Technique for minimizing decision feedback equalizer wordlength in the presence of a DC component
First Claim
1. A method for improving the quality of a digital signal evaluated by a digital decision circuit that produces an output signal and an error signal, the digital signal including a pilot for carrier recovery, the method comprising:
- applying the digital signal to a feed forward filter (FFF) to produce a partially compensated signal;
applying the output signal to a decision feedback filter (DFF);
adjusting coefficients of the DFF responsive to the error signal;
adjusting coefficients of the FFF responsive to the error signal;
forming a DC offset signal representative of the coefficients of the DFF;
modifying the DC offset signal with a signal representative of the pilot;
forming a feedback signal by combining the output of the DFF and the modified DC offset signal; and
combining the feedback signal and the partially compensated signal to form an input signal; and
applying the input signal to the decision circuit.
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Accused Products
Abstract
A system for reducing the complexity of an adaptive decision feedback equalizer, for use in connection with a dual-mode QAM/VSB receiver system is disclosed. QAM and VSB symbols, which are expressed in two'"'"'s compliment notation, include an extra bit required to compensate for a fixed offset term introduced by the two'"'"'s compliment numbering system. A decision feedback equalizer includes a decision feedback filter section which operates on symbolic decisions represented by a wordlength which excludes the added bit representing the offset. The vestigal word is convolved with the decision feedback filter'"'"'s coefficients, while a DC component, corresponding to the excluded bit, is convolved with the same coefficient values in a correction filter. The two values are summed to provide an ISI compensation signal at the input of a decision device such as a slicer. A DC component representing a pilot tone in VSB transmission systems also introduces a DC component, and additional bits, to a VSB wordlength. These additional bits are similarly excluded and the vestigal representation convolved with coefficient values in a decision feedback filter. The DC component, including the pilot tone representation, is convolved with the same coefficient values in a correction filter.
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Citations
3 Claims
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1. A method for improving the quality of a digital signal evaluated by a digital decision circuit that produces an output signal and an error signal, the digital signal including a pilot for carrier recovery, the method comprising:
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applying the digital signal to a feed forward filter (FFF) to produce a partially compensated signal;
applying the output signal to a decision feedback filter (DFF);
adjusting coefficients of the DFF responsive to the error signal;
adjusting coefficients of the FFF responsive to the error signal;
forming a DC offset signal representative of the coefficients of the DFF;
modifying the DC offset signal with a signal representative of the pilot;
forming a feedback signal by combining the output of the DFF and the modified DC offset signal; and
combining the feedback signal and the partially compensated signal to form an input signal; and
applying the input signal to the decision circuit. - View Dependent Claims (2, 3)
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Specification