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US 4,057,696 AGranted
Recursive-like adaptive echo canceller
AssigneeBell Telephone Laboratories, Incorporated
InventorsRichard Dennis Gitlin, John Stewart Thompson
Life of this patent
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AssigneeBell Telephone Laboratories, Incorporated
InventorsRichard Dennis Gitlin, John Stewart Thompson
Estimating the term…
The circuit complexity of a closed-loop echo cancellation system for use in a two-way communication circuit is reduced by employing a second adjustable signal processing network of the transversal type positioned in the control loop to emulate the characteristic of a recursive adjustable signal processing network. The two signal processing networks in the control loop are adjusted simultaneously to effect echo cancellation. The second signal processing network compensates for the effect of transmission poles in the echo return path and reduces the duration of the impulse response of the echo return path significantly so that the first signal processing network in the control loop is greatly simplified. A third signal processing network of the recursive type is adjusted in accordance with the internal settings of the second network to perform signal processing inverse to that of the second network. The recursive network is utilized to provide a clear signal path through the echo cancellation system which is essentially free of echo.
An echo canceller of the type having a transversal filter means for synthesizing from an input signal on a receiving signal path a replica signal to approximate an echo signal on a sending signal path for subtraction from the echo signal, means for subtracting the replica signal from the echo signal to produce a residual echo signal, said transversal filter means responsive to the residual echo signal for changing the replica signal to reduce the residual echo signal, said canceller further comprising first adaptive signal processing means responsive to the residual echo signal for modifying the echo signal on said sensing signal path before the subtraction, and second adaptive signal processing means coupled to receive the residual echo signal and responsive to said first adaptive processing means for providing an operation inverse to that of said first processing means to produce a clear sending signal essentially free of the echo signal.
Echo cancellation apparatus comprising:
In a closed loop, an adaptive echo cancellation system for use in a two-way communication system, the combination which comprises:
In an echo canceller of the type having a transversal filter means for synthesizing from an input signal on a receiving signal path a replica signal to approximate an echo signal on a sending signal path for subtraction from the echo signal, means for subtracting the replica signal from the echo signal to produce a residual echo signal, said transversal filter means responsive to the residual echo signal for changing the replica signal to reduce the residual echo signal, said canceller further comprising first adaptive signal processing means responsive to the residual echo signal for modifying the echo signal on said sending signal path before the subtraction, and second adaptive signal processing means coupled to receive the replica signal and responsive to said first adaptive processing means, said second adaptive processing means selectively altering the replica signal to make an altered replica signal suitable for subtraction directly from the echo signal, and subtracting means for combining the altered replica signal and the echo signal on said sending path to provide a clear sending signal essentially free of the echo signal.
In a closed loop, an adaptive echo cancellation system for use in a two-way communication system, the combination which comprises:
Dependencies are inferred from the claim text.