Underwater Wireless Sensor Networks: Design and Communication Challenges

Underwater wireless sensors are an advancement on how data can be collected and monitored from underwater in water bodies such as lakes, oceans and even seas. These networks consist of distributed sensors nodes which can communicate wirelessly. This sensor technology is used in applications such as oceanographic data collection, environmental monitoring, underwater surveillance and in disaster management.

Application of underwater wireless sensor networks might present challenges compared to traditional terrestrial technology used in the past. These challenges are posed mainly due to the harsh and unpredictable underwater environment and conditions. With the underwater conditions in considerations, the underwater wireless sensors ought to be designed in a manner that they can be of functionality despite all these harsh conditions which are always present underwater.

Aspects to consider include limitations imposed by the physical medium, energy constraints, communication protocols and the network architecture. To achieve the desired data collection or monitoring underwater environment, these factors must be considered.

Underwater environment differs greatly from those terrestrial environments, this difference poses a challenge for the sensor network. Main environmental factors that affect underwater sensor networks are pressures at different water levels, temperature variations, salinity of the water in which the sensor networks are to be installed and biofouling. Such factors impact performance and longevity of the sensor nodes. Pressures at significant depths can cause damage to the electronic components used, temperature variations on other hand can lead to inaccurate sensor readings while biofouling which is accumulation of marine organisms on the sensors can also degrade sensor performance.

Also, the immobility of the underwater sensor nodes which are typically fixed on seafloor or anchored in specific locations limit flexibility in the network reconfiguration. To power the underwater sensor nodes, energy is required and due to the remote location of the sensors underwater, recharging or replacing the power sources of the sensors can be very difficult. This calls for efficient energy consumption for the sensor nodes due to the limited energy sources in the remote underwater locations. Also, energy-efficient communication techniques must be employed to ensure nodes longevity and the overall network.

Signal transmission underwater for communication over the network is done through acoustic waves as radio waves are unable to propagate efficiently in water. The acoustic communication used is limited in terms of bandwidth and latency. Bandwidth underwater is lower than in terrestrial environment thus the data transferred at a given time is limited. This poses a challenge especially in applications that require large amounts of data for functionality The acoustic signals used in underwater wireless sessor networks are highly prone to attenuation and signal distortion. Attenuation is due to factors such as the salinity of the water, temperatures difference and distance space between the receiver and transmitter nodes. This leads to loss of signal strength which in turn degrades the quality of communication.

Underwater there is a lot of noise and interference. Marine life being the leading source of noise and interference such as noises made by whales, ships and other underwater machinery. The noise can interfere with the communication and reduce the signal-to-noise ratio. This makes the sensor nodes to find it difficult for sensor nodes to accurately detect and decode messages. Also, other concurrent transmissions can interfere within the network or adjacent network causing distortions. To minimize this, effective coordination and scheduling of transmissions are thus required for effective results.

Some nodes in underwater sensor networks are mobile such as underwater vehicles or drifting sensors. This brings about additional complexity into the network design. As nodes move, also the network topology changes dynamically and there is need to adjust them to maintain continuous communication. The motion of the sensor nodes can also affect the stability of the communication links in that if a sensor nod drifts out of network range, it may lose its connection to the rest of the network.

A variety of communication protocols have been developed for underwater wireless sensor networks to address the challenge of limited bandwidth and high latency. These protocols aim to improve the efficiency and reliability of acoustic communication underwater in underwater environments. One good approach is that a hybrid scheme of communication is developed in that it incorporates both acoustic and radio frequency communication. This hybrid approach complements each other and help balance trade offs between energy consumption, latency and bandwidth.

Routing protocols play a vital role in ensuring efficient data transfer as the dynamic of underwater networks and the limitations of acoustic communication. These protocols have to adapt to deal with the changing network topologies and also cope with the mobility of the nodes.