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Summary: Underwater Wireless Communication is a rapidly growing technology in the research domain. The researchers have been working towards the developments in underwater communication by investigating climatic changes, prediction of natural disasters, marine environment, monitoring aquatic life, oceanographic transmission, and data collection. The main objective of underwater communication is to achieve lossless, high transmission with the least power consumption. The Unmanned Underwater Vehicles (UUVs) and Autonomous Underwater Vehicles (AUVs) are set up with remote instruments and sensors to enable the natural exploration of the resources in the undersea environment. This research article is based on the study of various modes of communication, architectures, and protocol layers involved in underwater communication. Furthermore, an underwater hybrid connection is established by opto‐acoustic signals, and the overview of various performance characteristics, channel behaviors, and issues in the underwater scenario are investigated. [ABSTRACT FROM AUTHOR]

To improve the observation capability of the ocean, the combination of the static cabled ocean observatory network and the dynamic autonomous underwater vehicle has attracted more and more attention. In this paper, a non-contact docking system for the autonomous underwater vehicle is developed to combine the advantages of the cabled ocean observatory network and the autonomous underwater vehicle. The system includes both acoustic and optical navigation, underwater wireless communication, non-contact power transfer, and monitoring and controlling of the docking system. This docking system was verified by sea trials at depths of 50 and 105 m. The autonomous underwater vehicle successfully docked 11 times, during which non-contact power transfer and wireless communication were completed. The charging power reached 682 W, with a total efficiency of 78.5%, and the efficiency of the power transfer unit was 92%. The rate of wireless data transfer reached 3.1 MB/s. For the first time, this docking system has realized complete homing and docking navigation, wireless communication and charging in a water depth of more than 100 m, thus establishing a good foundation for the combination of the cabled ocean observatory network and autonomous underwater vehicles. [ABSTRACT FROM AUTHOR]

Autonomous Underwater Vehicles (AUVs) are robotic devices with a propulsion system for navigation and an onboard computer for decision making. AUV research is gaining popularity because of its extensive applications in fields from military to science. Robotic systems are need of the hour for exploration and environmental safety of the vast and deep oceans and water bodies. This paper presents current research trends in the field of AUVs and highlights future research directions. Here localization and navigation techniques such as inertial navigation to simultaneous localization and mapping being used in current AUVs are discussed in detail. Different optimal path planning and control methods are highlighted. Use of different sensor technology like sonar, laser, acoustic modems and stereo vision systems for localization, navigation and mapping is presented. Recent developments in underwater wireless communication along with the commercially available devices are discussed. • Review of AUVs based on structural design and propulsion technique are presented.. • Different adaptive control and path-planning techniques have been reviewed.. • Underwater localization techniques suitable for different applications are discussed.. • Developments of relatively new Intervention AUVs are presented.. • Underwater wireless communication methods and available systems are discussed.. [ABSTRACT FROM AUTHOR]

The technologies used in underwater and air–water (A–W) wireless communication networks (WCN) are increasingly attracting attention due to numerous modern applications, e.g., internet of underwater things etc. However, for practical implementations of these modern applications, the security of the underwater and A–W WCNs needs to be ensured beforehand. Thus, the main focus of this survey is to systematically discuss the security needs of underwater and A–W WCNs, and solutions proposed to date. Before extending our discussion on security, we initially cover the fundamentals of underwater and A–W WCNs. First, we provide a comprehensive overview of different underwater communication technologies: radio frequency (RF), acoustic, optical, and magnetic induction (MI) in terms of channel characteristics, merits, and demerits. The discussion is further extended to A–W wireless communication by presenting direct and indirect (relay-aided) techniques. Then we present the primer on information security which highlights the four fundamental properties of security (i.e., confidentiality, integrity, authentication, and availability) and security solutions (i.e., cryptography and physical layer security) built for the considered underwater communication technologies. In addition, we discuss at length the security aspects of the underwater and A–W WCNs by reviewing and summarizing the existing work in the literature. We notice that the related work on security of RF-based, magnetic induction-based underwater WCNs, and A–W WCNs is practically non-existent. Thus, we highlight this research gap in the literature, and propose a few additional security-related open problems too, that we believe deserve to receive more attention from the underwater, marine, and oceanic research community. [ABSTRACT FROM AUTHOR]

The existing technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in the aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. For high data-rates and real-time applications it is necessary to use frequencies in the MHz range, allowing communication distances of hundreds of meters with a delay of milliseconds. To achieve this goal, it is necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. This work shows how the acoustic impedance influences the performance of an ultrasonic emitter transducer when digital modulations are used and operating at frequencies between 100 kHz and 1 MHz. The study includes a Finite Element Method and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based on ceramics (high acoustic impedance) with a resonance design and the other based in polymer (low acoustic impedance) designed to optimize the performance when digital modulations are used. The transducers performance for Binary Amplitude Shift Keying, On–Off Keying, Binary Phase Shift Keying and Binary Frequency Shift Keying modulations with a 1 MHz carrier at 125 kbps baud rate are compared. [ABSTRACT FROM AUTHOR]

In this paper, a new variable-focus LED light device is developed for underwater communication. Usually used as an underwater lighting fixture, the LED light device in this study is utilized as an underwater communication device (UCD) by controlling the distance between light source and lens when communication is needed. A transmission and a receiving part of LED light for communication using photoelectric sensor and Fresnel lens are also developed. The communication system was tested in fresh water and sea water to verify its communication performance; results of which are presented in this study. [ABSTRACT FROM AUTHOR]

This paper has presented our interesting in wireless underwater communications for different ocean water types. Recent interest in ocean exploration has brought about a desire for developing wireless communication techniques in this challenging environment. Due to its high attenuation in water, a radio frequency (RF) carrier is not the optimum choice. Acoustic techniques have made tremendous progress in establishing wireless underwater links, but they are ultimately limited in bandwidth. In traditional communication systems, constructing a link budget is often relatively straight forward. In the case of underwater optical systems the variations in the optical properties of ocean water lead to interesting problems when considering the feasibility and reliability of underwater optical links. The main focus of this paper is to construct an underwater link budget which includes the effects of scattering and absorption of realistic ocean water. As well as we have developed the underwater optical wireless communication systems to have shorter ranges, that can provide higher bandwidth (up to several hundred Mbit/s) communications by the assistant of exciting high brightness blue LED sources, and laser diodes suggest that high speed optical links can be viable for short range application. The received signal power, signal to noise ratio, bit error rate, transmitted signal bandwidth, and transmission bit rates are the major interesting parameters for different ocean water mediums as a criteria of the best signal transmission characteristics of short wireless optical communications over wide range of the affecting parameters. [ABSTRACT FROM AUTHOR]