Signal decoding for either Manhattan or Hamming metric based Viterbi decoders

A method and apparatus is presented for establishing an equivalence between the Hamming branch metric scheme and the Manhattan branch metric scheme. A signal format converter is presented to convert input signal in a first number system such as binary or two's complement, into a second number system. The signal format converter implemented at the input to a Viterbi decoder allows the use of a Viterbi decoder designed for a Manhattan metric sceme in an application where the signals are represented in two's complement. Similarly a Viterbi decoder designed for a Hamming metric scheme can be implemented in an application where the signals are represented in unsigned binary. The signal format converter can be used with both a hard decision Viterbi decoder and a soft decision Viterbi decoder. Where a soft decision Viterbi decoder is used the soft symbol of a Manhattan metric scheme based Viterbi decoder can be converted to an equivalent Hamming soft symbol by taking the two's complement of the absolute value of the accumulated cost difference. Where the Viterbi decoder is based on a Hamming metric scheme, an equivalent Manhattan soft symbol can be obtained by taking the absolute value of the soft symbol decoded output.