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02-04-2010, 03:02 AM
Post: #1
Rainbow Global positioning system report and ppt
Global Positioning System
Global Positioning System is an System to Identify the Position on Globe through a Network Of Satellites.
The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users. The Space, Control and User are the three segments of this . The User Segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service. The Space Segment is composed of 24 to 32 satellites in Medium Earth Orbit . The Control Segment is composed of a Master Control Station, an Alternate Master Control Station, and a host of dedicated and shared Ground Antennas and Monitor Stations.

Basic concept of GPS:
A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages like, precise orbital information, the time the message was transmitted, system health and rough orbits.

Space segment:
It is is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. It has six planes with four satellites each and the six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension .

Control segment:
There are a)a Master Control Station (MCS),
b)Alternate Master Control Station
c)four dedicated Ground Antennas and
d)six dedicated Monitor Stations.

User segment:
It is is composed of U.S. and allied military users of the secure GPS Precise Positioning Service. civil, commercial and scientific users of the Standard Positioning Service come inder this segment. GPS receivers may include an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of an RS-232 port at 4,800 bit/s speed. Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol

for more etails, visit the page:
http://en.wikipedia.org/wiki/Global_Positioning_System
Visit this link for a report:
http://geology.isu.edu/geostac/Field_Exe...lox_en.pdf

PPT:


Attached File(s)
.ppt  Global Positioning System.ppt (Size: 1.14 MB / Downloads: 810)

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02-04-2010, 03:54 PM
Post: #2
RE: Global positioning system report and ppt
Find where your kids have been! Verify employee driving routes! Review family members driving habits! Watch large shipment routes! Know where anything or anyone has been! All this can be done merely by sitting at your own desk!

Finding your way across the land is an ancient art and science. The stars, the compass, and good memory for landmarks helped you get from here to there. Even advice from someone along the way came into play. But, landmarks change, stars shift position, and compasses are affected by magnets and weather. And if you've ever sought directions from a local, you know it can just add to the confusion. The situation has never been perfect. This has led to the search of new technologies all over the world .The outcome is THE GLOBAL POSITIONING SYSTEM. Focusing the application and usefulness of the GPS over the age-old challenge of finding the routes, this paper describes about the Global Positioning System, starting with the introduction, basic idea and applications of the GPS in real world.

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13-04-2010, 06:39 PM
Post: #3
RE: Global positioning system report and ppt

.ppt  GPS & its applications.ppt (Size: 6.35 MB / Downloads: 1288)

GLOBAL POSITIONING SYSTEM & ITS APPLICATIONS

PRESENTED BY :
KIRAN LAL A
ROLL NO 06238

CONTENTS
INTRODUCTION
HISTORY
ELEMENTS
PRINCIPLE OF OPERATION
MEASURING DISTANCE
SOURCES OF ERROR
APPLICATIONS

INTRODUCTION
GIS

It is a computerized information storage processing and retrieval system that has hardware and software especially designed to cope with geographical referenced spatial data

GIS

Techniques to input geographical information converting the information to digital form
Techniques for sorting information in a compact format on computer disk or digital storage media
Can analyze, make measurements and find optimum sites or routes and a hosts of other tasks
Can predict outcome of various scenarios, can display data in the form of maps, images etc
GPS HISTORY

LAUNCH OF SPUTNIK IN 1957
TRANSIT SYSTEM IN 1960
FIRST SATELLITE IN 1970
F.O.C (Full Operational Capacity) IN JULY 17 1995
$ 12 BILLION
NAVSTAR
DESIGNED BY U.S DoD
PRIMARY USE- MILITARY

GPS ELEMENTS

1. SPACE SEGMENT

2. CONTROL SEGMENT

3. USER SEGMENT

SPACE SEGMENT

24 SATELLITES IN A CONSTELLATION OF 6 ORBITAL PLANES, EACH SATELLITE COMPLETES 1 REVOLUTION IN 12 HOURS
6 ORBITS INCLINED 55 DEGREES FROM THE EQUATOR
4 SATELLITES FOR 3-D POSITIONING
This configuration provides for at least 4 equally spaced satellites within each of the orbital planes

SPACE SEGMENT
CONTROL SEGMENT
MONITOR STATIONS
MASTER CONTROL STATION
Frequency L1=1575.42 MHz C/A code, L2=1227.60 MHz P code

CONTROL SEGMENT
USER SEGMENT

CONSISTS OF GPS RECEIVER,ANTENNA AND PROCESSOR
SPS-STANDARD POSITIONING SERVICE
PPS-PRECISE POSITIONING SERVICE


PRINCIPLE OF OPERATION

TRILATERATION PRINCIPLE
A body cannot occupy 2 positions in space simultaneously

2D TRILATERATION
3D LATERATION

2-D TRILATERATION
3-D TRILATERATION
MEASURING DISTANCE





SATELLITE AND THE RECEIVER GENERATE SAME PSEUDO-RANDOM CODES AT THE SAME TIME

MEASURING HOW LONG THE SIGNAL TAKES TO REACH US

MULTIPLY THE TRAVEL TIME BY THE SPEED OF LIGHT

SOURCES OF ERROR


SOURCES OF ERROR

SIGNAL ARRIVAL TIME MEASUREMENT
CLOCK ERRORS
ATMOSPHERIC EFFECTS
MULTIPATH EFFECT
GEOMETRIC DILUTION OF PRECISION
SELECTIVE AVAILABILITY
APPLICATIONS


LOCATION

NAVIGATION

TRACKING

MAPPING

TIMING

LOCATION
NAVIGATION
TRACKING
MAPPING
TIMING
FIELDS OF APPLICATIONS


MILITARY

CIVILIAN

MILITARY
CIVILIAN
LAND NAVIGATION
AVIATION





ACCURATE POSITION DATA
SHORTEST ROUTES
SURVEYING





REDUCE AMOUNT OF LABOUR & EQUIPMENT

CONCLUSION

Satellite based navigational aid
Guided by 24 satellites round the globe in 6 orbits
3D positioning and time
Type of terrain and weather does not effect positioning
Cheap and precise operating equipment
Inherent error correction mode
A variant of GPS , DGPS has already been introduced

REFERENCES

GIS and Remote Sensing Applications in Environmental Management (Indian Institute of Science, Bangalore)
http://www.en.wikipedia.org
Trimbleâ„¢s online GPS tutorial
http://www.howstuffworks.com

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18-04-2010, 10:51 PM
Post: #4
RE: Global positioning system report and ppt

.ppt  Seminar on GPS.ppt (Size: 603 KB / Downloads: 253)


GLOBAL POSITIONING SYSTEM

Why do we need GPS?
The Global Positioning System (GPS) is a space-based global navigation system.

It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.

On the whole, GPS works efficiently with the help of satellite communication.



Components of the GPS


Space Segment:

The Space Segment is composed of 24 to 32 satellites in Medium earth orbit and also includes the boosters required to launch them into orbit.


Control Segment:

The control segment comprises of 5 stations.
They measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control.
Here the satellite orbit, clock performance and health of the satellite are determined and determines whether repositioning is required.
This information is sent to the three uplink stations


User Segment:

It consists of receivers that decode the signals from the satellites.

The receiver performs following tasks:
Selecting one or more satellites
Acquiring GPS signals
Measuring and tracking
Recovering navigation data
Emergence of GPS:
Before the invention of GPS, the device that is used for tracing is a micro tracing device, which is mainly used for tracing the movement of animals(mainly Birds).This device weighs nearly 1 to10 grams, which is fixed with the body of the animal.
How does the GPS work?

Requirements
Triangulation from satellite
Distance measurement through travel time of radio signals
Very accurate timing required
To measure distance the location of the satellite should also be known
Finally delays have to be corrected
Working process


GPS or Global Positioning System is a technology for locating a person or an object in three dimensional spaces anywhere on the Earth or in the surrounding orbit. GPS is a very important invention of our time on account of the many different possibilities it brings.

To understand the working of GPS we should mainly need to know the satellite communication, which includes three main links namely
~>Uplink
~>Downlink
~>Crosslink

Pictorial representation

Triangulation

Position is calculated from distance measurement
Mathematically we need four satellites but three are sufficient by rejecting the ridiculous answer
Measuring Distance
Distance to a satellite is determined by measuring how long a radio signal takes to reach us from the satellite
Assuming the satellite and receiver clocks are sync. The delay of the code in the receiver multiplied by the speed of light gives us the distance


Applications

Defense purpose
Recovery of theft
Tracing objects
In predicting purpose
In heart failure alert system
Unmanned control service (Artificial Intelligence).

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17-08-2010, 05:49 PM
Post: #5
RE: Global positioning system report and ppt

.ppt  Seminar on GPS.ppt (Size: 896 KB / Downloads: 222)
Why do we need GPS?
Trying to figure out where you are is probable manâ„¢s oldest pastime.

Finally US Dept of Defense decided to form a worldwide positioning system.

Also known as NAVSTAR ( Navigation Satellite Timing and Ranging Global positioning system) provides instantaneous position, velocity and time information.

Components of the GPS
Space segment
control segment
user segment

Space Segment:
24 GPS space vehicles(SVs).
Satellites orbit the earth in 12 hrs.
6 orbital planes inclined at 55 degrees with the equator.
This constellation provides 5 to 8 SVs from any point on the earth.

Control Segment:

The control segment comprises of 5 stations.
They measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control.
Here the satellite orbit, clock performance and health of the satellite are determined and determines whether repositioning is required.
This information is sent to the three uplink stations

User Segment:
It consists of receivers that decode the signals from the satellites.

The receiver performs following tasks:
Selecting one or more satellites
Acquiring GPS signals
Measuring and tracking
Recovering navigation data

User Segment:
There are two services SPS and PPS
The Standard Positioning Service
SPS- is position accuracy based on GPS measurements on single L1 frequency C/A code
C/A ( coarse /acquisition or clear/access) GPs code sequence of 1023 pseudo random bi phase modulation on L1 freq

The Precise Position Service
PPS is the highest level of dynamic positioning based on the dual freq P-code
The P-code is a very long pseudo-random bi phase modulation on the GPS carrier which does not repeat for 267 days
Only authorized users, this consists of SPS signal plus the P code on L1 and L2 and carrier phase measurement on L2

Cross Correlation

Anti- spoofing denies the P code by mixing with a W-code to produce Y code which can be decoded only by user having a key.
What about SPS users?
They use cross correlation which uses the fact that the y code are the same on both frequencies
By correlating the 2 incoming y codes on L1 and L2 the difference in time can be ascertained
This delay is added to L1 and results in the pseudorange which contain the same info as the actual P code on L2

GPS Satellite Signal:
L1 freq. (1575.42 Mhz) carries the SPS code and the navigation message.
L2 freq. (1227.60 Mhz) used to measure ionosphere delays by PPS receivers
3 binary code shift L1 and/or L2 carrier phase
The C/A code
The P code
The Navigation message which is a 50 Hz signal consisting of GPs satellite orbits . Clock correction and other system parameters

How does the GPS work?
Requirements
Triangulation from satellite
Distance measurement through travel time of radio signals
Very accurate timing required
To measure distance the location of the satellite should also be known
Finally delays have to be corrected

Triangulation
Position is calculated from distance measurement
Mathematically we need four satellites but three are sufficient by rejecting the ridiculous answer

Measuring Distance

Distance to a satellite is determined by measuring how long a radio signal takes to reach us from the satellite
Assuming the satellite and receiver clocks are sync. The delay of the code in the receiver multiplied by the speed of light gives us the distance

Getting Perfect timing

If the clocks are perfect sync the satellite range will intersect at a single point.
But if imperfect the four satellite will not intersect at the same point.
The receiver looks for a common correction that will make all the satellite intersect at the same point

Error Sources
95% due to hardware ,environment and atmosphere
Intentional signal degradation
Selective availability
Anti spoofing

Selective Availabity

Two components
Dither :
manipulation of the satellite clock freq

Epsilon:
errors imposed within the ephemeris data sent in the broadcast message

Anti spoofing
Here the P code is made un gettable by converting it into the Y code.
This problem is over come by cross correlation

DGPS
Errors in one position are similar to a local area
High performance GPS receiver at a known location.
Computes errors in the satellite info
Transmit this info in RTCM-SC 104 format to the remote GPS

Requirements for a DGPS
Reference station:
Transmitter
Operates in the 300khz range
DGPS correction receiver
Serial RTCM-SC 104 format
GPS receiver

Data Links
Land Links
MF,LF,UHF/VHF freq used
Radiolocations,local FM, cellular telephones and marine radio beacons
Satellite links
DGPS corrections on the L band of geostaionary satellites
Corrections are determined from a network of reference Base stations which are monitored by control centers like OmniSTAR and skyFix

RTCM-SC 104 format
DGPS operators must follow the RTCM-SC 104 format
64 messages in which 21 are defined
Type 1 contains pseudo ranges and range corrections,issue of data ephemeris (IODE)and user differential range error(URDE)
The IODE allows the mobile station to identify the satellite navigation used by the reference station.
UDRE is the differential error determined by the mobile station

DGPS
DGPS gives accuracy of 3-5 meters,while GPS gives accuracy of around 15-20 mts

Removes the problem associated with SA.


.ppt  Seminar on GPS.ppt (Size: 896 KB / Downloads: 222)

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16-10-2010, 11:58 AM
Post: #6
RE: Global positioning system report and ppt


.ppt  GPS Presentation.ppt (Size: 1.32 MB / Downloads: 160)


Introduction

Global Positioning System (GPS) is a world-wide navigational system that can tell you with pinpoint accuracy your exact current location.

Global Positioning System, commonly known as GPS system, was the 1st satellite navigation system. It was launched in 1978 and is technically known as NAVSTAR GPS (Navigation Satellite with Timing and Ranging Global Positioning System ).

The GPS system was initially developed as a navigation aid for the military, however later it was made available to civilians as well & is now used in everyday life. But to keep the military applications at priority the United States Department of Defence provides two levels of GPS positioning & timing service.
(i) The Precise Positioning Service (PPS)
(ii) The standard Positioning Service (SPS)
19-10-2010, 12:42 PM
Post: #7
RE: Global positioning system report and ppt
Global positioning system report and ppt

INTRODUCTION

Have u ever been lost and wished there was an easy way to find out which way u
needed to go? How about finding yourself out hiking and then not knowing 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 navigation system which provides continuous, all
weather, worldwide navigation capability for sea, land and air applications. So
things are much, much easier today. For less than $100, you can get a pocketsized
gadget that will tell you exactly where you are on Earth at any moment. As
long as you have a GPS receiver and a clear view of the sky, you'll never be lost
again.
Navigation in three dimensions is the primary function of GPS. Navigation
receivers are made for aircraft, ships, ground vehicles, and for hand carrying by
individuals. Precise positioning is possible using GPS receivers at reference
locations providing corrections and relative positioning data for remote
receivers. Surveying, geodetic control, and plate tectonic studies are examples.
Time and frequency dissemination, based on the precise clocks on board the SVs
and controlled by the monitor stations, is another use for GPS. Astronomical
observatories, telecommunications facilities, and laboratory standards can be set
to precise time signals or controlled to accurate frequencies by special purpose
GPS receivers.

for more :-
http://www.forests.tn.nic.in/geomatics/g...ystem.html

http://www.gisdevelopment.net/technology...gp0038.htm
24-12-2010, 04:35 PM
Post: #8
RE: Global positioning system report and ppt


.ppt  gps final presentation.ppt (Size: 1.81 MB / Downloads: 138)

By – Rajkaran Chauhan


WHAT IS GPS
GPS, which stands for Global Positioning System, As the name suggest it is a system to find out your location any where and anytime on the surface or near the earth surface. Developed by the United States Department of Defense, GPS is officially named NAVSTAR-GPS.

At 12,600 miles (20,200 km) altitude. (12 hour orbit period).
30 satellites (24+6) with 6 spare space Vehicles or SVs.
6 orbital planes (55° inclination).
4 satellites in each plane. Monitored by 5 ground control stations.
Manufactured by Rockwell International, later by Lockheed M&S
Satellite weighs ~1900 lbs, 2.2m body, 7m with solar panels.
7-10 year expected lifetime.
GPS satellites use Atomic Clocks for accuracy, but because of the expense, most GPS receivers do not.
It works by using radio frequency broadcast from the orbiting satellite.
Civilian units only receive the L1 frequency.
History and facts
Started development in 1973.First four satellites launched in 1978.
Full Operational Capacity (FOC) reached on July 17, 1995.
In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
3 satellite signals are necessary to locate the receiver in 3D space 4th satellite is used for time accuracy.
GPS receiver uses latitude, longitude, and altitude to calculate its three-dimensional location
The most recent launch was on May 28, 2010.The oldest GPS satellite still in operation was launched on November 26, 1990.
Glonas and Galileo are another positioning system developed by Russia and European union respectively Glonas-24 and Galileo -30




30-12-2010, 12:21 PM
Post: #9
RE: Global positioning system report and ppt



.docx  ajay-Global positioning system.docx (Size: 932.53 KB / Downloads: 119)


Introduction

The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.
GPS is made up of three parts: between 24 and 32 satellites orbiting the Earth, four control and monitoring stations on Earth, and the GPS receivers owned by users. GPS satellites broadcast signals from space that are used by GPS receivers to provide three-dimensional location (latitude, longitude, and altitude) plus the time.
Since it became fully operational on April 27, 1995, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, tracking and surveillance, and hobbies such as geocaching and waymarking. Also, the precise time reference is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular network protocols.
GPS has become a mainstay of transportation systems worldwide, providing navigation for aviation, ground, and maritime operations. Disaster relief and emergency services depend upon GPS for location and timing capabilities in their life-saving missions. Everyday activities such as banking, mobile phone operations, and even the control of power grids, are facilitated by the accurate timing provided by GPS. Farmers, surveyors, geologists and countless others perform their work more efficiently, safely, economically, and accurately using the free and open GPS signals.

History


The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Friedwardt Winter berg proposed a test of General Relativity using accurate atomic clocks placed in orbit in artificial satellites. To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks.
The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS came when the Soviet Union launched the first man-made satellite, Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler Effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.
After Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's prohibited airspace, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. The first satellite was launched in 1989 and the 24th and last satellite was launched in 1994.
Initially the highest quality signal was reserved for military use, and the signal available for civilian use intentionally degraded ("Selective Availability", SA). Selective Availability was ended in 2000, improving the precision of civilian GPS from about 100m to about 20m.

Working of GPS

A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages which include

the time the message was sent
precise orbital information (the ephemeris)
the general system health and rough orbits of all GPS satellites.
The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the satellite’s locations to obtain the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units also show derived information such as direction and speed, calculated from position changes.
Three satellites might seem enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light, the speed at which satellite signals propagate, results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time. The very accurately computed time is effectively hidden by most GPS applications, which use only the location. A few specialized GPS applications do however use the time; these include time transfer, traffic, signal timing, and synchronization of cell phone base stations.
Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. (For example, a ship or plane may have known elevation.) Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible.
21-02-2011, 04:09 PM
Post: #10
RE: Global positioning system report and ppt

.pptx  Global Positioning System (GPS).pptx (Size: 614.96 KB / Downloads: 111)
Global Positioning System (GPS)
What is GPS ?

 world wide radio-navigation system formed from a constellation of 24 satellites.
 provides continuous three-dimensional positioning 24 hours a day.
 GPS provides specially coded satellite signals that can be processed with a GPS receiver.
Three Parts
 Space segment
 Control Segment
 User segment
How Does a GPS Work?
 GPS satellites circle the earth twice a day in the same orbit .
 use triangulation to calculate the user's exact location.
 compares the time a signal was transmitted by a satellite with the time it was received.
How GPS Determines a Location:
 calculating the distances between the receiver and the position of 3 or more satellites.
 Adding additional spheres will further reduce the number of possible locations
Computing the Distance
 measuring the amount of time it takes a radio signal to travel from the satellite to the receiver.
 distance = speed x time
Uses of GPS Technology
 The main purpose of these devices was for mapping locations.
 adjust to different time zones when users travel.
 keep an eye on their children.
 during war to keep track of every soldier's location and movements.
Factors that can degrade the GPS signal
 Signal multipath
 Receiver clock errors
 Number of satellites visible
23-03-2011, 02:46 PM
Post: #11
RE: Global positioning system report and ppt

.docx  What is GPS.docx (Size: 115.37 KB / Downloads: 116)
What is 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. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
How it works
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.
How accurate is GPS?
Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Garmin's 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters on average.
Newer Garmin GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to take advantage of WAAS. Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters. The U.S. Coast Guard operates the most common DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters. In order to get the corrected signal, users must have a differential beacon receiver and beacon antenna in addition to their GPS.
The GPS satellite system
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour.
GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.
Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):
o The first GPS satellite was launched in 1978.
o A full constellation of 24 satellites was achieved in 1994.
o Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
o A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
o Transmitter power is only 50 watts or less.
What's the signal?
GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.
A GPS signal contains three different bits of information - a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS unit's satellite page, as it identifies which satellites it's receiving.
Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.
The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.
Sources of GPS signal errors
Factors that can degrade the GPS signal and thus affect accuracy include the following:
o Ionosphere and troposphere delays - The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
o Signal multipath - This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
o Receiver clock errors - A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
o Orbital errors - Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
o Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
o Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
o Intentional degradation of the satellite signal - Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
28-03-2011, 09:49 AM
Post: #12
RE: Global positioning system report and ppt
Submitted by:
Kali Kedar Nath Behera


.ppt  GPS.ppt (Size: 1.31 MB / Downloads: 135)
GLOBAL POSITIONING SYSTEM
INTRODUCTION

 GPS is a Global Navigation Satellite System(GNSS).
 Uses a constellation of at least 24 satellites orbiting around the earth.
 Transmits precise microwave signals, enabling GPS receivers to determine their location, speed, direction and time.
 First developed by United States Department of Defense- official name is NAVSTAR-GPS.
 GPS satellite navigation system includes
* Russian GLONASS
* European Galileo positioning system.
* Compass navigation system of China.
* IRNSS of India.
 Fig: GPS Navigation
2. TECHNICAL DESCRIPTION
2.1 System Segmentation

GPS consists of three major segments:
 Space Segment(SS)
 Control Segment(CS)
 User Segment(US)
Fig: Segments of Navigation
2.1.1 Space Segment:
• Comprises the orbiting GPS satellites or Space Vehicles(SV) in GPS parlance.
• GPS design originally called for 24 SVs, 8 in each three circular orbital planes. Now modified to 6 planes with 4 satellites each.
• Orbiting at an altitude of approx. 20,200 km, each SV makes two complete orbits.
2.1.2 Control Segment:
 The flight paths of the satellites tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado.
 The tracked information sent to the Air Force Space Commands master control station at Schriever Operation Squadron(2 SOPS) of USAF.
 SOPS contacts each GPS satellites regularly with a navigational updates which are created by a Kalman filter using inputs from the ground monitoring stations, space weather information.
2.1.3 User Segment:
 GPS receiver is the user segment of GPS.
 GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock.
 It include a display for providing location and speed information to the user.
 A receiver is often described by its number of channels: signifies how many satellites it can monitor simultaneously.
2.2 Navigation Signals:
 Each GPS satellites broadcasts a Navigation Message at 50 bits/sec giving the time-of-week, GPS week number and satellite
* health information (all transmitted in the first part of the message).
* ephemeris( transmitted in the second part of the message).
* almanac(later part of the message).
• The messages are sent in frames, each taking 30 sec to transmit 1500 bits. The first 6 sec of every frame contains data describing the satellite clock & its relationship to GPS time.
• The next 12 sec contain the ephemeris data, giving the satellite’s own precise orbit.
• The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model & information to relate GPS derived time to Coordinated Universal Time(UTC).
2.2 Navigation Signals
 Each satellite transmits its navigation message with at least two distinct spread spectrums codes:
* Coarse/Acquisition (C/A) code.
* Precise(P) code.
(C/A) code:
 It is freely available to the public.
 C/A code is 1023 chip pseudo-random number(PRN) code at 1.023 million chips per second so that it repeats every millisecond.
 Each satellite has its own C/A code so that it can be uniquely identified and received separately from other satellites transmitting on the same frequency.
2.2 Navigation Signals:
 Precise(P) code:
 It is encrypted and reserved for military applications.
 It is a 1023 mega chip per second PRN code that repeats only every week.
 P code is encrypted by the Y-code to produce the P(Y) code, which can only by decrypted by units with a valid decryption key.
 Both C/A and P(Y) codes impart the precise time-of-day to the user.
2.3 GPS Frequencies:
2.4 Accuracy and error sources:
2.4.1 Atmospheric Effects:

* The travel time of GPS satellite signals can be altered by atmospheric effects; when a GPS signal passes through the ionosphere and troposphere it is refracted, causing the speed of the signal to be different from the speed of a GPS signal in space. Sunspot activity also causes interference with GPS signals.
2.4.2 Multipath Effects:
* It arises when signals transmitted from the satellites bounce
off a reflective surface before getting to the receiver antenna.
When this happens, the receiver gets the signal in straight
line path as well as delayed path (multiple paths). The effect
is similar to a ghost or double image on a TV set.
2.4.3 Ephemeris and Clock errors:
* Errors in the ephemeris data (the information about satellite orbits) will also cause errors in computed positions, because the satellites weren't really where the GPS receiver "thought" they were (based on the information it received) when it computed the positions.
* Small variations in the atomic clocks (clock drift) on board the satellites can translate to large position errors; a clock error of 1 nanosecond translates to 1 foot or 0.3 meters user error on the ground.
2.4.4 Selective Availability:
 Selective Availability, or SA, occurred when the DoP(Dilution of Precision)
intentionally degraded the accuracy of GPS signals by introducing artificial clock and ephemeris errors.
 When SA was implemented, it was the largest component of GPS error, causing error of up to 100 meters. SA is a component of the Standard Positioning Service (SPS),
which was formally implemented on March 25, 1990, and was intended to protect national defense. SA was turned off on May 1, 2000.
2.4 Accuracy & error sources:
2.4.5 Sagnac Distortion

 GPS observation processing must also compensate for the Sagnac effect. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.
*Potential errors are one of several accuracy-degrading effects outlined in the table below:
2.5 GPS Interference & Jamming:
2.5.1 Natural sources:

 Since GPS signals at terrestrial receivers tend to be relatively weak, it is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible.
 Solar flares are one such naturally occurring emission with the potential to degrade GPS reception, and their impact can affect reception over the half of the Earth facing the sun.
 GPS signals can also be interfered with by naturally occurring geomagnetic storms, predominantly found near the poles of the Earth's magnetic field.
2.5.2 Artificial sources:
 In automotive GPS receivers, metallic features in windshields such as defrosters, or car window tinting films can act as a Faraday cage, degrading reception just inside the car.
 Man-made EMI (electro-magnetic interference) can also disrupt, or jam, GPS signals.
 Stronger signals can interfere with GPS receivers when they are within radio range, or line of sight.
3.Techniques to improve accuracy:
3.1 Augmentation:

 This method of improving accuracy rely on external information being integrated into calculation process.
 Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.
3.2 Precise Monitoring:
• This method uses two approaches:
 Carrier-Phase Enhancement(CPGPS)
 Relative Kinematic Positioning(RKP)
3.Techniques to improve accuracy:
CPGPS:
* This technique resolve the uncertainty that arises in GPS due to pulse transition of PRN is not instantaneous & thus correlation operation is imperfect.
* It utilizes the L1 carrier wave to resolve the uncertainty.
RKP:
*In this approach, determination of range signal can be resolved to a precision of less than 10cm. This is done by resolving the number of cycles in which the signal is transmitted and received the receiver.
3.Techniques to improve accuracy:
3.3 GPS time and date:

* While most clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC.
* To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal.
3.4 GPS modernization:
*This approach aims to improve the accuracy and availability for all users and involves new ground stations, new satellites & four additional navigation signals.
4.Applications:
GPS has significant applications for both military and civilian industry.
Military Applications:
 Navigation
 Target tracking
 Missile and projectile guidance
 Search and rescue
 Map creation
4.Applications:
Civilian:
 GPS receivers act as a surveying tool to determine the absolute location.
 GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere & gravity field.
 The capacity to determine relative movement enables a receiver to calculate local velocity & orientation, useful in vessels or observations of the Earth.
5.Conclusion
 GPS continues to perform as the world’s premier space-based positioning, navigation and timing-service.
 Endeavors such as mapping, aerial refueling, geodetic surveying, search & rescue operations have all benefitted greatly from GPS’s accuracy.
 GPS receivers are incorporated into every type of system used by aircraft, ground vehicles and ships.
30-03-2011, 10:51 AM
Post: #13
RE: Global positioning system report and ppt
Presented by:
Nipun Tripathi


.ppt  PreWork.ppt (Size: 974 KB / Downloads: 73)
Global Positioning System
User Segment

 Military.
 Search and rescue.
 Disaster relief.
 Surveying.
 Marine, aeronautical and terrestrial navigation.
 Remote controlled vehicle and robot guidance.
 Satellite positioning and tracking.
 Shipping.
 Geographic Information Systems (GIS).
 Recreation
Four Primary Functions of GPS
 Position and coordinates.
 The distance and direction between any two waypoints, or a position and a waypoint.
 Travel progress reports.
 Accurate time measurement.
Position Fix
 A position is based on real-time satellite tracking.
 It’s defined by a set of coordinates.
 It has no name.
 A position represents only an approximation of the receiver’s true location.
 A position is not static. It changes constantly as the GPS receiver moves (or wanders due to random errors).
 A receiver must be in 2D or 3D mode (at least 3 or 4 satellites acquired) in order to provide a position fix.
 3D mode dramatically improves position accuracy.
Waypoint
 A waypoint is based on coordinates entered into a GPS receiver’s memory.
 It can be either a saved position fix, or user entered coordinates.
 It can be created for any remote point on earth.
 It must have a receiver designated code or number, or a user supplied name.
 Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.
07-04-2011, 03:07 PM
Post: #14
RE: Global positioning system report and ppt

.ppt  gps-1216310990826489-9.ppt (Size: 282.5 KB / Downloads: 59)
GLOBAL POSITIONING SYSTEM
1. INTRODUCTION

 Trying to figure out where you are and where you're going is probably one of man's oldest pastimes. Navigation and positioning are crucial to so many activities and yet the process has always been quite complicated .
 So the result is the Global Positioning System, a system that's changed navigation forever.
2. WHAT IS GPS ?
 The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their groundstations.There are 5 ground stations: Hawaii, Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs.
3. FACTS ABOUT GPS !
 The first GPS satellite was launched in 1978.
 A full constellation of 24 satellites was achieved in 1994.
 Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
 A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
 Transmitter power is only 50 watts or less.
4. HOW GPS WORKS?
Here's how GPS works in five logical steps:
 The basis of GPS is “triangulation” from satellites.
 To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
 To measure travel time, GPS needs very accurate timing which it achieves with some tricks.
 Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret.
 Finally you must correct for any delays the signal experiences as it travels through the atmosphere .
5.What's the signal?
 GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received.
 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 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, called atomic clocks, equipped in the satellites.
 Now the Distance = Velocity X Time
 So Distance= 1,86,000 X 0.06
 =11,160 miles.
 A GPS signal contains three different bits of information —
1.A pseudorandom code
2.Ephemeris data
3.Almanac data.
ERRORS
 Sometimes errors are occurred while the data are transmitted from the satellites to the GPS receivers.
 Ionosphere and troposphere delays —
 Signal multipath —
 Receiver clock errors —
 Orbital errors —
 Number of satellites visible —
 Satellite geometry/shading —
 Intentional degradation of the satellite signal —
CORRECTING ERRORS
 1. Some errors can be factored out using mathematics and modeling.
 2. The configuration of the satellites in the sky can magnify other errors.
 3. Differential GPS can eliminate almost all error.
12-04-2011, 04:14 PM
Post: #15
RE: Global positioning system report and ppt
PRESENTED BY:
Mr.Prashant Kumar & Mr. Sugat Misra


.doc  GLOBAL POSITIONING SYSTEM.DOC (Size: 82 KB / Downloads: 67)
GLOBAL POSITIONING SYSTEM
ABSTRACT
Global Positioning System (GPS) is the only system today able to show ones own position on the earth any time in any weather, anywhere. This paper addresses this satellite based navigation system at length. The different segments of GPS viz. space segment, control segment, user segment are discussed. In addition, how this amazing system GPS works, is clearly described. The various errors that degrade the performance of GPS are also included. DIFFERENTIAL GPS, which is used to improve the accuracy of measurements, is also studied. The need, working and implementation of DGPS are discussed at length. Finally, the paper ends with advanced application of GPS.
INTRODUCTION:
The Global Positioning System (GPS) is a satellite-based navigation system developed and operated by the US Department of Defense. GPS permits land, sea and airborne users to determine their three-dimensional position, velocity and time. This service is available to military and civilian users around the clock, in all weather, anywhere in the world.
The main principle behind the GPS system is “a transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the "noise" encountered on the way to the ground”.
GPS ELEMENTS:
GPS has 3 parts: the space segment, the user segment, and the control segment. The space segment consists of 24 satellites, each in its own orbit 11,000 nautical miles above the Earth. The user segment consists of receivers, which you can hold in your hand or mount in your car. The control segment consists of ground stations (five of them, located around the world) that make sure the satellites are working properly.
ELEMENTS OF GLOBAL POSITIONING SYSTEM
SPACE SEGMENT:

The complete GPS space system includes 24 satellites, 11,000 nautical miles above the Earth, which take 12 hours each to go around the Earth once (one orbit). They are positioned so that we can receive signals from six of them nearly 100 percent of the time at any point on Earth. There are six orbital planes (with nominally four Space Vehicles in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane.Satellites are equipped with very precise clocks that keep accurate time to within three nanoseconds. This precision timing is important because the receiver must determine exactly how long it takes for signals to travel from each GPS satellite. The receiver uses this information to calculate its position.
The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I. From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24 satellites in 1994 completed the system. The control segment consists of a worldwide system of tracking and monitoring stations.The 'Master Control Facility' is located at Falcon AFB in Colorado Springs, CO.
The monitor stations measure signals from the GPS satellites and relay the information they collect to the Master Control Station. The Master Control Station uses this data to compute precise orbital models for the entire GPS constellation. This information is then formatted into updated navigation messages for each satellite.
USER SEGMENT:
The user segment consists of the GPS receivers, processors and antennas utilized for positioning and timing by the community and military. The GPS concept of operation is based on satellite ranging. Users figure their position on the earth by measuring their
distance to a group of satellites in space. Each GPS satellite transmits an accurate
position and time signal. The user's receiver measures the time delay for the signal to
reach the receiver. By knowing the distance to four points in space, the GPS receiver is
able to triangulate a three-dimensional position.
WORKING 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 where they are in their orbits above the Earth. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time dissemination, and other research.
One trip around the Earth in space equals one orbit. The GPS satellites each take 12 hours to orbit the Earth. Each satellite is equipped with an accurate clock to let it broadcast signals coupled with a precise time message. The ground unit receives the satellite signal, which travels at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver. The difference between the time the signal is sent and the time it is received, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite. To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four separate satellites to get to the receiver.
It works something like this: If we know our exact distance from a satellite in space, we know we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. If we know our exact distance from two satellites, we know that we are located somewhere on the line where the two spheres intersect. And, if we take a third measurement, there are only two possible points where we could be located. By taking the measurement from the fourth satellite we can exactly point out our location.
SOURCES OF GPS SIGNAL ERRORS:
Factors that can degrade the GPS signal and thus affect accuracy include the following-
• Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
• Signal multi path — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
• Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
• Number of satellites visible — The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
• Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
DIFFERENTIAL GPS:
NEED FOR DGPS:

As the GPS receivers use timing signals from at least four satellites to establish a position, each of those timing signals is going to have some error or delay, depending on what sort of perils have befallen it on its trip down to receiver. Since each of the timing signals that go into a position calculation has some error, that calculation is going to be a compounding of those errors.
The sheer scale of the GPS system solves the problem. The satellites are so far out in space that the little distances we travel here on earth are insignificant. So if two receivers are fairly close to each other, say within a few hundred kilometers, the signals that reach both of them will have traveled through virtually the same slice of atmosphere, and so will have virtually the same errors.
WORKING:
The underlying premise of differential GPS (DGPS) is that any two receivers that are relatively close together will experience similar atmospheric errors.
Differential GPS involves the cooperation of two receivers, one that's stationary and another that's roving around making position measurements. Since the reference receiver has no way of knowing which of the many available satellites a roving receiver might be using to calculate its position, the reference receiver quickly runs through all the visible satellites and computes each of their errors. Then it encodes this information into a standard format and transmits to the roving receivers. It's as if the reference receiver is saying: "OK everybody, right now the signal from satellite #1 is ten nanoseconds delayed, satellite #2 is three nanoseconds delayed, satellite #3 is sixteen nanoseconds delayed..." and so on.The roving receivers get the complete list of errors and apply the corrections for the particular satellites they're using.
IMPLEMENTING DGPS:
The three main methods currently used for ensuring data accuracy are real-time differential correction, reprocessing real-time data, and post processing.
1.REAL TIME DGPS
Real-time DGPS occurs when the base station calculates and broadcasts corrections for each satellite as it receives the data. The roving receiver via a radio signal receives the correction, if the source is land based or via a satellite signal, if it is satellite based and applied to the position it is calculating. As a result, the position displayed and logged to the data file of the roving GPS receiver is a differential corrected procedure.
2. REPROCESSING REAL TIME DATA:
Some GPS manufacturers provide software that can correct GPS data that was collected in real time. This is important for GIS data integrity. When collecting real-time data, the line of sight to the satellites can be blocked or a satellite can be so low on the horizon that it provides only a weak signal, which causes spikes in the data. Reprocessing real-time data removes these spikes and allows real-time data that has been used in the field for navigation or viewing purposes to be made more reliable before it is added to a GIS.
3. POST PROCESSING CORRECTION:
Differentially correcting GPS data by post processing uses a base GPS receiver that logs positions at a known location and a rover GPS receiver that collects positions in the field. The files from the base and rover are transferred to the office processing software, which computes corrected positions for the rover's file. This resulting corrected file can be viewed in or exported to a GIS.
Thus, Differential GPS or "DGPS" can yield measurements good to a couple of meters in moving applications and even better in stationary situations. That improved accuracy has a profound effect on the importance of GPS as a resource. With it, GPS becomes more than just a system for navigating boats and planes around the world. It becomes a universal measurement system capable of positioning things on a very precise scale.
14-04-2011, 04:41 PM
Post: #16
RE: Global positioning system report and ppt

.docx  Imamul Report.docx (Size: 478.38 KB / Downloads: 58)
ABSTRACT
This is a new technique for the protection of transmission systems by using the global positioning system (GPS) and fault generated transients. In this scheme the relay contains a fault transient detection system together with a communication unit, which is connected to the power line through the high voltage coupling capacitors of the CVT. Relays are installed at each bus bar in a transmission network. These detect the fault generated high frequency voltage transient signals and record the time instant corresponding to when the initial traveling wave generated by the fault arrives at the busbar.
The decision to trip is based on the components as they propagate through the system extensive simulation studies of the technique were carried out to examine the response to different power system and fault condition. The communication unit is used to transmit and receive coded digital signals of the local information to and from associated relays in the system.
At each substation relay determine the location of the fault by comparing the GPS time stay measured locally with those received from the adjacent substations, extensive simulation studies presented here demonstrate feasibility of the scheme.
CHAPTER 2
INTRODUCTION

Accurate location of faults on power transmission systems can save time and resources for the electric utility industry. Line searches for faults are costly and can be inconclusive. Accurate information needs to be acquired quickly in a form most useful to the power system operator communicating to field personnel.
To achieve this accuracy, a complete system of fault location technology, hardware, communications, and software systems can be designed. Technology is available which can help determine fault location to within a transmission span of 300 meters. Reliable self monitoring hardware can be configured for installation sites with varying geographic and environmental conditions. Communications systems can retrieve fault location information from substations and quickly provide that information to system operators. Other communication systems, such as Supervisory Control and Data Acquisition (SCADA), operate fault sectionalizing circuit breakers and switches remotely and provide a means of fast restoration. Data from SCADA, such as sequence of events, relays, and oscillographs, can be used for fault location selection and verification. Software in a central computer can collect fault information and reduce operator response time by providing only the concise information required for field personnel communications. Fault location systems usually determine “distance to fault” from a transmission line end. Field personnel can use this data to find fault locations from transmission line maps and drawings. Some utilities have automated this process by placing the information in a fault location Geographical Information System (GIS) computer. Since adding transmission line data to the computer can be a large effort, some utilities have further shortened the process by utilizing a transmission structures location database. Several utilities have recently created these databases for transmission inventory using GPS location technology and handheld computers.
The inventory database probably contains more information than needed for a fault location system, and a reduced version would save the large data-collection effort. Using this data, the power system operator could provide field personnel direct location information.
Field personnel could use online information to help them avoid spending valuable time looking for maps and drawings and possibly even reduce their travel time. With precise information available, crews can prepare for the geography, climatic conditions, and means of transport to the faulted location. Repair time and resources would be optimized by the collected data before departure. Accurate fault location can also aid in fast restoration of power, particularly on transmission lines with distributed loads. Power system operators can identify and isolate faulted sections on tap-loaded lines and remove them by opening circuit breakers or switches remotely along the line, restoring power to the tap loads serviced by the unfaulted transmission sections.
CHAPTER 3
TRANSMISSION SYSTEM
GENERATION TRANSMISSION DISTRIBUTION

Electric power transmission, a process in the delivery of electricity to consumers, is the bulk transfer of electrical power. Typically, power transmission is between the power plant and a substation near a populated area. Electricity distribution is the delivery from the substation to the consumers. Electric power transmission allows distant energy sources (such as hydroelectric power plants) to be connected to consumers in population centers, and may allow exploitation of low-grade fuel resources that would otherwise be too costly to transport to generating facilities. Due to the large amount of power involved, transmission normally takes place at high voltage (110 kV or above). Electricity is usually transmitted over long distance through overhead power transmission lines. Underground power transmission is used only in densely populated areas due to its high cost of installation and maintenance, and because the high reactive power produces large charging currents and difficulties in voltage management. A power transmission system is sometimes referred to colloquially as a "grid"; however, for reasons of economy, the network is not a mathematical grid. Redundant paths and lines are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical or thermal limit of the line.
CHAPTER 5
WHAT IS TRAVELING WAVE FAULT LOCATION

Faults on the power transmission system cause transients that propagate along the transmission line as waves. Each wave is a composite of frequencies, ranging from a few kilohertz to several megahertz, having a fast rising front and a slower decaying tail. Composite waves have a propagation velocity and characteristic impedance and travel near the speed of light away from the fault location toward line ends. They continue to travel throughout the power system until they diminish due to impedance and reflection waves and new power system equilibrium is reached. The location of faults is accomplished by precisely time-tagging wave fronts as they cross a known point typically in substations at line ends. With waves time tagged to sub microsecond resolution of 30 m, fault location accuracy of 300 m can be obtained. Fault location can then be obtained by multiplying the wave velocity by the time difference in line ends. This collection and calculation of time data is usually done at a master station. Master station information polling time should be fast enough for system operator needs.
CHAPTER 6
BENEFITS OF TRAVELING WAVE FAULT LOCATION

Early fault locators used pulsed radar. This technique uses reflected radar energy to determine the fault location. Radar equipment is typically mobile or located at substations and requires manual operation. This technique is popular for location of permanent faults on cable sections when the cable is de-energized. Impedance-based fault locators are a popular means of transmission line fault locating. They provide algorithm advances that correct for fault resistance and load current inaccuracies. Line length accuracies of ±5% are typical for single-ended locators and 1-2% for two-ended locator systems. Traveling wave fault locators are becoming popular where higher accuracy is important. Long lines, difficult accessibility lines, high voltage direct current (HVDC), and series-compensated lines are popular applications. Accuracies of <300 meters have been achieved on 500 kV transmission lines with this technique. Hewlett-Packard has developed a GPS-based sub microsecond timing system that has proven reliable in several utility traveling wave projects. This low-cost system can also be used as the substation master clock.
22-04-2011, 09:29 AM
Post: #17
RE: Global positioning system report and ppt

.doc  Global Positioning System.doc (Size: 205.5 KB / Downloads: 59)
GLOBAL POSITIONING SYSTEM
A review as a communication systems application
ABSTRACT: -

The last decade saw the emergence of yet another satellite-based navigational system called the GLOBAL POSITIONING SYSTEM, which is today capable of providing accuracy levels of less than a centimeter. The GLOBAL POSITIONING SYSTEM is a radio-based navigation system that gives 3-D coverage of the earth 24 hours a day in all weather conditions. Using a commercial GLOBAL POSITIONING SYSTEM locator, the user can determine his position on the earth .Out of 24 NAVSTAR satellites 21 are operational satellites and the other three are standby satellites. The control segment comprises five monitoring stations that are capable of transmitting data to the satellite. The user segment consists of receivers, which could be handheld or installed on aircrafts, ships, tanks, submarines, etc. Receivers detect, decode and process GLOBAL POSITIONING SYSTEM satellite signals and convert them into position, velocity and time estimates.
INTRODUCTION: -
GLOBAL POSITIONING SYSTEM :-

It is new generation of universal navigational aid based on satellite. In GLOBAL POSITIONING SYSTEM, radio signals from number of orbiting satellites are received by an aircraft or ships, as the case may be the GLOBAL POSITIONING SYSTEM is most cost effective and versatile universal navigational aid for the coming years.
GLOBAL POSITIONING SYSTEM:-
It is a second generation satellite navigational based on the measurement of the times of arrival of time signal received from three or more orbiting satellite, whose positional co-ordinates in the space are also transmitted. There are now 21 GLOBAL POSITIONING SYSTEM satellites including three spares, in 12 hours circular orbits inclined at an angle of 55 0 to the altitude of 20,200 Km. This altitude is about half way lower then geostationary satellite. This will ensure that, at least 4 satellites will be visible at a time from any location round the world for position determination from the aircraft and the ship. Signals from up to 10 number of GLOBAL POSITIONING SYSTEM satellite may be received in a GLOBAL POSITIONING SYSTEM receiver and typically up to 7 satellites are involved at a time for position determination of GLOBAL POSITIONING SYSTEM station. The timing pulses are sent out by each satellite in the L band using spread spectrum modulation and received by the GLOBAL POSITIONING SYSTEM receiver in aircraft or ships, as the case may be processed by match filter which is required to be increased the precision of arrival time measurement of the pulse. The onboard GLOBAL POSITIONING SYSTEM receivers are however much simpler then required for Doppler Navigations and they are excepted to determine the position of an aircraft or ships with precision of 16 meter as better in 3-dimension. It is planned by International Civil Aviation Organization (ICAO), to install GLOBAL POSITIONING SYSTEM round the world and eventually renders the conventional navigational aid for airport and ships.
PRINCIPLE OF OPERATION OF GLOBAL POSITIONING SYSTEM NAVIGATION.:
GLOBAL POSITIONING SYSTEM for navigations use to determine the positional coordinator of user weaker which may be aircraft or ship or land mobile vehicle by measuring its distance by range from 3 or more satellites, whose positional coordinates are telemeter to the user by radio links using a coed. If the delay of the received code relative to the locally generated identical Reference code at the users location be T1, T2 , T3 for the satellite transmission from SV1,SV2,SV3 respectively. Then respective ranges are given by
* R1=C T1
* R2=C T2
* R3=C T3
The point of intersection of this three lines representing the ranges R1,R2 and R3 defines the special coordinates of the user vehicle and then it can be converted into latitude, longitude and altitude, by transformation of coordinates using computers. In an GLOBAL POSITIONING SYSTEM navigation system the information about time is required for which the signal from the fourth GLOBAL POSITIONING SYSTEM satellite at a range R4 has also to be utilized to obtain 4 equations relating R1, R2 ,R3 and R4 to t1, t2, t3 and t4 respectively. Three of these equations will allow us to determine the positional coordinates, while the fourth is used to derive the time information. Another way of looking at the problem would be consider that we must have at least four equations to solve for the four unknowns X, Y, Z and T .To measure the value of time delay for wave propagation between satellite transmitter and users receiver phase modulated radio signals in L-band are first received by the GLOBAL POSITIONING SYSTEM receiver from the GLOBAL POSITIONING SYSTEM satellites. The received signals are then demodulated by phase demodulator and resulting pseudo noise code is compared by locally generated code to measure the delay between the envelope delay the range of satellite is determine.
RF SOLUTIONS FOR GLOBAL POSITIONING SYSTEM: -
RF front end of GLOBAL POSITIONING SYSTEM receiver converts the equencythe signal received by the helical antenna to an intermediate frequency by double
Super heterodyne technique to process the data digitally for determining the users geographic position.
Low noise pre amplification is done either by: -
1). Low noise bipolar transistor OR
2). Low noise High electron mobility Transistor OR
3). Pseudomorphic High electron mobility Transistor OR
4). Ga As MOSET OR
5). Silicon MMICS OR
6). Schottky diodes.
Silicon MMICS or PIN attenuators diodes are used for AGC.Bipolar transistor provides a low phase noise for the local oscillator Phase. Locked to the crystal reference oscillator. The signal processing circuit is comprised of coherent clocked Detector for the C/A code and/or P-code, estimate for latitude, longitude &altitude of the GLOBAL POSITIONING SYSTEM station together with their errors X Y, Z. And time error T.
GLOBAL POSITIONING SYSTEM SEGMENTS: -
GLOBAL POSITIONING SYSTEM is comprised of three distinct segments.
1) Space segment.
2) Control segment.
3) User segment.
1) GLOBAL POSITIONING SYSTEM SPACE SEGMENT: -
It comprises of 18 satellites orbiting in a circular orbits at an altitude of 20,200 Km at an inclination of 55 Degree with a period of 12 hours. The relative position is arrange in such a way that at least four satellites will be visible to any user at a given instant of time thus, ensuring a GLOBAL coverage.(A broad beam antenna used in GLOBAL POSITIONING SYSTEM receiving system ,up to 10 satellite signals can be received.) Each satellite is design to transmit radio signals at two L-band frequencies for commercial services 1575.42 MHz , and for military purpose 1277.6 MHz is used.
The radiation pattern of L-band transmitting antenna at the GLOBAL POSITIONING SYSTEM satellite are specially designed to produce uniform signal strength at earth surface independent of
Position of user. Besides this for allowing control and telemetry function by ground station, the satellite has S-band antenna operating on a down link frequency of 22 to 27.5 MHz and up link frequency is 1783.74 MHz.
27-07-2011, 12:13 PM
Post: #18
RE: Global positioning system report and ppt

.ppt  13_GPS.PPT (Size: 4.18 MB / Downloads: 47)
Global Positioning System (GPS)
Introduction

The current global positioning system (GPS) is the culmination of years of research and unknown millions of dollars.
Navigational systems have been and continue to be developed and funded by the U.S. government.
The current system is managed by the U.S Air Force for the Department of Defense (DOD).
The current system became fully operational June 26, 1993 when the 24th satellite was lunched.
While there are millions of civil users of GPS worldwide, the system was designed for and is operated by the U. S. military.
Introduction-History
Introduction-History

Introduction--cont.
GPS provides specially coded satellite signals that can be processed with a GPS receiver, enabling the receiver to compute position, velocity and time.
A minimum of four GPS satellite signals are required to compute positions in three dimensions and the time offset in the receiver clock.
Accuracy and precision of data increases with more satellites.
Three Parts
Space segment
Control segment
User segment
Space Segment
The Air force insures that at least 24 satellites are operational at all times.
There are six orbital planes (with nominally four space vehicles (SVs) in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane.
The satellite orbits are controlled so that at least six should be available, unobstructed location, at all times.
Each satellite circles the earth twice a day.
Control Segment
The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado.
Control Segment--cont.
User Segment
The primary use of GPS is navigation.
Navigation receivers are made for aircraft, ships, ground vehicles, surveying, and for hand carrying by individuals.
The accuracy of a receiver depends on the number of channels, compatibility with other navigational systems (WAAS, GLONAS, etc.) and design of the receiver (cost).
User Segment--cont.
The GPS User Segment consists of all GPS receivers.
Surveying
Recreation
Navigation
GPS receivers convert satellite signals into position, velocity, and time estimates.
Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time.
User Segment--cont.
Time and frequency dissemination, based on the precise clocks on board the SVs and controlled by the monitor stations, is another use for GPS.
Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
The GPS signals are available to everyone, and there is no limit to the number and types of applications that use them.
Principles
The GPS system operates on the principles of trilateration, determining positions from distance measurements.
This can be explained using the velocity equation.
Trilateration Example
The signals from the GPS satellites travel at the speed of light--186,000 feet/second.
How far apart are the sender and the receiver if the signal travel time was 0.23 seconds?
Satellite Signals
Each satellite has its own unique signal.
It continuously broadcasts its signal and also sends out a time stamp every time it starts.
The receiver has a copy of each satellite signal and determines the distance by recording the time between when the satellite says it starts its signal and when the signal reaches the receiver.
GPS Trilateration
Each satellite knows its position and its distance from the center of the earth.
Each satellite constantly broadcasts this information.
With this information the receiver tries to calculate its position.
Just knowing the distance to one satellite doesn’t provide enough information.
GPS Trilateration--cont.
When the receiver knows its distance from only one satellite, its location could be anywhere on the earths surface that is an equal distance from the satellite.
All the receiver can determine is that it is some where on the perimeter of a circle that is an equal distance from the satellite.
The receiver must have additional information.
GPS Trilateration--cont.
With signals from two satellites, the receiver can narrow down its location to just two points on the earths surface.
GPS Trilateration--cont.
Knowing its distance from three satellites, the receiver can determine its location because there is only two possible combinations and one of them is out in space.
In this example, the receiver is located at b.
Most receivers actually require four to insure the receiver has full information on time, and satellite positions.
The more satellite positions that are used, the greater the potential accuracy of the position location.
Factors Influencing Position Accuracy
The number of satellites (channels) the receiver can track.
The number of channels a receiver has is part of it’s design.
The higher the number of channels---the greater the potential accuracy.
The higher the number of channels---the greater the cost.
The number of satellites that are available at the time.
Because of the way the satellites orbit, the same number are not available at all times.
When planning precise GPS measurements it is important to check for satellite availability for the location and time of measurement.
If a larger number of channels are required (6-10), and at the time of measurement the number available was less than that, the data will be less accurate.
Factors Influencing Position Accuracy--cont.
The system errors that are occurring during the time the receiver is operating.
The GPS system has several errors that have the potential to reduce the accuracy.
To achieve high levels of precision, differential GPS must be used.
Differential GPS uses one unit at a known location and a rover.
The stationary unit compares its calculated GPS location with the actual location and computes the error.
The rover data is adjusted for the error.
Real Time Kinematic (RTK)
Post processing
Location
Once the GPS receiver has located its position it is usually displayed in one of two common formats:
Latitude and longitude
Universal transverse mercator (UTM).
Latitude and Longitude
Latitudes and longitudes are angles.
Latitude
Latitude gives the location of a place on the Earth north or south of the Equator.
Latitude is an angular measurement in degrees (marked with °) ranging from 0° at the Equator to 90° at the poles (90° N for the North Pole or 90° S for the South Pole)
Latitude--Equator
The equator divides the planet into a Northern Hemisphere and a Southern Hemisphere.
The latitude of the equator is, by definition, 0°.
Latitude--cont.
Four lines of latitude are named because of the role they play in the geometrical relationship with the Earth and the Sun.
Longitude
Longitude--cont.
The circumference of the earth at the equator is approximately 24,901.55 miles.
Longitude--cont.
There is an important difference between latitude and longitude.
The circumference of the earth declines as the latitude increase away from the equator.
This means the miles per degree of longitude changes with the latitude.
This makes determining the distance between two points identified by longitude more difficult.
Mercator Projection
A Mercator projection is a ‘pseudocylindrical’ conformal projection (it preserves shape).
Points on the earth are transferred, on an angle from the center of the earth, to the surface of the cylinder.
What you often see on poster-size maps of the world is an equatorial mercator projection that has relatively little distortion along the equator, but quite a bit of distortion toward the poles.
Mercator Projection
What a transverse mercator projection does, in effect, is orient the ‘equator’ north-south (through the poles), thus providing a north-south oriented swath of little distortion.
By changing slightly the orientation of the cylinder onto which the map is projected, successive swaths of relatively undistorted regions can be created.
UTM Zones
These zones begin at 180o longitude and are numbered consecutively eastward.
UTM Zones--cont.
The conterminous United States is covered by 10 UTM grid zones.
In the Northern Hemisphere each zone's northing coordinate begins at the equator as 0,000,000 and is numbered north in meters.
UTM--cont.
The UTM system uses a different grid for the polar regions.
These areas are covered by a different conformal projection called the Polar Stereographic.
Since compass directions have little meaning at the poles, one direction on the grid is arbitrarily designated "north-south" and the other "east-west" regardless of the actual compass direction.
The UTM coordinates are called "false northing" and "false easting.”
Using Location Information
Determining UTM Zone

Treat west longitude as negative and east as positive.
Add 180 degrees; this converts the longitude to a number between zero and 360 degrees.
Divide by 6 and round up to the next higher number.
Example:
The location of the intersection of Hall of Fame and Virginia on OSU campus is 56 7 23.71 N and 97 05 16.079 W.
Determining a UTM Grid Value for a Map Point
The UTM grid is shown on all quadrangle maps prepared by the U.S. Geological Survey (USGS).
On 7.5-minute quadrangle maps (1:24,000 and 1:25,000 scale) and 15-minute quadrangle maps (1:50,000, 1:62,500, and standard-edition 1:63,360 scales), the UTM grid lines are indicated at intervals of 1,000 meters, either by blue ticks in the margins of the map or with full grid lines.
The 1,000-meter value of the ticks is shown for every tick or grid line.
Determining a UTM Grid Value for a Map Point--cont.
To use the UTM grid, you can place a transparent grid overlay on the map to subdivide the grid, or you can draw lines on the map connecting corresponding ticks on opposite edges.
The distances can be measured in meters at the map scale between any map point and the nearest grid lines to the south and west.
The northing of the point is the value of the nearest grid line south of it plus its distance north of that line; its easting is the value of the nearest grid line west of it plus its distance east of that line.
Determining Distance Using UTM
In the illustration the UTM coordinates for two points are given.
The distance can be determined using Pythagorean Theorem because UTM is a grid system.
UTM Example--cont.
Subtracting the easting proved the length of the horizontal side: 208,000 meters.
Subtracting the northing proves the length of the vertical side: 535,000 meters.
The distance between the two points is:
GPS Errors
Noise
Biases
Blunder
Clock
Noise Error
Noise errors are the combined effect of code noise (around 1 meter) and noise within the receiver noise (around 1 meter).
Bias Error
Selective Availability (SA)
SA is the intentional degradation of the SPS signals by a time varying bias. SA is controlled by the DOD to limit accuracy for non-U. S. military and government users.
Selective availability is turned off.
Ephemeris data errors: 1 meter
Satellite orbits are constantly changing. Any error in satellite position will result in an error for the receiver position.
SV clock errors uncorrected by Control Segment can result in one meter errors.
Tropospheric delays: 1 meter.
The troposphere is the lower part (ground level to from 8 to 13 km) of the atmosphere that experiences the changes in temperature, pressure, and humidity associated with weather changes.
Complex models of tropospheric delay require estimates or measurements of these parameters.
Bias Error--cont.
Unmodeled ionosphere delays: 10 meters.
The ionosphere is the layer of the atmosphere from 50 to 500 km that consists of ionized air. The transmitted model can only remove about half of the possible 70 ns of delay leaving a ten meter un-modeled residual.
Multipath: 0.5 meters.
Multipath is caused by reflected signals from surfaces near the receiver that can either interfere with or be mistaken for the signal that follows the straight line path from the satellite.
Blunder
Blunders can result in errors of hundred of kilometers.
Control segment mistakes due to computer or human error can cause errors from one meter to hundreds of kilometers.
User mistakes, including incorrect geodetic datum selection, can cause errors from 1 to hundreds of meters.
Receiver errors from software or hardware failures can cause blunder errors of any size.
29-08-2011, 11:43 AM
Post: #19
RE: Global positioning system report and ppt

.doc  gps.doc (Size: 441 KB / Downloads: 66)
ABSTRACT
Where am I? Where am I going? Where are you? What is the best way to get there? When will I get there? GPS technology can answer all these questions. GPS satellite can show you exact position on the earth any time, in any weather, no matter where you are! GPS technology has made an impact
On navigation and positioning needs with the use of satellites and ground stations the ability to track aircrafts, cars, cell phones, boats and even individuals has become a reality.
This paper describes the Global positioning system (GPS) satellite. It depicts what GPS satellite is, how it works and its tracking features. This paper also gives how
the GPS satellite has been used to compute position and time, gives the details of various
segments in which the GPS system is useful. The paper gives the benefits of GPS satellite such as ability to track an object, due to reduced cost it is more affordable for everyone and helps you to find out where you are and how to get to your destination,
where ever you are going on land or sea.,
Applications such as military, car alarms, home security and home monitoring
INTRODUCTION
Trying to figure out where you are and where you're going is probably one of man's oldest pastimes. Navigation and positioning are crucial to so many activities and yet the process has always been quite cumbersome. Over the years all kinds of technologies have tried to simplify the task but everyone has had some disadvantages. Finally, the U.S. Department of Defense decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money ($12 billion!) it took to build something really good. The result is the Global Positioning System, a system that's changed navigation forever.
GPS initially created by the U.S Defense Department for the military has later been made available to the public. GPS technology is not just a handheld “help-me-find-my-way-home” operation anymore. GPS is finding its way into cars, boats, planes, construction equipment, moviemaking gear, farm machinery, even laptop computers. Move over Mr. Bell, it won’t be long until GPS will become as basic as the telephone.
ALL ABOUT GPS
A constellation of 24 satellites
A system of satellites, computers, and receivers that is able to determine the latitude and longitude of a receiver on Earth by calculating the time difference for signals from The Global Positioning different satellites to reach the receiver. System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. GPS uses these "man-made stars" as reference points to calculate positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to better than a centimeter! In a sense it's like giving every square meter on the planet a unique address. GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. And that makes the technology accessible to virtually everyone.
Technical description
The system consists of a "constellation" of at least 24 satellites in 6 orbital planes. The GPS satellites were initially manufactured by Rockwell; the first was launched in February 1978, and the most recent was launched November 6 2004. Each satellite circles the Earth twice every day at an altitude of 20,200 kilometers (12,600 miles). The satellites carry atomic clocks and constantly broadcast the precise time according to their own clock, along with administrative information including the Orbital elements of their own motion, as determined by a set of ground-based observatories.
The receiver does not need a precise clock, but does need to have a clock with good short-term stability and receive signals from four satellites in order to find its own latitude, longitude, elevation, and the precise time. The receiver computes the distance to each of the four satellites from the difference between local time and the time the satellite signals were sent (this distance is called a pseudo range). It then decodes the satellites' locations from their radio signals and an internal database. The receiver should now be located at the intersection of four spheres, one around each satellite, with a radius equal to the time delay between the satellite and the receiver multiplied by the speed of the radio signals. The receiver does not have a very precise clock and thus cannot know the time delays. However, it can measure with high precision the differences between the times when the various messages were received. This yields 3 hyperboloids of revolution of two sheets, whose intersection point gives the precise location of the receiver. This is why at least four satellites are needed: fewer than 4 satellites yield 2 hyperboloids, whose intersection is a curve; it is impossible to know where the receiver is located along the curve without supplemental information, such as elevation. If elevation information is already known, only signals from three satellites are needed (the point is then defined as the intersection of two hyperboloids and an ellipsoid representing the Earth at this altitude). The receiver contains a mathematical model to account for these influences, and the satellites also broadcast some related information, which helps the receiver in estimating the correct speed of propagation. High-end receiver /antenna systems make use of both L1 and L2 frequencies to aid in the determination of atmospheric delays.
08-02-2012, 10:39 AM
Post: #20
RE: Global positioning system report and ppt
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31-05-2012, 05:06 PM
Post: #21
RE: Global positioning system report and ppt
GLOBAL Positioning System


.pdf  GLOBAL Positioning System.pdf (Size: 378.36 KB / Downloads: 14)

INTRODUCTION

GLOBAL Positioning System (GPS) receivers for the consumer
market require solutions that are compact, cheap, and low power.
Manufacturers of cellular telephones, portable computers, watches, and other
mobile devices are looking for ways to embed GPS into their products. Thus,
there is a strong motivation to provide highly integrated solutions at the lowest
possible power consumption. GPS radios consist of a front-end and a digital
baseband section incorporating a digital processor. While for the baseband
processor, cost-reduction reasons dictate the use of the most dense digital
CMOS technology, for the front-end, the best option in terms of power
consumption is a SiGe BiCMOS technology.

ARCHITECTURE AND SPECIFICATIONS

The GPS signal code is a direct-sequence spread spectrum, and the type
of spread spectrum employed by GPS is known as binary phase-shift keying
direct-sequence spread spectrum (BPSK DSSS). In a spread-spectrum system,
data are modulated onto the carrier such that the transmitted signal has a larger
bandwidth than the information rate of the data. The term “direct sequence” is
used when the spreading of the spectrum is accomplished by phase modulation
of the carrier.

CHIP DESIGN

As stated, the overall design has been geared to a high level of
integration and reduction of silicon area at the lowest possible power
consumption. Below, the detailed design choices in the various sections are
described.
RF Section
The LNA has been designed to have a very low noise since it sets a lower
bound for the total receiver sensitivity. A high voltage gain is necessary to
sufficiently reduce the noise contribution of the following mixers.
A common source configuration with inductive degeneration provides
high voltage gain and low NF, as shown in Fig. 3. In fact, in a narrow band,
this structure allows achieving a noise factor close to the theoretical minimum.
31-07-2012, 09:50 AM
Post: #22
RE: Global positioning system report and ppt

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