An Acoustic Network Navigation System

This work describes a system for acoustic‐based navigation that relies on the addition of localization services to underwater networks. The localization capability has been added on top of an existing network, without imposing constraints on its structure/operation. The approach is based on the inclusion of timing information within acoustic messages through which it is possible to know the time of an acoustic transmission in relation to its reception. Exploiting such information at the network application level makes it possible to create an interrogation scheme similar to that of a long baseline. The advantage is that the nodes/autonomous underwater vehicles (AUVs) themselves become the transponders of a network baseline, and hence there is no need for dedicated instrumentation. The paper reports at sea results obtained from the COLLAB–NGAS14 experimental campaign. During the sea trial, the approach was implemented within an operational network in different configurations to support the navigation of the two Centre for Maritime Research and Experimentation Ocean Explorer (CMRE OEX) vehicles. The obtained results demonstrate that it is possible to support AUV navigation without constraining the network design and with a minimum communication overhead. Alternative solutions (e.g., synchronized clocks or two‐way‐travel‐time interrogations) might provide higher precision or accuracy, but they come at the cost of impacting on the network design and/or on the interrogation strategies. Results are discussed, and the performance achieved at sea demonstrates the viability to use the system in real, large‐scale operations involving multiple AUVs. These results represent a step toward location‐aware underwater networks that are able to provide node localization as a service.     

An autonomous underwater vehicle and SUNSET to bridge underwater networks composed of multi-vendor modems

Nowadays, underwater acoustic communication is an interesting topic of research. This is especially true in the case of Autonomous Underwater Vehicles (AUVs): due to the limitations of the underwater environment, where WiFi and radio communications are limited, it is very important to rely on efficient and reliable tools for acoustic data exchange. Indeed, an underwater network of acoustic nodes can enhance the navigation and localization capabilities of one or more vehicles. However, cooperation and networking is not feasible in underwater networks composed of vehicles with different software architecture and multi-vendor modems due to the lack of communication standards. In this paper, the authors investigate the use of an AUV as a mobile bridging node within a network of fixed heterogeneous acoustic modems. In particular, MARTA AUV, developed and built by the Department of Industrial Engineering of the University of Florence, is employed to enable data transmission between modems of different manufacturers. The networking and the handling of multiple and multi-vendor modems are instead performed through the SUNSET Software Defined Communication Stack (SDCS) framework, developed by University of Rome La Sapienza jointly with WSENSE Srl. Different bridging tests have been performed in field to evaluate the feasibility of such approach, showing that AUVs can efficiently accomplish the role of gateway between the nodes of the network communicating through the SUNSET SDCS framework.     

水声通信网络设计与OPNET平台下仿真

水声通信网络是当代海洋研究、海洋资源勘探和开发、海洋环境立体监测、地震海啸监测和战术监测等水下系统无线信息传输的主要手段,但其性能受水声信道特性影响严重。采用OPNET对水声通信网络节点模型与分层协议进行设计与实现,包括基于MC-CDMA的多用户检测以及基本CSMA/CA机制的信道握手流程与网络分配向量（NAV）帧冲突处理机制等。同时建立并测试了一个包含1个主节点与4个传感器节点的水声通信网络,仿真结果表明设计的水声通信网络能够更好的克服冲突,减少数据包重发,从而获得更高水声通信网络的吞吐量,减少端对端传输延时与能量消耗。     

水声通信网络信道仿真研究

根据海洋环境下水声信道的特性,提出一个面向水声通信网络信道的仿真框架,其中包括传播延迟、接收功率、背景噪声、干扰噪声、信噪比与误码率等若干模型,并以一个典型的水声网络仿真场景为例,给出了部分仿真试验结果.     

水声传感网MAC协议综述

海洋在人类发展中扮演着越来越重要的角色。水下通信技术作为人类认识海洋的重要手段,成为研究界的热点与难点。由于水下通信技术有不同于陆地无线通信的信道特点和性能要求,传统无线通信MAC(medium access controD协议难以直接应用于水声通信,因此相继提出针对各种应用场景的水声MAC协议。在简述水声传感网(Undcrwatcr Acoustic Sensor Nctwork,UWASN)特点和MAC协议设计准则后,根据信道获取方式将当前典型协议分为基于竟争和基于调度两大类。根据冲突处置方式进一步将基于竞争的协议分为随机多址和冲突避免,根据信道分配的动态性将基于调度的协议分为动态分配和静态分配。在此分类基础上,描述了近期出现的典型协议的设计思想、主要机制,并比较了协议在能耗、信道利用、吞吐量等方面的差异,最后指出提高MAC协议性能的发展方向。     

考虑水流影响的水下传感器网络移动算法研究*

随着世界各国海洋开发和海洋军事的飞速发展,水下传感器网络成为一个新的研究热点,其中失效补偿和高效节能是水下传感器网络研究的重要问题。水声通信的特点使得移动节点在水下传感器网络中得到较为广泛的使用,以其作为失效补偿和提高覆盖效率的有效手段。为了减小移动节点的能耗,改进了现有的移动部署方案,提出一种新的水下传感节点移动算法,在移动路径规划时充分利用水流和重力、浮力的影响来减少节点的移动能量。数值计算和仿真结果表明,本算法有效节省了移动节点的能量消耗,验证了其有效性和正确性。     

Typhoon at CommsNet13: Experimental experience on AUV navigation and localization

This paper presents two acoustic-based techniques for Autonomous Underwater Vehicle (AUV) navigation within an underwater network of fixed sensors. The proposed algorithms exploit the positioning measurements provided by an Ultra-Short Base Line (USBL) transducer on-board the vehicle to aid the navigation task. In the considered framework the acoustic measurements are embedded in the communication network scheme, causing time-varying delays in ranging with the fixed nodes. The results presented are obtained with post-processing elaborations of the raw experimental data collected during the CommsNet13 campaign, organized and scientifically led by the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (CMRE). The experiment involved several research institutions and included among its objectives the evaluation of on-board acoustic USBL systems for navigation and localization of AUVs. The ISME groups of the Universities of Florence and Pisa jointly participated to the experiment with one Typhoon class vehicle. This is a 300 m depth rated AUV with acoustic communication capabilities originally developed by the two groups for archaeological search in the framework of the THESAURUS project. The CommsNet13 Typhoon, equipped with an acoustic modem/USBL head, navigated within the fixed nodes acoustic network deployed by CMRE. This allows the comparison between inertial navigation, acoustic self-localization and ground truth represented by GPS signals (when the vehicle was at the surface).     

Cooperative navigation of AUVs via acoustic communication networking: field experience with the Typhoon vehicles

A cooperative navigation procedure for a team of autonomous underwater vehicles (AUVs) is described and validated on experimental data. The procedure relies on acoustic communication networking among the AUVs and/or fixed acoustic nodes, and it is suitable as a low-cost solution for team navigation. Embedding the acoustic localization measurements in the communication scheme causes delays and sometimes loss of acoustic data, depending on acoustic propagation conditions. Despite this drawback, the results obtained show that on-board localization estimates have an error of the order of few meters, improving the overall navigation performance and leading the system towards long-term autonomy in terms of operating mission time, without the need of periodic resurfacings dedicated to reset the estimation error. The data were collected during the CommsNet ’13 experiment, led by the NATO Science and Technology Organization Center for Maritime Research and Experimentation (CMRE), and the Breaking The Surface ’14 workshop, organized by the University of Zagreb.     

Evaluating acousticcommunication performance of micro autonomous underwater vehicles in confined spaces

Micro-sized autonomous underwater vehicles (μAUVs) are well suited to various applications in confined underwater spaces. Acoustic communication is required for many application scenarios of μAUVs to enable data transmission without surfacing. This paper presents the integration of a compact acoustic communication device with a μAUV prototype. Packet reception rate (PRR) and bit error rate (BER) of the acoustic communication link are evaluated in a confined pool environment through experiments while the μAUV is either stationary or moving. We pinpoint several major factors that impact the communication performance. Experimental results show that the multi-path effect significantly affects the synchronization signals of the communication device. The relative motion between the vehicle and the base station also degrades the communication performance. These results suggest future methods towards improvements.     

水下无线传感器网络信道研究

水下无线传感器网络通信信道是一种环境噪声高、传播时延长、误比特率高、多径干扰、多普勒效应严重的时、频、空变复杂的随机信道。水下声信道的复杂性和多变性严重限制了水下声通信的性能。本文使用Matlab软件研究、仿真分析了上述因素对水下无线传感器网络通信性能的影响,为更好地设计无线传感器网络信道模型、合理的水下无线传感器网络拓扑结构以及低功耗、高性能的路由协议提供一定的参考依据。     

面向能量和链路优化的水声移动传感器网络路由协议设计

针对水声移动传感器网络中存在水声通信环境恶劣、通信环境复杂多变以及节点能量受限造成的水声移 动传感器网络能量不均和路由链路断裂问题, 提出一种基于能量与链路度量路由的改进按需平面距离向量路由 (AODV)协议. 引入了以能量阈值为基准描述网络节点能量状态的能量指标以及以邻居节点间距离为基准描述链路 状态的链路指标, 并以综合考虑网络路由链路中节点的能量指标、路由链路指标以及路由链路跳数的路由度量作 为协议选择路径的优先条件, 并以此进行路由修复. 仿真实验表明, 本文所设计的改进AODV协议可提升网络整体 数据量、均衡网络节点能量、延长网络的生存周期.     

水声信道的多模型模拟和试验

水声信道是一个时变的多径信道，且在不同的时间由于海面的状况不同而不同。为较好地实现水声通信．必须对各种水声信道进行较好地了解，研究出适合水下通信，尤其是水下实时通信的较为实际的模型，增加水下声通信的可靠性和水声实时通信的可懂率。该文在前期研究的基础上，将多模型方法应用于水下声信道的研究，并得出了相应的实验方法。     

基于量子隐形传态的水下传感器网络分级加密通信协议

针对水下传感器网络中通信信息安全性与水声信道通信特性的不足,提出了一种基于量子隐形传态的水下传感器网络分级加密通信协议.一级在水面基站与自由水下航行器之间,采用量子隐形传态实现两者之间共享量子密钥,利用纠缠关联空间非定域性保证其通信信息安全性;二级在水下节点到水下自由航行器之间,采用对称加密算法实现两者之间信息的加密传输,利用对称加密快捷的优点提高其通信信息效率.分别对量子攻击、经典攻击及通信效率这3个方面进行了分析,证明该协议能有效防止量子态截获、重构、替换等攻击.     

稀疏水下传感网中AUV数据移动收集技术研究

由于水下传感器节点的水声通信距离有限、价格昂贵,水下传感器网络中一般采用稀疏方式部署,因此很难保证整体网络的连通性及数据采集效率。自主水下航行器AUV（Autonomous Underwater Vehicle）作为天然的移动数据采集平台,可以弥补固定Sink节点数据采集方式的缺陷。提出了一种基于移动AUV的水下传感网移动数据收集机制。以AUV覆盖区域内的传感器节点作为临时Sink节点,其他传感器节点以临时Sink节点为根节点,采用最小生成树MST（Minimum Spanning Tree）方法将传感数据传输到这些临时Sink节点,然后通过临时Sink节点将汇聚数据传输给AUV。随着AUV的自主移动轨迹,水下传感网的传感数据都能简单高效地被收集起来。仿真结果验证了该方法在保证网络能耗的前提下提高了数据采集效率。     

基于复合AUVs的水声传感网拓扑优化机制

为提高网络拓扑的健壮性和自适应性, 基于拓扑重构思想提出基于复合自主式水下航行器的水声传感网拓扑智能优化机制来提高网络的连通性; 进一步, 在发现水声传感网拓扑结构形成的内在规律的基础上, 提出三角淡化关键节点网络拓扑优化方法, 该方法有助于提高网络抗毁再生能力. 最后通过仿真实验对比分析验证了所提出机制的有效性, 实验结果表明, 在牺牲约8.5\%覆盖度的条件下, 抗毁性能提高约50\%.     

一种基于水声通信网络的实时路由协议

水声通信网络的传输特点使得实现实时传输的路由协议非常困难。在SPEED协议的基础上综合考虑了节点的能量消耗,提出了一个适用于水下通信网络的实时路由协议。该协议在实现实时传输的基础上,通过能量感知功能来延长网络的生存期。通过仿真论证,结果表明所提出的实时路由协议在水声通信网络中具有很好的性能。     

基于通信网络算法在水下通信中仿真研究

研究通信网络在水下通信效率优化问题,由于海洋的复杂环境、水声不稳定以及水声受到介质噪声的干扰,造成水下通信率低。为了解决上述问题,建立了一种H∞滤波器节点移动预测算法的资源预留机制,为节点在水声网络中提供基于移动IP的QoS保障。根据移动节点的移动方向判断其即将加入的子网,在子网中提前预留资源,其它子网不再为移动节点提前预留资源,从而节约水声无线通信网络有限的带宽、能量等资源,并进行仿真。仿真结果表明,改进的方法能够为水声网络提供较高的资源利用率,在时延、吞吐量等方面提供有效保障。     

基于多AUV协作的稀疏水下传感网定位技术研究

如何在稀疏部署的水下传感器网络中实现传感器节点的高效定位是一个研究热点.提出了一种基于多个移动AUV协作的水下传感器网络内节点定位机制,利用AUV的精确自导航功能实现对网内未知位置节点的定位协助.提出的协作定位算法扩展了水下传感器网络的网内节点位置迭代估计方法,将信标节点和多AUV联合作为定位参考点,然后推导了基于最小二乘法的定位估计方程.仿真结果验证了该方法可以在定位节点比例、归一化定位误差和平均置信度等几个方面提高定位性能.     

Cooperative bathymetry-based localization using low-cost autonomous underwater vehicles

We present a cooperative bathymetry-based localization approach for a team of low-cost autonomous underwater vehicles (AUVs), each equipped only with a single-beam altimeter, a depth sensor and an acoustic modem. The localization of the individual AUV is achieved via fully decentralized particle filtering, with the local filter’s measurement model driven by the AUV’s altimeter measurements and ranging information obtained through inter-vehicle communication. We perform empirical analysis on the factors that affect the filter performance. Simulation studies using randomly generated trajectories as well as trajectories executed by the AUVs during field experiments successfully demonstrate the feasibility of the technique. The proposed cooperative localization technique has the potential to prolong AUV mission time, and thus open the door for long-term autonomy underwater.     

一种水声通信中的自适应ARQ方案

在水声通信系统中,由于水声信道的半双工、时变和长传播时延等特性,导致用于水声通信中的停等自动重传请求(SW ARQ)方案的吞吐性能显著下降。本文首先利用扩频通信技术,将单个信道分成两个子信道：一个用于前向信道(从发送方到接收方),另一个用于反向信道(从接收方到发送方),充分地利用水声信道。在此基础上,结合选择自动重传请求(SRARQ)方案与返回-n自动重传请求(GBNARQ)方案的混合式自动重传请求(SR GBNARQ)方案的优良性能,提出了一种随水声信道的时变特性改变分组长度的自适应ARQ方案。仿真结果表明：该方案能有效地提高水声通信系统的吞吐性能。