Method of decoding a correcting code, for example a turbo-code, by analysis of the extended spectrum of the words of the code
AssigneeThales
InventorsBenjamin GADAT, Nicolas VAN WAMBEKE, Lionel RIES
Life of this patent
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Abstract
An improved decoding method is provided making it possible to solve the problem of the error floor of a turbo-code or of an LDPC code, or more generally of a correcting code from the family of “turbo-like codes”, while preserving the same spectral efficiency, without any decrease in the useful throughput of the encoded stream. This result is obtained by an identification, on input to the decoder, of the bits on which an error has a strong impact, and a modification of the likelihoods corresponding to these bits so as to improve the convergence of the decoder.
Claims14
An iterative method of decoding a code word received from a correcting code, the said code word being represented by an item of information regarding local likelihood of each bit of which it consists, the iterative method comprising the following steps:
- a step of analysing the extended spectrum of the words of the code to generate a table containing, for each bit of a code word, an item of information regarding distance between the said code word and the code word obtained by decoding and then re-encoding the said code word for which the value of a bit is erroneous, and
- for each bit of index i of a subset of the bits of the code word received, executing in an iterative manner the following steps:
- a step of decoding the said code word received,
- a step of calculating an item of information regarding overall likelihood IM(i) of the decoded code word,
- a step of comparing, onwards of the second iteration (i=2), the item of information regarding overall likelihood IM(i) calculated at the current iteration with the item of information regarding overall likelihood IM(i−1) calculated at the previous iteration,
- a step of modifying the amplitude and the sign of the item of information regarding local likelihood LLR(i) of a bit of index i of the said code word received, the selected index i corresponding to that index of the said table which is associated with the lowest distance in the table, from among the indices not selected at a previous iteration,
- onwards of the second iteration (i=2), if the item of information regarding overall likelihood IM(i) calculated at the current iteration is less than the item of information regarding overall likelihood IM(i−1) calculated at the previous iteration, a step of reinitializing the item of information, modified at the previous iteration, regarding local likelihood LLR(i−1) of the said bit of index i−1 of the said code word received.
Dependencies are inferred from the claim text.