This document provides an overview of global navigation satellite systems (GNSS) such as GPS, GLONASS, Galileo, and Compass. It discusses the history and development of satellite navigation systems, comparing the key aspects of different GNSS. It also describes the typical three-segment architecture of GNSS including space, ground, and user segments. Finally, it outlines several applications of satellite-based positioning in areas like agriculture, aviation, marine, and more.

1. Global Navigation Satellite System
based Positioning
Presented By: Mehjabin Sultana (437589)
Sami Romo (69293A)
Nuno Silva (335872)

2. A little bit of history
● First navigation satellite belonged to Russia (former Soviet Union): they
launched the first artificial Earth satellite “Sputnik 1”, in 1957. The initial
approach towards the position location was based on measuring the
Doppler shift of the satellite.
● US was also a pioneer in the development of navigation satellites:
“Transit” system was introduced in the 1960s, mostly for targeting
submarine-launched long-range missiles. “Transit” was effective but
required expensive receiver systems
● US moved to the Global Positioning System (GPS) or Navstar system in
the 1980s.

3. History (cont..)
● Russia also developed a GPS-like system named GLONASS (abbreviation
for the Russian “Globalnaya Navigatsionnay Sputnikovaya Sistema”) in the
1980s.
● Nowadays, both Japan and the European Space Agency (ESA) are
working on GPS augmentation systems, such as MTSAT (Multifunction
Transport Satellite Space based Augmentation System), EGNOS
(European Geostationary Navigation Overlay System)
● Also new stand-alone satellite navigation systems are developed, such as
Galileo (the future European satellite system) and Compass (in China).
● Most common abbreviation for a generic satellite positioning system is
GNSS (Global Navigation Satellite System).

4. GNSS System Comparison
GPS (US) GALILEO (Europe) GLONASS (Russia) COMPASS (China)
First launch 1978 2011 1982 2007
Full Operational Capability
(FOC)
1995 2018 2011 2020
Number of satellites 32 30 31 35
Orbital planes 6 3 3 3
Access Scheme CDMA CDMA FDMA/CDMA CDMA
Current Status 32 operational 4 IOV satellites,
22 operational
satellites budgeted
24 operational,
1 in preparation,
2 on maintenance,
3 reserved and
1 on test
14 operational satellites,
full coverage on Asia
pacific region

5. Why do we need satellite-based positioning?
Satellite-based positioning provides us some services:
Location = determining a basic position (e.g., emergency calls)
Navigation = getting from one location to another (e.g., car navigation)
Tracking = monitoring the movement of people and things (e.g., fleet
management, workforce management, lost child/pet tracking)
Mapping = creating maps of the world
Timing = bringing precise timing to the world

6. GNSS system architecture
GNSS systems are quite complex, involving many different components.
- All GNSS systems are based on the same architecture (3-segment
architecture):
● Space segment: satellites
● Ground segment: monitoring, controlling and uploading stations
● User segment: user community/GNSS receivers
- The number of satellites and monitor stations differ according to the
GNSS system (GPS, Glonass, Galileo, ...)

7. The three segments of GNSS

8. Tasks of different segments
The space segment is formed by the satellites, also abbreviated by SV (Satellite Vehicle). The functions of a
satellite are:
● It receives and stores data from the ground control segment.
● It maintains a very precise time. In order to achieve such a goal, each satellite usually carries several
atomic clocks of two different technologies (e.g., cesium and rubidium), depending on the generation of
the satellite.
● It transmits data to users through the use of several frequencies
● It controls both its altitude and position
● It may enable a wireless link between satellites
Tasks of ground segment
● The main functions of the ground segment are to:
● Monitor the satellites; activate spare satellites (if available) to maintain system availability; check the SV
health
● Estimate the on-board clock state and define the corresponding parameters to be broadcast (with
reference to the constellation’s master time)
● Define the orbits of each satellite in order to predict the ephemeris data, together with the almanac;
● Ephemeris = accurate orbit and clock corrections for the satellites. Each satellite broadcast only its
ephemeris data. In GPS, ephemeris is broadcast every 30 s.
● Almanac= coarse orbital parameters/information of the satellites (valid for up to several months)

9. Tasks of different segments (cont)
Tasks of user segment
● The main functions of a GPS receiver are:
● Receive the data from the satellites belonging to one or several constellations (e.g. GPS; Galileo) on one
or several frequencies. If several constellation => multi-system receivers. If several frequencies => multi-
frequency receivers (dual-frequency GPS-GLONASS receivers are rather common nowadays)
● Acquire the signal from each satellite on sky (acquisition = identification of satellite code and coarse
estimation of time delays and Doppler shifts)
● Track the signal received from the satellites on sky (tracking = fine estimation of time delay and Doppler
shifts)

10. How GNSS works? : Time Difference
- The GNSS receiver compares the time a signal
was transmitted by a satellite with the time
it was received.
- The time difference tells
the GNSS receiver how far
away the satellite is.

11. How GNSS works? : Travel Distance
Velocity x Time = Distance
Radio waves travel at the speed of light, roughly 299 792 458 m/s (i.e.,
around 3*108 m/s)
If it took, for example, 0.067 seconds to receive a signal transmitted by a
satellite floating directly overhead, use this formula to find your distance
from the satellite.
Travel Distance: 299792458 m/s x 0.067 s = 20086094.69 m

12. How GNSS works? : Triangulation in 2D (I)
Geometric Principle:
You can find one location if
you know its distance from
other, already-known locations.
Location can be anywhere on
the periphery of the circle.

13. How GNSS works? : Triangulation in 2D (II)
Location can be any of
the two intersecting
points (red dots)

14. How GNSS works? : Triangulation in 2D (III)
Location is exactly
at the intersecting
point of the three
circles (red dot)

15. How GNSS works?: 3D Trilateration
1 Satellite
2 Satellites
3 Satellites

16. How GNSS works? Position Determination
● GNSS systems use the concept of Time-Of-Arrival (TOA) of signals +
triangulation/trilateration to determine user position.
● Minimum 3 satellites
needed in order to
determine the user
coordinates xu, yu, zu
(horizontal, vertical &
height). The 4th satellite
is needed to determine
the clock error.
4 unknowns

17. Applications - Military
● Joint Direct Attack Munition (JDAM) smart bomb, Tomahawk cruise
missile...
o No need for ground support
o Guidance system can be used in all weather conditions
o Reverts to inertial navigation when GPS signal is lost
● Combat Survivor Evader Locator (CSEL)
o All weather availability
o Ease of use (fast and accurate)

18. Applications - Agriculture
● Tractor guidance
o Tractor drives itself minimizing over-lap and
under-lap
o Shortens the amount of time used per field
o Ability to work in low visibility conditions
increases productivity
● Yield mapping
o GPS with grain flow and grain moisture
sensors
o Processed yield maps can be used to
investigate factors affecting the yield

19. Applications - Marine
● Automatic Identification System (AIS) is used for vessel traffic control
around busy seaways
o http://www.landsort-ais.se

20. Applications - Surveying and Mapping
● Survey vessels combine GPS positions with sonar depth soundings to
make the nautical charts that alert mariners to changing water depths and
underwater hazards

21. Applications - Aviation
● Enhanced Ground Proximity Warning System (EGPWS) reduces the risk
of controlled flight into terrain, a major cause of many aircraft accidents

22. Applications - Rail
● Positive Train Control (PTC) systems prevent collisions, derailments, work
zone incursions, and passage through switches in the wrong position

23. Applications - Recreation
● Geocaching
● “Checking-in” in social media
● Sports tracker: saving and sharing
your jog route with friends
● Andropas journey planner: see the bus
or train location real time, will you
make it to the bus or not?

24. Applications - Space
● Launch vehicle tracking
o Replacing or augmenting tracking radars with higher
precision, lower-cost GPS units for range safety and
autonomous flight termination
● Timing solutions
o Replacing expensive spacecraft atomic clocks with
low-cost, precise time GPS receivers
● Constellation control
o Providing single point-of-contact to control for the orbit
maintenance of large numbers of space vehicles such
as telecommunication satellites

25. Applications - Timing
● Wireless telephone and data networks use GPS time to keep all of their base stations in sync
● Major investment banks use GPS to synchronize their network computers located around the
world
● Integration of GPS time into seismic monitoring networks enables researchers to quickly locate
the epicenters of earthquakes and other seismic events
● The U.S. Federal Aviation Administration (FAA) uses GPS to synchronize reporting of hazardous
weather from its 45 Terminal Doppler Weather Radars located throughout the United States
● By analyzing the precise timing of an electrical anomaly as it propagates through a grid,
engineers can trace back the exact location of a power line break

26. References
● An introduction to GPS, mms.nps.gov/gis/gps/How_GPS_Works.ppt
● http://www.colorado.edu/geography/gcraft/notes/gps/gps_ftoc.html
● European GNSS Supervisory Authority GSA - www.gsa.europa.eu
● European Space Agency ESA - http://www.esa.int/esaNA/galileo.html
● ION Institute of Navigation - http://www.ion.org/
● www.GPS.gov

27. Thanks!!