How Does GPS Keep Track of My Location?

The Global Positioning System, or GPS, has countless applications both for civilians and the military. We use GPS for clock synchronization, emergency services, aircraft tracking, navigation, cellular location, search and rescue missions, missile guidance, and even to improve our Google search results. It may be surprising how complicated this location service actually is for something that has become so common that it is found in every Smartphone.

The GPS is a series of 27 to 32 satellites which orbit the Earth. Each satellite circles the globe twice a day, and they are positioned so that at least four of them are visible in the sky at all times and anywhere on earth. The United States military originally designed this system to overcome shortcomings of previous navigational systems. In 1995 the program became a reality and the military allowed civilians to utilize this amazing technology as well.

Each satellite has its own atomic clock which is synchronized to all the other GPS satellites and to clocks here on Earth. They individually broadcast a signal 24/7 including their time and position in space. The United States Air Force is responsible for operating and maintaining the satellites and their orbits.

The GPS acquires and keeps track of your location by following a series of mathematical equations. If having multiple coordinated satellites orbiting Earth is not amazing enough, then surely the exceptional mathematical calculations will demonstrate the complexity of this system. The device which is recording your location is called the GPS receiver because it receives the information from the available space satellites. First, the satellites individually send the receiving device their time of transmission. From there, the receiver takes the time of transmission and the time of arrival according to the receiver’s clock to form four time of flight values.

These time of flight values from the four satellites are then used in a series of complicated equations to determine the receiver’s position. To simplify the math, basically each satellite produces a three-dimensional sphere and the only area in which all the spheres intersect is the receiver’s current location. Increasing the number of satellites that are visible in an area will increase the amount of spheres to calculate from which in turn makes the GPS more accurate.

Once the position is calculated by the receiver, it is converted into latitude, longitude, and height. These coordinates can then be placed on a map to track the receiver’s location. The satellite and receiver can continuously communicate and track movement on a moving map display or be recorded and used for something like vehicle guidance. This tracking is calculated with the receiver’s track algorithm which combines several sets of satellite broadcasts collected at different points in time. After several measurements are calculated and placed on the map, the track algorithm can then predict where the receiver will be for the next transmission.

This system which is utilized daily by people around the globe is much more complicated than it appears.