Patent ID: 6771629
Filing Date: 2004-08-03
Classification: H04B,H04J,H04W

Abstract:
In a voice communications network, a method for synchronizing a remote unit with a reference oscillator of a reference station, comprising:establishing an audio call path between the reference station and the remote unit; transmitting an audio-frequency reference signal from the reference station over the call path, the reference signal being transmitted for a predetermined reference duration; receiving the reference signal at the remote unit; generating an audio-frequency reply signal at the remote unit in response to the reference signal; waiting a preselected reply delay interval beginning at an observed time of receipt of the reference signal; transmitting the reply signal from the remote unit over the call path after waiting the reply delay interval, the reply signal being transmitted for a predetermined reply duration; receiving the reply signal at the reference station; measuring at the reference station a round-trip time difference between the transmission of the reference signal and an observed time of receipt of the reply signal; calculating a total latency based on the round-trip time difference, the reference duration, the reply duration, and the reply delay interval; selecting a synchronization reference time corresponding to a time mark output by the reference oscillator; defining a correction time preceding the synchronization time by one-half the total latency; transmitting a synchronization signal from the reference station over the call path at the correction time; receiving the synchronization signal at the remote unit; and in the remote unit, synchronizing the remote unit with the reference oscillator in response to the synchronization signal.