The sketch here is a simplified satellite communication system . The radio signal transmitted by the earth station A via directional antenna pointing to communication satellite, is received first by communication satellite antenna . After being amplified and converted by satellite transponders, the signal will be transmitted to the earth station B by satellite antenna . As soon as the earth station B receives the signal , the information transfer process from station A to station B is completed. The communication path from the earth station to the space station ( communication satellite ) is called uplink . The communication path from the space station( communication satellite ) to the earth station is called downlink. Similarly, the earth station B can also transmit signal to the earth station A through satellite to transfer information.