Electrical and Electronic Engineering - Theses
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ItemNovel all-optical signal processing schemes and their applications in packet switching in core networks(University of Melbourne, 2007)
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ItemResource allocation for multiuser OFDM systems(University of Melbourne, 2006)
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ItemTransthoracic resistance during cardiac defibrillation( 1983)Before entering into a description of the scope of this project, it is worth mentioning that human transthoracic resistance, not impedance, is the subject of this thesis. The relationship between voltage and current in the human body is known to-vary with both current and time. Complex impedance is an abstraction, and is not useful for describing such a non-linear, time varying system. The concept is best suited to linear, time invariant systems or, at worst, non-linear time invariant systems because of the system model which is implied with complex impedance. Certainly, it may be reasonable to represent the electrical transfer function of the thorax as a combination of non linear phase lead, phase lag and transconductance parameters, but such a model loses significance when the only waveform available for testing is a very slightly underdamped sinusoid (the usual DC defibrillating waveform). Of course, measurements can be taken at low current levels, below a few tens of milliamps, with different source waveforms and with no adverse effects on the subject; however, this does not necessarily give information about what happens at the higher current levels. Voltage and current are the only two "real" parameters available for measurement. The transfer function between these two variables for the human thorax can be completely described for a particular current (or voltage) waveform if they are both measured at each point in time for the duration of the waveform. The term "resistance" will be used hereafter to refer to the instantaneous ratio of this voltage and current. Closed chest defibrillation of the heart is carried out frequently in hospitals as treatment for cardiac arrest, ventricular fibrillation and other cardiac arrythmias. The success rate is not 100%, and since the turn of the century much work has been done to isolate and quantify thevariables affecting the oùtcome of such resuscitation attempts. Most workers now agree that the peak current density in the myocardium during defibrillation is one of the most important factors determining success. It is clear that this will be critically affected by the electrical resistance of the thorax, where the defibrillating electrodes are applied. (From Ch. 1)
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ItemSignal processing techniques for optical fiber networks( 2007)At present, optical fiber transmissions are dominated by intensity modulation and direct detection, which fundamentally limit the signal processing capabilities in optical fiber networks. On the other hand, manipulation of optical phase enables advanced signal processing techniques for various applications. This thesis includes three parts and makes contributions in three research areas in optical fiber networks, by applying optical and electronic signal processing techniques. In the first part of the thesis, optical signal processing is employed to realize a novel all-optical label swapping (AOLS) technique using synchronous phase modulation. This technique is shown to address the forwarding speed bottleneck in optical packet switched networks (OPSN). By exploiting the unique symmetry of phase-shift keying (PSK), for the first time, label erasure and insertion are performed in a single step by a phase modulator without wavelength conversion. We also propose and demonstrate a polarization insensitive phase modulator to address the polarization sensitivity of AOLS. Furthermore, we emulate multi-hop all-optical label swapping in a re-circulating loop to investigate the power penalties from the accumulated phase errors and the timing mismatch. Based on the experimental and analytical results, we show that this technique can save wavelength converters significantly if compared with conventional AOLS techniques requiring dedicate wavelength converters.
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ItemPerformance of estimation and detection algorithms in wireless networks( 2007)This thesis focuses on techniques for analyzing the performance of estimation and detection algorithms under conditions which could be encountered in wireless networks, with emphasis on wireless sensor networks. These include phenomena such as measurement losses, fading channels, measurement delays and power constraints. We first look at the hidden Markov model (HMM) filter with random measurement losses. The loss process is governed by another Markov chain. In the two-state case we derive analytical expressions to compute the probability of error. In the multi-state case we derive approximations that are valid at high signal-to-noise ratio (SNR). Relationships between the error probability and parameters of the loss process are investigated. We then consider the problem of detecting two-state Markov chains in noise, under the Neyman-Pearson formulation. Our measure of performance here is the error exponent, and we give methods for computing this, firstly when channels are time-invariant, and then for time-varying fading channels. We also characterize the behaviour of the error exponent at high SNR. We will look at the fixed lag Kalman smoother with random measurement losses. We investigate both the notion of estimator stability via expectation of the error covariance, and a probabilistic constraint on the error covariance. A comparison with the Kalman filter where lost measurements are retransmitted is made. Finally we consider the distributed estimation of scalar linear systems using multiple sensors under the analog forwarding scheme. We study the asymptotic behaviour of the steady state error covariance as the number of sensors increases. We formulate optimization problems to minimize the sum power subject to error covariance constraints, and to minimize the error covariance subject to sum power constraints. We compare between the performance of multi-access and orthogonal access schemes, and for fading channels the effects of various levels of channel state information (CSI).
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ItemAnalysis and optimization of MAC protocols for wireless networks( 2007-06)Medium access control (MAC) plays a vital role in satisfying the varied quality of service (QoS) requirements in wireless networks. Many MAC solutions have been proposed for these networks, and performance evaluation, optimization and enhancement of these MAC protocols is needed. In this thesis, we focus on the analysis and optimization of MAC protocols for some recently emerged wireless technologies targeted at low-rate and multimedia applications.
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ItemPerformance evaluation and enhancement of mobile and sensor networks( 2006)This thesis addresses the performance evaluation and enhancement of wireless networks. Part I investigates the problem of resource allocation in cellular networks, focusing on handoff, and Part II investigates resource allocation in sensor networks focusing on power management. (For complete abstract open document)
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ItemResource allocation in OFDM cellular networks( 2006-12)The efficient use of radio resources is crucial in order for future wireless systems to be able to meet the demand for high speed data communication services. Orthogonal Frequency Division Multiplexing (OFDM) is an important technology for future wireless systems as it offers numerous advantages over other existing technologies, such as robust performance over multipath fading channels and the ability to achieve high spectral efficiency. Dynamic resource allocation can fully exploit the advantages of OFDM, especially in multiple user systems. In this thesis, we investigate a resource allocation problem in a multiple user, multiple cell OFDM cellular network focusing on downlink communications. (For complete abstract open document)
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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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ItemSignal processing for optical performance monitoring and impairment mitigation( 2006)Optical performance monitoring is essential for managing optical networks. One important quantity to monitor is the optical signal-to-noise ratio (OSNR). And in high bit rate fiber optical systems operating at 10 Gb/s or beyond, compensating optical impairments becomes important. In this thesis, we investigate OSNR monitoring using beat noise and present two new OSNR monitoring techniques. We propose an OSNR monitoring technique using uncorrelated beat noise and show by experiment for a 10 Gb/s system that in the OSNR range from 10 dB to 30 dB, the proposed OSNR monitoring scheme has a measurement error of less than 0.5 dB. Then, we propose and experimentally demonstrate for the first time an OSNR monitoring technique using beat noise for optical packet switched networks which performs monitoring on a packet basis. The response time of the OSNR monitor can be around 10 ns and the OSNR measurement error is found to be less than 0.6 dB for OSNR from 10 dB to 30 dB. We also explore chromatic dispersion and polarization-mode dispersion (PMD) mitigation using Viterbi equalization in 10 Gb/s nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and differential quadrature phase-shift keying (NRZ-DQPSK) systems. We show through simulations that using Viterbi equalizers improves the performance of NRZ-OOK, NRZ-DPSK and NRZ-DQPSK receivers. For NRZ-DQPSK receiver with a Viterbi equalizer, the chromatic dispersion tolerance is about 5048 ps/nm and the PMD tolerance is about 160 ps at 3 dB OSNR penalty.