Answer the following question given this paragraph: 

You must have a GPS receiver to use the system. You can buy many types of these in stores. The GPS receiver detects radio signals from nearby GPS satellites. There are precise clocks on each satellite and in the receiver. The receiver measures the time for radio signals from satellites to reach it. The receiver uses the time and the speed of radio signals to calculate the distance between the receiver and the satellite. The receiver does this with at least four different satellites to locate its position on the Earth’s surface ( Figure above ). GPS receivers are now being built into many items, such as cell phones and cars.


Q: What do we call the worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations?


A:
gps