Equalization and decision-directed loops with trellis demodulation in high definition TV
First Claim
1. A method for processing a digital input signal with a receiver having a feed forward equalizer (FFE) with adjustable taps and a decision feedback equalizer (DFE), the method comprising:
- applying an input signal to the FFE to produce a first frequency compensated signal;
producing a second frequency compensated signal from the DFE;
combining the first and second signals to produce a third frequency compensated signal;
producing tentative decisions of the third signal based on the history of prior decisions;
applying the tentative decisions to the DFE;
producing an error signal representative of the difference between the tentative decisions and the third signal; and
adjusting the taps of the ffe responsive to the error signal so as to reduce the error signal;
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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
12 Claims
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1. A method for processing a digital input signal with a receiver having a feed forward equalizer (FFE) with adjustable taps and a decision feedback equalizer (DFE), the method comprising:
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applying an input signal to the FFE to produce a first frequency compensated signal;
producing a second frequency compensated signal from the DFE;
combining the first and second signals to produce a third frequency compensated signal;
producing tentative decisions of the third signal based on the history of prior decisions;
applying the tentative decisions to the DFE;
producing an error signal representative of the difference between the tentative decisions and the third signal; and
adjusting the taps of the ffe responsive to the error signal so as to reduce the error signal;
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification