ABSTRACT
Runlength-limited (RLL) codes have found widespread usage in
optical and magnetic recording products. Specifically, the RLL codes
EFM and its successor, EFMPlus, are used in the Compact Disc (CD) and
the Digital Versatile Disc (DVD), respectively.
EFMPlus offers a 6% increase in storage capacity with respect to EFM.
The work reports on the feasibility and limits of EFM-like codes
that offer an even larger capacity. To this end, we will
provide an overview of the various limiting factors, such as runlength
constraint, dc-content, and code complexity, and outline their relative effect
on the code rate. In the second part of the article we will
show how the performance predicted by the tenets of information
theory can be realized in practice. A worked example of a
code whose rate is 7.5% larger than EFMPlus, namely a
rate 256/476, (d=2, k=15) code, showing a 13 dB attenuation at
fb=10-3, will be given to illustrate the theory.
Key Words: EFM, Compact Disc, DVD, constrained code, recording code, run-length-limited