Even mark modulation for optical recording

A novel modulation coding technique, even mark modulation (EMM), is proposed and shown to improve the performance of input-restricted partial-response class I and II optical recording channels. The coding technique produces a spectral null in the code power spectrum which coincides with the zero in the partial-response channel transfer functions at one-half the symbol frequency. This matched spectral null property of the code signals provides coding gains of 3 dB and 4 dB, respectively, compared to the uncoded input-restricted channels. Viterbi detection algorithms are derived which realize the theoretical gains with reduced complexity trellis structures. A rate 2/3 sliding block code satisfying the EMM constraints is described, and bit-by-bit simulation results confirm the predicted gains