Graph representation for joint channel estimation and symbol detection

A unified structure is proposed for joint channel tracking and symbol detection in multipath fading channels. Based on the expectation maximization (EM) algorithm, a group of recursive stochastic filters is derived for blind channel estimation, using the maximum likelihood and minimum mean squared error criteria. In conjunction with the BCJR algorithm, it is shown that the recursive procedure for joint channel estimation and maximum a posteriori symbol detection can be represented as a message-passing scheme on a factor graph. The graphical model not only provides a generalized implementation architecture for existing training-based schemes, it also greatly reduces the complexity of existing algorithms for blind channel tracking.