System for biometric identity confirmation
A biometric identity confirmation system is based on both pulse wave shape data and spirometric data for the subject. During an initial enrollment mode, pulse wave shape and spirometric data for a known subject are used to generate subject characterization data for the known subject by computing an exemplar and selectively weighting portions of the exemplar based, for example, on repeatability or distinguishing characteristic features over the population of known subjects. During a subsequent identity authentication mode, pulse wave shape and spirometric data for a test subject are analyzed using the subject characterization data to confirm whether the identity of the test subject matches the known subject.
1. A method for biometric identity confirmation of a subject having a pulse and a respiratory cycle, said method comprising:
during an initial training mode, simultaneously acquiring pulse wave shape data and spirometric data from a known subject;
generating and storing subject characterization data for the known subject derived at least in part from both the pulse wave shape data and spirometric data for the known subject by:
(a) computing an exemplar from the pulse wave shape data and spirometric data for the known subject during the initial training mode; and
(b) selectively weighting portions of the exemplar; and
during a subsequent identity authentication mode, simultaneously acquiring pulse wave shape data and spirometric data from a test subject, and analyzing the pulse wave shape data and spirometric data with the subject characterization data for the known subject to confirm whether the identity of the test subject matches the known subject.
2. The method of claim 1 wherein portions of the exemplar are selectively weighted based on their repeatability among known subjects.
3. The method of claim 1 wherein portions of the exemplar are selectively weighted based on distinguishing characteristic features among known subjects.
4. The method of claim 1 wherein the exemplar is computed at least in part from the pulse wave shape data by synchronous averaging of multiple pulse cycles.
5. The method of claim 1 wherein the subject characterization data is derived at least in part from a first derivative of the pulse wave shape data with respect to time.
6. The method of claim 1 wherein the step of generating subject characterization data further comprises use of a second derivative of the pulse wave shape data with respect to time to identify pulse cycle start points for synchronous averaging of multiple pulse cycles to create an exemplar for the known subject.
7. The method of claim 6 wherein the second derivative of the pulse wave shape data is used to identity trigger candidates for the pulse cycle start point; and further comprising an analysis of a time delay between trigger candidates to thereby discard false trigger candidates and identify true trigger candidates for synchronous averaging of multiple pulse cycles.
8. The method of claim 1 wherein the step of generating subject characterization data further comprises:
computing an exemplar in the form of a parameter vector from the pulse wave shape data and spirometric data for the known subject;
computing a covariance matrix from the pulse wave shape data and spirometric data for the known subject;
computing an optimal composite parameter from the covariance matrix and parameter vector that is characteristic of the known subject; and
computing an authentication threshold corresponding to a desired true authentication probability for the known subject.
9. The method of claim 8 wherein the step of analyzing the pulse wave shape data and spirometric data with the subject characterization data for the known subject to confirm whether the identity of the test subject matches the known subject further comprises:
computing a deviation of the pulse wave shape data and spirometric data for the test subject from the exemplar for the known subject;
computing an optimal composite parameter from the deviation; and
confirming the identity of the test subject matches the known subject if optimal composite parameter is greater than the authentication threshold for the known subject.
10. The method of claim 1 wherein the step of generating subject characterization data further comprises:
computing an exemplar in the form of a parameter vector from the pulse wave shape data and spirometric data for the known subject;
computing a covariance matrix from the pulse wave shape data and spirometric data for the known subject; and
computing a probability distribution ratio of a weighted subject/impostor probability density by a Bayesian optimal decision analysis of the parameter vector, covariance matrix, and data from other subjects as potential impostors for the known subject.
11. The method of claim 10 wherein the step of analyzing the pulse wave shape data and spirometric data with the subject characterization data for the known subject to confirm whether the identity of the test subject matches the known subject further comprises:
computing a deviation of the pulse wave shape data and spirometric data for the test subject from the exemplar for the known subject;
computing a weighted subject/impostor probability density ratio for the deviation; and
confirming the identity of the test subject matches the known subject if the weighted subject/impostor probability density ratio is greater than zero.
12. A method of claim 1 wherein the step of generating subject characterization data for the known subject further comprises measurement of characteristic changes in the pulse wave shape data as a function of the phase of the respiratory cycle of the known subject.