Phase invariant rate 8/10 matched spectral null code for PRML

A method for coding a binary data string for a partial-response channel having a transfer function with a spectral null at zero frequency, said method comprising the steps of:

• (a) providing from a matched spectral null canonical state diagram a code which does not generate quasi-catastrophic sequences and having a coding rate and an output which is invariant to 180-degree phase shifts in a channel output signal;
• (b) creating a fininte-state machine having a plurality of pairs of states and a plurality of codewords each corresponding to a respective binary data byte;
• (c) responsive to a data byte in the binary data string, generating one of two complementary codewords from the one of that pair of said states designated by said machine as corresponding to said data byte for a then current state of the machine for thereby encoding the binary data string into a string of binary codewords having a spectral null constraint producing a power spectrum value of zero for a frequency of zero;
• (d) repeating step (c) for successive bytes of the binary data string to generate a sequence of codewords;
• and
• (e) providing a Viterbi detector having a finite path memory;
• (f) matching a trellis in the Viterbi detector to the spectral null constraint for generating from a potentially noisy channel output signal an estimate of the most probable sequence of binary codewords produced by said finite-state machine;
• and
• (g) decoding said sequence of codewords in a decoder requiring no look-ahead or look-back for providing the same binary data string output for said sequence or its complement.