Global Navigation Satellite
Systems
GNSS
Accuracy 10m or better
Galileo
EU/ESA
GPS
USA
Planned
India, Japan, Korea
GLONASS
Russia
Compass
China
Space Based Augmentation Systems
Improves GNSS accuracy to 3 metres
GNSS
Errors
Ionospheric & Tropospheric
diffraction 10 + 1 metres
Canyon Effect – 1 metre
Part copied from http://www.kowoma.de/en/gps/errors.htm
Geometry up to 100m
Timimg errors 4m –
Rounding errors 1m
Orbits up to 5m
Ionospheric effects ± 5 metres
Shifts in the satellite orbits ± 2.5 metres
Clock errors of the satellites' clocks ± 2 metres
Multipath effect ± 1 metre
Tropospheric effects ± 0.5 metre
Calculation & rounding errors
± 1 metre
All adds up to +- 15m – 10m typically stated
With EGNOS still +-3 to 5m according to this source
However +- 1m considered realistic
R1
Ephemeris – Actual Position of the Satellite
Time – determines how far away we are R1
Geometry locates us anywhere on the surface of a sphere
R2
R1
Ephemeris – Actual Position of the Satellite
Time – determines how far away we are R1
Geometry locates us anywhere on the surface of a sphere
Intersect 2 Spheres gives a ring
R2
R1
R3
Ephemeris – Actual Position of the Satellite
Time – determines how far away we are R1
Geometry locates us anywhere on the surface of a sphere
Intersect 2 Spheres gives a ring
Intersect 3 Spheres gives 2 points
4 spheres gives a 3D position
CODE DIVISION MULITPLE ACCESS – CDMA SPREAD SPECTRUM
GNSS DATA
+
TRANSMISSION
SPREADING CODE
CORRELATOR
DATA OR PRN
RECEPTION
http://www.novatel.com/an-introduction-to-gnss/chapter-1-gnss-overview/
http://www.navipedia.net/
http://www.ni.com/whitepaper/7139/en/#toc1
http://www.nbmg.unr.edu/Staff/pdfs/Blewitt%20Basics%20of%20GPS.pdf
Coarse Acquistion
1023 bits, 1.023MHz = 1 ms repetition rate
Precise Code
6.1871 × 1012 bits long (6,187,100,000,000 bits)
Part of 2.35 × 1014 bits in length (235,000,000,000,000 bits)
10.23MHz
May be modulates with a W-code to prevetn Spoofing
Navigation Message
50 BPS – Date & Time – Ephmeris – Almanac
1500 Bit frame in 5 sub-frames of 300 bits - each takes 6
seconds to arrive
Cold Start – Load The Almanac – where are the satellites
Warm start – get satellite data and extract Ephemeris (position) and
time
Calculate UTC
Do Geometry and get a 3D fix
Use SBAS to correct Fix
Use 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 Systems
Improves GNSS accuracy to 3 metres
INTRODUCTION TO DATA OVER GSM
ANALOGUE – e.g V22 etc
SHORT MESSAGE SERVICE – SMS
GPRS
BASIC SMS COMMANDS
AT+CMGS=”+447967123456”
>
ENTER TEXT
CONTROL Z
AT+CMGR=NN
AT+CMGD=NN
AT+CMGW=”+44796123456”
>
ENTER TEXT
CONTROL Z
AT+CMSS = NN