Apparatus and robust method for detecting tones
First Claim
1. A method for detecting one or more tones being received in a communications channel comprising the steps of:
- applying a single discrete prolate spheroidal sequence (DPSS) taper to a prescribed portion of a signal received in said communications channel to produce a tapered version of said signal;
performing a plurality of Fourier transforms for each of a plurality of expected tones, a separate Fourier transform being performed at each of a corresponding plurality of prescribed frequencies related in a prescribed fashion to a nominal frequency of an expected tone of said tapered version of said received signal;
utilizing results of said Fourier transforms to obtain a frequency domain representation of energy for at least one of said plurality of expected tones;
obtaining a time domain representation of energy in said prescribed portion of said received signal; and
using said time domain representation of energy and said frequency domain representation of energy to determine whether at least one valid tone has been received.
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Accused Products
Abstract
A robust tone detector is realized by applying a single taper, which provides a relatively narrow bandwidth filter, to a received signal and, then, performing a Discrete Fourier Transform of the tapered signal. The result of the Fourier transform is used to obtain an estimate of energy in the frequency domain of the expected tone. A prescribed selection algorithm based on the relationship of the received signal energy in the time domain and the energy estimate in the frequency domain is used to determine whether a valid tone has been received. Robustness of the tone detector is improved by performing a plurality of Discrete Fourier Transforms of the single tapered version of the received signal at a corresponding plurality of frequencies relative to the nominal frequency of an expected one or more tones. A further improvement in the tone detector is obtained by the dynamically adjusting tone acceptance thresholds based on a measure of channel impairments.
56 Citations
26 Claims
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1. A method for detecting one or more tones being received in a communications channel comprising the steps of:
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applying a single discrete prolate spheroidal sequence (DPSS) taper to a prescribed portion of a signal received in said communications channel to produce a tapered version of said signal; performing a plurality of Fourier transforms for each of a plurality of expected tones, a separate Fourier transform being performed at each of a corresponding plurality of prescribed frequencies related in a prescribed fashion to a nominal frequency of an expected tone of said tapered version of said received signal; utilizing results of said Fourier transforms to obtain a frequency domain representation of energy for at least one of said plurality of expected tones; obtaining a time domain representation of energy in said prescribed portion of said received signal; and using said time domain representation of energy and said frequency domain representation of energy to determine whether at least one valid tone has been received. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. Apparatus for detecting one or more tones being received in a communications channel comprising:
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means for applying a single discrete prolate spheroidal sequence (DPSS) taper to a prescribed portion of a signal received in said communications channel to produce a tapered version of said signal; means for performing a plurality of Fourier transforms for each of a plurality of expected tones, a separate Fourier transform being performed at each of a corresponding plurality of prescribed frequencies related in a prescribed fashion to a nominal frequency of an expected tone of said tapered version of said received signal; means for utilizing results of said Fourier transforms to obtain a frequency domain representation of energy for at least one of said plurality of expected tones; means for obtaining a time domain representation of energy in said prescribed portion of said received signal; and means for using said time domain representation of energy and said frequency domain representation of energy to determine whether at least one valid tone has been received. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification