Apparatus and robust method for detecting tones

Details Apparatus and robust method for detecting tones Apparatus and robust method for detecting tones

1992-03-23

1994-06-28

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Signal receiver

379283, H04M 300

Patent

active

053254279

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.

REFERENCES:
patent: 4833399 (1989-05-01), So
patent: 4990848 (1991-02-01), So
"A New Digital DTMF Receiver" by V. K. Jain pp. 189-195.
"Digital MF Receiver Using Discrete Fourier Transform" by Ivan Koval & George Gara, pp. 1337-1335.
"Prolate Spheroidal Wave Functions, Fourier Analysis, and Uncertainty--V: The Discrete Case", D. Slepian, The Bell System Technical Journal, vol. 57, No. 5, May 1978, pp. 1371-1430.

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