Short for pseudosatellite, a pseudolite is a ground-based differential GPS transmitter simulating the signal of a real GPS satellite, used for precise ranging applications like aircraft autolanding systems.

To reduce interference to signals from GPS satellites, the pseudolite signal is transmitted only 1/11th of each millisecond, and thus interferes only 10% of the time. The interfering position is changed each millisecond. Signal range is usually around 50 km, requiring about 30 milliwatts of power.