Viterbi algorithm for Decoding :
     The viterbi algorithm uses the trellis representation of the code. The principle behind the trellis is that the equivalence between maximum likelihood decoding and minimum distance decoding can be used in choosing a path in the code tree whose coded sequence differs from the received sequence in the fewest number of places.

     Consider the trellis diagram for convolutional code described in Figure 3.1 and Figure 3.2. The viterbi algorithm performs the following steps as it walks over the trellis.