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US 2003/0012358 A1Published application
Tone detection
AssigneeAdaptive Digital Technologies
InventorsScott David Kurtz, Brian Michael McCarthy SR.
Life of this patent
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Abstract
A DFT is used to compute the magnitude and phase of the frequencies desired to be detected in a frame of sampled data by performing 2 dot products for each such frequency. The two dot products are calculated using the samples in the frame and an equal number of equally spaced cosine and sine coefficients for each frequency to be detected.
Claims7
A method for determining whether any of a predetermined set of tones present in a plurality of successive frames of digital samples of a received signal falls within a predetermined frequency tolerance, comprising the steps of:
- obtaining discrete Fourier transform pairs of in-phase and quadrature dot products of said samples and integer multiples of a base frequency;
- determining the phase angle for the highest power ones of said products obtained on successive frames;
- and
- subtracting an offset phase from the phase angle of said highest power ones of said products to determine the deviation of an observed tone from said predetermined frequency tolerance.
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Dependencies are inferred from the claim text.