IEEE Consumer Electronics Magazine - November/December 2021 - 35

classification standard, there exists three achievable
architecture of IoUT.
Figure 3. Some smart underwater devices
presented in a recent CES. (a) Navatics Mito camera.
(b) Robosea's Biki. (c) Robo-shark.
of a return-to-base feature that uses its built-in
GPS when it operates on the surface. Another
example is Robo-shark, which can dive up to 300
m, and has a range of 1.5-3 km. It uses infrared
sensors for obstacle avoidance up to 1 m away,
and its shell consists of sound-absorbing material.
The Sublue scooter used for divers in underwater
traveling and exploration consists of a
built-in motor that is battery-powered, and its
cost is approximately $500. These smart underwater
objects are evolving day by day that makes
the CE industry effectively participating in
marine applications.
Architecture of IoUT
Smart underwater objects in IoUT can operate
either in an infrastructure or in an ad-hoc
modality: The infrastructure-based IoUT might
compose of underwater base stations that are
responsible for creating an underwater local area
network. This network not only serves the underlying
nodes but also monitor their intercoordination
and cell coverage area. In contrast, the adhoc
IoUT are mainly distributed wireless networks
that do not depend upon the availability of
the prefitted equipment for the given underwater
network. Therefore, the nodes actively participate
in the traffic requests alongside with dynamically
determined routing path and rely on
network connectivity. This modality requires the
skills of self-alignment and self-association in the
absence of a centralized controlling unit.
Figure 1 provides a basic 3-D architecture of
IoUT, where the underwater objects use various
communication mediums, such as acoustic or
optical waves. These objects not only communicated
with each other but with the base stations
as well. The surface buoy gathers the required
information at the surface, and communicate it
to mobile and onshore base stations through an
RF communication network. Based on the
November/December 2021
Spatial coverage: Based on the coverage, the
IoUT can be classified into 1-D, 2-D, and 3-D
networks.
Mobility: Depending upon the movement of
smart objects, IoUT can be classified as stationary
or mobile networks.
Channel: The various wireless channels that
are used for underwater communications
can be classified as RF, acoustic, optical, MI,
and hybrid.
Communication in IoUT
Communication among the smart underwater
objects in IoUT is difficult due to the harsh and
turbid nature of the seawater. Presently, there
are four technologies to enable communication
in IoUT, i.e., acoustic waves, RF waves, optical
waves, and MI. In the following, we briefly discuss
each of these underwater communication
technologies.
Acoustic waves are the most used communication
technology for underwater applications
due to their long transmission range. In the literature,
many underwater acoustics networks are
presented that can achieve data rates up to
20 kb/s for a distance up to 1 km in the deep
underwater environment. However, for larger
distances up to 100 km, the data rate is reduced
to 250-550 b/s. Nonetheless, this long-distance
communication is achieved at the cost of greater
latenc.11 Moreover, the high latency introduces
the synchronization problem for acoustic-based
underwater communication systems.
Alternatively, the RF-based underwater communication
networks have two advantages. First,
the RF waves usually provide a smooth transition
at interfaces like air and water. This property can
provide cross-boundary communication that
combines terrestrial and underwater RF communication
networks. Second, RF waves not only tolerates
the turbulence but also turbidity in
water.11 However, the major limitation of RFbased
systems is their limited transmission range
in water at very low frequencies range from 30 to
300 Hz. Moreover, the underwater RF transmission
networks require large-size antenna that
leads to high design costs and, thus, consumes
more energy.
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