Latest Advances in GPS technology Seminar report

Latest Advances in GPS Technology
Department of ECE, MRITS.
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CHAPTER 1
INTRODUCTION
1.1. Review of GPS
Our ancestors had to go to pretty extreme measures to keep from getting lost.
They erected monumental landmarks, laboriously drafted detailed maps and learned to
read the stars in the night sky.
Things are much, much easier today. The Global Positioning System (GPS) is
a space-based satellite navigation system that provides location and time information
in all weather conditions, anywhere on or near the Earth where there is an unobstructed
line of sight to four or more GPS satellites. The system provides critical capabilities to
military, civil and commercial users around the world. It is maintained by the United
States government and is freely accessible to anyone with a GPS receiver.
When people talk about "a GPS," they usually mean a GPS receiver. The Global
Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24
in operation and three extras in case one fails). The U.S. military developed and
implemented this satellite network as a military navigation system, but soon opened it
up to everybody else.
Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe
at about 12,000 miles (19,300 km), making two complete rotations every day. The
orbits are arranged so that at anytime, anywhere on Earth, there are at least four
satellites "visible" in the sky.
A GPS receiver's job is to locate four or more of these satellites, figure out the
distanc-e to each, and use this information to deduce its own location. This operation is
based on a simple mathematical principle called trilateration.
1.2. Introduction to Satellite Signals
All satellites broadcast at the same two frequencies, 1.57542 GHz (L1 signal)
and 1.2276 GHz (L2 signal). The satellite network uses a CDMA spread-spectrum
technique where the low-bitrate message data is encoded with a high-rate pseudo-
random (PRN) sequence that is different for each satellite. The receiver must be aware
of the PRN codes for each satellite to reconstruct the actual message data. The

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C/A code, for civilian use, transmits data at 1.023 million chips per second, whereas
the P code, for U.S. military use, transmits at 10.23 million chips per second. The actual
internal reference of the satellites is 10.22999999543 MHz to compensate for
relativistic effects that make observers on Earth perceive a different time reference with
respect to the transmitters in orbit.
The L1 carrier is modulated by both the C/A and P codes, while the L2 carrier
is only modulated by the P code. The P code can be encrypted as a so-called P(Y) code
that is only available to military equipment with a proper decryption key. Both the C/A
and P(Y) codes impart the precise time-of-day to the user.
The L3 signal at a frequency of 1.38105 GHz is used to transmit data from the
satellites to ground stations. This data is used by the United States Nuclear Detonation
(NUDET) Detection System (USNDS) to detect, locate, and report nuclear detonations
(NUDETs) in the Earth's atmosphere and near space. One usage is the enforcement of
nuclear test ban treaties.
The L4 band at 1.379913 GHz is being studied for additional ionosphere
correction.
The L5 frequency band at 1.17645 GHz was added in the process of GPS
modernization. This frequency falls into an internationally protected range for
aeronautical navigation, promising little or no interference under all circumstances. The
first Block IIF satellite that would provide this signal is set to be launched in 2009. The
L5 consists of two carrier components that are in phase quadrature with each other.
Each carrier component is bi-phase shift key (BPSK) modulated by a separate bit train.
"L5, the third civil GPS signal, will eventually support safety-of-life applications for
aviation and provide improved availability and accuracy.
1.3. Segments of GPS
There are three segments in GPS, they are
1. The Space segment: The space segment consists of 24 satellites circling the
earth at 12,000 miles in altitude. This high altitude allows the signals to cover a
greater area. The satellites are arranged in their orbits so a GPS receiver on earth
can always receive a signal from at least four satellites at any given time. Each

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satellite transmits low radio signals with a unique code on different frequencies,
allowing the GPS receiver to identify the signals. The main purpose of these
coded signals is to allow for calculating travel time from the satellite to the GPS
receiver. The travel time multiplied by the speed of light equals the distance
from the satellite to the GPS receiver. Since these are low power signals and
won’t travel through solid objects, it is important to have a clear view of the
sky.
Fig 1.1 Segments of GPS
2. The Control segment: The control segment tracks the satellites and then
provides them with corrected orbital and time information. The control segment
consists of four unmanned control stations and one master control station. The
four unmanned stations receive data from the satellites and then send that
information to the master control station where it is corrected and sent back to
the GPS satellites.
3. The User segment: The user segment consists of the users and their GPS
receivers. The number of simultaneous users is limitless.
1.4. Properties of GPS
Navigation enables a user to process his current location based on GPS data
and travel to his desired location, also based on accurate GPS data. Any user with a
working GPS receiver can navigate to a particular destination, whether traveling on

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foot, by automobile, by airplane or by ship. GPS navigation is even accurate
underground.
The standard mode of high accuracy differential positioning requires one
reference GPS receiver to be located at a "base station" whose coordinates are known,
while the second user GPS receiver simultaneously tracks the same satellite signals.
When the carrier phase data from the two receivers is combined and processed, the user
receiver's coordinates are determined relative to the reference receiver. However, the
use of carrier phase data comes at a cost in terms of overall system complexity because
the measurements are ambiguous, requiring the incorporation of an "ambiguity
resolution" (AR) algorithm within the data processing software. Developments in GPS
user receiver hardware have gone a significant way towards improving the performance
of AR.
The distance from the user receiver to the nearest reference receiver may range
from a few kilometres to hundreds of kilometres. As the receiver separation increases,
the problems of accounting for distance-dependent biases grows and, as a consequence,
reliable ambiguity resolution becomes an even greater challenge. On the other hand,
developments in "GPS Geodesy" have been so successful in the last 15 years, that
relative accuracies of "a few parts per billion" are now possible even without AR.
However, for so-called "high productivity" carrier phase-based GPS techniques, AR is
crucial when small amounts of data are used.

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CHAPTER 2
Objectives of GPS
The Global Positioning System (GPS) is a satellite-based navigation system
made up of a network of 24 satellites placed into orbit by the U.S. Department of
Defense. Military actions was the original intent for GPS, however in the 1980s, the
U.S. government decided to allow the GPS program to be used by civilians. Weather
conditions do not affect the ability for GPS to work. The systems works 24/7 anywhere
in the world. There are no subscription fees or setup charges to use GPS.
2.1. Main objectives of GPS devices in military:
1) Military GPS user equipment has been integrated into fighters, bombers, tankers,
helicopters, ships, submarines, tanks, jeeps, and soldiers' equipment.
2) In addition to basic navigation activities, military applications of GPS include
target designation of cruise missiles and precision-guided weapons and close air
support.
3) To prevent GPS interception by the enemy, the government controls GPS receiver
exports
4) GPS satellites also can contain nuclear detonation detectors.
2.2. Main objectives of GPS devices in others:
a. Automobiles are often equipped GPS receivers.
1) They show moving maps and information about your position on the map, speed
you are traveling, buildings, highways, exits etc.
2) Some of the market leaders in this technology are Garmin and Tom Tom, not to
mention the built in GPS navigational systems from automotive manufacturers.
b. For aircraft, GPS provides
1) Continuous, reliable, and accurate positioning information for all phases of flight
on a global basis, freely available to all.
2) Safe, flexible, and fuel-efficient routes for airspace service providers and airspace
users.

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3) Potential decommissioning and reduction of expensive ground based navigation
facilities, systems, and services.
4) Increased safety for surface movement operations made possible by situational
awareness.
c. Agriculture
1) GPS provides precision soil sampling, data collection, and data analysis, enable
localized variation of chemical applications and planting density to suit specific
areas of the field.
2) Ability to work through low visibility field conditions such as rain, dust, fog and
darkness increases productivity
d. Disaster Relief
1) Deliver disaster relief to impacted areas faster, saving lives.
2) Provide position information for mapping of disaster regions where little or no
mapping information is available.
3) Example, using the precise position information provided by GPS, scientists can
study how strain builds up slowly over time in an attempt to characterize and
possibly anticipate earthquakes in the future.
Sports that entail navigation can opt to leave out their compass and other traditional
navigation gadgets and go for the digital and technologically advanced gadgets. Sports
enthusiasts who are constantly on the move, like mountaineers, hikers or even runners,
can sport the GPS sports watch, which works like a small computer.
There is a more specialized GPS system on the market that caters to users who drive
cars. This is called a sat-nav or street navigation GPS system. Not only does this type
of GPS system tell you where your destination is in detailed directions, it can also tell
you your car's mileage, the estimated time of arrival and the speed at which your car is
going. It can also employ a voice system to "speak" to you and tell you the directions.
Technological advancements have given way to the integration of GPS into our
mobile phones, whether in the form of Personal Digital Assistant (PDA) phones or the
standard mobile phone. Most advanced phones have built-in GPS systems with a pre-
loaded map or with an additional card slot to accommodate more memory for
downloaded maps

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CHAPTER 3
GPS Working
3.1. Logical steps of Working
GPS works in six logical steps:
1. The basis of GPS is "triangulation" from satellites.
2. To "triangulate," a GPS receiver measures distance using the travel time of radio
signals.
3. To measure travel time, GPS needs very accurate timing which it achieves with
some tricks.
4. Along with distance, you need to know exactly where the satellites are in space.
High orbits and careful monitoring are the secret.
5. You must correct for any delays the signal experiences as it travels through the
atmosphere.
6. Finally (for us), you can now obtain the precise time from the GPS satellites.
3.2. Triangulation
1. Position is calculated from distance measurements (ranges) to satellites.
2. Mathematically we need four satellite ranges to determine exact position.
3. Three ranges are enough if we reject ridiculous answers or use other tricks.
4. Another range is required for technical reasons to be discussed later.
Triangulation is a process by which the location of a radio transmitter can be
determined by measuring either the radial distance, or the direction, of the received
signal from two or three different points. Triangulation is sometimes used in cellular
communications to pinpoint the geographic position of a user. The drawings below
illustrate the basic principle of triangulation. In the scenario shown by the top drawing,
the distance to the cell phone is determined by measuring the relative time delays in the
signal from the phone set to three different base stations. In the scenario shown by the
bottom drawing, directional antennas at two base stations can be used to pinpoint the
location of the cell phone.

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Fig: 3.1 Triangulation
Triangulation is difficult to carry out unless the person using the cell phone
wants to be located. This might be the case, for example, in an emergency situation.
Triangulation is the method by which the so-called 911 cell phones work.
Triangulation apparatus can be confused by the reflection of signals from
objects such as large steel-frame buildings, water towers, communications towers, and
other obstructions. For this reason, at least two independent triangulation
determinations should be made to confirm the position of a cell phone or other radio
transmitter.
3.3. Measuring Distance
1. Distance to a satellite is determined by measuring how long a radio signal takes to
reach us from that satellite.
2. To make the measurement we assume that both the satellite and our receiver are
generating the same pseudo-random codes at exactly the same time.
3. By comparing how late the satellite's pseudo-random code appears compared to our
receiver's code, we determine how long it took to reach us.
4. Multiply that travel time by the speed of light and you've got distance.

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Discussion we saw in the last section that a position is calculated from distance
measurements to at least three satellites.
But how can you measure the distance to something that's floating around in
space? We do it by timing how long it takes for a signal sent from the satellite to arrive
at our receiver.
3.3.1. The Math
In a sense, the whole thing boils down to those "velocity times travel time" math
problems we did in high school. Remember the old: "If a car goes 60 miles per hour for
two hours, how far does it travel?"
Velocity (60 mph) x Time (2 hours) = Distance (120 miles)
In the case of GPS we're measuring a radio signal so the velocity is going to be
the speed of light or roughly 186,000 miles per second. The problem is measuring the
travel time .The timing problem is tricky. First, the times are going to be awfully short.
If a satellite were right overhead the travel time would be something like 0.06 seconds.
So we're going to need some really precise clocks. We'll talk about those soon. But
assuming we have precise clocks, how do we measure travel time? To explain it let's
use a goofy analogy:
Suppose there was a way to get both the satellite and the receiver to start playing
"Stairway to Heaven" at precisely 12 noon. If sound could reach us from space then
standing at the receiver we'd hear two versions of the 'Stairway to Heaven', one from
our receiver and one from the satellite. These two versions would be out of sync. The
version coming from the satellite would be a little delayed because it had to travel more
than 11,000 miles.
If we wanted to see just how delayed the satellite's version was, we could start
delaying the receiver's version until they fell into perfect sync. The amount we have to
shift back the receiver's version is equal to the travel time of the satellite's version. So
we just multiply that time times the speed of light and voila! We’ve got our distance to
the satellite.
That's basically how GPS works. Only instead of 'Stairway to Heaven' the
satellites and receivers use something called a "Pseudo Random Code" - which is
probably quicker to sing than 'Stairway to Heaven'.

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3.4. Random Code
The Pseudo Random Code (PRC) 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.
The signal is so complicated that it almost looks like random electrical noise.
Hence the name "Pseudo-Random." There are several good reasons for that complexity:
First, the complex pattern helps make sure that the receiver doesn't accidentally sync
up to some other signal. The patterns are so complex that it's highly unlikely that a stray
signal will have exactly the same shape.
Since each satellite has its own unique Pseudo-Random Code this complexity
also guarantees that the receiver won't accidentally pick up another satellite's signal. So
all the satellites can use the same frequency without jamming each other. And it makes
it more difficult for a hostile force to jam the system. In fact the Pseudo Random Code
gives the Department of Defense a way to control access to the system.
But there's another reason for the complexity of the Pseudo Random Code, a
reason that's crucial to making GPS economical. The codes make it possible to use
"information theory" to "amplify" the GPS signal. And that's why GPS receivers don't
need big satellite dishes to receive the GPS signals.
We glossed over one point in our silly 'Stairway to Heaven' analogy. It assumes
that we can guarantee that both the satellite and the receiver start generating their codes
at exactly the same time. But how do we make sure everybody is perfectly synced? Stay
tuned and see.
3.5. Timing
Achieving Perfect Timing
1. Accurate timing is the key to measuring distance to satellites.
2. Satellites are accurate because they have atomic clocks on board.
3. Receiver clocks don't have to be too accurate because an extra satellite range
measurement can remove errors
Discussion: If measuring the travel time of a radio signal is the key to GPS, then
our stop watches had better be darn good, because if their timing is off by just a
thousandth of a second, at the speed of light, that translates into almost 200 miles of
error! Onthe satellite side, timing is almost perfect because they have incredibly precise
atomic clocks on board. But what about our receivers here on the ground? Remember

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that both the satellite and the receiver need to be able to precisely synchronize their
pseudo-random codes to make the system work. (to review this point click here) If our
receivers needed atomic clocks (which cost upwards of $50K to $100K) GPS would be
a lame duck technology.
Nobody could afford it. Luckily the designers of GPS came up with a brilliant
little trick that lets us get by with much less accurate clocks in our receivers. This trick
is one of the key elements of GPS and as an added side benefit it means that every GPS
receiver is essentially an atomic-accuracy clock.
The secret to perfect timing is to make an extra satellite measurement. That's
right, if three perfect measurements can locate a point in 3-dimensional space, then four
imperfect measurements can do the same thing. Extra Measurement Cures Timing
Offset If our receiver's clocks were perfect, then all our satellite ranges would intersect
at a single point (which is our position). But with imperfect clocks, a fourth
measurement, done as a cross-check, will NOT intersect with the first three. So the
receiver's computer says "Uh-oh! There is a discrepancy in my measurements. I must
not be perfectly synced with universal time." Since any offset from universal time will
affect all of our measurements, the receiver looks for a single correction factor that it
can subtract from all its timing measurements that would cause them all to intersect at
a single point.
That correction brings the receiver's clock back into sync with universal time,
and bingo! - You’ve got atomic accuracy time right in the palm of your hand. Once it
has that correction it applies to all the rest of its measurements and now we've got
precise positioning. One consequence of this principle is that any decent GPS receiver
will need to have at least four channels so that it can make the four measurements
simultaneously. With the pseudo-random code as a rock solid timing sync pulse, and
this extra measurement trick to get us perfectly synced to universal time, we have got
everything we need to measure our distance to a satellite in space.
But for the triangulation to work we not only need to know distance, we also
need to know exactly where the satellites are. In the next section we'll see how we
accomplish that.

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3.6. Satellite Tracking
1. To use the satellites as references for range measurements we need to know exactly
where they are.
2. GPS satellites are so high up their orbits are very predictable.
3. Minor variations in their orbits are measured by the Department of Defense.
4. The error information is sent to the satellites, to be transmitted along with the timing
signals.
Discussion: Thus far we've been assuming that we know where the GPS
satellites are so we can use them as reference points. But how do we know exactly
where they are? After all they're floating around 11,000 miles up in space. That 11,000
mile altitude is actually a benefit in this case, because something that high is well clear
of the atmosphere. And that means it will orbit according to very simple mathematics.
The Air Force has injected each GPS satellite into a very precise orbit, according to the
GPS master plan.
On the ground all GPS receivers have an almanac programmed into their
computers that tells them where in the sky each satellite is, moment by moment. The
basic orbits are quite exact but just to make things perfect the GPS satellites are
constantly monitored by the Department of Defense.
They use very precise radar to check each satellite's exact altitude, position and
speed. The errors they're checking for are called "ephemeris errors" because they affect
the satellite's orbit or "ephemeris." These errors are caused by gravitational pulls from
the moon and sun and by the pressure of solar radiation on the satellites. The errors are
usually very slight but if you want great accuracy they must be taken into account.
Once the Department of Defense has measured a satellite's exact position, they
relay that information back up to the satellite itself. The satellite then includes this new
corrected position information in the timing signals its broadcasting. So a GPS signal
is more than just pseudo-random code for timing purposes. It also contains a navigation
message with ephemeris information as well. With perfect timing and the satellite's
exact position you'd think we'd be ready to make perfect position calculations. But
there's trouble afoot. You can't manage what you don't measure - use GPS fleet tracking
3.7. Handling Errors
1. The earth's ionosphere and atmosphere cause delays in the GPS signal that translate
into position errors. See a summary of error sources.

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2. Some errors can be factored out using mathematics and modelling.
3. The configuration of the satellites in the sky can magnify other errors.
4. Differential GPS can eliminate almost all error.
Discussion: Up to now we've been treating the calculations that go into GPS
very abstractly, as if the whole thing were happening in a vacuum. But in the real world
there are lots of things that can happen to a GPS signal that will make its life less than
mathematically perfect.
To get the most out of the system, a good GPS receiver needs to take a wide
variety of possible errors into account. Here's what they've got to deal with.
First, one of the basic assumptions we've been using is not exactly true. We've been
saying that you calculate distance to a satellite by multiplying a signal's travel time by
the speed of light. But the speed of light is only constant in a vacuum.
As a GPS signal passes through the charged particles of the ionosphere and then
through the water vapour in the troposphere it gets slowed down a bit, and this creates
the same kind of error as bad clocks. There are a couple of ways to minimize this kind
of error. For one thing we can predict what a typical delay might be on a typical day.
This is called modelling and it helps but, of course, atmospheric conditions are rarely
exactly typical.
Another way to get a handle on these atmosphere-induced errors is to compare
the relative speeds of two different signals. This "dual frequency" measurement is very
sophisticated and is only possible with advanced receivers. Trouble for the GPS signal
doesn't end when it gets down to the ground. The signal may bounce off various local
obstructions before it gets to our receiver.
This is called multi-path error and is similar to the ghosting you might see on a
TV. Good receivers use sophisticated signal rejection techniques to minimize this
problem. Trouble for the GPS signal doesn't end when it gets down to the ground. The
signal may bounce off various local obstructions before it gets to our receiver. This is
called multi-path error and is similar to the ghosting you might see on a TV. Good
receivers use sophisticated signal rejection techniques to minimize this problem.
Satellite Errors Even though the satellites are very sophisticated they do account for
some tiny errors in the system.
The atomic clocks they use are very, very precise but they're not perfect. Minute
discrepancies can occur, and these translate into travel time measurement errors.

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And even though the satellites positions are constantly monitored, they can't be watched
every second. So slight position or "ephemeris" errors can sneak in between monitoring
times. Basic geometry itself can magnify these other errors with a principle called
"Geometric Dilution of Precision" or GDOP. It sounds complicated but the principle is
quite simple.
There are usually more satellites available than a receiver needs to fix a position,
so the receiver picks a few and ignores the rest. If it picks satellites that are close
together in the sky the intersecting circles that define a position will cross at very
shallow angles. That increases the grey area or error margin around a position. If it
picks satellites that are widely separated the circles intersect at almost right angles and
that minimizes the error region. Good receivers determine which satellites will give the
lowest GDOP.

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CHAPTER 4
APPLICATIONS OF GPS
4.1. Current Applications
4.1.1. Tracking Devices
One of the easiest applications to consider is the simple GPS tracking device;
which combines the possibility to locate itself with associated communications
technologies such as radio transmission and telephony.
Tracking is useful because it enables a central tracking centre to monitor the
position of several vehicles or people, in real time, without them needing to relay that
information explicitly. This can include children, criminals, police and emergency
vehicles, military applications, and many others.
The tracing devices themselves come in different flavours. They will always
contain a GPS receiver, and GPS software, along with some way of transmitting the
resulting coordinates. GPS watches, for example, tend to use radio waves to transmit
their location to a tracking center, while GPS phones use existing mobile phone
technology.
The tracking centre can then use that information for co-ordination or alert
services. One application in the field is to allow anxious parents to locate their children
by calling the tracking station - mainly for their peace of mind.
GPS vehicle tracking is also used to locate stolen cars, or provide services to
the driver such as locating the nearest petrol station. Police can also benefit from using
GPS tracing devices to ensure that parolees do not violate curfew, and to locate them if
they do.
4.1.2. Navigation Systems
Once we know our location, we can, of course, find out where we are on a map,
and GPS mapping and navigation is perhaps the most well-known of all the applications
of GPS. Using the GPS coordinates, appropriate software can perform all manner of
tasks, from locating the unit, to finding a route from A to B, or dynamically selecting
the best route in real time.
These systems need to work with map data, which does not form part of the
GPS system, but is one of the associated technologies that we spoke of in the
introduction to this article. The availability of high powered computers in small,

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portable packages has lead to a variety of solutions which combines maps with location
information to enable the user to navigate.
One of the first such applications was the car navigation system, which allows
drivers to receive navigation instructions without taking their eyes off the road, via
voice commands.
4.1.3. Recreation
Outdoor exploration carries with it many intrinsic dangers, one of the most
important of which is the potential for getting lost in unfamiliar or unsafe territory.
Hikers, bicyclists, and outdoor adventurers are increasingly relying on GPS instead of
traditional paper maps, compasses, or landmarks. Paper maps are often outdated, and
compasses and landmarks may not provide the precise location information necessary
to avoid venturing into unfamiliar areas. In addition, darkness and adverse weather
conditions may also contribute to imprecise navigation results.
Man fishing in a stream GPS technology coupled with electronic mapping has
helped to overcome much of the traditional hardships associated with unbounded
exploration. GPS handsets allow users to safely traverse trails with the confidence of
knowing precisely where they are at all times, as well as how to return to their starting
point. One of the benefits is the ability to record and return to waypoints. Similarly,
fishermen typically use GPS signals as a means to continually stay apprised of location,
heading, bearing, speed, distance-to-go, time-to-go, chart plotting functions, and most
importantly, returning to a location where the fish are plentiful.
An advantage in newer GPS receivers is the capability to transfer data to and
from a computer. Outdoor enthusiasts can download waypoints from an exciting
adventure and share them. An example of this is a web site based in Malaysia dedicated
to GPS for mountain biking enthusiasts. Riders post waypoint files marking their
favourite rides allowing other riders to try out the trails.
Golfers use GPS to measure precise distances within the course and improve
their game. Other applications include skiing, as well as recreational aviation and
boating. Man kneeling next to an outdoor geocache and looking at his handheld receiver
GPS technology has generated entirely new sports and outdoor activities. An example
of this is geocaching, a sport which rolls a pleasurable day’s outing and a treasure hunt
into one. Another new sport is geodashing, a cross-country race to a predefined GPS
coordinate.

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GPS modernization efforts, designed to enhance more serious applications than
recreation have provided direct and indirect benefits to the user. Various GPS
augmentation systems that were developed in several countries for commerce and
transportation are also being widely used by outdoor enthusiasts for recreational
purposes. Modernization plans for GPS will result in even greater reliability and
availability for all users, such as under a denser forest cover -- just the environment in
which many adventurers most need this capability.
4.1.4. Surveying and Mapping
The surveying and mapping community was one of the first to take advantage
of GPS because it dramatically increased productivity and resulted in more accurate
and reliable data. Today, GPS is a vital part of surveying and mapping activities around
the world.
When used by skilled professionals, GPS provides surveying and mapping data
of the highest accuracy. GPS-based data collection is much faster than conventional
surveying and mapping techniques, reducing the amount of equipment and labor
required. A single surveyor can now accomplish in one day what once took an entire
team weeks to do.
Municipal workers in hard hats using GPS equipment to record the location of
a fire hydrant GPS supports the accurate mapping and modeling of the physical world
— from mountains and rivers to streets and buildings to utility lines and other resources.
Features measured with GPS can be displayed on maps and in geographic information
systems (GIS) that store, manipulate, and display geographically referenced data.
Fig 4.1 Surveying Fig 4.2 Scanning Sea Bed
Governments, scientific organizations, and commercial operations throughout
the world use GPS and GIS technology to facilitate timely decisions and wise use of
resources. Any organization or agency that requires accurate location information about
its assets can benefit from the efficiency and productivity provided by GPS positioning.

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Unlike conventional techniques, GPS surveying is not bound by constraints such as
line-of-sight visibility between survey stations. The stations can be deployed at greater
distances from each other and can operate anywhere with a good view of the sky, rather
than being confined to remote hilltops as previously required.
Diagram of a hydrographic survey vessel scanning the bottom of a waterway
GPS is especially useful in surveying coasts and waterways, where there are few land-
based reference points. Survey vessels combine GPS positions with sonar depth
soundings to make the nautical charts that alert mariners to changing water depths and
underwater hazards. Bridge builders and offshore oil rigs also depend on GPS for
accurate hydrographic surveys.
4.1.5. Agriculture Applications
The development and implementation of precision agriculture or site-specific
farming has been made possible by combining the Global Positioning System (GPS)
and geographic information systems (GIS). These technologies enable the coupling of
real-time data collection with accurate position information, leading to the efficient
manipulation and analysis of large amounts of geospatial data. GPS-based applications
in precision farming are being used for farm planning, field mapping, soil sampling,
tractor guidance, crop scouting, variable rate applications, and yield mapping. GPS
allows farmers to work during low visibility field conditions such as rain, dust, fog, and
darkness.
In the past, it was difficult for farmers to correlate production techniques and
crop yields with land variability. This limited their ability to develop the most effective
soil/plant treatment strategies that could have enhanced their production. Today, more
precise application of pesticides, herbicides, and fertilizers, and better control of the
dispersion of those chemicals are possible through precision agriculture, thus reducing
expenses, producing a higher yield, and creating a more environmentally friendly farm.
Fig 4.3 Farming Fig 4.4 GPS based Cultivation

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Man operating farm equipment Precision agriculture is now changing the way
farmers and agribusinesses view the land from which they reap their profits. Precision
agriculture is about collecting timely geospatial information on soil-plant-animal
requirements and prescribing and applying site-specific treatments to increase
agricultural production and protect the environment. Where farmers may have once
treated their fields uniformly, they are now seeing benefits from micromanaging their
fields. Precision agriculture is gaining in popularity largely due to the introduction of
high technology tools into the agricultural community that are more accurate, cost
effective, and user friendly. Many of the new innovations rely on the integration of on-
board computers, data collection sensors, and GPS time and position reference systems.
Many believe that the benefits of precision agriculture can only be realized on
large farms with huge capital investments and experience with information
technologies. Such is not the case. There are inexpensive and easy-to-use methods and
techniques that can be developed for use by all farmers. Through the use of GPS, GIS,
and remote sensing, information needed for improving land and water use can be
collected. Farmers can achieve additional benefits by combining better utilization of
fertilizers and other soil amendments, determining the economic threshold for treating
pest and weed infestations, and protecting the natural resources for future use.
4.1.6. Aviation Application
Aviators throughout the world use the Global Positioning System (GPS) to
increase the safety and efficiency of flight. With its accurate, continuous, and global
capabilities, GPS offers seamless satellite navigation services that satisfy many of the
requirements for aviation users. Space-based position and navigation enables three-
dimensional position determination for all phases of flight from departure, en route, and
arrival, to airport surface navigation.
Cockpit view of pilots landing a plane the trend toward an Area Navigation
concept means a greater role for GPS. Area Navigation allows aircraft to fly user-
preferred routes from waypoint to waypoint, where waypoints do not depend on ground
infrastructure. Procedures have been expanded to use GPS and augmented services for
all phases of flight. This has been especially true in areas that lack suitable ground based
navigation aids or surveillance equipment.
New and more efficient air routes made possible by GPS are continuing to
expand. Vast savings in time and money are being realized. In many cases, aircraft
flying over data-sparse areas such as oceans have been able to safely reduce their

20
separation between one another, allowing more aircraft to fly more favourable and
efficient routes, saving time, fuel, and increasing cargo revenue.
Fig 4.5 Cock pit of Plane Fig 4.6 AirPlane Navigation
Improved approaches to airports, which significantly increase operational
benefits and safety, are now being implemented even at remote locations where
traditional ground-based services are unavailable. In some regions of the world, satellite
signals are augmented, or improved for special aviation applications, such as landing
planes during poor visibility conditions. In those cases, even greater precision
operations are possible.
The good news for the aviation community is that GPS is being constantly
improved and modernized. A main component of the ongoing civilian modernization
effort is the addition of two new signals. These signals complement the existing civilian
service. The first of these new signals is for general use in non-safety critical
applications. The second new signal will be internationally protected for aviation
navigational purposes. This additional safety-of-life civilian signal will make GPS an
even more robust navigation service for many aviation applications.

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CHAPTER 5
FUTURE TECHNOLOGY
5.1. Future Uses
The future of GPS is looking bright. Programs like Google Earth are just the
beginning of what can be done with global positioning technology. Militarily, more
accurate and faster GPS systems can give troops and commanders up to date analysis
of friendly and enemy troop movement. With GPS becoming smaller and more
powerful, it can also be used for individual soldiers in the field to triangulate their
position. Commercially, the technology has exploded in the past few years, allowing
anyone and everyone to afford powerful GPS units in their automobiles and homes.That
technology is now making the jump to mobile smart phones.
The future of precise GPS kinematic positioning is dependent on a number of
factors, including developments in receiver hardware, carrier phase data processing
algorithms and software, operational procedures, the Internet and mobile
communications, as well as the augmentation of GPS with pseudolites and inertial
navigation systems/sensors, implementation of the WAAS system, the combination of
GPS with GLONASS, the development of the Galileo system, and the modernization
of GPS to transmit a second and third civilian frequency. All of these will significantly
improve the reliability, integrity, and accuracy of the position results.
The GPS modernization program is an ongoing, multibillion-dollar effort to upgrade
the GPS space and control segments with new features to improve GPS performance.
These features include new civilian and military signals. The U.S. government is well
underway on a $5.5 billion project to roll out GPS III, with the goal of making GPS
more powerful and more accurate than ever.
In addition to the specific new features noted above, GPS modernization is
introducing modern technologies throughout the space and control segments that will
enhance overall performance. For example, legacy computers and communications
systems are being replaced with a network-centric architecture, allowing more frequent
and precise satellite commands that will improve accuracy for everyone.
The GPS modernization program involves a series of consecutive satellite acquisitions,
including GPS IIR(M), GPS IIF, and GPS III. It also involves improvements to the GPS
control segment, including the Architecture Evolution Plan (AEP) and the Next
Generation Operational Control System (OCX).

22
Lockheed Martin announced it had delivered its first test satellite for GPS III.
This satellite isn’t intended to go into space: Instead, it’s a testbed prototype that will
be be run through a broad range of tests, including being subjected to very low-
temperature conditions and radiation to mimic the effects of being in orbit, along with
interference tests. If all goes well, the first launch able GPS III satellite should go into
orbit in May 2014.
The U.S. government started gearing up for GPS III all the way back in 1998,
and authorized funding for the effort in 2000 — that means some benefits and
improvements have begun rolling out already. As originally deployed for civilian use,
the GPS system uses one type of radio signal, called L1 C/A. GPS III will add three
new civilian signals to that mix — L2C, L1C, and L5 — while keeping the L1 C/A
signal operational for a total of four civilian signals.
With GPS tracking systems popping up in cell phones, watches, and shoes,
there's no doubt that GPS tracking devices are making their way into all walks of daily
life. Considering the increased popularity of GPS tracking systems, what can we expect
from the next generation of these tracking devices in
1. Increased Business Use
2. Business Opportunities
3. Advancements in Software
4. Personal Safety

23
CHAPTER 6
CONCLUSION
We finally got acquainted of GPS working and its application.so far these are the points
we have covered and also some points to be summarized
a) Carrier phase-based GPS positioning has evolved rapidly over the last ten years
so that it can now position: (a) kinematically, (b) in real-time, and (c)
instantaneously.
b) There is therefore a blurring of the distinction between precise GPS navigation
and GPS surveying.
c) If certain conditions are fulfilled, carrier phase-based positioning is almost
indistinguishable from pseudo-range-based DGPS, but at a much higher
accuracy.
d) However, there are very real constraints to the universal use of GPS carrier
phase-based positioning.
e) If these constraints are accepted, then the trend to very fast OTF-AR is a
welcome one.
f) Advances in hardware, software and operational procedures has made possible
very fast OTF-AR under restrictive conditions of satellite-receiver geometry
and baseline length.
g) Network-based techniques hold the promise of relaxing one of the critical
constraints to very fast OTF-AR, permitting the maximum baseline length to be
increased to many tens of kilometres.
h) The establishment of continuously-operating GPS reference receiver networks
is an important trend as it will permit the gradual implementation of network-
based techniques, in the post-processed or real-time mode.

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REFERENCES
[1]. http://en.wikipedia.org/wiki/Global_Positioning_System
[2]. http://electronics.howstuffworks.com/gadgets/travel/gps.htm
[3]. http://en.wikipedia.org/wiki/GPS_navigation_device
[4]. http://www.ehow.com/about_5730112_objectives-global-positioning-system.html
[5]. http://www.ehow.com/about_6595713_purpose-gps-system-started.html
[6]. http://www.webmapsolutions.com/future-developments-gps-technology

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