Viterbi decoding of convolutional code with half rate & four state. It can done by two matrics . that is branch metrics and path metrics. Branch metrics is hamming distance between the parity bits and received bits. If branch metrics is zero then no error. Otherwise bit error occurred.path metrics is the hamming distance of path initial state to current state.the path with smallest distance result in less number of bit errors.-Viterbi decoding of convolutional code with half rate & four state. It can done by two matrics . that is branch metrics and path metrics. Branch metrics is hamming distance between the parity bits and received bits. If branch metrics is zero then no error. Otherwise bit error occurred.path metrics is the hamming distance of path　initial state to current state.the path with smallest distance result in less number of bit errors.