Clock synchronization using correlation events
First Claim
Patent Images
1. At a device, a method implemented on a processor, said method comprising:
- identifying a plurality of correlation events having an initiating timestamp and a receiving timestamp, said correlation events occurring between a first device having a first clock and a second device having a second clock, said plurality of correlation events comprising a first correlation event having said initiating timestamp correlated to said first clock and a second correlation event having said initiating timestamp correlated to said second clock;
determining that a solution set for an expression of the differences between said first clock and said second clock is not bounded, the solution set defining a linear relationship between said first clock and said second clock based on said first and second correlation events;
in response to determining that said solution set is not bounded;
identifying a further correlation event between said first device and said second device;
calculating a further linear inequality for said further correlation event;
and including said further linear inequality in said solution set;
determining that said solution set including said further linear inequality is a bounded solution set;
identifying a first event not being one of said plurality of correlation events, said first event having a third timestamp being defined by said second clock;
and using said bounded solution set to determine a fourth timestamp from said third timestamp, said fourth timestamp being with respect to said first clock.
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Abstract
Two clocks may be synchronized by calculating skew and offset values that may be determined from several correlation events. A correlation event may be the passing of messages in both directions between the two devices. The skew and offset values may be used to determine the time of non-correlated events. The clock synchronization may be performed on a real time basis or may be performed on a post processing basis. One method for calculating the skew and offset may use inequalities within a solution space to refine a solution set with multiple sets of correlation events.
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Citations
20 Claims
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1. At a device, a method implemented on a processor, said method comprising:
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identifying a plurality of correlation events having an initiating timestamp and a receiving timestamp, said correlation events occurring between a first device having a first clock and a second device having a second clock, said plurality of correlation events comprising a first correlation event having said initiating timestamp correlated to said first clock and a second correlation event having said initiating timestamp correlated to said second clock; determining that a solution set for an expression of the differences between said first clock and said second clock is not bounded, the solution set defining a linear relationship between said first clock and said second clock based on said first and second correlation events; in response to determining that said solution set is not bounded; identifying a further correlation event between said first device and said second device;
calculating a further linear inequality for said further correlation event;and including said further linear inequality in said solution set;
determining that said solution set including said further linear inequality is a bounded solution set;identifying a first event not being one of said plurality of correlation events, said first event having a third timestamp being defined by said second clock; and using said bounded solution set to determine a fourth timestamp from said third timestamp, said fourth timestamp being with respect to said first clock. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 15, 18)
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10. A system comprising:
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a first clock; a first communication mechanism configured to send and receive messages and include a timestamp on each of said messages using said first clock; a clock synchronization mechanism configured to synchronize a second clock from a second device with said first clock by a method comprising; identifying a plurality of said messages transmitted to said second device and received from said second device, said plurality of messages having a timestamp from said second clock; determining that a solution set for an expression of the differences between said first clock and said second clock is not bounded, the solution set defining one or more linear relationships between said first clock and said second clock based on said identified plurality of messages; in response to determining that said solution set is not bounded; identifying a further message involving said second device; calculating a further linear inequality for said further message; and including said further linear inequality in said solution set; determining that the solution set including said further linear inequality is a bounded solution set; and using said bounded solution set to estimate synchronization between said first clock and said second clock. - View Dependent Claims (11, 12, 16, 19)
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13. A computer storage device comprising computer executable instructions configured to perform a method comprising:
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reading a log file to identify a plurality of correlation events having an initiating timestamp and a receiving timestamp, said correlation events occurring between a first device having a first clock and a second device having a second clock, said plurality of correlation events comprising a first correlation event having said initiating timestamp created by said first device and a second correlation event having said receiving timestamp created by said second device; determining that a solution set for an expression of the differences between said first clock and said second clock is not bounded, the solution set defining a linear relationship between said first clock and said second clock based on said first and second correlation events; in response to determining that said solution set is not bounded; reading said log file to identify a further correlation event between said first device and said second device; calculating a further linear inequality based on said further correlation event; and including said further linear inequality in said solution set; determining that said solution set including said further linear inequality is a bounded solution set; and using said bounded solution set to estimate synchronization between said first clock and said second clock. - View Dependent Claims (14, 17, 20)
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Specification