2005:044 CIV MASTER'S THESIS - DiVA 1027218/ ¢  2016. 10. 4.¢  This master thesis uses

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  • 2005:044 CIV

    M A S T E R ' S T H E S I S

    A Software Implemented Receiver for Satellite Based Augmentation Systems

    An Enhancement to Global Navigation Satellite Systems

    Henrik Ripa Mikael Larsson

    Luleå University of Technology

    MSc Programmes in Engineering

    Department of Computer Science and Electrical Engineering Division of EISLAB

    2005:044 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--05/044--SE

  • A Software Implemented Receiver for Satellite Based Augmentation Systems

    An enhancement to Global Navigation Satellite Systems

    Master Thesis in Computer Science

    Henrik Ripa & Mikael Larsson

    Luleå University of Technology, 10 February 2005

  • Abstract The global navigation satellite system GPS (Global Positioning System) offers a position ac- curacy of about 10-15 meters today. However, this is not enough for some applications such as navigating ships through narrow channels. Furthermore, GPS does not provide any integ- rity of the system (a maximum error bound of the position). Integrity is critical for safety-of- life applications, such as in the aviation industry.

    EGNOS (European Geostationary Navigation Overlay System) is a satellite based augmenta- tion system in development, that together with GPS provides integrity and improved accuracy of the user position. EGNOS works by closely monitor the GPS satellites at monitoring sta- tions scattered around Europe. Corrections and integrity bounds of the GPS signals are com- puted and encoded into messages. These messages are transferred to the users via geostation- ary satellites on the same frequency as GPS.

    This thesis describes a receiver implementation for decoding the EGNOS signal-in-space into messages and applying those messages to GPS measurements. Those steps are done in real- time. The EGNOS receiver is built as an extension to an existing GPS receiver.

    The EGNOS receiver decodes the signal-in-space into messages using a Viterbi decoder. These messages are then processed to compute local corrections and integrity information which are applied to the position solution. The position accuracy is found to be improved by the use of EGNOS.

  • Preface We have done our Master Thesis at a company called NordNav Technologies. This project has been performed mainly during the spring of 2004. Our supervisor was Per-Ludvig Nor- mark, CTO at NordNav Technologies AB. Our examiner was Dennis Akos, visiting professor at Luleå University of Technology. We would also like to thank Glenn McGougan who is an employee at NordNav and who has helped us very much.

    Luleå, September 2004

    Mikael Larsson

    Henrik Ripa

  • Table of Contents 1 Introduction ...................................................................................................................... 1

    1.1 NordNav Technologies AB........................................................................................ 1 1.2 Project goals ............................................................................................................... 1 1.3 Demands and limitations ............................................................................................ 2 1.4 Previous work............................................................................................................. 2 1.5 Outline........................................................................................................................ 2

    2 Background....................................................................................................................... 4

    2.1 Global Navigation Satellite System ........................................................................... 4 2.1.1 Global Positioning System ................................................................................. 4 2.1.2 Differential GPS................................................................................................. 6

    2.2 Satellite Based Augmentation System ....................................................................... 6 2.2.1 Wide Area Augmentation System...................................................................... 7 2.2.2 European Geostationary Navigation Overlay System........................................ 8

    2.2.2.1 SISNeT ........................................................................................................... 9 2.2.3 Multifunctional Transport Satellite Based Augmentation System..................... 9

    2.3 Minimum Operational Performance Standard ........................................................... 9 3 GPS receivers.................................................................................................................. 11

    3.1 NordNav software receiver ...................................................................................... 12 4 Our EGNOS receiver implementation ......................................................................... 13

    4.1 Software tools........................................................................................................... 13 4.1.1 Development tools............................................................................................ 14 4.1.2 Other tools ........................................................................................................ 14

    5 EGNOS decoder ............................................................................................................. 15

    5.1 Design....................................................................................................................... 15 5.2 Forward Error Correction......................................................................................... 16

    5.2.1 Convolutional code structure ........................................................................... 16 5.2.2 Viterbi decoding............................................................................................... 17 5.2.3 Our Viterbi implementation ............................................................................. 21

    5.3 Error detection.......................................................................................................... 22 5.3.1 Structure of MOPS messages........................................................................... 22 5.3.2 Cyclic Redundancy Code ................................................................................. 23

    5.4 Symbol alignment .................................................................................................... 25 5.5 Preamble search and message locking ..................................................................... 25 5.6 Receive messages ..................................................................................................... 27 5.7 No message found .................................................................................................... 27

    6 EGNOS applier............................................................................................................... 28

    6.1 Design....................................................................................................................... 28 6.2 Ionosphere ................................................................................................................ 29

    6.2.1 Ionospheric corrections in MOPS .................................................................... 31 6.3 Troposphere.............................................................................................................. 32

    6.3.1 Tropospheric corrections in MOPS.................................................................. 33 6.4 Long term corrections .............................................................................................. 33

    6.4.1 Long term corrections in MOPS ...................................................................... 33

  • 5

    6.5 Fast correction .......................................................................................................... 34 6.5.1 Fast corrections in MOPS ................................................................................ 34

    6.6 Shared....................................................................................................................... 35 6.6.1 PRN mask......................................................................................................... 35

    6.7 Integrity .................................................................................................................... 35 6.7.1 Receiver Autonomous Integrity Monitoring .................................................... 35 6.7.2 Integrity in MOPS ............................................................................................ 36

    7 Analysis ........................................................................................................................... 37

    7.1 Test setup.................................................................................................................. 37 7.2 Data collection.......................................................................................................... 37 7.3 Position accuracy...................................................................................................... 38 7.4 Integrity .................................................................................................................... 40 7.5 Performance ..................................................................................