GENERATION METHOD FOR CONFIDENCE LEVEL OF SOFT SYMBOL

PROBLEM TO BE SOLVED: To generate a soft symbol which is used when the received digital signals are decoded by deciding the difference between the accumulation costs of the next states having the 1st and 2nd possibilities and also performing the comparison and selection operations to specify one of both accumulation costs as the extreme value of the 1st and 2nd next states. SOLUTION: A data arithmetic unit 20 performs the calculation of a pipeline system to decide the difference between the accumulation costs PNS00 and PNS01 of the next states having the 1st and 2nd possibilities. The unit 20 also simultaneously gives the PNS00 and PNS01 to the adders 26 and 30 respectively. The adder 26 compares the PNS00 with PNS01 and the adder 30 defines the difference between them as a soft shift confidence level. Then the unit 20 selects the PNS00 or PNS01 as the maximum or minimum value based on the flag that is set via the comparison of the adder 26 and also stores one or more trace back bits in a register. Thus, it is possible to generate the soft symbol confidence level that is used for decoding the received digital signals.