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US 4,072,830 AGranted
Variable phase shifter for adaptive echo cancellers
AssigneeBell Telephone Laboratories, Incorporated
InventorsRichard D. Gitlin, John S. Thompson
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AssigneeBell Telephone Laboratories, Incorporated
InventorsRichard D. Gitlin, John S. Thompson
Estimating the term…
The echo path of an echo signal subjected to a time-varying phase shift is bridged by echo cancelling apparatus including a variable phase shifter and an adaptive echo canceller connected in series. The variable phase shifter includes an adaptive control loop whose operation is compatible with that of an adaptive echo canceller. The phase-shifter control loop derives a control signal from the output signal synthesized by the echo cancelling apparatus and the residual echo produced by subtracting this output signal from the echo path signal. The control signal is used to produce a variable phase shift on the signal passing through the variable phase shifter in the echo cancelling apparatus. The echo canceller adaptively synthesizes a replica of the echo signal produced by the linear dispersive portion of the echo channel, while the variable phase shifter is adapted to impart a time-varying phase shift corresponding to the time-varying phase shift encountered by the echo signal in the echo path. The echo cancelling apparatus is therefore able to produce an output signal which closely approximates the echo signal including the time-varying phase shift for more effective echo cancellation.
Echo cancelling apparatus comprising a variable phase shifter and an adaptive echo canceller connected in series and forming a shunt signal path across an echo path containing an echo signal which includes a time-varying phase shift, said shunt path producing an output signal formed by the serial signal processing of said phase shifter and said canceller, subtracting means for producing a residual echo as the difference between the output signal and the echo signal, said canceller responsive to the residual echo by changing the output signal to reduce the residual echo, and said phase shifter responsive to the residual echo and the output signal for producing a time-varying phase shift in the output signal corresponding to the time-varying phase shift of the cho signal to minimize the residual echo signal.
Echo cancelling apparatus comprising a variable phase shifter and an adaptive echo canceller connected in series to provide a shunt signal path between two one-way signal paths having one of said two paths containing an echo signal subjected to a time-varying phase shift, said canceller processing the original signal which produces the returned echo signal to provide a replica of the echo signal absent the time-varying phase shift as one component of the composite output signal of said shunt path for subtraction from the echo signal including the time-varying phase shift, said canceller responsive to the residual echo resulting from the subtraction for changing the replica to reduce the residual echo, and said variable phase shifter responsive to the residual echo signal and the output signal for producing a time-varying phase shift in the composite output signal so that the residual echo is minimized.
In echo cancellation apparatus which includes an adaptive echo canceller coupled across the echo path of a four-to-two wire junction wherein the echo path introduces a time-varying phase shift component on the echo signal, said cancellation apparatus being characterized by variable phase shifting means connected serially in circuit with said echo canceller for synthesizing an output signal which is a composite duplicate of the echo signal including the time-varying phase shift signal component by the serial signal processing of said echo canceller and said variable phase shifting means, means for producing a residual echo by subtracting the output signal from the echo signal, said canceller being responsive to the residual echo by modifying the output signal to reduce the residual echo, and said variable phase shifting means including controlling means responsive to the output signal and the residual echo for adapting the phase of said variable phase shifting means to impart a time-varying phase shift to the output signal corresponding to the phase shift component of the echo signal to minimize the residual echo.
Dependencies are inferred from the claim text.