Method and apparatus having cascaded decoding for multiple runlength-limited channel codes

Abstract

Two different (d,k)-RLL codes can be used in systems such as erasable and writable dense optical disks. This is because it is typically possible to make readers capable of reading information written at a higher resolution (by a short wavelength authoring system) than the resolution that can be written by a consumer writer (using a laser of the same or longer wavelength as the reader). For one embodiment, two different decoders are used to decode the data. Alternately, we present an encoding scheme which operates with a single decoder. In one case, q1=q2 (and as a result p1<p2), so that the decoders D1 and D2 actually process blocks of the same length. The decoding of the sequences encoded by E1 is done using the decoder D2 plus an additional function ψ which maps the restored p2-blocks into p1-blocks in a to very simple manner. This way, we do not need a separate circuit for the (d1,k1)-RLL decoder, because D1 is obtained as a cascading of D2 and another very simple circuit ψ. For one embodiment, the decoder D2 is a block decoder, and, consequently D1 is also a block decoder. The conversion performed by the function ψ is simply a removal of bits in fixed and pre-specified locations, thus getting the shorter p1-block out of the p2-block. The use of two coding schemes provides a method of making a lower performance recording system that produces recordings that are compatible with standard full performance readers. For example, this technique will allow a half capacity DVD to be written with a lower resolution system.

Dependencies are inferred from the claim text.