Method and system for HARQ combining in a telecommunication system

1. A method for HARQ combining of a received codeword in a receiver with a FEC decoder, the method comprising:

computing Log Likelihood Ratios (LLRs) of demodulated soft symbols of said received codeword and outputting said LLRs as a-priori soft bits;

performing iterative decoding of said a-priori soft bits in a Forward Error Correction (FEC) decoder;

outputting a-posteriori soft bits of said a-priori soft bits of said received codeword from said FEC decoder;

selecting either said a-priori soft bits or said a-posteriori soft bits of said codeword for HARQ combining based on a comparison between a variance associated with said a-priori soft bits and a variance associated with said a-posteriori soft bits; and

HARQ combining said selected soft bits with a retransmission of said received codeword.

2. The method according to claim 1 , further comprising storing said selected soft bits in a HARQ memory before said HARQ combining.

3. The method according to claim 1 , further comprising:

computing a variance (σ 2 0 ) of at least one demodulated a-priori soft symbol related to said a-priori soft-bits, wherein σ 2 0 comprises said variance associated with said a-priori soft bits; and

computing a variance (σ 2 1 ) of at least one a-posteriori soft symbol remodulated from said a-posteriori soft-bits, wherein σ 2 1 comprises said variance associated with said a-posteriori soft bits.

4. The method according to claim 1 , wherein said HARQ combining is selected from one or both of Chase combining and Incremental Redundancy combining.

5. A receiver for a wireless telecommunication system, the receiver comprising:

an LLR computation and HARQ combining module configured to provide a-priori soft bits;

a FEC decoder coupled to said LLR computation and HARQ combining module, said FEC decoder configured to receive said a-priori soft bits and output a-posteriori soft bits corresponding to said a-priori soft bits;

a compare and select module configured to select either said a-priori soft bits or said a-posteriori soft bits of said codeword for HARQ combining based on a comparison between a variance associated with said a-priori soft bits and a variance associated with said a-posteriori soft bits; and

a HARQ memory coupled to said FEC decoder, said HARQ memory configured to receive and store said selected soft bits;

said HARQ memory being coupled to said LLR computation and HARQ combining module and configured to provide said selected soft bits to said LLR computation and HARQ combining module.

6. The method according to claim 3 , wherein said selecting comprises:

selecting said a-posteriori soft bits in response to a determination that σ 2 1 is greater than σ 2 0 .

7. The method according to claim 3 , wherein said selecting comprises:

selecting said a-priori soft bits in response to a determination that σ 2 0 is greater than σ 2 1 .

8. The method according to claim 3 , further comprising:

determining whether said iterative decoding of said a-priori soft bits was successful.

9. The method according to claim 8 , further comprising:

soft-remodulating said a-posteriori soft bits to said at least one a-posteriori soft symbol in response to a determination that said decoding was unsuccessful.

10. The receiver according to claim 5 , wherein said compare and select module is further configured to:

compute a variance (σ 2 0 ) of at least one demodulated a-priori soft symbol related to said a-priori soft-bits, wherein σ 2 0 comprises said variance associated with said a-priori soft bits; and

compute a variance (σ 2 1 ) of at least one a-posteriori soft symbol remodulated from said a-posteriori soft-bits, wherein σ 2 1 comprises said variance associated with said a-posteriori soft bits.

11. The receiver according to claim 10 , wherein said compare and select module is further configured to:

select said a-posteriori soft bits in response to a determination that σ 2 1 is greater than σ 2 0 .

12. The receiver according to claim 10 , wherein said compare and select module is further configured to:

select said a-priori soft bits in response to a determination that σ 2 0 is greater than σ 2 1 .

13. The receiver according to claim 10 , wherein said compare and select module is further configured to:

determine whether said iterative decoding of said a-priori soft bits was successful.

14. The receiver according to claim 13 , wherein said compare and select module is further configured to:

soft-remodulate said a-posteriori soft bits into said at least one a-posteriori soft symbol in response to a determination that said decoding was unsuccessful.

15. The receiver according to claim 5 , wherein said LLR computation and HARQ combining module is configured to perform HARQ combining selected from one or both of Chase combining or Incremental Redundancy combining.

16. An apparatus for HARQ combining of a received codeword, said apparatus comprising:

means for computing Log Likelihood Ratios (LLRs) of demodulated soft symbols of said received codeword and outputting said LLRs as a-priori soft bits;

means for performing iterative decoding of said a-priori soft bits in a Forward Error Correction (FEC) decoder;

means for outputting a-posteriori soft bits of said a-priori soft bits of said received codeword from said FEC decoder;

means for selecting either said a-priori soft bits or said a-posteriori soft bits of said codeword for HARQ combining based on a comparison between a variance associated with said a-priori soft bits and a variance associated with said a-posteriori soft bits; and

means for HARQ combining said selected soft bits with a retransmission of said received codeword.

17. The apparatus according to claim 16 , further comprising:

means for storing said selected soft bits in a HARQ memory before said HARQ combining.

18. The apparatus according to claim 16 , further comprising:

means for computing a variance (σ 2 0 ) of at least one demodulated a-priori soft symbol related to said a-priori soft-bits, wherein σ 2 0 comprises said variance associated with said a-priori soft bits; and

means for computing a variance (σ 2 1 ) of at least one a-posteriori soft symbol remodulated from said a-posteriori soft-bits, wherein σ 2 1 comprises said variance associated with said a-posteriori soft bits.

19. The apparatus of claim 18 , wherein said means for selecting comprises:

means for selecting said a-posteriori soft bits in response to a determination that σ 2 1 is greater than σ 2 0 .

20. The apparatus of claim 18 , wherein said means for selecting comprises:

means for selecting said a-priori soft bits in response to a determination that σ 2 0 is greater than σ 2 1 .

21. The apparatus of claim 18 , further comprising:

means for determining whether said iterative decoding of said a-priori soft bits was successful.

22. The apparatus of claim 21 , further comprising:

means for soft-remodulating said a-posteriori soft bits to said at least one a-posteriori soft symbol in response to a determination that said decoding was unsuccessful.

23. The apparatus of claim 16 , wherein said HARQ combining is selected from one or both of Chase combining or Incremental Redundancy combining.