An Introduction GPS An Introduction GPS TechnologyTechnology

PANKAJ AGARWALPANKAJ AGARWAL

March 12, 2014March 12, 2014

ICL GROUP OF COLLEGE

OverviewOverview

What is GPS?What is GPS? What does the GPS do? How it worksHow it works GPS codesGPS codes

Application with GPSApplication with GPS Pocket StreetPocket Street FarmingFarming agricultureagriculture Automated Vehicle Location SystemAutomated Vehicle Location System

Global Positioning System Global Positioning System (GPS)(GPS)

The Global Positioning The Global Positioning System (GPS)System (GPS)

is a satellite-based navigation is a satellite-based navigation system made up of a network system made up of a network of 24 satellites placed into orbit of 24 satellites placed into orbit by the U.S.Department of by the U.S.Department of Defense.Defense.

GPS satellitesGPS satellites 24 Satellites in 6 planes, each 24 Satellites in 6 planes, each

plane has 4 satellitesplane has 4 satellites These space vehicles (SVs) These space vehicles (SVs)

send radio signals from space.send radio signals from space.

What does the GPS do

Satellite signals can be Satellite signals can be processed in a GPS receiver.processed in a GPS receiver.

GPS receiver will show your GPS receiver will show your EXACT location on the EarthEXACT location on the Earth (latitude and longitude)

Helps you find your way to a specified location

Let’s you know what direction you are heading and how fast you are going

GPS- How it worksGPS- How it works Measuring the distance from a satellite by measuring Measuring the distance from a satellite by measuring

travel time of radio signals secondstravel time of radio signals seconds

Distance = speed of light * latency in timeDistance = speed of light * latency in time Four GPS satellite signals are used to compute positions Four GPS satellite signals are used to compute positions

in three dimensions and the time offset in the receiver in three dimensions and the time offset in the receiver clock.clock.

GPS- How it worksGPS- How it works

Given 1 satellite …Given 1 satellite …

We can locate our We can locate our position on the position on the surface of a spheresurface of a sphere

With two satellites you could narrow your With two satellites you could narrow your location down to two possible locations.location down to two possible locations.

You Could Be Here?

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With three satellites you could get a better estimate With three satellites you could get a better estimate on your location. It would narrow it down to one on your location. It would narrow it down to one point.point.

YOU ARE HERE

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YOUR ARE DEFFINATELY RIGHT

HERE

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for your location to be accurately measured. you have for your location to be accurately measured. you have at least four satellites.at least four satellites.

“”“” The GPS receiver compares the time a signal was The GPS receiver compares the time a signal was

transmitted by a satellite with the time it was received. transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away The time difference tells the GPS receiver how far away the satellite is.the satellite is.

With four or more satellites in view, the receiver can With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and determine the user's 3D position (latitude, longitude and altitude).altitude).

When GPS receives a signalWhen GPS receives a signal

It compares that signal with all the known codes It compares that signal with all the known codes (there are currently 37). (there are currently 37).

The receiver determines which satellite it is.The receiver determines which satellite it is. It decodes the timing information, multiplies by It decodes the timing information, multiplies by

the speed of light to find the radius of the the speed of light to find the radius of the sphere.sphere.

Once it has done that for 3 satellites, it can Once it has done that for 3 satellites, it can determine the location.determine the location.

How do GPS signals send all How do GPS signals send all this information?this information?

They use codes! Binary codes.They use codes! Binary codes. Each satellite has a different code.Each satellite has a different code.

00001000101001110000111001001000100001000101011000111101110010101101100111101011 00101100101001100111111011001111001001100110100011100010010001011000101101110000 00110110010001000101101000101001000000011111000110001011111011111100110111001011 01111000111111010100101000010101001110000110100111011000111101111100001111111111 01001001001001100111010101111100001000101101001111110000100110111100111000110110 10110110101000010110100101000101001000111001110001010010111010111010101000001011 01110011011001101000000000001110111011000110110101010110110001110001100110011111 01011111001110101010000011111100100101000000111010001111011010010110110000010010 01001100001101100001111011101110001101110110100111001000110101010000110110100101 11001011111111101100011100000011011100011000000100000000100000110101000101011110 11000111011010001100101011111001111010000000110111100110011101011110000011110110 01000100101011100000000100001010101001111101100111011011111100101111000100110101

For example, here are the first 1000 numbers of the code for satellite 1

10011110111010001001101111111110111100101101111011001101111101010100011111011000 11000100110011010000100000101111111000010000110101101011101011010011000001101000 01100010101011001000100100000110000011110000111010000011100100111011000000010110 01111000100101010111110101001111001011111011001010001011100001001110000111110111 01011101011011001111001001101011100100011011011111011001101011100001110101110001 10001111000001000111011011100010000011010011001001110000100010111000100100011011 11100011101010100110000000011001111001110101000010010001110010101010011100101101 11110011111110011010011101100111011001010010100110010101110111001110001101111001 10000010100011110011011110110011110100110111010011100110101010110100000101110001 11000111010110001111000100101001110101011000011000100011001010111001100001111100 00011111000100100011010001010001010010010001100001100100000110001100010100001101 10010110100110011000101101110011110010001010010100011110011101100001111101100101

This is the code for satellite 6

StrategyStrategy

First we need to learn how GPS creates First we need to learn how GPS creates these codesthese codes

Then we need to come up with a way to Then we need to come up with a way to quickly tell the codes apart.quickly tell the codes apart.

How do you create codes?How do you create codes?

You use binary addition rules.You use binary addition rules. 0+0=00+0=0 1+0=11+0=1 0+1=10+1=1 1+1=10 (but only use the last bit, 0)1+1=10 (but only use the last bit, 0) GPS uses “shift registers.” GPS uses “shift registers.” The more shift registers you have, the more The more shift registers you have, the more

complicated you can make your code.complicated you can make your code.

Register1 Register2 Register3 Code

1 1 1 -

Start with all 1’s in your shift registers

Add Register 1 and Register 3

The answer 0 goes into Register 1 and everything shifts to the right.

Here is an example with 3 shift registers

For this example, 1+1 =10 ==> 0

After 2After 2NN -1 steps (N is the number of -1 steps (N is the number of registers), the code repeatsregisters), the code repeats

Register1 Register2 Register3 Code

1 1 1 -

0 1 1 1

1 0 1 1

0 1 0 1

0 0 1 0

1 0 0 1

1 1 0 0

1 1 1 0

For 3 shift registers, the code repeats after 7 steps.

Real GPSReal GPS

Uses 10 shift registers.Uses 10 shift registers. They add different registers to produce the They add different registers to produce the

codes for different satellites.codes for different satellites. Satellite 1 uses 2 and 6.Satellite 1 uses 2 and 6. Satellite 2 uses 3 and 7, and so on.Satellite 2 uses 3 and 7, and so on. A 10-shift register code repeats after 2A 10-shift register code repeats after 21010-1, -1,

or 1023. or 1023.

How do you compare codes?How do you compare codes?

100111101110100010011011111111101000010001010011100001110010010001

Every time the numbers agree, add 1.

Every time the numbers disagree, subtract 1.

This example: 2 different satellitesThis example: 2 different satellites

100111101110100010011011111111111000010001010011100001110010010001

14 agree

11 disagreeTotal score: 3

Perfect agreement would be 35

Why are the codes shifted? The shift gives the GPS receiver the time difference.

Time Difference (in seconds) * 2.99792458 108 meters/second = Distance (in meters)

What is a typical Time Difference? GPS satellites are ~20,000,000 meters above the Earth.

20,000,000/300,000,000~ 70 milliseconds

Pocket Streets- an example with Pocket Streets- an example with GPS GPS

Pocket Streets offers exciting Pocket Streets offers exciting

features such as street-smart features such as street-smart

mapping, map customization, mapping, map customization,

GPS and Microsoft OutlookGPS and Microsoft Outlook

integration. integration. With Pocket Streets on your With Pocket Streets on your

Pocket PC, you will take a smart Pocket PC, you will take a smart

map with you wherever you go.map with you wherever you go.

Pocket Streets- an example with Pocket Streets- an example with GPS GPS

Download the map for the city.Download the map for the city.

Connect the GPS receiver to Connect the GPS receiver to

Pocket PC. Pocket PC.

Choose "Track Position" from theChoose "Track Position" from the

GPS menu to show your current GPS menu to show your current

position on the map. position on the map.

The position moves when you move.The position moves when you move.

FarmingFarming

Farmers can use GPS Farmers can use GPS to help them plow to help them plow very straight rows very straight rows to enable them use to enable them use their land more their land more efficiently.efficiently.

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AgricultureAgricultureFarmers can use GPS to help Farmers can use GPS to help

mark areas for pesticide or mark areas for pesticide or fertilizer application. Thus fertilizer application. Thus reducing waste. reducing waste.

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Automated Vehicle Location Automated Vehicle Location SystemSystem

Where is the bus What direction is

the bus traveling to What is the travel

speed Where is stop How long is the stop

Automated Vehicle Location Automated Vehicle Location SystemSystem

How Do GPS Relate? GPS receiver calculates its position (latitude and

longitude) and record the information at fixed time

interval GPS transmitter transmits location and vehicle

dynamic data to control center at prescribed interval Control center system process data accoding to

customer specifications

Automated Vehicle Location Automated Vehicle Location SystemSystem

Applications – MilitaryApplications – Military

Military GPS user equipment has been Military GPS user equipment has been integrated into fighters, bombers, tankers, integrated into fighters, bombers, tankers, helicopters, ships, submarines, tanks, helicopters, ships, submarines, tanks, jeeps, and soldiers' equipment. jeeps, and soldiers' equipment.

To prevent GPS interception by the To prevent GPS interception by the enemy, the government controls GPS enemy, the government controls GPS receiver exportsreceiver exports

Another GPS application?Another GPS application?

Besides being used by the military, Besides being used by the military, GPS is used in forestry, biology, GPS is used in forestry, biology, fishing, hunting, boating, racing, fishing, hunting, boating, racing, nursing, and many other fields.nursing, and many other fields.

GPS technology can be effectively GPS technology can be effectively used in your classroom as well.used in your classroom as well.

ConclusionsConclusions

GPS can show your EXACT location on the EarthGPS can show your EXACT location on the Earth (latitude and longitude)

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THANKSTHANKS