Combined turbo equalization and decoding for frequency-selective fading channels

RF sky wave transmissions undergo multipath fading due to propagation through the ionospheric layers. The HF channel is time varying and can be modeled by a tapped delay line of independent complex fading processes each exhibiting correlated fading characteristics specified in the ITU-R recommendation. A practical configuration for a turbo equalizer to combat the effects of intersymbol interference (ISI) in the HF channel, consisting of a soft decision feedback equalizer (SDFE), an interference canceller and a turbo decoder, all being SISO (soft in soft out) processes, is presented. The tap coefficients of the interference canceller filters are updated at each iteration with extrinsic information from the previous decoding operation.