6. What is GPS ?
The Global Positioning System (GPS) can show
you your exact position on Earth any time,
anywhere, in any weather. The system
consists of a constellation of 24 satellites
(with about 7 "spares") that orbit 20372 km
(11,000 n.m)above Earth’s surface and
continuously send signals to ground stations
that monitor and control GPS operations.
7. Origination of GPS
After the Successive use of LORAN(LOng RAnge
Navigation and Decca Navigator System, in
world war II, more efficient and sophisticated
system was required not only to find the
friendly area but the exact location of the
aircraft so pilot and control tower will not
waste time to declare area or premises.
8. Origination of GPS
SputniK 1
So to achieve this goal, Soviet
Union launched first
satellite in 1957 named
Sputnik 1.
From here the cold war begun
when two American
physicists decided their
own to monitor Sputnik's
radio transmissions.
9. Origination of GPS
Transit
The first satellite navigation
system, Transit, used by the
United States Navy, was first
successfully tested in 1960. It
used a constellation of five
satellites and could provide a
navigational fix
approximately once per hour.
10. Origination of GPS
In Civilians' Use : After Korean Air Lines Flight
007, carrying 269 people, was shot down in
1983 after straying into the USSR's prohibited
airspace, in the vicinity of Sakhalin and
Moneron Islands, President Ronald Reagan
issued a directive making GPS freely available
for civilian use, once it was sufficiently
developed, as a common good. The first
satellite was launched in 1989, and the
24th satellite was launched in 1994.
11. Fundamentals of GPS
• Orbiting navigational satellites
– Transmit position and time data
• Handheld receivers calculate
– latitude
– longitude
– altitude
– velocity
12. Fundamentals of GPS
Orbiting navigational
satellites :
a system of satellites that
provide autonomous geo-
spatial positioning with
global coverage and
allows small electronic
receivers to determine
their location.
13. Fundamentals of GPS
Handheld receivers:
Calculate latitude,
longitude, Altitude
some may also
calculate Velocity
after receiving
signals from
satellite.
14. Working of GPS
• Satellite ranging
– Satellite locations
– Satellite to user distance
– Need four satellites to determine position
• Distance measurement
– Radio signal traveling at speed of light
– Measure time from satellite to user
• Low-tech simulation
15. Working of GPS
• Distance to a satellite is determined by
measuring how long a radio signal takes Pseudo-Random
to reach us from that satellite. Code:
• To make the measurement we assume • Complex signal
that both the satellite and our receiver • Unique to each
are generating the same pseudo-random satellite
codes at exactly the same time.
• All satellites
• By comparing how late the satellite's use same
pseudo-random code appears compared frequency
to our receiver's code, we determine
how long it took to reach us.
• Multiply that travel time by the speed of
light and you've got distance.
16. Working of GPS
• Accurate timing is the key to measuring
distance to satellites.
• Satellites are accurate because they have four
atomic clocks on board.
• Receiver clocks don't have to be too accurate
because an extra satellite range
measurement can remove errors.
17. Working of GPS
• To use the satellites as references for range
measurements we need to know exactly where
they are.
• GPS satellites are so high up their orbits are very
predictable.
• All GPS receivers have an almanac programmed
into their computers that tells them where in
the sky each satellite is, moment by moment.
• Minor variations in their orbits are measured by
the Department of Defense.
• The error information is sent to the satellites, to
be transmitted along with the timing signals.
19. GPS System Performance
Standard Positioning Precise Positioning
System: System:
– 100 meters horizontal – 22 meters horizontal
accuracy accuracy
– 156 meters vertical – 27.7 meters vertical
accuracy accuracy
– Designed for civilian use – Designed for military
– No user fee or use
restrictions
20. GPS System Performance
Selective availability
• Intentional degradation of signal
• Controls availability of system’s full
capabilities
Reasons
– Enhanced Emergency services
– Vehicle navigation
– Adoption of GPS time standard
21. GPS System Performance
• The earth's ionosphere and atmosphere
cause delays in the GPS signal that translate
into position errors.
• Some errors can be factored out using
mathematics and modeling.
• The configuration of the satellites in the sky
can magnify other errors.
• Differential GPS can reduce errors.
22. GPS’ Applications
• Location - determining a basic position
• Navigation - getting from one location to
another
• Tracking - monitoring the movement of
people and things
• Mapping - creating maps of the world
• Timing - bringing precise timing to the world
23. GPS’ Applications
• Private and recreation
– Traveling
– Hiking, climbing, biking
– Vehicle control
• Mapping, survey, geology
• English Channel Tunnel
• Aviation
– General and commercial
– Spacecraft
• Maritime
24. Military Example
Operation - Desert Storm:
• Featureless terrain
• Initial purchase of 1000
portable commercial
receivers
• More than 9000 receivers
in use by end of the
conflict
• Foot soldiers
• Vehicles
• Aircraft
• Marine vessels
25. Cell Phones with GPS
Due in part to regulations
encouraging Cell phone tracking,
including E911, the majority of
GPS receivers are built into mobile
telephones, with varying degrees
of coverage and user accessibility.
Commercial navigation software is
available for most 21st
century Smartphone as well as
some Java-enabled phones that
allows them to use an internal or
external GPS receiver.
26. Parallel Systems
Not only GPS shares
MEO at 20,200km,
the two other
Navigation systems
are also running
parallel to GPS.
1. Glonass -19,100
km.
2. Galileo – 23,22 km.
27. Parallel Systems
Galileo: is a satellite
navigation system
currently being built by
the European
Union (EU)
and European Space
Agency (ESA). This
project is named after
the famous Italian
astronomer Galileo
Galilei.
28. Parallel Systems
GLONASS: Global GLONASS logo :
Navigation Satellite
System, is a radio-
based satellite
navigation
system operated for
the Russian governmen
t by the Russian Space
Forces.
29. Message format
• Each GPS satellite continuously broadcasts a navigation
message at a rate of 50 b/s. Each complete message is composed
of 30-second frames, distinct groupings of 1,500 bits of
information. Each frame is further subdivided into 5 sub-frames of
length 6 seconds and with 300 bits each. Each sub-frame contains
10 words of 30 bits with length 0.6 seconds each. Each 30 second
frame begins precisely on the minute or half minute as indicated
by the atomic clock on each satellite.
• The first part of the message encodes the week number and the
time within the week, as well as the data about the health of the
satellite. The second part of the message, the ephemeris, provides
the precise orbit for the satellite. The last part of the message,
the almanac, contains coarse orbit and status information for all
satellites in the network as well as data related to error
correction.
30. Random Code
The Pseudo Random Code is a fundamental
part of GPS. Physically it's just a very
complicated digital code, or in other words, a
complicated sequence of "on" and "off"
pulses
31. Atomic Clocks
• Most Accurate
• The principle of operation of an atomic clock
is not based on atomic physics and using
the microwave signal that electrons in atoms
emit when they change energy levels.
• Example is NIST-F1
32. Satellite Orbits
• LEO – Low earth Orbit, the commonly
accepted definition for LEO is between 160 –
2,000 km.
• MEO – Medium Earth Orbit , lies between
altitude of 2,00km to 35,786 km.
• GEO - Geostationary Earth Orbit, from
35,786 km to 265,000 km (Clarke Orbit).
