Yuan Ruiman, Zhang Tinglu, Li Cong, Gao Hong, Hu Lianbo
College of Marine Technology, Ocean University of China, Qingdao 266100, China.
Laboratory for Regional Oceanography and Numerical Modeling, Qingdao Marine Science and Technology Center, Qingdao 266237, China.
Sensors (Basel). 2025 May 12;25(10):3057. doi: 10.3390/s25103057.
Channel modeling of seawater is essential for understanding the transmission process of underwater laser light and optimizing the system design of underwater wireless laser communication. This study systematically examined the transmission characteristics of underwater blue-green laser communication, such as the angle of arrival, beam spreading, and channel loss, based on the Monte Carlo ray tracing method, across three different waters. The statistical analysis has led to the following definitive conclusions: (a) The differences in average AOA are profound in clear water and at short attenuation lengths in coastal and turbid harbor waters and are small at long attenuation lengths. The differences in average AOA between the offsets of 0 m and 10 m are about 62.3° and 12.9° at the attenuation lengths of 1 and 25 in clear water. The differences between offsets of 0 m and 10 m in average AOAs are about 74.4° and 5.8° in coastal water and 67.2° and 12.2° in turbid harbor water at the attenuation lengths of 1, 20, and 35, respectively. (b) The beam diameters are 0.1 m at the attenuation length of 25 in clear water and 83.8 m and 25.3 m when the attenuation length is 35 in coastal and turbid harbor waters. It manifests that the beam spreading is indistinctive in clear water while prominent in coastal and turbid harbor waters. (c) The difference in the received power at the various offsets decreases with increasing attenuation length but with distinct patterns. Take the offsets of 0 m and 10 m as examples. The absolute difference in the power loss reduces from 88.0 dB·m to 46.8 dB·m when the attenuation length reaches 25 in clear water. At the attenuation lengths of 1 and 35, the power losses are 94.9 dB·m and 4.3 dB·m in coastal water and 117.4 dB·m and 12.6 dB·m in turbid harbor water. Moreover, the minimum underestimation of power loss by applying Beer's Law could be almost 2 dB·m in turbid harbor waters. To achieve a high receiving gain, the weighted average angles of arrival at different offsets indicate that a small field of view is advantageous in clear water and at short transmission distances in coastal and turbid harbor waters. In contrast, a larger field of view is effective at long transmission distances in coastal and turbid harbor waters. Additionally, the absolute differences in channel losses at various offsets suggest that alignment between the transmitter and the receiver is crucial in clear water and at short transmission distances in coastal and turbid harbor waters. In contrast, misalignment may not lead to significant channel loss at longer transmission distances in turbid harbor water. The results of this study underscore the importance of considering water type, transmission distance, and offsets relative to the beam center when selecting receiver parameters.
海水信道建模对于理解水下激光的传输过程以及优化水下无线激光通信的系统设计至关重要。本研究基于蒙特卡罗射线追踪方法，系统地研究了水下蓝绿激光通信在三种不同水域中的传输特性，如到达角、光束扩展和信道损耗。统计分析得出了以下明确结论：(a) 在清水以及沿海和浑浊港口水域中短衰减长度时，平均到达角的差异很大，而在长衰减长度时差异很小。在清水衰减长度为1和25时，0 m和10 m偏移处的平均到达角差异分别约为62.3°和12.9°。在沿海水中衰减长度为1、20和35时，0 m和10 m偏移处的平均到达角差异分别约为74.4°和5.8°，在浑浊港口水中分别约为67.2°和12.2°。(b) 在清水衰减长度为25时光束直径为0.1 m，在沿海和浑浊港口水域衰减长度为35时分别为83.8 m和25.3 m。这表明光束扩展在清水中不明显，而在沿海和浑浊港口水域中很突出。(c) 不同偏移处接收功率的差异随着衰减长度的增加而减小，但模式不同。以0 m和10 m偏移为例。在清水衰减长度达到25时，功率损耗的绝对差异从88.0 dB·m降至46.8 dB·m。在沿海水中衰减长度为1和35时，功率损耗分别为94.9 dB·m和4.3 dB·m，在浑浊港口水中分别为117.4 dB·m和12.6 dB·m。此外，在浑浊港口水域中应用比尔定律时功率损耗的最小低估可能接近2 dB·m。为了实现高接收增益，不同偏移处的加权平均到达角表明，在清水中以及沿海和浑浊港口水域中短传输距离时，小视场是有利的。相比之下，在沿海和浑浊港口水域中长传输距离时，较大视场是有效的。此外，不同偏移处信道损耗的绝对差异表明，在清水中以及沿海和浑浊港口水域中短传输距离时，发射器和接收器之间的对准至关重要。相比之下，在浑浊港口水中长传输距离时，不对准可能不会导致显著的信道损耗。本研究结果强调了在选择接收器参数时考虑水的类型、传输距离以及相对于光束中心的偏移的重要性。
