Table Of ContentOperational Evaluation of a GBAS system
Paulo Alexandre Ferreira Esteves
A Thesis submitted in fulfillment of the requirements for the
Degree of Master of Science in
Aerospace Engineering
Jury
President Dr. Horácio Cláudio de Campos Neto
Advisor Dr. Agostinho Rui Alves da Fonseca
Co-Advisor Dr. José Raul Carreira Azinheira
Vogal Dr. Bertinho Manuel D’Andrade da Costa
September 2007
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Acknowledgments
First of all, I would like to thank Prof. Agostinho Fonseca for giving me the opportunity of
working with him in the realization of this exciting project and for all the support he gave me
during its execution. His always positive thoughts and good moods really helped me during the
hardest times.
To my colleagues at Instituto Superior Técnico it is hard to describe how grateful I am. It was
really a luck to have met such special people, with whom I spent five wonderful years. Their
support and friendship were something that I will never forget. Although the names are too
many to be mentioned, a special word has to be given to Fred and Nuno, two exceptional
persons and friends without whom I do not picture my future without. If I am what I am today,
also to them I own it.
To my family, who provided me with the perfect environment and stability to grow and all the
conditions to fulfill my studies, goes the deepest gratitude of all. Their love and support were
always unconditional and they are the great responsible for what I am today, which at least
comprises happiness.
To Ana, who was always there, standing by my side, giving me the strength to keep on going
whenever I needed it the most, I dedicate this work. Your company and encouragement got me
through everything and I will never forget it.
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Abstract
Satellite navigation (GNSS) is a worldwide available technology that represents a full range of
opportunities. For civil aviation, these systems represent a new era, as they have the potential
to provide an all-weather gate-to-gate guidance within a global coverage, and will allow
decommissioning most traditional navigation aids. Their sole performance, however, is not
compliant with the requirements for the most demanding civil aviation operations, as GNSS
systems particularly fail to grant integrity to the navigation solution they are providing, and
therefore they require augmentation.
The Ground-Based Augmentation System (GBAS) intends to help GNSS meet the requirements
for Precision Approach operations, this way fulfilling the objective of gate-to-gate navigation. As
an additional feature, GBAS systems will also provide a Positioning service that will allow
GNSS-supported Departure, Landing and Surface Movements operations.
This dissertation presents the process of operational evaluation of a GBAS system, by
simulation of a GBAS ground station at the Lisbon International Airport. This simulation will be
performed using PEGASUS, a program developed intentionally for the purpose of augmentation
systems operational evaluation. GBAS state-of-the-art is also presented and it is seen that
GBAS systems are already being acknowledged as a valid alternative to CAT-I ILS and are
expected to be the primary system to support CAT-I Precision Approach operations by 2015.
Keywords: GNSS, Civil Aviation, Integrity, GBAS, Precision Approach, PEGASUS
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Resumo
Os sistemas de navegação por satélite (GNSS) estão actualmente disponíveis mundialmente e
representam um vasto leque de oportunidades. Para a aviação civil representam o início de
uma nova era, dado serem potencialmente capazes de suportar qualquer operação de voo, em
quaisquer condições atmosféricas. No entanto, os sistemas GNSS são incapazes, por si sós,
de cumprir os requisitos de desempenho das operações de voo mais exigentes, falhando
especialmente em assegurar a integridade dos dados que fornecem. Esta limitação levou ao
desenvolvimento de sistemas complementares (de aumento), que pretendem ajudar os
sistemas GNSS a cumprirem os requisitos das operações da aviação civil.
Em particular, o sistema de aumento baseado no solo (GBAS) foi desenvolvido com o intento
de permitir aos sistemas GNSS cumprir os requisitos para aproximações de precisão,
conferindo-lhes assim em definitivo a capacidade para providenciarem uma cobertura total de
todas as fases de voo. Adicionalmente, os sistemas GBAS também providenciarão um serviço
de posicionamento que permitirá operações de descolagem, aterragem e movimentos à
superfície baseados em GNSS.
Nesta dissertação apresenta-se o processo de avaliação operacional de um sistema GBAS,
através da simulação de uma estação GBAS no Aeroporto Internacional de Lisboa. Esta
simulação será efectuada através do uso do software PEGASUS, desenvolvido
propositadamente para permitir a avaliação operacional de sistemas de aumento. O estado
actual dos sistemas GBAS é também apresentado e será visto que estes sistemas são já
reconhecidos como uma alternativa válida ao ILS, esperando-se que em 2015 sejam o principal
sistema para executar aproximações de precisão CAT-I.
Palavras-Chave: GNSS, Aviação Civil, Integridade, GBAS, Aproximação de Precisão,
PEGASUS
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Table of Contents
ACKNOWLEDGMENTS...............................................................................................................II
ABSTRACT..................................................................................................................................III
RESUMO......................................................................................................................................IV
TABLE OF CONTENTS................................................................................................................V
LIST OF TABLES......................................................................................................................VIII
LIST OF FIGURES.......................................................................................................................IX
LIST OF ABBREVIATIONS.........................................................................................................XI
CHAPTER 1 - INTRODUCTION...................................................................................................1
1.1. RESEARCH OBJECTIVES.................................................................................................2
1.2. THESIS OUTLINE............................................................................................................3
CHAPTER 2 - BACKGROUND....................................................................................................4
2.1. HISTORICAL BACKGROUND.............................................................................................4
2.2. GLOBAL NAVIGATION SATELLITE SYSTEM........................................................................5
2.3. AUGMENTATION SYSTEMS..............................................................................................6
2.4. GROUND-BASED AUGMENTATION SYSTEM.......................................................................8
2.5. REQUIRED GNSS PERFORMANCE...................................................................................9
CHAPTER 3 - GNSS OVERVIEW..............................................................................................11
3.1. GNSS ELEMENTS........................................................................................................11
3.2. PRINCIPLE OF WORK....................................................................................................12
3.3. CORE CONSTELLATIONS...............................................................................................14
3.3.1. Global Positioning System (GPS).....................................................................14
3.3.2. Global Navigation Satellite System (GLONASS)..............................................17
3.3.3. Galileo...............................................................................................................17
3.4. GNSS ERROR SOURCES..............................................................................................19
3.4.1. Dominant Error Sources....................................................................................19
3.4.1.1. Satellite Clock Errors.................................................................................................19
3.4.1.2. Orbital Errors.............................................................................................................19
3.4.1.3. Ionospheric Delay......................................................................................................20
3.4.1.4. Tropospheric Delay...................................................................................................20
3.4.2. Secondary Error Sources..................................................................................20
3.4.2.1. Receiver Clock Errors................................................................................................21
3.4.2.2. Receiver Measurement Noise...................................................................................21
3.4.2.3. Multipath....................................................................................................................21
3.4.3. Satellite Geometry.............................................................................................22
3.5. AUGMENTATION SYSTEMS............................................................................................22
3.5.1. Aircraft-Based Augmentation System (ABAS)..................................................22
3.5.2. Satellite-Based Augmentation System (SBAS).................................................23
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3.5.3. Ground-Based Augmentation System (GBAS).................................................25
3.6. GNSS PERFORMANCE EVALUATION..............................................................................26
3.6.1. Accuracy............................................................................................................27
3.6.2. Integrity..............................................................................................................28
3.6.3. Availability.........................................................................................................30
3.6.4. Continuity..........................................................................................................30
CHAPTER 4 - DIFFERENTIAL CORRECTION.........................................................................31
4.1. DIFFERENTIAL PRINCIPLE..............................................................................................32
4.2. PSEUDORANGE CORRECTION CALCULATION..................................................................33
4.3. PSEUDORANGE CORRECTION APPLICATION...................................................................34
4.4. CORRECTED PSEUDORANGE ERRORS...........................................................................36
4.5. POSITIONING ERRORS DERIVATION...............................................................................37
4.6. POSITION ERRORS IN A LOCAL COORDINATE FRAME......................................................40
CHAPTER 5 - GROUND-BASED AUGMENTATION SYSTEM................................................43
5.1. GBAS MISSION............................................................................................................43
5.2. GBAS STATE-OF-THE-ART...........................................................................................45
5.2.1. Local Area Augmentation System.....................................................................45
5.2.2. Differential GPS.................................................................................................46
5.2.3. Ground-based Regional Augmentation System................................................46
5.3. GBAS ARCHITECTURE.................................................................................................47
5.3.1. Ground Subsystem............................................................................................47
5.3.1.1. Receiving Unit...........................................................................................................48
5.3.1.2. Processing Unit.........................................................................................................49
5.3.1.3. Transmission Unit......................................................................................................49
5.3.2. Aircraft Subsystem............................................................................................50
5.4. GBAS INTEGRITY AND PERFORMANCE..........................................................................51
5.4.1. Integrity Allocation.............................................................................................51
5.4.2. Ground Subsystem Performance......................................................................53
5.4.2.1 Ground Accuracy Designator (GAD).........................................................................53
5.4.2.2 Ground Continuity and Integrity Designator (GCID)..................................................54
5.4.2.3 B-values.....................................................................................................................55
5.4.2.4 Ground Station Standard Deviation...........................................................................55
5.4.3. Aircraft Subsystem Performance......................................................................57
5.4.4. Atmospheric effects...........................................................................................57
5.5. PRECISION APPROACH SERVICE....................................................................................59
5.5.1. Operational Categories.....................................................................................59
5.5.2. Final Approach Segment Definition...................................................................59
5.5.3. Ground Subsystem Requirements....................................................................60
5.5.4. Procedure..........................................................................................................60
5.5.5. Deviations..........................................................................................................61
5.5.5.1. Lateral........................................................................................................................61
5.5.5.2. Vertical.......................................................................................................................62
5.5.6. Protection Levels...............................................................................................63
5.5.7. Alert Limits.........................................................................................................64
5.6. POSITIONING SERVICE..................................................................................................66
5.6.1. Procedure..........................................................................................................66
5.6.2. Ground Subsystem Requirements....................................................................66
5.6.3. Deviations..........................................................................................................67
5.6.4. Protection Levels...............................................................................................67
5.6.5. Alert Limits.........................................................................................................67
5.7. GBAS ECONOMICS......................................................................................................68
CHAPTER 6 - GBAS OPERATIONAL EVALUATION IN LISBON...........................................69
6.1. RESEARCH CONSIDERATIONS.......................................................................................69
6.2. GBAS SIMULATION......................................................................................................70
6.2.1. Scenario 1.........................................................................................................71
6.2.2. Scenario 2.........................................................................................................72
6.2.3. Data Evaluation.................................................................................................72
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6.3. STATIC EVALUATION.....................................................................................................73
6.4. DYNAMIC EVALUATION..................................................................................................76
6.5. WORLDWIDE GBAS OPERATIONAL EVALUATION ACTIVITIES...........................................79
CHAPTER 7 - CONCLUSIONS AND FINAL REMARKS..........................................................80
7.1. SUMMARY....................................................................................................................80
7.2. CONCLUSIONS..............................................................................................................81
7.3. FUTURE WORK.............................................................................................................81
REFERENCES............................................................................................................................82
ANNEX A - GPS NAVIGATION MESSAGE...............................................................................85
ANNEX B - PSEUDORANGE CORRECTION CALCULATION AND APPLICATION..............88
ANNEX C - GBAS MESSAGES.................................................................................................92
C.1. MT1............................................................................................................................93
C.2. MT2............................................................................................................................94
C.3. MT4............................................................................................................................95
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List of Tables
Table 2.1 – GNSS CAT-I performance requirements versus Stand-alone GPS performance...10
Table 3.1 – GNSS SIS performance requirements.....................................................................27
Table 3.2 – Alert Limits for GNSS operations.............................................................................28
Table 5.1 – GBAS benefits [17]...................................................................................................44
Table 5.2 – “Memphis Plan” benefits [24]..................................................................................46
Table 5.3 – GBAS messages types............................................................................................49
Table 5.4 – GAD parameters for GPS satellites [3]....................................................................54
Table 5.5 – Aircraft GPS receiver accuracy requirement [3].......................................................57
Table 5.6 – PA operational categories minima...........................................................................59
Table 5.7 – Channel Number mapping scheme [3].....................................................................61
Table 5.8 – Conditions for PA LAL [33].......................................................................................65
Table 5.9 – Conditions for PA VAL [33]......................................................................................65
Table 5.10 – GBAS CAT-I Ground Subsystem associated costs [39]........................................68
Table 6.1 – GNSS performance requirements............................................................................73
Table 6.2 – GBAS static performance.........................................................................................76
Table 6.3 – GBAS dynamic performance....................................................................................78
Table A.1 – GPS Ephemeris data [21]........................................................................................86
Table A.2 – Algorithm for GPS satellites position calculation [32]..............................................87
Table C.1 – GBAS MT structure..................................................................................................92
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List of Figures
Figure 2.1 – GNSS as a navigation system..................................................................................5
Figure 2.2 – SBAS and GBAS supported flight phases................................................................7
Figure 2.3 – ECAC navigation strategy roadmap [31]..................................................................8
Figure 2.4 – Overall GBAS architecture........................................................................................9
Figure 2.5 – Performance requirements hierarchy......................................................................10
Figure 3.1 – GNSS principle of work...........................................................................................12
Figure 3.2 – Effect of satellite-user clock deviation.....................................................................13
Figure 3.4 – GPS space segment...............................................................................................15
Figure 3.5 – WGS84 coordinate system.....................................................................................16
Figure 3.6 – Galileo space segment...........................................................................................18
Figure 3.7 – Multipath caused by ground reflection....................................................................21
Figure 3.8 – Satellite geometry effect.........................................................................................22
Figure 3.9 – EGNOS service area...............................................................................................24
Figure 3.10 – Differential Correction...........................................................................................25
Figure 3.11 – Navigation accuracy: TSE, NSE and FTE............................................................28
Figure 3.12 – Protection Levels and Alert Limits for NSE...........................................................29
Figure 3.13 – Integrity and Availability definition.........................................................................30
Figure 4.1 – Fixed-based GNSS receiver...................................................................................32
Figure 4.2 – Schematic Model for PRC Computation [29]..........................................................34
Figure 4.3 – North/East/Down coordinate system.......................................................................40
Figure 4.4 – Horizontal Error.......................................................................................................42
Figure 5.1 – Overall GBAS architecture......................................................................................47
Figure 5.2 – Ground Subsystem organization.............................................................................48
Figure 5.3 – Aircraft Subsystem organization.............................................................................50
Figure 5.4 – GBAS CAT-I service Integrity allocation [27]..........................................................51
Figure 5.5 – Ground Subsystem Integrity monitoring function [37].............................................52
Figure 5.6 – GAD assessment [41].............................................................................................54
Figure 5.7 – FAS definition [33]...................................................................................................60
Figure 5.8 – Lateral deviation from the FAS [33]........................................................................62
Figure 5.9 – Vertical deviation from the FAS [33].......................................................................62
Figure 5.10 – ACU coordinate frame..........................................................................................63
Figure 5.11 – D and H definition [3]........................................................................................65
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Figure 5.12 – GBAS and ILS performance.................................................................................66
Figure 6.1 – PEGASUS main window.........................................................................................71
Figure 6.2 – GBAS static HPE, HPL and NSV............................................................................74
Figure 6.3 – GBAS static VPE, VPL and NSV............................................................................74
Figure 6.4 – GBAS static horizontal NSE....................................................................................75
Figure 6.5 – EGNOS and GPS static horizontal NSE.................................................................75
Figure 6.6 – PoAF Falcon 50......................................................................................................76
Figure 6.7 – GBAS dynamic HPE, HPL and NSV.......................................................................77
Figure 6.8 – GBAS dynamic VPE, VPL and NSV.......................................................................77
Figure 6.9 – GBAS flight trajectory..............................................................................................78
Figure 6.10 – Braunschweig GBAS test HPE and VPE..............................................................79
Figure 6.11 – Sendai experimental GBAS station.......................................................................79
Figure A.1 – GPS navigation message structure [32].................................................................85
Figure B.1 – Schematic model for PRC calculation [29].............................................................88
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Description:Aerospace Engineering. Jury comprises happiness. To Ana, who For civil aviation, these systems represent a new era, as they have the potential.
