How does GPS work?

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Some interesting GPS trivia

  • GPS refers to the U.S. Department of Defense’s GNSS (Global Navigation Satellite System), also known as NAVSTAR. There are other GNSS around the world including the Russian GLONASS, the Chinese Compass and the planned EU Galileo system however NAVSTAR is the only fully-functioning GNSS at this time.
  • 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.
  • 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 or under water (which is why Garmin haven’t released a GPS unit for submarines!).
  • A GPS signal contains three different bits of information – a pseudorandom code, ephemeris data and almanac data. This information identifies the satellite, its current status, date and time as well where it should be at any given time.
  • Transmitter power is only 50 watts or less.
  • It takes between 65 and 85 milliseconds for a signal to come from a GPS satellite to a receiver on earth.

GPS is a complicated subject so let’s get right back to the basics of GPS; what is it and how it works. As an example in demonstrating how GPS technology is being used, we will look at how it is helping the ground transportation sector to route vehicles more efficiently.

Making an informed choice about GPS systems

If you’re looking to invest in a GPS system you don’t necessarily need to know exactly how it works, just like you don’t have to know how a car works to drive one. You just get in and shift it into drive.

But understanding how GPS works can help you to make a better decision when it comes to choosing the best GPS system. Unfortunately many people who buy GPS systems don’t know much about them. They end up making the mistake of getting something that is overkill, with features they’ll never need and a price tag to match. In some ways it’s like buying a car without knowing that the more liters a vehicle’s engine has affects its power and fuel consumption – if you didn’t need the extra power why pay for a fuel guzzler? Then again buying a Prius when you need to tow a 240-foot super-yacht could be disastrous.

In a similar way, different GPS systems work in different ways, some are better suited to specific environments, some are free, and others have ongoing charges. By understanding some of the science behind GPS and how it works you can make sure you get the best GPS navigation system for your needs, or the needs of your business.

What is GPS?

GPS works using the NAVSTAR constellation of 24 satellites

GPS works using the NAVSTAR constellation of 24 satellites

GPS stands for Global Positioning System and is a network that is made up of 3 main segments:

  • Space segment – 24 satellites orbit the earth twice a day, traveling at over 7,000 mph. They are solar powered but have battery backup for when they are in the earth’s shadow. They are positioned so that at any given time there are at least 4 satellites ‘visible’ from any point on earth.
  • Control segment – A master control station (located in Colorado Springs), unmanned monitor stations and ground antennas work together to make sure the satellites are working correctly and the information they beam down to earth is accurate.
  • User segment – This is where you, the user comes into the picture. The user segment is made up of GPS receivers, which is any device built to receive signals from a GPS satellite. This can include mobile phones, laptops, in-car navigation devices and hand-held tracking units.

How does GPS work?

So how do a bunch of satellites buzzing around in space help us down here on earth? Watch the video below to get some background on how GPS got started and how it works.



If you’re in a hurry here are the main points

  • GPS is a system that uses radio frequencies to find your exact location
  • Developed by the military to know the location and movement of planes, ships and soldiers
  • Accurate to meters, and even centimeters
  • Now used in cars, planes, boats, laptop computers and construction equipment
  • When a GPS receiver is switched on it ‘listens’ to find the 4 nearest satellites to help calculate its current location
  • A GPS systems can tell you how far you’ve traveled, your current direction, your speed and ETA
  • The ways in which GPS is being used are constantly growing as people think of new ways to apply GPS technology. For example, seismologists use GPS units to detect plate movement.

In the video it’s mentioned that satellites determine position using trilateration. It’s not an easy concept to explain with words so have a look at this animated sequence that shows how several satellites work together to provide an accurate intersection point, or location.

Credit: Animation courtesy of howstuffworks.com

Telogis GPS Fleet Management Software logo

The Telogis rings hint at the trilateration process employed by GPS satellites

Looking at how satellites use trilateration to pinpoint your location might remind you of certain company’s logo, proving that not all logos are meaningless squiggles.

Now that we have an overview of how these satellites are used to locate objects on earth, we can start to understand the many uses of GPS. One of these uses is GPS navigation systems as used for ground transportation (also referred to as AVL or Automatic Vehicle Location) and in our next post we’ll look at the two main variations of GPS navigation systems – connected and non-connected.

Knowing the difference can help save you money and you’ll get the best GPS system for your needs!

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4 Responses to “How does GPS work?”

  1. Tamika Smith Says:

    Hey! I Love Your website. I’m gonna post a link on my MySpace Site.

  2. ShawnR Says:

    On step one, knowing the distance from the first satellite, assumes that my receiver has an atomic clock capable of knowing how long the radio signal took to get to it. This is false. So, how can the receiver start to calculate its position? Using the receiver’s clock would create a sphere with an unknown thickness, based on how far off the receiver’s clock is to the true time.

  3. types of technology Says:

    types of technology…

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  4. Tony Cooper Says:

    Are we all idiots? Every website I have tried says ‘it calculates the its distance from a satellite’ … HOW??????

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