Nested LDPC encoders and decoder

1. A method for encoding a block of b data bytes, the method including the steps of:

A. encoding sub-blocks of the data using a first low density parity check (LDPC) code H 1 to produce sub-block parity bits;

B. producing sub-block code words by appending the sub-block parity bits to the corresponding sub-blocks of data bytes;

C. combining the sub-block code words to produce an H 1 block code word;

D. encoding the H 1 block code word using a second LDPC code H 2 to produce block parity bits; and

E. producing an encoded block by concatenating the sub-block code words and the block parity bits.

2. A method of decoding an encoded block that includes b data bytes that are encoded into i sub-block code words and p block parity bits, the method including the steps of:

A. decoding the i sub-blocks using a first LDPC code H 1 and retaining sign values for sub-blocks that converge;

B. determining if any sub-block fail to converge and

if none of the sub-blocks fail to converge determining the block successfully decoded,

if more than one fails to converge determining the block decoded unsuccessfully, and

if only one sub-block fails to converge performing an extended decoding operation that uses the p block parity bits, the extended decoding operation including the steps of

i. combining the sign values for the i−1 sub-block code words that converged to produce a vector C;

ii. combining the failed sub-block code word with the vector C to produce an H 1 block code word and appending the block parity bits to the H 1 block code word to produce a code word of a second LDPC code H 2 with the H 1 block code word as a data portion;

iii. decoding the H 2 code word over the H 2 LDPC code to produce an updated H 2 code word;

iv. combining the vector C with the data portion of the updated H 2 code word and providing the result as an updated failed sub-block code word to an ISI detector;

v. further updating the failed sub-block code word in the ISI detector;

vi. combining the vector C with the updated failed sub-block code word and appending the p parity bits to produce a further updated H 2 code word;

vii. decoding the further updated H 2 code word over the H 2 LDPC code to produce a further updated H 2 code word; and

viii. repeating steps iv-vii until the H 2 code word either converges over the H 2 LDPC code or a predetermined number of iterations have been performed;

ix. if the H 2 code word converges removing the vector C from the data portion and including the result with the i−1 previously decoded sub-block code words as a successfully decoded block; and

x. if the H 2 code word fails to converge determining that the block unsuccessfully decoded.

3. The method of claim 2 further including

providing the p parity bits to the ISI detector, and

updating the p parity bits and appending the updated parity bits to the updated H 1 block code word to produce the updated H 2 code word.

4. A system for decoding an encoded block that includes d data bytes that are encoded into i sub-block code words over a first LDPC code H 1 and p block parity bits that correspond to a second LDPC code H 2 , the system including:

A. an ISI detector for assigning sign values and reliability information to the respective sub-block code words and separately assigning sign values to the p parity bits;

B. an LDPC decoder for decoding H 1 code words over the H 1 LDPC code and H 2 codewords over the H 2 LDPC code; and

C. one or more buffers for retaining sign values for the decoded sub-block code words that converge;

D. one or more XOR gates or firmware for

i. producing a vector C that is a combination of i−1 correctly decoded sub-block code words,

ii. combining the vector C with a failed sub-block code word to produce an H 1 a block code word that is also a data portion of an H 2 code word, and

iii. combining the vector C with the data portion of an updated H 2 code word to produce an updated failed sub-block code word,

 wherein the ISI detector and the LDPC decoder decode the sub-block code words over the H 1 LDPC code in an on-the-fly decoding operation and in an extended decoding operation the ISI detector decodes an updated failed sub-block code word and the LDPC decoder decodes the corresponding H 1 block code word and appended p parity bits as an H 2 code word over the H 2 LDPC code.

5. The system of claim 4 wherein the ISI detector further

assigns reliability information to the p parity bits, and

during the extended decoding operation updates the sign values and the reliability information separately for the failed sub-block code word and the p parity bits.

6. The system of claim 4 wherein the LDPC decoder in an extended decoding operation further decodes over the H 1 LDPC code an updated failed sub-block code word that corresponds to the H 2 code word that converged over the H 2 LDPC code.

7. A method of decoding an encoded block that includes b data bytes that are encoded into i sub-block code words and p block parity bits, the method including the steps of:

a. independently decoding respective sub-block code words over a first LDPC code;

b. if all of the sub-block code words converge, determining the block successfully decoded;

c. if more than one sub-block code word does not converge, determining that the block decoded unsuccessfully; and

d. if a single sub-block code word fails to converge iteratively decoding the failed sub-block code word by

i. producing an associated code word of a block-level LDPC code by combining sign values associated with the failed sub-block with a vector C that is a combination of the i−1 sub-block code words that converged, associating therewith the reliability information that corresponds to the failed sub-block code word and appending thereto sign values and reliability information for the p parity bits,

ii. decoding the code word over the block-level LDPC code to produce an updated code word,

iii. removing the vector C from the non-parity portion of the updated code word to produce an updated sub-block code word that corresponds to the failed sub-block code word,

iv. decoding the updated sub-block code word to further update the associated sign and reliability information associated with the failed sub-block code word, and

v. repeating steps i-iv using the updated sign value and reliability information until the code word converges over the block-level LDPC code or until a predetermined number of iterations have been performed, and

vi. if the code word converges over the block-level LDPC code removing the vector C from the non-parity portion of the code word and using the result in the decoded block to produce a successfully decode block, and

vii. if the code word does not converge over the block-level LDPC code determining that the block decoded unsuccessfully.

8. The method of claim 7 further including the steps of

updating the sign and reliability information associated with the p parity bits; and

in the step of repeating the steps i-iv including the updated sign and reliability information for the p parity bits.

9. The method of claim 8 wherein the step of decoding the updated sub-block code word includes decoding using an ISI detector.

10. The method of claim 9 wherein the step of producing an associated code word of a block-level LDPC code further includes re-reading the failed sub-block code word.

11. The method of claim 10 wherein the step of producing an associated code word of a block-level LDPC code further includes re-reading the sub-block code words that converged.