Double equalizer for multi-path rejection

1. An apparatus in a receiver for improving reception of a signal, comprising:

an equalizer, including:

first and second cascaded maximum-likelihood detectors, wherein the second maximum-likelihood detector is configured to receive an output of the first maximum-likelihood detector; and

an adjustable delay unit configured to delay an input signal to the second maximum-likelihood detector by an amount associated with an output delay of the first maximum-likelihood detector and a multi-path delay associated with a multi-path signal, and

wherein the equalizer and the adjustable delay unit are configured for adaptation in accordance with one or more multi-path signals in a communication channel that conveys the signal.

2. The apparatus of claim 1 , wherein the one or more multi-path signals include a pre-multi-path signal, the multi-path delay includes a pre-echo delay associated with the pre-multi-path signal, and the apparatus further comprises control logic configured to set the adjustable delay unit in accordance with the pre-echo delay.

3. The apparatus of claim 1 , wherein the one or more multi-path signals comprise a plurality of multi-path signals, and the signal and each of the multi-path signals have a corresponding temporal characteristic, and wherein the temporal characteristic of a first multi-path signal of the plurality of multi-path signals occurs prior to the temporal characteristic of the signal, the temporal characteristic of a second multi-path signal of the plurality of multi-path signals occurs after the temporal characteristic of the signal, and the apparatus further comprises control logic configured to set the adjustable delay unit in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

4. The apparatus of claim 1 , wherein the one or more multi-path signals include a plurality of multi-path signals each having a respective temporal centroid, and the apparatus further comprises control logic configured to set the adjustable delay unit in accordance with two or more of the respective temporal centroids associated with the plurality of multi-path signals.

5. The apparatus of claim 1 , wherein the one or more multi-path signals include a pre-multi-path signal and a post-multi-path signal, the pre-multi-path signal has a temporal characteristic that occurs prior to a temporal characteristic of the signal and the post-multi-path signal has a temporal characteristic that occurs after the temporal characteristic of the signal, and the apparatus further comprises control logic configured to set the adjustable delay unit in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

6. The apparatus of claim 1 , wherein the signal comprises a digital television signal.

7. The apparatus of claim 6 , wherein the digital television signal is compatible with an 8-VSB modulation format.

8. The apparatus of claim 1 , wherein at least one of the first and second cascaded maximum-likelihood detectors includes a Viterbi detector.

9. The apparatus of claim 1 , wherein the equalizer and the adjustable delay unit are configured for adaptation in accordance with a channel characteristic of the communication channel.

10. The apparatus of claim 1 , further comprising one or more additional cascaded maximum-likelihood detectors.

11. The apparatus of claim 1 , wherein the adjustable delay unit is configured to enable the equalizer to correct both pre-multi-path and post-multi-path signals.

12. A method of improving reception of a signal, comprising:

determining an estimated first symbol stream from a received signal using a first maximum likelihood detector in an equalizer;

generating a delayed version of the received signal, wherein the delayed version of the received signal has an adjustable delay relative to the received signal that is determined in accordance with one or more multi-path signals in the communication channel; and

determining an estimated second symbol stream from the delayed version of the received signal and a characteristic of the estimated first symbol stream using a second maximum likelihood detector in the equalizer.

13. An apparatus for improving reception of a signal, comprising:

a first means for determining an estimated first symbol stream from a received signal;

means for adjustably delaying the received signal to produce a delayed version of the received signal, wherein the delay corresponds to an output delay of the first determining means and a multi-path delay associated with one or more multi-path signals; and

a second means for determining an estimated second symbol stream from the delayed version of the received signal produced by the adjustable delay means and a characteristic of the estimated first symbol stream produced by the first determining means.

14. The apparatus of claim 13 , wherein the one or more multi-path signals include a pre-multi-path signal, the multi-path delay includes a pre-echo delay associated with the pre-multi-path signal, and the apparatus further comprises means for setting the adjustable delay means in accordance with the pre-echo delay.

15. The apparatus of claim 13 , wherein the one or more multi-path signals include a post-multi-path signal, the multi-path delay includes a post-echo delay associated with the post-multi-path signal, and the apparatus further comprises means for setting the adjustable delay means in accordance with the post-echo delay.

16. The apparatus of claim 13 , wherein the one or more multi-path signals comprise a plurality of multi-path signals, and the signal and each of the multi-path signals have a corresponding temporal characteristic, and wherein the temporal characteristic of a first multi-path signal of the plurality of multi-path signals occurs prior to the temporal characteristic of the signal, the temporal characteristic of a second multi-path signal of the plurality of multi-path signals occurs after the temporal characteristic of the signal, and the apparatus further comprises means for setting the adjustable delay means in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

17. The apparatus of claim 13 , wherein the one or more multi-path signals include a plurality of multi-path signals each having a respective temporal centroid, and the apparatus further comprises means for setting the adjustable delay means in accordance with two or more of the respective temporal centroids associated with the plurality of multi-path signals.

18. The apparatus of claim 13 , wherein the one or more multi-path signals include a pre-multi-path signal and a post-multi-path signal, the pre-multi-path signal has a temporal characteristic that occurs prior to a temporal characteristic of the signal and the post-multi-path signal has a temporal characteristic that occurs after the temporal characteristic of the signal, and the apparatus further comprises means for setting the adjustable delay means in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

19. The apparatus of claim 13 , wherein at least one of the first and second determining means includes a Viterbi detector.

20. The apparatus of claim 13 , wherein the first and second determining means and the adjustable delay means are configured for adaptation in accordance with a channel characteristic of the communication channel.

21. The method of claim 12 , wherein the one or more multi-path signals includes a pre-multi-path signal, the multi-path delay includes a pre-echo delay associated with the pre-multi-path signal, and the method further comprises setting the adjustable delay in accordance with the pre-echo delay.

22. The method of claim 12 , wherein the one or more multi-path signals includes a post-multi-path signal, the multi-path delay includes a post-echo delay associated with the post-multi-path signal, and the method further comprises setting the adjustable delay in accordance with the post-echo delay.

23. The method of claim 12 , wherein the one or more multi-path signals comprise a plurality of multi-path signals, and the received signal and each of the multi-path signals have a corresponding temporal characteristic, and wherein the temporal characteristic of a first multi-path signal of the plurality of multi-path signals occurs prior to the temporal characteristic of the signal, and the temporal characteristic of a second multi-path signal of the plurality of multi-path signals occurs after the temporal characteristic of the signal, the method further comprising setting the adjustable delay in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

24. The method of claim 12 , wherein the one or more multi-path signals include a pre-multi-path signal and a post-multi-path signal, and wherein the pre-multi-path signal has a temporal centroid that occurs prior to a temporal centroid of the signal and the post-multi-path signal has a temporal centroid that occurs after the temporal centroid of the signal, the method further comprising setting the adjustable delay in accordance with two or more of the respective temporal centroids associated with the plurality of multi-path signals.

25. The method of claim 12 , wherein the one or more multi-path signals include a pre-multi-path signal and a post-multi-path signal, and wherein the pre-multi-path signal has a temporal characteristic that occurs prior to a temporal characteristic of the signal and the post-multi-path signal has a temporal characteristic that occurs after the temporal characteristic of the signal, the method further comprising setting the adjustable delay in accordance with two or more of the respective temporal characteristics associated with the plurality of multi-path signals.

26. The method of claim 12 , wherein determining the estimated first and second symbol streams includes applying Viterbi detection criteria to the received signal and the delayed version of the received signal, respectively.

27. The method of claim 12 , further comprising:

estimating a channel characteristic of the communication channel; and

adjusting the adjustable delay in accordance with the estimated channel characteristic.

28. The apparatus of claim 1 , wherein the output of the first maximum-likelihood detector received by the second maximum-likelihood detector includes at least one of an estimated symbol stream, data estimates and an estimated error rate associated with data estimates.

29. The apparatus of claim 1 , wherein the one or more multi-path signals include a post-multi-path signal and wherein the multi-path delay includes a post-echo delay associated with the post-multi-path signal, the apparatus further comprising control logic configured to set the adjustable delay unit in accordance with the post-echo delay.