07-04-2011, 03:07 PM
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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.
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.
