Arduino DGPS System Implementation

80 Pages·2016·3.9 MB·English

by  Martin Svaton

Linköping University
Institute of Technology - Intelligent Transport Systems and Logistics

Low-cost implementation of Differential
GPS using Arduino

Master thesis

Martin Svatoň

13. September 2016

Supervisor: David Gundlegård
Examiner: Carl Henrik Häll
ČESKÉ VYSOKÉ UČENÍ TECHNICKÉ V PRAZE
Fakulta dopravní
Ústav letecké dopravy

Nízkonákladavoá realizace Diferenciální GPS
pomocí systému Arduino

Low-cost implementation of Differential GPS using Arduino

Diplomová práce

Studijní program: Technika a technologie v dopravě a spojích
Studijní obor: Inteligentní dopravní systémy

Vedoucí práce: Ing. Petr Bureš, Ph.D.
David Gundlegård, MSc

Martin Svatoň

Acknowledgment
This thesis was carried out with the Department of Science and Technology at the
Linköping University, and Department of Transport Telematics at Czech Technical
University in Prague as a final part of the Double Degree study program Intelligent
Transport Systems. I would like to thanks to my examiner Carl Henrik Häll (LIU),
supervisors David Gundlegård(LIU) and Petr Bureš (CTU) for introductory lectures in
GPS positioning and their contributions during the thesis progress.
Special thanks to Donghwan Yoon from Sejong University for providing materials
and description about the position-domain projection algorithm.

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© Martin Svaton

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Abstract
In today’s technical dimensions, there are various autonomous gadgets as drones or
autonomous lawnmowers, which are widely used by the public to facilitate everyday
life. Drones become more and more popular due to mobility and autonomous air
operations. The continuous development leads to finding of diverse application for
drones such as delivery service or filming.
These autonomous devices are used to navigate themselves and operate without
human intervention. It predominantly uses a GPS as a source of position information,
which is provided by GPS receiver attached to the device. However, these
measurements are not accurate enough to estimate the exact position, which is one of
the major requirements for autonomous operation. The main objective of this thesis is
to propose the solution for improving the positioning accuracy, which is not expensive
and easy to implement.
The Arduino DGPS solution implemented in this thesis proposes the algorithms for
position accuracy improvements in two ways. The first mode uses a range residual
computed by the receiver to estimate pseudorange corrections (PRCs) and
corresponding position correction. The second mode works as an advanced Satellite-
Based Augmentation System (SBAS) correction repeater, which uses the SBAS
correction to acquire the position correction. Both solutions are implemented to the
Arduino and user can choose, which correction method will be used.

Keywords: Differential GPS, Arduino, Low-cost implementation

Abstrakt
V dnešní přetechnizované době je využívano mnoha autonomních zařízení, jako jsou
autonomní sekačky či drony, které jsou široce využívány v soukromém sektoru. Drony
jsou velmi populární díky své mobilitě a schopnosti autonomních letů. Postupný vývoj
těchto zařízení vedl k objevu mnoha aplikací, jako například filmování z ptačí
perspektivy nebo autonomní doručování.
Tyto autonomní zařízení se samy navigují a fungují bez uživatelských intervencí. Pro
navigaci se převážně využívá systému GPS. Běžně dostupné GPS příjmače však
poskytují poziční data s určitou chybou, které je třeba eliminovat pro přesnou navigaci.
Hlavním cílem této práce je návrh řešení zpřesňování GPS pozice, které je levné a
snadno použitelné.
Navrhované řešení Arduino DGPS využívá dvou principů zpřesňování GPS měření.
První mód počítá korekce pseudovzdáleností na základě rozdílu sledované a vypočtené
pseudovzdálenosti (range residuals). Druhý mód pracuje na principu opakovače SBAS
korekcí, kde se přijímané korekce SBAS aplikují na měřenou pozici, čímž dojde ke
zpřesnění GPS pozice. Obě rešení jsou implementována do systému Arduino a uživatel
si může vybrat jednu z korekčních metod.

Klíčová slova: Diferenční GPS, Arduino, Nízkonákladová implementace

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Table of Contents
1 INTRODUCTION .........................................................................................................................................8
1.1 BACKGROUND ........................................................................................................................................... 8
1.2 AIM ............................................................................................................................................................. 8
1.3 OBJECTIVES ............................................................................................................................................... 8
1.4 SCOPE ......................................................................................................................................................... 9
1.5 RELATED WORK ....................................................................................................................................... 9
1.6 OUTLINE .................................................................................................................................................... 9
2 GLOBAL NAVIGATION SATELLITE SYSTEM ................................................................................... 10
2.1 GNSS HISTORY ..................................................................................................................................... 10
Radio based navigation systems ................................................................................... 10
Doppler-based navigation systems .............................................................................. 11
Current GNSS situation ..................................................................................................... 12
2.2 GPS ......................................................................................................................................................... 13
System composition ........................................................................................................... 13
GPS signals.............................................................................................................................. 14
Code measurement determination .............................................................................. 15
GPS access regulation ........................................................................................................ 15
2.3 GPS DATA ............................................................................................................................................ 16
RAW Navigation messages .............................................................................................. 16
NMEA ........................................................................................................................................ 17
RTCM ........................................................................................................................................ 18
UBX ............................................................................................................................................ 18
RINEX........................................................................................................................................ 18
2.4 REFERENCE SYSTEM ............................................................................................................................. 19
WGS84 ...................................................................................................................................... 19
Positioning quality .............................................................................................................. 20
2.5 POSITIONING METHOD ......................................................................................................................... 21
Pseudorange Code measurement ................................................................................. 21
Pseudorange Phase measurement ............................................................................... 22
Lateration ............................................................................................................................... 23
Doppler Shift positioning ................................................................................................. 25
2.6 GPS ERRORS .......................................................................................................................................... 26
Clock errors ............................................................................................................................ 26
Ionospheric Errors .............................................................................................................. 26
Tropospheric errors ........................................................................................................... 27
Ephemeris Error .................................................................................................................. 27
Multipath ................................................................................................................................. 27
Dilution of Precision ........................................................................................................... 28
3 POSITION AUGMENTATION TECHNIQUES ..................................................................................... 29
3.1 SBAS ....................................................................................................................................................... 29
EGNOS ...................................................................................................................................... 29
WAAS ........................................................................................................................................ 30
3.2 DIFFERENTIAL GPS (DGPS) .............................................................................................................. 30
Position domain DGPS ....................................................................................................... 31
Range domain DGPS ........................................................................................................... 32
Low cost receivers and DGPS ......................................................................................... 34
DGPS errors ............................................................................................................................ 35
4 DGPS SYSTEM PROPOSAL .................................................................................................................... 36
4.1 FUNCTIONAL PROPOSAL ...................................................................................................................... 37
3
Range Residuals (MODE1) .............................................................................................. 37
SBAS corrections (MODE2) ............................................................................................. 37
Application of the PRC ....................................................................................................... 38
4.2 PRC PROJECTION TO POSITION DOMAIN ......................................................................................... 38
Projection matrix H ............................................................................................................ 39
4.3 GPS RECEIVERS SETTING .................................................................................................................... 43
Rover Station ......................................................................................................................... 43
Reference Station (RS) ...................................................................................................... 43
4.4 ALGORITHM IMPLEMENTATION ......................................................................................................... 44
Rover Station ......................................................................................................................... 44
Reference Station (RS) ...................................................................................................... 45
4.5 DATA TRANSMISSION ........................................................................................................................... 49
Data Formats ......................................................................................................................... 50
4.6 SELF-ACCURACY MONITORING .......................................................................................................... 51
Integrity Monitoring ........................................................................................................... 51
Accuracy Monitoring .......................................................................................................... 52
5 HARDWARE DESIGN ............................................................................................................................. 53
5.1 PARTS DESCRIPTION ............................................................................................................................ 53
GPS Receivers ........................................................................................................................ 53
Wi-Fi ESP8266 ...................................................................................................................... 53
QVGA ILI9341 ....................................................................................................................... 53
Arduino .................................................................................................................................... 54
Wiring Diagram .................................................................................................................... 54
5.2 PCB DESIGN .......................................................................................................................................... 56
5.3 IN OPERATION ....................................................................................................................................... 57
RS MODE1 (RES) ................................................................................................................. 57
RS MODE2 (SBAS) ............................................................................................................... 58
Rover Station ......................................................................................................................... 58
6 TEST RESULTS ........................................................................................................................................ 59
6.1 STATIC MEASUREMENTS ...................................................................................................................... 59
MODE1 (RES) ........................................................................................................................ 59
MODE 2 (SBAS) .................................................................................................................... 61
6.2 DYNAMIC MEASUREMENTS.................................................................................................................. 63
MODE1 (RES) ........................................................................................................................ 63
MODE2 (SBAS) ..................................................................................................................... 65
6.3 DEVICE POWER REQUIREMENTS ....................................................................................................... 66
6.4 RESULT BENCHMARKING .................................................................................................................... 66
7 DISCUSSION ............................................................................................................................................. 67
7.1 FUNCTIONAL LIMITATIONS ................................................................................................................. 67
7.2 MEASUREMENT RESULTS EVALUATION ............................................................................................ 68
7.3 FUTURE DEVELOPMENT ....................................................................................................................... 69
8 CONCLUSION ........................................................................................................................................... 69
9 REFERENCES ........................................................................................................................................... 70

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