Ahmad, Zahir Uddin (2013) Underwater optical wireless sensor network. PhD thesis, University of Warwick.

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Abstract

The thesis details the development of a short range, multi-hop underwater optical
wireless sensor network. Multi-hop underwater optical wireless communication
using a line of sight (LOS) link can provide a greater range compared to a single hop
network, and provide physically secure connections for underwater sensor networks.
This kind of system can be very power efficient, and supported data rate can be from
tens of kbps up to a few hundred kbps. The aims were to build a cheap
communication prototype using “off the shelf” components, such as a
microcontroller, optoelectronics etc. for demonstration purpose. To support the built
prototype, a directional MAC protocol has been developed which considers the
directionality of light propagation. The multi-hop approach has not been considered
for underwater optical wireless communication before, while most of the research
focus is to develop long range and high powered communication links.
In this thesis, a custom built transceiver using blue and green LEDs has been
developed, which supports a data rate up to 140kbps, when the NRZ-OOK
modulation technique is used. For the transmitter part, a digital LED driver has been
used, while on the receiver side, a transimpedance amplifier using a single transistor has been developed. This configuration for optical wireless receiver system design
has not been usual, but it works very well for the proposed prototype. A second stage
voltage amplifier was also designed to boost the signal up to 5V for the
microcontroller, which was also based on transistors.
To demonstrate the principle of multi-hop communication, a line-type network
prototype using two sensor nodes and a gateway node has been designed, built and
tested in the lab environment. Each node was equipped with two transceivers
controlled by a microcontroller to make a full-duplex communication system. To
minimize the cost, all components of a node were built on a single PCB board. To
upload data from the sensor node to the gateway node, a green LED has been used,
and to transmit the control signal from gateway node to sensor nodes, a blue LED
was used. For the demonstration purpose the communication range was considered
up to 1m, which can be increased significantly by using high powered LED, and
external optics such as lenses, concentrators, etc.
A directional MAC protocol has been designed, considering the directionality of the
network. The designed protocol is based on TDMA techniques, but modified for the
proposed application. The gateway node controls all other nodes in the network and
acts as a master node. Because of the directional full-duplex network, there is much
less chance of a collision, when using a TDMA approach. Therefore, a random
access protocol was not needed for the proposed architecture.
Finally, experimental results validate the fact that the multi-hop approach is a viable
solution to increase the communication ranges for underwater optical wireless sensor
networks. Different sets of experiments show that the proposed system can be
implemented in the real environment, such as, oceans, canals and ponds.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Wireless sensor networks, Optical communications, Underwater acoustics, Line-of-sight radio links
Official Date:	September 2013
Dates:	Date Event September 2013 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Green, Roger J.; Hines, Evor, 1957-
Extent:	xxiii, 181 leaves : illustrations.
Language:	eng

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