ADS-B (Automatic Dependent Surveillance Broadcast) system
is widely used globally for real-time tracking of flights. Currently around 60%
of passenger aircrafts are equipped with ADS-B transponder. When in flight the
aircraft gets its GPS location from the satellite in space. Then ADS-B
transponder in the aircraft now transmits the GPS location details (and other
information including speed, vertical speed, Skuawk signal etc.) to nearby
aircrafts and receivers on land. ADS-B signal is received by the receiver and
information is analyzed and sent to base stations (including live tracking
systems, ATC).
Further resources: