New type of Viterbi decoding with path reduction

A new type of Viterbi decoding algorithm is proposed to realize fast decoding by reducing add-compare-select (ACS) operations, which occupy the dominant part of Viterbi decoding. In the decoding trellis, the branches with low probability to be the correct path are eliminated before decoding based on the detected signal level, which leads to the reduction of merge events in which ACS operation should be done. The reduction rate of the number of ACS operations and the bit-error probability with hard decision are derived for the codes with rate 1/2. It is shown that the number of ACS operations is considerably reduced and that, because of the decrement of the incorrect path, the error performance of the proposed decoding is superior to that of conventional hard-decision Viterbi decoding when the error due to correct path elimination is negligible. Reduced Viterbi decoding reduces the number of ACS operations up to 10% with additional coding gain of 0.6 dB for the code k = 3 and up to about 20% without performance degradation for k = 5.