Underwater wireless communications refer to data transmission in unguided water environment through wireless carriers, i.e., radio-frequency (RF) wave, acoustic wave, and optical wave. In comparison to RF and acoustic counterparts, underwater optical wireless communication (UOWC) can provide a much higher transmission bandwidth and much higher data rate. Therefore, we focus, in this paper, on the UOWC that employs optical wave as the transmission carrier. In recent years, many potential applications of UOWC systems have been proposed for environmental monitoring, offshore exploration, disaster precaution, and military operations. However, UOWC systems also suffer from severe absorption and scattering introduced by underwater channels. In order to overcome these technical barriers, several new system design approaches, which are different from the conventional terrestrial free-space optical communication, have been explored in recent years. We provide a comprehensive and exhaustive survey of the state-of-the-art UOWC research in three aspects: 1) channel characterization; 2) modulation; and 3) coding techniques, together with the practical implementations of UOWC.

A Survey of Underwater Optical Wireless Communications

https://iris.unito.it/bitstream/2318/1695314/1/HE-S-18-04814-final.pdf

Application of Hydrides in Hydrogen Storage and Compression: Achievements, Outlook and Perspectives

The deep sea remains the largest unknown territory on Earth because it is so difficult to explore1–4. Owing to the extremely high pressure in the deep sea, rigid vessels5–7 and pressure-compensation systems8–10 are typically required to protect mechatronic systems. However, deep-sea creatures that lack bulky or heavy pressure-tolerant systems can thrive at extreme depths11–17. Here, inspired by the structure of a deep-sea snailfish15, we develop an untethered soft robot for deep-sea exploration, with onboard power, control and actuation protected from pressure by integrating electronics in a silicone matrix. This self-powered robot eliminates the requirement for any rigid vessel. To reduce shear stress at the interfaces between electronic components, we decentralize the electronics by increasing the distance between components or separating them from the printed circuit board. Careful design of the dielectric elastomer material used for the robot’s flapping fins allowed the robot to be actuated successfully in a field test in the Mariana Trench down to a depth of 10,900 metres and to swim freely in the South China Sea at a depth of 3,224 metres. We validate the pressure resilience of the electronic components and soft actuators through systematic experiments and theoretical analyses. Our work highlights the potential of designing soft, lightweight devices for use in extreme conditions. A free-swimming soft robot inspired by deep-sea creatures, with artificial muscle, power and control electronics spread across a polymer matrix, successfully adapts to high pressure and operates in the deep ocean.

Self-powered soft robot in the Mariana Trench

Self-localization of an underwater vehicle is particularly challenging due to the absence of Global Positioning System (GPS) reception or features at known positions that could otherwise have been used for position computation. Thus Autonomous Underwater Vehicle (AUV) applications typically require the pre-deployment of a set of beacons. 
This thesis examines the scenario in which the members of a group of AUVs exchange navigation information with one another so as to improve their individual position estimates. 
We describe how the underwater environment poses unique challenges to vehicle navigation not encountered in other environments in which robots operate and how cooperation can improve the performance of self-localization. As intra-vehicle cornmunication is crucial to cooperation, we also address the constraints of the communication channel and the effect that these constraints have on the design of cooperation strategies. 
The classical approaches to underwater self-localization of a single vehicle, as well as more recently developed techniques are presented. We then examine how methods used for cooperating land-vehicles can be transferred to the underwater domain. An algorithm for distributed self-localization, which is designed to take the specific characteristics of the environment into account, is proposed. 
We also address how correlated position estimates of cooperating vehicles can lead to overconfidence in individual position estimates. 
Finally, key to any successful cooperative navigation strategy is the incorporation of the relative positioning between vehicles. The performance of localization algorithms with different geometries is analyzed and a distributed algorithm for the dynamic positioning of vehicles, which serve as dedicated navigation beacons for a fleet of AUVs, is proposed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

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Cooperative localization for autonomous underwater vehicles

This paper describes an algorithm for distributed acoustic navigation for A utonomous Underwater Vehicles (AUVs). Whereas typical AUV navigation systems utilize pre-calibrated ar rays of static transponders, our work seeks to create a fully mobile network of AUVs that perform acoustic rang ing and data exchange with one another to achieve cooperative positioning for extended duration missions over lar ge areas. The algorithm enumerates possible solutions for the AUV trajectory based on dead-reckoning and range-o ly measurements provided by acoustic modems that are mounted on each vehicle, and chooses the trajectory via minimizatio n of a cost function based on these constraints. The resulting algorithm is computationally efficient, meets the stric t bandwidth requirements of available AUV modems, and has potential to scale well to networks of large numbers of vehicles. The method has undergone extensive experimentation, and results from three different scenario s re reported in this paper, each of which utilizes MIT SCOUT Autonomous Surface Craft (ASC) as convenient platform s for testing. In the first experiment, we utilize three ASCs, each equipped with a Woods Hole acoustic modem, as surrog ates for AUVs. In this scenario, two ASCs serve as Communication/Navigation Aids (CNAs) for a third ASC that compu tes its position based exclusively on GPS positions of the CNAs and acoustic range measurements between platf orms. In the second scenario, an undersea glider is used in conjunction with two ASCs serving as CNAs. Finally, in the third e xperiment, a Bluefin12 AUV serves as the target vehicle. All three experiments demonstrate the succ s ful operation of the technique with real ocean data. Index Terms autonomous underwater vehicles, cooperative navigation, mobile robo tics, sensor networks I. I NTRODUCTION The absence of Global Positioning System (GPS) signals unde rwat r makes navigation for Autonomous Underwater Vehicles (AUVs) a difficult challenge. Without an exte rnal reference in the form of acoustic beacons at known positions, the vehicle has to rely on proprioceptive inform ation obtained through a compass, a Doppler Velocity Logger (DVL) or an Inertial Navigation System (INS) [WYSH00] . Independent of the quality of the sensors used, the error in the position estimate based on dead-reckoning i formation grows without bound. Typical navigation The authors are with the Computer Science and Artificial Intel lig nce Laboratory, Massachusetts Institute of Technolog y, Cambridge, MA 02139, USA October 30, 2008 DRAFT 2 errors are 0.5 % to 2 % of distance traveled for vehicles opera ting within a few hundred meters of the sea floor such that their DVL has a lock on the bottom. Errors as low as 0. 1 % can be obtained with large and expensive INS systems, but for vehicles relying only on a compass and a s peed estimate, errors can be as high as 20 %. By surfacing the AUV can obtain a position update through its GP S, but this is impossible (under ice) or undesirable for many applications. The use of static beacons in the form o f a Long Baseline (LBL) array limits the operation area to a few km and requires a substantial deployment effort before operat ions, especially in deep water. As underwater vehicles become more reliable and affordable the simultaneous use of several AUVs recently became a viable option and multi-vehicle deployments will b ecome standard in the upcoming years. This will not only make possible entirely new types of missions which r ely on cooperation, but will also allow each individual member of the group to benefit from navigation inf ormation obtained from other members. For optimal cooperative localization a few dedicated Communication an d Navigation Aid-AUVs (CNAs), which maintain an accurate estimate of their position through sophisticated DVL and INS sensors, can enable a much larger group of vehicles with less sophisticated navigation suites to main tain an accurate position, as described in [VLCW04a]. The idea of an underwater equivalent to the terrestrial GPS h as long held appeal to AUV researchers. For example, A.C.S.A. has developed a portable undersea tracking range t hat provides a form of “underwater GPS” in a local area [Tho01]. In the A.C.S.A. system, a network of four surfa ce buoys equipped with GPS and RF communications utilize passive acoustic range measurements to track the po sition of a time-synchronized mobile undersea device. While the base system usually employs moored or drifted surfa ce buoys, experiments using self-powered surface craft have also been performed. Further extensions of this c oncept could employ acoustic communications to relay the vehicle pose estimate obtained by the surface buoys back to the undersea vehicle itself. The motivation behind our research is to enable multiple AUV s to cooperatively navigate. The ideal solution would enable heterogeneous teams of AUVs to operate with hig navigational precision, without frequent surfacing for GPS measurements, even for the case when only a small numb er of the AUVs in the team are equipped with expensive inertial sensors. One application of this capabi lity would be to perform rapid, large-area search with a mixed AUV network consisting of Comm/Nav-Aid AUVs, Search -Classify-Map AUVs, and Reacquire-Identify AUVs [VLCW04b]. The problem of cooperative navigation of AUVs is highly inte rconnected to the problem of undersea acoustic communications [Cat90], [KB00], [FJG 01]. Our work capitalizes on recent progress by the Acoustic Modem Group at Woods Hole Oceanographic Institution (WHOI) in deve loping integrated communication and navigation (ranging) capabilities for small AUVs. This application ra ises several interesting challenges for acoustic telemetr y research, such as the need to handle a fully mobile network an d the goal of achieving accurate one-way ranging through stable clock synchronization. There has been a great deal of work in terrestrial settings on the problem of cooperative navigation of multiple mobile robots. Often the problem is cast in terms of a mix of mo bile and static nodes in a large-scale sensor network, with either angle-only or range-only measurement s. A variety of state estimation approaches have been followed, including Markov chain Monte Carlo and set-theor etic state estimators. For example, Liao et al. [LHDS06] October 30, 2008 DRAFT 3 employed a particle filter state estimator for cooperative l oca ization of multiple ground robots using range-only measurements. Djugash et al. [DKSZ06] developed an approach that integrated Simultaneo us Localization and Mapping (SLAM) with mobile sensor networks, achieving self -calibration of a network consisting of mobile and stationary nodes with range measurements. Grocholsky et al. [GSSK06] used nonlinear set-based state estimation techniques for localization of multiple mobile robots with range measurements between platforms. The underwater setting presents some unique challenges for cooperative mobile robotics. The assumption of a fast and reliable communication channel between all parti cipants of the cooperative navigation effort, as made in [RB00], [RDM02], and [MLRT04], does not hold underwater. Due to the strong attenuation of electro-magnetic waves underwater, radio or optical communication is not pra ctic lly feasible except for distances of a few meters. As a result acoustic modems, typically operating between 15 and 30 kHz, provide the only possible means of communicating at long ranges underwater. Data rates are typ ically several orders of magnitude below those achieved with radio-based communication channels [KB00]. With soun d propagation being dependent on temperature and salinity, which can both vary strongly within the water colu mn, the acoustic communication channel is unreliable and its performance hard to predict. This is especially true in shallow water, where severe multi-path is often encountered. The concept of portable landmarks as outlined in [KNH94] is not feasible as it is often difficult for an AUV to hold its position, especially in strong currents. The objective for our work is to develop and test an algorithm for cooperative positioning of multiple mobile undersea vehicles that can use acoustic modems concurrentl y for both ranging and for communication [FJG 01]. The solution must be robust to the errors and time delays that are inherent to acoustic range measurements and must take into account the severe bandwidth constraints of state -of-the-art undersea acoustic modems. This restriction prevents the transfer of full state information between veh icl s. The cooperative navigation problem is complementary to the problems of cooperative motion planning and control for underwater platforms. For example, Leonard et al. have addressed a class of cooperative adaptive sampling problems for networks of AUVs and underwater gliders [LPL 07]. In this work the motion of a fleet of vehicles is directed to acquire optimal data sets based on the predict ions of numerical ocean models. This work typically assumes that accurate navigation information is available , for example through GPS measurements obtained at the surface. This scenario provides a compelling application s cenario in which our cooperative navigation techniques could be applied, obviating the need for all vehicles in the fl e t to surface for positioning. Using a one-way messaging system with the WHOI modem, Eustice et al. [EWSG07] recently implemented a least squares version of a maximum likelihood algorithm to c arry out moving baseline navigation. The approach utilized a particularly accurate heading and dead-reckoni ng system and as well as a specially designed low drift timing clock. II. T ECHNICAL APPROACH In order to cooperate during their mission the AUVs will be ou tfitted with acoustic modems. Data rates on the order of 100 bytes/s over distances of up to 5 km have been a chieved, but given varying channel quality, October 30,

/pdf/cooperative-localization-for-autonomous-underwater-vehicles-43ea7067xr.pdf

Cooperative Localization for Autonomous Underwater Vehicles

This paper presents an integrated navigation system for underwater vehicles to improve the performance of a conventional inertial acoustic navigation system by introducing range measurement. The integrated navigation system is based on a strapdown inertial navigation system (SDINS) accompanying range sensor, Doppler velocity log (DVL), magnetic compass, and depth sensor. Two measurement models of the range sensor are derived and augmented to the inertial acoustic navigation system, respectively. A multirate extended Kalman filter (EKF) is adopted to propagate the error covariance with the inertial sensors, where the filter updates the measurement errors and the error covariance and corrects the system states when the external measurements are available. This paper demonstrates the improvement on the robustness and convergence of the integrated navigation system with range aiding (RA). This paper used experimental data obtained from a rotating arm test with a fish model to simulate the navigational performance. Strong points of the navigation system are the elimination of initial position errors and the robustness on the dropout of acoustic signals. The convergence speed and conditions of the initial error removal are examined with Monte Carlo simulation. In addition, numerical simulations are conducted with the six-degrees-of-freedom (6-DOF) equations of motion of an autonomous underwater vehicle (AUV) in a boustrophedon survey mode to illustrate the effectiveness of the integrated navigation system.

Simulation of an Inertial Acoustic Navigation System With Range Aiding for an Autonomous Underwater Vehicle

We measured a significantly low off-state current (135 yA/µm at 85 °C) of a metal oxide semiconductor (MOS) transistor using indium–gallium–zinc oxide (IGZO), which is an oxide semiconductor material. Note that "y" is 10-24. A transistor in which the hydrogen concentration in an IGZO film is lowered (5×1019 cm-3 or lower) was used. To estimate the minute current accurately, we established a measurement method in which changes in the amount of electrical charge are measured for a long time. Such extremely low off-state current characteristics show promise for new applications of IGZO transistors in memories.

https://iopscience.iop.org/article/10.1143/JJAP.51.021201/pdf

Evaluation of Off-State Current Characteristics of Transistor Using Oxide Semiconductor Material, Indium--Gallium--Zinc Oxide

An autonomous underwater vehicle (AUV) is equipped with an inertial navigation system (INS) in order to understand its own position in real time while it cruises without the communication with the external environment such as a support ship and GPS. Japan Agency for Marine-Earth Science and Technology has the cruising AUV URASHIMA, and it is also equipped with the INS. However the INS outputs its own absolute position containing the error that increases with time. It means, it is very difficult for URASHIMA to cruise dependent only on the position data outputted by the INS for a long time. So we have proposed the method to improve the performance of the INS, and its effect was confirmed in experiments. In the method, it was put on a turntable with assumption that it is fixed inside URASHIAM and the INS has been rotated by it around one rotation axis according to some rules. Consequently, the INS's position error was decreased by the rotational motion. In order to cause this effect, a precondition had to be met. It was that URASHIMA keeps its own posture to near-horizontal while cruising. However URASHIMA usually cruises with the roll motion which is caused by its shape. So the roll motion such as URASHIMA's one in a sea trial was applied to the turntable, and the INS was rotated in the situation. As the result, the INS's position error was decreased about half of the original one.

Accuracy Improvement of an Inertial Navigation System Brought about by the Rotational Motion

Japan Marine Science and Technology center (JAMSTEC) developed a full ocean depth research ROV (remotely operated vehicle), "KAIKO", whose construction started in January, 1991, and whose sea trial was carried out from May, 1993 to March, 1995. The sea trial had three separated phases, that is, the first test at 1000 m deep ocean near the main land of Japan, the second test at Nansei Shoto Trench of 6500 m deep, and the final test at Mariana Trench in order to confirm the capability of the system at the deepest ocean bottom on Earth. The original plan for the final sea trial had been scheduled in July, 1993, however, it was delayed by some troubles. The main trouble was on the data transmission through a secondary cable between a launcher and a vehicle of "KAIKO". After clearing up all causes of the troubles, the authors carried out the sea trial again at Mariana Trench in March, 1995, and succeeded in the deepest challenge. This paper described the feature of "KAIKO" and the result of the sea trial.

The sea trial of "KAIKO", the full ocean depth research ROV

There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. AUVs (Autonomous Underwater Vehicle) were considered and chosen, as the most suitable tool for conducting surveys concerning these global environmental problems. JAMSTEC has started building a long range cruising AUV. The plan for its development is in several steps. As the first step an AUV, named “URASHIMA”, was built in 1999, and sea trials have been held since 2000. URASHIMA dived to 3,518 meters depth in 2001. At the end of February 2005, URASHIMA was able to cruise autonomously and continuously for 317 kilometers, beyond its target range of 300 kilometers. This record is the longest one in the world. PEFC (Polymer electrolyte Fuel Cell) power system with Metal Hydrogen storage has been developed for expanding its cruising range. As the second step, an AUV “URASHIMA-2”, which will cruise more than 3,000 kilometers, will be developed from 2007. The development plan of the next AUV was selected as one of the official national important technologies in Japan. The deep-sea areas we know of constitute only a small fraction of the entire deep-sea. The information that can be obtained by man-made satellites is limited to that pertaining to the surface or subsurface portions of the sea. Today, man does not have the means to canvass the entire deep-sea at one time. If a number of AUVs like the URASHIMA autonomously cruise in various deep-sea areas of the world, man will then, for the first time, be able to get the entire picture of the deep-sea.

Taro Aoki

Papers

Simulation of an Inertial Acoustic Navigation System With Range Aiding for an Autonomous Underwater Vehicle

Evaluation of Off-State Current Characteristics of Transistor Using Oxide Semiconductor Material, Indium--Gallium--Zinc Oxide

Accuracy Improvement of an Inertial Navigation System Brought about by the Rotational Motion

The sea trial of "KAIKO", the full ocean depth research ROV

Advanced Technologies For Cruising AUV URASHIMA