Multiple-Pass Decision-Directed Channel Estimation for Highly Mobile MIMO Communications

In multiple-input multiple-output (MIMO) wireless communication systems employing coherent detection, good performance depends on the availability of accurate channel estimates. This is a significant challenge in mobile MIMO systems where the channel coefficients change too rapidly for the effective use of traditional training methods. In this paper, we present a multiple-pass decision-directed scheme for channel estimation and symbol decoding in scenarios for which the MIMO channel varies rapidly. In this scheme, pilot symbols are embedded over a block of data symbols at the transmitter, and the receiver uses this pilot information to iteratively optimize the channel and symbol estimates over the entire symbol block. The optimization is carried out over a posterior distribution which incorporates information about the channel model and noise properties. The conjugate gradient algorithm is used to jointly optimize the channel estimates over the block. Simulations show the benefits of using embedded training and demonstrate the utility of this multiple-pass method