Variable phase shifter for adaptive echo cancellers

Details Variable phase shifter for adaptive echo cancellers Variable phase shifter for adaptive echo cancellers

1976-10-04

1978-02-07

Claffy, Kathleen H.

H04B 324

Patent

active

040728307

ABSTRACT:
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.

REFERENCES:
patent: 3597541 (1971-08-01), Proakis et al.
patent: 3721777 (1973-03-01), Thomas
Demytko and Mackechnie, "A High Speed Digital Adaptive Echo Canceller," A.T.R. Australian Telecommunications Research, vol. 7, No. 1, 1973, pp. 20-28.

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