Underwater wireless communications can be carried out through acoustic, radio frequency (RF), and optical waves. Compared to its bandwidth limited acoustic and RF counterparts, underwater optical wireless communications (UOWCs) can support higher data rates at low latency levels. However, the severe aquatic channel conditions (e.g., absorption, scattering, turbulence, etc.) pose great challenges for UOWCs and significantly reduce the attainable communication ranges, which necessitates efficient networking and localization solutions. Therefore, we provide a comprehensive survey on the challenges, advances, and prospects of underwater optical wireless networks (UOWNs) from a layer by layer perspective which includes: (1) Physical layer issues including propagation characteristics, channel modeling, and modulation techniques (2) Data link layer problems covering link configurations, link budgets, performance metrics, and multiple access schemes; (3) Network layer topics containing relaying techniques and potential routing algorithms; (4) Transport layer subjects such as connectivity, reliability, flow and congestion control; (5) Application layer goals, and (6) Localization and its impacts on UOWN layers. Finally, we outline the open research challenges and point out the prospective directions for underwater optical wireless communications, networking, and localization studies.

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Underwater Optical Wireless Communications, Networking, and Localization: A Survey

The Internet of Underwater Things (IoUT) is a novel class of Internet of Things (IoT), and is defined as the network of smart interconnected underwater objects. IoUT is expected to enable various practical applications, such as environmental monitoring, underwater exploration, and disaster prevention. With these applications, IoUT is regarded as one of the potential technologies toward developing smart cities. To support the concept of IoUT, Underwater Wireless Sensor Networks (UWSNs) have emerged as a promising network system. UWSNs are different from the traditional Territorial Wireless Sensor Networks (TWSNs), and have several unique properties, such as long propagation delay, narrow bandwidth, and low reliability. These unique properties would be great challenges for IoUT. In this paper, we provide a comprehensive study of IoUT, and the main contributions of this paper are threefold: (1) we introduce and classify the practical underwater applications that can highlight the importance of IoUT; (2) we point out the differences between UWSNs and traditional TWSNs, and these differences are the main challenges for IoUT; and (3) we investigate and evaluate the channel models, which are the technical core for designing reliable communication protocols on IoUT.

https://ir.nctu.edu.tw:443/bitstream/11536/145904/1/6e62f04f95711ec31f1c7143d47fd8cd.pdf

A Comprehensive Study on the Internet of Underwater Things: Applications, Challenges, and Channel Models

The Internet-of-Things (IoT) is the future of the Internet, where everything will be connected. Studies have revealed that fog/edge computing-based services will play a major role in extending the cloud by carrying out intermediary services at the edge of the network. Fog/edge computing-based IoT’s (FECIoT) distributed architecture enhances service provisioning along the Cloud-to-Things continuum, thereby making it suitable for mission-critical applications. Furthermore, the proximity of fog/edge devices to where the data is produced makes it stand-out in terms of resource allocation, service delivery, and privacy. From the business perspective, FECIoT will lead to a boom and spring up of small-to-medium-sized enterprises, thereby encouraging inclusion for all. To this end, we present a comprehensive survey on state-of-the-art IoT literature over the period 2008–2018 and propose the FECIoT framework which covers the enabling technologies, services, and open research issues. A tutorial approach is employed, progressing from basic to more advanced concepts within the IoT domain. Lastly, we show how FECIoT can be deployed in real-life cyber-physical systems, such as the intelligent transportation system, smart grid, smart health-care, smart homes, and smart environment.

Fog/Edge Computing-Based IoT (FECIoT): Architecture, Applications, and Research Issues

The development of the smart ocean requires that various features of the ocean be explored and understood. The Underwater Internet of Things (UIoT), an extension of the Internet of Things (IoT) to the underwater environment, constitutes powerful technology for achieving the smart ocean. This article provides an overview of the UIoT with emphasis on current advances, future system architecture, applications, challenges, and open issues. The UIoT is enabled by the most recent developments in autonomous underwater vehicles, smart sensors, underwater communication technologies, and underwater routing protocols. In the coming years, the UIoT is expected to bridge diverse technologies for sensing the ocean, allowing it to become a smart network of interconnected underwater objects that has self-learning and intelligent computing capabilities. This article first provides a horizontal overview of the UIoT. Then, we present a five-layer system architecture for the future UIoT, which consists of a sensing, communication, networking, fusion, and application layer. Finally, we suggest the current challenges and the future UIoT research trends, in which cloud computing, fog computing, and artificial intelligence are combined.

Underwater Internet of Things in Smart Ocean: System Architecture and Open Issues

Internet of Things (IoT) constitutes the next step in the field of technology, bringing enormous changes in industry, medicine, environmental care, and urban development. Various challenges are to be met in forming this vision, such as technology interoperability issues, security and data confidentiality requirements, and, last but not least, the development of energy efficient management systems. In this paper, we explore existing networking communication technologies for the IoT, with emphasis on encapsulation and routing protocols. The relation between the IoT network protocols and the emerging IoT applications is also examined. A thorough layer-based protocol taxonomy is provided, while how the network protocols fit and operate for addressing the recent IoT requirements and applications is also illustrated. What is the most special feature of this paper, compared to other survey and tutorial works, is the thorough presentation of the inner schemes and mechanisms of the network protocols subject to IPv6. Compatibility, interoperability, and configuration issues of the existing and the emerging protocols and schemes are discussed based on the recent advanced of IPv6. Moreover, open networking challenges such as security, scalability, mobility, and energy management are presented in relation to their corresponding features. Lastly, the trends of the networking mechanisms in the IoT domain are discussed in detail, highlighting future challenges.

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Network Protocols, Schemes, and Mechanisms for Internet of Things (IoT): Features, Open Challenges, and Trends

With the advance of the Internet of Underwater Things, smart things are deployed under the water and form the underwater wireless sensor networks (UWSNs), to facilitate the discovery of vast unexplored ocean volume. A routing protocol, which is not expensive in packets forwarding and energy consumption, is fundamental for sensory data gathering and transmitting in UWSNs. To address this challenge, this paper proposes Enhanced CARP (E-CARP), which is an enhanced version of the channel-aware routing protocol (CARP) developed by S. Basagni et al. , to achieve the location-free and greedy hop-by-hop packet forwarding strategy. In general, CARP does not consider the reusability of previously collected sensory data to support certain domain applications afterward, which induces data packets forwarding which may not be beneficial to applications. Besides, the PING - PONG strategy in CARP can be simplified for selecting the most appropriate relay node at each time point, when the network topology is relatively steady. These two research problems have been addressed by our E-CARP. Simulation results validate that our technique can decrease the communication cost significantly and increase the network capability to a certain extent.

E-CARP: An Energy Efficient Routing Protocol for UWSNs in the Internet of Underwater Things

A routing protocol, which is not expensive in packets forwarding and energy consumption, is fundamental for sensory data gathering and transmitting in underwater wireless sensor networks. To solve this issue, this paper proposes E-CARP, which is an enhanced version of the Channel-Aware Routing Protocol (CARP), to achieve the location-free and greedy hop-by-hop packet forwarding strategy. Generally, CARP does not consider the reusability of previously collected sensory data to support certain domain applications in the following, which induces data packets forwarding which may not be beneficial to applications. Besides, the PING-PONG strategy in CARP could be simplified for selecting the most appropriate relay node at each time point, when the network topology is relatively steady. These two research problems have been addressed by our E-CARP.

An Energy Efficient Routing Protocol for Underwater WSNs

This paper proposes to detect event coverage and determines event sources. Generally, an appropriate sensor node is selected as the relay node for gathering and routing sensory data to sink node(s). When sensory data are collected at sink node(s), the event coverage is detected and represented as a weighted graph. Event sources are determined which correspond to the barycenters in this graph. Experiments show that this technique is more energy efficient, especially when the network topology is relatively steady.

Riliang Xing

Papers

E-CARP: An Energy Efficient Routing Protocol for UWSNs in the Internet of Underwater Things

An Energy Efficient Routing Protocol for Underwater WSNs

Underwater event identification and determination in UWSNs