基于光声融合的水下无线传感器网络关键问题研究

Marine power and competition of strategic resources are the important international background of the development of the marine science and technology, national "Transparent Ocean" strategy urgently needs the high-speed underwater wireless transmission technology to real-time or timely transmit the three-dimensional high-resolution observation data. Currently, underwater acoustic sensor networks have obtained high transmission distance, but with low date rate, high power consumption, high cost and damage to marine ecology. Meanwhile, underwater optical communications can achieve high date rate, but with difficult networking and short communication distance. This project intends to propose an optical-acoustic fusion underwater wireless sensor network, which can use the ability of optical communication to achieve high-speed transmission at close range and use the characteristics of acoustic communication to transmit control command and node localization, and achieve long-distance optical transmission through the directional optical communication and multi-hop transmission mechanism. It also intends to design the whole space optical repeater to solve the problem of difficult networking. The physical layer can realize adaptive optical-acoustic switch, code modulation and demodulation to meet the needs of different communication scenes. With the characteristics of directional optical transmission, the data link layer employs the space division multiple access technology to improve the data transmission efficiency, designs a routing protocol to improve the network life cycle and adapt to the network topology changes frequently, and provides the analysis of the network energy efficiency and the optimization strategy. With the advantages of low power consumption, low cost, and strong network robust, the proposed system will solve the high-speed wireless transmission problem of real-time video images in marine exploration and provide new solutions for the high-speed transmission of marine information detection.

海洋强国和战略资源竞争是发展海洋科技的国际大背景，国家“透明海洋”战略部署急需水下高速无线传输技术实时或及时传输海域三维立体高分辨率观测数据。目前水下声无线传感网传输距离远但速率低、功耗大、成本高、破坏海洋生态，水下光通信速率高但组网难、通信距离短。本项目拟提出一种光声融合的水下无线传感网，利用光通信实现近距离高速传输、利用声通信传输控制命令及节点定位，通过定向光传输及多跳机制实现光通信远距离传输，研究全空间覆盖的光中继器解决光通信组网难问题。本项目在物理层将实现自适应光声切换及编码调制解调，在数据链路层接入时利用光的定向传输特性引入空分多址技术提高数据传输效率，研究可提高网络生命周期并适应网络拓扑频繁变化的路由协议，研究网络能量效率评价机制和优化策略。本项目研究功耗小成本低网络健壮性强的新型无线传感网，解决海洋探测中实时视频和图像高速无线传输难题，为海洋信息探测领域提供高速传输新方案。

针对海洋探测中实时或准实时视频和图像高速无线传输难题，提出一种自适应光声切换的水下无线通信系统及组网方案。针对该新型网络的物理层、数据链路层和网络层关键问题开展了具体研究。主要成果包括：（1）提出一种光声融合的无线传感网，利用光通信实现近距离高速传输、利用声通信传输控制命令及节点定位，通过定向光传输及多跳机制实现光通信远距离传输，利用全空间覆盖的光中继器解决光通信组网问题。通过检测水下无线传感网两个通信节点间的信噪比，并根据其信噪比等级自适应选择采用声通信模式或者光通信模式作为通信节点间约定通信模式，进而执行节点间数据传输。当光链路不可用时，声链路作为备用链路以低速模式传输高优先级数据。由于系统采用定向光通信发送以及多跳机制，大大增加了传输距离。（2）提出一种适用于水下光声融合无线传感网络的低功耗竞争MAC协议（简称OA-CMAC协议），OA-CMAC协议通过声握手进行节点定位，通过光握手进行光束对准，声握手和光握手均成功后进行数据传输。通过OMNeT++仿真可以看出，该协议在光握手成功率高于50%时，与水声通信MAC协议相比，吞吐量成倍数提高，并且节点的生存周期提高33%，极大程度上降低网络成本。采用OA-CMAC协议可实现更高的吞吐量和更低的节点能耗，适用于高负载大容量数据的水下无线通信环境。（3）考虑到水下通信环境恶劣、网络节点受海流影响具有三维移动性等问题，针对水下网络节点电池不易更换、有限生命周期等特点，充分利用光信号在水下通信传输速率较高的特点，提出一种适用于光声融合无线传感网的反向路由搜索算法实现最优路由查找，并由Sink节点发起周期性组建临时网络的路由协议。该路由协议在组网过程中充分降低能耗、并合理选择传输路径提高了网络生存时间。以上工作解决了海洋探测中实时或准实时的视频和图像高速无线传输难题，在海洋信息传输领域发挥重要作用。