Abstract: Distance spectrum is the main factor in determining the event error probability when maximum-likelihood decoding is used for convolutional codes [13]. In this paper we compute the distance spectrum for the best R=1/N channel codes obtained using convolutional (linear trellis) codes together with known offset sequence addition on precoded partial-response 1-D channel proposed in [4]. To this end we have modified the BIFAST algorithm [11] in order to enable the distance spectrum evaluation in the supper-trellis [1], a technique necessary for this type of channel codes.
Key words: Trellis codes, cahannel codes, convolution codes, distance spectrum, Viterbi detectors, partial response signalling.