基于多光束MIMO的海水/大气激光跨介质传输方法研究

As the increasing attention paid by whole country to the development of ocean resources and scientific survey, higher requirements are put forward for the performance of underwater and cross-media communications. However, the traditional underwater communication systems are unable to meet the growing needs of communication speed, distance and capacity. Through the preliminary investigation, we summarized the related underwater/cross-media communication technologies, then compared the advantages and disadvantages of them. Based on these conclusions, the research team has carried out corresponding analysis, and verified the potential superiority of underwater optical communication. With the support of the NSFC, firstly, this project intends to combine the theory of atmospheric and underwater optical wireless communication; secondly, use blue-green lasers as signal carriers to establish short-distance seawater/atmospheric laser uplink. The underwater optical wireless communication will be regarded as the major research subject. In this uplink, the optical channel transmission method between 30 meters above the surface of water and 30 meters underwater will be studied, and based on the research above, the cross-medium optical wireless MIMO theory will be further analysed. This project will help summarizing the general rules of optical wireless communication uplink, adopting the spatial diversity combinations appropriately and improving the performance of communication system significantly. Finally, this research will fill the gaps in seawater/atmosphere cross-medium optical wireless MIMO communication.

随着国家对海洋资源开发，海洋科学勘测等方面的关注力度逐渐加大，这就对水下及跨介质通信的性能提出了更高的要求，然而目前的水下通信系统已无法满足通信速率、距离和容量等方面日益增长的需求。通过前期调查，我们总结了相关水下及跨介质通信的技术，比较了不同通信技术之间的优缺点。本科研团队基于这些结论开展了相应的研究，验证了水下光通信在水下通信技术中的潜在优势。本项目拟通过国家自然科学基金支持，结合大气和水下光通信相关理论，采用蓝绿激光作为信号载体建立短距离海水/大气激光上行通信链路，以水下无线光通信为研究主体，对水下30米至水上30米光信道传输特性展开跨介质传输方法研究，并以此为基础进一步开展基于海水/大气无线光通信MIMO的理论研究。该研究对激光跨介质传输上行链路的一般规律，采用合适的空间分集技术和提高通信系统的整体性能，填补目前国内海水/大气跨介质光通信MIMO技术的空白均具有重要意义。

首先，分析了基于海洋-大气湍流的线性高斯阵列光束（Linear Gaussian array beams, LGAB），基于随机波理论和广义惠更斯-菲涅耳原理推导了LGAB的均方波束宽度和瑞利区间理论表达式。研究分别对均方光束宽度的特性与传播距离的关系、瑞利区间与海洋湍流参数/波束数/间隔距离的关系进行了深入研究，在海水-空气界面，LGAB的瑞利区间比水下环境高数倍（≥3）。此外，LGAB的瑞利区间随着海洋湍流/大气湍流间隔距离的增加而线性增加，而且相较于温度和盐度的影响，其受湍流动能耗散率和均方温度耗散率的影响更为显著。..其次，研究了三种典型的高斯阵列光束（Gaussian array beams, GABs）在海洋湍流下通过海水传播到空气中的光学分布结构，创新性地演示了海水-空气GABs的理论模型，该模型可以计算湍流介质中的平均GABs强度。基于这项研究总结了在海水-空气复杂环境中，强度的下降程度受到海浪、海洋湍流和光束分布结构的影响，在50m以下的通信距离，强度对传播距离更为敏感。光强度分布受到海洋湍流影响较为显著，而受到海浪泡沫层的影响较小。..最后，设计了阵列式光束组合，匹配了激光器，使用了基于雪崩光电二极管（APD）的探测器进行跨介质接收，最终研制了跨介质激光MIMO通信实验装置。通过误码率（BER）评估了光学多路复用（MIMO）通信系统的理论结果，研究结果表明，4×4 MIMO系统的误码率显著低于其他APD系统（超过10倍当平均能量高于−165 dBJ时更好）。因此确定了MIMO技术在海洋跨介质激光通信领域的研究前景和价值。.