Stabilization of frequency and power in an airborne communication system

摘要

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. The air terminal then transmits a channel seizing signal at a reduced bandwidth less than a full normal bandwidth to the ground station at the set level and frequency. The ground station measures the level and frequency of the seizing signal and transmits to the air terminal information acknowledging the seizure of the selected channel and reporting the level and frequency of the seizing signal. The air terminal corrects the transmitted level and frequency and then switches the transmission bandwidth to the full normal bandwidth at the corrected level.