Supervisory audio tone detection in a radio channel
AssigneesAmerican Telephone and Telegraph Company, Bell Telephone Laboratories, Incorporated
InventorsRoss McPherson, Kenneth F. Smolik, David J. Thomson
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Abstract
Supervisory audio tones received from a mobile telephone unit are converted from analog to digital form. The tone is then converted to a complex number by bifurcating the tone path and multiplying one path by a sine function and the other path by a cosine function. The complex numbers are accumulated and the frequencies where significant power exists is found using the discrete Fourier transform. If the power at an assigned frequency exceeds a threshold, the corresponding supervisory audio tone is declared to have been detected.
Claims8
A method for detecting the presence of one of a plurality of supervisory audio tones (SAT) associated with a channel comprising the steps of
- (a) receiving said tone,
- (b) converting said tone from analog to digital form,
- (c) reducing spurious signals,
- (d) bifurcating said tone into first and second paths,
- (e) multiplying said tone in said first path by a cosine function and integrating over a predetermined time interval to obtain a real component of a complex number,
- (f) multiplying said tone in said second path by a sine function and integrating to obtain an imaginary component of said complex number,
- (g) repeating steps (a) through (f) over a number of sequential but not necessarily contiguous time intervals to obtain a plurality of said complex numbers,
- (h) finding a maximum absolute amplitude among a plurality of frequencies by performing a discrete Fourier transform on said complex numbers,
- (i) comparing said maximum amplitude with a threshold, and
- (j) declaring the presence of a SAT when said maximum amplitude exceeds said threshold.
Apparatus for detecting the presence of one of a plurality of supervisory audio tones (SAT) associated with a channel, said apparatus comprising
- means for receiving said tone,
- means for converting said tone from analog to digital form,
- means for reducing spurious signals,
- means for bifurcating said tone into first and second paths,
- means for multiplying said tone in said first path by a cosine function and summing over a predetermined number of samples at predetermined times to obtain a real component of a complex number,
- means for multiplying said tone in said second path by a sine function and concurrently summing to obtain an imaginary component of said complex number,
- the aforesaid means being operated repeatedly to obtain a sequence of said complex numbers,
- means for finding a maximum amplitude among a plurality of frequencies by performing a discrete Fourier transform on said complex numbers,
- means for comparing said maximum amplitude with a threshold, and
- means for delcaring the presence of a SAT when said maximum amplitude exceeds said threshold.
A method for detecting the presence of one of a plurality of supervisory audio tones (SAT) associated with each of a plurality of channels comprising the steps of
- (a) receiving said tones at each of a plurality of channel receivers concurrently,
- (b) sampling said tones in each of said receivers sequentially and repetitively,
- (c) converting each of said tones from analog-to-digital form,
- (d) reducing spurious signals,
- (e) bifurcating said tones into first and second paths,
- (f) multiplying said tones in said first path by a cosine function and integrating over a predetermined time interval to obtain a real component of a complex number,
- (g) multiplying said tones in said second path by a sine function and integrating to obtain an imaginary component of said complex number,
- (h) repeating steps (a) through (g) successively and consecutively for a predetermined number of times to obtain a plurality of said complex numbers for each of said channels,
- (i) finding a maximum absolute amplitude among a plurality of frequencies by performing a discrete Fourier transform on said complex numbers for each of said channels,
- (j) comparing said maximum amplitude with a threshold for each channel, and
- (k) declaring the presence of a SAT when said maximum amplitude exceeds said threshold for each channel.
Apparatus for detecting the presence of one of a plurality of supervisory audio tones (SAT) associated with each of a plurality of channels, said apparatus comprising
- a plurality of receiving means, each receiver means connected to one of said channels for receiving one of said tones thereat,
- means for sampling each of said tones from each of said receiver means sequentially and repetitively,
- means for converting each of said tones from analog-to-digital form,
- means for reducing spurious signals,
- means for bifurcating each of said tones into first and second paths,
- means for multiplying each of said tones in said first path by a cosine function and summing over a fixed number of samples to obtain a real component of a complex number,
- means for multiplying each of said tones in said second path by a sine function and summing to obtain an imaginary component of said complex number,
- said means being operated sequentially and repetitively to obtain a plurality of said complex numbers concurrently for each of said channels,
- means for finding a maximum amplitude among a plurality of frequencies by performing a discrete Fourier transform on said complex numbers for each of said channels,
- means for comparing said maximum amplitude with a threshold for each of said channels, and
- means for declaring the presence of a SAT when said maximum amplitude exceeds said threshold for a given channel.
Dependencies are inferred from the claim text.