Conexant Systems, Inc.

Pctel, Inc.

Rockwell Semiconductor Systems, Inc.

Elias Bjarnason

Sverrir Olafsson

Olafur Orn Jonsson

Ragnar Hlynur Jonsson

Adeline Tracz

A pulse code modulation (PCM) modem system employs a relatively white training signal to optimize the adaptive filter coefficients in the receiver equalizers. During the training mode, any line coding or equivalent spectral shaping is disabled to provide a training signal sequence having a substantially even spectral content. The presence of DC within the training signal reduces the likelihood that the error function of the equalizers will settle at a local minimum. Following the training interval, the encoder enables the line coder to condition the digital input sequences, introduce DC nulls, and reduce the detrimental effects of baseline wander.

Method and apparatus for training linear equalizers in a PCM modem

A full duplex speaker-phone that performs adaptive filtering to provide increased loop stability between users of the speaker-phone. The invention employs a sliding filter that performs adaptive frequency dependent attenuation of the speech signals within a speaker-phone. By detecting the mode of operation of the speaker-phone in real time, the speaker-phone performs adaptive filtering to ensure a high perceptual quality for the users of the speaker-phone. The sliding filtering is performed using a sliding low pass filter (LPF) in certain embodiments of the invention. Perceptually, the speaker-phone does not surrender the appearance of a full duplex speaker-phone from the perspective of the users. In addition, by performing frequency dependent filtering of the speech signals, the speaker-phone offers improved stability in the speaker-phone loop and reduces residual echoes significantly over conventional technology employed in speaker-phones. The sliding filter built in accordance with the present invention is easily implemented, having computational load and memory requirements that are negligible when compared with traditional systems that try to perform filtering in speaker-phones. In certain embodiments of the invention, the attenuation of the speech signals within the speaker-phone are concentrated at higher frequencies.

Full duplex speaker-phone providing increased loop stability

A tone predictor may be employed in a modem system to cancel periodic interference components present in a received signal. The tone predictor may be implemented in a receiver arrangement to cancel such periodic interference and to condition a decision error signal utilized to update the adaptive equalizers. The tone predictor may also be implemented in an echo canceler arrangement to cancel such periodic interference and to condition the error signal used to update the echo canceler filter. The tone predictor includes a delay element, configured to decouple the periodic interference component from other noise components, and an adaptive filter structure configured to generate a periodic interference estimate.

Method and apparatus for canceling periodic interference signals in a digital data communication system

A preferred timing recovery scheme is particularly suitable for a high speed digital data communication system that employs T-spaced equalization in the receiving device, where echo cancellation occurs after equalization. The timing recovery technique is based upon an analysis of the impulse response of the equalizer structure (e.g., a structure having a feedforward equalizer and a decision feedback equalizer). The filter tap coefficients of the equalizer elements are analyzed and the sampling phase is adjusted such that a cost function associated with the performance of the equalizer structure is substantially optimized. The sampling phase of the receiver is adjusted in response to a control signal generated as a result of the timing recovery techniques.

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Reykjavik, Iceland

Elias Bjarnason