Optical Wireless Communication

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ABSTRACT

Title of Thesis:

FREE-SPACE OPTICAL COMMUNICAITONS THROUGH A FOREST CANOPY Clinton Lee Edwards, Master of Science, 2004

Thesis Directed By:

Professor Christopher C. Davis, Department of Electrical and Computer Engineering

This paper models the effects of the leaves of mature broadleaf trees on air-to-ground free-space optical (FSO) communication systems operating through the leaf canopy. Ecological radiation transfer models are considered and the concept of Leaf Area Index (LAI) is reviewed and related to a probabilistic model. Leaf transmittance is experimentally measured for different leaf types and determined to be very close to zero. A probabilistic canopy model of foliage is developed as obscuring leaves are randomly distributed throughout the treetops. The expected fractional unobscured area statistic is derived as well as the variance around the expected value. Monte Carlo simulation results confirm the probabilistic model’s statistical conclusions. Multi-site passive optical measurements are taken in a mature broadleaf forest environment with increasing leaf obscuration then fitted to the model. The model’s implications to FSO system links are considered and simulated. Conclusions are discussed as well as further research.

FREE-SPACE OPTICAL COMMUNICAITONS THROUGH A FOREST CANOPY

by Clinton Lee Edwards

Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master of Science 2004

Advisory Committee: Professor Christopher C. Davis, Chair Professor William S. Levine Professor Thomas E. Murphy

© Copyright by Clinton Lee Edwards 2004

Dedication
I would like to dedicate this work to my wife, Corinne. She has supported my desire to further my education despite the abject poverty that is associated with being a graduate student. Only with her unflinching love and support, this work has been completed. I also dedicate this to my children, Sheely and Xavier, who have tolerated my absences from the dinner table to complete this work as well. Finally, I would like to dedicate this to my parents, M. Lee Edwards and Patricia H. Edwards.

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Acknowledgements
This is certainly not the result of my efforts only. There are many people to whom I owe a great debt of gratitude for giving encouragement and inspiration throughout this project. First, I must thank my advisor, Dr. Chris Davis, for functioning as a sounding board for ideas and helping this project take shape. Dr. Davis has also provided the funding for this work. I want to thank Dr. William Levine for helping with the random processes and probability issues that are contained in this paper. Also I would like to thank Dr. Thomas Murphy for agreeing to serve on my thesis committee.

I would like to acknowledge Dr. Robert Gammon and Mr. Allen Monroe for the use of the Physics Graduate Laboratory resources to experimentally measure foliage transmittance. PhD Candidate Jon Alder of The Johns Hopkins University was instrumental in assisting with the passive optical canopy imaging and measurements. My officemates, Jaime Llorca, Shawn Ho, and Sugi Trisno have been invaluable in developing many of these ideas.

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Table of Contents
Dedication ..................................................................................................................... ii Acknowledgements...................................................................................................... iii Table of Contents......................................................................................................... iv List of Tables ................................................................................................................ v List of Figures .............................................................................................................. vi Chapter1: Introduction .....................................
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