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Title: Underwater optical wireless sensor network
Author: Ahmad, Zahir Uddin
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering