Estimation Of Transmission Parameters In an

Underwater Acoustic Communication

TS Vishnu Priya, G.Vinitha Sanchez, N.R.Raajan

School of Electrical & Electronics Engineering,

SASTRA Deemed University, Thanjavur, India

tsvpriya1995@gmail.com, gvinithasanchez2592@gmail.com, nrraajan@ece.sastra.edu

Abstract—A microphone that are used for communication

in underwater for receiving and also for listening to the

sound is a hydrophone. Here the frequencies associated

with the underwater acoustic communications are about

10Hz-1MHz. In Underwater wireless communication the

information is transmitted through the channel named

as UAC channel. In this paper OFDM is considered to

have more advantages in dealing with the UWA channels

due to the multipath and frequency selective channels.

Also the transmitter and the receiver is designed with an

adaptive OFDM modulation technique to increase the

rate of data that is being transmitted by the transmitter.

This paper mainly observe the different waveforms

obtained by changing the transmitter and receiver at the

different heights to choose the appropriate one for

effective communication in underwater Acoustic

communication channel.

Key Words - Hydrophones, Orthogonal frequency

division multiplexing, Surface Reflections, Bottom

Reflections

I. INTRODUCTION

The technology of underwater communication grows

expeditiously because the underwater acoustic channel is

used in many applications like Seismic monitoring,

Pollution monitoring, To avoids data spoofing, Ocean

current monitoring etc. There are many such methods to

perform underwater Communication but the most effective

one is by using hydrophone. In this work the parameters of

the communication channel are varied and the

corresponding waveforms are observed by keeping the

transmitter and the receiver at the different heights in order

to choose the best waveform. Underwater Acoustic

communication uses sound waves instead of radio waves.

There are certain limitations in the wired communications

like breaking of wires, temporary environment, needs more

cost for constructing cables for transmitting data. To cope

up the pre-mentioned problems we go with the wireless

communication.

II. METHODOLOGY

Limitations in the current underwater acoustic

communication:

There are certain limitations by using the physical carrier for

underwater communication

1.Radio Waves

Radio waves can propagate under water extremely

at low frequency i.e.(30 Hz-300Hz) [1]. Radio waves can

travel only to a very short distance at about 10m [2] and also

if the depth increases the radio waves cannot penetrate into

the water.

2.Optical Waves

Optical waves are not affected by attenuation by it is

very much affected by dispersion. Also, the optical signal

transmission need more accuracy in pointing the narrow

beam of light. So the sound waves is the best waves for

underwater communication.

III. FACTORS INFLUENCING UNDERWATER COMMUNICATION

A. Path loss

This type of loss may occur due to refraction, scattering,

dispersion, absorption and attenuation. In path loss the depth

of the water plays a vital role in calculating the attenuation.

The absorption loss at the surface of the sea is constant the

absorption loss at the bottom can be given as below

equation.

𝜌− =

𝜌1

𝜌𝑐𝑜𝑠𝜃 − (

𝑐

𝑐1)2−𝑠𝑖𝑛 2𝜃

𝜌1

𝜌𝑐𝑜𝑠𝜃 + (

𝑐

𝑐1)2−𝑠𝑖𝑛 2𝜃

(1)

Here in the above equation, 𝜃 is the incident angle

𝜌1

𝜌 denotes the density of water in surface and in the

bottom

𝑐

𝑐1 denotes the velocity of sound in water and sound

in bottom

B. Noise

In underwater communication two types of noise may

occur

Man made Noise: This noise may occur due to shipping activity

and machinery movements

Ambient Noise: Generally, four types of ambient noise may

occur they are noise due to movement of ship(𝑀𝑠), wind (𝑀𝑤), thermal noise (𝑀𝑡),turbulence (𝑀𝑡).

10 𝑙𝑜𝑔𝑀𝑠 𝑛 = 25 log 𝑛 − 60 log 𝑛 + 0.03 + 40 − 20 𝑛 − 0.5 (2)

International Journal of Pure and Applied MathematicsVolume 119 No. 15 2018, 1889-1893ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

1889

10 𝑙𝑜𝑔𝑀𝑤 𝑛 = 20 log 𝑛 − 7.5𝑤12 + 50

− 40 log +0.3 (3)

10 𝑙𝑜𝑔𝑀𝑡 𝑛 = −14 + 20 log 𝑛 (4)

10 𝑙𝑜𝑔𝑀𝑡 𝑛 = 17 − 30 log 𝑛 (5)

The overall noise can be represented as below,

𝑁 𝑓 = 𝑀𝑠 𝑛 + 𝑀𝑤 𝑛 + 𝑀𝑡 𝑛 + 𝑀𝑡 𝑛 (6)

C. Multipath propagation

Multi-dimension propagation will cause the distortion

in signal which in turn will degrade the system[5]. In

shallow water the multipath propagation may occur due to

signals reflecting from the surface and reflecting from the

bottom, in depth water the multi-dimension propagation

may occur due to the bending of ray.

Surface reflection

Direct Link

Reflection from bottom

Fig.1. Multi-Dimension Propagation

D. High propagation Delay

The speed of propagation in underwater acoustic

communication channel is four times lower when

compared to the speed of propagation in the radio

channels[7]. It may degrade the overall performance

of the data transmission.

E. Attenuation

Underwater Acoustic Communication (UAC) can be affected by three type of losses they are loss

due to absorption, Reflection, spreading. The

spreading loss can either be spherical spreading or

cylindrical spreading .For Spherical spreading (A)=2;

For Cylindrical spreading (A)=1;For practical

spreading (A)=1.5

Hence, the attenuation 𝑁 𝑚, 𝑓 can be represented as

below,

10 log 𝑁 𝑚, 𝑓 = 𝐴. 10 log 𝑚

+ 10 log ∝ (𝑓) . 𝑚 (7)

∝ 𝑓 − 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑑𝑢𝑒 𝑡𝑜 𝑎𝑏𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛

𝑓 − 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

The absorption coefficient can be given as the below

equation,

10 log ∝ 𝑓 =11

100.

𝑓2

1 + 𝑓2+ 44

𝑓2

4100 + 𝑓2

+ 2.75𝑓2 + 0.003 (8)

the above equation is applicable only for 𝑓 >

400𝐾𝐻𝑧 and for 𝑓 < 400𝐾𝐻𝑧 the equation will

become,

10 log ∝ 𝑓 = 0.11𝑓2

1 + 𝑓2+ 0.011𝑓2

+0.002 (9)

By considering the attenuation the total path loss can

be given as ,

𝐿𝑝 =𝜌𝑝

𝐴(𝑙, 𝑓) (10)

IV. TRANSMITTER DESIGN

In the transmitter side the OFDM with spatial multiplexing

is considered and the signaling used here is Zero padded

OFDM. The spacing between the sub carriers can be

computed as by using the below equation,

𝑔 =𝑏

𝑘 (11)

𝑏 − Bandwidth

𝑘 −Total number of sub carriers

𝑔 −guard time duration

The block duration is ,

𝑠 =1

𝑔=

𝑘

𝑏 (12)

In order to eliminate the inter-symbol interferences guard

time are inserted .The sub carriers that carry data can be

expressed as,

𝑀𝑙 = 𝑀𝑀𝑜𝑀𝑠 (13)

𝑀𝑜 −null sub carriers which means it does not carry any

information

𝑀𝑠 −Pilot tones which means carry known symbols

Feed back

Fig.2. Block Diagram of Adaptive OFDM

Transmit

er

Receive

rr

Receiver

Doppler

and

channel

estimator

Channel

Prediction

Adaptive

allocation

Detection

UWA

Chan

nel

Transmitt

er

International Journal of Pure and Applied Mathematics Special Issue

1890

The spectral efficiency can be computed as,

𝑈 = 𝑃𝑡𝑇.𝑆𝑔

𝑆 + 𝑆𝑔.𝑘

𝑘𝑟 𝑙𝑜𝑔2𝑀 (14)

The data rate can be calculated by the below equation,

𝐷 = 𝑈𝑏 (15)

𝐷 −data rate(bits/sec)

𝑏 −bandwidth

𝑈 −spectral efficiency

To estimate the channel every transmitter is allocated with a

set of non overlapping pilot sub carriers.

V. RECEIVER DESIGN

The receiver part of the system consist of an Doppler and

channel estimator, a channel predictor subsystem, an

adaptive power allocation and a detection subsystem. The

Doppler effects of the signal are estimated and corrected

using methods like the time wrapping techniques etc. A

channel predictor is used to predict the signal transmitted in

order to obtain the signal without any attenuation the power

is allocated more efficiently using the adaptive power

allocation and the detection subsystem in the receiver gets

the original transmitted signal.

Table 1 Comparison of various waves for communication

Radio Optical Acoustic

Velocity of

sound in

underwater

33,333,333

m/s

33,333,333

m/s

1.5

× 103 𝑚

/𝑠𝑒𝑐

Bandwidth In MHz 20-100

MHz

Few kHz

Power loss 28 db/km Vary 0.1 db/m

Frequency MHz 1014-1015 Few kHz

Operation in

range

10 meters 10-100

meters

Few Km

RESULTS AND DISCUSSIONS

Fig.3.Multi-DimensionPropagation

Fig.4. Observed Waveform

Table 2 Channel Parameters

Surface height 200 m

Channel distance 2000 m

Transmitter height 100 m

Receiver height 100 m

The figure -3 Shows that the transmitter hydrophone is

placed at 100 m and the receiver hydrophone is placed at the

height of 100m and the range of the channel is taken as 2000

m and the height of the surface is kept as 200 m. The figure-

4 Shows the waveforms obtained by placing the transmitter

hydrophone at 100 m and the receiver hydrophone at 100 m

in terms of doppler rate relative to horizontal.

Fig.5.Multi-Dimension Propagation

Table 4 Channel Parameters

Surface height 100 m

Channel distance 3000 m

Transmitter height 85 m

Receiver height 65 m

International Journal of Pure and Applied Mathematics Special Issue

1891

Fig.6. Observed Waveform

The Figure -5 Shows that the transmitter hydrophone is

placed at 85 m and the receiver hydrophone is placed at the

height of 65m and the range of the channel is taken as

3000m and the height of the surface is kept as 100 m. The

Figure-6 Shows the waveforms obtained by placing the

transmitter hydrophone at 85m and the receiver hydrophone

at 65 m above the surface of the water in terms of doppler

rate relative to horizontal.

Fig.7. Multi-Dimension Propagation

Fig.8. Observed Waveform

Table 4 Channel Parameters

The Figure -7 Shows that the transmitter hydrophone is

placed at 70 m and the receiver hydrophone is placed at the

height of 70m and the range of the channel is taken as 2000

m and the height of the surface is kept as 100 m. The

Figure-8 Shows the waveforms obtained by placing the

transmitter hydrophone at 70 m and the receiver hydrophone

at 70 m in terms of doppler rate relative to horizontal.

VI. CONCLUSION

The objective of this paper is to observe the waveforms

obtained by setting the transmitter and receiver at different

heights and analyzing the different waveforms and

computing the most efficient waveforms . Here the

simulation results shows that the waveforms observed

relative to the Doppler effects are better when keeping the

transmitters and receivers at lower heights from the surface

of the water for a efficient underwater acoustic

communication the transmitter and the receiver is also been

designed by using the adaptive OFDM modulation

technique that will increase the data rate transmission.

REFERENCES

[1] Catipovic J., "Performance limitations in underwater acoustic

telemetry", IEEE J. Oceanic Eng., Vol. 15, (1990), 205–216.

[2] F. Akyildiz, D. Pompili, and T. Melodia, "Challenges for Efficient

Communication in Underwater Acoustic Sensor Networks," ACM

Sigbed Review, July 2004.

[3] W. H. Thorp, “Analytic description of the low frequency attenuation

coefficient,” Journal of the Acoustical Society of America, vol. 33,

pp. 334–340, 1961.

[4] M. U. Cella, R. Johnstone, and N. Shuley, "Electromagnetic wave

wireless communication in shallow water coastal environment,"

Theoretical analysis and experimental results. Berkeley, California,

USA, 2009.

[5] N. Farr, A. Bowen, J. Ware, C. Pontbriand, and M. Tivey, "An

integrated, underwater optical/acoustic communications system," In

Proc. of IEEE OCEANS, pages 16, 2010.

[6] Eggen T. H., Baggeroer A. B., Preisig J. C., "Communication Over

Doppler Spread Channels", Part I: Channel and Receiver Presentation,

IEEE J. Ocean. Eng., 2000, Vol. 25,No 1..

[7] J. Zhang and Y. R. Zheng, “Frequency-domain turbo equalization

with soft successive interference cancellation for single carrier mimo

underwater acoustic communications,” IEEE Transactions on

Wireless Communications, vol. 10, no. 9, pp.2872–2882, 2011.

[8] M. Zatman and B. Tracey, “Underwater acoustic mimo channel

capacity,” in Proceedings of 36th Asilomar conf., vol. 2, 2002, pp.

1364–1368.

[9] Syed and J. Heidemann, "Time synchronization for high latency

acoustic net-works," In Proc. of IEEE INFOCOM, Barcelona, Spain,

2006.

[10] J. Bai, Q. Liang and H. Yu, "Research on the channel simulation of

underwater acoustic networks," Journal of Chinese Computer

Systems, vol.29, no.1, pp.185-188, 2008.

Surface height 100 m

Channel distance 2000 m

Transmitter height 70 m

Receiver height 70 m

International Journal of Pure and Applied Mathematics Special Issue

1892

1893

1894