Receivers for Coded Signals: A Unified View Based on Factor Graph

Normal factor graphs are a graphical representation of the factorization of a function of several variables into a product of functions of a lower number of variables. This representation yields efficient algorithms for computing the marginals of the original function with respect to any one of its variables. Originally developed for decoding turbo codes, it was recognized that factor graphs are a natural setting for the description of a number of general iterative and noniterative techniques for detecting coded signals transmitted on a variety of channels. In addition, they provide a unified framework allowing one to understand the connections among seemingly different detection problems. This talk summarizes the application of normal factor graphs to a number of these problems, such as equalization of coded signals, multiuser detection, decoding of multilevel coded modulation, and reception of space-time coded signals.