Pruning the algorithm complexity of the Add-Compare Select Unit (ACSU) for the Viterbi Decoder - A Review

Viterbi decoders are widely employed along with convolutional encoders to provide an excellent error correction probability in digital wireless transmissions. To achieve lower error rates, the constraint length (k) of the encoder, has to be defined at higher values. However, higher (k) results in increasingly complex implementations of the Viterbi algorithm. As a result, the power consumption of the Viterbi decoder will increase exponentially which is to the disadvantage of many wireless communication devices. Many reduced complexity decoding techniques of the Viterbi decoder presented in the past focused on algorithm and architecture specific levels. Most of the studies concentrated on the Add-Compare Select Unit (ACSU) of the decoder, due to its nature of repetitive processing; also add to the complexity of the process. This paper presents a review of several variations of the Viterbi algorithm performed in the ACSU. The comparison was made among several different algorithms with the most optimal algorithm presented in this paper. A combined algorithm approach is proposed at the end of the review for future improvement.