Coding and signal processing for three level run-length limited optical recording channel

Abstract

ABSTRACT A new high ecient DC-free 3-ary run-length limited (RLL) code for 3-level optical recording system is presented.Signal processing techniques, partial-response maximum-likelihood (PRML), which is used for recovery data fromreadout signal, is discussed.Keywords: optical recording, multi-level, RLL, PRML, DC-free 1. INTRODUCTION Traditional digital optical and magnetic recording channels have been of the saturation type, which limits therecorded information to binary values, wherefore conventional optical recording systems like the compact disc(CD) and digital versatile disc (DVD) use binary signaling in conjunction with run-length limited (RLL) codes,which are used to provide an eective increase in the recording densities. 1 This can be essentially seen as apulse width modulation (PWM) scheme, where information is conveyed in the length of the marks on the discand the spacing between them. As jitter, producing variations in the pulse widths of the recorded waveforms,is the dominant source of errors in traditional optical storage systems, therefore researchers tried to encodinginformation in the amplitude of the signal. This has led to research and implementations of systems storingnonbinary ( M -ary) signals using “xed-length, pulse amplitude modulation (PAM) in an attempt to store moreinformation per unit area. Various papers addressing “xed-length multi-level marks have appeared, using 8-12levels . The “rst 8 level CD-R and CD-RW compatible system achieves 2.5bits/0.6-micrometer mark comparedto a conventional CD system that stores 1.4bits/0.83-micrometer mark.