Dual-mode equalizer in an ATSC-DTV receiver
View Patent ↗A decision feedback equalizer for processing a data signal provides concurrent equalizer outputs (Z ok , Z 1k ) for hard decision directed and soft decision directed modes. The joint architecture in accordance with the present invention takes advantage of the fact, herein recognized, that for each equalizer output symbol soft decision bit representation, a subset of these bits corresponds to the hard decision representation. As a result, the invention permits the concurrent output of two distinct modes with essentially the same hardware as a one output equalizer.
1. A receiver, comprising:
an equalizer that has at least two coefficient modes of operation;
a sync generator for generating a synchronization signal from a received signal and for providing a status signal; and
a controller for setting the equalizer in one of the at least two coefficient modes of operation as a function of the status signal;
wherein in a first coefficient mode, the equalizer starts with a preset non-zero value in at least one tap; while in a second coefficient mode, the equalizer starts such that all taps are set equal to a same value;
wherein in the first coefficient mode the equalizer starts with the preset non-zero value in said at least one tap and the equalizer equalizes a received signal in accordance with a blind mode of operation and a decision-directed mode of operation; wherein the equalizer transits from the blind mode to the decision-directed mode as a function of a mean square error estimate of an output signal from the equalizer;
wherein the sync generator comprises at least two modes of operation, wherein in a first mode of operation the sync generator generates the synchronization signal as a function of a channel virtual center signal and in a second mode of operation the sync generator generates the synchronization signal as a function of a correlation signal.
2. The receiver of claim 1 , wherein the equalizer comprises a feedback filter for which the feedback filter input signal under the blind mode or the decision directed mode comprises at least one of: the equalizer output signal, a slicer output signal or an external input signal.
3. The receiver of claim 1 , wherein in the second coefficient mode the equalizer starts such that all taps are set equal to a value of zero.
4. The receiver of claim 1 , wherein in the first coefficient mode the at least one tap is a main tap of the equalizer.
5. The receiver of claim 1 , further comprising:
a processor for setting the equalizer in one of the coefficient modes of operation as a function of a received signal.
6. The receiver of claim 5 , wherein the received signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) signal.
7. The receiver of claim 5 , wherein the processor further controls the operation of the equalizer from initialization to tap adaptation.
8. The receiver of claim 1 , wherein the synchronization signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) segment sync signal.
9. The receiver of claim 1 , wherein the synchronization signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) frame sync signal.
10. The receiver of claim 1 , further comprising:
a centroid calculator responsive to a demodulated signal for providing the channel virtual center signal and the correlation signal.
11. The receiver of claim 1 , further comprising:
a correlator responsive to a demodulated signal for providing the correlation signal, which is representative of a correlation between a demodulated signal and a data pattern representing the synchronization signal.
12. The receiver of claim 1 , further comprising:
a centroid calculation loop for providing the channel virtual center signal as a function of a data pattern conveyed within a demodulated signal, wherein the data pattern is representative of the synchronization signal.
13. The receiver of claim 1 , wherein the sync generator generates the synchronization signal as a function of a difference between a value of the channel virtual center signal and a value that is a function of the correlation signal.
14. The receiver of claim 1 , wherein the sync generator generates the synchronization signal as a function of a lock signal, the lock signal representing a lock status of the equalizer.
15. The receiver of claim 1 , wherein the sync generator generates the synchronization signal as a function of a lock signal occurring within a time interval, ΔT, the lock signal representing a lock status of the equalizer.
16. The receiver of claim 1 , wherein in the first coefficient mode the at least one tap is a predetermined feed-forward filter tap of the equalizer.
17. A method for use in a receiver, the method comprising:
setting an equalizer to one of a number of coefficient modes of operation; and
equalizing a signal in accordance with the set coefficient mode;
providing a status signal from a sync generator; and
wherein the setting step sets the equalizer in one of said number of coefficient modes of operation as a function of the status signal;
wherein the providing step includes the steps of:
providing a synchronization signal in a first mode as a function of a channel virtual center signal; and
providing the synchronization signal in a second mode as a function of a correlation signal;
wherein in a first coefficient mode, the equalizer starts with a preset non-zero value in at least one tap; while in a second coefficient mode, the equalizer starts such that all taps are set equal to a same value;
wherein in the first coefficient mode the equalizer starts with the preset non-zero value in said at least one tap and the equalizing step includes;
equalizing a received signal in accordance with a blind mode of operation; and
equalizing the received signal in accordance with a decision-directed mode of operation;
wherein the equalizer transits from the blind mode to the decision-directed mode as a function of a mean square error estimate of an output signal of the equalizer.
18. The method of claim 17 , wherein at least one equalizing step comprises a feedback filtering step for filtering an input signal, wherein the input signal comprises at least one of: the equalizer output signal, a slicer output signal or an external input signal.
19. The method of claim 17 , wherein in the second coefficient mode the equalizer starts such that all taps are set equal to a value of zero.
20. The method of claim 17 , wherein in the first coefficient mode the at least one tap is a main tap of the equalizer.
21. The method of claim 17 , wherein the setting step sets the equalizer in one of the coefficient modes of operation as a function of a received signal.
22. The method of claim 21 , wherein the received signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) signal.
23. The method of claim 21 , wherein the setting step further sets the equalizer in initialization or tap adaptation as a function of the received signal.
24. The method of claim 17 , wherein the setting step further sets the equalizer in initialization or tap adaptation as a function of the status signal.
25. The method of claim 17 , wherein the synchronization signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) segment sync signal.
26. The method of claim 17 , wherein the synchronization signal represents an ATSC-DTV (Advanced Television Systems Committee-Digital Television) frame sync signal.
27. The method of claim 17 , further comprising:
processing a demodulated signal to provide the channel virtual center signal and the correlation signal.
28. The method of claim 17 , further comprising:
providing the correlation signal, which is representative of a correlation between a demodulated signal and a data pattern representing the synchronization signal.
29. The method of claim 17 , further comprising:
providing the channel virtual center signal as a function of a data pattern conveyed within a demodulated signal, wherein the data pattern is representative of the synchronization signal.
30. The method of claim 17 , further comprising
providing the synchronization signal as a function of a difference between a value of the channel virtual center signal and a value that is a function of the correlation signal.
31. The method of claim 17 , further comprising
providing the synchronization signal as a function of a lock signal, the lock signal representing a lock status of the equalizer.
32. The method of claim 17 , further comprising
providing the synchronization signal as a function of a lock signal occurring within a time interval, ΔT, the lock signal representing a lock status of the equalizer.
33. The method of claim 17 , wherein in the first coefficient mode the at least one tap is a predetermined feed-forward filter tap of the equalizer.
34. A receiver, comprising:
an equalizer that has at least two coefficient modes of operation;
wherein in a first coefficient mode, the equalizer starts with a preset non-zero value in at least one tap; while in a second coefficient mode, the equalizer starts such that all taps are set equal to a same value; wherein in the second coefficient mode the equalizer starts such that all taps are set equal to the same value and the equalizer equalizes a signal in accordance with a training mode of operation; a blind mode of operation; and a decision-directed mode of operation; wherein the equalizer transits between the training mode, the blind mode and the decision-directed mode as a function of a mean square error estimate of an output signal of the equalizer.
35. The receiver of claim 34 , wherein the equalizer comprises a feedback filter for which the feedback filter input signal under the blind mode or the decision directed mode is at least one of: the equalizer output signal, a slicer output signal or an external input signal.
36. A method for use in a receiver, the method comprising:
setting an equalizer to one of a number of coefficient modes of operation; and
equalizing a signal in accordance with the set coefficient mode;
wherein in a first coefficient mode, the equalizer starts with a preset non-zero value in at least one tap; while in a second coefficient mode, the equalizer starts such that all taps are set equal to a same value;
wherein in the second coefficient mode the equalizer starts such that all taps are set equal to the same value and the equalizing step includes;
equalizing the received signal in accordance with a training mode of operation;
equalizing the received signal in accordance with a blind mode of operation; and
equalizing the received signal in accordance with a decision-directed mode of operation;
wherein the equalizer transits between the training mode, the blind mode and the decision-directed mode as a function of a mean square error estimate of an output signal of the equalizer.
37. The method of claim 36 , wherein at least one equalizing step comprises a feedback filtering step for filtering an input signal, wherein the input signal comprises at least one of: the equalizer output signal, a slicer output signal or an external input signal.