Performance of Modulation Codes in Various Optical Recording Media : Drive Technology

The performance of modulation codes has been measured in ablative and magneto-optic recording media as well as in mastered direct discs. The modulation codes studied include NRZ (i.e. the uncoded bit stream), runlength limited sequences, multi-level recording schemes, and differentially detectable codes. We also studied the performance of codes when the optical channel is equalised, particularly the case of partial response detection of NRZ. The general conclusions are that: 1) differentially detectable codes require the full penalty in data density caused by the loss in code rate, 2) multi-level recording does not offer significant advantages, and step-constrained multi-level codes perform worse than their unconstrained counterparts, 3) runlength limited sequences are useful codes to enhance the density while offering additional practical advantages, and 4) partial response detection of uncoded bit streams transmitted through an equalised optical recording channel achieves the highest density.