IEEE Consumer Electronics Magazine - November/December 2021 - 36

Communications Technology
In contrast, the optical communication
medium offers a high data rate and low latency for
IoUT. These two features of underwater optical
communication enable real-time underwater telephony
and multimedia applications. Moreover,
the size of optical waves-based IoUT is small and
has low cost as the transceivers are made up of
either photodiodes or laser diodes. All these properties
make optical-waves based IoUT an attractive
technology. However, the implementation of
optical-IoUT is more complex since the range of
optical waves in underwater is limited, and it also
requires accurate pointing and tracking between
the transmitter and the receiver.
Lately, MI is utilized to provide averagespeed
omnidirectional short-range underwater
communications.12 The response of MI channel
is more predictable and stabilized as compared
to the other three communication techniques.
The MI waves usually penetrate the lossy
medium in an underwater environment at a
speed approximately equal to the speed of light.
This indicates that MI waves can travel faster
and overcome the latency problems usually
caused by acoustic waves. Last but not the least,
MI communication is accomplished by using
small-size transmitter and receiver coils with
nonvisible and nonaudible waves that can be
efficiently utilized in numerous wide range of
civilian and military applications.
CHALLENGES IN IoUT
The existing research on IoUT encounters
many challenges due to the unique, misty, and
harsh underwater environment. In this section,
we briefly discuss the significant challenges of
IoUT.
Transmission Medium: Most of the existing
underwater communications systems use
acoustic waves due to their long transmission
range. However, the acoustic-waves-based
systemcan only support lowdata rate applications.
Therefore, efforts have been made to
enhance the overall data rate of the underwater
communication system by utilizing optical
waves. However, optical waves have their limitations,
such as low transmission range and
directional communication. Hence, depending
on the application of IoUT, the transmission
36
mediumcan be selected, for example, the optical
waves can be utilized to provide high data
rate, low-latency, and reliable short-range
communications while acoustic waves can
provide long-range communication at the cost
of higher latency and lowdata rate.
Latency: As mentioned earlier, the commercial
modems for underwater communications
uses acoustic waves, and therefore,
their transmission speed is almost 100 thousand
times slower as compared to the communication
speed in the terrestrial IoT
networks.13 Hence, the low speed of sound
waves restricts real-time communications in
IoUTs. The development of optical modems
for IoUTs can enable low-latency real-time
communication. However, the research on
the development of optical modems is still in
the academic research phase.
Transmission Range: Another major challenge
for IoUT is the limited transmission range
of wireless communication technologies.
Although acoustic waves provide transmission
in the range of few kilometers but at the
cost of a low data rate. Other high-speed
underwater communication technologies,
such as RF, optical, and MI, have limited transmission
range. For example, the transmission
range of optical waves is in 100 m, and therefore,
there is dire need to design novel optical
modems capable of providing long transmission
range. Moreover, the transmission range
can also be improved by using relays. However,
deployment and modeling of relays in
the dynamic, misty, and harsh underwater
environment is a challenging task.
Mobility: Mobility is one of the significant
issues for IoUT due to the dynamic nature
of the underwater environment. IoUT
mainly consists of a network of smart
objects where the movement of water randomly
changes its topology. Therefore,
tackling such kind of dynamic topologies is
a cumbersome problem and needs to be
investigated.
Network Lifetime: IoUT mainly consists of
sensors that are battery powered with a limited
amount of energy. Therefore, either
energy harvesting or energy-efficient networking
solutions are required for IoUT to improve
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