Method and device for decoding LDPC encoded codewords with a fast convergence speed

1. A method for decoding a Low-Density Parity-Check (LDPC) encoded codeword, the LDPC code being represented by a bipartite graph between check nodes and variable nodes including first variable nodes and second variable nodes of degree two connected to the check nodes via a zigzag connectivity, the method comprising:

defining from the check nodes at least two groups of at least two check nodes mutually connected through at least one internal second variable node, each group being connected to a neighboring group by one second variable node defining a connecting second variable node;

updating, for each group, by jointly updating the check nodes of the group with a Maximum-A-Posteriori (MAP) type process in a decoder, and updating all the first variable nodes connected to the check nodes of the group and updating each connecting second variable node connected to the group without updating the internal second variable nodes; and

iteratively repeating the updating.

2. The method according to claim 1 , wherein for each group, all the check nodes of the group are respectively connected to different first variable nodes.

3. The method according to claim 1 , wherein the MAP type process comprises at least one of a LogMAP process and a MaxLogMAP process.

4. The method according to claim 1 , wherein the first variable nodes define information nodes, and the second variable nodes define parity nodes.

5. The method according to claim 1 , wherein the LDPC code comprises an Irregular Repeat-Accumulate (IRA) code.

6. The method according to claim 1 , wherein the LDPC code comprises at least one of a DVB-S2 LDPC code, a WLAN 802.11n defined code and a WIMAX 802.16e defined code.

7. The method according to claim 1 , wherein the LDPC encoded codeword is received from a wireless medium of a wireless communication system.

8. A decoder for decoding a Low-Density Parity-Check (LDPC) encoded codeword, the LDPC code being represented by a bipartite graph between check nodes and variable nodes including first variable nodes and second variable nodes of degree two connected to the check nodes via a zigzag connectivity, the decoder comprising:

a processor including a check nodes processor to update check nodes and a variable nodes processor to update variable nodes, the check nodes defining at least two groups of at least two check nodes mutually connected through at least one internal second variable node, each group being connected to a neighboring group by one second variable node defining a connecting second variable node, the check nodes processor implementing a Maximum-A-Posteriori (MAP) type process to jointly update the check nodes of a group; and

a controller to iteratively activate the processor and during each iteration to activate, for each group, the check nodes processor and the variable nodes processor to jointly update the check nodes of the group, to update the first variable nodes connected to the check nodes of the group and to update each connecting second variable node connected to the group, without updating the internal second variable nodes.

9. The decoder according to claim 8 , wherein for each group, the check nodes of the group are respectively connected to different first variable nodes.

10. The decoder according to claim 8 , wherein the MAP type process comprises at least one of a LogMAP process and a MaxLogMAP process.

11. The decoder according to claim 8 , wherein the processor updates the check nodes and variable nodes with updating messages comprising Log-Likelihood Ratios (LLR).

12. The decoder according to claim 8 , wherein the first variable nodes comprise information nodes and the second variable nodes comprise parity nodes.

13. The decoder according to claim 12 , wherein the LDPC code comprises an Irregular Repeat-Accumulate (IRA) code.

14. The decoder according to claim 12 , wherein the LDPC code comprises at least one of a DVB-S2 LDPC code, a WLAN 802.11n defined code and a WIMAX 802.16e defined code.

15. A data communications component of a communication system comprising at least one of a wireless communication system, a wireline communication system, an xDSL system and an optical fiber system, the data communications component comprising:

a decoder for decoding a Low-Density Parity-Check (LDPC) encoded codeword, the LDPC code being represented by a bipartite graph between check nodes and variable nodes including first variable nodes and second variable nodes of degree two connected to the check nodes via a zigzag connectivity, the decoder including

a processor including a check nodes processor to update check nodes and a variable nodes processor to update variable nodes, the check nodes defining at least two groups of at least two check nodes mutually connected through at least one internal second variable node, each group being connected to a neighboring group by one second variable node defining a connecting second variable node, the check nodes processor implementing a Maximum-A-Posteriori (MAP) type process to jointly update the check nodes of a group; and

a controller to iteratively activate the processor and during each iteration to activate, for each group, the check nodes processor and the variable nodes processor to jointly update the check nodes of the group, to update the first variable nodes connected to the check nodes of the group and to update each connecting second variable node connected to the group, without updating the internal second variable nodes.

16. The data communications component according to claim 15 wherein the processor updates the check nodes and variable nodes with updating messages comprising Log-Likelihood Ratios (LLR).

17. The data communications component according to claim 15 , wherein the first variable nodes comprise information nodes and the second variable nodes comprise parity nodes.

18. The data communications component according to claim 15 , wherein the component defines at least one of a terminal, a base station and an access point of a wireless communication system.