Equalization and decision-directed loops with trellis demodulation in high definition TV
First Claim
1. In a digital receiver,a feedforward equalizer (FFE) adapted to process a digital input signal, the FFE having a plurality of adjustable taps that control its frequency response;
- a trellis decoder adapted to produce tentative evaluations of the processed input signal and an FFE error signal;
a decision feedback equalizer (DFE) adapted to process the tentative evaluations;
means for coupling the trellis decoder to the DFE to process the tentative evaluations;
means for coupling a combination of the outputs from the FFE and the DFE to the trellis decoder; and
means responsive to the FFE error signal from the trellis decoder for adjusting the taps of the FFE to reduce the error.
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Accused Products
Abstract
Improved decision feedback equalizer and decision directed timing recovery systems and methods suitable for use in connection with a dual mode QAM/VSB receiver system are disclosed. A trellis decoder operates in conjunction with a decision feedback equalizer circuit on trellis coded 8-VSB modulated signals. The trellis decoder includes a 4-state traceback memory circuit outputting a maximum likelihood decision as well as a number of intermediate decisions based upon the maximum likelihood sequence path. Any number of decisions, along the sequence, may be provided as an input signal to timing recovery system loops, with the particular decision along the sequence chosen on the basis of its delay through the trellis decoder. Variable delay circuitry is coupled to the other input of the timing recovery system loops in order to ensure that both input signals bear the same timestamp. Final decisions are output from the trellis decoder to a DFE in order to enhance the DFE'"'"'s ability to operate in low SNR environments. A decision sequence estimation error signal is also generated and used to drive the tap updates of both the DFE and an FFE portion of the equalizer.
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Citations
9 Claims
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1. In a digital receiver,
a feedforward equalizer (FFE) adapted to process a digital input signal, the FFE having a plurality of adjustable taps that control its frequency response; -
a trellis decoder adapted to produce tentative evaluations of the processed input signal and an FFE error signal;
a decision feedback equalizer (DFE) adapted to process the tentative evaluations;
means for coupling the trellis decoder to the DFE to process the tentative evaluations;
means for coupling a combination of the outputs from the FFE and the DFE to the trellis decoder; and
means responsive to the FFE error signal from the trellis decoder for adjusting the taps of the FFE to reduce the error. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification