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(2013)ThesisDue to the general failure of Global Positioning System (GPS) for indoor positioning, non-satellite-based technologies are important for indoor localization. Using wireless networks based on the Received Signal Strength (RSS) location fingerprinting technique is the most popular positioning method used for indoor environments. This research proposes a new positioning technique based on fingerprinting that utilises one of the most available signals of opportunity (SoOP), which is frequency modulated (FM) broadcast radio signals. Then the fusion of FM and Wi-Fi is investigated. The result outperformed the previous methods in terms of accuracy and a more robust and reliable positioning system is presented. Moreover, an analytical framework for estimating the accuracy performance of fingerprinting indoor positioning systems is suggested. Using this model, the most common signal distances such as Euclidean, Manhattan and Chebychev are fully analyses and compared together both mathematically and by simulation so that we can identify which provides least positioning error. Crame-Rao lower bound (CRB) is widely used for assessing localization performance limits but the recent measurement revealed that CRB does not always represent an actual lower bound for indoor positioning. We utilise and modify two more advanced lower bounds and propose an optimization trend in system configuration such that the attained root mean square error in the position estimator gets closer to the minimal attainable variance in the fingerprinting position estimator. Finally, a new method for error estimation in indoor localization systems is designed and novel precision measurements factors for fingerprinting method is developed. Thus the quality of service of the positioning system is improved and the integrity of the system is guaranteed. In this research, the problem of evaluation and enhancement the accuracy of fingerprinting positioning systems utilizing terrestrial FM signals is addressed and analytical frameworks and appropriate solid tools for designing more precise indoor positioning systems are developed. In summary, the FM-based positioning analysis, analytical position error estimation tools, statistical analysis on the accuracy of the indoor positioning systems, and the design criteria tools in this thesis are novel and provide interesting insights into the positioning system performance. These tools are used to optimise the system performance under given performance objectives and constraints.
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(2010)ThesisAs the backbone for the global communication network, optical dense wavelength division multiplexed (DWDM) systems are facing challenges in capacity, flexibility, reliability and cost effectiveness. In my thesis research I developed five novel optical devices or subsystems to combat these technical challenges. Each of these devices/subsystems is described in an individual chapter including background survey, proposal of new features, theoretical analysis, hardware design, prototype fabrication and characterization, and experimental verification in DWDM systems. The first is a novel tunable asymmetric interleaver that allows the interleaving ratio to be adjusted dynamically. Two design methods were proposed and implemented. Spectral usage optimisation and overall system performance improvement in 10G/40G and 40G/100G systems were successfully demonstrated through simulations and experiments. The second is a colourless intra-channel optical equalizer. It is a passive periodic filter that restores the overall filter passband to a raised cosine profile to suppress the filter narrowing effect and mitigate the inter-symbol interference. 20% passband widening and 40% eye opening were experimentally achieved. The third is a flexible band tunable filter that allows simultaneous tuning of centre frequency and passband width. Based mainly on this filter, a low cost expendable reconfigurable optical add/drop multiplexer (ROADM) node was developed. Its flexible switching features were experimentally demonstrated in a two-ring four-node network testbed. The fourth is a transponder aggregator subsystem for colourless and directionless multi-degree ROADM node. Using the unique characteristics of the coherent receiver, this technology eliminates the requirement of wavelength selector, thus reduces power consumption, size and cost. I experimentally demonstrated that it can achieve < 0.5 dB penalty between receiving single channel and 96 channels. The last is a real-time feedforward all-order polarization mode dispersion (PMD) compensator. It first analyses spectral interference pattern to retrieve phase information and calculate PMD, then it uses a pulse shaper to restore the pulse shape and thus compensates the PMD. These functions were demonstrated through experiments and simulations. All of these novel devices and subsystems deliver new functional features and are suitable to be applied in the next generation DWDM systems to improve capacity, flexibility, and reliability and to reduce cost.
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(2011)ThesisThis dissertation presents a novel prototype optical interconnect system achieved by MEMS technology for stacked silicon dies. The overall approach is drawn from concepts on 3D-TSV metal interconnect and introducing an optical interconnect. Optical interconnect is a promising solution for future global interconnect inside a chip package consisting of a stack of multiple dies. The design allows an optical beam to propagate both in plane and out-of-plane, hence establishing optical communication between stacked dies. The entire system includes a pair of 45 micromirrors with one in an upward-facing (front) position and the other in downward-facing (rear) position. Fiber grooves were fabricated on each dies for the purpose of optical testing. Passive alignment structures have been integrated in the system to achieve accurate horizontal alignment. The research work have also proposed a planar silica graded index lens integrated 3D optical interconnect system. A pair of planar silica graded index lens is designed to sit in front of the 45 micromirror pair to mitigate the free space propagation loss. Optical beam free space spot sizes from these planar lenses are commensurate with the micromirror dimensions. To fabricate high quality ultra-smooth 45 micromirror on the (100) monocrystalline silicon surface by anisotropic wet etching, surfactant added TMAH etching behavior was first investigated. Non-ionic surfactants NCW-601A, Triton X-100, NCW-1002 with both high concentration (25%) and low concentration (10%) TMAH solutions was extensively studied for their etching properties on (100) and (110) silicon surfaces. Etch rate, selectivity and surface roughness were studied. Etchant temperature was also varied from 60C to 90C to see the effects on etching behaviour. This research is the first reported use of a new surfactant NCW-1002 in low concentration TMAH. Better selectivity and surface roughness of the (110) plane (i.e. micromirror surface) can be achieved with this surfactant added low concentration TMAH at 60C. In view of the intrinsic partial isotropic etching behavior in the vicinity of the (100) plane for low concentration TMAH with high concentration surfactant, this work has established and demonstrated for the first time in published literature that only a limited portion of the micromirror is truly 45 and is located approximately at the middle of the slope. To reduce the top curved portion, two new techniques have been developed. One technique involves timed HF dip treatments during the etching process to remove the overhanging oxide, which has impeded the etching at the top part of the slope due to the diffusion-dependant effect. The other technique involves a maskless etching. The entire top curved slope can thus be straightened out. To avoid the bottom curved portion, another technique was developed to allow a deeper etch at the lower end of the micromirror to recess the non-45 lower portion of the slope. Both these techniques can nearly double the size of the truly 45 portion of the micromirror. Based on the framework of a front upward-facing 45 micromirror, a processing technique was developed to fabricate a novel rear downward-facing 45 micromirror using electro-chemical TMAH release. With the assistance of passive alignment structures, optical test was conducted to confirm successful optical interconnect between stacked dies using optical fiber. The loss was measured to be 14.7dB, among which free space transmission loss is approximately 10dB. To reduce the free space propagation loss, a pair of planar silica graded index lens integrated optical interconnect system was then proposed. Fabrication of the planar silica graded index lens with front 45 micromirror is confirmed in this research work.
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(2013)ThesisBeamforming in wireless communications have gathered great interests in recent years due to its ability to enhanced the performance of networks significantly by exploiting intensively the spatial diversity. In this work, the objectives of beamforming design consist of several optimization targets ranging from minimizing the beamforming power subject to quality-of-service (QoS) constraints to maximizing the minimum QoS regarding fixed budgets of transmitting power. The design problems of beamforming are intrinsically challenging because their natural formulations are nonconvex optimization problems. Moreover several problems are proved to be non-deterministic polynomial-time hard (NP-hard) such as beamforming in multicast transmission. These problems are very difficult to solve at optimality in practical sense. Therefore, there is a strong motivation to convert the original design problems into a series of convex problems with desirable computational complexity by applying efficient optimization techniques. This dissertation contributes mainly in exploiting the convex optimization algorithms to solve nonconvex beamforming problems in several network settings. First, the transmit beamforming for downlink communication of multicast transmission with spectrum sharing is investigated. Secondly, the beamforming design is applied on amplify-forward (AF) wireless relaying systems using single-antenna relays. The key contribution is to derive the beamforming schemes applied on transmit antennas so that the beamforming power is minimized while all users' signal-to-interference-and-noise ratios (SINRs) are guaranteed. The formulation results in nonconvex optimization problems due to SINR constraints hence require to be converted into semidefinite programming (SDP) forms. The SDP problems are again nonconvex regarding the rank-one constraints on semidefinite variables. Conventionally, the rank-one constraints are relaxed hence the problems cannot be solved thoroughly. In this work, nonsmooth optimization techniques are employed to tackle with the nonconvex rank-one constraints and are successfully to deliver efficient solutions that can outperform the conventional methods. Finally the precoding design problems in mutiple-input multiple-output (MIMO) relaying scenarios are considered. The difference-of-two-convex-function (D.C.) programming technique is employed to solve the problems at optimality with significantly lower complexity compared with conventional method.
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(2010)Conference PaperWe demonstrate radio frequency (RF) readout of electrically detected magnetic resonance in phosphorus-doped silicon metal-oxide field-effecttransistors (MOSFETs), operated at liquid helium temperatures. For the first time, the Si:P hyperfine lines have been observed using radio frequency reflectometry, which is promising for high-bandwidth operation and possibly time-resolved detection of spin resonance in donor-based semiconductor devices. Here we present the effect of microwave (MW) power and MOSFET biasing conditions on the EDMR signals.
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(2012)ThesisFuel cells (FCs) are a promising alternative energy solution and a reliable technology for niche applications providing high conversion efficiency. FCs are generally classified according to the type of the electrolyte. Proton exchange membrane FCs (PEMFCs) combine the hydrogen fuel with the oxygen from the atmosphere to produce water, heat (at temperature up to 90°C) and electricity. The major advantages of the PEMFCs include: being environmentally friendly, offering high efficiency and low operating temperature while providing increased safety. When low-voltage unregulated FC output is conditioned to generate AC power, two stages are generally required: a boost stage and an inversion one. However, due to the cascaded power stage conventional two-stage FC systems have unavoidable drawbacks such as being bulky, inefficient and having a high cost. Moreover, FC systems require an auxiliary unit to improve efficiency, lifetime and safety by cancelling the ripple current and supporting its slow dynamics. In this thesis, single-stage FC systems are reported to overcome the disadvantages of the conventional FC systems caused by cascaded power stages. The proposed FC systems provide high power conversion efficiency, low-cost and compactness for standalone and grid connected applications in single- and three-phase systems. Analysis, simulation and experimental results taken from 1kW laboratory prototypes operating at 20 kHz are presented to validate the performance of the proposed FC systems. Single conversion stage FC systems based on the boost-inverter and buck-boost inverter with a back-up energy storage unit have been developed in this research as follows: • A single power stage FC system based on a boost-inverter with a battery back-up unit • A grid-connected FC system based on a boost-inverter with a battery back-up unit • A single conversion stage FC system based on a buck-boost inverter with a battery back-up unit • A single conversion stage three-phase FC system based on a boost-inverter with a battery back-up unit • Design and implementation of digital control as implemented in an FC energy system The proposed FC systems has achieved satisfactory performance for delivering boosting and inversion functions within the single power conversion offering high efficiency and compactness. Moreover, an integrated battery back-up energy storage unit has also performed two functions: providing the ramping operation to deal with the slow dynamics of the FC and eliminating the ripple current to increase the efficiency and life time of the FC.
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(2012)ThesisGrowing concerns over high and volatile fossil-fuel prices, energy security and climate change present significant sustainability challenges for electricity industries around the world. They have particular implications for generation investment and planning as decisions to build power plants represent major commitments with regard to future electricity industry costs, fuel dependencies, energy security outcomes, and greenhouse emissions. Increasing uncertainty about future fuel prices, plant construction costs, climate change policies and electricity demand adds to the challenges. In consequence, generation investment decision-making is transitioning from traditional cost minimisation approaches towards more complex assessments incorporating future uncertainties and a range of industry objectives. This thesis presents a novel generation investment and planning decision-support tool for assessing possible future generation portfolios within an electricity industry under uncertainty and multiple policy objectives. The tool extends conventional optimal generation mix concepts by using Monte Carlo simulation and portfolio analysis techniques to determine probability distributions of future expected generation costs and greenhouse emissions for a wide range of generation portfolios. The tool can incorporate complex and correlated probability distributions for future fossil-fuel prices, carbon prices, plant investment costs, and electricity demand including price elasticity impacts. It supports sophisticated risk assessments, including downside economic risks, for any generation portfolio. A post-processing analysis is also implemented to assess the potential operational dispatch constraints and costs associated with different portfolios in meeting time-varying demand. Applications of this tool are demonstrated through case studies of electricity industries with different generation options facing a range of future uncertainties. The results provide high-level insights into issues that will likely be key drivers of future industry performance such as the impact of different sources of uncertainty, the role of future demand changes in response to electricity prices, and the interaction between wind penetration and carbon pricing on the expected costs, cost risks, and emissions of different portfolios. The implications of nuclear power and the value of different technologies within generation portfolios are also explored. These results highlight the potential value of the tool in facilitating utility and policy decision-making in the challenging task of generation investment and planning for increasingly uncertain future electricity industries.
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(2012)ThesisAs a well-established multilevel converter topology, the cascaded H-bridge (CHB) is suitable for large-scale PV grid-integration due to its high-voltage and high-power capability, high power quality, modular structure, and multiple DC-links which are able to incorporate a large number of PV generators. Since PV system grounding is required by most countries grid codes and the modulation process of the CHB introduces high potentials upon the DC-side of the converter, galvanic isolation between the PV and the grid is essential to avoid the potential induced degradation (PID) of the PV modules, and to prevent the leakage current, as a result of the PV panel-to-ground parasitic capacitance, from flowing through the converter and ground, posing serious safety concerns. PV isolation can be achieved by the implementation of isolated DC/DC converters. The DC/DC converters connect the PV sources to the CHB converter through DC-links, performing maximum power point tracking (MPPT) and necessary DC voltage amplification, while the imbedded high-frequency transformers isolate the PV from the AC-side. The thesis presents the system validation and documents the performance evaluation of the CHB converter with isolated DC/DC converters for large-scale PV grid-integration, featuring different power and voltage level configurations, tailored with two control approaches, and through specific case studies. Two isolated DC/DC converter topologies, namely the boost-half-bridge (BHB) and the flyback are implemented. The CHB converter provides good quality voltage and current waveforms and is capable of medium-voltage grid-connection of the PV system. The system can be well regulated with voltage-oriented control (VOC) schemes both in the synchronous frame using Proportional-Integral (PI) controllers, and in the stationary frame using Proportional-Resonant (PR) controllers. Both DC/DC converters are able to perform MPPT under Standard Test Conditions (STC) and track the varying input voltage reference signal in a wide range fast and accurately. Compared with the flyback, the BHB converter presents lower ripples on the control variables and offers better MPPT efficiency at a higher component count. As the building block of the multiphase DC/DC converters, which feature high-voltage and high-current capability with modular and interleaved structures, the BHB makes a competitive candidate for this application.
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(2012)ThesisIn this work the modeling and performance analysis are present for a proposed MIMO Free-Space system called "Phase-Fading" system, which is a single-user with multiple-antenna system, where the transmitters and receivers are randomly located in specific areas and the links are dominated by Line-of-Sight (LoS) components. Since Free-Space Phase-Fading MIMO system channel is stochastic, based on Telatar's research, its capacity is determined by singular eigenvalue distribution of the random correlation matrix corresponding to channel transmit matrix. Firstly, for proposed Free-Space MIMO system, the asymptotic analysis was performed for the ergodic capacity with respect to the infinite number of transmit and receive antennas while keeping the aspect ratio beta constant, for which the explicit expression of asymptotic capacity was uncovered. In addition, an unification property has been found for asymptotic capacity performances in Phase-fading and Rayleigh channel. Secondly, considering the finite order channel capacity, simulation plots were present and the Phase-Fading System has better capacity than the conventional Free-Space MIMO systems and Rayleigh channel. Moreover, the singular value distribution has been worked out for 2 by 2 Phase-fading channel as well the capacity formula. Besides, an essential part has been discovered in the joint probability density function of eigenvalues.
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(2012)ThesisIn recent years, optical fibre laser-based sensors have attracted great research attention. Numerous types of optical fibre laser-based sensors have been demonstrated for various applications with desirable features such as high signal power, low noise, small size, inherited fibre compatibility, single polarization and single longitudinal mode operation. In particular, fibre laser-based sensors with high spectral resolution are appropriate for high sensitivity and low concentration gas detection applications. This thesis reports the research work on a fibre laser-based intra-cavity absorption gas sensor (ICAGS). The ICAGS has many advantages such as long interaction length, compact configuration and capability of multiplexing and distributed measurement. A few key technical issues related to modeling, design, evaluation and fabrication of a fibre-ring laser based ICAGS were systematically investigated. The system technologies, parameters, conditions, considerations and their impacts on the ICAGS based on an erbium doped fibre (EDF) were investigated theoretically and experimentally. Firstly we studied in great detail the effects of key system parameters on the performance of the ICAGS. Based on the rate equations and propagation equations, a theoretical model to evaluate the output characteristics of the ICAGS was established. For the first time, the relations between the key design parameters (EDF dopant concentration, EDF length, cavity loss and pump power) and the system performance parameters, e.g. sensitivity enhancement factor, of an ICAGS were systematically studied. Especially, appropriate selections of the design parameters, i.e. EDF factor (the product of EDF dopant concentration and EDF length), cavity loss and pump power, for optimal performance in terms of sensitivity enhancement and signal output power were obtained. Secondly we established an EDF based ICAGS experimental system. Detailed system considerations, hardware selections and software designs are presented. The nonlinearity of the wavelength selective element - Fabry-Perot tunable filter, was investigated. A method for compensating the effects of the nonlinearity was proposed. This method reduces the error in identifying the central wavelength of the absorption lines and increases the accuracy of the central wavelength detection effectively without a feedback system. Thirdly we proposed and analyzed a new design of miniature gas cell to solve the problems of previous gas cells in extreme environment applications. This gas cell was made of a pair of gradient-index fibre lenses and a narrow capillary which made it compact and stable. Good coupling efficiency could be achieved if proper gradient-index fibre is chosen. Theoretical analysis and experiments were carried out to prove the feasibility of the design. Fourthly experiments on gas sensing using a wavelength sweep technique were conducted. By selecting appropriate system operational parameters, 6 strong absorption lines near 1530 nm of acetylene can be obtained with good spectrum resolution in one scanning period. For various concentration cases, by choosing proper absorption lines and performing weighted averaging, detection accuracy can be enhanced. To further improve the accuracy in determining the central wavelength of the absorption lines and to realize multi-gases recognition, a fibre Bragg grating (FBG) as the wavelength reference has been introduced. Finally, potential applications of micro-structured fibre (MOF) in an ICAGS were explored. Optical fibre gas sensors using MOF open up new opportunities for exploiting the interaction of light with gases and exhibit great sensing potential. The splicing techniques of MOF to SMF were studied using a commercial fusion splicer. With proper splicing parameters, a splice loss of about 1.62 dB was realized by a commercial splicer.