Synchronizing clocks across a communication link
View Patent ↗A slave clock may be synchronized to a master clock by means of a synchronization signal sent from the master to the slave clock side of the link. The synchronization signal may be an expected signal pattern sent at intervals expected by the slave side. The slave clock may correlate received signals with a representation of the expected synchronization signal to produce a correlation sample sequence at a first sample rate which is related as n times the slave clock rate. A best interpolation may in turn be further refined by estimating between interpolator outputs adjacent to the best interpolation output. The synchronization signal receipt time thus determined is compared to the expected time based upon the slave clock, which is adjusted until the times match. The best interpolation may in turn be further refined by estimating between interpolator outputs adjacent to the best interpolation output.
1. A system in a transmitting communication station to transmit information sufficient to enable a receiving station to synchronize a plurality of clocks at the receiving station to a corresponding plurality of clocks at the transmitting station, the system comprising:
a noncommon clock;
a modulator module including circuitry to modulate a carrier to contain data for transmission to the receiving station, the modulator module being configured to modulate the carrier with a predetermined pattern in a periodic manner, the period being defined by a predetermined number of cycles of the noncommon clock; and
a secondary clock module including a secondary clock which is asynchronous to the noncommon clock, the secondary clock module being configured to obtain comparison data reflecting a comparison between the secondary clock and the noncommon clock, the data being derived from a count of either (i) a number of secondary clock cycles occurring within a predetermined number of noncommon clock cycles, or (ii) a number of noncommon clock cycles occurring within a predetermined number of secondary clock cycles, and provide the comparison data to the modulator module for transmission to the receiving station.
2. A system in a receiving communication station to respond to clock information received from a transmitting station by adjusting a plurality of clocks at the receiving station to track a corresponding plurality of clocks at the transmitting station as represented by the received clock information, the system comprising:
a demodulator module including circuitry to demodulate a signal received from the transmitting station, the demodulator module being configured to determine a precise time of arrival of a predetermined synchronization signal pattern, and to derive data including secondary clock relationship information;
a noncommon clock module configured to adjust a noncommon clock in accordance with a difference between the time of arrival of the synchronization signal and an expected time of arrival based on a known number of cycles of the noncommon clock; and
a secondary clock module configured to determine clock comparison data reflecting a count of either (i) a number of secondary clock cycles occurring within a predetermined number of noncommon clock cycles, or (ii) a number of noncommon clock cycles occurring within a predetermined number of secondary clock cycles, and adjust a secondary clock frequency based on a difference between the comparison data and the received secondary clock relationship information.