1. A combinational fuzzy-decision Viterbi decoder, comprising: a parallel to serial (P/S) converter, for converting parallelly transmitted signals into serially transmitted signals; a fuzzy decision constellation decoder, for estimating a received signal based on a combination of modified Π and S-membership functions; and a Viterbi decoder, using the estimation based on the combination of modified Π and S-membership functions as the input thereof to calculate analog path metrics while each path metric being calculated by weighting the square Hamming distance between zero and one and thus ranged between zero and one; wherein, a minimal path metric is acquired by using the traceback through the trellis and thus transmitted message bits are determined.