Before revision: Function GNSSs (GPS , GLONASS, GALILEO, BEIDOU, QZSS) provide a way to learn one's location, but these methods require free field conditions in order to receive the radio signal.
After revision: Function GPS or other satellite based systems ( GLONASS, GALILEO, BEIDOU, QZSS) provide a way to learn one's location, but these methods require free field conditions in order to receive the radio signal.