at 60°N. However, it must be noted thatthese results have been achieved with the following sizing parameters :

A 10° mask angle


Index

1409

1410

1411

1413

1414

1415

1416

ID

DD-036-3095

DD-036-3096

DD-036-3097

DD-036-3102

DD-036-3103

DD-036-3104

DD-036-3105


A high multipath budget

Sensitivity of the SAS-G/ Cat1 and GAS-G performances to these sizing parameters will be studied in §6.3.4.


Figure 86 : Average HPL distribution forSAS-G/Cat1 and GAS-G

Figure 87 : Average VPL distribution forSAS-G/Cat1 and GAS-G

From these figures, the margin between average HPL and the corresponding requirement seems correct (maximum value ofaverage HPL is 6.32m wrt a requirement of 11m) whereas the margin between average VPL and vertical alarm limit is negative: VAL value is overshot by some average VPL even when no satellite failures are introduced (maximal average value reached is15.95m wrt a requirement of 15m). This explains the poor availability noticed on Figure 85.

6.3.3.4 SAS-R

SAS-R service is equivalent to SAS-G. Indeed, it has been defined for regions different from Europe that may have the intentionto implement regional service under their responsibility. So performances are the same as the ones obtained for SAS-G (cf. lastparagraph).

6.3.3.5 SAS-L and GAS-L


Index

1417

1418

1419

1420

1421

1422

1423

ID

DD-036-3106

DD-036-3107

DD-036-3108

DD-036-3109

DD-036-3110

DD-036-3111

DD-036-3112…


As all parameters defining SAS-L and GAS-L services are the same, only one simulation has been made. The difference betweenthese two services is indeed at the level of control access management.


This part is aimed at assessing the availability of accuracy of SAS-L and GAS-L users. Accuracy requirements taken intoaccount are those detailed in the mission requirements :

HNSEreq=1m

VNSEreq=1.5m



Index

1424

1425

1426

ID

…DD-036-3112

DD-036-3113

DD-036-3114

DD-036-3115


Figure 88 : Accuracy availability for SAS-L and GAS-L

It shows that availability performances achieved for SAS-L and GAS-L services are compliant with the requirements (99.9%)and even better. However, as already mentioned, the accuracy of the simulation is not sufficient to allow a more precisecharacterization (above 99.9%) of the availability figures.

The following figures give the average accuracy (HNSE and VNSE) distributions in the case with no satellite failures.


Index

1428

1429

1430

1431

1432

1433

1434

1435

ID

DD-036-3120

DD-036-3121

DD-036-3122

DD-036-3123

DD-036-3124

DD-036-3125

DD-036-3126

DD-036-3127…


Figure 89 : Average HNSE distribution for SAS-Land GAS-L

Figure 90 : Average VNSE distribution for SAS-Land GAS-L

From these figures, good margins with respect to requirements that could already be foreseen from the average accuracyavailability obtained in Figure 88 are confirmed.


The SAS-L and GAS-L services provide their users with integrity information.

So in this paragraph the availability of integrity for SAS-L and GAS-L services on a zone representative of Galileo performancesis assessed. Alarm limits requirements taken into account are those detailed in the mission requirements :

HAL=3m

VAL=5.5m



Index

1436

1437

1438

ID

…DD-036-3127

DD-036-3128

DD-036-3129

DD-036-3130


Figure 91 : Integrity availability for SAS-L and GAS-L

It can be concluded that integrity availability performances achieved for SAS-L and GAS-L services are also compliant with therequirements (99.9%). However, as already mentioned, the accuracy of the simulation is not sufficient to allow a more precisecharacterization (above 99.9%) of the availability figures.



Index

1440

1441

1442

1443

1444

1445

1446

1447

ID

DD-036-3135

DD-036-3136

DD-036-3137

DD-036-3138

DD-036-3139

DD-036-3140

DD-036-3141

DD-036-3142


Figure 92 : Average HPL distribution for SAS-Land GAS-L

Figure 93 : Average VPL distribution for SAS-Land GAS-L

They confirm good margins with respect to requirements that could already be foreseen from the average accuracy availabilityobtained in Figure 91.

6.3.4 Sensitivity analysis

Sensitivity analysis have been done for SAS-G / Cat1 and GAS-G services only because the performances achieved for all otherservices are compliant with the requirements, when the baseline simulation parameters are used. In particular the followingsensitivity studies have been performed :

Sensitivity to the multipath error budget

Sensitivity to the user mask angle

Sensitivity to the horizontal / vertical allocation of the integrity risk

Sensitivity to the vertical alarm limit value

6.3.4.1 Sensitivity to the multipath error budget


Index

1448

1449

1450

1451

ID

DD-036-3143

DD-036-3144

DD-036-3145

DD-036-3146


In §4, two UERE budgets are presented :

One taking into account pessimistic assumptions for multipath. This budget is the one that has been used to assess baselineperformances in the last paragraph.

Another taking into account lower multipath environment. The results presented in the current paragraph correspond to thisbudget.

The following map represents the average accuracy availability obtained with this new assumption, all other simulationparameters being kept at the same values (baseline assumptions described in §6.1).


Index

1452

1453

1454

1455

ID

DD-036-3147

DD-036-3148

DD-036-3149

DD-036-3150


Figure 94 : SAS-G/Cat1 and GAS-G accuracy availability for low multipath conditions

From this map, SAS-G/Cat1 and GAS-G accuracy availability performances seem compliant with the requirements with thesemultipath conditions. The availability is indeed greater than 99.4% on the whole studied zone, with the main part of the areacovered with an availability better than 99.7% (only three users are below this figure).

The next map shows the UIM availability performances achieved in the same multipath conditions :


Index

1456

1457

ID

DD-036-3151

DD-036-3152


Figure 95 : SAS-G/Cat1 and GAS-G UIM availability for low multipath conditions

It appears that integrity availabilityperformances are greatly improved when alower multipath budget is considered(compare Figure 95 with Figure 85).

Figure 96 : Service area where UIMavailability is greater than 99%


Index

1459

1460

1461

ID

DD-036-3157

DD-036-3158

DD-036-3159


The UIM availability is still below therequirement (99%) for some regions of thestudied zone (latitude comprised between10°N and 30°N and above 70°N), but asignificant part of the zone is, in theseconditions, covered with the requiredavailability (cf. Figure 96).

6.3.4.2 Sensitivity to the user mask angle

Baseline results presented in §6.3.3.3 were achieved with a user mask angle equal to 10°. As for SAS and GAS users, theenvironment can be more open, the sensitivity of their performances to the mask angle value has been studied by assessing theimpact of reducing it to 5° (all other parameters being kept to their baseline values described in §6.1). This value is actually inline with the MOPS requirement.

First the impact of this change on the average number of visible satellites from the user is presented on the following figures :


Index

1463

1464

ID

DD-036-3164

DD-036-3165…


Figure 97 : Average number of visible satellitesseen with a mask angle of 10°

Figure 98 : Average number of visible satellitesseen with a mask angle of 5°

The impact of reducing the user mask angle from 10° to 5° is a significant increase of the number of visible satellites : theaverage values are indeed quasi-uniformly increased by one. Then, an improvement of availability figures can be foreseen : itcan be checked on the following maps representing the accuracy and the integrity availability.


Index

1465

1466

ID

…DD-036-3165

DD-036-3166

DD-036-3167


Figure 99 : SAS-G/Cat1 and GAS-G accuracy availability for 5° mask angle

It appears that with this reduced mask angle, SAS-G/Cat1 and GAS-G accuracy availability performances seem compliant withthe requirements. The availability is indeed greater than 99.5% on the whole studied zone, with the main part of the areacovered with an availability better than 99.7%.


Index

1467

1468

1469

ID

DD-036-3168

DD-036-3169

DD-036-3170


Figure 100 : SAS-G/Cat1 and GAS-G UIM availability for 5° mask angle

Integrity availability performances are also well improved when a lower mask angle is considered (compare with Figure 85).The UIM availability is still below the requirement (99%) for some regions of the studied zone (latitude comprised between 10°Nand 30°N and above 70°N), but a great part of the zone is, in these conditions, covered with the required availability. It can benoticed also that the improvement observed in this sensitivity case in less important than for the reduction of multipath level.


Index

1470

1471

1472

1474

1475

1476

1477

1478

ID

DD-036-3171

DD-036-3172

DD-036-3173

DD-036-3178

DD-036-3179

DD-036-3180

DD-036-3181

DD-036-3182


6.3.4.3 Sensitivity to the horizontal / vertical allocation of the integrity risk

In the baseline simulation, the integrity risk has been allocated equally on the vertical and horizontal dimension.

Now, when an analysis of the causes of outages occurring in the nominal conditions (no satellite failures) is made (cf. thefollowing figures), it shows that all the outages correspond to VPL overshooting the VAL.

Figure 101 : HPL analysis during outages Figure 102 : VPL analysis during outages

Indeed, it can be noticed that during outage periods, HPL reaches at a maximum 7.81m (wrt a requirement of 11m) whereas,VPL values are always above the alarm limit and are comprised between 15m and 21.3m.

From these results, it can be tried to change the allocation of the integrity risk between horizontal and vertical components.

In the baseline, the total integrity risk allocated to GIC (fault free case) is equal to 1 10-7/150s (=1 10-7 per independent sample)and is allocated equally to horizontal and vertical dimensions, that is to say :

5 10-8 on the horizontal dimension, which corresponds to 5.45σ on the gaussian distribution

5 10-8 on the vertical dimension, which corresponds to 5.45σ on the gaussian distribution


Index

1479

1480

1481

1482

1483

1484

ID

DD-036-3183

DD-036-3184

DD-036-3185

DD-036-3186

DD-036-3187

DD-036-3188…


So this coefficient (5.45) has been used both in the horizontal and in the vertical protection level computations.

Now, taking into account outage analysis presented above, this allocation could be changed to be more constraining on thehorizontal dimension where margin has been observed and less constraining on the vertical one. An example of adaptation ofthis allocation is :

10-10 on the horizontal dimension, which corresponds to 6.47σ on the gaussian distribution

~1 10-7 on the vertical dimension, which corresponds to 5.33σ on the gaussian distribution

Taking into account this new allocation, and all other parameters being kept at their baseline values, the UIM availability hasbeen recomputed and compared to the availability achieved in the baseline case. The result of this comparison is presented onthe following figure :


Index

1485

1486

ID

…DD-036-3188

DD-036-3189

DD-036-3190


Figure 103 : Difference between UIM availability achieved with the new allocation and with the baseline one

From Figure 103, it appears that the newallocation globally improves the UIM availability,except for a particular zone located at 60° latitude


Index

1488

1489

1490

ID

DD-036-3195

DD-036-3196

DD-036-3197…


North where a little degradation of availability isobserved (-0.04%). This zone is very limited andcorresponds certainly to locations where, due tothe new allocation made, which is veryconstraining for HPL, cases of outages due toHPL>HAL appear.

However, improvement induced by this allocationis not sufficient to make the SAS-G/Cat1 andGAS-G performances compliant with therequirements : this can be seen on Figure 104. Itis not very surprising, since by increasing the

integrity risk allocated to vertical axis from 5 10-8

to 10-7, the vertical protection levels are onlyreduced of 2%(corresponding to 5.45/5.33).

Nevertheless, this optimization will have to be

Figure 104 : SAS-G/Cat1 and GAS-G UIMavailability achieved with new allocation of

integrity risk

6.3.4.4 Sensitivity to the vertical alarm limit value

Given the outage analysis made in the last paragraph (cf. Figure 101 and Figure 102), the vertical alarm limit appears to be thedriving factor for the availability. That is why, sensitivity analysis to this parameter is here presented : the following UIMavailability map corresponds to a vertical alarm limit of 20m, all other parameters being kept to their baseline values :


Index

1491

1492

ID

…DD-036-3197

DD-036-3198

DD-036-3199


Figure 105 : SAS-G/Cat1 and GAS-G UIM availability for VAL=20m

It can be deduced that with a vertical alarm limit of 20m, the UIM availability is greatly improved and is compliant with therequirement (99%) on the main part of the zone. Only a latitude band located at 10°N shows some availability holes. Availabilitylevel achieved at these locations is nevertheless very near of 98%.


Index

1493

1494

1495

1496

ID

DD-036-3200

DD-036-3201

DD-036-3202

DD-036-3203


6.3.4.5 Sensitivity to the vertical accuracy requirement value

From Figure 82, the system is only partially compliant to the accuracy requirements. Given the results of an outage analysisanalog to the one presented in Figure 101 and Figure 102, it appears that the vertical accuracy requirement is the driving factorfor the accuracy availability. Therefore a sensitivity analysis to this parameter is here presented.

The following map corresponds to a vertical accuracy requirement of 6.3m. It represents the service area where the accuracyavailability is above 99% :


Index

1497

1498

ID

DD-036-3204

DD-036-3205


Figure 106 : SAS-G/Cat1 accuracy service area at 99% for VNSEreq=6.3m

It can be deduced that, by increasing the vertical accuracy requirement of only 30cm, the non compliance observed on Figure 82at the pole, is overcome. On the contrary, on the zone close to the equator, this requirement adaptation is not sufficient : it isnecessary to increase this value to 6.8m to have a full compliance on the whole zone.


Index

1499

1500

1501

1502

1503

1504

1505

1506

1507

1508

1509

1510

1511

ID

DD-036-3206

DD-036-3207

DD-036-3208

DD-036-3209

DD-036-3210

DD-036-3211

DD-036-3212

DD-036-3213

DD-036-3214

DD-036-3215

DD-036-3216

DD-036-3217

DD-036-3218


7 Performance with External system

7.1 Global Positioning System (GPS+)

7.1.1 Assumptions

At the edge of 2008 the GPS system will be different from what it is today. The current GPS satellites will be replaced by the GPSblock IIF satellites. They are the next generation satellites that will be launched starting in late 2001 (TBC) to replace the IIA andIIR vehicles. The Block IIF is assumed to provide significant enhancements over the IIA and IIR. The design enhancement issupposed to lead to a lower URE and lower positioning error. The design enhancement concerns:

Better performance of the frequency standards

Reduction in the age of data of the broadcast navigation message to <3 hours

Provision for C/A code and P-code on L2

Provision of a third frequency in ARNS band: L5

Increased user received power level

A detailed description of what would be the GPS system is available in Integrity Trade-off deliverable [RD-07]. The relevantparameter for performance assessment are recalled here after.

7.1.1.1 Constellation parameter

7.1.1.1.1 GPS constellation parameter

The constellation parameters used to simulate GPS are the same as the ones of the current constellation. The number ofsatellites is 24 spread on 6 plans with 4 satellites per plan. One could argue that the constellation will most likely evolved inthe future in the frame of GPS upgrade. According to [RD-017], the number of satellite may increase from 24 to 30 in thefuture. Nevertheless, the results obtained with the 24 satellite constellation can be interpreted as a minimal bound of theperformance that can be achieved combining Galileo and GPS all together. The GPS orbital parameters used for the simulationcan be found in ANNEX A.


Index

1512

1513

1514

1515

1516

ID

DD-036-3219

DD-036-3220

DD-036-3221

DD-036-3222

DD-036-3223


One issue when combining Galileo and GPS is that the periods of the constellations are not identical. Therefore oneconstellation will move slowly comparing to the other and the performance of the combined system may change with the years. This issue has been addressed in [RD-06]. It shows that the difference of performance due to this effect is marginal.

7.1.1.2 UERE

As for the constellation, GPS signal will most likely evolve in the future. Up to now the civil signal was concentrated on a singlecarrier L1 with a chip rate of 1.023 Mchips/s. In the future the carrier L2 that is currently dedicated to military used will beavailable to the civil community. Furthermore, a third frequency on L5 with a high chip rate will also be available to civil user. Therefore the structure of the signal will be quite similar to the Galileo one. A civil receiver will probably uses the L1 and L5carriers to correct ionospheric delay. The following figure shows the GPS UERE deduced from offical source (DoD/DoT) and theUERE computed in the frame of GALA taken into account the GPS block IIF signal structure and the SAS user assumptions. The UERE appear quite similar. The major difference is on the low elevation angle. This comes from more optimistic value formulitpath budget. It is also interesting to note that the budget for clock and ephemeris error is equal to 1.2 m (DoD/DoT)whereas for Galileo, this budget is equal to 0.65 m.

0

1

2

3

4

5

6

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Elevation Angle

Err

or

at 1

sig

ma

in m

DoD/DoTGALA

Figure 107: GPS UERE budget


Index

1517

1518

1519

1520

1521

1522

1523

1524

ID

DD-036-3224

DD-036-3225

DD-036-3226

DD-036-3227

DD-036-3228

DD-036-3229

DD-036-3230

DD-036-3231…


For performance estimation the GPS UERE computed with GALA assumptions will be used.

7.1.2 Combined Galileo/GPS Navigation Performance

7.1.2.1 Performance of GPS only

The following graph shows the performance of GPS, without any augmentation such as SBAS or GBAS. For safety of lifeapplication the availability targeted is 99.9% (SAS requirement in line with CAT1). The following map shows the availabilityof GPS for a vertical accuracy of 30 meters. We can see that the availability is quite good on the main part of the globe butdecreases drastically in certain area. Basically, the performance got from GPS are much worse than the ones expected fromGalileo for three reasons:

The UERE is degraded comparing to the ones expected for Galileo because of signals less powerful and an error oforbito-synchro larger (1.2 meter instead of 0.65 meter). The better performance of Galileo on this budget relies on the fact thatthe clocks are assumed as stable as the GPS ones and the update rate of the clock and ephemeris data is faster than for GPS. Itis worth to be noted that with SBAS augmentation, this budget can be reduced back to 0.65m

Galileo satellites are more numerous than GPS ones (30 instead of 24). It is sure than this assumptions is questionable sincecurrently the number of GPS satellites is equal to 27. However, no one knows how the constellation will evolve in the future. For the moment the only official source is the GPS-ICD from US DoD. In this document it is stated that the GPS constellationincludes 24 satellites. Once this document is updated, this assumption can be reviewed.

The GPS constellation is not symmetrical. Therefore, as shown in the following maps, GPS has very poor availability on somearea. This has very penalizing effect on the performance of the system. Indeed it is very difficult (almost impossible) toguaranty a “good” service on a wide area with this kind of worm hole inside.


Index

1525

1526

ID

…DD-036-3231

DD-036-3232

DD-036-3233…


Figure 108: GPS vertical Availability (VNSE=30m)


Index

1527

1528

1529

1530

1531

ID

…DD-036-3233

DD-036-3234

DD-036-3235

DD-036-3236

DD-036-3237

DD-036-3238


Figure 109: GPS VNSE average

7.1.2.2 Baseline Availability of Service for combined use of GPS and Galileo

7.1.2.2.1 OAS-GS

This part is aimed at assessing the availability of accuracy of a user using both OAS service of Galileo and GPS in nominalconditions, that is to say with a masking equal to 10° in all the directions. Accuracy requirements taken into account are thosedetailed in the mission requirements :

HNSEreq=4m


Index

1532

1533

1534

1535

1536

ID

DD-036-3239

DD-036-3240

DD-036-3241

DD-036-3242

DD-036-3243


VNSEreq=10m


Figure 110 : Accuracy availability for OAS-GS

It can be deduced that availability performances achieved for OAS-GS service are on the main part of the zone compliant withthe requirement (99%). However, on a latitude band located between 35°N and 60°N, this figure is not achieved. In addition, therequirement is not met at some isolated locations, but probably because GPS constellation is not symmetrical.


Index

1537

1539

1540

1541

1542

1543

1544

ID

DD-036-3244

DD-036-3249

DD-036-3250

DD-036-3251

DD-036-3252

DD-036-3253

DD-036-3254



Figure 111 : Average HNSE distribution forOAS-GS

Figure 112 : Average VNSE distribution forOAS-GS

They confirm that the margins with respect to requirements are quite reduced for OAS-GS service, particularly for horizontalaccuracy.

7.1.2.2.2 CAS1-GS

7.1.2.2.2.1 Accuracy performance

In this part is studied the availability of accuracy of a user using both CAS1-G service of Galileo and GPS (with SBAS, implyingthat UERE of GPS can be considered as equivalent as the one achieved with Galileo) in nominal conditions, that is to say with amasking equal to 10° in all the directions. Accuracy requirements taken into account are those detailed in the missionrequirements :

HNSEreq=4m


Index

1545

1546

1547

1548

ID

DD-036-3255

DD-036-3256

DD-036-3257

DD-036-3258


VNSEreq=10m


Figure 113 : Accuracy availability for CAS1-GS


Index

1549

1550

1552

1553

1554

1555

1556

1557

1558

ID

DD-036-3259

DD-036-3260

DD-036-3265

DD-036-3266

DD-036-3267

DD-036-3268

DD-036-3269

DD-036-3270

DD-036-3271


It can be concluded that availability performances achieved for CAS1-GS service are on the main part of the zone compliantwith the requirement (99%). However, on a latitude band located between 35°N and 60°N, this figure is not achieved. Moreover,it must be noted that performances are globally better than for OAS-GS, due to the use of Galileo UERE assumptions also forGPS satellites.


Figure 114 : Average HNSE distribution for CAS1-GS Figure 115 : Average VNSE distribution for CAS1-GS

The same remark as for OAS-GS can be made on the reduced margins.

7.1.2.2.2.2 Integrity performance

The CAS1-GS service provides its users with integrity information.

Alarm limits requirements taken into account are those detailed in §in the mission requirements :

HAL=13m

VAL=32m


Index

1559

1560

1561

1562

ID

DD-036-3272

DD-036-3273

DD-036-3274

DD-036-3275



Figure 116 : Integrity availability for CAS1-GS

This shows that integrity availability performances achieved for CAS1-GS service are compliant to and even much better thanthe requirements (99%) on the major part of the zone : only one user location does not meet this availability figure. Theavailability is indeed greater than 99.8% on the main part of the zone, with only a point where an availability of 98.73% isachieved.


Index

1563

1565

1566

1567

1568

1569

1570

1571

1572

ID

DD-036-3276

DD-036-3281

DD-036-3282

DD-036-3283

DD-036-3284

DD-036-3285

DD-036-3286

DD-036-3287

DD-036-3288


The following figures represent the average protection levels (HPL and VPL) distributions in the case with no satellite failures.

Figure 117 : Average HPL distribution for CAS1-GS Figure 118 : Average VPL distribution for CAS1-GS

It appears that the margin with respect to requirements is much more important for vertical dimension than for horizontal one.

7.1.2.2.3 SAS-GS/Cat1 and GAS-GS

As all parameters defining SAS-GS/Cat1 and GAS-GS services are the same, only one simulation has been made. The differencebetween these two services is indeed at the level of control access management.

7.1.2.2.3.1 Accuracy performance

This part deals with the availability of accuracy of SAS-GS/Cat1 and GAS-GS users. Accuracy requirements taken into accountare those detailed in §4.2 :

HNSEreq

=3m

VNSEreq=4m



Index

1573

1574

1575

1576

ID

DD-036-3289

DD-036-3290

DD-036-3291

DD-036-3292


Figure 119 : Accuracy availability for SAS-GS/Cat1 and GAS-GS

It can be concluded that availability performances achieved for SAS-GS/Cat1 and GAS-GS services are not compliant with therequirement (99.9%). 99% level is achieved on the main part of the zone (except above 65° and for isolated points) but 99.9% isonly achieved for a few user locations.



Index

1578

1579

1580

1581

1582

1583

1584

1585

ID

DD-036-3297

DD-036-3298

DD-036-3299

DD-036-3300

DD-036-3301

DD-036-3302

DD-036-3303

DD-036-3304…


Figure 120 : Average HNSE distribution forSAS-GS/Cat1 and GAS-GS

Figure 121 : Average VNSE distribution forSAS-GS/Cat1 and GAS-GS

From these figures, the margin between average HNSE and the corresponding requirement seems correct (maximum value ofaverage HNSE is 1.86m wrt a requirement of 6m) whereas the margin between average VNSE and required vertical accuracy isvery reduced (maximal average value reached is 3.96m wrt a requirement of 4m).

7.1.2.2.3.2 Integrity performance

The SAS-GS/Cat1 and GAS-GS services provide their users with integrity information.

Alarm limits requirements taken into account are those detailed in §4.2 :

HAL=8m

VAL=10m



Index

1586

1587

1588

1589

ID

…DD-036-3304

DD-036-3305

DD-036-3306

DD-036-3307

DD-036-3308


Figure 122 : Integrity availability for SAS-GS/Cat1 and GAS-GS

It appears that integrity availability performances achieved for SAS-GS/Cat1 and GAS-GS services are very poor. Theavailability does only reach a level of 97% at isolated user locations. However, it must be noted that these results have beenachieved with the following sizing parameters :

A 10° mask angle

A high multipath budget


Index

1590

1591

1593

1594

1595

1596

1597

ID

DD-036-3309

DD-036-3310

DD-036-3315

DD-036-3316

DD-036-3317

DD-036-3318

DD-036-3319


Sensitivity of the SAS-GS/ Cat1 and GAS-GS performances to these sizing parameters will be studied in §7.1.2.2.4.


Figure 123 : Average HPL distribution for SAS-GS/Cat1and GAS-GS

Figure 124 : Average VPL distribution for SAS-GS/Cat1and GAS-GS

From these figures, the margin between average HPL and the corresponding requirement seems correct (maximum value ofaverage HPL is 4.67m wrt a requirement of 8m) whereas the margin between average VPL and vertical alarm limit is negative :VAL value is overshot by some average VPL even when no satellite failures are introduced . Maximal average value reached isindeed 12.01m wrt a requirement of 10m and only 80% of the average VPL values are below this requirement. This explains thepoor availability observed on Figure 122.

7.1.2.2.4 SAS-RM

The definition of this service is nearly the same as for SAS-GS/Cat1, except that it is a regional service and it uses thegeostationary satellites of GNSS1, that is to say :

Inmarsat satellites (AOR-E, IOR, AOR-W, POR)

Artemis


Index

1598

1599

1600

1601

1602

1604

ID

DD-036-3320

DD-036-3321

DD-036-3322

DD-036-3323

DD-036-3324

DD-036-3329


MTSAT satellites (MTSAT-1, MTSAT-2)

For these GEOs, the ephemeris and clock error and its corresponding estimated bound are taken equal to the specified values inthe frame of EGNOS project, that is to say :

Real error = 1.0m

Estimated error =1.2m

The fact that it is a regional service implies that the requirement do not necessary to be met world wide. The regional segmentcomposed of the three geo-stationary satellites has been designed to cover ECAC region. Therefore, the compliance against therequirements will be done on ECAC only. With these assumptions, the availability is significantly improved with respect to theone achieved for SAS-GS/Cat1 service : this improvement is represented on the following figures.

Figure 125 : Accuracy availability differencebetween SAS-RM and SAS-GS/Cat1 services

Figure 126 : UIM availability difference betweenSAS-RM and SAS-GS/Cat1 services

This leads to a good coverage of the studied zone with the required accuracy and accuracy availability. This service area isshown on the following figure.


Index

1605

1606

1607

ID

DD-036-3330

DD-036-3331

DD-036-3332


Figure 127 : Accuracy service area (99.9% accuracy availability zone) for SAS-RM


Index

1608

1609

1610

ID

DD-036-3333

DD-036-3334

DD-036-3335


It can be concluded that accuracy availability performances achieved for SAS-RM are compliant with the requirement (99.9%)on the major part of the zone that covers the European region. The area above 65°N and some isolated locations below thislatitude are however not covered with the required availability.

Now, the improvement of UIM availability observed on Figure 126 leads to the following integrity availability map :


Index

1611

1612

1613

1614

1615

1616

1617

1618

1619

1620

1621

1622

1623

ID

DD-036-3336

DD-036-3337

DD-036-3338

DD-036-3339

DD-036-3340

DD-036-3341

DD-036-3342

DD-036-3343

DD-036-3344

DD-036-3345

DD-036-3346

DD-036-3347

DD-036-3348


Figure 128 : Integrity availability for SAS-RM

It appears that integrity availability performances achieved for SAS-RM are well improved with respect to SAS-GS service butare still below the requirement (99.9%). The worst availability performances are obtained at latitudes above 70°N (availabilityfigures between 0% and 90%) and for a band located between 10°N and 40°N (availability between 87% and 97%). However, theavailability reaches a level of 99% on a significant part of the zone. On Europe, the service would be compliant for anavailability of 99%.

7.1.2.3 Sensitivity analysis of the availability for combined use of Galileo and GPS

As seen in the last paragraph, performances achieved by the combined use of GPS and Galileo are not fully compliant with therequirements specified for these services. So, in this part, different sensitivity analysis have been performed to assess theimpact of the change of different parameters. In particular, the following issues have been investigated :

Sensitivity to the multipath error budget

Sensitivity to the user mask angle

Sensitivity to the requirements

7.1.2.3.1 OAS-GS

For this service, only the sensitivity to the multipath budget and to the requirement have been analyzed.

7.1.2.3.1.1 Sensitivity to the multipath level




Index

1624

1625

1626

1627

ID

DD-036-3349

DD-036-3350

DD-036-3351

DD-036-3352




Figure 129 : OAS-GS accuracy availability for low multipath conditions


Index

1628

1629

1630

1632

1633

1634

ID

DD-036-3353

DD-036-3354

DD-036-3355

DD-036-3360

DD-036-3361

DD-036-3362…


From this map, OAS-GS accuracy availability performances seem, with these multipath conditions, compliant with therequirements. The availability is indeed greater than 99.4% on the whole studied zone, with a significant part of the areacovered with an availability better than 99.6%.

7.1.2.3.1.2 Sensitivity to the requirement

An analysis of the causes of outages occurring in the nominal conditions (no satellite failures) has been made (cf. the followingfigures). It shows that all the outages correspond to HNSE overshooting the corresponding requirement.

Figure 130 : HNSE analysis during outages Figure 131 : VNSE analysis during outages

Indeed, it can be noticed that during outage periods, VNSE reaches at a maximum 7.25m (wrt a requirement of 10m) whereas,HNSE values are always above the corresponding requirement and are comprised between 4m and 4.73m.

Given this outage analysis, the horizontal accuracy requirement appears to be the driving factor for the accuracy availability.That is why, sensitivity analysis to this parameter is here presented : the following accuracy availability map corresponds to anhorizontal accuracy requirement of 6m, all other parameters being kept to their baseline values :


Index

1635

1636

1637

ID

…DD-036-3362

DD-036-3363

DD-036-3364

DD-036-3365


Figure 132 : OAS-GS accuracy availability for HNSEreq=6m

It can be deduced that with an horizontal accuracy requirement of 6m, the accuracy availability is improved and is compliantwith the requirement (99%) on the whole zone. Moreover the main part of the zone benefits from availability figures above99.4%.

7.1.2.3.2 CAS1-GS


Index

1638

1639

1640

1641

1642

1643

1644

ID

DD-036-3366

DD-036-3367

DD-036-3368

DD-036-3369

DD-036-3370

DD-036-3371

DD-036-3372…


For this service, only the sensitivity to the multipath budget and to the requirement have been analyzed.

7.1.2.3.2.1 Sensitivity to the multipath level






Index

1645

1646

1647

ID

…DD-036-3372

DD-036-3373

DD-036-3374

DD-036-3375


Figure 133 : CAS1-GS accuracy availability for low multipath conditions

From this map, with these multipath conditions, CAS1-GS accuracy availability performances are compliant with therequirements (99%) and even much better. The availability is indeed greater than 99.9% on the whole studied zone.

The next map shows the UIM availability performances achieved in the same multipath conditions :


Index

1648

1649

1650

1651

1652

ID

DD-036-3376

DD-036-3377

DD-036-3378

DD-036-3379

DD-036-3380


Figure 134 : CAS1-GS UIM availability for low multipath conditions

It can be concluded that with these multipath conditions, CAS1-GS UIM availability performances are also compliant with therequirements (99%) and even much better. The availability is indeed greater than 99.9% on the whole studied zone.


An analysis of the causes of outages occurring in the nominal conditions (no satellite failures) has been made (cf. the followingfigures). It shows that all the outages correspond to HNSE or HPL overshooting the corresponding requirements.


Index

1655

ID

DD-036-3388


Figure 135 : HNSE analysis during accuracy outages Figure 136 : VNSE analysis during accuracy outages

Figure 137 : HPL analysis during integrity outages Figure 138 : VPL analysis during integrity outages

Indeed, it can be noticed that during outage periods, VNSE reaches at a maximum 6.94m (wrt a requirement of 10m) whereas,HNSE values are always above the corresponding requirement and are comprised between 4m and 4.71m. In the same way,VPL reaches at a maximum 18.65m (wrt a requirement of 32m) whereas, HPL values are always above the alarm limit and arecomprised between 13m and 13.55m. Finally, it can be noted also that the integrity outages occur much less frequently than theaccuracy ones.


Index

1656

1657

1658

1659

ID

DD-036-3389

DD-036-3390

DD-036-3391

DD-036-3392


Given this outage analysis, the horizontal requirements appear to be the driving factors for the availability. That is why,sensitivity analysis to this parameter is here presented : the following availability maps corresponds to an horizontal accuracyrequirement of 5m and an HAL=14m, all other parameters being kept to their baseline values :

Figure 139 : CAS1-GS accuracy availability for HNSEreq=5m


Index

1660

1661

1662

1663

ID

DD-036-3393

DD-036-3394

DD-036-3395

DD-036-3396


It can be deduced that with an horizontal accuracy requirement of 5m, the accuracy availability is improved and is compliantwith the requirement (99%) on the whole zone. Moreover the main part of the zone benefits from availability figures above99.4%.

Figure 140 : CAS1-GS integrity availability for HAL=14m

It can be deduced that with an horizontal alarm limit of 14m, the UIM availability is improved and is compliant with therequirement (99%) on the whole zone. Moreover the main part of the zone benefits from availability figures above 99.5%.


Index

1664

1665

1666

1667

1668

1669

1670

1671

1672

1673

1674

ID

DD-036-3397

DD-036-3398

DD-036-3399

DD-036-3400

DD-036-3401

DD-036-3402

DD-036-3403

DD-036-3404

DD-036-3405

DD-036-3406

DD-036-3407…


7.1.2.3.3 SAS-GS and GAS-GS

For these services, given the poor availability achieved with the baseline parameters, only two changes have been analyzed :

One grouping the impacts of reducing both the multipath error budget and the user mask angle

Another assessing the sensitivity to requirements

7.1.2.3.3.1 Sensitivity to the multipath level and the user mask angle




In addition, as for SAS and GAS users, the environment can be considered as open, the user mask angle has been reduced to 5°.

The following map represents the average accuracy availability obtained with this new assumptions (low multipath budget + 5°mask angle), all other simulation parameters being kept at the same values (baseline assumptions described in §6.1).


Index

1675

1676

1677

ID

…DD-036-3407

DD-036-3408

DD-036-3409

DD-036-3410


Figure 141 : SAS-GS and GAS-GS accuracy availability for low multipath conditions and reduced user mask angle (5°)

It can be concluded that with these multipath conditions and a user mask angle of 5°, SAS-GS and GAS-GS accuracyavailability performances are greatly improved and are, on the main part of the zone, compliant with the requirements (99.9%).The main area not covered with the required availability is located above 65°N. Some other points located below 10°N do notmeet the requirement either.

The next map shows the UIM availability performances achieved in the same conditions :


Index

1678

1679

1680

1681

ID

DD-036-3411

DD-036-3412

DD-036-3413

DD-036-3414


Figure 142 : SAS-GS and GAS-GS UIM availability for low multipath conditions and reduced user mask angle (5°)

From this map, it can be concluded that even with these multipath conditions and reduced mask angle, SAS-GS and GAS-GSUIM availability requirement is not met. The availability is however greatly improved wrt the baseline case (cf. Figure 122), insuch proportions that a level of 99% is achieved on a significant part of the studied zone.



Index

1682

1683

1684

1685

ID

DD-036-3415

DD-036-3416

DD-036-3417

DD-036-3418


From the baseline analysis described in §7.1.2.2.3, it is clear that the driving factor for SAS-GS and GAS-GS servicesavailability is the vertical alarm limit. That is why, sensitivity analysis to this parameter is here presented : the followingavailability map corresponds to a VAL=12m, all other parameters being kept to their baseline values :

Figure 143 : SAS-GS and GAS-GS integrity availability for VAL=12m

It can be deduced that even with a vertical alarm limit of 12m, the UIM availability is not compliant with the requirement(99.9%). The availability is however greatly improved wrt the baseline case (cf. Figure 122), in such proportions that a level of99% is achieved on a significant part of the studied zone.


Index

1686

1687

1688

1689

1690

1691

1692

ID

DD-036-3419

DD-036-3420

DD-036-3421

DD-036-3422

DD-036-3423

DD-036-3424

DD-036-3425


7.2 Loran C/ Eurofix

7.2.1 Introduction

The radio-navigation system Loran C has got two features that may be appealing for integration with Galileo.

The first one is its robustness. Although the accuracy of the system does not match the one of satellite based navigationsystems, the integrity continuity and availability of the system have been already demonstrated. This is especially true instressed environment with high masking angle such as urban environment. L band signals cannot get through buildings orobstacles whereas low frequency signals such as the ones used by Loran C system can penetrate the buildings and provide apositioning in urban area with an acceptable availability.

One important drawback of Loran C is of course that it does not provide any navigation information in the vertical dimension. Therefore it is of little use for aviation application.

The second is its communication link capability. Loran C station could be used to broadcast on a long range the informationgenerated by a local differential station. Integrity information could be also transmitted through this communication link. Since integrity data flow increases significantly the bit rate of the system and consequently decreases the navigationperformance of Galileo, such alternative is worthy to investigate. This concept has been already exploited on GPS by the systemEurofix.

As far as performance estimation is concerned, the use of Eurofix concept is not different from the concept of local differential. Therefore, integration of Loran C communication link with Galileo will be simulated as such.


Index

1693

1694

1695

1696

1697

1698

1699

ID

DD-036-3426

DD-036-3427

DD-036-3428

DD-036-3429

DD-036-3430

DD-036-3431

DD-036-3432


Figure 144: Eurofix concept

7.2.2 Loran C performance assumption

Characteristics of Loran C are described in the GALA work-package dealing with “The use of other system” [RD-011]. According to this document the behavior of this system in terms of performance can be is the following: The absolute accuracyof the system is according to the situation, between 200 and 400 meters at 95%. However the relative accuracy of the system ismuch better. It is estimated at about 20 m with current typical receiver and could be improved to 5 meter at 1 sigma withbetter performance receiver. The bad performance in absolute positioning service is due to the presence of bias on the rangemeasurement. Those bias are due to lack of knowledge on the way path of the signals from the emitter to the user receiver. However, those biases move slowly and can be calibrate with another system such as Galileo. Taking this into account, theassumption proposed in [RD-011] to assess navigation performance of a system combining Galileo and Loran C are thefollowing:

- Relative accuracy (or repeatable accuracy) at 1 sigma equal to 5m

- No range bias thanks to the possibility to calibrate them with Galileo

- When Galileo is no longer able to calibrate the biases, the position will drift back to the Loran C only position estimation with adrift of 20m per 24 hours (assessed in static only).


Index

1700

1701

1702

1703

1704

1705

1706

1707

1708

1709

1710

1711

1712

ID

DD-036-3433

DD-036-3434

DD-036-3435

DD-036-3436

DD-036-3437

DD-036-3438

DD-036-3439

DD-036-3440

DD-036-3441

DD-036-3442

DD-036-3443

DD-036-3444

DD-036-3445


- The Loran C availability in urban environment is estimated at 90%

7.2.3 Combined Galileo/Loran C expected performance.

7.2.3.1 Performance Allocation

Performance of a combined Galileo + Loran C system appears very difficult to assess. Indeed as explained above the protocol touse Loran C with Galileo should be as follows:

- When Galileo is available the user position is computed with Galileo while Loran C biases are calibrated.

- When Galileo is not available, the user position is computed with Loran C.

The availability of the service will most likely not exceed the availability of Loran C (ie 90%). Indeed, in urban environment, theperformance of Galileo in terms of availability are very poor. In fact, an availability of 90% could be reached with a combinedsystem only if the availability of Galileo is high enough in order to calibrate Loran C sensors often enough.

The accuracy target for a Loran C + Galileo service is 15 meters at 95% in horizontal. This budget as first to be allocatedbetween Galileo and Loran C. Indeed, as soon as Galileo is no longer operational the accuracy of the position will degradeslowly. For instance, if the Galileo accuracy is required at 10 meters and the Loran C position drift with a rate of 20m per 24hours, Loran C could theoretically allow to provide a service of 15 meters accuracy for a period of 4.5 hours. Actually theallocation depends of the trade off between availability of Galileo and speed of divergence of Loran C.

If the Galileo availability was good in urban environment and the speed of divergence of Loran C high, most of the accuracybudget should be allocated to Loran C. On the contrary for a low accuracy of Galileo and a slow drift of Loran C, the main partof the budget should be allocated to Galileo. In order to preliminary assess the performance of a combined system the allocationof 10 meters on Galileo and 5 meters for Loran C.

7.2.3.2 Availability Performance in Urban canyon

As such statistics require extensive simulations, performances have been computed at a limited number of locations (5), (called“towns”) which have been selected because they offer a coverage of latitude from 0° to 80°.

The longitude selected is 0°. This is not restricting the validity of this study, as the selected MEO constellation provideshomogeneous performances with respect to longitude.

The selected user co-ordinates are


Index

1713

1714

1715

1716

1717

1718

1719

1720

1721

1722

1723

ID

DD-036-3446

DD-036-3447

DD-036-3448

DD-036-3449

DD-036-3450

DD-036-3451

DD-036-3452

DD-036-3453

DD-036-3454

DD-036-3455

DD-036-3456


Town #1 Latitude = 0° Longitude = 0°





7.2.3.3 Outage Characterization

The following results shows the Galileo performance in urban canyon for a town 3 type of city. All the performance computed forthe other type of city are detailed in Annex.

7.2.3.3.1 Mean number of satellites in visibility

The following statistics present the mean number of satellite in view, for a user located in different environments. The azimuthrepresents the main direction of the canyon with respect with the north pole.

Mean SAT Az=0°Road 1/2 Width

Build. 5 m 10 m 15 m10 m 2,5 4,4 5,815 m 1,7 3,2 4,420 m 1,2 2,5 3,525 m 1,0 2,0 2,9


Index

1724

1725

1726

1727

1728

ID

DD-036-3457

DD-036-3458

DD-036-3459

DD-036-3460

DD-036-3461…



Build. 5 10 1510 m 3,5 5,7 6,415 m 2,6 4,5 5,420 m 2,0 3,8 4,625 m 1,7 3,3 4,0


Build. 5 10 1510 3,8 5,7 6,715 2,9 4,5 5,720 2,1 3,8 4,825 1,6 3,3 4,3

Mean SAT- All AzRoad 1/2 Width

Build. 5 10 1510 3,3 5,2 6,315 2,4 4,1 5,120 1,8 3,4 4,325 1,4 2,8 3,7


Index

1729

1730

1731

1732

ID

…DD-036-3461

DD-036-3462

DD-036-3463

DD-036-3464

DD-036-3465


5 m 10 m 15 mS1

S2

S3

S4

Distance to building

Building Heigh

Sat In visibility (Mean All Az. ) Town #1

6,0-8,0

4,0-6,0

2,0-4,0

0,0-2,0

Town 3

7.2.3.3.2 satellites availability

4 SAT Availability - Az=0°Road 1/2 Width

Build. 5 m 10 m 15 m10 m 4,0% 100,0% 100,0%15 m 0,0% 47,0% 100,0%20 m 0,0% 4,0% 59,0%25 m 0,0% 0,0% 29,0%


Index

1733

1734

1735

1736

1737

ID

DD-036-3466

DD-036-3467

DD-036-3468

DD-036-3469

DD-036-3470…



Build. 5 10 1510 m 52,0% 100,0% 100,0%15 m 20,0% 95,0% 100,0%20 m 12,0% 55,0% 91,0%25 m 7,0% 31,0% 70,0%


Build. 5 10 1510 55,0% 100,0% 100,0%15 20,0% 95,0% 100,0%20 10,0% 55,0% 100,0%25 4,0% 31,0% 83,0%

4 SAT Availability - All AzRoad 1/2 Width

Build. 5 10 1510 37,0% 100,0% 100,0%15 13,3% 79,0% 100,0%20 7,3% 38,0% 83,3%25 3,7% 20,7% 60,7%


Index

1738

1739

ID

…DD-036-3470

DD-036-3471

DD-036-3472…


5 m 10 m 15 m10

15

20

25

Distance to building

Building Heigh

4 SAT Availability (Mean) deg T3

80,0%-100,0%

60,0%-80,0%

40,0%-60,0%

20,0%-40,0%

0,0%-20,0%

7.2.3.3.3 Horizontal Accuracy availability statistics


Index

1740

1741

1742

ID

…DD-036-3472

DD-036-3473

DD-036-3474

DD-036-3475


5 m 10 m 15 m10 m

15 m

20 m

25 m

Distance to Building

Building Heigh10m horizontal availability - Town #3

80,0%-100,0%

60,0%-80,0%

40,0%-60,0%

20,0%-40,0%

0,0%-20,0%

10 meters Availabili tyRoad 1/2 Width

Build. 5 m 10 m 15 m10 m 0,4% 61,0% 93,5%15 m 0,0% 12,2% 61,0%20 m 0,0% 0,4% 18,7%25 m 0,0% 0,0% 5,3%

7.2.3.4 Conclusion

As shown by the preceding simulations, the availability on Galileo in urban environment can vary a lot according to the kind ofcanyon considered. Although, according to the assumptions made on Loran C, a poor Galileo availability may allow to coastwith a combined receiver the bottom line for Galileo availability should not be below 20 or 10% at last. This condition is fulfilledin some of the canyon but not in all. However, taking into account that the user is supposed to be moving and therefore does notstay all the time in penalizing environment, the availability of Galileo appears sufficient to allow navigation in urban city whencombined with Loran C. However this conclusion has to be weighted with the following arguments:


Index

1743

1744

1745

1746

1747

1748

ID

DD-036-3476

DD-036-3477

DD-036-3478

DD-036-3479

DD-036-3480

DD-036-3481


- The assumptions made on Loran C appear quite optimistic and shall be validated with measurement campaigns.

- The combination of Loran C and Galileo can allow radio navigation in “mean” urban environment. But there is always a limitto this combination. In the case that the environment is too stressed in terms of masking, Galileo may not be available at all.

Therefore, as a first estimation, the availability required for a Galileo/Loran C (15m at 90%) may be feasible. However,measurement campaign to better characterize urban environment and Loran C performance are mandatory to confirm thisassumption.

7.3 Hybridization with other system

Estimation of Galileo combined with other sensors such as inertial sensor and altimeter is something very difficult thatdemands the development of new tools as described in WP7.2. It is clear that users can take great benefit from other sensors. For instance, the mission requirements as they are expressed in [RD-01] are services with a 10 degrees elevation angle. It isclear urban users will navigate in much more stringent environment and that therefore, the performance detailed in themission requirements will be only achievable with the combination of Galileo with other sensors. Indeed, although the accuracyof those external sensors is less than Galileo or GPS, once calibrated they can allow to maintain navigation capability during acertain period of time when Galileo is not available. As explained in the Loran C performance estimation section, thecomplementarity between Galileo and the sensor considered depends on the outage duration and the sensor drift rate. For astatic user the outage periods are due to dynamic of the constellation. Therefore sensors with a slow drift is necessary. Fordynamic users, outage periods are due to dynamic of the user itself. Therefore they will be much shorter and more frequentwhich demands a sensor that can take advantage of the dynamic but that does not need to have a drift rate too slow.

In general, the performance detailed in the mission requirements relies on specific scenario in terms of masking angle,interference, multipath, user dynamic, ect… In more stringent conditions, a combination with other sensors will be necessary toreach performance equivalent to the mission requirements.


Index

1749

1750

ID

DD-036-3482

DD-036-3483


8 Synthesis : Availability compliance matrix for GALILEO and Galileo+GPS services

The following table summarizes the outcomes of the last paragraphs, giving for each Galileo and Galileo+GPS service : itscompliance vs the requirements (C : compliant, PC : Partially Compliant, NC : Non Compliant) and if it is not compliant withbaseline assumptions, examples of compliance conditions (when investigated).

Service Compliance with availability requirements :

OAS-G1 C

OAS-G2 C

CAS1-G C

CAS1-L C

SAS-G/En route C

SAS-G/NPA C

SAS-G/Cat1 andGAS-G

PC for accuracy availability with baseline assumptions (cf. Figure82)NC for integrity availability with baseline assumptions (cf. Figure85)

Compliance conditions for UIM availability:



• lower multipath level (as defined in §4) and lower maskangle (5°) :

• or, lower mask angle (5°) and relaxed VAL (20m) :

Compliance conditions for accuracy availability: VNSEreqrelaxed to 6.3m to overcome non compliance at the pole and 6.8m forFC on the whole zone.



OAS-GS PC with baseline assumptionsFull Compliance conditions :• lower multipath error budget defined in §4 (cf. Figure 129) • or relaxed HNSE requirement (6m) (cf. Figure 132)

CAS1-GS PC with baseline assumptionsFull Compliance conditions :• lower multipath error budget of §4 (cf. Figure 133 andFigure 134) • or relaxed HNSE and HAL requirements (5m, 14m) (cf.Figure 139 and Figure 140)

SAS-GS/Cat1 andGAS-GS

NC with baseline assumptions (cf. Figure 119 and Figure 122) but :

• for accuracy, PC at 99% (FC at 99% except at high latitudeand for isolated points) • for accuracy, PC at 99.9% with low multipath of §4 and lowmasking (5°) • for Integrity, PC at 99% with 12 meters vertical alarm limit

SAS-RM C for accuracy availability with baseline assumptions NC for integrity availability with baseline assumptions

Compliance conditions :for integrity, PC at 99% with baseline assumptions (except onborder zone of ECAC) cf : Figure 128


Index

1763

1764

1765

1766

1767

1768

1769

1770

ID

DD-036-3521

DD-036-3522

DD-036-3523

DD-036-3524

DD-036-3525

DD-036-3526

DD-036-3527

DD-036-3528


9 Conclusion And Open Points

9.1 Open points and recommendation

The goal of this document was to assess the feasibility of the Galileo mission performance requirements. Through, thisassessment several assumptions have been made. According to the situation those assumptions may have been verydimensioning on the performance results. Therefore they clearly need to be studied in more detail in order to solve the openpoints and consolidate the conclusions of this report. This section aims at pointing out those open issues and propose actions toclose them:

9.1.1 Local effects characterization

One main uncertainty in the performance estimation is the impact of the local effects on the accuracy, integrity, continuity andavailability of the system.

9.1.1.1 Multipath contribution in UERE budget

As explained in section 4 the UERE budget depends on several factors that are, satellite clock and ephemeris error, ionospheredelay, troposphere delay and receiver budget. Receiver budget includes multipath and interference effects. For most of theservice, Galileo users will apply dual frequency processing to cancel delay due to ionosphere. But this has the drawback toamplify all uncorrelated errors on each frequency. It means that when the receiver error is not negligible on one of the bothfrequency, it becomes the driving budget when dual frequency processing is used. Therefore, in order to be able to make areliable performance assessment, it is mandatory to characterize in more detail the error due to multipath. It is worth toremind that GPS is already broadcasting L band navigation signals. Therefore it would be strongly recommended to use thosesignals to characterize in detail the impact of multipath on pseudo-range measurements

9.1.1.2 Multiple and single failure due to local effects


Index

1771

1772

1773

1774

1775

1776

1777

1778

ID

DD-036-3529

DD-036-3530

DD-036-3531

DD-036-3532

DD-036-3533

DD-036-3534

DD-036-3535

DD-036-3536


As explained 4.7.1.1, the strategy in this document has been to separate as far as possible the integrity processing functions thathandle failures due to satellite and failures due to local effects. Failures due to satellites are assumed handled by GIC whereasfailure due to local effects are handled by RAIM. The fault tree analysis has been derived, taking as assumption that theprobability of occurrence of failure due to local effect was 10-4/h. It goes without saying that this figure that is verydimensioning in the system design has to be further consolidated. This depends very much of the capacity of the receiver todetect and cancel local errors on pseudo-ranges. Indeed, putting a probability on this kind of phenomena is rather difficult. Thesolution is to design the receiver to be able to cope with this kind of effects and make them negligible at the end. If notnegligible, with a probability of occurrence low enough to be handle by RAIM or RAIM hybridized. Further study specifically onthis topic involving receiver manufacturers are clearly necessary if Galileo intends to provide an integrity service at user level.

9.1.1.3 Masking angle and Interference mask

In this document, assumption have been taken on masking angles and interference mask in order to assess system performance. Those assumptions may be reliable for some applications such as air navigation. However for applications in urbanenvironment those two parameters have two be further consolidated. In this case as well, a measurement campaign aiming atbetter characterizing user environment are clearly recommended. Galileo should take advantage that other systems like GPSand GLONASS are already available to assess the impact of user environment on the final system performance.

9.1.2 Allocation assumptions

9.1.2.1 RAMS analysis

All the requirements expressed in chapter 3 have been deducted from an a priori allocation. The idea was to allocate theperformance got from mission requirements to the system components. However, although this allocation has been done usingEGNOS experience on similar systems, this process needs now to get some feedback from the components on the requirementsthat have been put on them. Up to now the allocation have been made in open loop. It is therefore necessary to close loop withdifferent component designers in order to consolidate the requirements and re-allocate form one component to another ifnecessary. This has been initiated in GALA (space segment performance, receiver performance…) but needs to be furtheranalyzed in the next phase of the study

9.1.2.2 Clock stability

In this document, one driving assumption that has been made is to consider the Galileo satellite clocks as stable as the GPSones. Since Europe is currently working on the design and the development of such equipment this assumption may beoptimistic. Clocks stability can be considered as the key point of the system in terms of performance. It impacts:


Index

1779

1780

1781

1782

1783

1784

1785

1786

1787

1788

1789

ID

DD-036-3537

DD-036-3538

DD-036-3539

DD-036-3540

DD-036-3541

DD-036-3542

DD-036-3543

DD-036-3544

DD-036-3545

DD-036-3546

DD-036-3547


- Accuracy through the clock contribution to UERE

- Integrity through the probability of occurrence of satellite failure

- Continuity and availability through the concept of SISA/IF

- Designing the system making too optimistic assumptions on this topic could jeopardize the whole project. Since Europe aslittle experience on this topic it is clearly recommended to be cautious on this specific point and to set up all back up solutionspossible in order to cope with potential clock non stability.

9.1.2.3 Network reliability

Through EGNOS experience, we are learning that one hard point to meet the final continuity requirements is the reliability ofthe network used for internal communication. It appears that small interruption called micro failure that last a few seconds are quite frequent. Therefore the system design has to be robust to this kind of event.

9.1.2.4 Up-link capabilities with dynamic antennas

One point of concern about the system performance is the up-link and down-link of the information trough the MEO’s. This is agreat modification comparing to the system already existing such as WAAS and EGNOS that broadcast the information throughstable geo stationary satellites. Broadcasting integrity information through the MEO’s as clear advantaged in terms of maskingangle for the users. However the feasibility of the concept has still to be proven. It means tracking dynamically a large numberof satellite with large antennas. May be more appropriate techniques like phase array antennas should be considered.

9.1.3 Integrity concept

9.1.3.1 Feasibility of the GIC concept

One assumption that has also been made in this document is to consider that the GIC integrity concept works. It means thatthe ground segment is able to detect and broadcast an alarm within the Time To Alarm in case of a failure on the spacesegment. This kind of statement should not be taken for granted. EGNOS is currently working on this problem and thesolutions are not that obvious. Many points are still under study such as the number of station really needed to monitor asatellite, the value of the SISA/UDRE that can be warranty by the ground segment, ect … Therefore stating that integrityworks because it has already be done in EGNOS is not recommended. A lot of efforts are still necessary on this topic to insurefinal integrity performance to the Galileo users.


Index

1790

1791

1792

1793

1794

1795

1796

1797

1798

1799

1800

1801

1802

1803

ID

DD-036-3548

DD-036-3549

DD-036-3550

DD-036-3551

DD-036-3552

DD-036-3553

DD-036-3554

DD-036-3555

DD-036-3556

DD-036-3557

DD-036-3558

DD-036-3559

DD-036-3560

DD-036-3561


9.1.3.2 Integrity performance concept

The Galileo integrity concept relies on the broadcast of a parameter characterizing the signal in space accuracy (SISA) and thebroadcast of an alarm IF in the case that information due to SISA is incorrect. This choice has been made in order to optimizethe amount of data to broadcast to the users. But this relies on the fact that the clocks are assumed stable, then that the SISAparameter is quasi constant and does not need to be transmitted frequently. This option presents real advantages only if:

- The Galileo clocks are indeed stable

- Alarms does not need to be broadcast too often.

It is clear that if the alarm are broadcast in a regular basis, this option will degrade the continuity and availability on thesystem. Furthermore, flags will be sent to fulfill the most stringent requirements and may penalize other users that requiresless performance (NPA vs Cat 1).

Furthermore, as explained before in section 9.1.2.3, another weak point may be the network. The micro failures could resultfrequently in “satellite not monitored” situation. In the current baseline, an alarm is sent when a satellite becomes suddenly notmonitored. If this occurs frequently, alarms may overload the bandwidth available.

Therefore, although the baseline solution appears suited if the clocks are stable, it is recommended (as it is done in GALA) tokeep the possibility to broadcast SISA on more frequent basis as it is done for the SBAS UDRE.

9.1.4 Model limitations

9.1.4.1 Integrity modeling

As explained in the section 9.1.3.1, the GIC has been assumed meeting the right performance. This implies in terms of integrityavailability modeling two main assumptions:

- One satellite is considered monitored when seen by 4 monitoring stations

- The estimation error of the SISA value is considered equal at 30% of the clock and ephemeris value.

Those assumptions where made following EGNOS experience. However, even in EGNOS, those points are still under study. Therefore the result presented using those models have to be used with caution.

9.1.4.2 Availability modeling


Index

1804

1805

1806

1807

1808

1809

1810

1811

1812

ID

DD-036-3562

DD-036-3563

DD-036-3564

DD-036-3565

DD-036-3566

DD-036-3567

DD-036-3568

DD-036-3569

DD-036-3570


The availability has been modeled in this document using the “mean availability” concept. This means that the availability isaveraged on the whole life of the system. Although it is already a good indicator it might not be enough to fully characterize thesystem performance at user level. In [RD-09], an update definition of the system availability has been proposed. Themotivation was to characterize the availability of the system in terms more meaningful to the users. This new definition willimply a different way to compute availability figures that will provide different results. This will have to be taken into accountin the definition of the Galileo performance mission requirements for next phases. Indeed, before requiring availability figuresthe first step is to clearly define what the users understand by availability.

9.1.4.3 Other sensor/ system simulation

One issue met in this document is the problem to simulate in a relevant way other system such as Loran C and other sensorssuch as inertial devices.

For Loran C, as explained in 7.2.3.4, the conclusion relies on assumption on Loran C performance. A measurement campaign isrecommended in order to back up those assumptions and characterize in more reliable way the performance that can beexpected from a combination of Galileo and Loran C.

For other sensors, as stated in chapter 7.3, development of adapted simulation tools is clearly necessary to go on with this kindof concept.

9.2 Conclusion

The goal of this document was to assess the feasibility of the Galileo mission performance requirements.

In order to do this the performance requirements have been first allocated to the different components of the system. Next thefeasibility of those requirements assuming that the system would follow the GALA baseline has been assessed. This has implieda detail computations of the UERE budget for each service.

The main conclusions of this performance assessment is the following. As detailed in the chapter 7, the performancerequirements are globally met for the different services. However for the service requiring Cat 1 capabilities the compliance canonly be partially stated. Indeed, although the 6 m vertical required with Galileo only appear achievable, the 15 m vertical alarmlimit required by civil aviation may rise some problems. Nevertheless this compliance attempt is strongly related withmultipath assumptions made. When low multipath is considered Cat 1 performance (15m vertical alarm limit) appearsachievable.


Index

1813

1814

1815

ID

DD-036-3571

DD-036-3572

DD-036-3573


For services that will be provided with GPS the targeted performance were a 4 meters vertical accuracy and 10 meters verticalalarm limit with 99.9% availability. Although the result of the simulation has to taken with caution, even with GPS it appearsdifficult to reach this kind of performance. The performance reachable would closer to 4 meters vertical accuracy and 10 metersvertical alarm limit but with 99% availability.

Nevertheless, as detailed in the preceding chapter, the results provided in this document rely on many assumptions. Let usremind that the goal of this document was to assess the feasibility of the requirements. It does not pretend stating finalcompliance to the Galileo mission requirements. Before doing this, consolidation of the assumptions and feed back from thedifferent component designers is necessary. In particular, all the open points detailed in the preceding chapter need to beaddressed in more detail in order to be able to derive compliance statement with respect to performance.

END DOCUMENT

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