Turbo equalization with nonlinear Kalman filtering for time-varying frequency-selective fading channels

In this paper, we present a low complexity turbo equalization receiver for data transmission over time-varying frequency-selective fading channels. In the receiver, an adaptive equalizer using nonlinear Kalman filters with delay is coupled with a soft-in soft-cut (SISO) decoder to perform the reception process iteratively. The proposed adaptive equalizer jointly optimizes the estimates for channel taps and data symbols in each iteration with the assistance of a priori information for the data symbols supplied by the SISO decoder. In this way, the correlation between the estimates of data symbols and channel taps is taken into account in the equalization process. This correlation is usually ignored in many other turbo equalizers with separated channel estimation and data equalization. The complexity of the proposed equalizer does not grow exponentially with the modulation constellation size, and is usually lower than that of many maximum a posteriori equalizers with joint channel estimation and data detection. Performance comparison with different types of turbo equalizers over different channel conditions by Monte Carlo simulations demonstrates the advantage of the proposed turbo equalizer for fast time-varying fading channels