The non-line-of-sight (NLOS) underwater communication can offer a viable route in signal propagation and coverage, thus mitigating the pointing, acquisition, and tracking difficulties in line-of-sight optical communication. However, implementing the NLOS link is non-trivial. While the NLOS technique relies on light scattering, i.e., channel turbulence can facilitate NLOS communication, the associated path-loss (PL) can be significant. Signal fading can degrade link robustness, which arises due to ocean water temperature and salinity fluctuation and gradients. To evaluate the robustness of NLOS in natural waters, we systematically measure the link metrics, such as the bit error ratio, PL, and signal-to-noise ratio (SNR), of water bodies of uniform and nonuniform vertical salinity ranging from 30–40‰ (part-per-thousand). We found that salinity-induced turbulence can establish NLOS communication with PL reduction of 2.35 dB/m and SNR increase by 32.5\%\% for dynamic water. Furthermore, a strong correlation was obtained between the strength of signal fluctuations and the received SNR. Finally, we obtained a Gaussian distribution of the statistical scintillation behavior. These results demonstrated the benefit of using the NLOS regime for underwater wireless sensor networks for aiding designers and engineers.

中文翻译：

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垂直盐度梯度对水下非视距光无线通信的影响


非视距（NLOS）水下通信可以为信号传播和覆盖提供可行的路线，从而缓解视距光通信中的指向、捕获和跟踪困难。然而，实现 NLOS 链路并非易事。虽然 NLOS 技术依赖于光散射，即通道湍流可以促进 NLOS 通信，但相关的路径损耗 (PL) 可能很大。信号衰落会降低链路的鲁棒性，这是由海水温度和盐度波动和梯度引起的。为了评估 NLOS 在自然水域中的鲁棒性，我们系统地测量了垂直盐度范围从 30 到 30 的均匀和非均匀垂直盐度水体的链路指标，例如误码率、PL 和信噪比 (SNR)。 40‰（千分之一）。我们发现，盐度引起的湍流可以建立非视距通信，动态水的 PL 降低 2.35 dB/m，SNR 提高 32.5\%\%。此外，信号波动强度与接收到的信噪比之间存在很强的相关性。最后，我们获得了统计闪烁行为的高斯分布。这些结果证明了将 NLOS 机制用于水下无线传感器网络可以为设计师和工程师提供帮助。