High capacity run-length-limited coding system employing asymmetric and even-spaced codes

摘要

A system for encoding and decoding binary data in a data transmission system, such as a magnetic or optical data storage channel. The encoding process is implemented as a two-step RLL coding procedure wherein the original user bit data are first encoded as an asymmetric RLL code signal at a reduced clock rate and then translated to a second even- spaced RLL code signal suitable for recording to a data storage medium at a full- speed clock rate. The system also provides for recovering suitable even- spaced RLL codes recorded at a full-speed clock rate, translating the recovered even-spaced RLL code signal to an asymmetric RLL code signal at a reduced clock rate, and then decoding the asymmetric RLL code signal to recover the original user bit data. A preferred embodiment uses a rate 2/5 (2, 16, 2) even-spaced RLL code at a full- speed clock rate and a rate 4/5 (0,7; 1,8) asymmetric RLL code at a half- speed clock rate. The rate 4/5 asymmetric RLL code has a high capacity and the rate 2/5 even-spaced RLL code has a wide detection window. The intercode translation procedure requires only simple time-delay circuitry.