Apparatus and method for encoding/decoding block low density parity check codes having variable coding rate

1. A method for encoding a rate-compatible block Low Density Parity Check (LDPC) code, the method comprising the steps of:

designing, by a puncturing unit, specific LDPC codes for a predetermined number of coding rates, and generating a pruning pattern by comparing information node degrees of the predetermined number of LDPC codes;

matching, by the puncturing unit, check node degrees of the predetermined number of LDPC codes;

generating a predetermined number of puncturing patterns according to the check node degrees when the matched check node degrees are calculated;

determining, by the puncturing unit, whether a first condition given for the generated puncturing patterns is satisfied; and

determining the generated puncturing patterns as rate-compatible puncturing patterns when the puncturing patterns satisfy the first condition.

2. The method of claim 1 , further comprising generating rate-compatible puncturing patterns according to a second condition given for the predetermined number of the generated puncturing patterns when the puncturing patterns do not satisfy the first condition.

3. The method of claim 2 , wherein the second condition represents a condition of generating rate-compatible puncturing patterns while maintaining a property of a puncturing pattern corresponding to a low coding rate.

4. The method of claim 1 , wherein the step of generating a pruning pattern comprises generating a pruning pattern by comparing degree distribution of each variable node, wherein the pruning pattern reduces the degree of the variable node.

5. The method of claim 1 , wherein the step of matching check node degrees comprises matching a number of ‘1’s per row of a predetermined number of parity check matrixes, wherein the matched check node degrees are calculated by an equation

d c =gcd ( d c,1 −2, d c,2 −2, . . . , d c,m −2)+2

where d c denotes a matched check node degree.

6. The method of claim 1 , further comprising calculating the matched check node degree, and converting the LDPC codes into a predetermined number of punctured LDPC codes according to the calculated check node degree.

7. The method of claim 6 , wherein the LDPC code converting step is differently applied according to structure of the LDPC codes.

8. The method of claim 1 , wherein the puncturing pattern generating step comprises combining a predetermined number of punctured LDPC codes changed according to the check node degree, into one rate-compatible LDPC code.

9. The method of claim 1 , wherein the first condition is defined so for all i, a puncturing pattern (P i ) is a prime factor of (P j ), where j=i+1, . . . , m.

10. An apparatus for encoding a rate-compatible block Low Density Parity Check (LDPC) code, the apparatus comprising:

an encoder for encoding information data into coded symbols with a predetermined coding scheme;

a puncturing and pruning unit for puncturing a predetermined number of coded symbols from the coded symbols received from the encoder, the predetermined number corresponding to coding rate information set in a system; and

a modulator for modulating the coded symbols into modulation symbols with a predetermined modulation scheme,

wherein the puncturing and pruning unit generates LDPC codes for a predetermined number of coding rates, generates a pruning pattern by comparing information node degrees of a predetermined number of LDPC codes, matches check node degrees of the predetermined number of LDPC codes, generates a predetermined number of puncturing patterns according to the check node degree if the matched check node degree is calculated, compares the puncturing patterns with a first condition, and generates rate-compatible puncturing patterns according to the comparison result.

11. The apparatus of claim 10 , wherein the puncturing and pruning unit performs pruning on an information node for generating an information node corresponding to a set degree from a mother code for each coding rate, and punctures a predetermined number of bits every parity bits given for each coding rate, for the parity bits left after the pruning.

12. The apparatus of claim 11 , wherein the puncturing and pruning unit generates a pruning pattern by comparing degree distribution of each variable node, and reduces a degree of the variable node according to the pruning pattern.

13. The apparatus of claim 10 , wherein the puncturing and pruning unit determines the generated puncturing patterns as the rate-compatible puncturing patterns when the puncturing patterns satisfy the first condition, and the puncturing and pruning unit generates rate-compatible puncturing patterns according to a second condition given for the puncturing patterns when the puncturing patterns do not satisfy the first condition.

14. The apparatus of claim 13 , wherein the second condition represents a condition of generating rate-compatible puncturing patterns while maintaining a property of a puncturing pattern corresponding to a low coding rate.

15. The apparatus of claim 10 , wherein the puncturing and pruning unit matches the check node degrees by matching a number of ‘1’s per row of a predetermined number of parity check matrixes, wherein the matched check node degrees are calculated by the equation

d c =gcd ( d c,1 −2 ,d c,2 −2, . . . , d c,m −2)+2

where d c denotes the matched check node degree.

16. The apparatus of claim 10 , wherein the puncturing and pruning unit generates puncturing patterns by combining a predetermined number of punctured LDPC codes changed according to the check node degree, into one rate-compatible LDPC code.

17. The apparatus of claim 10 , wherein the first condition is defined so for all i, a puncturing pattern (P i ) is a prime factor of (P j ), where j=i+1, . . . , m.