This letter addresses the problem of channel estimation in fast time-varying frequency selective channels. Considering orthogonal frequency division multiplexing in a multipleinput multiple-output system, we perform soft-Kalman filtering for channel estimation in conjunction with soft-interference canceling at the receiver to reduce the inter-carrier interference. We also propose two simplified implementations of the soft-Kalman filter for the case of constant-modulus signal constellations that allow considerable reductions in the receiver computational complexity, while performing more or less closely to the exact soft-Kalman estimator, depending on channel conditions. For non-constant-modulus signal constellations, however, the exact formulation of the soft-Kalman filter should be used.
