Method, Apparatus and System for Frequency Synchronization Between Devices Communicating over a Packet Network
First Claim
1. An apparatus comprising:
- a communication device comprising a clock recovery module;
the communication device being operative as a slave device relative to another communication device that is operative as a master device;
the clock recovery module comprising a clock recovery loop configured to control a slave clock frequency of the slave device so as to synchronize the slave clock frequency with a master clock frequency of the master device;
the clock recovery loop comprising;
a frequency error estimator configured to generate an estimate of error between the master clock frequency and the slave clock frequency; and
a loop filter;
wherein the frequency error estimator comprises a maximum-likelihood estimator with slope fitting based on a sequence of arrival timestamps generated in the slave device for respective timing messages received from the master device; and
wherein the loop filter comprises a series combination of an adaptive-bandwidth filter and a proportional-integral controller.
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Accused Products
Abstract
An endpoint or other communication device of a communication system includes a clock recovery module. The communication device is operative as a slave device relative to another communication device that is operative as a master device. The clock recovery module comprises a clock recovery loop configured to control a slave clock frequency of the slave device so as to synchronize the slave clock frequency with a master clock frequency of the master device. The clock recovery loop utilizes a frequency error estimator implemented as a maximum-likelihood estimator with slope fitting based on a sequence of arrival timestamps, and a loop filter implemented as a series combination of an adaptive-bandwidth filter and a proportional-integral controller. The clock recovery module may further comprise a discontinuity detector configured to detect a discontinuity in delays of respective timing messages, and a loop controller operative to place the clock recovery loop in a particular state responsive to detection of the discontinuity.
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Citations
30 Claims
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1. An apparatus comprising:
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a communication device comprising a clock recovery module; the communication device being operative as a slave device relative to another communication device that is operative as a master device; the clock recovery module comprising a clock recovery loop configured to control a slave clock frequency of the slave device so as to synchronize the slave clock frequency with a master clock frequency of the master device; the clock recovery loop comprising; a frequency error estimator configured to generate an estimate of error between the master clock frequency and the slave clock frequency; and a loop filter; wherein the frequency error estimator comprises a maximum-likelihood estimator with slope fitting based on a sequence of arrival timestamps generated in the slave device for respective timing messages received from the master device; and wherein the loop filter comprises a series combination of an adaptive-bandwidth filter and a proportional-integral controller. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A method for use in a communication device, the communication device being operative as a slave device relative to another communication device that is operative as a master device, the method comprising the steps of:
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receiving timing messages from the master device; generating arrival timestamps for respective ones of the timing messages; generating an estimate of error between a master clock frequency of the master device and a slave clock frequency of the slave device; and controlling the slave clock frequency based on the error estimate to synchronize the slave clock frequency with the master clock frequency; wherein the generating step comprises generating the error estimate as a maximum-likelihood estimate using slope fitting based on the arrival timestamps; and wherein the controlling step comprises filtering the error estimate using a series combination of an adaptive-bandwidth filter and a proportional-integral controller. - View Dependent Claims (29)
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30. A communication system, comprising:
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at least first and second communication devices configured to communicate with one another over a packet network; a first one of the communication devices being operative as a slave device relative to another one of the communication devices operative as a master device; the first communication device comprising a clock recovery module; the clock recovery module comprising a clock recovery loop configured to control a slave clock frequency of the slave device so as to synchronize the slave clock frequency with a master clock frequency of the master device; the clock recovery loop comprising; a frequency error estimator configured to generate an estimate of error between the master clock frequency and the slave clock frequency; and a loop filter; wherein the frequency error estimator comprises a maximum-likelihood estimator with slope fitting based on a sequence of arrival timestamps generated in the slave device for respective timing messages received from the master device; and wherein the loop filter comprises a series combination of an adaptive-bandwidth filter and a proportional-integral controller.
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Specification