Underwater Acoustic Wireless Sensor Networks: Advances and Future Trends in Physical, MAC and Routing Layers

Salvador Climent, Antonio Sanchez, Juan Capella, Nirvana Meratnia, Juan Serrano
2014 Sensors  
This survey aims to provide a comprehensive overview of the current research on underwater wireless sensor networks, focusing on the lower layers of the communication stack, and envisions future trends and challenges. It analyzes the current state-of-the-art on the physical, medium access control and routing layers. It summarizes their security threads and surveys the currently proposed studies. Current envisioned niches for further advances in underwater networks research range from efficient,
more » ... low-power algorithms and modulations to intelligent, energy-aware routing and medium access control protocols. During the last decade, this form of communication has received increasing attention, owing to its many scientific, military and commercial applications. These applications range from tactical surveillance to the study of marine life and include unmanned vehicle communication, pollution monitoring, oil extraction monitoring and aquiculture monitoring. Electromagnetic waves, optical waves and acoustic waves have been successfully used in underwater wireless sensor networks (UWSNs) [2, 3] . Nevertheless, radio frequency (RF) waves are affected by high attenuation in water (especially at higher frequencies) [2], thus requiring high transmission power and large antennae [4] . Optical waves can be used to achieve ultra-high-data-rate communications (Gbit/s), but are rapidly scattered and absorbed in water, so they are only reliable for short-distance links [2] . In contrast, acoustic waves enable communications over long-range links, because they suffer from relatively low absorption. Thus, this is the preferred technology to develop reliable UWSNs [3] and is the main focus of this paper. In [5] , the characteristics of the acoustic underwater channel and the difficulties in underwater communication are discussed. The differences between acoustic and radio-based communication open a new research field in UWSNs. Despite the increased complexity of acoustic transmissions when compared to RF transmissions, researchers have made enormous advances since the underwater telephone. Nowadays, commercially available underwater modems are able to transmit up to 30 kbps over distances ranging from a hundred meters to a few kilometers [6, 7] . Given these advances in underwater transmission capabilities, an increasing amount of research has been focused on building networks of underwater nodes. Given the long propagation delays, direct use of medium access control (MAC) and routing protocols of previously existing RF networks is not advisable. Hence, a great deal of research has been focused on this issue. Moreover, some of these protocols require time synchronization and localization. These problems must be revisited, because propagation time is not usually taken into account in RF networks. This survey aims to provide a comprehensive overview of the current research on underwater wireless sensor networks, focusing on the lower layers of the communication stack, and envisions future trends and challenges. It analyzes the current state-of-the-art for the physical (Section 2), MAC (Section 3) and routing layers (Section 4). In addition, it summarizes their security threads and surveys the currently proposed studies. Finally, conclusions on the current state-of-the-art in UWSNs and future challenges to be faced are presented. Modem Physical Layer The physical layer defines the mechanism for transmitting bits over a physical link channel connecting network nodes. The transmitter converts bit streams into a physical signal that is propagated through the physical layer. On the other side, the receiver should be able to reverse the process and provide the original bit stream to the upper communication layers. The main issues tackled by the physical layer in a UWSN and discussed throughout this section are as follows: interface to physical transmission media, modulation, equalization filtering, efficient carrier sense and collision detection (used by the MAC layer); additionally, other essential services include bit rate, bit synchronization and forward error correction.
doi:10.3390/s140100795 pmid:24399155 pmcid:PMC3926587 fatcat:3ngjsezgofe55awjynox34adzm