Kokusai Denshin Denwa Co., Ltd.

Fumiaki Sugaya

Youtaro Yatsuzuka

Yotaro Yatsuzuka

Parallel multi-value neural networks

In an echo canceller used in a four-wire digital telephone circuit, a main echo estimator (21) and a sub echo estimator (22) are coupled with a receive path for measuring a receive signal, and subtracters (25, 26) are inserted in a transmit path for cancelling an echo component in a transmit signal. Filter coefficients in said estimators (21, 22) are adaptively controlled by a convergence control processor (24). The main echo estimator has a small step gain for updating filter coefficients so that the response to an echo is slow, while the sub echo estimator (22) has a large step gain and quick response for an echo. An register accumulator (23) is provided so that the filter coefficients by the sub echo estimator (22) are selectively accumulated on the related filter coefficients in the main echo estimator (21) according to operation modes, ordinary mode, accumulating mode, and reset mode. In an ordinary mode, said two echo estimators (21, 22) operate independently from each other, updating the filter coefficients. In an accumulating mode, when an echo output of the second subtracter (26) is lower than that of the first subtracter (25), and the filter coefficients in the sub echo estimator (22) converge, the filter coefficients in the sub echo estimator (22) are accumulated on the related ones in the main echo estimator (21), respectively, and after reset of the coefficients in the sub echo estimator (22), the mode is then switched to the ordinary mode. When the filter coefficients in the sub echo estimator (22) diverge, or echo output of the second subtracter (26) is larger than that of the first subtracter (25), the sub echo estimator (22) is reset, and then, the mode is switched to the ordinary mode.

Echo canceller

In an echo canceller having PCM interfaces used in a PCM telephone circuit, an echo estimator (65) is coupled with a receive path through a linear code converter (632) for measuring a linear receive input signal, and a subtracter (7) is inserted after a linear code converter (631) in a transmit path for cancelling an echo component in a linear transmit input signal. The same procedure as that in a conventional echo canceller is performed in a divergent situation in the echo estimator (65) in which a large step gain is assigned, and in a convergent situation in the echo estimator (65) in which a relatively small step gain is assigned, a non-linear quantization processor (27,271) is inserted between the subtracter (7) and the echo estimator (65). The non-linear quantization processor (27,271) produces a new echo estimate containing a quantization noise, based on an echo estimate which is derived from the echo estimator (65). The new echo estimate can cancel not only the echo but also the quantization noise in the linear transmit input signal. The echo canceller having the non-linear quantization processor (27,271) can achieve a high echo return loss enhancement even for a multi-linked PCM channel.

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Tokyo, Japan

Fumiaki Sugaya