ABSTRACT
The paper describes a new technique for constructing
fixed-length (d,k) runlength-limited block codes.
The new codes are very close to block-decodable codes, as decoding
of the retrieved sequence can be accomplished by observing (part of)
the received codeword plus a very small part (usually only a single
bit) of the previous codeword. The basic idea of the new construction
is to uniquely represent each source word by a (d,k) sequence with
specific predefined properties, and to construct a bridge of beta merging bits
between every pair of adjacent words. An essential element of the new coding
principle is look ahead. The merging bits are governed by the state of
the encoder (the history), the present source word to be translated,
and by the upcoming source word. The new constructions have the virtue that
only one look-up table is required for encoding and decoding.
Key Words: RLL code, look-ahead encoding, error propagation