Galileo EU/ESA

GPSUSA

GLONASSRussia

Global Navigation Satellite Systems

GNSSAccuracy 10m or better

CompassChina

PlannedIndia, Japan, Korea

Space Based Augmentation SystemsImproves GNSS accuracy to 3 metres

Part copied from http://www.kowoma.de/en/gps/errors.htm

GNSS Errors

Geometry up to 100m Orbits up to 5m

Canyon Effect – 1 metreIonospheric & Tropospheric

diffraction 10 + 1 metres

Timimg errors 4m – Rounding errors 1m

Ionospheric effects ± 5 metresShifts in the satellite orbits ± 2.5 metresClock errors of the satellites' clocks ± 2 metresMultipath effect ± 1 metreTropospheric effects ± 0.5 metreCalculation & rounding errors ± 1 metre

All adds up to +- 15m – 10m typically stated

With EGNOS still +-3 to 5m according to this sourceHowever +- 1m considered realistic

R1

Ephemeris – Actual Position of the SatelliteTime – determines how far away we are R1Geometry locates us anywhere on the surface of a sphere

R1

Ephemeris – Actual Position of the SatelliteTime – determines how far away we are R1Geometry locates us anywhere on the surface of a sphereIntersect 2 Spheres gives a ring

R2

R1

Ephemeris – Actual Position of the SatelliteTime – determines how far away we are R1Geometry locates us anywhere on the surface of a sphereIntersect 2 Spheres gives a ringIntersect 3 Spheres gives 2 points4 spheres gives a 3D position

R2

R3

CODE DIVISION MULITPLE ACCESS – CDMA SPREAD SPECTRUM

GNSS DATA

SPREADING CODE

+ TRANSMISSION

RECEPTIONCORRELATOR

DATA OR PRN

http://www.novatel.com/an-introduction-to-gnss/chapter-1-gnss-overview/http://www.navipedia.net/

http://www.ni.com/white-paper/7139/en/#toc1

http://www.nbmg.unr.edu/Staff/pdfs/Blewitt%20Basics%20of%20GPS.pdf

Coarse Acquistion1023 bits, 1.023MHz = 1 ms repetition rate

Precise Code6.1871 × 1012 bits long (6,187,100,000,000 bits)Part of 2.35 × 1014 bits in length (235,000,000,000,000 bits)10.23MHzMay be modulates with a W-code to prevetn Spoofing

Navigation Message 50 BPS – Date & Time – Ephmeris – Almanac1500 Bit frame in 5 sub-frames of 300 bits - each takes 6 seconds to arrive

Cold Start – Load The Almanac – where are the satellitesWarm start – get satellite data and extract Ephemeris (position) and timeCalculate UTCDo Geometry and get a 3D fixUse SBAS to correct FixUse Regression to get better accuracy

ASSISTED GPS – this is a technique whereby another source of location data is used to enable the device to start seeking the most apprpriate satellites. E.G. CELL-ID, dead reckoning or just memeory

Space Based Augmentation SystemsImproves GNSS accuracy to 3 metres

INTRODUCTION TO DATA OVER GSM

ANALOGUE – e.g V22 etcSHORT MESSAGE SERVICE – SMSGPRS

BASIC SMS COMMANDSAT+CMGS=”+447967123456”>ENTER TEXTCONTROL Z

AT+CMGR=NN

AT+CMGD=NN

AT+CMGW=”+44796123456”>ENTER TEXTCONTROL Z

AT+CMSS = NN