3com Corporation

Alexandre L Leonidov

Vladimir G Parizhsky

Ying Wu

Vitali Vinokour

Benjamin Dolnik

Methods and systems pertaining to preventing the corruption of filter coefficients due to near end speech in an echo canceller that uses an adaptive filter to create a local replica of an echo signal are provided. In accordance with a preferred method, a far end signal is received and the presence of near end speech is indicated. A filter coefficient vector is updated, and copies of the filter coefficient vector are periodically stored. A stored copy of the filter coefficient vector is recovered for use in the echo canceller. Further, an improved echo canceller that prevents the corruption of filter coefficients due to near end speech, having a near end speech indicator, a first buffer, a filter, and a second buffer connected to the filter, is provided. The first buffer receives a far end signal. The filter is responsive to the first buffer and the near end speech indicator. The filter includes a filter coefficient vector generator, wherein the generator generates, updates, and provides copies of filter coefficient vectors. The second buffer is connected to the filter and stores the copies of the filter coefficient vectors for restoration to the filter.

Echo canceller having improved noise immunity

Methods and systems pertaining to estimating and compensating for a round-trip or flat delay portion of an echo channel characteristic in an echo canceller are provided. According to a particular method, a filter coefficient vector of an adaptive filter that models the echo channel characteristic is updated. An instant flat delay is estimated by analyzing the filter coefficient vector after each update, and periodic averages of the instant flat delay estimate are performed. A final flat delay estimate average is determined when the flat delay estimate average has converged. The length of the adaptive filter is adjusted in response to the final flat delay estimate average. Further, an improved echo canceller apparatus that compensates for a flat delay portion of an echo channel characteristic is provided. The improved echo canceller includes an adaptive filter, a position detector, a periodic averager, and a level detector. The adaptive filter has an initial length N. The position detector is connected to the adaptive filter and locates the position of the maximum valued filter tap. The periodic averager is connected to the position detector and provides an average of the location position. The level detector responsive to the periodic averager provides a flat delay estimate, D. The adaptive filter shortens from the initial length N to a length N&minus;D, responsively to the flat delay estimate.

Round trip delay estimator and compensator for the echo canceller

Disclosed is an apparatus and method for low complexity, phase independent reception of FSK signals. A finite series of delay elements produces a plurality of equidistant samples of a received FSK signal. The plurality of equidistant samples is processed by an arithmetic unit using a phase independent algorithm to obtain an estimate of the received signal. The estimate of the received signal is then compared to a threshold value to determine if the estimate corresponds to a binary 1 or binary 0, which increments a counter corresponding to each binary value. Multiple estimates are counted over a baud interval of the received FSK signal and a binary 1 or binary 0 is output as a received data signal value depending upon which binary value the counter having the higher value corresponds to.

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Skokie, IL, United States of America

Alexandre L Leonidov