Permuted trellis codes for input restricted partial response channels

A method for maximum likelihood detection of a trellis code, comprising the steps of:

• using an encoder, encoding sequences of digital electrical signals constituting input data into codewords consisting of sequences of coded bits;
• inputting said codewords to a partial response channel;
• supplying a channel response to the codewords, corrupted by noise, to a Viterbi detector;
• constructing the Viterbi detector from connected trellises that are associated with the channel, each trellis repeated in periodic fashion and comprising subtrellises with nodes representing a current state of the channel and a value of a predetermined tracked attribute of each codeword;
• reassigning a survivor metric and survivor sequence from a node at the end of one subtrellis to a node having a different value of the tracked attribute at the beginning of an adjacent subtrellis to provide a time-varying trellis structure with periodic state metric permutations ensuring prospecified minimum distance properties;
• and
• using the Viterbi detector to provide as output sequences maximum likelihood estimates of the sequences of coded bits.

A method of creating a rate x/y trellis code, comprising the steps of:

• specifying sets of sequences and concatenation rules which will generate a collection of y-length code sequences ensuring prespecified minimum distance properties;
• encoding a series of x-length sequences into y-length code sequences;
• using said sets and rules, generating a trellis structure comprising connected trellises, each consisting of at least one subtrellis, each subtrellis having nodes representing a current state of a partial response channel and a value of a predetermined tracked attribute;
• and
• mating at least one pair of nodes at the proximate ends of adjacent subtrellises that have different values of the tracked attribute by reassigning the value of one of said pair of nodes to the other said pair.

Apparatus for maximum likelihood detection of a rate x/y trellis code, comprising:

• an encoder for encoding a series of x-length sequences of digital electrical signals constituting input data into codewords, each consisting of a series of y-length sequences of coded bits;
• a partial response channel for receiving said codewords from the encoder;
• a Viterbi detector for receiving from the channel responses to the codewords, corrupted by noise, to provide output sequences constituting maximum likelihood estimates of said codewords, said Viterbi detector being constructed from trellises that are associated with the channel and track a predetermined attribute of each codeword, each trellis (i) having a period equal to the length of at least one codeword and (ii) comprising subtrellises with nodes representing a current state of the channel and a value of the tracked attribute, at least one pair of the end nodes of adjacent subtrellises having different values, said detector comprising means for reassigning a survivor metric and survivor sequence of one of said nodes of the pair to the other node of said pair to provide a time-varying trellis structure with periodic state metric permutations for providing selected minimum distance properties between output sequences supported by the time-varying trellis structure;
• and
• a decoder for converting into an estimate of the input data sequences output by the detector as maximum likelihood estimates of the sequences of the coded bits.