Multiplex communications – Wide area network – Packet switching
Patent
1989-08-29
1991-05-07
Dwyer, James L.
Multiplex communications
Wide area network
Packet switching
379406, 379411, H04B 323
Patent
active
050142631
ABSTRACT:
Method and apparatus are disclosed which provide echo-cancellation in subscriber line audio-processing circuits (SLACs) and modulator-demodulators (modems). The echo-canceller provides a response independent of the amplitude of an error signal representing the difference between the desired and generated signal. The convergence of the echo-cancelling is not influenced by the size of the error signal but only by its sign. In a preferred embodiment, a cannonic signed digit filter coefficient updating technique is used for a digital filter (10) implementing the echo-cancellation function. A double-talker detector is advantageously used in conjunction with the echo-canceller. Detection of "double-talker" near-end signals inhibits updating of the echo-canceller filter coefficients. Near-end signals are detected by an energy-averaging filter (26) which selectively samples (28) low-pass filtered signals received by the adaptive filter as received from the far-end talker and low-pass filtered signals received from the near-end talker. Near-end speech or signal is detected if the latter signal exceeds a predetermined function of the former signal.
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McLeod Paul
Vairavan Kannan P.
Advanced Micro Devices , Inc.
Dwyer James L.
Shehata M.
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