The factor graph EM Algorithm: applications for LDPC codes

The factor graph EM (FGEM) algorithm is introduced, which is a way of describing the EM algorithm as a message-passing algorithm over a factor graph. Some interesting properties of this algorithm are discussed, such as its ability to break certain cycles in factor graphs. Systems with LDPC codes are used as a starting point for practical applications of the FGEM algorithm. In particular, in channels with an unknown channel state, FGEM-based estimation-decoding algorithms can be straightforwardly obtained, and specific examples are given using the block fading channel. Applications for LDPC-based source coding, especially the Slepian-Wolf coding problem, are also given.