Abstract
Water covers a greater part of the Earth’s surface. However, little knowledge has been achieved regarding the underwater world as most parts of it remain unexplored. Oceans, including other water bodies, hold substantial natural resources and also the aquatic lives. These are mostly undiscovered and unknown due to the unsuited and hazardous underwater environments for the human. This inspires the unmanned exploration of these dicey environments. Neither unmanned exploration nor the distant real-time monitoring is possible without deploying Underwater Wireless Sensor Network (UWSN). Consequently, UWSN has drawn the interests of the researchers recently. This vast underwater world is possible to be monitored remotely from a distant location with much ease and less risk. The UWSN is required to be deployed over the volume of the water body to monitor and surveil. For vast water bodies like oceans, rivers and large lakes, data is collected from the different heights/depths of the water level which is then delivered to the surface sinks. Unlike terrestrial communication and radio waves, conventional mediums do not serve the purpose of underwater communication due to their high attenuation and low underwater-transmission range. Instead, an acoustic medium is able to transmit data in underwater more efficiently and reliably in comparison to other mediums. To transmit and relay the data reliably from the bottom of the sea to the sinks at the surface, multi-hop communication is utilized with different schemes. For seabed to surface sink communication, leading researchers proposed different routing protocols. The goal of these routing protocols is to make underwater communications more reliable, energy-efficient and delay efficient. This paper surveys the advancement of some of the routing protocols which eventually helps in finding the most efficient routing protocol and some recent applications for the UWSN. This work also summarizes the remaining challenging issues and the future trends of those considered routing protocols. This survey encourages further research efforts to improve the routing protocols of UWSN for enhanced underwater monitoring and exploration.
Highlights
Water-bodies cover two-thirds of the Earth’s surface
Neither unmanned exploration nor distant real-time monitoring is possible without deploying Underwater Wireless Sensor Networks (UWSN)
The data rate of the acoustic communication varies from 31 kb/s to 125 kb/s depending on the channel encoding and the number of transmitters and receivers [27]
Summary
Water-bodies cover two-thirds of the Earth’s surface. from the very beginning of human civilization, people have been choosing water-bodies to live near. The number of sensor nodes depends on the volume of the sea that is to be covered and other factors such as the transmission range of the nodes, the desired performance of the network, and so forth These sensor nodes at different levels of the sea collect the necessary data and eventually send it to the data sinks at the sea surface. Real-life applications of UWSN include seismic monitoring, ocean sampling, vision-based underwater mine searches, ecological monitoring, monitoring of underwater marine cables, pipelines of gas and oil, and so forth For these applications, the location of the source of the data needs to be known. Keeping in mind the challenging factors, researchers have proposed different routing protocols for UWSN Most of these routing protocols using acoustic medium are either single-hop or multi-hop, or, either clustering or clustering-multi-hop communication.
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