Underwater acoustic (UWA) channels exhibit a sparse multipath structure, with each path having its corresponding direction of arrival (DOA). Conventional MIMO receivers process received signals hydrophone by hydrophone, disregarding the angle domain information. This paper presents a MIMO beamforming receiver for UWA communications. The proposed method estimates DOAs of multipath signals firstly, then forms directional signals with high signal-to-noise ratio by beamforming. Subsequently, it demodulates MIMO signals for these directional signals, leading to performance improvement. The wideband and high-frequency characteristics of UWA communication signals result in the receiving array element spacing being significantly larger than the signal wavelength. The proposed method adopts frequency-difference (FD) DOA estimation, solving the issue of bearing ambiguity arising from the large element spacing. Moreover, non-overlapping pilots of MIMO-OFDM signals are employed by the proposed method to estimate multipath DOA, resulting in increased resolution for multipath DOA from different transducers. Simulation results demonstrate the outstanding performance of the proposed beamforming receiver under low signal-to-noise ratio (SNR) and multi-interference conditions. The stability of the proposed beamforming receiver is additionally validated in lake trials employing UWA communication signals in the frequency bands of kHz and kHz. The receiver utilizes an 8-element receiving array with a 0.25 m element spacing.

中文翻译：

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用于高速率水声通信的基于多路径 DOA 的 MIMO 波束成形接收机方案

水下声学 (UWA) 通道呈现稀疏多径结构，每条路径都有其相应的到达方向 (DOA)。传统的MIMO接收器逐个水听器处理接收到的信号，忽略角域信息。本文提出了一种用于 UWA 通信的 MIMO 波束成形接收器。该方法首先估计多径信号的DOA，然后通过波束形成形成高信噪比的定向信号。随后，它解调这些定向信号的 MIMO 信号，从而提高性能。 UWA通信信号的宽带和高频特性导致接收阵元间距明显大于信号波长。该方法采用频差（FD）DOA估计，解决了大单元间距引起的方位模糊问题。此外，所提出的方法采用MIMO-OFDM信号的非重叠导频来估计多径DOA，从而提高了来自不同换能器的多径DOA的分辨率。仿真结果表明，所提出的波束成形接收器在低信噪比（SNR）和多干扰条件下具有出色的性能。所提出的波束成形接收器的稳定性在使用 kHz 和 kHz 频段内的 UWA 通信信号的湖泊试验中得到了进一步验证。接收器采用8单元接收阵列，单元间距为0.25 m。