Welcome to the wonderful world of GPS

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Welcome to the wonderful world of GPS
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What you should know by the end of this lecture?

• What is GPS
• Applications of GPS
• How GPS works
• GPS error sources
• The differences between data acquisition using
  GPS and traditional equipment
• Other satellite positioning systems

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One thing which makes GPS so exciting is that its
theory traverses from Pythagoras, Kepler, Newton
to Einstein, the complete spectrum of Physics and
its practice covers communication, computer,
software engineering, semiconductor,
microelectronics design and automation, every
discipline of modern technology.
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What do we use GPS for?

• Military
• Surveying
• Navigation
• Mapping
• Leisure

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Picture the desert, with its wide, featureless
expanses of sand. The terrain looks much the same
for miles. Without a reliable navigation system,
U.S. forces could not have performed the
manoeuvres of Operation Desert Storm. With GPS,
the soldiers were able to go places and manoeuvre
in sandstorms or at night when even the troops
who lived there couldn't. Initially, more than
1,000 portable commercial receivers were
purchased for their use. The demand was so great
that, before the end of the conflict, more than
9,000 commercial receivers were in use in the
Gulf region. They were carried by foot soldiers
and attached to vehicles, helicopters, and
aircraft instrument panels. GPS receivers were
used in several aircraft, including F-16
fighters, KC-135 aerial refuelers, and B-2
bombers Navy ships used them for rendezvous,
minesweeping, and aircraft operations. The
system provides a built-in frame of reference for
all military activities, so units can synchronise
their manoeuvres.
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Mapping and surveying companies use GPS
extensively. During construction of the tunnel
under the English Channel, British and French
crews started digging from opposite ends one
from Dover, England, one from Calais, France.
They relied on GPS receivers outside the tunnel
to check their positions along the way and to
make sure they met exactly in the middle.
Otherwise, the tunnel might have been crooked.
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Vehicle tracking is one of the fastest-growing
GPS applications. GPS-equipped fleet vehicles,
public transportation systems, delivery trucks,
and courier services use receivers to monitor
their locations at all times. GPS is also
helping to save lives. Many police, fire, and
emergency medical service units are using GPS
receivers to determine the police car, fire
truck, or ambulance nearest to an emergency,
enabling the quickest possible response in
life-or-death situations. Automobile
manufacturers are offering moving-map displays
guided by GPS receivers as an option on new
vehicles. American rental car companies offer
GPS-equipped vehicles that give directions to
drivers on display screens and through
synthesised voice instructions.
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In the field of wildlife management, endangered
species such are being fitted with GPS receivers
and tiny transmitters to help determine
population distribution patterns and possible
sources of disease. GPS-equipped balloons are
monitoring holes in the ozone layer over the
polar regions, and air quality is being monitored
using GPS receivers. Buoys tracking major oil
spills transmit data using GPS.
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Archaeologists and explorers are using the
system. Anyone equipped with a GPS receiver can
use it as a reference point to find another
location. With a basic hand-held GPS receiver,
you could be an instant hero if you and friends
got lost on a camping trip.
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The future of GPS is as unlimited as your
imagination. New applications will continue to be
created as the technology evolves. The GPS
satellites, like handmade stars in the sky, will
be guiding you well into the 21st century.
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So how does GPS work?
The Characters Vickie, the hostage The
kidnappers Mr. Sherlock Holmes III, super
detective "Big Ben Stereo radio receiver.
The Place The city of London, England
The Details Let's assume that it's bell rings
every hour, for example, it knocks twelve times
at twelve o'clock and the time interval between
the rings is 4 seconds. Since the sound of the
bell can only reach a very limited distance,
there is also a radio station in England
broadcasts the bell chimes at the same time with
Big Ben at 12 Oclock everyday. So that people
in other parts of England can hear the lovely
and cheerful clock bell chime, using their radio
receivers.
The Story All About GPS Sherlock Holmes' Guide
to the Global Positioning System

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Oh yeah theres more..
Sound travels at the speed of 320 metres per
second in the air radio waves travel at the
speed of light which is 300,000 kilometres per
second, much faster than the speed of sound. This
is why you always see the lightning before you
hear the thunder. Radio waves and visible light
are all travelling at the same speed. The speed
of light is so much faster than the speed of
sound, that you can ignore the propagation time
for the radio wave when compared with the
propagation time of the sound wave.
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The science..
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1. Different duration of the rings. 2. Different
time interval between the rings. The above two
are by means of different code patterns, like
GPS. 3. Different pitch for each Big Ben, like
GLONASS.
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The Space Segment

• 24 satellites
• 12 hour, geosynchronous orbits
• 20,000km
• Block I, Block II, Block IIR
• atomic clocks - key to the systems accuracy
• spread spectrum signal - less subject to
  intentional jamming
• transmit within the L band of the frequency
  spectrum, microwaves
• L1 - 1575.42MHz
• L2 - 1227.60MHz

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The Space Segment

• Dual frequencies eliminate the effect of the
  atmosphere - major source of error
• modulated with 2 pseudo random noise codes
• coarse acquisition code
• precise code
• data message
• satellite identification number PRN codes
• 4-8 satellites can be observed anywhere on the
  Earth above 15o

L1
L2
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The Space Segment

• C/A code allows access to the standard
  positioning service (SPS)
• positioning accuracy of around 100m,
• P code allows access to the precise positioning
  service (PPS)
• positioning accuracy of around 15m
• C/A code gives approximate position, it assists
  with acquisition of the P-code for more precise
  positioning

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The Control Segment

• 5 monitor stations globally
• orbit determination using precise cesium clocks
  and P code receivers
• private monitoring networks also exist5 monitor
  stations globally
• 3 ground control stations collocated with the
  monitor stations
• mainly consist of ground antennas
• communication links to the satellites

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The User Segment

• Military - Department of Defense
• Civilian
• high precision - geodetic surveying
• low precision - leisure activities, hiking,
  yachting

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Biases and Noise

• Code and phase pseudoranges affected by by
  systematic errors, biases and random noise

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Biases and Noise

• Systematic errors can be modelled and solved in
  the observation equations
• differencing between receivers eliminates
  satellite specific errors
• differencing between satellites eliminates
  receiver specific errors
• random noise contains actual observation noise
  plus multipath effects

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Positioning with GPS

• Absolute (lt100m)
• DGPS(lt5m)
• Carrier phase differential(lt50cm)

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Atmospheric Effects

• Ionosphere
• troposphere

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GPS Receivers

• Single frequency (code)
• Absolute
• Code differential
• Single frequency (code/carrier)
• Absolute
• Code differential
• Phase differential over short baseline
• Dual Frequency
• Phase differential over long baselines

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GPS Surveying

• Static
• Stop and go
• kinematic
• kinematic on the fly
• navigation

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GPS

• Large scale surveys - traditional methods
  inefficient
• Three dimensional positioning
• military system developed in the 1970s
• superseded the TRANSIT system- gaps in coverage
  and low navigation accuracy
• all weather, 24hrs