1. A high-rate constrained encoder for encoding a communications signal, the encoder comprising: a data transformer configured to translate a binary data sequence into a transformed data sequence of a different alphabet size, wherein the data transformer comprises an indicator selector to select at least one word that appears as a prefix of at most a fixed number of words in the binary data sequence; and a finite-state encoder for imposing at least one constraint on the transformed data sequence and outputting the transformed data sequence.