Iterative block Decision Feedback Equalizer with Soft Detection for underwater acoustic channels

In single-carrier modulation system with frequency domain equalization, Decision Feedback Equalizer with a Hybrid time-frequency structure (H-DFE) is attractive for its performance; the complexity is also significant, especially for very dispersive channels. Iterative Block Decision Feedback Equalizer with Hard Detection (HD-IBDFE) system performance degrades caused by errors in symbol decision and it needs to calculate the correlation factor of the transmitted and hard detected data. To solve these problems, Iterative Block Decision Feedback Equalizer with Soft Detection (SD-IBDFE) is introduced to improve the system performance. The receiver feedbacks the soft information of the equalizer's output. The iterative channel estimation is adopted in order to deal with the time-varying underwater acoustic channels. Simulation results show that SD-IBDFE is superior to HD-IBDFE obviously for underwater acoustic channel. One underwater acoustic communication system is designed and tested in the lake. At a distance of 1.8 km with complex channel condition, the useful data rate of around 3000 bps is achieved with uncoded bit error rates 10^-3 in lake experiment.