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.     

A high-resolution AUV navigation framework with integrated communication and tracking for under-ice deployments

We developed an environmentally adaptive under-ice navigation framework that was deployed in the Arctic Beaufort Sea during the United States Navy Ice Exercise in March 2020 (ICEX20). This navigation framework contained two subsystems developed from the ground up: (1) an on-board hydrodynamic model-aided navigation (HydroMAN) engine, and (2) an environmentally and acoustically adaptive integrated communication and navigation network (ICNN) that provided acoustic navigation aiding to the former. The HydroMAN synthesized measurements from an inertial navigation system (INS), ice-tracking Doppler velocity log (DVL), ICNN and pressure sensor into its self-calibrating vehicle flight dynamic model to compute the navigation solution. The ICNN system, which consisted of four ice buoys outfitted with acoustic modems, trilaterated the vehicle position using the one-way-travel-times (OWTT) of acoustic datagrams transmitted by the autonomous underwater vehicle (AUV) and received by the ice buoy network. The ICNN digested salinity and temperature information to provide model-assisted real-time OWTT range conversion to deliver accurate acoustic navigation updates to the HydroMAN. To decouple the contributions from the HydroMAN and ICNN subsystems towards a stable navigation solution, this article evaluates them separately: (1) HydroMAN was compared against DVL bottom-track aided INS during pre-ICEX20 engineering trials where both systems provided similar accuracy; (2) ICNN was evaluated by conducting a static experiment in the Arctic where the ICNN navigation updates were compared against GPS with ICNN error within low tens of meters. The joint HydroMAN-ICNN framework was tested during ICEX20, which provided a nondiverging high-resolution navigation solution—with the majority of error below 15 m—that facilitated a successful AUV recovery through a small ice hole after an 11 km untethered run in the upper and mid-water column.     

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.     

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.     

Cooperative localization of a team of AUVs by a tetrahedral configuration

This paper investigates the principles of a Cooperative Localization Algorithm for a team of at least three Autonomous Underwater Vehicles (AUVs) with respect to a surface support ship, without the use of Ultra-Short Baseline (USBL). It is assumed that each AUV is equipped with a low-cost Inertial Measurement Unit (IMU), a compass and a depth sensor, but only one of them has a high accuracy navigation sensor such as the Doppler Velocity Log (DVL). The surface boat locates itself by means of Global Positioning System (GPS). Range measurements provided by acoustic modems allow to avoid an unbounded error growth in the position estimate of each AUV. A geometric method, based on a tetrahedral configuration to obtain a deterministic fix for position, is proposed. This method allows to extend the advantages of the use of the DVL to the position estimate of other vehicles not equipped with DVL. The paper addresses also some of the problems related to the limitations of acoustic communication. The algorithm has been implemented and tested in simulations for a fleet of three AUVs and a surface support ship.     

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。     

一种针对全海深载人潜水器的异步融合组合导航算法

全海深载人潜水器（HOV）组合导航中会产生异步融合现象,传统的组合导航算法在处理时会产生较大的误差．针对这一问题,提出了一种基于机器学习和无迹卡尔曼滤波（UKF）的异步融合组合导航算法．首先建立了针对超短基线（USBL）声学定位系统预测的机器学习模型,通过USBL声学定位系统的观测数据集来训练该模型,并用得到的模型来预测更新间隔内的数据．最后使用UKF将已更新的数据集进行融合．仿真结果表明,相比传统的组合导航算法,本文的异步融合组合导航算法可以将USBL声学定位系统数据异步问题所引起的误差降低17%,有效提高了组合导航系统的精度．     

A time differences of arrival‐based homing strategy for autonomous underwater vehicles

A new sensor‐based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in 3‐D, using the information provided by an ultra‐short baseline (USBL) positioning system. The guidance and control law is first derived at a kinematic level, expressed on the space of the time differences of arrival (TDOAs), as directly measured by the USBL sensor, and assuming the plane wave approximation. Afterwards, the control law is extended for the dynamics of an underactuated AUV resorting to backstepping techniques. The proposed Lyapunov‐based control law yields almost global asymptotic stability (AGAS) in the absence of external disturbances and is further extended, keeping the same properties, to the case where known ocean currents affect the motion of the vehicle. Simulations are presented and discussed that illustrate the performance and behavior of the overall closed‐loop system in the presence of realistic sensor measurements and actuator saturation. Copyright © 2009 John Wiley & Sons, Ltd.     

Towards an autonomous underwater vehicles test range: At-sea experimentation of bearing-only tracking algorithms

Underwater navigation performance of Autonomous Underwater Vehicles (AUVs) strongly affects the quality of the collected data. Scientific literature extensively addresses the AUV tracking and self-localisation problems. However, no standard evaluation methods for vehicle navigation exist. Therefore, the authors’ visionary perspective is to develop and implement an Underwater Test Range (UTR) to certify the vehicle compliance with long-term underwater navigation. This paper describes a first step along this research path represented by an in field validation of such conceived measurement network. Experiments are soundly based on extensive simulation analysis presented in previous works. In particular, an underwater network composed of acoustic modems with Ultra Short BaseLine capabilities is deployed as measurement rig. This setup, through bearing-only measurements, allows the tracking of an Autonomous Surface Vehicle (ASV) equipped with Differential GPS as position ground truth. Results show how the proposed methodology performs in a real marine scenario with challenging conditions due to shallow waters and magnetically noisy environment.     

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.     

多AUV协同导航问题的研究现状与进展

自主水下航行器(Autonomous underwater vehicle, AUV)协同导航是未来50年解决水下中间层区域AUV导航定位的重要方法. 本文针对多AUV协同导航, 对该领域相关问题的研究进展进行了综述, 包括: 1)论述多AUV协同导航领域的研究现状, 包括协同导航问题界定、特点综述与讨论; 2)分析多AUV协同导航系统模型及相关算法的研究进展, 包括基于优化的、 基于参数估计的和基于贝叶斯估计的滤波算法; 3)对协同导航网络下的误差建模与补偿方法的研究进展进行了综述, 包括未知洋流的影响、水声通信延迟补偿等; 4)从影响协同导航定位精度的角度出发, 对AUV协同导航的可观测性与编队最优构型设计的研究进展进行了一系列的分析; 5)陈述目前多AUV协同导航中存在的关键问题, 并讨论其发展趋势.     

Field Testing of Moving Short‐baseline Navigation for Autonomous Underwater Vehicles using Synchronized Acoustic Messaging

This paper presents the results from field testing of a unique approach to the navigation of a fleet of autonomous underwater vehicles (AUVs) using only onboard sensors and information provided by a moving surface ship. The approach, considered moving short‐baseline (MSBL) navigation, uses two transponders mounted on a single surface ship that alternately broadcast acoustic messages containing one of the parameters of the kinematic state of the surface ship. The broadcasts are initiated according to a predefined schedule so that the one‐way travel time (OWTT) of the acoustic messages may be used to determine the range to the transponder. Each AUV in the fleet uses the surface ship state measurements and ranges provided by the acoustic messages in two extended Kalman filters (EKFs) for state estimation. The first EKF merges the intermittent surface ship state measurements with a kinematic model to estimate the state of the surface ship. This is necessary because the presented approach uses 13‐bit acoustic messages as opposed to the more commonly used 32‐byte messages, which allow the full state to be encoded in a single broadcast. The second EKF uses the current surface ship state estimate to properly interpret the acoustic ranges, combining them with a kinematic model to estimate the state of the AUV itself. Numerous MSBL navigation experiments were compared against a more traditional approach using a long‐baseline (LBL) array of transponders and OWTT acoustic ranging. The results of all tests were verified by independent LBL measures of position.     

Toward Autonomous Exploration in Confined Underwater Environments

In this field note, we detail the operations and discuss the results of an experiment conducted in the unstructured environment of an underwater cave complex using an autonomous underwater vehicle (AUV). For this experiment, the AUV was equipped with two acoustic sonar sensors to simultaneously map the caves' horizontal and vertical surfaces. Although the caves' spatial complexity required AUV guidance by a diver, this field deployment successfully demonstrates a scan‐matching algorithm in a simultaneous localization and mapping framework that significantly reduces and bounds the localization error for fully autonomous navigation. These methods are generalizable for AUV exploration in confined underwater environments where surfacing or predeployment of localization equipment is not feasible, and they may provide a useful step toward AUV utilization as a response tool in confined underwater disaster areas.     

Robot Navigation in a Decentralized Landmark-Free Sensor Network

A wireless sensor network has the ability to autonomously perform event detection over large areas, but power and/or cost constraints limit the addition of equipment such as cameras onto sensor modules to verify events. Accordingly, verification must be performed by an independent mobile robotic vehicle which has sensing equipment for improved event detection. The main challenge, however, is that the robotic vehicle itself is typically located somewhere in the sensor field and has no prior knowledge of the geographic location of the event. In this paper, we specifically focus upon the scenario of navigating a robotic vehicle through a stationary wireless sensor network as a means to perform event verification. The underlying assumptions are that the robotic vehicle has distance traveled and heading measurements, but the only additional information provided by the stationary sensors is a communication boundary. More significantly, we emphasize that under this scenario, neither the robot nor the ground-fixed sensing nodes have location or any other geographical landmark information. The paper introduces two distinct and novel navigation algorithms that permit the robotic vehicle to travel from one fixed node to another along a communication path established in an ad-hoc fashion. These navigation algorithms have been tested on a newly developed UTrekr robotic vehicle within a hardware based ground-fixed sensor network and under assumption of perfect communication and network operations, we report a nearly 100% success rate even while using open-loop robot control.     

A Sensor-Based Controller for Homing of Underactuated AUVs

A new sensor-based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in three dimensions, using the information provided by an ultrashort baseline (USBL) positioning system. The guidance and control law is first derived using quaternions to express the vehicle's attitude kinematics, which are directly obtained from the time differences of arrival (TDOA) measured by the USBL sensor. The dynamics are then included resorting to backstepping techniques. The proposed Lyapunov-based control law yields global asymptotic stability in the absence of external disturbances and is further extended, keeping the same properties, to the case where constant known ocean currents affect the dynamics of the vehicle. Finally, a globally exponentially stable nonlinear TDOA and range-based observer is introduced to estimate the ocean current and uniform asymptotic stability is obtained for the overall closed-loop system. Simulations are presented illustrating the performance of the proposed solutions.      

Terrain‐aided navigation for long‐endurance and deep‐rated autonomous underwater vehicles

Terrain‐aided navigation (TAN) is a localisation method which uses bathymetric measurements for bounding the growth in inertial navigation error. The minimisation of navigation errors is of particular importance for long‐endurance autonomous underwater vehicles (AUVs). This type of AUV requires simple and effective on‐board navigation solutions to undertake long‐range missions, operating for months rather than hours or days, without reliance on external support systems. Consequently, a suitable navigation solution has to fulfil two main requirements: (a) bounding the navigation error, and (b) conforming to energy constraints and conserving on‐board power. This study proposes a low‐complexity particle filter‐based TAN algorithm for Autosub Long Range, a long‐endurance deep‐rated AUV. This is a light and tractable filter that can be implemented on‐board in real time. The potential of the algorithm is investigated by evaluating its performance using field data from three deep (up to 3,700 m) and long‐range (up to 195 km in 77 hr) missions performed in the Southern Ocean during April 2017. The results obtained using TAN are compared to on‐board estimates, computed via dead reckoning, and ultrashort baseline (USBL) measurements, treated as baseline locations, sporadically recorded by a support ship. Results obtained through postprocessing demonstrate that TAN has the potential to prolong underwater missions to a range of hundreds of kilometres without the need for intermittent surfacing to obtain global positioning system fixes. During each of the missions, the system performed 20 Monte Carlo runs. Throughout each run, the algorithm maintained convergence and bounded error, with high estimation repeatability achieved between all runs, despite the limited suite of localisation sensors.     

自主式水下机器人数据采集与管理系统及其可靠性

自主式水下机器人(以下简称AUV)数据采集与管理系统(以下简称DCAM)利用多线程同步和通信机制实现了多串口数据采集,利用循环缓存区和存储转发的机制实现了将数据通过网络定时传送给工控机并将数据在本地保存。最后采用白盒测试的方法对该系统进行了测试并利用Musa执行时间模型对该系统进行了定量估计和预测其可靠性,预测结果显示该系统可以达到预计要求。     

RT2: real-time ray-tracing for underwater range evaluation

The paper deals with the distributed acoustic localization of teams of autonomous underwater vehicles (AUVs) and proposes a novel algorithm, real-time ray-tracing (RT²), for evaluating the distance between any pair of AUVs in the team. The technique, based on a modified formulation of the non-linear sound-ray propagation laws, allows efficient handling of the distorted and reflected acoustic ray paths. The proposed algorithm can be easily implemented on-board of low-cost AUVs, requiring the presence, on each vehicle, of an acoustic modem and a pair of look-up tables, a-priori built on the basis of the assumed knowledge of the depth-dependent sound velocity profile. On such a basis, every AUV can compute its distance w.r.t. to any other neighbor team member, through time-of-flight measurements and the exchanges of depth information only.     

一种改进的多AUV协同导航数学模型

自主式水下航行器(Autonomous Underwater Vehicle,AUV)代表了未来水下航行器发展的方向,多AUV协同导航系统通过信息的共享,可以获得单AUV导航系统无法具备的优势。分析了多AUV协同导航基本原理和两种网络结构的优缺点,提出了一种新的改进的多AUV协同导航网络结构,并推导出了其运动模型和量测模型,为后续协同导航算法的研究打下了基础。     

基于多描述编码和距离的车载网DSR路由技术研究

研究了车载自组网中基于多描述编码技术和车载节点间通信距离的按需路由DSR技术.针对车载自组网络拓扑的动态变化、车辆高速运动、车辆运行方向及其速度不可预知等特点,基于Ad Hoc网络按需路由协议DSR,研究了一种能较好地应用于车载自组网路由技术.该技术采用多描述编码技术和车载节点剩余能量改进了DSR的路由发现和回复过程....