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Title: System and method for constructing filters for detecting signals whose frequency content varies with time

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{2.pi..phi.(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 {.phi.'(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 .function., 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 functionmore » 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 .phi.'(t) which best fits the multivalued function f(t), a trajectory of the joint time-frequency domain representation of x(t). Integrating .phi.'(t) along t yields .phi.(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.« less
Inventors:
 [1];  [2]
  1. (Austin, TX)
  2. (Los Alamos, NM)
Issue Date:
OSTI Identifier:
870687
Assignee:
National Instruments Corporation (Austin, TX) LANL
Patent Number(s):
US 5574639
Contract Number:
W-7405-ENG-36
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM
Country of Publication:
United States
Language:
English
Subject:
method; constructing; filters; detecting; signals; frequency; content; varies; time; bank; detect; presence; novel; developing; templates; designed; match; received; matched; filter; compares; signal; respective; unique; template; approximate; form; robust; domain; assumed; cos; phi; trajectory; joint; time-frequency; representation; approximation; instantaneous; function; numerous; data; samples; collected; applied; represent; preferably; distribution; series; gabor; spectrogram; transformation; represents; analyzed; energy; three-dimensional; plot; vs; reduced; multivalued; dimensional; thresholding; process; curve; fitting; steps; performed; levenberg-marquardt; techniques; derive; fits; integrating; yields; inserted; equation; suitable; amplitude; determined; developed; version; received signal; instantaneous frequency; curve fitting; matched filters; frequency domain; frequency content; time domain; received signals; curve fit; frequency distribution; fitting technique; unique time; content varies; matched filter; /708/