Turbo-codes: the ultimate error control codes?

Turbo-codes have attracted a great deal of interest since their discovery in 1993. This paper reviews the reasons for this, in particular their attainment of the ultimate limits of the capacity of a communication channel. The paper describes the two fundamental concepts on which they are based: concatenated coding and iterative decoding. This latter is the real 'turbo-principle', which is the real secret of their remarkable performance. The paper also reviews the direction of research in this area since 1993, and shows that, far from bringing coding research to an end, turbo-codes have led to a renaissance. In particular, other applications of the 'turbo-principle' have emerged, and these are discussed, along with the practical applications of turbo-codes that have appeared, from mobile radio to deep-space exploration.