Virata Corporation

Texas Instruments Corporation

Globespan Virata Corporation

Amati Communications Corporation

Debajyoti Pal

Chung-Li Lu

Sujai Chari

Christopher Taylor Hansen

Dirk Slock

The present invention, generally speaking, provides for cancellation of non-linear distortions within the echo path of a communications system by characterizing the nonlinearity, performing digital processing of a data signal to cause substantially the same nonlinearity to be applied to the data signal, and inputting a resulting data signal to a non-linear echo-cancellation path. In an exemplary embodiment, the non-linear echo-cancellation path includes as a nonlinear echo canceller a transversal filter or the like. A separate linear echo cancellation path is also provided. Training of the nonlinear echo canceller follows training of the linear echo canceller. This technique is particularly applicable to cancelling the effects of DAC nonlinearity, which can be readily characterized. Using this technique, cancellation improvement of about 3dB can readily be obtained. Alternatively, instead of achieving a lower residual echo floor, the linearity requirements for the transmit DAC can be relaxed. A lower number of bits of precision allows for lower DAC power consumption. The technique is particularly applicable to DSL applications.

Non-linear echo cancellation for wireless modems and the like

The present invention, generally speaking, accelerates convergence of a fast RLS adaptation algorithm by, following processing of a burst of data, performing postprocessing to remove the effects of prewindowing, fictitious data initialization, or both. This postprocessing is part of a burst mode adaptation strategy in which data (signals) get processed in chunks (bursts). Such a burst mode processing approach is applicable whenever the continuous adaptation of the filter is not possible (algorithmic complexity too high to run in real time) or not required (optimal filter setting varies only slowly with time). Postprocessing consists of a series of &ldquo;downdating&rdquo; operations (as opposed to updating) that in effect advance the beginning point of the data window. The beginning point is advanced beyond fictitious data used for initialization and beyond a prewindowing region. In other variations, downdating is applied to data within a prewindowing region only. The forgetting factor of conventional algorithms can be eliminated entirely. Performance equivalent to that of GWC RLS algorithms is achieved at substantially lower computational cost. In particular, a postprocessing Fast Kalman Algorithm in effect transforms an initialized/prewindowed least squares estimate into a Covariance Window least squares estimate. Various further refinements are possible. Initialization may be cancelled completely or only partially. For example, in order to reduce the dynamic range of algorithmic quantities, it may be advantageous to, in a subsequent initialization, add an increment to a forward error energy quantity calculated during a previous burst. Postprocessing may then be performed to cancel only the added increment. Also, to reduce the usual large startup error transient, the desired response data can be modified in a way that dampens the error transient. The modified desired response data are saved for use in later postprocessing. Furthermore, to allow for more rapid adaptation without the use of an exponential forgetting factor, a weighting factor less than one may be applied to the forward error energy quantity during initialization from one burst to the next. This allows for the most efficient use of data but limited adaptation within a burst, but more rapid adaptation from one burst to the next.

Initialization /prewindowing removal postprocessing for fast RLS filter adaptation

The present invention, generally speaking, provides a digitally-tunable, echo-cancelling analog front end (AFE) for wireline digital communications. The analog front end is especially useful in a High-bit-rate Digital Subscriber Line (HDSL) or HDSL environment. An analog echo simulation path is provided capable of simulating echo from a wide variety of echo paths. Digitally controlled attenuators are provided in the transmission path and in the analog echo simulation path. Also provided is a digital-tunable equalizer stage. The equalizer stage is tuned to match the characteristics of the receive path. The same arrangement may be adapted for various DSL technologies, i.e., xDSL. There results an analog front end that is well-adapted to high-speed wireline communications.

Digitally-tunable echo-cancelling analog front end for wireline communications devices

Improved techniques for time domain equalization are disclosed. The improved techniques include (i) improved time domain equalization techniques referred to as poly-path time domain equalization techniques; (ii) improved training methods for training transmitters and/or receivers of a data transmission system; and (iii) techniques for providing time domain equalization to a transmitter side of a data transmission system. These techniques are particularly suitable for time domain equalization in multicarrier modulation systems where channel shortening provided by time domain equalization is particularly needed.

Poly-path time domain equalization

A high speed, low power parallel multiplier is described. The parallel multiplier includes specialized hardware circuitry designed to perform complex multiplication operations at high speeds. The parallel multiplier requires significantly less die area than conventionally required, which results in reduced manufacturing costs and reduced power consumption.

Growing community of inventors

Fremont, CA, United States of America

Debajyoti Pal