Time-selective signaling for turbo-equalization

Time selective signaling is an important technique for improving effectiveness of the traditional error correcting codes in data transmission systems that exhibit multipath fading. Such channels often arise in mobile wireless communications systems. The time selective signaling method which spreads the modulated data with a limited number of spreading sequences like m-sequences can be used for intersymbol interference cancellation at the receiver. The number of spreading sequences depends on the number of the tabs considered for the frequency selective fading channels. Mathematically, it is shown that, from the perspective of the received signal, this algorithm can effectively transform an arbitrary frequency selective fading channel into a nonfading channel or marginally additive white Gaussian noise (AWGN) channel. Finally, we propose a low complex turbo equalizer based on the time selective signaling which can be considered as an alternative to the linear, nonlinear, and iterative turbo equalizers. Simulation results show that the proposed turbo equalizer is much less sensitive to the SNR mismatch and channel estimation error variance than the conventional turbo MAP equalizer.