Layered decoding approach for low density parity check (LDPC) codes

1. A method of decoding in layers data received in a communication system, comprising:

receiving a codeword containing a plurality of elements, the codeword encoded according to a low density parity check code represented by a parity check matrix having rows and columns, each of the plurality of elements associated with a column of the parity check matrix, the columns of the parity check matrix corresponding to input nodes and the rows of the parity check matrix corresponding to parity check sums;

dividing the rows of at least one column of the parity check matrix into groups;

separately processing each of at least some of the groups by performing a sequence of operations comprising:

for each row of the group, subtracting a previous check node value from a probability value for each input node contributing to the parity check sum for that row;

generating a new check node value for that row using the result of the subtracting step; and

for each input node contributing to the parity check sum for that row, updating a probability value using the new check node value and the result of the subtracting step; and

then combining the updated probability values of the at least one column from each of the separately processed groups.

2. The method of claim 1 , wherein combining is performed during a time period within which substantially no other processes are being performed for said at least one column.

3. The method of claim 1 , wherein dividing the rows of the parity check matrix into groups comprises partitioning the at least one column such that at least one block row is in a different group than a next block row.

4. The method of claim 1 , wherein the rows of the parity check matrix are grouped into subsets in which each column has a maximum column weight of one.

5. The method of claim 1 , wherein the parity check matrix is represented by a macro matrix having zero-valued and non-zero-valued entries arranged in block rows and block columns and in which each zero-valued entry corresponds to a p×p zero-valued matrix and each non-zero-valued entry corresponds to a p×p permutation matrix that has at most a single “1” entry in each row and each column and “0” entries elsewhere to define a parity check matrix.

6. A system for decoding a received signal stream that was encoded according to a low density parity check code represented by a parity check matrix having rows and columns, each of the plurality of elements associated with a column of the parity check matrix, the columns of the parity check matrix corresponding to input nodes, comprising:

a plurality of parallel computation blocks coupled to a memory;

a plurality of parity check update blocks (PCUBs) coupled to said computation blocks, for updating check node values corresponding to participating input nodes for a row of the parity check matrix; and

a plurality of column store blocks (CSBs) coupled to the PCUBs, each CSB comprising a memory for storing an updated probability value corresponding to a plurality of input nodes associated with each of a plurality of rows of the parity check matrix, each of the column store blocks comprising:

a first memory portion for storing updated probability values for at least one input node associated with a first group of rows;

a second memory portion for storing updated probability values for at least one input node associated with a second group of rows; and

circuitry for combining updated probability values from the first and second memory portions for at least one input node.

7. The system of claim 6 , wherein the combining circuitry is operable to combine at least some of the probability values for at least one input node during a time period within which the plurality of parity check update blocks and column store blocks are not operating on information associated for for the at least one input node.