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Recommended by Yanmin Zhu
Department of Computer Science, Faculty of Computing, University Technology Malaysia (UTM), UTM Skudai, 81310 Johor Bahru, Malaysia
Received 14 March 2013; Revised 10 June 2013; Accepted 13 June 2013
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
Only less than one third of earth's surface is covered by land, and the rest is covered by water. Due to several reasons such as vast area, high pressure, and harshness of underwater environment, human presence in this area is very limited. Hence, human knowledge about underwater environment is so negligible in comparison with land. In recent decades, since the use of WSNs in different applications has brought tremendous revolution, researchers have been interested recently in using these networks for gathering data from underwater environments [1, 2]. To this end, they have proposed underwater acoustic sensor networks (UWASNs) that are composed of a number of autonomous and self-organizing sensor nodes. These nodes are manually or randomly scattered in different depths in underwater environments to collect specific data from deep or shallow water. Then, they transfer collected data via acoustic waves to the sink(s) located on water surface. In these networks, the ordinary sensor nodes are equipped with acoustic modem to communicate with each other, while sinks are equipped with both acoustic and radio modems in order to receive the data from underwater nodes via acoustic waves and transmit them to the onshore base station by radio waves [3]. UWASNs can be used for a wide range of marine applications, including oceanography, environment monitoring, undersea exploration, disaster prevention, equipment monitoring, military oversight, and navigation [1-4].
The main challenge of employing WSNs in underwater environment is that high radio frequency is rapidly absorbed in water and low radio frequency requires a very large antenna [3]. In addition, the optical waves are not efficient in underwater environments because they may be scattered [3]. Since acoustic waves have a good performance in underwater environments, they are used as a wireless communication medium [3]. Acoustic waves have high propagation delay, high path loss, low bandwidth, and high-energy consumption in...