Defect sensing Viterbi based detector

1. A detector comprising:

a Viterbi based detector configured to utilize a decoding trellis to assign values to bits associated with a data signal, wherein the Viterbi based detector determines a plurality of survivor paths to respective states of the decoding trellis in a decoding window representing a number of bits, wherein the Viterbi based detector assigns a value to one or more bits associated with the decoding window if survivor paths merge within the decoding window; and

an erasure detector that identifies one or more bits associated with the decoding window as erasures if survivor paths do not merge within the decoding window.

2. The detector of claim 1 wherein the erasure detector sets one or more erasure flags for the one or more bits.

3. The detector of claim 2 wherein the erasure detector includes in the erasure a predetermined number of bits in the decoding window.

4. The detector of claim 3 wherein the erasure detector includes in the erasure a predetermined number of bits before the decoding window, after the decoding window, or both.

5. The detector of claim 1 wherein the one or more bits are data symbols.

6. The detector of claim 1 wherein the erasure detector detects an erasure if at least one of the survivor paths does not merge.

7. The detector of claim 1 wherein the erasure detector detects an erasure if a predetermined number of the survivor paths do not merge.

8. The detector of claim 1 wherein the Viterbi based detector is a soft output detector and the erasure detector further detects erasures if the soft information for the respective survivor paths does not match.

9. A computer-implemented method of decoding comprising:

determining a plurality of survivor paths through a portion of a decoding trellis that corresponds to a decoding window, the plurality of survivor paths representing paths to respective states in the portion of the decoding trellis;

determining, using a processor of a computer, if the plurality of survivor paths merge within the decoding window such that the survivor paths trace back to a same state in the decoding window;

if the survivor paths merge within the decoding window, assigning a value to one or more bits corresponding to the decoding window based on the merged survivor paths; and

if the survivor paths do not merge within the decoding window, assigning an erasure to one or more bits corresponding to the decoding window.

10. The method of claim 9 wherein the step of assigning includes including in the erasure a predetermined number of bits in the decoding window.

11. The method of claim 9 wherein the step of assigning includes including in the erasure a predetermined number of bits preceding the decoding window, following the decoding window or both.

12. The method of claim 9 wherein the decoding trellis includes associated soft values and the step of determining erasures further includes determining an erasure when the soft output values associated with the survivor paths do not match.

13. The method of claim 9 wherein the step of determining if the survivor paths merge includes determining if at least one of the survivor paths does not merge.

14. The method of claim 9 wherein the step of determining if the survivor paths merge includes determining if a predetermined number of the survivor paths merge.

15. A system comprising:

a soft output Viterbi based detector configured to utilize a decoding trellis to assign values to bits associated with a data signal, wherein the Viterbi based detector determines a plurality of survivor paths to respective states of the decoding trellis in a decoding window representing a number of bits, wherein the Viterbi based detector assigns a value to one or more bits associated with the decoding window if survivor paths merge within the decoding window;

an erasure detector that identifies one or more bits associated with the decoding window as erasures when survivor paths do not merge within the decoding window; and

an iterative decoder that decodes data based on bit values and soft information produced by the Viterbi based detector with the soft information for the erasures set to a predetermined minimum value.

16. The system of claim 15 wherein the erasure detector includes in the erasure a predetermined number of bits in the decoding window.

17. The system of claim 16 wherein the erasure detector further includes in the erasure a predetermined number of bits preceding the decoding window, following the decoding window or both.

18. The system of claim 15 wherein the one or more bits are data symbols.

19. The system of claim 15 wherein the erasure detector detects an erasure if at least one of survivor paths does not merge.

20. The system of claim 15 wherein the erasure detector detects an erasure if a predetermined number of the survivor paths do not merge.

21. The system of claim 15 wherein the erasure detector further detects erasures if the soft information produced by the Viterbi based detector for the survivor paths does not match.