Experiment results of iterative block-based decision feedback equalizer with spatial diversity in underwater acoustic channels

The use of multiple hydrophones at the receiver brings several advantages to an underwater communication system, such as improved signal-to-noise (SNR) ratio and spatial diversity gain. Many existing array combining techniques have implicitly assumed that the channel undergoes flat fading, with either perfect time-domain equalization (TDE) or OFDM-based (Orthogonal Frequency Division Multiplexing) modulation. Unfortunately, direct applications of these methods to underwater acoustic (UWA) channels are severely limited by the long delay spread and the low dynamic range of hydrophones. In this paper, a receiver structure based on the recently developed iterative block (IB) decision-feedback equalization (DFE) with single-carrier frequency domain equalization (SC-FDE) was applied to the real underwater acoustic data from CAPEx09. We investigated the performance improvement of this nonlinear equalizer with respect to the regular linear MMSE equalizer. Our results show that the IB-DFE are more immune to the noise contaminations compared with MMSE equalizer.