| 摘要 |
PROBLEM TO BE SOLVED: To improve accuracy of decoding by improving the decoding algorithm in a soft output Viterbi algorithm SOVA. SOLUTION: A Two-Step SOVA decoder 20 is provided with a post-stage branch metric calculation circuit 25 that re-calculates a branch metric from a delayed input signal S26, a post-stage ACS circuit 26 that conducts add- compare-select(ACS) processing for LVA decoding on the basis of a branch metric signal S27 and a state metric stored in the inside, a selection circuit 27 that selects a state signal corresponding to delayed state information S25 from among metric difference delay signals S30, a post-stage path memory circuit 28 that outputs decoded data S34 on the basis of delay state information S25 outputted from the pre-stage path memory circuit 23, and a likelihood update circuit 29 that outputs likelihood, information, before the cutting-off length U of the post-stage path memory circuit 28, as a logarithmic likelihood ratio S35.
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