Latest Advances in GPS technology Seminar report

Latest Advances in GPS Technology

Department of ECE, MRITS. 1

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

distance 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 signa l)

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



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



satellite transmits low radio signals with a unique code on different frequenc ies,

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



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.



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.



3) Potential decommissioning and reduction of expensive ground based navigat ion

facilities, systems, and services.

4) Increased safety for surface movement operations made possible by situationa l

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 traditiona l

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



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.



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 triangula t ion

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.



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'.



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! On the 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



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.



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 naviga t ion

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.



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.



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 monitor ing

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.



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 communicat ions

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,



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. Simila r ly,

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.



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 recreationa l

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 conventiona l

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.



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



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



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 moderniza t ion

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.



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 analys is

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 inertia l

navigation systems/sensors, implementation of the WAAS system, the combination of

GPS with GLONASS, the development of the Galileo system, and the moderniza t ion

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 communicat ions

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).



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



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 naviga t ion

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.



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