HDTV channel equalizer

• US 6,816,548 B1
• Filed: 06/23/1998
• Issued: 11/09/2004
• Est. Priority Date: 06/23/1998
• Status: Expired due to Term

• Current Assignee: Thomson Licensing Dtv
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: Ramaswamy, Kumar, Knutson, Paul Gothard, Shiue, Dong-Chang
• Primary Examiner(s): Ha, Dac V.
• Application Number:
  US09/102,885
• Time in Patent Office: 2,331 Days
• Field of Search: 375/233, 375/321, 375/350, 360/65, 348/726, 455/47, 455/204
• US Class Current: 375/233
• CPC Class Codes: H04N 5/211 Ghost signal cancellation H04N23/81 takes precedence

Abstract

An adaptive channel equalizer (50) for processing a demodulated VSB signal containing terrestrial broadcast high definition television information includes an adaptive feed forward filter (FFF 20) and an adaptive decision feedback filter (DFF 30). The equalizer is preceded by a demodulator/carrier recovery network (18) and does not include a carrier recovery function in the equalizer control loop. The equalizer FFF and DFF elements operate adaptively in blind, training, and decision-directed modes. A direct connection provided from the equalizer output to the DFF facilitates coarse signal acquisition and equalization during the blind operating mode.

Claims

1. A system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition video information represented by a VSB constellation of symbols and subject to exhibiting unwanted perturbations, comprising:

a demodulator responsive to said received VSB modulated signal for producing a baseband demodulated signal; and

an adaptive equalizer having an input for receiving said baseband demodulated signal and an output at which an equalized baseband signal is produced, said adaptive equalizer including

(a) an adaptive feed forward filter (FFF) for equalizing said demodulated signal, said FFF exhibiting (1) linear, non-decision directed blind operation in a first operating mode, and (2) decision-directed operation in a subsequent second operating mode; and

(b) an adaptive decision feedback filter (DFF) for equalizing said demodulated signal, said DFF exhibiting (1) linear, non-decision directed blind operation in said first operating mode, and (2) non-linear decision-directed operation in said second operating mode.

2. A system according to claim 1, wherein

said demodulator includes a carrier recovery network; and

said FFF and said DFF do not perform carrier derotation.

3. A system according to claim 1, wherein

said signal input of said DFF is directly connected to said equalized signal at said equalizer output during said blind operation in said first mode.

4. A system according to claim 3, wherein

said signal input of said DFF receives a slicer output signal during said decision-directed operation in said second mode.

5. A system according to claim 1, wherein

said feed forward filter and said decision feedback filter operate at a symbol rate, on-line in real time.

6. A system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition video data represented by a VSB constellation of symbols and subject to exhibiting unwanted perturbations, said data having a data frame format constituted by a succession of data frames comprising a field sync component prefacing a plurality of data segments having an associated segment sync component, comprising:

a demodulator responsive to said received VSB modulated signal for producing a baseband demodulated signal; and

an adaptive equalizer having an input for receiving said demodulated baseband signal and an output at which an equalized baseband signal is produced, said adaptive equalizer including

(a) an adaptive feed forward filter (FFF) for equalizing said demodulated signal, said FFF exhibiting (1) a linear, blind operating mode, and (2) a subsequent non-linear decision-directed operating mode; and

(b) an adaptive decision feedback filter (DFF) for equalizing said demodulated signal, said DFF exhibiting (1) a linear, blind operating mode, and (2) a subsequent non-linear decision-directed operating mode.

7. A system according to claim 6, wherein

in said blind mode said signal input of said DFF is directly connected to said equalized signal at said equalizer output, and coefficient control inputs of said FFF and DFF respond to a blind adaption algorithm; and

in said decision mode said DFF signal input responds to a slicer output signal, and coefficient control inputs of said FFF and DFF respond to an error signal representing the difference between said slicer output signal and said equalizer output signal.

8. A system according to claim 7, wherein

said DFF responds to a training signal during field sync intervals and responds to said slicer output signal during non-field sync intervals;

during non-field sync intervals of a data frame, coefficient control inputs of said FFF and DFF respond to a slice error signal representing the difference between a slicer output signal and said equalizer output signal; and

during field sync intervals of a data frame, coefficient control inputs of said FFF and DFF respond to a training error signal representing the difference between a training signal component of said equalizer output signal and a reference training signal.

9. A system according to claim 8, wherein

said training signal is a PN sequence.

10. A system according to claim 6, wherein

said feed forward filter and said decision feedback filter operate at a symbol rate, on-line in real time.

11. In a system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition video information represented by a VSB constellation of symbols and subject to exhibiting unwanted perturbations, said system including a channel equalizer comprising a feedforward filter (FFF) and a decision-feedback filter (DFF) for producing an equalized output signal, a signal processing method comprising the steps of:

demodulating said VSB modulated signal to produce a baseband demodulated signal;

conveying said demodulated baseband signal to said equalizer;

linearly adapting said FFF during an blind first operating mode;

linearly adapting said DFF during said blind operating mode;

non-linearly adapting said FFF in a subsequent decision-directed operating mode; and

non-linearly adapting said DFF in a subsequent decision-directed operating mode.

12. A method according to claim 11, wherein said step of linearly adapting said DFF during said blind operating mode includes the step of

directly connecting said equalized output signal to a signal input of said DFF during said blind operating mode to permit coarse equalization by said DFF during said blind mode.

13. In a system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition video data represented by a VSB constellation of symbols and subject to exhibiting unwanted perturbations, said data having a data frame format constituted by a succession of data frames comprising a field sync component prefacing a plurality of data segments having an associated segment sync component, said system including a feedforward filter (FFF) and a decision-feedback filter (DFF) constituting a channel equalizer for producing an equalized output signal, a signal processing method comprising the steps of:

demodulating said VSB modulated signal to produce a baseband demodulated signal;

conveying said demodulated baseband signal to said equalizer;

linearly adapting said FFF during a blind first operating mode;

linearly adapting said DFF during said blind operating mode;

non-linearly adapting said FFF in a subsequent decision-directed operating mode; and

non-linearly adapting said DFF in said subsequent decision-directed operating mode.

14. A method according to claim 13, comprising the step of

directly connecting said equalized output signal to a signal input of said DFF during said blind operating mode to permit coarse equalization by said DFF during said blind mode.

15. A method according to claim 13, comprising the further steps of:

generating a slicer output signal in response to said equalizer output signal;

coupling said slicer output signal to a signal input of said DFF in said decision-directed mode; and

coupling an error signal representing the difference between said slicer output signal and said equalizer output signal to coefficient control inputs of said FFF and DFF during said decision-directed mode.

16. In a system for processing a received Vestigial Sideband (VSB) modulated signal containing high definition video data represented by a VSB constellation of symbols and subject to exhibiting unwanted perturbations, said data having a data frame format constituted by a succession of data frames comprising a field sync component prefacing a plurality of data segments having an associated segment sync component, said system including a feedforward filter (FFF) and a decision-feedback filter (DFF) constituting a channel equalizer for producing an equalized output signal, a signal processing method comprising the steps of:

demodulating said VSB modulated signal to produce a baseband demodulated baseband signal;

applying said demodulated signal to said channel equalizer constituted by said FFF and said DFF;

(a) during a blind, non-decision directed equalizing interval,

(1) applying said equalizer output signal to a signal input of said DFF;

(2) adapting said FFF in a linear manner;

(3) adapting said DFF in a linear manner;

(b) during a subsequent training equalizing interval during field sync component intervals,

(1) applying a training signal to said signal input of said DFF;

(2) adapting said FFF and said DFF in response to a training error signal representing the difference between a reference training signal and a training signal component of said equalizer output signal;

(c) during a decision-directed equalizing interval following said training interval and comprising non-field sync component intervals,

(1) applying a symbol slicer output signal to said signal input of said DFF; and

(2) adapting said FFF and said DFF in response to a slice error signal representing the difference between a symbol slicer output signal and said equalizer output signal.