Patent US4529619A successfully refreshed from Google Patents.
Patent EP0589595A2 successfully refreshed from Google Patents.
EP0589595A2
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Method and apparatus for detecting a supervisory audio tone
Assignee: AT&T Inc
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Filing: 1993-09-09
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Granted: —
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Expires: 2013-09-09
Abstract
Abstract The presence of a supervisory audio tone signal (SAT), superimposed on a voice/data signal transmitted in a cellular telephone system, is carried out by first deleting (by 12,14,16,18,20,22) the voice/data signal, leaving only the SAT signal. Thereafter, the SAT signal power and noise power are determined (by 24,26,28,30,32,34; and 36,38,40,42, respectively). During intervals when the SAT signal rises and falls, the SAT noise power and signal power move in opposite directions. By comparing (in 44) the SAT noise power to the SAT signal power, a fast, accurate deterrnination can be made as to whether the SAT signal is present. <IMAGE>
Inventors
- 👤 Robert Chuenlin Wang
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 05:48
CPC Classifications
H; H04; H04W; H04W88/00; H04W88/08; H04B; H04B17/00; H04B17/30; H04B17/309; H04B17/346; H04B17/0082; H04B17/0085
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
93 words
A method for detecting the presence of a Supervisory Audio Tone (SAT) signal superimposed on a voice/data signal, which combined signal is periodically sampled, CHARACTERIZED BY the steps of: (a) deleting the voice/data signal from a sample containing the combined voice/data signal and SAT signal so that only the SAT signal remains; (b) determining the signal power of the SAT signal; (c) determining the noise power of the SAT signal; and (d) comparing the signal power to the noise power of the SAT signal to detect if the SAT signal is indeed present.
Claim 2
Dependent Claim
69 words
The method according to claim 1 CHARACTERIZED IN THAT the voice/data signal is deleted from the combined voice/data signal and SAT signal sample by the steps of: (a) shifting the combined voice/data signal and SAT signal sample to an approximate DC value; (b) low-pass filtering the approximate DC value; and (c) shifting the approximate DC value to a prescribed frequency depending on the original frequency of the SAT signal.
Claim 3
Dependent Claim
36 words
The method according to claim 2 CHARACTERIZED IN THAT the step of shifting the combined voice/data signal and SAT signal sample to an approximate DC value comprises the step of performing a complex mixing operation thereon.
Claim 4
Dependent Claim
27 words
The method according to claim 2 CHARACTERIZED IN THAT the low-pass filtering step is performed by performing at least one decimation operation on the approximate DC value.
Claim 5
Dependent Claim
23 words
The method according to claim 4 CHARACTERIZED IN THAT the low-pass filtering step is carried out by performing a pair of successive decimations.
Claim 6
Dependent Claim
59 words
The method according to claim 2 CHARACTERIZED IN THAT the step of determining the SAT signal power comprises the steps of: (a) low-pass filtering the frequency-shifted, approximate DC value; (b) squaring the low-pass-filtered, frequency-shifted, approximate DC value; and (c) subjecting the square of the low-passed-filtered, frequency-shifted DC value to a low-pass filtering operation by a an infinite-impulse-response low-pass filter.
Claim 7
Dependent Claim
86 words
The method according to claim 6 CHARACTERIZED IN THAT the step of determining the SAT noise power comprises the steps of: detecting the difference between first and second frequency-shifted, approximate DC values associated with first and second successive samples of the voice/data signal and SAT signal, respectively; determining the square of the difference between the first and second frequency-shifted approximate DC values; and subjecting the square of the difference between the first and second frequency-shifted approximate DC values to a finite-impulse-response and infinite-impulse-response low-pass filtering operation.
Claim 8
Independent Claim
98 words
A system for detecting the presence of a Supervisory Audio Tone (SAT) signal superimposed on a voice/data signal, which combined signal is periodically sampled, CHARACTERIZED BY: means (12,14,16,18,20,22) for deleting the voice/data signal from a sample of the combined voice/data signal and SAT signal so that only the SAT signal remains; means (24,26,28,30,32,34) for determining the signal power of the remaining SAT signal; means (36,38,40,42) for determining the noise power of the remaining SAT signal; and means (44) for comparing the SAT signal power to the SAT noise power to detect if the SAT signal is indeed present.
Claim 9
Dependent Claim
106 words
The apparatus according to claim 8 CHARACTERIZED IN THAT the means for deleting the voice/data signal from the combined voice/data signal and SAT signal sample comprises: a first complex mixer (12) for performing a first complex mixing operation on the combined voice/data signal and SAT signal sample to shift the sample to an approximate DC value decimating means (14,16,18,20) for low-pass filtering the approximate DC value produced by the complex mixer; and a second complex mixing means (22) for performing a second complex mixing operation on the low-pass-filtered, approximate DC value to shift the frequency thereof in accordance with the frequency of the incoming SAT signal.
Claim 10
Dependent Claim
58 words
The apparatus according to claim 9 wherein the means for determining the SAT signal power comprises: low-pass filtering means (24,26,28,30) for low-pass filtering the frequency-shifted, approximate DC value; means (32) for determining the square of the low-pass-filtered, frequency-shifted, approximate DC value; and an infinite-impulse response filter (34) for filtering the square of the low-pass-filtered, frequency-shifted, approximate DC value.
Claim 11
Dependent Claim
106 words
The apparatus according to claim 9 wherein the means for determining the SAT noise power comprises: means (36,38) for determining the difference between the first and second frequency-shifted, approximate DC values associated with first and second successive samples of the voice/data signal and SAT signal, respectively; means (40) for determining the square of the difference between the first and second frequency-shifted, approximate DC values associated with successive combined voice/data signal and SAT signal samples; and an infinite-impulse and finite-impulse response filter (42) for filtering the square of the difference between the low-pass-filtered, frequency-shifted, approximate DC values associated with successive combined voice/data signal and SAT signal samples.
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