Abstract: The present invention relates generally to satellite communication systems, and more particularly to a method and system for stabilizing transmission frequencies in a mobile satellite communication system. The preferred embodiment of the invention involves adjusting the transmit frequency of the gateway to account for a frequency shift from the reference frequency on the link between the gateway and the satellite. The preferred method of stabilizing the transmission frequency of a mobile terminal in a mobile satellite communication system involves receiving frequency offset information transmitted by a gateway in the mobile satellite system, and adjusting a reference oscillator in a mobile terminal based on the frequency offset information. The preferred embodiment of the system includes a plurality of mobile terminals, a satellite adapted to communicate with the mobile terminals, and a gateway in communication with the satellite.

Abstract: The frequency and power of transmissions in a mobile communication system, such as an air-to-ground telephony system, are stabilized without a priori knowledge of the system gain factors or frequency references. The ground station monitors the available channels and modifies a vacant channel broadcast message to provide information that the channel is available. In this way, the air terminals have knowledge of all available channels. The ground station transmits a pilot signal. Upon request by a user for a dial tone at the air terminal, the air terminal selects a vacant channel and scans for the pilot signal. The air terminal estimates a distance to the ground station and sets a power level of a seizing transmission based on the estimated distance. The air terminal also estimates a Doppler frequency shift of the selected channel due to the relative movement of the air terminal with respect to the ground station and sets a frequency of the seizing transmission based on the estimated Doppler frequency shift.