Semi‐blind MIMO‐OFDM channel estimation using expectation maximisation like techniques

This study deals with semi‐blind (SB) channel estimation of multiple‐input multiple‐output orthogonal frequency‐division multiplexing (MIMO‐OFDM) system using maximum likelihood (ML) technique. For the ML cost optimisation function, new expectation maximisation (EM) algorithms for the channel taps estimation are introduced. Different approximation/simplification approaches are proposed for the algorithm's computational cost reduction. The first approach consists of decomposing the MIMO‐OFDM system into parallel multiple‐input single‐output OFDM systems. The EM algorithm is then applied to estimate the MIMO channel in a parallel way. The second approach takes advantage of the SB context to reduce the EM cost from exponential to linear complexity by reducing the size of the search space. Finally, the last proposed approach uses a parallel interference cancellation technique to decompose the MIMO‐OFDM system into several single‐input multiple‐output OFDM systems. The latter are identified in a parallel scheme and with a reduced complexity. The performance of the proposed approaches are discussed, assessed through numerical experiments and compared with respect to the Cramèr Rao Bound and to other EM‐based solutions reported in the literature.