Polarity-Freedom Codes for High Information Entropy Recording

季兆澍(Chao S. Chi)

《Chinese Journal of Physics》 25卷3期 (1987/09) Pp. 499-511

並列摘要

A novel recording technique, based on controlled high-frequency dithering on the record side to create position-dependent ”breaks” is presented. These breaks permit the polarity of flux transition to convey useful information in addition to the conventional flux transition positions. Furthermore, the width of the breaks can be modulated to create different amplitude levels. By utilizing polarity, amplitude, and position parameters independently and collectively, the encoding variable can be expanded from one- (position) into two- (position and polarity) and three- (position, polarity, and amplitude) dimensional freedoms. Thus, information entropy is greatly increased without violating the Wallace wavelength-limited basic principle. This technique may point to a new class of modulation schemes, where a significant areal density increase over the conventional position-modulation method can be made practically feasible. Two actual implementations, the ”CRA” ternary code and the ”Triplex” quarternary code, are illustrated. Signal spectral density and information entropy evaluation of these codes are calculated.