Methods and apparatus for feature recognition time shift correlation

A method of correlation, the method comprising the steps of:

• searching for transitions of cycle periods in an input data stream including a number of subsections to determine a transition time for each of the subsections;
• identifying a feature in the input data stream;
• storing a starting time associated with the identified feature;
• calculating a first offset between the stored starting time and a nearest earlier determined transition time;
• calculating a second offset between the nearest earlier determined transition time and a boundary of the input data stream;
• comparing the calculated first offset with a set of valid offset values for the identified feature to identify the subsection in which the feature is located;
• and
• subtracting the second offset from a known offset between a transition time for the identified subsection and a boundary of a reference data sequence;
• wherein the result of the subtraction determines an amount that the input data stream must be time-shifted to achieve correlation with the reference data sequence.

A correlator, comprising:

• a start feature state machine that identifies a feature in an input data stream and determines a start time relative to a boundary of the input data stream when the feature is identified;
• an end feature state machine that determines an end time when the identified feature is next repeated in the input data stream;
• an interval subtractor that subtracts the start time from the end time to define an interval for the identified feature;
• memory including a set of stored valid interval values for the identified feature and a set of reference start times relative to a boundary of a reference data sequence, each reference time corresponding to a respective one of the stored valid interval times for the identified feature;
• a feature interval state machine that validates the interval produced by the interval subtractor for the identified feature by comparing the interval with each of the valid interval values for the identified feature stored in the memory;
• and
• a position subtractor that calculates the difference between the start time relative to the boundary of the input data stream and a reference time corresponding to a valid interval value that matches the interval produced by the interval subtractor;
• wherein the calculated difference determines an amount that the input data stream must be time-shifted to achieve correlation with the reference data sequence.