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Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 176 p.; also includes graphics (some col.). Includes bibliographical references (p. 171-176). Available online via OhioLINK's ETD Center

A wireless sensor network (WSN) consists of a large number of networked sensor nodes deployed to sense and report a particular phenomenon to a base station. Currently, most WSNs use radio frequency (RF) communications, and this accounts for a significant amount of energy expended. Free space optical (FSO) communications using modulating retroreflectors is potentially attractive for WSNs, due to the lower communications energy required. However, for FSO communications, line of sight (LOS) is required between the transmitter and the receiver. In this thesis, a hybrid Radio Frequency/Free Space Optical (RF/FSO) WSN is proposed. FSO links are used for communications, with RF links providing backup in the absence of LOS. This network has the potential to lower the overall energy consumption of a traditional RF-only WSN. Chapter 1 introduces the WSN and outlines the motivation for the RF/FSO WSN. Chapters 2 and 3 describe the RF and FSO link models used for the RF/FSO WSN. Chapter 4 describes how the WSN networks are configured. The energy model for the sensor node is discussed in Chapter 5. Chapter 6 discusses how network traffic and energy consumption are modelled. The results of the RF/FSO WSN simulations are presented in Chapter 7. Chapter 8 discusses the conclusions from the thesis and suggests areas for future work. Simulations show that for the wide range of scenarios considered, the RF/FSO WSN consumes less energy and has a lifetime at least twice as long as the RF-only WSN. For low and average optical blocking conditions, the RF/FSO WSN is also able to offer at least the same level of network coverage as the RF-only WSN.

We optimize secret key rates (SKRs) of weak coherent pulse (WCP)-based quantum key distribution (QKD) over time-varying free-space optical channels affected by atmospheric turbulence. The random irradiance fluctuation due to scintillation degrades the SKR performance of WCP-based QKD, and to improve the SKR performance, we propose an adaptive scheme in which transmit power is changed in accordance with the channel state information. We first optimize BB84 and decoy state-based QKD protocols for different channel transmittances. We then present our adaptation method, to overcome scintillation effects, of changing the source intensity based on channel state predictions from a linear autoregressive model while ensuring the security against the eavesdropper. By simulation, we demonstrate that by making the source adaptive to the time-varying channel conditions, SKRs of WCP-based QKD can be improved up to over 20%.

<p>In this thesis work, a free space microwave sensing technique to be used for power process control was investigated. Evaluation of the possibility to apply this sensing technique for determination of permittivity properties is the primary objective. Further these properties could be related to the material physical properties such as moisture content and density. Due to the fact that the permittivity properties of the material under measurement determine its measured S-parameters, such were performed throughout the whole work for the calculation of materials properties. Free space type of measurements were the primary focus of this work. Some uncertainties of free space measurement resulting from limitations in the measurement setups, instrumentation, algorithm were explored and methods to secure our measurement results to be within a specified confidence level are also discussed.</p><p>Based on the configuration of the measurement setup, two types of free space measurement were carried out. One was the reflection method where a perfect conducting metal plate is inserted between two antennas for calibration purposes and the material is placed above the plate. Only one reflection coefficient was then measured. The other was the transmission method where the measured material as placed between two antennas and all S-parameters measured. In both cases the amplitude and the phase of the S-parameters were recorded.</p><p>Three models, Debye, Cole-Cole, and Cole-Davidson have been also tested in this work to model permittivity properties of materials. Used test materials were air, plastic plate, water and icrocrystalline cellulose(MCC). Different methods using measured S-parameters for permittivity reconstruction that have been explored in previous work also were utilized in this work for same purpose. The validity of this sensing technique is determined by checking out the deviation of the recovered dielectric constant. The investigation demonstrated that the transmission method works well for reconstruction of permittivity properties as long as the material under test is low-loss. The results of the reflection method were not as satisfactory as we expected. The method was insitive to the sample thickness and shape. Also very precise measurements of the S-parameters were necessary for the correct inversion to dielectric properties, which is generally difficult due to complex measurements environment(multipath). Some of the above could be compensated with good calibration method, but it is not enough, at least with the currently existing approaches. Precise sample preparation and some improvement on the antenna should be further carried out for the reflection method to be performed better.</p>

In this thesis work, a free space microwave sensing technique to be used for power process control was investigated. Evaluation of the possibility to apply this sensing technique for determination of permittivity properties is the primary objective. Further these properties could be related to the material physical properties such as moisture content and density. Due to the fact that the permittivity properties of the material under measurement determine its measured S-parameters, such were performed throughout the whole work for the calculation of materials properties. Free space type of measurements were the primary focus of this work. Some uncertainties of free space measurement resulting from limitations in the measurement setups, instrumentation, algorithm were explored and methods to secure our measurement results to be within a specified confidence level are also discussed. Based on the configuration of the measurement setup, two types of free space measurement were carried out. One was the reflection method where a perfect conducting metal plate is inserted between two antennas for calibration purposes and the material is placed above the plate. Only one reflection coefficient was then measured. The other was the transmission method where the measured material as placed between two antennas and all S-parameters measured. In both cases the amplitude and the phase of the S-parameters were recorded. Three models, Debye, Cole-Cole, and Cole-Davidson have been also tested in this work to model permittivity properties of materials. Used test materials were air, plastic plate, water and icrocrystalline cellulose(MCC). Different methods using measured S-parameters for permittivity reconstruction that have been explored in previous work also were utilized in this work for same purpose. The validity of this sensing technique is determined by checking out the deviation of the recovered dielectric constant. The investigation demonstrated that the transmission method works well for reconstruction of permittivity properties as long as the material under test is low-loss. The results of the reflection method were not as satisfactory as we expected. The method was insitive to the sample thickness and shape. Also very precise measurements of the S-parameters were necessary for the correct inversion to dielectric properties, which is generally difficult due to complex measurements environment(multipath). Some of the above could be compensated with good calibration method, but it is not enough, at least with the currently existing approaches. Precise sample preparation and some improvement on the antenna should be further carried out for the reflection method to be performed better.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "May, 2008." Includes bibliographical references (leaves 50-55). Online version available on the World Wide Web.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, December 2002. / Thesis advisor(s): Bert Lundy, Mike Tatom. Includes bibliographical references (p. 123-125). Also available online.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Optical wireless communication systems based on ultraviolet (UV)-band has a lot inherent advantages, such as low background solar radiation, low device dark noise. Besides, it also has small restrictive requirements for PAT (pointing, acquisition, and tracking) because of its high atmospheric scattering with molecules and aerosols. And these advantages are driving people to explore and utilize UV band for constructing and implementing a high-data-rate, less PAT communication links, such as diffuse-line-of-sight links (diffuse-LOS) and non-line-of-sight (NLOS). The responsivity of the photodetector at UV range is far lower than that of visible range, high power UV transmitters which can be easily modulated are under investigation. These factors make it is hard to realize a high-data-rate diffuse-LOS or NLOS UV communication links. To achieve a UV link mentioned above with current devices and modulation schemes, this thesis presents some efficient modulation schemes and available devices for the time being. Besides, a demonstration of ultraviolet-B (UVB) communication link is implemented utilizing quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM). The demonstration is based on a 294-nm UVB-light-emitting-diode (UVB-LED) with a full-width at half-maximum (FWHM) of 9 nm, and according to the measured L-I-V curve, we set the bias voltage as 7V for maximum the ac amplitude and thus get a high signal-noise-ratio (SNR) channel, and the light output power is 190 μW with such bias voltage. Besides, there is a unique silica gel lens on top of the LED to concentrate the beam. A -3-dB bandwidth of 29 MHz was measured and a high-speed near-solar-blind communication link with a data rate of 71 Mbit/s was achieved using 8-QAM-OFDM at perfect alignment, and 23.6 Mbit/s using 2-QAM-OFDM when the angle subtended by the pointing direction of the UVB-LED and photodetector (PD) is 12 degrees, thus establishing a diffuse-line-of-sight (LOS) link. The measured bit-error rate (BER) of 2.8 × 10−4 and 2.4 × 10−4, respectively, are well below the forward error correction (FEC) criterion of 3.8 × 10−3. The demonstrated high data-rate OFDM-based UVB communication link paves the way for realizing high-speed non-line-of-sight free-space optical (FSO) communications.