Frequency domain direct adaptive turbo equalization based on block least mean square for underwater acoustic communications

In this paper, a novel frequency domain direct adaptive turbo equalizer (FDDA-TEQ) is proposed for time-varying underwater acoustic (UWA) channels. The proposed equalizer uses a modified frequency domain block normalized least mean square (FBNLMS) algorithm to update filter coefficients, which can effectively solve the problem of insufficient filter length in traditional adaptive frequency domain equalization. A sliding window strategy is adopted to deal with the rapid time-varying characteristic of UWA channels. Meanwhile, an iterative structure in the equalizer is proposed to further improve performance. The proposed method (FDDA-TEQ) is tested by simulation and the data collected in the real-world underwater experiments. Both simulation and experimental results can prove the effectiveness and superiority of the proposed method. (C) 2022 Elsevier Ltd. All rights reserved.