Masters Degrees (Electrical and Electronic Engineering)

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A 10 GHz oversampling delta modulating analogue-to-digital converter implemented with hybrid superconducting digital logic
(Stellenbosch : Stellenbosch University, 2001-03) Fourie, Coenrad Johann; Perold, W. J.; De Swardt, J. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: Rapid Single Flux Quantum (RSFQ) logic cells are discussed, and new cells developed. The expected yield of every cell is computed through a Monte Carlo analysis, and where necessary these cells are optimized for use in a complex system. A mathematical study of the Josephson junction and SQUIDs (Superconducting Quantum Interference devices) as switching elements precede a discussion on the operation of RSFQ and COSL (Complementary Output Switching Logic.) These logic families are implemented in low temperature niobium technology, and require liquid helium cooling. A 10 GHz oversampling delta modulating analogue-to-digital converter is then designed and constructed using RSFQ and COSL building blocks in a hybrid configuration. The design emphasis is on devising ways to test the operation of RSFQ with limited equipment. Yield analysis procedures on the complex system are discussed, followed by a detailed discussion on the circuit layout and layout problems. Software routines are developed to calculate the required dimensions of layout structures.
10 kW L-Band planar power combiner
(Stellenbosch : University of Stellenbosch, 2006-12) Fourie, Gerhardus Johannes; Van Niekerk, C.; Van der Walt, P. W.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
This thesis relates to the design and characterization of a 10 kW L-band power combiner consisting of 8 input ports. The design is implemented in a non-radial planar transmission line architecture and operates between 1.2 and 1.4 GHz. Because of the ultra high power requirements for the combiner, special attention is given to the power handling capabilities of the transmission lines and the other components involved. Simulated S-parameter models of connector to stripline transitions and a one to four-way junction, as well as measured S-parameter models of high power terminations are incorporated in the final design. A 10 kW combiner was built and measured at low power only due to time constraints and the limited availability of high power sources. Satisfactory results were obtained in terms of the graceful degradation of unit amplifiers, port mismatches and power combining efficiency.
A 22.2 GHz Antenna for water vapour radiometry
(Stellenbosch : Stellenbosch University, 2019-04) Cerfonteyn, William; De Villiers, D. I. L.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: For this thesis a low-cost antenna solution for a low-cost water vapour radiometry system is designed. The most important specifications for the antenna is that it has to have a -20 dB sidelobe level, a 3° -3 dB beamwidth and have to be electronically steerable. It also has to be low-cost. The first design that is considered is the phased array solution as it can be electronically steered. Since components can be etched onto the design the manufacturing cost is also reduced. The number of elements required for this design to reach the specifications is determined to be more than 16x16 elements, and thus proves to be cost impractical. The analysis is tested by designing a 1x4 and 2x2 multilayered aperture coupled patch antenna array with a corporate feed network, to both test if a better antenna element design can improve the results, and if the analysis is accurate in determining the impracticality of an array design. This also proves that the array design is infeasible. A reflector solution is then considered. The reflector system is designed to statically observe in a few specified directions, removing the need for electronic steering. Two parabolic reflectors and a conical horn is designed. The reflectors are combined through interpolation into one larger reflector. After the horn design proves to be ineffective, a new horn is considered that almost allows the reflector system to meet the specifications. Finally the system is measured, but unfortunately the measured result proves that the physical system does not meet all the specifications. The sidelobe level is around -16 dB, however, the -3 dB beamwidth is well below 3°.
2D Edge-based finite elements for guided and scattered wave problems
(Stellenbosch : Stellenbosch University, 1999-03) Hansmann, Riana Helena; Davidson, D. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis may be divided into two parts: the first describes the Finite Element Method (FEM) and its application to guided wave problems. The second part is devoted to scattering configurations, specifically the use of the Boundary Element Method (BEM) and the hybrid Finite Element Method-Boundary Element Method (FEM-BEM) to obtain solutions for scattering problems. The formulations are restricted to two dimensions throughout the thesis. A variational formulation is introduced and the implementation of boundary conditions is described. The use of vector approximation functions for the Finite Element Method is explained and the advantages highlighted. The properties of these functions are derived and graphical representations are given. A comparison between a lower order and higher order approximation is made. This is applied to problems which demonstrate the capabilities of the Finite Element Method such as ridged waveguides and circular waveguides containing eccentric dielectric rods. Results obtained compare well to analytic solutions, in the cases where these are available. An integral equation for scattering problems is derived. This relates the tangential field components on a contour enclosing a scattering object to the scattered fields and enables a solution to be obtained when the tangential components on the contour are known. It is shown how the interior region enclosed by the contour is discretised and how the Finite Element Method can be coupled with the Boundary Element Method by imposing continuity conditions on the enclosing contour. The resulting system of equations obtained may be solved. Solutions for scattering from perfectly conducting cylinders are obtained and compare well to analytic results.
A 3-axis attitude control system hardware design for a CubeSat
(Stellenbosch : Stellenbosch University, 2014-12) Gerber, Jako; Steyn, W. H.; Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: With CubeSats becoming popular as a cheap alternative to larger satellites, the need for advanced miniature attitude determination and control systems (ADCS) arises to meet the pointing requirements of satellite operations such as earth imaging and orbit maintenance. This thesis describes the design of a complete ADCS for use on CubeSats. A previously designed CubeSat on-board-computer, CubeComputer, and ne sun and nadir sensor, CubeSense, is incorporated in the design. The remaining requirements with regard to sensors and actuators were met by CubeControl, an additional module, the design, manufacturing and testing of which are described. CubeControl can implement magnetic control with the use of a magnetometer and three magnetorquers. It is also capable of driving three reaction wheels for accurate active 3-axis stabilization.
3-Axis geomagnetic magnetometer system design using superconducting quantum interference devices
(Stellenbosch : Stellenbosch University, 2014-04) Kilian, Anton Theo; Fourie, C. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This work discusses the design of a 3-axis Geomagnetometer SQUID System (GSS), in which HTS SQUIDs are used unshielded. The initial GSS installed at SANSA was fully operable, however the LN2 evaporation rate and SQUID orientation required improving. Magnetic shields were also developed in case the SQUIDs would not operate unshielded and to test the system noise with geomagnetic variations removed. To enable removing the double layer shield from the probes while the SQUIDs remain submerged in LN2, the shield was designed to disassemble. The shields proved to be effective, however due to icing the shields could not be removed without removing the SQUIDs from the LN2.
3-D face recognition
(Stellenbosch : Stellenbosch University, 1999-12) Eriksson, Anders; Weber, D.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical & Electronic Engineering.
ENGLISH ABSTRACT: In recent years face recognition has been a focus of intensive research but has still not achieved its full potential, mainly due to the limited abilities of existing systems to cope with varying pose and illumination. The most popular techniques to overcome this problem are the use of 3-D models or stereo information as this provides a system with the necessary information about the human face to ensure good recognition performance on faces with largely varying poses. In this thesis we present a novel approach to view-invariant face recognition that utilizes stereo information extracted from calibrated stereo image pairs. The method is invariant of scaling, rotation and variations in illumination. For each of the training image pairs a number of facial feature points are located in both images using Gabor wavelets. From this, along with the camera calibration information, a sparse 3-D mesh of the face can be constructed. This mesh is then stored along with the Gabor wavelet coefficients at each feature point, resulting in a model that contains both the geometric information of the face as well as its texture, described by the wavelet coefficients. The recognition is then conducted by filtering the test image pair with a Gabor filter bank, projecting the stored models feature points onto the image pairs and comparing the Gabor coefficients from the filtered image pairs with the ones stored in the model. The fit is optimised by rotating and translating the 3-D mesh. With this method reliable recognition results were obtained on a database with large variations in pose and illumination.
3D tracking between satellites using monocular computer vision
(Stellenbosch : University of Stellenbosch, 2005-03) Malan, Daniel Francois; Steyn, W. H.; Herbst, B. M.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
Visually estimating three-dimensional position, orientation and motion, between an observer and a target, is an important problem in computer vision. Solutions which compute threedimensional movement from two-dimensional intensity images, usually rely on stereoscopic vision. Some research has also been done in systems utilising a single (monocular) camera. This thesis investigates methods for estimating position and pose from monocular image sequences. The intended future application is of visual tracking between satellites flying in close formation. The ideas explored in this thesis build on methods developed for use in camera calibration, and structure from motion (SfM). All these methods rely heavily on the use of different variations of the Kalman Filter. After describing the problem from a mathematical perspective we develop different approaches to solving the estimation problem. The different approaches are successfully tested on simulated as well as real-world image sequences, and their performance analysed.
3D turning analysis of a Bipedal Robot
(Stellenbosch : Stellenbosch University, 2022-04) Pretorius, Dean; Fisher, Callen; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: There is stark contrast between the abilities of legged locomotion found in nature, and locomotion found in lab environments. This performance gap is indicative of a large knowledge gap. Roboticists are required to bridge these gaps to truly invite robots to detach from their support rigs, and actuate within the real world. In this thesis, non-planar contact and discontinuous locomotive dynamics were modeled as a trajectory optimization problem. Consequently, this made understanding the complexities of legged locomotion more tractable. Understanding, and being able to leverage, contact is crucial to successful legged locomotion. Therefore, a comprehensive investigation was conducted into non-planar contact dynamics using a monopod robot. Here, methods of modeling the Coulomb friction cone in contact implicit trajectory optimization were implemented. Literature suggests replacing the friction cone with a polyhedral approximation thereof. However, this method is known to underestimate the resultant friction in non-planar environments. This thesis presents a novel method of modeling the 3D friction cone and compares it to an implementation of the polyhedral approximation. Results from this comparison show that the novel method was significantly more computationally efficient than the polyhedral approximation, without underestimating the friction cone. Dynamic bipedal locomotion remains a struggle for most robotic platforms. Robotics literature provides few examples of robots achieving agile, dynamic locomotion. Therefore, trajectories realizing non-planar dynamic bipedal motion were generated. Experiments were conducted into acceleration, steady-state, deceleration, and rapid turning off the sagittal plane. Optimal trajectories displayed the robot walking at speeds resulting in a Froude number less than 0.5, and running at speeds resulting in a higher Froude number. This is consistent with dynamic gaits found in nature. A sliding-mass velocity profile emerged when conducting long-time-horizon trajectories where the robot accelerated from a rest position and decelerated back to rest after completing multiple steps in a periodic steady-state gait. Additionally, when turning off the sagittal plane, slip occurred at least 93.32% of the duration of contact, and turn overshoot is present in all turn trajectories.
Accelerating the method of moments implementation on FPGA hardware
(Stellenbosch : Stellenbosch University, 2021-12) Mnisi, Caleb; Ludick, Danie; Barnard, Arno; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: Advances in transistor technology have reached a point where the physical limitations on chip design means that we are starting to approach a decline in the curve that used to follow Moore’s law. Engineers and Scientists are now turning to Hyper-Scale computing and parallel systems to be able to continue the trend of Moore’s law and offset this decreased cadence. This naturally means that the traditional way of running operations also has to be revised to facilitate implementation on parallel systems. This project aims to develop hardware architecture that optimizes the computation of electromagnetic problems using the Method of Moments (MoM) formulation on field programmable gate array (FPGA) hardware. This can be accomplished by exploiting inherent properties in the formulation that allow for parallel computation of independent sections, and then running these computations in parallel, using dedicated computation units on the FPGA fabric. FPGAs and reconfigurable systems provide a combination of low power consumption and flexibility for applications in computation. We aim to exploit the reconfigurable structure of the FPGA to help facilitate the development of the hardware architecture. The configurable interconnect of the FPGA also allows us to arrange the FPGA resources in a manner that will optimize the specific computation and thus reduce the computation time.
Accurate autonomous landing of a fixed-wing unmanned aerial vehicle
(Stellenbosch : Stellenbosch University, 2012-12) Alberts, Frederik Nicolaas; Jones, T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis presents the analysis, design, simulation and practical implementation of a control system to achieve an accurate autonomous landing of a fixed-wing unmanned aerial vehicle in the presence of wind gust atmospheric disturbances. Controllers which incorporate the concept of direct-lift control were designed based on a study of the longitudinal dynamics of the UAV constructed as a testbed. Direct-lift control offers the prospect of an improvement in the precision with which aircraft height and vertical velocity can be controlled by utilising actuators which generate lift directly, instead of the conventional method whereby the moment produced by an actuator results in lift being indirectly generated. Two normal specific acceleration controllers were designed. The first being a conventional moment-based controller, and the second a direct-lift-augmented controller. The moment-based controller makes use of the aircraft’s elevator while the direct-lift augmented controller in addition makes use of the flaps of the aircraft which serve as the direct-lift actuator. Controllers were also designed to regulate the airspeed, altitude, climb rate, and roll angle of the aircraft as well as damp the Dutch roll mode. A guidance controller was implemented to allow for the following of waypoints. A landing procedure and methodology was developed which includes the circuit and landing approach paths and the concept of a glide path offset to calibrate the touchdown point of a landing. All controllers and the landing procedure were tested in a hardware-in-the-loop simulation environment as well as practically in a series of flight tests. Five fully autonomous landings were performed, three of these using the conventional NSA controller, and the final two the direct-lift-augmented NSA controller. The results obtained during the landing flight tests show that the project goal of a landing within five meters along the runway and three meters across the runway was achieved in both normal wind conditions as well as in conditions where wind gusts prevailed. The flight tests also showed that the direct-lift-augmented NSA controller appears to achieve a more accurate landing than the conventional NSA controller, especially in the presence of greater wind disturbances. The direct-lift augmented NSA controller also exhibited less pitch angle rotation during landing.
Accurate autonomous landing of a fixed-wing unmanned aircraft under crosswind conditions
(Stellenbosch : Stellenbosch University, 2017-03) De Bruin, Andrew; Jones, Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis presents the design, implementation and verification of an autopilot system with strong disturbance rejection characteristics, capable of landing a fixed-wing unmanned aircraft accurately under crosswind conditions. All aspects of the autopilot design are considered, from first principles to the final practically verified product. A mathematical aircraft model is derived, verified and analysed in detail to ensure the design of a high-fidelity, high-bandwidth flight control system. A synergistic controller architecture is proposed, where the approach is to design a structure capable of executing one of three crosswind landing techniques, or a combination thereof, by strategically sequencing controllers throughout the landing procedure. Various landing techniques, developed for manned aircraft, are investigated and emulated by the flight control system to exploit the advantages of each and to mitigate the risks associated with crosswind landings. A highbandwidth acceleration-based control architecture was augmented with Direct Lift Control to improve gust alleviation performance in the aircraft’s longitudinal axis. A state machine was used to facilitate effective controller sequencing and continuous hierarchical monitoring through strategically planned state transitions. Monte Carlo simulations were used to develop a landing accuracy prediction system that provides statistical information regarding the expected touchdown region given certain atmospheric conditions. Results from sixteen days of flight tests demonstrate the autopilot’s success, and correspond exceptionally well with results obtained from high-fidelity hardware-in-the-loop simulations. Verification of the autopilot through practical flight testing and extensive simulations proved that the system is capable of performing crosswind landings accurate to within 0.5 m of the intended touchdown point.
Accurate localisation of a multi-rotor using monocular vision
(Stellenbosch : Stellenbosch University, 2018-03) Blom, Josua; Wiid, P. G.; Van Daalen, C. E.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: The mid-frequency aperture array (MFAA) is planned for phase two of the square kilometre array project, which has its design phase scheduled for 2018. The MFAA's antenna arrays need to be characterised in their real world environment. The antenna array characterisation can be done with a test source mounted on a multi-rotor which is own over the antennas. However, the test source needs to be localised accurately relative to the antenna array, which is currently achieved by expensive and cumbersome methods. Accurate vision-based localisation is one possible inexpensive solution, provided arti cial reference points can be placed in the environment. Many vision-based localisation methods exist; however, the focus is often on simultaneous localisation and mapping as opposed to localisation only. The problem is simpli ed signi cantly when arti cial reference points, referred to as landmarks, are manually placed in the environment wherein the multi-rotor needs to be localised. The focus of the research presented in this thesis is therefore on accurate localisation of a multi-rotor aircraft specifically through monocular vision using manually placed artificial landmarks. The multi-rotor's state propagation was described according to a kinematic motion model. Additionally, a measurement model was designed which relates camera image measurements to the system's states. A localisation algorithm using the unscented Kalman filter (UKF) was designed and integrated. The UKF uses the sensor data from the multi-rotor as well as measurements derived from image processing to best estimate the pose of the multi-rotor. The localisation algorithm was first tested and refined in simulation, after which experimental flight tests were performed and the resulting data sets were analysed. The experimental results are promising; the algorithm localised the multi-rotor with a mean accuracy of around six centimetres relative to a differential GPS (DGPS) that was used as a baseline. A high quality DGPS can localise at an accuracy of up to two centimetres; however, the Piksi DGPS used in this project proved to be intermittently accurate and unreliable. The current accuracy of the localisation algorithm would be suitable for other radio telescope antenna arrays which operate at lower frequencies than the MFAA. However, with some improvements in hardware integration, it should be possible to achieve better accuracy than differential GPS systems at a fraction of the cost, making it a promising solution for localisation in antenna characterisation application on the MFAA.
Accurate modelling and realisation of a 4th generation wireless communication system
(Stellenbosch : University of Stellenbosch, 2006-12) Schulze, Shaun; Palmer, K. D.; Kuhnert, C.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
A great demand exits for higher data rates and increased reliability of future consumer based mobile communication systems while being more bandwidth and power efficient. Orthogonal frequency division multiplexing (OFDM) in combination with multiple-input multiple-output (MIMO) schemes has become a promising candidate for fulfilling the demand of next generation communication systems. The sensitivity of MIMO OFDM systems to physical impairments is of great interest and particularly the Alamouti space-time block code is under investigation in this thesis. Generic and comprehensive simulation models of an OFDM communication system incorporating the spacetime block code are developed in a modular fashion and used in a performance evaluation with non-ideal component and channel behaviour.
Acoustic detection of the short pulse call of Brydes whales using time domain features and hidden Marcov models
(Stellenbosch : Stellenbosch University, 2020-03) Wache Ngateu, Gaelle Venessa; Versfeld, Daniel Jaco J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: The biological group of cetaceans is frequently studied nowadays as passive acoustic monitoring (PAM) is commonly used to extract the acoustic signals produced by cetaceans, in the midst of noise sounds made by either man during shipping, gas and oil explorations or by natural sounds like seismic surveys, wind and rain. In this research work, the acoustic signal of short pulse call of inshore Bryde's whales is detected using time domain features and hidden Markov models (HMM). HMM is deployed as a detection and classi cation technique due to its robustness and low time complexity during the detection phase. However, some parameters such as the choice of features to be extracted from the acoustic short pulse call of inshore Bryde's whales, the frame durations of each call and the number of states used in the model affect the performances of the automated HMM. Therefore, to measure performances like sensitivity, accuracy and false positive rate of the automated HMM; three time domain features (average power, mean and zero-crossing rate) were extracted from a dataset of 44hr26mins recordings obtained close to Gordon's bay in False bay, South Africa. Moreover, to extract these features the frame durations of each vocalisation was varied thrice; 1 ms, 5 ms and 10 ms. Also, the HMM used three different number of states (3 states, 5 states and 10 states) which were varied independently so as to evaluate the HMM. On an overall performance, the HMM yields best performances when it uses 10 states with a short frame duration of 1 ms and average power as the extracted feature. With regard to this, the automated HMM shows to be 99:56% sensitive, and dependable as it exhibits a low false positive rate of 0:1 with average power inferred as the best time domain feature used to detect the short pulse call of inshore Bryde's whales using the HMM technique.
Active capacitor voltage stabilisation in a medium-voltage flying-capacitor multilevel active filter
(Stellenbosch : University of Stellenbosch, 2005-03) Hansmann, Chirstine Henriette; Mouton, H. du T.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
A switching state substitution must be developed that will make use of both single-phase redundancies and three-phase redundancies in the flying-capacitor topology. Losses should be taken into consideration and the algorithm must be designed for implementation on the existing PEC33 system, with on-board DSP (TMS320VC33) and FPGA (EP1K50QC208). The specific power-electronics application is a medium-voltage active filter. Existing capacitor voltage stabilisation schemes are investigated and a capacitor-voltage based algorithm is developed that is investigated in parallel with the Donzel and Bornard algorithm. Detailed simulation models are built for the evaluation of both existing and the proposed algorithm. Three-phase control is also evaluated. Timing analysis of the proposed algorithm shows that a DSP-only implementation of the proposed capacitor-based solution is not feasible. Detail design of the digital controller hereof is implemented in VHDL. Finally, a four-cell controller is fitted into the FPGA. A scalable hardware sorting architecture is utilised.
An active receiving antenna for borehole pulsed radar applications
(Stellenbosch : University of Stellenbosch, 2002-12) Van Wyk, M. D.; Palmer, K. D.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
An efficient radiating strucllire was needed for borehole pulsed radar applications in the 10-100 MHz frequency band. Both resistively loaded and insulated wire antennas were investigated and an active antenna is proposed as a fmal solution. The study proceeded from the characterization of the origin of radiation on a conductive dipole wire antenna when excited with a transient. Different radiation mechanisms were identified when the antenna was excited with a current or voltage source. The wire antenna in insulated surroundings was modelled using transmission line theory to simulate the antenna in the borehole environment. The transmission line model proved to be useful for investigating conducting and resistively loaded antennas for the dimensions associated with borehole surveys. From the modelling results, it became apparent that the asymmetric resistively loaded antenna might provide the best practical solution. This antenna displays reasonably stable input impedance and low far-field variations for different theta angles across the desired frequency band. Different percentage Wu-King resistive profiles were studied to show that a 50% reduction in the normal Wu-King resistor values will add only a little ringing but have better amplitude response than the 100% Wu-King loading. The asymmetric resistively loaded antenna has better sensitivity to receiving transients when combined with a high impedance source load than when symmetrically loading the antenna. An active antenna incorporating the asymmetric resistively loaded antenna and a low noise current feedback front end amplifier was built and measured in an air environment. The results show that the active antenna has a flat transfer function and reacts as a wide band electric field probe with better resolution than in the conventional 50 Q loaded case
Adaptation, optimisation and simulation of the CSMA/CA protocol for a low earth orbit satellite UHF link
(Stellenbosch : University of Stellenbosch, 2006-12) Cawood, Andrew Dudley; Wolhuter, R.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
A low earth orbit satellite is to provide the telecommunications link to facilitate email services to rural areas, where the infrastructure necessary for e-mail is lacking (e.g. no telephone lines). Communication time with this satellite from any particular point on the ground is less than one hour per day. It is thus of utmost importance to maximise the data throughput rate for the system. The contribution of this thesis is to improve the performance of CSMA/CA by adapting and optimising it for the above application. This improved protocol is used to regulate data flow through the system. Specific attention is given to the comparison of various random variable distributions for use as the back-off random variable. Two pieces of software are further contributed. First, a set of MATLAB scripts which are used for comparing various back-off random variable distributions and optimising each of these distributions. Secondly, an extensive (more than 2500 lines of code) OMNeT++ simulation of the improved CSMA/CA protocol, complete with MATLAB scripts for setting up multiple simulation runs and plotting the results. Both pieces of software accept the system constraints as parameters, and are thus easily adaptable for a similar system which may use the same protocol, but has different parameters. It is concluded that the set of MATLAB scripts are a fairly accurate tool for optimising throughput, as is confirmed by the OMNeT++ simulations, and that OMNeT++ has merit for simulating the given type of system and protocol.
Adaptive cross approximation for electromagnetic analysis of superconducting circuits
(Stellenbosch : Stellenbosch University, 2019-04) Nel, Abraham Pieter Ben; Botha, Matthys M.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: Electromagnetic analysis of superconducting integrated circuits is routinely required for inductance extraction. FastHenry is a magnetoquasistatic (MQS) analysis tool suitable for this task. It is based on the partial element equivalent circuit (PEEC), integral equation method, with the structure discretised into hexahedral filaments. FastHenry’s multilevel fast multipole algorithm (MLFMA) implementation is especially memory efficient, given certain approximations and algorithmic parameter choices. However, errors are introduced into the matrix representation. This thesis describes the implementation of a multilevel adaptive cross approximation solver with singular value decomposition recompression (MLACA-SVD) inside FastHenry as an alternative to its existing MLFMA solver. The thesis also presents two modified grouping strategies to further improve MLACA-SVD efficiency by compressing interactions between larger groups, while maintaining scaling performance consistent with a valid admissibility condition. MLACA-SVD compresses off-diagonal matrix blocks to a specified error tolerance, based on evaluating selected entries. Quadrature recipes presented in this thesis provide guaranteed accuracy of matrix entry evaluation. Numerical results for examples of practical interest show that the MLACA-SVD memory scaling versus number of filaments, denoted b, is practically identical to that of FastHenry’s MLFMA, and is close to O(b log b). The MLACA-SVD requires less memory for the same solution accuracy, and furthermore offers complete control over matrix approximation errors. For the examples considered, it is found to be a more efficient solver. The results of the group merging strategies show that required memory is further reduced by approximately 30%. The MLACA-SVD solver with merging requires about four times less memory than FastHenry’s MLFMA, for similar accuracy.
Adaptive estimation of speech parameters
(Stellenbosch : Stellenbosch University, 1994-03) Basson, J. A. L; Du Preez, J. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical & Electronic Engineering.
ENGLISH ABSTRACT: Linear predictive coding(LPC), and transformations of it, is currently the most popular way of analysing speech signals. Major limitations of using a frame-based technique are that each frame is analysed in isolation of the rest while assuming the excitation source to be a white, gaussian process. In order to reduce computation time, an all pole model is usually employed. In this project an adaptive algorithm is proposed for speech signal analysis. The algorithm is based on the recursive least mean squares method with a variable forgetting factor. A pole-zero model is used to: estimate the anti-formants present in certain sounds (i.e. nasals and nasalized vowels). This method offers better detection of poles and zeros in stationary environments and faster tracking of pole and zero frequencies in nonstationary signals than other sequential methods. An effective input estimation algorithm eliminates the influence of pitch on the parameter estimates by assuming the input to be a white noise process or a pulse sequence.

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