A Survey of High-Rate Constrained Codes

The construction of high-rate codes is far from obvious, as table look-up for encoding and decoding is an engineering impracticality. The usual approach is to supplement the p source bits withm = q p bits. Under certain, usually simple, rules the source word is modi ed in such a way that the modi ed word plus supplement bits comply with the constraints. The information that certain modi cations have been made is carried by the m supplement bits. The receiver, on reception of the word, will undo the modi cations. In order to reduce complexity and error propagation, the number of bits a ected by a modi cation should be as small as possible. We will survey some examples of code constructions.