Electrical and Electronic Engineering - Theses
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ItemAn adaptive system for patient-controlled analgesia vol.1( 1995-11)Patient-Controlled Analgesia (PCA) has become accepted as an important means of self-regulated relief from post-surgical pain. In commonly used PCA systems, patients use a hand-held push-button to indicate the presence of pain and initiate a predetermined bolus of drug infusion. A disadvantage of this system is that no means is provided to accommodate variations in the intensity of pain or the sensitivity of the patient to the analgesic in use apart from the frequency of button pushing. A fixed rate background infusion is usually an option. A new adaptive PCA system is proposed to provide improved PCA through the use a variable background infusion, the provision for an extended high range of analgesic dosages and a novel handset which allows patients to rate their pain. The total system is under the control of an expert algorithm and is proposed to overcome some of the shortcomings of current systems. (For complete abstract open document)
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ItemManaged DC power reticulation systems( 1999-11)Electric power engineering, as it applies to low-voltage power reticulation in buildings and industrial sites, is ripe for a ‘paradigm shift’ to bring it properly into the Electronic Age. The conventional alternating-current approach, now over a hundred years old, is increasingly unsatisfactory from the point of view of plant and appliance requirements. Alternative approaches can deliver substantial cost savings, higher efficiencies, power quality improvements, and greater safety. Power reticulation systems in the future can be expected to differ from present systems in two key respects. The first is a greatly increased role for direct current; the second is the augmentation of the power system with a wide range of ‘management’ technologies. Combining these two trends, which can already be observed today, leads to consideration of ‘managed DC’ power reticulation systems, operating from AC bulk supply mains via AC-DC converters.
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ItemOptical fibre-loop buffers( 1996)This thesis contains a detailed investigation of fibre-loop buffers. Fibre-loop buffers will be required in all-optical packet-switching networks which may be the basis of future telecommunications networks. The term "all-optical" or "Photonic" refers to the fact that this buffer stores this data in an optical form. At no stage is optical data converted from an optical into an electrical form or vice-versa. The buffer investigated in this thesis achieves all-optical data storage using an optical fibre delay-line (hence “fibre-loop”). Data entering the buffer passes into the input of this delay-line. Some time later (typically less than a microsecond) the data appears at the output of the delay-line. The data can be passed back into the input of this delay-line and the process repeated, thereby extending the storage time. Optical power loss is inevitable as stored data make repeated round-trips through the fibre delay-line. A semiconductor optical amplifier (SOA) is inserted in series with this delay-line to provide all-optical amplification and compensate for this power loss. Unfortunately, a SOA also generates amplified spontaneous emission noise (ASE) which successively adds to and degrades stored data as it makes multiple passes through the SOA. The presence of ASE therefore limits the maximum number of roundtrips (recirculations) that data can be stored in the memory loop. This thesis contains new experimental data showing the accumulation of ASE. A characteristic of the fibre-loop buffer is that small changes in the gain of the SOA can have a cumulative effect on the power level of stored data after a few recirculations. Such large changes of power level must be avoided if the fibre-loop buffer is to be reliable storage system with predictable characteristics. One cause of such gain changes is gain compression which causes the gain of a SOA to decrease at high input power levels. Previous researchers have utilised the negative-feedback effect caused by gain compression to stabilise the power level of stored data in a fibre-loop buffer, in what is a partial answer to the above requirement. Near-travelling-wave SOAs also possess Fabry-Pérot ripple in their gain spectra which is caused by residual end-facet reflections. This ripple is shown in this thesis to also affect the power levels of stored data as well as making the performance (i.e. the maximum storage time) of a fibre-loop buffer dependent on its wavelength. It is shown in this thesis that the thermal characteristics of the SOA active region also influence the power levels of stored data. Both the gain and Fabry-Pérot ripple characteristics depend on the temperature of the active region. This latter quantity is in turn dynamically coupled to the bias current level (with microsecond to millisecond time constants) of the SOA. It is shown in this thesis that since the bias current level is likely to vary in a complicated manner with time in a practical application, the cumulative effect of the SOA thermal characteristics on the power level of stored data can be large and unpredictable unless corrective measures are taken. The phenomena described above are complicated by the carrier recombination dynamics in the SOA, which affects the degree of gain compression and also the Fabry-Pérot ripple characteristics on sub-nanosecond time scales. It is shown in this thesis that the dynamic behaviour of gain compression significantly distorts high bit-rate data as well as affecting the bit-error-rate (BER) at subsequent detection. It is shown by experiment in this thesis that all of the phenomena described above affect fibre-loop buffer performance to a significant degree. These experiments have been performed using a prototype fibre-loop buffer constructed by the author. Optical component characteristics (the SOA, as well as other components) which significantly affect the operation of the prototype fibre-loop buffer are discussed in detail. This thesis also contains a time-domain model of the prototype fibre-loop buffer which incorporates all of the above phenomena. This model successfully (and quantitatively) accounts for all of the observed behaviour of the prototype buffer. The time-domain model, having been proven, is then used to predict the performance of the prototype fibre-loop buffer under realistic operating conditions at data-rates up to 40 Gbit/s. This model is also used to predict the performance of an improved fibre-loop buffer design using a strained-quantum-well SOA. It is also shown using the time-domain model that the use of gain compression to stabilise power levels requires a fibre-loop buffer to operate in such a way that it provides sub-optimal storage times. An active feedback mechanism is shown be a better way of guaranteeing repeatable operation of a fibre-loop buffer. This feedback mechanism monitors the power level of stored data and adjusts the gain of the memory loop by changing the bias current level of the SOA.
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ItemPerformance analysis of Hidden Markov Model based tracking algorithms( 1997)This thesis investigates the performance of Hidden Markov Model (HMM) based tracking algorithms. The algorithms considered have applications in frequency line tracking and target position tracking. The performance of these algorithms are investigated by a combination of theoretical and simulation based approaches. The theoretical based approach focuses on deriving upper bounds on probabilities of error paths in the output of the tracker. Upper bounds on specific error paths, conditioned on typical true paths are derived for a HMM based frequency line tracker that uses continuous valued observation vectors. These bounds are derived by enumerating possible estimated state sequences, and using necessary conditions on the Viterbi scores of these sequences. The derived upper bounds are found to compare well with simulation results. Next, upper bounds on average error event probabilities (averaged over all possible true paths) are derived for the same HMM based frequency tracker. Here, 'error event' refers to a brief divergence of the estimated track from the true path. Numerical computation of the derived upper bounds are shown to compare well with simulation results. Using these bounds a theorem is established which states that optimum tracking, corresponding to minimum error probability, is achieved when model transition probabilities are matched to 'true' transition probabilities of the underlying signal. Other interesting features of this algorithm are analysed, including robustness of the algorithm to variations in model transition probabilities, and characterisation of the benefits of using HMM based tracking as opposed to a simple approach based on isolated Maximum Liklihood estimators. The theoretical analysis is extended to two other HMM based frequency line trackers that use discrete valued observation vectors. A comparative study of the three HMM based frequency line trackers is carried out to arrive at conditions for the superiority of one algorithm over another. The simulation based approach to analysing performance consists of a combination of Monte-Carlo (MC) and Importance Sampling (IS) simulations. MC simulations are carried out at moderate SNR where required computation time for estimating performance measures is feasible. At high SNR, the error probabilities are small and the required computation time becomes infeasible. To overcome this, importance sampling schemes are designed which reduce the computation time by orders of magnitude. Importance sampling is a modified Monte-Carlo method which is useful in the simulation of rare probabilities. The basic principle is to use a different simulation density to increase the relative frequency of "important" events and then weight the observed data in order to obtain an unbiased estimate of the parameter of interest. In this thesis, a systematic procedure based on minimizing an upper bound to the IS estimator variance is used in the simulation density design. High efficiency gains, of order 1013 are demonstrated with the proposed scheme.
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ItemTechnologies for millimetre-wave fibre-radio systems( 1999)The recent advances in mobile wireless technology have increased the need for more transmission bandwidth to accommodate for future telecommunication services. The millimetre-wave (mm-wave) hybrid fibre-radio system is one of the potential technologies for provision of these broadband services. With the advent of low-loss and high bandwidth optical fibre in telecommunication networks, it is an ideal medium for distributing the broadband mm-wave information. In addition to the provision of broadband services and high capacity, the hybrid fibre-radio system also enables customer mobility. This thesis investigates the performance of different architectures for distributing radio signals over fibre in mm-wave fibre-radio applications. In particular, networks incorporating radio signal distribution as mm-wave frequency and as baseband data over fibre are investigated. There have been many different downlink implementations incorporating mm-wave radio signal distribution over fibre for mm-wave fibre-radio system, however there has been little focus on the uplink path. For the first time a simple mm-wave uplink path in a mm-wave fibre-radio system is presented in this thesis which incorporates direct modulation of a multi-section mode-locked distributed-Bragg reflector (DBR) laser at the base station. The performance of the multi-section laser as a mm-wave optical transmitter is presented, and a detailed characterisation of the multi-section laser stabilised via hybrid mode-locking at fundamental and subharmonic frequencies is carried out. The uplink path implementation using the multi-section laser is further extended to incorporate multi-channel transmission. Efficient multi-channel transmission incorporating the multi-section laser requires the separation of the stabilisation and modulation functions of the drive signal applied to the laser. Two different stabilisation techniques namely fundamental hybrid and subharmonic synchronous mode-locking are considered for multichannel operation, and their performance investigated. A detailed theoretical analysis is then presented that quantifies the impact of fibre chromatic dispersion-induced rf power penalties when using the multi-section laser to transmit mm-wave frequencies over fibre. The model is also used to study the performance of the laser as a function of its operating conditions. The thesis also presents a detailed investigation of the implementation and performance of a mm-wave hybrid fibre-radio system with baseband data delivery over optical fibre, a technique which has not been previously reported. The first realisation of a mm-wave fibre-radio system with baseband data delivery over the optical fibre network is presented. This system incorporates a novel modulation scheme for simultaneous transmission of baseband digital data and remote local oscillator (LO) signal delivery. The modulation scheme exhibits several unique features including the use of a single dual-electrode Mach-Zehnder modulator and the delivery of the LO signal is such a way that it is not affected by fibre dispersion. A full-duplex mm-wave fibre-radio system comprising broadband baseband data transmission is implemented with custom-designed mm-wave diplexers and antennas. A theoretical model is also developed to quantify the performance of the baseband data modulation scheme. The analysis is used to determine the sensitivity of the modulator input parameters on the system performance and good agreement is obtained between the model and measurements of the fibre-radio link incorporating baseband data modulation.
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ItemEM algorithms for state and parameter estimation of stochastic dynamical systems( 1997)This thesis studies the use of the Expectation Maximization (EM) algorithm for state and parameter estimation of stochastic dynamical systems. Optimal maximum likelihood parameter estimates via the EM are computed for: i) Gaussian state space models, where explicit rules are given for optimally partitioning the parameter space to update some parameters using the Newton-Raphson method and the EM method (on the remaining parameters). The partitioning is optimized to ensure minimum processing time for computing the estimates, ii) Errors-in-variables models driven by additive Gaussian and finite-state Markovian disturbances, and iii) 1-bit quantized Markov modulated autoregressive process, generalizing the binary time series algorithm of [Kedem 1980] for linear time series to Markov modulated time series. While the EM is widely used as an iterative numerical method for maximum likelihood parameter estimation of partially observed stochastic models, a significant contribution here is to use the EM for optimal state estimation. In particular, the EM is used to compute maximum a posterior state sequence estimates of jump Markov linear systems. An off-line optimal state estimator is derived, which iteratively combines a Hidden Markov Model Smoother and a Kalman Smoother. Two applications are extensively studied: i) Maximum a posterior state estimates of a maneuvering target in clutter. and ii) Narrowband interference suppression in spread spectrum code division multiple access systems. This thesis also studies open-loop control strategies using information theoretic criteria. Optimal observer paths are derived for the bearings-only tracking problem. Optimal optimization techniques, such as forward and backward dynamic programming and enumeration with optimal pruning are derived. Furthermore, a number of computationally tractable suboptimal optimization techniques, such as approximate reduced complexity forward dynamic programming and one-step ahead (suboptimal) control strategies are presented.
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ItemTraffic modelling and analysis for cellular mobile networks( 1993)This thesis is concerned with the modelling and analysis of call control policies in cellular mobile networks. It addresses the important problem of finding policies which give sufficient priority to handover attempts between cells over new call attempts so that network congestion will not lead to handover failures and subsequent call dropouts. The major contribution of the thesis is the analysis of a class of priority queuing systems and a methodology for the modelling of cellular networks with non-uniform offered traffics. Three related priority queuing systems are considered for application to cellular mobile networks: a non-preemptive priority queue; a cutoff priority queue with a hysteresis mechanism and a non-preemptive priority queue with channel reservation and hysteresis. A matrix-geometric solution of the same form is shown to be common to all of these systems with a matrix-exponential form found for the delay distributions. It is also shown that these systems can be represented by an equivalent M/G/1 queue with multiple vacations and this reveals some insight into their behaviour. A new result is derived for the M/G/1 queue with multiple vacations and impatient customers and this allows for the priority systems to be extended so that new call arrivals are subject to a fixed timeout in queue. In some situations, this provides a more realistic model of the behaviour of new call attempts. Handover delay performance is treated at length. It is found that queuing of handover requests is highly desirable and that handover delay performance can be further improved by classifying handover requests and giving higher priority to the more urgent handover requests. Microcellular networks, for which handover delay requirements are quite stringent, are also considered. A micro cellular traffic model is proposed and a call repacking policy, which is particularly well-suited to microcells, is analysed. The effectiveness of a class of state-dependent call acceptance policies in improving handover delay performance is also considered. The performance of cellular networks is much dependent on the distribution of offered traffic. An approximation technique is developed which enables a wide class of call control policies to be investigated. It is based on decomposing a network into a number of subnetworks which are then assumed to be stochastically independent. This technique turns out to be fairly accurate under reasonable traffic assumptions.
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ItemStudies in nonlinear filtering theory: random parameter linear systems, target tracking and communication constrained estimation( 1998)The focus of this thesis is nonlinear filtering for discrete-time stochastic systems. In particular, we consider optimal and suboptimal filtering algorithms for random parameter linear systems and state estimation for Markov chains in the presence of communication constraints. The thesis presented in three parts. (For complete abstract open document)