A MATLAB code for calculating neutron energy spectra from JET discharges was developed. The code uses the fuel ion distribution calculated by the computer code SELFO to generate the spectrum through a Monte-Carlo simulation. The calculated spectra were then compared against experimental results from the neutron spectrometer TOFOR. In the calculations, the exact orbits of the fuel ions are taken into account, in order to investigate what effects this has on the spectrum. The reason for this is that, for certain plasma heating scenarios, large populations of fast fuel ions are formed. These fast ions may have Larmor radii of the order of decimeters, which is comparable to the width of the sight line of TOFOR, and may therefore affect the recorded neutron spectrum. A JET discharge with both NBI and 3rd harmonic ICRF heating was analyzed. The results show that the details of the line of sight of the detector indeed affects the neutron spectrum. This effect is probably important for other diagnostics techniques, such as gamma-ray spectroscopy and neutral particle analysis, as well. Good agreement with TOFOR data is observed, but not for the exact same time slice of the discharge, which leaves some questions yet to be investigated.

The thesis is mainly focused on a hybrid location system, which processes wireless and inertial measurements by extended Kalman filtering. Inertial location system is usually used with Dead-Reckoning method, which calculates the present location and heading direction from a previous known state by using measurements of accelerometer and gyroscope, which have immunity from the environment. The system estimates the position by integrates the measurements of sensors, resulting in high accuracy during a short period. However, the unreliability grows with time due to the bias effect on sensors. By combining the wireless location and inertial system, the uncertainty of estimation can be reduced. In wireless communications, the locations of base stations and the times of signal arrival can be used in locating a mobile station. However, signal propagation could be blocked by objects. The non-line of sight (NLOS) effects cause arrival delay and is usually modeled as exponential distributions. Previously, the improved biased Kalman filters were designed to mitigate the NLOS effect in base station measurements. The system design has difficulty in accommodating inertial measurements. The inertial has immunity to the environment. The property is of help in the NLOS mitigation. Therefore, we propose a hybrid location system that integrating the wireless and inertial measurements by using a hybrid biased extended Kalman filter at the stage of positioning. The system provides better prediction with the assistance of enviroment-free inertial measurements. The NLOS mitigation with prediction feedback scheme results in better mitigation performance. Simulations of different situations have been conducted based on parameters in the IEEE 802.15.3a ultra-wideband environment. The performance differences between the proposed method and other approaches show that inertial assisted system effectively reduces the NLOS effects. Also, the proposed hybrid location system has more efficient mitigation performance and better tracking results.

The technique of mobile location has become a popular research topic since the number of related applications for the location information is growing rapidly. The decision to make the location of mobile phones under the U.S. Federal Communications Commission (FCC) in 1996 is one of the driving forces to research and provide solutions to it. But, in wireless communication systems, non line of sight (NLOS) propagation is a key and difficult issue to improve mobile location estimation. We propose an efficient location algorithm which can mitigate the influence of NLOS error. First, based on the geometric relationship between known positions of the base stations, the theorem of ¡§Fermat Point¡¨ is utilized to collect the candidate positions (CPs) of the mobile station. Then, a set of weighting parameters are computed using a density-based clustering method. Finally, the location of mobile station is estimated by solving the optimal solution of the weighted objective function. Different distributions of NLOS error models are used to evaluate the performance of this method. Simulation results show that the performance of the least range measure (LRM) algorithm is slightly better than density-based clustering algorithm (DCA), and superior to the range based linear lines of position algorithm (LLOP) and range scaling algorithm (RSA) on location accuracy under different NLOS environments. The simulation results also satisfy the location accuracy demand of Enhanced 911 (E-911).

In the thesis, we propose a non-line of sight (NLOS) mitigation approach based on the interacting multiple model (IMM) algorithm. The IMM-based structure, composed of a biased Kalman filter (BKF) and a Kalman filter with NLOS-discarding process (KF-D), is capable of mitigating the ranging error caused by the NLOS effects, and therefore improving the performance and accuracy in wireless location systems. The NLOS effect on signal transmission is one of the major factors that affect the accuracy of the time-based location systems. Effective NLOS identification and mitigation usually count on pre-determined statistic distribution and hypothesis assumption in the signals. Because the variance of the NLOS error is much large than that of measurement noise, hypothesis testing on the LOS/NLOS status can be formulated.The BKF combines the sliding window and decides the status by using hypothesis testing. The calculated variance and the detection result are used in switching between the biased and unbiased modes in the Kalman filter. In the contrast, the KF-D scheme identifies the NLOS status and tries to eliminate the NLOS effects by directly using the estimated results from the LOS stage. The KF-D scheme can achieve reasonably good NLOS mitigation if the estimates in the LOS status are obtained. Due to the discarding process, changes of the state vector within the NLOS stage are possibly ignored, and will cause larger errors in the state estimates. The BKF and KF-D can make up for each other by formulating the filters in an IMM structure, which could tune up the probabilities of BKF and KF-D. In our approach, the measured data are smoothed by sliding window and a BKF. The variance of data and the hypothesis test result are passed to the two filters. The BKF switches between the biased/unbiased modes by using the result. The KF-D may receive the estimated value from BKF based on the results. The probability computation unit changes the weights to get the estimated TOA values. With the simulations in ultra-wideband (UWB) signals, it can be seen that the proposed IMM-based approach can effectively mitigate the NLOS effects and increase the accuracy in wireless position.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Ingram, Mary Ann; Committee Member: Durgin, Greg; Committee Member: Kenney, Steve; Committee Member: Landgren, Jack; Committee Member: Li, Ye. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis proposes two acoustic localisation techniques that are accurate in Non-Line-of-Sight (NLoS) conditions and system implementation of the proposed techniques. Such conditions can cause positive bias errors, namely NLoS errors, in the measured Time-of-Arrivals (ToAs) of first-arrival signals received by microphones and thus reduce the positioning accuracy. The primary issue of the thesis is to precisely estimate and correct the NLoS errors by modelling the received first-arrival signals. The first proposed technique uses multiple on-ground microphones to locate a sound source. The proposed technique approximately estimates and corrects the NLoS errors based on an initial guess of the sound source position and a map. The localisation is then achieved by iteratively correcting the ToAs and updating the sound source location. The strength of the proposed technique is that its accuracy is not notably affected by small or known obstacles. The proposed technique is implemented into two localisation systems of controlled and uncontrolled sound sources. The performance of the proposed technique is investigated by its comparison with three other time-based localisation techniques in series of experiments and simulations, showing at least 10% improvement by the proposed technique under various background noise levels. The second proposed technique localises a sound source using a single on-ground microphone subject to an assumption of a single diffraction in the first-arrival signal. To predict the angular and radial coordinates of the sound source relative to the diffraction point, a new magnitude delay frequency profile is proposed. The profile can be estimated by applying the uniform geometrical theory of diffraction and be extracted from measured signals using a derived formulation. Similar to the first technique, the second proposed technique estimates the measured delay of the first-arrival signal for computing the radial coordinate. The angular coordinate is then obtained by matching the estimated and measured profiles at the measured delay. A key achievement of the second proposed technique is enabling NLoS localisation using only one microphone without any time-consuming pre-measurement. This technique is implemented into a localisation system of a controlled sound source and validated experimentally with three different sound sources and under two background noise levels.

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.

The Internet of Underwater Things (IoUT) paradigm is expected to enable various practical applications such as environmental monitoring, underwater exploration, and disaster prevention. Supporting the concept of IoUT requires robust underwater wireless communication infrastructure. Optical wireless communication has the superiority of wide bandwidth, low latency, and high data capacity over its counterparts, namely, acoustic and radio-frequency. However, the transmission of the optical beam has inherent drawbacks in a harsh environment. Obstructions such as geometrical underwater terrains and underwater turbulence can pose a serious challenge to the alignment of the transmitter and the receiver. Non-line-of-sight (NLOS) configuration is a generalized alignment scheme between the transmitter and the receiver such that the strict requirement of precise alignment (point-to-point) is no longer needed. In this dissertation, the effectiveness of NLOS to withstand challenging underwater turbulence is examined. Thermal gradients with a maximum temperature difference of 10 ◦C had a negligible effect on the received power. The presence of air bubble clouds caused an increase of 38% of the received power when the bubble area increased from 5.2 to 80 mm$^2$. Additionally, various salinity concentrations ranging between 30-40‰ are emulated. A gain of 32.5% in the signal-to-noise ratio is observed when the salinity gradient increased from 0.08 to 0.4‰·cm$^{−1}$. Moreover, a reduction of 2.35 dB/m of the pathloss is noticed. The bit-error ratio is used to examine the communication quality using on-off-keying modulation scheme. In addition, this dissertation shows a practical wavelength-division multiplexing method based on large-area detection and wide field-of-view (FoV) photonic receiver. The dual-antenna is made of scintillating fibers with distinctive characteristics. An aggregated data rate of 1 Gbps is achieved. Two methods of wavelengths separation are demonstrated. Additionally a field deployment verification in an outdoor water pool is conducted at a maximum separation distance of 10m. The presented promising results pave the way for a robust underwater wireless optical sensor network that serves as a building block for achieving the goal of establishing IoUT.

Channel impulse responses collected on the Virginia Tech campus show combinations of specular multipath and diffuse scattering at LMDS frequencies. An algorithm is presented that estimates link performance based on the channel impulse response. Presented and analyzed are representative impulse responses (one is primarily specular in nature and one shows significant diffuse scattering) to show that the proposed algorithm is appropriate for analyzing channels exhibiting either of these characteristics. Monte Carlo simulations logged the sequence number of each bit error to gain an understanding of the distribution of errors over time. The results show that for these static channels the errors occur randomly rather than in bursts, leading to the conclusion that average bit-error rate statistics are appropriate for channel characterization. Zero-Forcing (Z-F) and Minimum Mean Square Error (MMSE) equalizers employed on these channels had a significant impact on the link quality. In many cases, the performance of the MMSE equalizer performed only slightly better than the Z-F equalizer. However, when deep nulls were present in the channel response, the MMSE equalizer performed significantly better. Algorithms for determining the number of taps necessary to approach an optimum equalization are presented for both types of equalizers and a '98%' rule of thumb is presented. The algorithm's role in adaptive and cognitive radio systems is discussed and two applications are presented to illustrate its utility. / Ph. D.

Measuring periodic changes in the line-of-sight velocities of stars via spectroscopy (the “radial velocity technique”) is a well-established method to detect planets orbiting stars other than the Sun. As those distant stars orbit their system’s center of mass the radial velocity technique confirms that companions exist and allows for the measurement of fundamental parameters: companion masses, orbital characteristics, and, in some cases, aspects of atmospheric chemistry. Until recently Doppler spectrometers have been limited to detecting radial velocity signals of larger than one meter-per-second, a constraint that significantly hinders our discovery and characterization of small rocky worlds similar to our own. This is the motivation for developing instruments sensitive to extremely precise radial velocities (EPRVs, ??? < 1ms−1). This dissertation describes critical aspects of the development of one such spectrometer: the Palomar Radial Velocity Instrument (PARVI).Chapter 2 presents the characterization of the fine-guiding camera used in the fiber injection unit that couples light from Palomar’s extreme adaptive optics to the spectrograph’s single-mode fiber feed. Chapter 3 describes the data acquisition and data reduction pipelines for PARVI. It includes the methodology for acquiring data with a Teledyne H2RG array, the description of the wavelength calibration using a laser frequency comb, and the process for reducing the 2D echellogram down to a 1D spectrum. Chapter 4 reveals the discovery of a new and significant, polarization-dependent, instrument noise and a warning for those considering using single-mode fibers for high resolution spectroscopy. Chapter 5 contains the first results from PARVI commissioning data. This includes the detection of the Rossiter-Mclaughlin signal of the transiting planet HD 189733 b, and presence of water and carbon monoxide in the atmosphere of HD 189733 b via transmission spectroscopy.