gps report raw

8/8/2019 Gps Report Raw

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GPS-an overview

I v s i t , m a t h u r a

[ T y p e t h e c o m p a n y a d d r e s s ]

[ T y p e t h e p h o n e n u m b e r ]

[ T y p e t h e f a x n u m b e r ]

2 7 n o v 2 0 1 0

Divyanshu gupta


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Executive Summary

There are many current uses for the Global Positioning System (GPS) and many morethat have not yet been thought of or implemented . This report will demonstrate how muchGPS has improved navigation and explain some of its lesser known applications. Acomparison to other navigational systems and a section on how GPS works are included. Theresearch for this report was concentrated in the field of open-pit mining and so thisapplication of GPS will be explained in greater detail than the other areas of applicability.Also explained is how society is being affected by these applications and what futureapplications may be in store.

Introduction

This report is about the Global Positioning System (GPS) and its many applications. Thehistory of navigation and how GPS works are important for understanding this report and soeach has its own section within the report. How it compares to other navigational systems andits uses outside of navigation will be discussed as well. The goal of this report is to explainhow GPS technology is affecting society. This report is intended for anyone who:- uses GPS in their job,- uses GPS for leisure activities,- is curious about the applications, or- is curious about how it works,

Actually, this report is for everyone since GPS affects us all whether we directly use it or not.

Ultimately, this report conveys that GPS is not just a navigational system. A goodanalogy is the clock which was originally used as a navigational tool. Since stars lookdifferent at different times, people who used celestial navigation needed to know what timeof night it was. The market forecasters shortly after the invention of the clock probably couldnot have imagined the impact that timekeeping would have on the world or the other productsand services that this technology would someday make possible. The same situation can befound now with GPS. In fact, it was first intended for military use but is now meetingnumerous civilian needs as well. We can only guess at some of the eventual uses that thisrelatively new technology will bring about.

What is GPS?


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GPS is a satellite-based navigation system originally developed for military purposes and ismaintained and controlled by the United States Department of Defense. GPS permits land,

sea, and airborne users to determine their three-dimensional position, velocity, and time. Itcan be used by anyone with a receiver anywhere on the planet, at any time of day or night, in

any type of weather. This is an amazing capability!

There are two GPS systems: NAVSTAR - United State's system, and GLONASS - theRussian version. The NAVSTAR system is often referred to as the GPS (at least in the U.S.)since it was generally available first. Many GPS receivers can use data from both NAVSTARand GLONASS; this report focuses on the NAVSTAR system.

Segments

GPS uses radio transmissions. The satellites transmit timing information and satellite locationinformation. The system can be separated into three parts:

Space Segment

Control Segment

User Segment

This page includes several figures to help describe the system. The following figureillustrates how the three segments fit together (Figure 1)

Figure 1 - GPS Segments


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Space Segment

The space segment consists of the satellites themselves. According to the United States NavalObservatory, there are currently 27 operational GPS satellites about 11,000 miles up in space.This constellation (see Figure 2 below) provides between five and eight GPS satellites visiblefrom any point on the earth. The next scheduled launch is May 10, 2000.

Figure 2 - The Space Segment

It takes each satellite about twelve hours to orbit the earth. There are six orbital planes with atleast four satellites in each plane.

Control Segment

The control segment is a group of ground stations that monitor and operate the GPS satellites.There are monitoring stations spaced around the globe and one Master Control Stationlocated in Colorado Springs, Colorado (see Figure 3 below). Each station sends informationto the Control Station which then updates and corrects the navigational message of thesatellites. There are actually five major monitoring systems, the figure below does not include

the Hawaiian station.


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Figure 3 - The Control Segment

User Segment

The user requires a GPS receiver in order to receive the transmissions from the satellites. TheGPS receiver calculates the location based on signals from the satellites. The user does nottransmit anything to the satellites and therefore the satellites don't know the user is there. Theonly data the satellites receive is from the Master Control Station in Colorado. The usersconsist of both the military and civilians.

History of Navigation

GPS is primarily a navigational system, so a background on navigation will give insight as tohow extraordinary the Global Positioning System is.

People first navigated only by means oflandmarks - mountains, trees, or leaving trails ofstones. This would only work within a local area and the environment was subject to change

due to environmental factors such as natural disasters.

For traveling across the ocean a process called dead reckoning, which used a magneticcompass and required the calculation of how fast the ship was going, was applied. Themeasurement tools were crude and inaccurate. It was also a very complicated process.

When traveling over the ocean, people began using the stars as guidelines. The stars appeardifferent from different locations on Earth so analyzing the stars gave sailers the basicdirection to follow. Celestial navigation was our primary means of navigation for hundreds of


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years. It was a time-consuming and complicated task of measuring the angles between stars -a process of triangulation. The degree of precision was limited. The sextant was developed

during this time but since it only measured latitude, a timepiece was also invented so that thelongitude could also be calculated. This type of navigation only worked at night and in clear

weather which was a great disadvantage.

It was not until the 20th century thatground-based radio navigation systems were introduced.Some are still in use today. GPS is a satellite radio navigation system, but the first systemswere ground-based. They work in the same way as does GPS: users (receivers) calculate howfar away they are from a transmitting tower whose location is known. When several towersare used, the location can be pinpointed. This method of navigation was a great improvement,yet it had its own difficulties. An example of such a system is LORAN. Each tower had arange of about 500 miles and had accuracy good to about 250 meters. LORAN was not aglobal system and could not be used over the ocean. Because ground based systems sendsignals over the surface of the earth, only two-dimenstional location can be determined. Thealtitude cannot be calculated so this system could not be applied to aviation. The accuracy ofsuch systems could be affected by geography as well. The frequency of the signal affectedaccuracy; a higher frequency would allow for greater accuracy, but the user would need to

remain within the line of sight. The first global navigation system was called OMEGA. It wasa ground-based system but has been terminated as of 1997.

Satellite navigation systems can provide high frequency signals allowing for high accuracy,as well as global access because the satellites are so high up that remaining within the line ofsight of the satellites is easy.

History ofGPS Prior to the development of the GPS system, the first satellite system was called Transit andwas operational begining in 1964. Transit had no timing devices aboard the satellites and thetime it took a receiver to calculate its position was about 15 minutes. Yet, much was learnedfrom this system. GPS is a great improvement over the Transit system. The original use ofGPS was as a military positioning, navigation, and weapons aiming system to replace not

only Transit, but other navigation sytems as well. It has higher accuracy and stable atomicclocks on board to achieve precise time transfer. The first GPS satellite was launched in 1978

and the first products for civilian consumers appeared in the mid 1980's. It was in 1984 thatPresident Reagan announced that a portion of the capabilities of GPS would be made availabeto the civil community. The system is still being improved and new, better satellites are still

being launched to replace older ones.

How does GPS work?


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Mathematical Basis

Each of the GPS satellites transmits radio signals. GPS receivers pick up these signals and

measure the distance to a satellite by multiplying the speed of the signal by the time it takesthe signal to get there. The speed of the signal is the speed of light and the time is encodedwithin the signal. The satellites also send information on their exact location.

In order to find longitude, latitude, and altitude, four satellites are needed. If a measurment istaken using just one satellite, then all that is known is that the receiver is on the surface of asphere with radius equal to the distance to the satellite. If two satellites are used, then thereceiver must be on the surface of both spheres which is the intersection of the two spheres orthe perimeter of a circle. If a third satellite is used, then the location of the user is narroweddown to the two points where the three spheres intersect. Three measurements are enough forland receivers since the lower of the two points would be selected. But when in the air orspace, four satellites are needed: the intersection of all four spheres will be the receiver'slocation. When more than four satellites are used, greater accuracy can be achieved.

Services

There are two types of GPS services. Precise Positioning Service (P-code) is more accurateand reserved for the U.S. military and select government agency users. The other service isthe Standard Positioning Service which is freely available to all users. The SPS code (C/Acode) has errors purposefully encoded into it for U.S. national security reasons and is used for

non-military applications. One source of error is Selective Availability (SA) and isimplenented into the signal in order to keep non U.S. military users from attaining highaccuracy. The errors in the signal are constantly changing. SA affects signals concerning thesatellite's clock and thereby gives false information on how far the satellite is from the userwhich makes the receiver give less accurate values. The following table compares PPS andSPS:

Accuracy in: PPS SPS

horizontal plane 22 meters 100 meters

vertical plane 27.7 meters 156 meters

time transfer 200 nanoseconds 340 nanoseconds

Augmentations


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We have learned how to improve the accuracy that can be attained using the freely availableSPS signals.

A technique called differential GPS allows for greater accuracy of the civilian code by

removing the error. This requires two receivers with one stationary knowing its exact locationand the other probably roaming about. Both receivers calculate their positions and the

stationary receiver takes the difference of the calculated position with that of its knownposition to calculate what the signal error is. Since the satellites are so far away, it can beassumed that both receivers are acquiring the same errors. Once the error is found thereceivers can communicate with each other to find the location of the moving receiver.Differential position accuracies of 1-10 meters are possible with DGPS.

Applications

The applications of the Global Positioning System fall into five categories: location,navigation, timing, mapping, and tracking. Each category contains uses for the military,industry, transportation, recreation and science.

Location

This category is for position determination and is the most obvious use of the GlobalPositioningSystem. GPS is the first system that can give accurate and precise measurements

anytime, anywhere and under any weather conditions. Some examples of applications withinthis category are:

1. Measuring the movement of volcanoes and glaciers.2. Measuring the growth of mountains.3. Measuring the location of icebergs - this is very valuable to ship captains

helping them to avoid possible disasters.4. Storing the location of where you were - most GPS receivers on the market

will allow you to record a certain location. This allows you to find it againwith minimal effort and would prove useful in a hard to navigate place such as

a dense forest.

Navigation

Navigation is the process of getting from one location to another. This was the what theGlobal Positioning System was designed for. The GPS system allows us to navigate on water,


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air, or land. It allows planes to land in the middle of mountains and helps medical evacuationhelicopters save precious time by taking the best route.

Timing

GPS brings precise timing to the us all. Each satellite is equipped with an extremely preciseatomic clock. This is why we can all synchronize our watches so well and make sure

international events are actually happening at the same time.

Mapping

This is used for creating maps by recording a series of locations. The best example issurveying where the DGPS technique is applied but with a twist. Instead of making errorcorrections in real time, both the stationary and moving receivers calculate their positionsusing the satellite signals. When the roving receiver is through making measurements, it thentakes them back to the ground station which has already calculated the errors for eachmoment in time. At this time, the accurate measurements are obtained.

Tracking

The applications in this category are ways of monitoring people and things such as packages.This has been used along with wireless communications to keep track of some criminals. Thesuspect agrees to keep a GPS receiver and transmitting device with him at all times. If hegoes where he's not allowed to, the authorities will be notified. This can also be used to trackanimals.

Many applications use a combination of the above categories. The following is a list of someadditional areas where the global positioning service is being applied:

1. precision farming2. open-pit mining3. oil exploration4. airport and harbor approaches5. animal migration and population studies6. vehicle tracking7. construction - tunnels, golf courses, roads, etc.8. emergency services - the closest ambulance or fire truck is sent to an

emergency, thereby saving time.

9. atmospheric studies - ozone layer, air quality, etc.10.archaeological explorations11.recreational activities - camping, boating, etc.12.astronomical telescope pointing13.networking - speed is increased, the Internet is highly synchronized because of

GPS.14.aiding the blind


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Open-pit Mining

This is an area where very high precision is needed, regular DGPS techniques are not

accurate enough. DGPS improves the accuracy from hundreds of meters down to less than 10meters, but a technique called Real Time Kinematic (GPS) can increase the accuracy to

within several centimeters. This RTK technique involves not only receiving signals fromsatellites but also receives correction information from nearby reference points.

RTK GPS is used in many other areas other than mining, but why does open-pit miningrequire such high accuracy? It can be used for measuring how steep a road should be, savingconstruction time. It can also be used for high accuracy with drills and shovels. The mainreason the high accuracy is needed is used for ore control to make sure the different levels ofore containing dirt go to the right places. Not all mines have the equipment to use RTK GPSyet, but it may become necessary as the minerals become less abundant and better techniquesmust be applied.

Conclusion

The technology of the Global Positioning System is allowing for huge changes in society.The applications using GPS are constantly growing. The cost of the receivers is dropping

while at the same time the accuracy of the system is improving. This affects everyone withthings such as faster Internet speed and safer plane landings.

Even though the system was originally developed for military purposes, civil sales nowexceed military sales (See Figure 1 below).

GPS Update

On May 1, 2000 President Clinton announced that the government will no longer scramblesignals from the GPS satellites. This means that civilians will be able to enjoy the high


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accuracy that the military has had for years. The DGPS techniques and the equipment neededto use them will no longer be necessary to get the same effects on accuracy. The affects on

society will be:more reliable and accurate measurements

less costly to corporations - since the error removing equipment will no longer be neededmore affordable and accessible to consumers

greater incentive for the development of new uses

The accuracy should increase ten-fold, from 100 meter to 10 meter accuracy. The $8 billiondollar a year GPS industry should also see a much larger than expected increase in sales.

Glossary and Acronyms

C/A code -The standard (Course/Acquisition) GPS code.A sequence of 1023 pseudo-random,binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz.Also known asthe "civilian code."

Control segment - A world-wide network of GPS monitor and control stations that ensurethe accuracy of satellite positions and their clocks.

Differential positioning - Accurate measurement of the relative positions of two receiverstracking the same GPS signals.

DGPS- Differential GPS

Ephemeris - The predictions of current satellite position that are transmitted to the user in the

data message. A table given for successive days the positions of heavenly bodies.

GLONASS - GLObalNAvigation Satellite System - Russian

GPS - Global Positioning System

Latitude - the location on the Earth measuring how far north or south of the equator one is.

Longitude - the location on the Earth measured east or west

LORAN - LOngRAnge Navigation

Nautical mile - length measurement used in navigation and is 1/60 of 1 degree of theequator. One nautical mile is 6,080.2 feet whereas one mile is 5,280 feet.

NAVSTARGPS - the Navigation Satellite Timing and Ranging GPS

P-code - The Precise code. A very long sequence of pseudo random binary biphasemodulations on the GPS carrier at a chip rate of 10.23 MHz which repeats about every 267days. Each one week segment of this code is unique to one GPS satellite and is reset eachweek.


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Precise Positioning Service (PPS) - The most accurate dynamic positioning possible withstandard GPS, based on the dual frequency P-code and no SA.

Pseudolite - A ground-based differential GPS receiver which transmits a signal like that of an

actual GPS satellite, and can be used for ranging.

RTK- Real Time Kinematic

Satellite constellation - The arrangement in space of a set of satellites.

Selective Availability (SA) - A policy adopted by the Department of Defense to introducesome intentional clock noise into the GPS satellite signals thereby degrading their accuracyfor civilian users.

Space segment - The part of the whole GPS system that is in space, i.e. the satellites.

Standard Positioning Service (SPS) - The normal civilian positioning accuracy obtained byusing the single frequency C/A code.

User segment - The part of the whole GPS system that includes the receivers of GPS signals.

Works Cited

Kaplan, E. (1996). Understanding GPS - Principles and Applications. Boston: Artech House.

U.S. Naval Observatory (2000).Current GPS Constellation.

http://tycho.usno.navy.mil/gpscurr.html

Trimble Navigation Limited (1998). Putting GPS to Work.http://www.trimble.com/gps/puttinggps/gpsfram1.htm

The Aerospace Corporation (1999). GPS Elements.http://www.aero.org/publications/GPSPRIMER/GPSElements.html

Dommety, G. and Jain, R. (1996).Potential Networking Applications of GPS Technical reportTR-24. http://www.cis.ohio-state.edu/~jain/papers/gps.htm

Dana, P. (1999) Global Positioning System Overview.http://www.colorado.Edu/geography/gcraft/notes/gps/gps_f.html

Critical Technologies Institute (1995). A Policy Direction for the Global PositioningSystem: Balancing National Security and Commercial Interests.


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http://www.rand.org/publications/RB/RB1501/RB1501.html

Holland, S. (2000, May 1). GPS Becomes 10X More Accurate. Reuters Limited.

http://live.altavista.com/scripts/editorial.dll?efi=980&ern=y&ei=1751558

Cover page

Table of Contents

Cover Page

Executive Summary

Introduction

Basic ConceptsWhat is GPS?Segments

HistoryHistory of Navigation - includes descriptions and shortcomingss

of other navigational systemsHistory of GPS

How does it work?Mathematical BasisServices (PPS vs. SPS)

Augmentations

ApplicationsApplication categoriesOpen-pit Mining


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Conclusion

GPS Update (May 2000)

Glossary

Works Cited

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