gps seminar final

7/31/2019 GPS Seminar Final

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Visvesvaraya Technological University

Belgaum

seminar report

on

GLOBAL POSITIONING SYSTEM

Submitted in the partial fulfillment of requirements for the award of

BACHELOR OF ENGINEERING IN

ELECTRONCIS AND COMMUNICATION

Submitted by

ASHISH S KANNAVAR

(1DA08EC010)

Dr.Ambedkar Institute of technology,

Bangalore-56

Department of electronics and communication Engineering

2011-12


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Dr.Ambedkar Institute of technology,

Bangalore-56

Department of electronics and communication Engineering

CERTIFICATE

Certified that the seminar report entitled GLOBAL POSITIONING SYSTEM is submitted by

ASHISH S KANNAVAR having the USN 1DA08EC010 in partial fulfillment for the award of

the degree of Bachelor Engineering in Electronics and Communication of the Visvesvaraya

Technological University, Belgaum, during the year 2011-12

The Seminar report has been approved as it satisfies the academic requirements in respect of the

seminar on current topics prescribed for Bachelor of Engineering degree

Signature of examiner Signature of HOD

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Acknowledgement

The satisfaction that accompanies the successful completion of the seminar would be

complete only with the mention of the people who made it possible, whose support rewarded our

effort with success.

I am grateful to Dr. Ambedkar Institute of Technology for its ideals and its inspirations for

having provided me with the facilities that have made this seminar a success.

I express my sincere thanks to our Principal Dr. K. L. Savithramma, Head of the

Department of Electronics and Communication Engineering Dr. G V Jayaramaiah, Seminar

Co-ordinates Mrs. G S Pushpalatha, Mr. Shivaputra, examiners Mrs. Girija.S and Mrs.

B.S.SUDHA and teaching and non-teaching staff of Electronics and Communication Engineering

Department, Dr. Ambedkar Institute of Technology, whose support and guidance were invaluable.

Finally I would like to thank my parents and friends for all support they provided during

the development of this seminar.


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Global Positioning System

CONTENTS

GLOBAL POSITIONING SYSTEM

P. Nos.

1.1 INTRODUCTION 04

1.2 WHAT IS GPS? 04

1.3 PRINCIPLES OF GPS 05

1.4TYPES OF POSITIONING 06

1.5 INFORMATION IN A GPS SIGNAL 07

1.6 How GPS WORKS? 07

1.7 GPS ELEMENTS 08

1.8 GPS SERVICES 13

1.9 GLOBAL POSITIONING 14

2.0 GPSACCURACY 17

2.1 ERRORS IN GPS 17

2.2 GPS APPLICATIONS 19

2.3 COST OF THE SYSTEM 21

2.4 CONCLUSION22

References

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1.1 INTRODUCTION:

Have u ever been lost and wished there was an easy way to find outwhich way u needed to go? How about finding yourself out hiking and then notknowing how to get back to your camp or car?

Ever been flying and wanted to know the nearest airport?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. GPS is a satellite based radio navigationsystem which provides continuous, all weather, worldwide navigation capability forsea, land and air applications. So things are much, much easier today. For less than$100, you can get a pocket sized gadget that will tell you exactly where you are onEarth at any moment. As long as you have a GPS receiver and a clear view of thesky, you'll never be lost again. Navigation in three dimensions is the primaryfunction of GPS. Navigation receivers are made for aircraft, ships, ground vehicles,and for hand carrying by individuals. Precise positioning is possible using GPSreceivers at reference locations providing corrections and relative positioning data

for remote receivers. Surveying, geodetic control, and plate tectonic studies areexamples. Time and frequency dissemination, based on the precise clocks on boardthe SVs and controlled by the monitor stations, is another use for GPS.Astronomical observatories, telecommunications facilities, and laboratory standardscan be set to precise time signals or controlled to accurate frequencies by specialpurpose GPS receivers.

1.2 WHAT IS GPS?

The Global Positioning System (GPS) is a satellite-

based navigation system made up of a network of24 satellites placed into orbit by the U.S.Department of Defense that continuouslytransmit coded information, which makes itpossible to precisely identify locations on earth bymeasuring the distance from the satellites. Thesatellites transmit very low power specially codedradio signals that can be processed in a GPSreceiver, enabling the receiver to computeposition, velocity and time thus allowing anyoneone with a GPS receiver to determine theirlocation on earth. Four GPS satellite signals are used to compute positions in three

dimensions and the time offset in the receiver clock. The system was designed sothat receivers did not require atomic clocks, and so could be made small andinexpensively. The gps system consists of three pieces. There are the satellites thattransmit the position information, there are the ground stations that are used tocontrol the satellites and update the information, and finally there is the receiverthat you purchased. It is the receiver that collects data from the satellites andcomputes its location anywhere in the world based on information it gets from the

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satellites. There is a popular misconception that a gps receiver somehow sendsinformation to the satellites but this is not true, it only receives data.

1.3 PRINCIPLE OF GPS:

The principle behind GPS is the measurement of distance (or "range")between the receiver and the satellites. The satellites also tell us exactly wherethey are in their orbits above the Earth. It works something like this-If we know ourexact distance from a satellite in space, we know we are somewhere on the surfaceof an imaginary sphere with radius equal to the distance to the satellite radius. Bymeasuring its distance from a second satellite, the receiver knows it is alsosomewhere on the surface of a second sphere with radius equal to its distance fromthe second satellite. Therefore, the receiver must be somewhere along a circlewhich is formed from the intersection of the two spheres. Measurement from a thirdsatellite introduces a third sphere. Now there are only two points which areconsistent with being at the intersection of all three spheres. One of these is usuallyimpossible, and the GPS receivers have mathematical methods of eliminating the

impossible location. Measurement from a fourth satellite now resolves theambiguity as to which of the two points is the location of the receiver. The fourthsatellite point also helps eliminate certain errors in the measured distance due touncertainties in the GPS receiver's timing as well.

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Global PositioningSystem

1.4 TYPES OF POSITIONING:

There are basically two types of GPS positioning

Single Point Positioning Relative Point Positioning

Single Point Positioning is also known as autonomous or absolutepositioning. In this type, the position of an unknown point is determined based onknown positions of GPS satellites in space. In Relative Positioning, the position ofunknown point is determined with respect to another known point (base orreference station). The term Differential Positioning (DGPS) is often used

interchangeably with Relative Positioning. Infact DGPS is a specific type of relativepositioning.

Again in GPS positioning there are two types

Static Kinematic

In Kinematic differential positioning one receiver is at known station referred toas base/reference (stationery) while second receiver referred to as rover is movedover path to be positioned.

Accurate positions in DGPS can be accomplished through two methods

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Real time processing Post processing

Real time processing requires a data link to transmit corrections from a basereceiver to a rover receiver. Real time processing yields low accuracy ascompared to post processing.

In post processing, observed data from all the receivers is processed usingspecial software.Thus all GPS positioning can be classified as static or kinematic, single point orrelative, real time or post processing.

1.5 INFORMATION IN A GPS SIGNAL :

The GPS signal contains ephemeris and almanac data:

Ephemeris data is constantly transmitted by each satellite and contains importantinformation such as status of the satellite (healthy or unhealthy), current date,and time. Without this part of the message, your GPS receiver would have no

idea what the current time and date are. This part of the signal is essential todetermining a position, as well see in a moment.

The almanac data tells the GPS receiver where each GPS satelliteshould be at any time throughout the day. Each satellite transmits almanac datashowing the orbital information for that satellite and for every other satellite in thesystem.

1.6 HOW GPS WORKS?

The satellites transmit very lowpower signals (20- 50 watts) allowing

anyone with a GPS receiver todetermine their location on earth. GPSreceivers passively receive satellitesignals; they do not transmit. Thesignals travel line of sight, meaning itwill pass through clouds, smoke, glassand plastic but not through solid objectslike buildings and mountains. So GPSreceivers require an unobstructed viewof the sky, they are used only outdoorsand they often do not perform wellwithin forested areas or near tall

buildings. GPS operations depend on avery accurate time reference, which isprovided by atomic clocks at the U.S.Naval Observatory. Each GPS satellitehas atomic clocks on board. Eachsatellite transmits a message whichessentially says, "I'm satellite #X, myposition is currently Y, and this message was sent at time Z."

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All GPS satellites synchronize operations so that theserepeating signals are transmitted at the same instant.The signals, moving at the speed of light, arrive at a GPSreceiver at slightly different times because some satellitesare farther away than others. Your GPS receiver readsthe message andsaves the ephemeris and almanac datafor continual use. The distance to the GPS satellites canbe determined by estimating the amount of time it takesfor their signals to reach the receiver. When the satelliteis generating the pseudo random code, the receiver isgenerating the same code and tries to match it up with the satellites code. Thereceiver then compares the two codes to determine how much it needs to delay (or

shift) its code to match the satellites code. This givesthe travel time. To determine your position the GPS receiver compares the time asignal was transmitted by a satellite with the time it was received by the GPS

receiver. The time difference tells the GPS receiver how far away that particularsatellite is (Range=travel time*velocity of light). Now that we have both satellite

location and distance, the receiver can determine a position. If we add distancemeasurements from a few more satellites, we can triangulate our position. This isexactly what a GPS receiver does. Lets say we are 11000 miles from one satellite,our location is some where on an imaginary sphere that has the satellite at thecenter with radius 11000 miles. Then lets say we are 12000 miles from anothersatellite; the second sphere would intersect the first sphere to create a commoncircle. If we add a third satellite, at a distance of 13000 miles, we now have twocommon points where the three spheres intersect. With a minimum of three ormore satellites, your GPS receiver can determine a latitude/longitude position -what's called a 2D position fix. With four or more satellites, a GPS receiver candetermine a 3D position, which includes latitude, longitude, and altitude. With thiscalculated position the exact location of the receiver can be pinpointed on adigitized map with the use of the proper GIS software tools. By continuouslyupdating your position, a GPS receiver can also accurately provide speed anddirection of travel (referred to as 'ground speed' and 'ground track'). The satellites,operated by the U.S. Air Force, orbit with a period of 12 hours. Ground stations areused to precisely track each satellite's orbit.

1.7 GPS ELEMENTS :

GPS elements: Space Segment Control Segment

User Segment

Space Segment:

The GPS technology is based on the NAVSTAR (NAVigation Satellite TimingAnd Ranging) constellation composed of 24 satellites in space, the space segmentof the GPS system. There are often more than 24 operational satellites as new ones

are launched to replace older satellites. The satellite orbits repeat almost the sameground track (as the earth turns beneath them) once each day. These 24 satellites

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BMSCE E&CE 2010-11


(21 navigational satellites and 3 active spares) are in 6 circular orbits (withnominally four SVs in each), equally spaced (60 degrees apart), at an inclinationangle of 55 degrees.

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These satellites weigh 1900 lbs in orbit, travel at speedsof about 14,000 kilometres

per hour or 8700 miles per hour with a 12hr period(precisely 11hr 58 min). It is at roughly 25,000kilometers from the earth's centre or 20,000 kms

above the earth's surface. The satellites are highenough to bypass the problems encounteredby land-based systems they send wireless radio signalsfrom space.

Their configuration providesthe user with between 5 and

8 space vehicles

anywhere on the earth.The spacing of satellites inorbit is arranged so thatundernormal conditions aminimum of five satelliteswill be in view to usersworldwide, with a positiondilution of precision (PDOP)of six or less. In practicethere are usually many

more than this, sometimesas many as 12.The satellites are generallyallowed to "float" in their

orbits and aren't rigidlyheld in position. The orbitalpaths of these satellites

take them between roughly 60 degrees North and 60 degrees South latitudes. Whatthis means is you can receive satellite signals anywhere in the world, at any time.As you move closer to the poles, you will still pick up the GPS satellites. TheNAVSTAR satellites can see from the northernmost and southern most parts of theirorbits. These satellites provide 24-hour-a-day coverage for both two-and three-

dimensional positioning anywhere on Earth. They also continuously broadcastposition and time throughout the world. Currently there are 27 total satellites in thesky and it is possible that there could be as many as 31 or 32. Each satellitecontains a supply of fuel and small servo engines so that it can be moved in orbit tocorrect for positioning errors. With update control from the ground units it canmaintain an essentially circular orbit around the earth. It also contains a receiver toget update information, a transmitter to send information to the gps receiver, anantenna array to magnify the weak transmitter signal, several atomic clocks to

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to anyone who does not know what the formula used to create it is. Some receiversidentify the satellites that they are listening to by SV, others by

PRN.

Control Segment:

It consists of a system of tracking stations located around the world. Thecontrol segment is composed of all the ground-based facilities that are used tomonitor and control the satellites. This segment is usually unseen by the user, butis a vital part of the system. The NAVSTAR control segment, called the operationalcontrol system (OCS) consists of 5 monitor stations, a master control station (MCS)and 3 uplink antennas. The satellites send down subsets of the orbital ephemerisdata. The monitor stations track GPS satellites in view, collect and send informationfrom the satellites back to the master control station that computes the preciseorbits. The master station uploads the data which is necessary for proper operationof the satellite, like ephemeris and clock data to the satellites. Then the informationis formatted into updated navigation messages that are transmitted through ground

antennas. The MCS is located at Schriever Air Force Base (formerly Falcon AFB) inColorado. and is managed by the U.S. Air Force's 2nd Space Operations Squadron(2nd SOPS). The MCS receives data from the monitor stations in real time 24 hoursa day and uses that information to determine if the satellites are experiencing clockor ephemeris changes, and to detect equipment malfunctions.New navigation and ephemeris information is calculated from the monitored signals

and uploaded to the satellites once or twice per day. There are severalremote monitor stations, which send their information to the master control station.These stations are able to track and monitor each satellite for 21 hours a day,resulting in 2 periods of 1.5 hours when the satellite is on the other side of theearth out of reach for that ground station. These passive monitor stations are

nothing more than GPS receivers that track all satellites in view and thusaccumulate ranging data from the satellite signals. There are five passive monitorstations, located at Colorado Springs, Hawaii, Ascencion Island, Diego Garcia and

Kwajalein. The monitor stations send the raw data back to the MCS for processing.The information calculated by the MCS, along with routine maintenance

commands are transmitted to the satellites by ground-based uplink antennas. Theground antennas are located at Ascencion Island, Diego Garcia and Kwajalein. Theantenna facilities transmit to the satellites via an S-band radio link. In addition toits main function, the MCS maintains a 24 hour computer bulletin board systemwith the latest system news and status. The civilian contact for this is the UnitedStates Coast Guards (USCG) Navigation Center (NAVCEN).

User segment :

The user segment is composed of GPS receivers composed ofprocessors and antennas that allow for sea, land and airborneoperators to receive the broadcast. The receivers convert spacevehicle signals into position, velocity and time. A total of 4satellites are required to compute these calculations. In order to


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make this simple calculation, then, the GPS receiver has to know two things:The location of at least three satellites above youThe distance between you and each of those satellites.The GPS receiver figures both of these things out by analyzing high-frequency, low-power radio signals from the GPS satellites. Better units have multiple receivers, so

they can pick up signals from several satellites simultaneously. Most modernreceivers are parallel multi-channel design. Parallel receivers typically have five totwelve receiver circuits, each devoted to one particular satellite at all times. Parallel

channels are quick to lock onto satellites when first turned on and they are able toreceive the satellite signals even in difficult conditions such as dense foliage orurban settings. If you want to have continuous real-time position measurements,then the receiver has to have at least four channels. If it does, then it can devoteone channel to each of the four satellites at the same time. Most of the time, thiskind of accuracy is not needed, so some receivers have only one channel. Oldersingle-channel designs were once popular, but were limited in their ability tocontinuously receive signals in the toughest environments. One of the problemswith this type of receiver is that it doesn't always do a good job of monitoring

velocity. Also, if there is any movement of the receiver while it is collecting the fourmeasurements, the accuracy of those measurements will be affected. Acompromise that is used quite often is the three channel receiver. One channel canbe collecting the data from one satellite while the other two channels are locking inon the satellites where the next measurements are going to come from. This typeof receiver doesn't waste time between measurements, because they can instantlyswitch to the next satellite's data. Another benefit to this type of receiver is that itcan track up to eight satellites, so if one satellite is blocked, it can switch to anotherone. Thus, the three channel receiver is more economical than a four channelreceiver, and it is more accurate than a one channel receiver. Position, velocity andtime are needed for marine, terrestrial & aeronautic applications.

A standard GPS receiver will not only place you on a map at anyparticular location, but will also trace your path across a map as you move. If you

leave your receiver on, it can stay in constant communication with GPS satellites tosee how your location is changing. With this information and its built-in clock, thereceiver can give you several pieces of valuable information:

How far you've traveled (odometer)How long you've been travelingYour current speed (speedometer)Your average speed A "bread crumb" trail showing you exactly where you have traveled on the map The estimated time of arrival at your destination if you maintain your current

speed

1.8 GPS SERVICES:

GPS provides two services

SPS-Standard Positioning Service PPS-Precise Positioning Service

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SPS:

The Standard Positioning Service is a positioning and timing service, whichwill be available to all GPS users on a continuous, worldwide basis with no directcharge. SPS will be provided on the GPS L1 frequency, which contains a coarseacquisition (C/A) code and a navigation data message. SPS provides apredictable positioning accuracy of 100 meters horizontally and 156 metersvertically and time transfer accuracy to UTC within 340 nanoseconds. The SPSaccuracy is intentionally degraded by the DOD by the use of SelectiveAvailability.

PPS:

The Precise Positioning Service is a highly accurate military positioning,velocity and timing service which will be available on a continuous, worldwide basisto users authorized by the U.S.P (Y) code capable military user equipment provides

a predictable positioning accuracy of at least 22 meters horizontally and 27.7meters vertically and time transfer accuracy to UTC within 200 nanoseconds. PPSwill be the data transmitted on the GPS L1 and L2 frequencies. PPS was designedprimarily for U.S. military use. It will be denied to unauthorized users by the use ofcryptography. PPS will be made available to U.S. and Allied military and U.S.Federal Government users. Limited, non-Federal Government, civil use of PPS, bothdomestic and foreign, will be considered upon request and authorized on a case-by-case basis.

2.0 GLOBAL POSITIONING:

Geometric View:In order to understand how the GPS satellite

system works, it is very helpful to understand the concept

oftrilateration.Let's look at an example to see how trilateration works.

Let's say that you are somewhere in the UnitedStates and you are TOTALLY lost -you don't have a cluewhere you are. You find a friendly-looking person and ask,"Where am I?" and the person says to you, "You are 625miles from Boise, Idaho." This is a piece of information, butit is not really that useful by itself. You could be anywhereon a circle around Boise that has a radius of 625 miles,

like this: So you ask another person, and he says, "Youare 690 miles away from Minneapolis, Minnesota."

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This is helpful - if you combine this information with the Boise information,you have two circles that intersect. You now know that you are at one of twopoints, but you don't know which one, likethis:If a third person tells you that you are 615miles from Tucson, Arizona, you can

figure out which of the two points you are at:

With three known points, you can see thatyou are near Denver, Colorado!Trilateration is a basic geometric principlethat allows you to find one locationif you know its distance from other, alreadyknown locations. The geometry

behind this is very easy to understand intwo dimensional space.

This same concept works in three dimensional space

as well, but you're dealing with spheres instead ofcircles. You also need 4 spheres instead of three circles to find your exact location.The heart of a GPS receiver is the ability to find the receiver's distance from 4 (ormore) GPS satellites. Once it determines its distance from the four satellites, thereceiver can calculate its exact location and altitude on Earth! If the receiver canonly find three satellites, then it can use an imaginary sphere to represent the earthand can give you location information but no altitude information.For a GPS receiver to find your location, it has to determine two things:

The location of at least three satellites above you The distance between you and each of those satellites

The gps receiver measures the length of time the signal takes to arrive at your

location and then based on knowing that the signal moves at the speed of light itcan compute the distance based on the travel time.

Measuring Distance :

1.Distance to a satellite is determined by measuring how long a radiosignal takes to reach us from that satellite(transit time orTDOA-Time Difference Of Arrival).

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2.To make the measurement we assume that both the satellite and ourreceiver are generating the same pseudo-random codes at exactly thesame time.3.By comparing how late thesatellite's pseudo-random

code appears compared toour receiver's code, wedetermine how long it took

to reach us. This is thetransit time.4.Multiply that travel timeby the speed of light andyou've got distance. Now, armed with the satellite location and the distance fromthe satellite we can expect that we are somewhere on a sphere that is described bythe radius (distance) and centered at the satellite location. By acquiring the sameinformation from a second satellite we can compute a second sphere that cuts thefirst one at a plane. Now we know we are somewhere on the circle that is described

by the intersection of the two spheres. If we acquire the same information from athird satellite we would notice that the new sphere would intersect the circle atonly two points. If we know approximately where we are we can discard one ofthose points and we are left with our exact fix location in 3D space. Now, whatwould happen if we were to acquire the information from a fourth satellite? Weshould expect that it would show us to be at exactly the same point we justcomputed above. But what if it isn't? Before we can answer that question we need alittle more background. A more basic question is, "How does the gps know thetravel time(TDOA) so that it can compute the distance?" The satellite sends thecurrent time along with the message so the gps can subtract its knowledge of thecurrent time from the satellite time in the message (which is the time that the

signal started its descent) and use this to compute the difference. Measuring thetime would be easy if you knew exactly what time the signal left the satellite andexactly what time it arrived at your receiver, and solving this problem is key to theGlobal Positioning System. One way to solve the problem would be to put extremelyaccurate and synchronized clocks in the satellites and the receivers. The satellitebegins transmitting a long digital pattern, called a pseudo-random code, as partof its signal at a certain time, let's say midnight. The receiver begins running thesame digital pattern, also exactly at midnight. When the satellite's signal reachesthe receiver, its transmission of the pattern will lag a bit behind the receiver'splaying of the pattern. The length of the delay is equal to the time of the signal'stravel. The receiver multiplies this time by the speed of light to determine how farthe signal traveled. If the signal traveled in a straight line, this distance would be

the distance to the satellite.The only way to implement a system like this would require a level of

accuracy only found in atomic clocks. This is because the time measured in thesecalculations amounts to nanoseconds. To make a GPS using only synchronizedclocks, you would need to have atomic clocks not only on all the satellites, butalso in the receiver itself. Atomic clocks usually cost somewhere between $50,000

and $100,000, which makes them a little too expensive for everyday consumer use!The Global Positioning System has a very effective solution to this problem - a

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GPS receiver contains no atomic clock at all. It has a normal quartz clock. Thereceiver looks at all the signals it is receiving and uses calculations to find boththe exact time and the exact location simultaneously.

Finding the Satellites:

The other crucial component of GPS calculations is the knowledge of wherethe satellites are. This isn't difficult because the satellites travel in a very high, andpredictable orbits. The satellites are far enough from the Earth (11,000 miles) thatthey are not affected by our atmosphere. The GPS receiver simply stores analmanac that tells it where every satellite should be at any given time. Things likethe pull of the moon and the sun do change the satellites' orbits very slightly, butthe Department of Defense constantly monitors their exact positions and transmitsany adjustments to all GPS receivers as part of the satellites' signals.

2.0. GPS ACCURACY:

The accuracy of a position determined with GPS depends on the type ofreceiver. Most hand-held GPS units have about 10-20 meter accuracy. Other typesof receivers use a method called Differential GPS (DGPS) to obtain much higheraccuracy. DGPS requires an additional receiver fixed at a known location nearby.Observations made by the stationary receiver are used to correct positions recordedby the roving units, producing an accuracy greater than 1 meter. When the systemwas created, timing errors were inserted into GPS transmissions to limit theaccuracy of non-military GPS receivers to about 100 meters. This part of GPSoperations, called Selective Availability, was eliminated in May 2000.

2.1 ERRORS IN GPS:

With simultaneous data received from four satellites, ones position (e.g.latitude, longitude, altitude and time) can be calculated. More the number ofsatellites visible, better the accuracy. Under ideal conditions, the location isprecisely and accurately determined. However, under real conditions, there isalways some degree of error. Despite the opportunity for error, positioning can becalculated to within a few hundred feet or less in most cases.Errors can be caused by:

Selective Availability or SA:

The degradation applied by the US DOD to the satellite signal. The SA

process induces an error; however, using data from more than four satellites canmitigate that error. Nevertheless, the SA-induced error is presently a fact of life ineach position calculation. Fortunately, SA will hamper very precise positioningaccuracy, but not to a point where it undermines the requirements for personalnavigation.

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Ionosphere and troposphere delays:

The GPS assumes that signals will be traveling between satellite andreceiver is in a straight line. The signal will actually be delayed upon goingthrough the

ionosphere and troposphere.

Receiver clock errors:

Since it is not practical to have atomic clocks in the receiver, the receivertiming references will have some small error.

Multi path error :

Multipath error can produce very large deviations. Multipath is caused bysatellite signals that arrive at the receiver after having bounced off some nearbystructure (e.g. a tall building), or the ground. Because the path is not straight, thetime delay will be longer, and the distance from the satellite will also seem to belonger (see figure 2). This can produce location errors that are unacceptable,particularly in urban automobile navigation applications.

Signal attenuation:

Non-restricted GPS signals are transmitted at 1.575 GHz, a microwavefrequency. Such signals are blocked by steel and concrete structures (e.g. buildingsand tunnels), and attenuated by passing through trees and leaves. The GPSspecification for minimum detectable signals renders reception marginal when thesignal is attenuated by foliage. Denser the foliage, more marginal the signal. As such,receivers that just meet this specification are not reliable for use in forests or even

tree-lined streets. To ensure being able to detect signals in a forest, the receivermust provide sensitivity that exceeds the current standard. For example, the receivermust be able to detect signals whose power has been attenuated to a level of about 5percent of the initial level.

Orbital errors:

Also known as ephemeris errors, these are inaccuracies in thesatellitesreported position.

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2.2 GPS APPLICATIONS:

GPS in air:

GPS offers an inexpensive and reliable supplement to existing navigationtechniques for aircraft. Civil aircraft typically fly from one ground beacon, orwaypoint, to another. Pilots on long distance flights without GPS rely onnavigational beacons located across the country. With GPS, an aircraft's computerscan be programmed to fly a direct route to a destination. The savings in fuel andtime can be significant. A GPS-based navigation system will increase the number ofairports that are able to help a well-equipped plane to land in low visibilityconditions. In the near future in the USA it will even be allowed to use GPS as theprimary form of navigation.

GPS on

land:

Everyone who has the proper equipment can use it. The user of the GPSsystem uses the satellite system to locate where he/she is, and with the help of aCD-rom or another large database that contains the GIS-map the car's computer isable to calculate the exact position of the car. Delivery trucks can receive GPSsignals and instantly transmit their position to a central dispatcher. Police and firedepartments can use GPS to dispatch their vehicles efficiently, reducing responsetime. GPS helps motorists find their way by showing their position and intended

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route on dashboard displays. Railroads are using GPS technology to replace older,maintenance-intensive mechanical signals.

GPS in sea:

GPS is a powerful tool that can save a ship's navigator hours of celestialobservation and calculation. GPS has improved efficient routing of vessels andenhanced safety at sea by making it possible to report a precise position torescuers when disaster strikes.

Military Uses for GPS:

With GPS, the soldiers are able to go places and maneuver in sandstormsorat night when even the troops who lived there couldnt. It is used also for troopdeployment, artillery fire etc. GPS has become important for nearly all militaryoperations and weapons systems. It is used on satellites to obtain highly accurateorbit data and to control spacecraft orientation. Picture the desert, with its wide,

featureless expanses of sand. GPS receivers were carried by foot soldiers andattached to vehicles, helicopters, and aircraft instrument panels.

GPS in scientific research

GPS has made scientific field studies throughout the world more accurateand has allowed scientists to perform new types of geographic analyses. Geologistsuse GPS to measure expansion of volcanoes and movement along fault lines.Ecologists can use GPS to map differences in a forest canopy. Biologists can trackanimals using radio collars that transmit GPS data. Geographers use GPS to definespatial relationships between features of the Earth's surface. Scientists use GPS for

a wide range of applications. Scientific analysis that formerly had to be conductedin a laboratory can now be done quicker and easier in the field.

Applications for your business:

By use of GPS an insurance company will be able to track down a stolenvehicle in every situation. A transport company which has GPS installed enables herdrivers to take the shortest route, avoiding traffic jams, to the delivery point usingGPS and GIS, thus offering better and faster service. For a transport company usingboats for transport, GPS can be of excellent use to locate a ship with a specificcargo. The captain of a ship can use GPS to directly locate his ship, and also theuse of a beacon to locate a drowning person is a good option for use of GPS.

Monitor Nuclear Explosions:

Nuclear explosions emit an X-ray flash lasting less than 1 microsecond. Thisflash can be seen by the X-ray flash detectors on several satellites. By measuringthe time delay of arrival of the flash at several satellites, the location of theexplosion can be determined. Several of the GPS satellites carry background Xrayradiation detectors to provide an accurate record of the X-ray environment aroundthe earth.

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Every Day Life:

During construction of the tunnel under the English Channel, British andFrench crews started digging from opposite ends: one from Dover, England, onefrom Calais, France. They relied on GPS receivers outside the tunnel to check theirpositions along the way and to make sure they met exactly in the middle.Otherwise, the tunnel might have been crooked. With GPS we would be able to helpships avoid icebergs by zeroing in on their position and notifying the ship of thelocation and possibly bypass a disaster.

Surveying and map making with GPS:

Surveying that previously required hours or even days using conventionalmethods can be done in minutes with GPS.

GPS for Horticulture:

In orchards, GPS is used mainly for orchard mapping or electrical mapping.The GPS system allows orchardist's to accurately keep records of chemicalapplications, which is extremely important where the government is concerned. Itcan keep track of orchard costs, record and track yields. GPS also allows for thefine-tuning of orchard management techniques for the grower.

Set Your Watch!

Because GPS includes a very accurate time reference, the system is alsowidely used for timekeeping. GPS receivers can display time accurate to within 150Billionths of a second.

2.3 COST OF THE SYSTEM:

This remarkable system was not cheap to build. Development of the $10billion GPS satellite navigation system was begun in the 1970s by the USDepartment of Defense, which continues to manage the system, to providecontinuous, worldwide positioning and navigation data to US military forces aroundthe globe. Ongoing maintenance, including the launch of replacement satellites,adds to the cost of the system. Amazingly ,GPS actually predates the introductionof the personal computer. Its designers may not have foreseen a day when wewould be carrying small portable receivers, weighing less than a pound, at a priceas less as $300, that would not only tell us where we are in position coordinates

(latitude/longitude), but would even display our location on an electronic map alongwith cities, streets and more. A commercial receiver used for navigation purposeswill be able to measure only the coarse pseudo range distances coded on one of thetwo frequencies. Such receivers are available from 1500 FF or 300 USD. On theopposite, dual frequency receivers able to measure both pseudo-range and phasedata on both carrier waves cost up to 150,000 FF or 30,000 USD. There is anintermediate category of receivers which allow relatively precise positioning withoutbeing excessively costly. Those are the single frequency receivers, which measurepseudo-range and phase data on only one of the two wavelength. Acquiring data

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only on the frequency with the higher signal/noise ratio, those receivers are builtwith relatively cheap electronic. There are no subscription fees or set up charges touse GPS. The designers originally had military application in mind. Fortunately, anexecutive decree in the 1980s made GPS available for civilian use also. Noweveryone gets to enjoy the benefits of GPS. The capability is almost unlimited.There are no subscription fees or set up charges to use GPS. (Well, its your taxmoney that paid for it)So we could just break out a GPS receiver, put the batteriesin and dive right into the fun!

2.4 CONCLUSION:

There will probably be a time soon when every car on the road can be equippedwith a GPS receiver, including a video screen installed in the dashboard. The indash

monitor will be a full-color display showing your location and a map of the roadsaround you. It will probably monitor your car's performance and your car phone aswell. Systems as amazing as this one are already being tested on highways in theUnited States.

Using a GPS receiver, one will be able to help ships avoid disaster by zeroing inon the position of the icebergs and notifying ship captains of their

locations, perhaps averting disasterGPS is rapidly changing the way people are finding their way around the earth.

Whether it is for fun, saving lives, getting there faster or whatever use you candream of, GPS navigation is becoming more common everyday. GPS will figure inhistory alongside the development of the sea-going chronometer. This deviceenabled seafarers to plot their course to an accuracy that greatly encouragedmaritime activity, and led to the migration explosion of the nineteenth century. GPSwill affect mankind in the same way. There are myriad applications that will benefitus individually and collectively.

Dr.AIT, ECE, 2012

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Bibl iography

http://www.montana.edu/p laces/gps/und erstd.html

http://tycho.usno.navy.mil/gpsinfo.html#seg

This docume nt prov ides a verba l exp lanat ion o f the

GlobalPosit ioningSys tem by D ianaCooksey

http://tycho.usno.navy.mi l/gpsinfo.h tml#segAn art ic le by US Nava l Obser vatory

http://www.cmt inc.com/gpsbook/ch ap7.h tmlIntroductionto the G loba l Pos i tion ing System

and b its and p ieces from

http://www.gpsinformation.net

http://www.AllGPS.com

http://www.sirf.com

http://www.amazon.com

http://groups.yahoo.com/group/gpsu/

http://garmin.com

http://colorado.edu/geography/gcraft/notes/gps

http://trimble.com

Dr.AIT, ECE, 201223
http://www.montana.edu/places/gps/understd.htmlhttp://www.gpsinformation.net/http://www.allgps.com/http://www.allgps.com/http://tycho.usno.navy.mil/gpsinfo.html#seghttp://www.sirf.com/http://www.amazon.com/http://groups.yahoo.com/group/gpsu/http://groups.yahoo.com/group/gpsu/http://colorado.edu/geography/gcraft/notes/gpshttp://www.gpsinformation.net/http://www.allgps.com/http://tycho.usno.navy.mil/gpsinfo.html#seghttp://www.sirf.com/http://www.amazon.com/http://groups.yahoo.com/group/gpsu/http://colorado.edu/geography/gcraft/notes/gpshttp://www.montana.edu/places/gps/understd.html


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gps seminar final

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