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  • How GPS Works
Technology Articles > Gadgets > GPS > How GPS Works

GPS stands for Global Positioning System. It is a brilliant technology that helps a lot of people get around. There are a generation of drivers that know getting around only through their SatNav. The technology is in all major smartphones, too. But do you know how GPS actually works? This article will get you clued up so that you can appreciate the technology that helps a lot of us get from A to B.
There are 24 satellites orbiting the Earth that make two full rotations each day. They are in a specific constellation so that at least four satellites can be received wherever you are. These satellites were originally made to be used for the United States military, but in 2000 they were opened up to everyone by President Bill Clinton. It cost around $11 billion for the system to be created and yearly upkeep is around $400 million. Each satellite is solar powered and will last for about 10 years.
Every satellite has an atomic clock built in. This is because GPS operates by using very accurate time references provided by the American Naval Observatory. The satellites transmit their location and the current time. All of these signals are sent out by the satellites simultaneously. The signals then move at the speed of light and are picked up by a GPS receiver (like a SatNav). The signals all arrive at different times, depending on how far away the satellite is. The time it takes for the signal to reach the receiver can determine how far away the satellite is. When the receiver collects four satellite signals it is then able to work out the distance of each one. This then allows it to calculate the current position on a three dimensional plane.
The accuracy of GPS will depend on the receiver. The majority of consumer devices will have an accuracy of around 15 meters. There is such a thing as Differential Global Positioning which can increase accuracy to 10cm. This works by connecting to a receiver that is fixed at a nearby location. It then works out the difference between the broadcasted satellite and the signals that the fixed receiver has collected. It is interesting to note that when GPS was first created, any GPS device receiving a signal that wasn’t from the military would have a limited accuracy of 100 meters.
GPS isn’t perfect. It can sometimes get your location wrong. This can be down to a variety of reasons. One of these is that the GPS receiver is not able to pick up four or more satellites. If you are in an area surrounded by large buildings or dense foliage then the signal will have a harder time reaching the receiver. As such, the position it gives you may be out of sync. If you are underground or indoors then a lot of GPS units will not be able to function. The signal can also get delayed as it passes through the atmosphere, depending on how dense it is at that time.