Pulse or digital communications – Systems using alternating or pulsating current – Antinoise or distortion
Reexamination Certificate
1998-01-12
2001-06-05
Chin, Stephen (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
Antinoise or distortion
C375S232000, C375S296000, C375S265000
Reexamination Certificate
active
06243425
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data communications equipment, e.g., modems, and, more particularly, to the equalization of data signals in a data communications system.
BACKGROUND OF THE INVENTION
Conventionally, a communications receiver employs an adaptive decision feedback equalizer (DFE) to compensate for changes in a communications channel. However, the use of a DFE introduces “error propagation” effects in the receiver. As such, it is known in the art to implement a precoder with modulo arithmetic (e.g., Tomlinson filter) in a remote transmitter in order to mitigate, if not eliminate, the problem of error propagation in the receiver This conventional precoder uses coefficient values generated by the receiver during an initialization phase, sometimes referred to as a training or a start-up phase.
However, if the response, i.e., characteristics, of the communications channel changes significantly, the precoder will fail to adequately compensate for the new communications channel. As a result, a disruptive retrain is usually required so that the receiver can generate a new set of precoder coefficients., which is then sent back to the transmitter. Unfortunately, each retrain disrupts the data flow and takes time to both calculate the equalizer coefficients and to communicate them back to the remote transmitter.
SUMMARY OF THE INVENTION
The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. The present invention provides an adaptive preceding system and method for preceding an input data signal to compensate for changes in a communications channel.
The adaptive precoding system and method of the present invention utilize a precoder filter and a converter. In accordance with the preferred embodiment of the present invention, the precoder filter is configured to maintain precoder values which may be used to precode input data signals prior to transmission on a communications channel. The converter is configured to receive equalizer coefficients periodically generated by a decision feedback equalizer and to slowly update each precoder value as conditions on the communications channel change.
As a result of slowly updating the precoder values, the quality of signals received by the decision feedback equalizer slowly improves. Accordingly, the decision feedback equalizer can update the equalizer coefficient values so that a disruptive retrain is not needed
The adaptive preceding system and method of the present invention have many advantages, a few of which are delineated hereafter, as examples.
An advantage of the adaptive precoding system and method is that they provide for a scheme of compensating for changes in a communications channel. Accordingly, more reliable communication can be established.
Another advantage of the adaptive precoding system and method is that they provide for a scheme of continuously updating precoder values as interference conditions on a communications channel change. Since interference typically vary in an unpredictable fashion, more reliable communication can be achieved.
Another advantage of the adaptive precoding system and method is that the precoding values may be updated without the occurrence of a disruptive retrain. This allows for more efficient data communication since retrains require time to implement.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings in the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention.
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Gut Richard
Langberg Ehud
Chin Stephen
Ghayour Mohammad
Globespan Technologies, Inc.
Thomas Kayden Horstemeyer & Risley
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