System and method for constructing filters for detecting signals whose frequency content varies with time
First Claim
1. A method for constructing one or more filters to detect signals having a frequency content which varies with time, comprising the steps of:
- collecting data regarding the signals;
computing a joint time-frequency representation of the signals;
mapping the joint time-frequency representation to a multi-valued function;
curve-fitting the multi-valued function to derive an instantaneous frequency function φ
'"'"'(t);
integrating the instantaneous frequency function φ
'"'"'(t) to obtain φ
(t);
determining a time template equation using said function φ
(t);
constructing one or more filters which receive the signals and compare the signals with one or more terms of said time template equation, wherein said one or more filters detect the signals.
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Abstract
A system and method for constructing a bank of filters which detect the presence of signals whose frequency content varies with time. The present invention includes a novel system and method for developing one or more time templates designed to match the received signals of interest and the bank of matched filters use the one or more time templates to detect the received signals. Each matched filter compares the received signal x(t) with a respective, unique time template that has been designed to approximate a form of the signals of interest. The robust time domain template is assumed to be of the order of w(t)=A(t)cos{2πφ(t)} and the present invention uses the trajectory of a joint time-frequency representation of x(t) as an approximation of the instantaneous frequency function {φ'"'"'(t). First, numerous data samples of the received signal x(t) are collected. A joint time frequency representation is then applied to represent the signal, preferably using the time frequency distribution series (also known as the Gabor spectrogram). The joint time-frequency transformation represents the analyzed signal energy at time t and frequency ƒ, P(t,f), which is a three-dimensional plot of time vs. frequency vs. signal energy. Then P(t,f) is reduced to a multivalued function f(t), a two dimensional plot of time vs. frequency, using a thresholding process. Curve fitting steps are then performed on the time/frequency plot, preferably using Levenberg-Marquardt curve fitting techniques, to derive a general instantaneous frequency function φ'"'"'(t) which best fits the multivalued function f(t), a trajectory of the joint time-frequency domain representation of x(t). Integrating φ'"'"'(t) along t yields φ(t), which is then inserted into the form of the time template equation. A suitable amplitude A(t) is also preferably determined. Once the time template has been determined, one or more filters are developed which each use a version or form of the time template.
36 Citations
35 Claims
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1. A method for constructing one or more filters to detect signals having a frequency content which varies with time, comprising the steps of:
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collecting data regarding the signals; computing a joint time-frequency representation of the signals; mapping the joint time-frequency representation to a multi-valued function; curve-fitting the multi-valued function to derive an instantaneous frequency function φ
'"'"'(t);integrating the instantaneous frequency function φ
'"'"'(t) to obtain φ
(t);determining a time template equation using said function φ
(t);constructing one or more filters which receive the signals and compare the signals with one or more terms of said time template equation, wherein said one or more filters detect the signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for constructing one or more filters to detect signals having a frequency content which varies with time, comprising the steps of:
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collecting data regarding the signals; computing a joint time-frequency representation of the signals; calculating an instantaneous frequency function φ
'"'"'(t) using said joint time-frequency representation of the signals;integrating the instantaneous frequency function φ
'"'"'(t) to obtain φ
(t);determining a time template equation using said function φ
(t);constructing one or more filters which receive the signals and compare the signals with one or more forms of said time template equation, wherein said one or more filters detect the signals. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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Specification