How Does A Handheld GPS System Work?

You may be wondering how the whole GPS system works for handheld units. Let’s go through the basics. There are three portions of the entire GPS system. There is the user segment, the control segment, and the space segment. Let’s look at each, in turn.

Learning About GPS Workings

First, there is the user segment. That’s the individual person who has a handheld GPS unit. It’s you and me, the ones who want to know where in the world Carmen Sandiego is – or at least where we are, at any given time. There are millions of users all over the world, who access the GPS system with handheld devices for their work and play.

There are people in the military who use them, and pilots who rely on them all the time. There are also surveyors who use them to complete their work in a fraction of the time it would take them if they didn’t have access to the GPS system with handheld devices. Those who “play” use them with their hobbies and sports, like fishing, hiking, boating, snowmobiling, and geocaching.

The GPS receiver has an antenna which is tuned to receive the information from the satellites, the processor to deal with the information it receives, and a usually crystal quartz clock, which is highly accurate (though not as accurate as an atomic clock). It can also give other information to the user, like longitude and latitude, elevation, speed of movement, direction of movement, etc.

The number of channels that many GPS receiver has is referring to how many satellites it can "listen to" at once. Normally, most receivers now have from 12 to 20 channels. The information on the handheld GPS for the system can sync up with a computer via serial connection, to send information both ways – to download information to the handheld unit, or to upload information from it.

The space segment is the 24 satellites that are orbiting our earth. They fly at about 12,000 miles above the earth, and travel at about 7,000 miles per hour, orbiting once every 12 hours. That high of an orbit allows them to cover a large area, and the satellites are arranged so that at any one time a GPS system user’s handheld unit can get information from at least four satellites.

The satellites send information in a "line of sight" way, meaning that they can send information through glass, plastic, and clouds, but not through most solids like mountains and buildings. Though the satellites do a tremendous job, they do need correction once in a while. That’s where the third segment comes in – the control segment. The control segment is made up of five stations located around our world.
Four of them are unmanned and collect information from the satellites all the time. They send all of it to the master control station. The master control station receives the information and decides what corrections are needed. Then the master control station sends the new information – the orders – to the satellite so they are always as accurate as possible.