Fundamentals of the Global Positioning System

As you make yourself comfortable inside your vehicle, you pull out your global positioning system (GPS) unit, type in a destination, and minutes later you are following instructions from your real-time location. This common navigational approach was not even fathomable 40 years ago. It would be an understatement to say that the GPS system has changed the way people live, yet for many people, these floating objects in the sky are a mystery.

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To shed some light, GPS actually refers to the system of satellites operated by the U.S. Department of Defense. The handheld electronic devices used by people, including phones, are actually GPS receivers. The receiver itself is physically very small, and its job is to pick up the signals that are transmitted by the satellites. The most common receivers people use are installed with programming software that use the signal's travel time and velocity to compute the distance to the satellite. Contrary to what some people might think, navigational tools, such as maps and compasses, are not part of the GPS receiver positioning software. Navigational software is responsible for using the real-time position of the device, given by the GPS, to guide the user to a known destination and to keep track of previously occupied locations. Four satellite distances must be known for a reliable location, so it's ideal to have a clear horizon line.

It's important to note that the GPS satellites are not the only positioning satellites orbiting the Earth. Russia and Europe have their own satellite systems up and running as well. This whole constellation of satellites is referred to as the Global Navigation Satellite System (GNSS). Any receiver with GNSS capabilities is able to tap into this system, allowing for better signal acquisition and positioning. Nothing about the satellite systems is perfect, expect real-world errors between 10 and 15 meters when using a phone or handheld unit. In North America, the receiver will sometimes have Wide Area Augmentation System (WAAS) capabilities — a feature that will allow the user to achieve meter accuracy. WAAS capabilities allow the receiver to pick up transmissions from geosynchronous satellites that give corrections to the errors found in the satellite signal. This process is operated by the Federal Aviation Administration (FAA), who is responsible for determining the errors and transmitting them to the geosynchronous satellites. As technology improves, expect to have stronger satellite signals and less error in the receiver.