Abstract

The use of modulation codes in magnetic and optical data storage systems is widespread and the advantages of modulation coding are well known [1-3]. Usually a 1 is used to represent a transition between the up and down states of the recording waveform, while a 0 represents no change. An unconstrained sequence of l's and 0's, however, is not acceptable, nor is it desirable, in practice. The objective of modulation coding is to create a one-to-one correspondence between sequences of user data (which are usually streams of random binary digits) and constrained binary sequences. The nature of the constraints imposed on the modulated signal must be determined by the system designer and is dependent on the particular characteristics of the system under consideration. A typical set of such restrictions is the so-called (d,k;c) constraint. Here d is the minimum allowed run-length of zeros, k is the maximum allowed run-length of zeros, and c is the maximum charge that the recording waveform is permitted to accumulate. In addition, certain sequences of bits may be reserved for special purposes (such as synchronization or signaling the beginning of a block) and thus banned from appearing in the modulated waveform.

© 1991 Optical Society of America