Viterbi decoder is mainly used in communication systems where error detecting and correcting is so important. This based on trailis diagram decoding methos. Which will use minimum humming distance formula to predect error and get corrected data instead of the wrong one. Main use of this type of decoding is in deep space communication. This code can transmitt 8 bit of data which is encoded in 14 bits in total while travelling through the channel. Many add , compare and units are connected together in a structure which can make branch metrix to move further, in short it is to make one pathe which can be seleted while tracking back.-Viterbi decoder is mainly used in communication systems where error detecting and correcting is so important. This is based on trailis diagram decoding methos. Which will use minimum humming distance formula to predect error and get corrected data instead of the wrong one. Main use of this type of decoding is in deep space communication. This code can transmitt 8 bit of data which is encoded in 14 bits in total while travelling through the channel. Many add , compare and　units are connected together in a structure which can make branch metrix to move further, in short it is to make one pathe which can be seleted while tracking back.