Under water acoustic (uw a) communication architecture and the key notions of uw-a propagation

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 02 | Feb-2014, Available @ http://www.ijret.org 16
UNDER WATER ACOUSTIC (UW-A) COMMUNICATION
ARCHITECTURE AND THE KEY NOTIONS OF UW-A PROPAGATION
Manujakshi B.C1
, Shashidhar T.M2
, Praveen Naik3
1, 3
Assistant Professor, Computer Science & Engg, AcIT, Karnataka, India
2
Assistant Professor, Electronics & Communication Engg, VVIT, Karnataka, India
Abstract
The study of the communication architecture for the underwater is very important due the wide applications based on these sensing
devices. The more observed examples of applications are climate change monitoring, study of marine life, pollution control, and
military purposes. It is observed the radio frequency (RF) electromagnetic waves [1], Optical electromagnetic waves, underwater
Optical communication [2] waves all have been used for the underwater sensor networking. But these have shown with its slight
disadvantages for the underwater related works. So this can be overcome by the usage of the acoustic communication as a means of
transmission technology for the underwater networked system. It is also observed that the underwater acoustic signals are suffering
from the some transmission loss, high propagation delay, limited bandwidth. So to eliminate these observed factors with respect to the
underwater sensor networks the communication architecture has been developed to provide the point to point, having low data rate
and high bandwidth signal and delay tolerant applications. Therefore this article has been written to give the details of how the
communication architecture can be designed and for the underwater network and the key factors which relates to the propagation of
underwater acoustic signals.
Keywords: UW-A, Doppler Spread, Attenuation, Variance
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1. INTRODUCTION
The study of the communication architecture for the
underwater is very important due the wide applications based
on these sensing devices. The more observed examples of
applications are climate change monitoring, study of marine
life, pollution control, and military purposes. It is observed the
radio frequency (RF) electromagnetic waves [1], Optical
electromagnetic waves, underwater Optical communication
[2] waves all have been used for the underwater sensor
networking. But these have shown with its slight
disadvantages for the underwater related works. So this can be
overcome by the usage of the acoustic communication as a
means of transmission technology for the underwater
networked system. It is also observed that the underwater
acoustic signals are suffering from the some transmission loss,
high propagation delay, limited bandwidth. So to eliminate
these observed factors with respect to the underwater sensor
networks the communication architecture has been developed
to provide the point to point, having low data rate and high
bandwidth signal and delay tolerant applications. Therefore
this article has been written to give the details of how the
communication architecture can be designed and for the
underwater network and the key factors which relates to the
propagation of underwater acoustic signals.
2. COMMUNICATION ARCHITECTURE FOR
THE UNDERWATERNETWORKS
The underwater networks mean it is a collection of sensor
nodes. Usually these nodes will be connected to the bottom of
the ocean or sea. Internally these will be connected with a
many underwater gateways through different wireless acoustic
links [3]. The sensor networks are done with usually by
selecting a multi hop paths because of its wide area to be
covered by those sensing devices. The information will be
taken from the bottom network of the ocean and connecting to
a surface station. The gateways used for the underwater
networking are equipped with three transceivers like vertical
and horizontal transceivers and acoustic transceivers.
2.1 Vertical Transceiver
The Vertical transceiver in the underwater gateways is used to
function as a relay data to the surface station. These are
usually long rage transceivers.
2.2 Horizontal Transceiver
The horizontal transceiver is used to communicate with the
sensor nodes and sends the commands as well as
Configuration data to the sensors along with that it also
collects the monitored data.

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2.3 Acoustic Transceiver
These are present on the surface station to handle multiple
parallel communications with the used and deployed
underwater gateways. Acoustic transceivers may also
communicate with the onshore sink or surface sink through a
radio transmitter and satellite transmitter.
3. WORKING OF SENSOR NODES IN A
COMMUNICATION ARCHITECTURE
Sensor nodes used for the communication in the underwater
networks can float at different depths mainly to observe given
phenomenon. Here each and every sensor node is attached to
the surface buoy [3] by wires and the length is regulated to
adjust the depth of each and every sensor node. This enables
the quick deployment of the sensor networks. These floating
buoys are usually vulnerable to the changes in the weather.
The sensing devices are attached to the bottom of the ocean.
The complete working of the UW-A communication network
is shown in the fig 1.
Fig.1 Communication Architecture for the UW-A Sensor
Network
4. BASICS OF UNDERWATER ACOUSTICS
COMMUNICATION
The main carriers of underwater communication are radio
frequency electromagnetic waves, optical waves and acoustic
waves. By some research work it is observed that radio
frequency waves are affected by high attenuation [4] in water.
These can be used only for short ranges of up to 10 to 15
meters. Optical waves are most rapidly scattered and very
often observed by water. So there is lot of advantage in using
the acoustic waves for the underwater communication over
long range links.
These Underwater Acoustic (UW-A) communication is also
being affected by noise, variable propagation delay [5], path
loss. This UW-A communication works for any rage of
systems with its varying frequencies based on the range of the
system. This operates for mostly low bit rates.
Based on their range, UW-A communication links can be
divided into some categories like long, very long, medium,
short and very short. The corresponding bandwidth is also
mentioned in the table below.
Table 1 Different types of UW-A Links with its range and
bandwidth
5. FACTORS AFFECTING THE UW-A
COMMUNICATIONS
5.1 Transmission Loss
The transmission loss is the major factor observed while using
the underwater acoustics. This is caused mainly by two factors
like geometric spreading loss and attenuation [5]. The
transmission loss for any signal with a frequency of F [kHz]
over a transmission distance of TD [m] can be expressed in
decibels [db] as,
10 log TL (TD, F) = N.10 log (TD) + TD. β (F) + TA ,
Where, N is the spreading factor, describes the geometry of
propagation, β (F) [db/m] is the absorption coefficient and TA
is the transmission anomaly which gives details about the
multipath propagation, scattering, refraction. The shallow will
be having higher values of attenuation compared to deep water
UW-A channel. But the transmission loss increases with the
distance and frequency for both.
Geometric Spreading Loss:
This is caused due to the spreading of acoustic energy to the
very large surface with expansion of acoustic waves. The
geometric spreading can be of two types they are Spherical
and Cylindrical. The spherical for deep water communication
and the cylindrical for shallow water communication.
Types Range [km] Bandwidth[kHz]
Short 0.1 > 100
Very short 0.1-1 20-60
Medium 1-15 10
Long 15-100 2-6
Very long 1000 < 1

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Attenuation:
The Attenuation is mainly concerned about the absorption. It
is caused due to the conversion of the energy of the acoustic
wave into heat. The absorption coefficient can be expressed
for any kind of frequencies in [kHz]. For the frequencies
above few hundred Hz the absorption coefficient [3] can be,
β(f) = (0.11 F2
+ 44 F2
+ 2.75 · 10-4
F2
+0.003) . 10-3
F2
+ 1 F2
+ 4100
For lower frequencies, absorption coefficient can be
considered as,
β(f) = (0.002 F2
+ 0.11 F2
+ 0.011 F2
) · 10-3
F2
+ 1 F2
+ 1
5.2 Noise
Acoustic noise for the underwater communication channel can
be of natural or it might be manmade. The noise during the
UW-A channel is caused mainly due to the machine parts like
pumps, gears or power plants. If not due to machinery noise it
may be due to the biological activities like tides, waves wind
or rain. The noise sources can be expressed through some
formulas, and that provides densities of source to the
frequency F [kHz]. The noise may be generated for any kind
of underwater acoustic communication.
Here each of the noise generated will have different range of
frequencies. The shallow water will be generating a noise
which is not predictable easily. But the deep water noise can
be predicted easily compared to shallow water. Based on these
factors the signal to noise ratio can be predicted based on the
transmission loss (TL) and the noise power density,
SNR (TD, F) = P/TL (TD, F)
N (F)B
Where, B is the receiver noise bandwidth and 1/ (TL(TD,F),
N(F))), is the factor which is defined as the effect of
transmission loss and the noise present in any UW-A
communication for any TD and F values.
5.3 Multipath
The multipath is the one of the factor which affects the UW-A
channel. This is usually caused by the wave reflections
generated from the surface and bottom. But the wave
refraction is by means of wave sound, spread variation with
depth. The geometry for the multipath may also depends on
the link configuration. The UW-A channel as discussed is of
two types. They are vertical channels and the horizontal
channels. The vertical channels have less time dispersion
compared to the horizontal channels.
5.4 Delay Variance
The speed of an acoustic signal is lower in magnitude
compared to the electromagnetic signal. The througput of the
system is reduced due to the high propagation delay. Usually
the propagation speed for tan underwater acoustic can be
considered as,
D ( d, s, t) = 1449 +45t – 5t2
+ 0.1t3
+ (1.3 – 0.1 + 0.00t2
) . (s -
30) + 16d +0.1d2
Where, t is the temperature, s is the salinity in ppt and d is the
depth of water in km.
5.5 Doppler Spread
The Doppler Effect is due to some range of frequencies. When
the Doppler power spectrum is nonzero then we say it as a
Doppler spread of UW-A channel. This can be denoted by Ds.
This spread may be occurred due to the Doppler shifts caused
by the motion in the source and destination. When the UW-A
channel experiences with the Doppler spread having b
bandwidth with some time t then it may have some BT
samples. When BT is very less then we say the Doppler effect
as under spread so that it can be ignored. With respect to the
coherence time the Doppler spread can be denoted as,
Tcoherence = 1/Ds
Sometimes it is also possible that the Doppler Spread may be
overspread. This Doppler spread is very important in the
underwater acoustic and so it is leading to a degradation of the
performance in the digital communication.
CONCLUSIONS
In this article we have given with the recent advances in the
underwater acoustic communication by the sensor networking.
We explained with the typical communication architecture of
a sensor network. The article also describes about the key
factors of UW-A propagation which is necessary to know the
efficiency of the sensor networking.
The main objective of the article is to encourage the research
work for the development of the communication technique for
the underwater networking. As a part of future work we are
planning to use effective protocols at the network layers to
increase the efficiency of the underwater communication.
REFERENCES
[1]. J.G Proakis Under Water Acoustic Networks. IEEE
Journal for Oceanic Engineering,2000
[2]. N Baldo,Zorzi M Efficient Routing schemes for under
water acoustic networks,2010
[3]. T C Yang, A study of the underwater acoustic
communication, IEEE Journal of Oceanic Engineering,2008

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[4]. L.Zheng, Multiplexing A fundamenta trade off in multiple
antenachanels, IEEE transaction,2003
[5]. J Friedman,T schmid,Srivasta, Software Defined acousstic
networking platform,2009
BIOGRAPHIES:
Manujakshi B.C , has received her
master’s from UBDTCE, Davanagere
,India Currently working as an Assistant
Professor in the department of Computer
Science & Engineering at Acharya
Institute of technology, Bangalore. Her
Research interest is in the field of
Computer Networking, Wireless Sensor Networks and
Underwater Sensor networks
Shashidhar T.M, has received his masters
from PESIT, Bangalore, India Currently
working as an Assistant Professor in the
department of Electronics &
Communication Engineering at Vijaya
Vittala Institute of technology, Bangalore.
His research work is in the area of Signals
& Systems. His other area of interest is in
the field of Computer networks, Wireless Sensor Networks.
Preveen Naik has received his master’s
from NMAMIT, Nitte, India. Currently
working as an Assistant Professor in the
department of Computer Science &
Engineering at Acharya Institute of
technology, Bangalore. His Research
interest is in the field of Computer
Networking.

Under water acoustic (uw a) communication architecture and the key notions of uw-a propagation

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Under water acoustic (uw a) communication architecture and the key notions of uw-a propagation