US3721777A
Expired / Lapsed
US
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Echo path delay simulator for use with adaptive echo cancellers
Assignee: AT&T Inc
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Filing: 1971-11-26
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Granted: 1973-03-20
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Expires: 1991-11-26
Abstract
Abstract The echo path of a four-to-two wire junction is bridged by a variable delay device and an adaptive echo canceller connected in series. If the variable delay device is controlled so as to provide a delay to an incoming signal equal to the echo path delay, the number of taps required in the echo canceller can be reduced and the stability of the canceller thereby improved. To this end, a delay measuring circuit serves to form the crosscorrelation function between the incoming or echo generating signal and the echo. The point at which this cross-correlation function is first determined to be a maximum corresponds to the echo path delay. The determination is then used to control the variable delay device so as to achieve a delay therein substantially equal to the echo path delay.
Inventors
- 👤 E Thomas
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 16:11
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/23
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
91 words
Echo cancelling apparatus comprising a variable delay device and an adaptive echo canceller connected in series across the echo path of a four-to-two wire junction, means bridging the echo path and serving to form the cross-correlation function between an incoming signal to the same and its echo, means for determining the point at which the cross-correlation function is first a maximum, and means operative in response to the determination of the last-recited means to control the variable delay device to achieve a delay therein substantially equal to the echo path delay.
Claim 2
Dependent Claim
91 words
Echo cancelling apparatus comprising a variable delay device and an adaptive echo canceller connected in series across the echo path of a four-to-two wire junction, means bridging the echo path and serving to form the cross-correlation function between an incoming signal to the same and its echo, means for determining the point at which the cross-correlation function is first a maximum, and means operative in response to the determination of the last-recited means to control the variable delay device to achieve a delay therein substantially equal to the echo path delay.
Claim 3
Dependent Claim
95 words
In echo cancellation apparatus which includes a variable delay device and an adaptive echo canceller connected in series across the echo path of a four-to-two wire junction, said cancellation apparatus being characterized by means bridging the echo path and serving to form the cross-correlation function between an incoming signal to the echo path and its echo, means for determining the point at which the cross-correlation function is first a maximum, and means coupled to the determining means for controlling the variable delay device to achieve a delay therein substantially equal to the echo path delay.
Claim 4
Dependent Claim
95 words
In echo cancellation apparatus which includes a variable delay device and an adaptive echo canceller connected in series across the echo path of a four-to-two wire junction, said cancellation apparatus being characterized by means bridging the echo path and serving to form the cross-correlation function between an incoming signal to the echo path and its echo, means for determining the point at which the cross-correlation function is first a maximum, and means coupled to the determining means for controlling the variable delay device to achieve a delay therein substantially equal to the echo path delay.
Claim 5
Dependent Claim
156 words
In echo cancellation apparatus which includes a delay device and an adaptive echo canceller series coupled across the echo path of a four-to-two wire junction, said cancellation apparatus being characterized by means for measuring the delay between an input signal to the echo path and the return echo signal and producing a signal for controlling the delay of said delay device in accordance therewith, the delay measuring means comprising a tapped delay line, means coupling said input signal to the tapped delay line, said delay line having a plurality of output taps with a delay between successive taps of T seconds, means for respectively multiplying the signals at the respective delay line taps with the echo signal, means for respectively integrating the product signals of the multiplying means over a predetermined period of time, and comparison means for determining the maximum of the integrated product signals, said maximum corresponding to the delay in said echo path.
Claim 6
Dependent Claim
156 words
In echo cancellation apparatus which includes a delay device and an adaptive echo canceller series coupled across the echo path of a four-to-two wire junction, said cancellation apparatus being characterized by means for measuring the delay between an input signal to the echo path and the return echo signal and producing a signal for controlling the delay of said delay device in accordance therewith, the delay measuring means comprising a tapped delay line, means coupling said input signal to the tapped delay line, said delay line having a plurality of output taps with a delay between successive taps of T seconds, means for respectively multiplying the signals at the respective delay line taps with the echo signal, means for respectively integrating the product signals of the multiplying means over a predetermined period of time, and comparison means for determining the maximum of the integrated product signals, said maximum corresponding to the delay in said echo path.
Claim 7
Dependent Claim
37 words
Echo cancellation apparatus as defined in claim 3 including means operative in response to the aforementioned maximum determination to control said delay device so as to provide a delay therein substantially equal to the eCho path delay.
Claim 8
Dependent Claim
19 words
Echo cancellation apparatus as defined in claim 4 wherein the tap delay T is equal to the Nyquist interval.
Claim 9
Dependent Claim
21 words
Echo cancellation apparatus as defined in claim 5 wherein said delay measuring means is time-shared between a plurality of echo cancellers.
Claim 10
Independent Claim
85 words
A method for measuring the delay between the input signal x(t) to an echo path and the return echo signal y(t) comprising the steps of delaying the input signal in increments of T so as to produce the delayed replicas x(t-T), x(t-2T)...x(t-NT), multiplying each of the replicas with the echo y(t), integrating the respective product signals of the respective multiplications over a predetermined period of time, and determining the maximum of the integrated product signals, said maximum corresponding to the delay of said echo path.
Claim 11
Independent Claim
85 words
A method for measuring the delay between the input signal x(t) to an echo path and the return echo signal y(t) comprising the steps of delaying the input signal in increments of T so as to produce the delayed replicas x(t-T), x(t-2T)...x(t-NT), multiplying each of the replicas with the echo y(t), integrating the respective product signals of the respective multiplications over a predetermined period of time, and determining the maximum of the integrated product signals, said maximum corresponding to the delay of said echo path.
Claim 12
Dependent Claim
28 words
The method as defined in claim 7 wherein T is equal to the Nyquist interval of 1/2B where B is the bandwidth of the echo path in Hertz.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-03-19 | 1976-09-18 | 1977-03-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-03-19 | 1980-09-18 | 1981-03-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-03-19 | 1984-09-18 | 1985-03-20 | $7700.00 | Window Closed / Lapsed |