GPS

GPS is a system that allows a device to find out where on Earth it is currently located. To do this, around 30 satellites orbit the planet at an altitude of about 20,000 kilometers. Each of these satellites continuously sends radio signals to Earth. A phone or a car navigation system receives these signals and calculates its position from them. The abbreviation stands for Global Positioning System. Importantly: the device only listens, it does not send anything back to the satellites.

From military project to invisible infrastructure

GPS was built up by the US military starting in the 1970s. For a long time, the precise signal was deliberately degraded so that no one else could use it for military purposes. It wasn’t until the year 2000 that the US government released full accuracy for everyone. After that, satellite navigation became a matter of course within just a few years.

Today, entire industries depend on it. Parcel services plan their routes with it, farmers steer tractors across fields with centimeter precision, and emergency services find accident sites faster. Stock trading and the power grid also need GPS, though not for location purposes. They use the extremely precise time signal that the satellites transmit along with their data.

This very dependency is also a risk. The signal from space is very weak and can be disrupted with simple devices. Experts speak of jamming when the signal is drowned out, and of spoofing when a false signal fakes an incorrect location. This is why competing systems now exist: Galileo from Europe, GLONASS from Russia, and Beidou from China.

Calculating with the travel time of radio waves

Each satellite sends two pieces of information: its own position and the exact time of transmission. The signal travels at the speed of light, roughly 300,000 kilometers per second. The receiver compares the transmission time with the arrival time. This time difference yields the distance to the satellite.

A single distance measurement is not enough. It only tells you that you are located somewhere on the surface of a sphere around the satellite. With a second and third satellite, these spheres intersect, and the number of possible locations keeps shrinking. A fourth satellite is needed to correct the clock in the receiver. That’s because a deviation of just one millionth of a second already amounts to an error of 300 meters.

This is why satellites carry atomic clocks that barely drift by a second over the course of years. Incidentally, a common misconception is that GPS doesn’t work without mobile network coverage. That’s not true: the positioning itself also works in airplane mode, as long as location services are turned on. Only reloading map imagery requires an internet connection.

GPS in phones, cars, and AI systems

GPS is most obviously encountered in navigation apps and while jogging with a smartwatch. Less visibly, it is embedded in photos, since many cameras store the location where a picture was taken. Package tracking, car sharing, and e-scooter rentals also only work because every vehicle knows and reports its position.

In the world of AI, GPS mainly appears in self-driving cars and drones. There, it provides the rough position on a map, accurate to about two to five meters. That’s far too imprecise for staying within a lane. That’s why such systems combine GPS with cameras, laser scanners, and motion sensors. Experts call this merging of multiple data sources sensor fusion.

In the news, GPS often comes up in connection with data privacy. Location data reveals a great deal about a person, such as their home, workplace, and habits. That’s why the European General Data Protection Regulation strictly regulates who may collect and share such data. A second recurring topic is signal disruptions over conflict zones, which affect air traffic.