How Does GPS Work In Cell Phones?

How does GPS work in cellphones? Its a good question and one certainly worth answering. Cell phones and GPS are becoming such an integral and important part of everyday life that our curiosity about how these devices work is bound to be tickled. Can your mobile phone really be tracked? Is there a way for the authorities to find out your every move? In case of an emergency can the source of your 911 call be found?

The answer to all these questions is yes, and the single principle that drives it all is called trilateration.

But before we get into exactly how these devices work we have to understand that the use of GPS in phones is not going to go anywhere anytime soon.  In fact, many leading analysts of the industry suggest that the next wave of GPS development is going to be in cell phones.  That makes understanding how they work as a consumer all the more important.

GPS enabled devices are able to determine their location because of a mathematical process called trilateration.

What trilateration does is it takes the known distance from three different object and finds out where you are in relation to those objects.

An example is always helpful. In the photo to the right we see an example of trilateration in action. You are somewhere between Fresno, Los Angeles, and Las Vegas - but you don't exactly know where you are. You find a nice old man and ask him where you are. He doesn't know either, but tells you that you are 300 miles from Los Angeles. You pull out your map and draw a circle on your map that has a radius of 300 miles. This is helpful, but you still don't know exactly where you are.

So you find an old woman and ask her if she knows where you are. She, unfortunately, does not - but she does know that you are 250 miles from Fresno. You now draw a circle around Fresno that has a radius of 250 miles. This is looking good because on your map the circle around Fresno and the circle around Los Angeles intersect at two different points. You still don't know where you are, but you have a really good idea.

Now you find a third person and ask them if they know where you are. They do not, but can tell you that you are 100 miles from Las Vegas. You again draw a circle, this time around Vegas and it is 100 miles in diameter. Now you have a single point on your map where all three circles intersect. This is where you are.

This is exactly the way that trilateration works in GPS enable cell phones. It takes the know distance from three or more objects (satellites or cell phone towers) and finds out exactly where the phone is at any given moment.

An important thing to remember is that not every cell phone uses the Global Positioning System (GPS) to complete this trilateration process. The Global Positioning System is a series of 29 satellites currently in orbit around the earth. They constantly emit signals that can be picked up by specialized receivers (GPS devices) that will then process the information in the signal to use it to find the exact location of the receiver. This system has been in use for many years now by the military and was made available for the public use in the 1980s under President Ronald Reagan. Many phones do make use of the GPS satellites but not all do. The cell phones that don't use GPS satellites make use of cell phone towers to figure out their location.