The document provides information about the Global Positioning System (GPS). It discusses how GPS uses a constellation of 24 satellites with atomic clocks to accurately determine the location of a GPS receiver anywhere on Earth. It explains how GPS measures the distance to multiple satellites to triangulate a user's 2D or 3D position via calculations based on the speed of light and signal travel times. Sources of error and techniques to improve accuracy like differential GPS are also summarized. The document outlines applications of GPS technology and its importance for navigation and other location-based services.

1. GLOBAL POSITIONING SYSTEM
(G.P.S)
TANMAY SHARMA
VGEC (GTU), Ahmedabad

2. Conventional Navigation Systems
Landmarks: Works in local area , subjected to
Environmental factors.
Celestial : Works at night and in good
Weather
Global Positioning System
World Wide Navigation:
Accurate Positioning:
Satellite based System
Visible from whole earth
Atomic Clocks and
Microprocessors are used
Need for GPS

3. GPS-Introduction
Global Positioning System (GPS) is satellite
navigation system which is based on a constellation of
24 satellites orbiting the earth at a very high altitude, that
can be used to continuously measures the position of
the object on the earth’s surface.
GPS was developed by the Department of Defense,
United Sates Of America to simplify accurate navigation.
US government is investing over $12 billion to build the
system which really works.

4. Other Satellite Based Navigation System
 Global Navigation Satellite System GLONASS
Developed by Russia during Cold War initially for Defense.
24 Satellite Constellation placed at 120
.
apart distributed in
3 planes each having 8 Satellites
Accuracy is not effective as GPS
 GALILEO
Developed by European Space Agency ESA, Only for
Civilians
Funded by INDIA nearly 35Crore USD
• GAGAN

5. The Earth Coordinate System : Latitude
Latitude parallel to equator
It gives position from North to South of
equator.
Range is from 0 deg to 90 deg.
Latitude
At Equator 1 deg = 110.88 Kms
1 Min = 1848 mts. = 1.848 Kms.
1 Sec = 30.8 mts

6. The Earth Coordinate System : Longitude
Longitude runs parallel to Prime Meridian
Gives us our position from East to West of
Prime meridian
Range is form 0 deg. To 180 deg.
Longitude
At Equator 1 deg. = 112.09 km
At Pole 1 deg. = 0 km
1 Min = 1868.16 mts = 1.87 Kms.
1 Sec = 31.13 mts

7. The Earth Coordinate System
•Horizontal lines are lines of
equal latitude (parallels)
•Vertical lines are lines of equal
longitude (meridians)
•Both together form the
Graticule network.
LONGITUDE and LATITUDE values are angles measured from the earth’s center
to the required point on the earth’s surface.
A point anywhere within the earth surface is addressed by its LONGITUDE and
LATITUDE value.

8. Satellites Available For GPS Service

9. Satellite Signaling and Orbital Details
• Global Coverage : Minimum 4 Satellites in view from
any place on Earth
• Operational in All Weather Conditions
• Distributed in 6 Orbital Plane each have 4 satellites
• 12 Hours Circular Orbit
• 20,200Kms Height Inclined at 55deg.
• Operates on L band Frequency.
• Messaging is Pseudo Random Code (PRC)

10. The 24 satellites that
make up the GPS space segment
are orbiting the earth about
20,200 km above us. They are
constantly moving, making two
complete orbits in less than 24
hours. These satellites are
travelling at speeds of roughly
7,000 miles an hour.
GPS satellites are
powered by solar energy. They
have backup batteries onboard to
keep them running in the event of
a solar eclipse, when there's no
solar power. Small rocket
boosters on each satellite keep
them flying in the correct path
GPS
satellites

11. A GPS signal contains three different bits of information —
(i) Pseudo random code, (ii) Ephemeris data (iii) Almanac data.
Pseudorandom code is simply an I.D. code that identifies which
satellite is transmitting information. You can view this number on
your GPS unit's satellite page, as it identifies which satellites it's
receiving.
Ephemeris data, which is constantly transmitted by each
satellite, contains important information about the status of the
satellite (healthy or unhealthy), current date and time. This part of
the signal is essential for determining a position.
Almanac data tells the GPS receiver where each GPS satellite
should be at any time throughout the day. Each satellite transmits
almanac data showing the orbital information for that satellite and
for every other satellite in the system.

12. Pseudo Random Code and Frequency
Band Information
L band (Carrier frequency) is spitted in 2 portion L1 and L2.
L1 works at 1575.42 MHz. And L2 works at 1227.60 MHz.
L1 contains PRC and Status Messaging
L1 is used for Civilian Purpose, called Coarse Acquitisation
(C/A Code)
L2 contains PRC
Used for Military Purpose which can be Encrypted by DoD
Whole of L2 information is called Precise Code (P Code)

13. How GPS works ?
This can be summarized by five individual processes:
1. Triangulation from Satellites is the basis of the system
2. To triangulate, GPS measures distance using the travel
time of a radio signal.
3. To measure travel time, GPS needs very accurate clocks.
4. Once you know distance to a satellite, you then need to
know where the satellite is in space.
5. Finally you must correct for any delays the signal
experiences as it travels through the atmosphere.

14. To make life easier
• In a 2D Co-ordinate system we require 2 point to locate our self
•We are 5 unit far from point ‘a’ and 10 unit far from point ‘b’
• Circles from point ‘a’ of radius 5 unit and of 10 unit from ‘b’
would intersect at point P which is desire location.
Let’s Explore now GPS
Positioning
• a
• b
5
10
P
R- plane

15. GPS Measurements
GPS is based on satellite
ranging, measuring distance from
Satellite
Two measurements puts us
somewhere on this circles
Three measurements puts us at one
of two points
Out of which only one is true another is far from
Earth

16. GPS Measurements
Accurate timing is key to measuring distance to satellites.
Satellites are accurate because they have atomic clocks on
board.
Mathematically, we need four measurements to determine
exact position because we are in 3D environment where we
require latitude(x), longitude(y),and height(z)
The GPS system works by timing how long it takes a radio
signal to reach us from a satellite and then calculating the
distance from that, it means :
Distance = (Speed of light) * (Time)

17. How do we know when the signal left the
satellite ?
We assume that both the satellite and our receiver are
generating the same pseudo random code at exactly
the same time
We know how long it took for the satellite’s signal
to get to us by comparing how late its pseudo
random code is, compared to our code

18. Knowing where a satellite is in space
To calculate our position we need precise
distance, for precise distance we need to
know where our satellites are in space
GPS satellites are so high up, their orbits are
very predictable.
Minor variations in orbits measured constantly
by the Department Of Defense and that data is
transmitted from the satellites themselves

19. GPS Receivers
GPS receiver comprises of an Antenna, a
Decoder and a Display unit.
Antenna - receives the electromagnetic
signals.
Decoder – decodes the information from
demodulated signal
Display – displays the filtered information
of position of the object

21. Sources of Errors
•Ionosphere and troposphere delays — The satellite signal slows as it
passes through the atmosphere.
•Signal multipath — This occurs when the GPS signal is reflected off objects
such as tall buildings etc. before it reaches the receiver.
•Receiver clock errors — A receiver's built-in clock is not as accurate as the
atomic clocks onboard the GPS satellites.
•Orbital errors — Also known as ephemeris errors, these are inaccuracies of
the satellite's reported location.
•Number of satellites visible — The more satellites a GPS receiver can "see,"
the better the accuracy.
•Satellite geometry/shading — This refers to the relative position of the
satellites at any given time. Ideal satellite geometry exists when the satellites
are located at wide angles relative to each other.
•Intentional degradation of the satellite signal — Selective Availability (SA)
is an intentional degradation of the signal once imposed by the U.S. Turn off SA
in May 2000, significantly improved the accuracy of civilian GPS receivers.

22. Differential GPS
GPS provides an accurate position for some
applications with the error of more than 10 meters.
Applications demanding
better accuracy of 10
Centimeters e.g. Robot
Movement during a
Disaster,Zero Visibility
Landing etc. requires a
precise positioning
System So…..

23. Differential GPS
DGPS requires co-operation of GPS receivers, one is fixed and
remaining are roving around it. Fixed GPS Receiver is a key and
serves as a Solid Reference to all other roving Receivers
Key idea is : A Reference receiver will measure timing error and
provide a correction to all other roving stations. Reference Station
has a separate RF link to all other Rovers

24. Differential GPS
All the receivers simultaneously
receives Satellite signals but since a
small motion on Earth’s surface is
insignificant from Satellite's view so
both the ROVER and Reference Point
will receive same signal from Satellite.
Reference Station is a accurately
surveyed point and it attacks the GPS
signal reversely i.e. it uses it’s position to
determine the timing. It figures out, “ What
travel time should a signal take to reach it
self and compares it with the actual
acquired timing.

25. Wide Area Augmentation System (WASS)
The Wide Area Augmentation
System (WAAS) is an extremely
accurate navigation system
developed for civil aviation. The
system augments the GPS to
provide the additional accuracy,
integrity, and availability necessary
to enable users to rely on GPS
within the WAAS coverage area.
The worst-case accuracy is within 7.6 meters of the true position 95% of
the time. This is achieved via a network of ground stations which monitor
and measure the GPS signal. Measurements from the reference stations
are routed to two master stations which generate and send the correction
messages to gestationary satellites. Those satellites broadcast the
correction messages back to Earth, where WAAS-enabled GPS receivers
apply the corrections to their computed GPS position.

26.  GPS Receivers may range, both by the level of accuracy
and cost.
 A GPS Receiver may range by an accuracy of the order of
30 Meters to the order of 10 mm.
 By using the Latest technologies like Digital Signal
Processing, the accuracy, cost and size of the receiver
can be optimized at a reasonable level.
GPS Receivers

27. Applications & Future Aspects
Location based Services
• Vehicle Tracking System
• Transport Engineering
Disaster Monitoring System
• Earthquake Monitoring
Surveying
Resource Utilization

28. Thank You