Integrity Monitoring Techniques in GPS/Galileo Aerospace Engineering

107 Pages·2015·6.38 MB·English

by  João Duarte

Integrity Monitoring Techniques in GPS/Galileo
João Pedro Duque Duarte
Thesis to obtain the Master of Science Degree in
Aerospace Engineering
Supervisor: Professor Fernando Duarte Nunes
Examination Committee
Chairperson: Prof. João Manuel Lage de Miranda Lemos
Supervisor: Prof. Fernando Duarte Nunes
Member of the Committee: Prof. José Eduardo Charters Ribeiro da Cunha Sanguino
May 2015
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Acknowledgments
To me, this thesis is a major milestone as it marks the end of a journey at Instituto Superior Técnico.
The journey was not always perfect or easy but I am very glad and proud to achieve many of the goals
I had when I enrolled in my master degree in Aerospace Engineering. Getting to this point was only
possible thanks to the support and motivation from my family and friends.
IwouldliketoexpressmyappreciationandgratitudetoProf. FernandoDuarteNunes,mysupervisor
in this thesis for his support, advice, help and availability during this master thesis.
To my colleagues, and friends for their help and friendship that made the journey easier.
ToDeimosEngenhariafortheirsupportprovidingmeprecioustimetocompletethisthesis,andgood
fellowship.
And finally to my family, specially my parents for all the emotional and financial support, patience
and motivation without which nothing of this would have been possible.
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Resumo
A utilização de sistemas de navegação em aviação requer um elevado nível de confiança na solução a ser
usada. Define-se integridade como o nível de confiança que se tem na exactidão da informação fornecida
pelo sistema de navegação. Existem várias arquitecturas que permitem verificar o nível de integridade
da solução apresentada pelo sistema. Uma dessas arquitecturas são as chamadas técnicas de RAIM que
consistememalgoritmosimplementadosaníveldoreceptorquepermitemmediresseníveldeintegridade
e em caso de existência de falha num satélite essa falha não só é detectada como o satélite com defeito
pode ser excluído.
Existemváriosalgoritmosdeintegridade,entreosquaisoLeast-Squares-ResidualseoRange-Comparison-
Method que foram os analisados nesta tese. Os algoritmos de monitorização de integridade vêem o seu
desempenho afectado pela geometria dos satélites. Interessa portanto comparar os dois algoritmos con-
siderados quanto ao seu desempenho em casos de diferentes geometrias.
Para testar o desempenho dos algoritmos foi simulada uma constelação de GPS e uma trajectória do
receptor cuja solução de posição foi calculada com recurso a um filtro de Kalman. Foram consideradas
duas geometrias distintas e ambos os algoritmos foram testados para as mesmas condições. Foi testada
não só a capacidade de detecção de falha como também a de exclusão.
Os resultados mostram que ambos os algoritmos têm desempenhos muito idênticos pelo que a maior
diferença é mesmo o nível de complexidade dos algoritmos que é consideravelmente superior no caso do
Range-Comparison-Method.
Palavras-chave:
GPS, Galileo, Integridade, RAIM
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Abstract
Theuseofnavigationsystemsinaviationrequiresahighleveloftrustinthesolutiontobeused. Integrity
isdefinedasthemeasureofthetrustthatcanbeplacedinthecorrectnessoftheinformationsuppliedbya
navigationsystem. Thereareseveralarchitecturesthatallowtocomputetheintegritylevelsonasolution
provided by the system. One of those architectures are the integrity monitoring techniques called RAIM
and these consist in algorithms implemented at the receiver and allow to measure the integrity level and
in case of a faulty satellite that fault is not only detected but the faulty satellite may be excluded.
Thereareseveralintegrityalgorithms,namelytheLeast-Squares-ResidualsandtheRange-Comparison-
Methodthatwereanalysedinthisthesis. Integritymonitoringalgorithmshavetheirperformanceaffected
bysatellitesgeometry. Thus,itisimportanttocompareboththeconsideredalgorithmsasitsperformance
in different geometry cases.
Totestthealgorithm’sperformanceaGPSconstellationwassimulatedalongwithatrajectorywhose
position solution was obtained using a Kalman filter. Two distinct geometries were considered and both
algorithms were tested for the same conditions. It was tested not only the ability to perform fault
detection as also exclusion.
The results show that both algorithms have similar performances whereby the major difference is at
the algorithms complexity level, which is considerable higher in the Range-Comparison-Method case.
Keywords:
GPS, Galileo, Integrity, RAIM
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Contents
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Structure and proposed approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 State of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Global Navigation Satellite Systems 5
2.1 GPS overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 GPS Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Space Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Control Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.3 User Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Galileo overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Galileo Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 Space Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.2 Control Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.3 User Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Fundamentals 11
3.1 Coordinate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.1 ECI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.2 ECEF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.3 ENU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Coordinate System Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1 Cartesian to Geodetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
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3.2.2 Geodetic to Cartesian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.3 ECEF to ENU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3 Receiver Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Measurement Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.1 Satellite Clock Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.2 Ephemeris Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.3 Atmospheric Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.4 Receiver Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4.5 Multipath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.4.6 Pseudorange Error Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.5 DOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 Position Determination 25
4.1 Least-Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 DOP calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 Position solution using Kalman Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3.1 Dynamics models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3.2 Clock state model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3.3 Extended Kalman filter: dynamics models . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.4 Extended Kalman filter: observations model . . . . . . . . . . . . . . . . . . . . . . 36
5 Integrity 41
5.1 SBAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.1.1 SBAS around the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.1.2 WAAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.1.3 EGNOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 GBAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.3 RAIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.1 FD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.2 FDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.3 RAIM algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.3.4 RAIM Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.4 Integrity in Galileo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4.1 Integrity parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4.2 Galileo user integrity algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6 Computer Simulation 65
6.1 Computer Simulation Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.2 Computer Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.2.1 Error calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
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