Factor graphs and iterative algorithms

We review the notion of factor graphs and give an overview of recent developments in the field. Factor graphs provide a framework in which iterative algorithms and iteratively decodable codes are easily described. They are obtained as a slight modification of the graphs, which were introduced by Wiberg, Loeliger and Koetter (1995). The notion of factor graphs is related to other graphical models, such as Bayesian networks and Markov random fields, and allows an easy integration of the decoding task and related problems in a communication system, such as channel estimation and equalization. Recently a number of research topics involving factor graphs have developed. These include the construction and representation of codes on graphs and an analysis of iterative decoding algorithm stemming from the theory of dynamical systems