Frequency-domain equalization (FDE) is a computationally efficient method to recover underwater acoustic single-carrier transmissions in a multipath environment. The FDE receivers often operate in a block-by-block manner, assuming that the channel is time invariant during a block duration. This assumption implies that traditional block-based FDE receivers experience performance degradation in fast time-varying channel conditions, since the interfrequency interference (IFI) is often not considered. Here, we focus on the IFI cancelation (IFIC) in single-carrier transmissions. The IFI formulations are developed for a blockwise FDE receiver, where the time reversal (TR) processing is incorporated to alleviate the interblock interference. Based on the formulations, the IFI is estimated by the time-varying impulse responses, which are obtained from an adaptive basis expansion model. A soft two-step IFIC strategy is then employed to address the IFI. In the first step, the main IFI is removed by the time-varying TR processing and explicit IFI cancelation. The residual IFI is suppressed by the frequency-domain decision feedback equalization (FD-DFE) in the second step. To further enhance the communication performance, we develop a soft-symbol-based iterative receiver, referred to as IFIC-FD-DFE. The impulse responses, explicit IFI, and residual IFI are updated in an iterative fashion, based on the soft symbol estimates. The proposed receiver has been tested using the at-sea measurements collected at the Gulf of Mexico in August 2017. Communication packets at four ranges at the carrier frequency of 160 kHz with a symbol rate of 32 kHz have been decoded. The effectiveness of the IFIC-FD-DFE receiver has been demonstrated via comparisons with several FDE schemes in the current literature.

中文翻译：

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快速时变水下声信道中单载波传输的频域决策反馈均衡

频域均衡（FDE）是一种在多路径环境中恢复水下声单载波传输的高效计算方法。假设信道在块持续时间内是时不变的，则FDE接收器通常以逐块方式进行操作。这种假设意味着传统的基于块的FDE接收器在快速时变的信道条件下会出现性能下降的情况，因为通常不考虑频率间干扰（IFI）。在这里，我们关注单载波传输中的IFI消除（IFIC）。IFI公式是针对逐块FDE接收器开发的，其中结合了时间反转（TR）处理以减轻块间干扰。根据公式，IFI是根据随时间变化的脉冲响应来估算的，这是从自适应基础扩展模型获得的。然后采用软两步IFIC策略来解决IFI。第一步，通过时变TR处理和显式IFI取消来删除主IFI。在第二步中，通过频域决策反馈均衡（FD-DFE）抑制残留IFI。为了进一步提高通信性能，我们开发了一种基于软符号的迭代接收器，称为IFIC-FD-DFE。基于软符号估计，以迭代方式更新脉冲响应，显式IFI和残余IFI。拟议中的接收机已使用2017年8月在墨西哥湾收集的海上测量值进行了测试。已解码四个频段，载波频率为160 kHz，符号率为32 kHz的通信数据包。