Network echo canceller
Patent 5307405 Issued on April 26, 1994. Estimated Expiration Date: 
September 25, 2012. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
September 25, 2012. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent ReferencesLinear predictive echo canceller integrated with RELP vocoder Process for determining an echo path flat delay and echo canceler using said process Echo cancellation in two-wire transmission path repeaters Patent #: 4782525 InventorApplicationNo. 951074 filed on 09/25/1992US Classes:379/406.08, Adaptive filtering370/290, Using a particular adaptive filter379/345, Including two-to-four wire conversion or hybrid circuit379/406.04Disable or inhibit functionExaminersPrimary: Dwyer, James L.Assistant: Fournier, Paul A. Attorney, Agent or FirmInternational ClassH04M 001/00AbstractAn echo canceller and method for cancelling in a return channel signal an echoed receive channel signal where the echoed receive channel signal is combined by an echo channel with an input return channel signal. The echo canceller has a first filter which generates first filter coefficients, generates a first echo estimate signal with the first filter coefficients, and updates the first filter coefficients in response to a first filter control signal. A first summer subtracts the first echo estimate signal from a combined return channel and echo receive channel signal to generate a first echo residual signal. A second filter generates second filter coefficients, generates a second echo estimate signal with the second filter coefficients, and updates the second filter coefficients in response to a second filter control signal. A second summer subtracts the second echo estimate signal from the combined signal to generate a second echo residual signal, and provides upon the return channel the second echo residual signal. A control unit determines from the receive channel signal, the combined signal, and the first and second echo residual signals, one of a plurality of control states wherein a first control state is indicative of a receive channel signal above a first predetermined energy level, wherein when the control unit is in the first control state it generates the first control signal and generates the second control signal when at least one of a first energy ratio of the first echo residual signal and the combined signal and a second energy ratio of the second echo residual signal and the combined signal exceed a predetermined level.Other References
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