Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / Next-generation nanosatellites are becoming a very cost effective solution to gain access to space. Modern manufacturing technology together with low power low cost devices makes the development of nanosatellites, using standard industrial components, very attractive. A typical nanosatellite will have only one microprocessor, capable of performing all the computing tasks onboard the satellite - housekeeping, AODC (Attitude and Orbit Control) and instructing the different payloads aboard the satellite. One of the major requirements was to choose a processor from a dominant manufacturer in the market that will still be available for future satellite missions. Just as the 8051 dominated the 8-bit market, the ARM7 processor is fast becoming a market leader in the segment for 16-bit applications. ARM processors has also been used much in handheld devices in recent years - which emphasize the low power requirements and stability of these processors in embedded applications. This thesis investigates the different processors that are currently available. A complete system design is done, taking into account all the different modules needed onboard a very small Low Earth Orbit (LEO) satellite. Finally, some test results are given showing how this system can be reliably used onboard a nanosatellite in future.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis documents the design and implementation of an S-band receiver for phasecomparison monopulse radar. The design and evaluation of the various sub-systems involved in realizing the receiver are discussed in detail. The designed sub-systems are connected via low loss coaxial cables to form the complete phase-comparison monopulse radar receiver. The performance of the receiver is evaluated and compared with the theoretical results, in terms of frequency response, gain and noise figure. The designed receiver is finally connected to an existing antenna system, and a preliminary test of the complete radar is performed. The initial results show that the design is successful, but the boresight-axis of the radar has shifted in angle and requires pre-comparator phase shifting in order to obtain accurate tracking. ii

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The aim of this thesis is to implement a Digital Audio Broadcasting (DAB) system in a Software Defined Radio (SDR). The physical modulation part of the DAB transmitter for one of the transmission modes as well as its receiver is to be implemented and tested in the SDR. DAB transmission mode II is implemented.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / With the rapid advancement of communication technologies and broadband communication, an era is starting to emerge where everything and everyone is always connected, regardless of geography. No other technology has made this more possible than over-the-air data communications technologies such as Wi-Fi, WiMAX and cellular technologies. With the possibility of connecting more devices to a common communications network, more and more applications become available and necessary. One such application is a concept designed to manage a different type of network; the traffic networks of large metropolitan areas. These networks carry more traffic with each passing year and the need to manage them fficiently has become essential. A system to manage traffic networks is an intelligent transport system (ITS), which integrates all methods of transportation into a single manageable resource. Information about the current status of the traffic network can be relayed to road users, allowing them to make informed decisions about alternative routes, or to emergency personnel to inform them of accidents that occurred on the traffic networks. In order to implement an ITS, a communication network is required. This thesis investigates different communication technologies, discussing their merits and shortcomings in an ITS implementation. A suitable technology is selected and a communications system is conceptualised. The communications system is an ad hoc wireless network and a routing protocol used to manage the network, is designed and tested through simulation. The TH(O)RP routing protocol was developed with a focus on scalability, stability and low latency in an ad hoc network. TH(O)RP was designed to operate in an ITS environment, where traffic intersection controllers (TIC) are monitored from a central entity, with optimal routes between the central entity and the TICs, that can be automatically configured and repaired.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / A navigation performance sensitivity study with respect to the quality variation of sensors and sensor combinations is presented in this thesis. Navigation simulation software capable of using real-time and simulated sensor data is developed in this project. The simulation software is used to simulate different sensor combinations and therefore evaluate the best configuration for each AUV mission. A sensor module is also developed to capture real-time sensor data. The sensor module includes a low-cost 6-degreeof- freedom inertial measurement module (rate gyroscopes and accelerometers), a three-axes magnetometer and other sensor interfaces. The real-time sensor data are used to test and calibrate the navigation simulation software. Different sensor combinations are evaluated by using the navigation simulation software with simulated sensor data as input. The quality of each sensor is varied by changing its noise characteristics. The performance study, together with the developed simulation tools, simplifies the process of selecting a sensor combination to fulfill a specific navigation accuracy requirement.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis investigates aggressive all-attitude flight control systems. These are flight controllers capable of controlling an aircraft at any attitude and will enable the autonomous execution of manoeuvres such as high bank angle turns, steep climbs and aerobatic flight manoeuvres. This class of autopilot could be applied to carry out evasive combat manoeuvres or to create more efficient and realistic target drones. A model for the aircraft’s dynamics is developed in such a way that its high bandwidth specific force and moment model is split from its lower bandwidth kinematic model. This split is done at the aircraft’s specific acceleration and roll rate, which enables the design of simple, decoupled, linear attitude independent inner loop controllers to regulate these states. Two outer loop kinematic controllers are then designed to interface with these inner loop controllers to guide the aircraft through predefined reference trajectories. The first method involves the design of a linear quadratic regulator (LQR) based on the successively linearised kinematics, to optimally control the system. The second method involves specific acceleration matching (SAM) and results in a linear guidance controller that makes use of position based trajectories. These position based trajectories allow the aircraft’s velocity magnitude to be regulated independently of the trajectory tracking. To this end, two velocity regulation algorithms were developed. These involved methods of optimal control, implemented using dynamic programming, and energy analysis to regulate the aircraft’s velocity in a predictive manner and thereby providing significantly improved velocity regulation during aggressive aerobatic type manoeuvres. Hardware in the loop simulations and practical flight test data verify the theoretical results of all controllers presented

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The Josephson effect of high-temperature superconducting nanobridge structures is studied worldwide. Until now, nanobridges are generally fabricated with focused ion beam milling on planar thin films. These nanobridges are employed as weak links in superconducting quantum interference devices (SQUIDs) and used in superconducting flux flow transistors and devices. This project had two main objectives: to improve the sidewall angle of photoresist lines, with the aid of atomic force microscopy (AFM) nanolithography; and to fabricate hightemperature Josephson junctions by constricting superconductive YBCO lines on MgO substrates with AFM nanolithography. The entire fabrication process is explained including photolithography, deposition of the YBCO thin films with pulsed laser deposition (PLD), nanolithography and wet etching. Although the testing of the junctions did not show any Josephson behaviour, it could be demonstrated that nanobridge structures can successfully be created by AFM nanolithography. The entire fabrication process has been demonstrated in detail for the benefit of future research.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / In this thesis we studied large-vocabulary continuous speech recognition. We considered the components necessary to realise a large-vocabulary speech recogniser and how systems such as Sphinx and HTK solved the problems facing such a system. Hidden Markov Models (HMMs) have been a common approach to acoustic modelling in speech recognition in the past. HMMs are well suited to modelling speech, since they are able to model both its stationary nature and temporal e ects. We studied HMMs and the algorithms associated with them. Since incorporating all knowledge sources as e ciently as possible is of the utmost importance, the N-Best paradigm was explored along with some more advanced HMM algorithms. The way in which sounds and words are constructed has been studied extensively in the past. Context dependency on the acoustic level and on the linguistic level can be exploited to improve the performance of a speech recogniser. We considered some of the techniques used in the past to solve the associated problems. We implemented and combined some chosen algorithms to form our system and reported the recognition results. Our nal system performed reasonably well and will form an ideal framework for future studies on large-vocabulary speech recognition at the University of Stellenbosch. Many avenues of research for future versions of the system were considered.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Phoneme recognition systems typically suffer from low classification accuracy. Recognition for South African English is especially difficult, due to the variety of vastly different accent groups. This thesis investigates whether a fusion of classifiers, each trained on a specific accent group, can outperform a single general classifier trained on all. We implemented basic voting and score fusion techniques from which a small increase in classifier accuracy could be seen. To ensure that similarly-valued output scores from different classifiers imply the same opinion, these classifiers need to be calibrated before fusion. The main focus point of this thesis is calibration with the Pool Adjacent Violators algorithm. We achieved impressive gains in accuracy with this method and an in-depth investigation was made into the role of the prior and the connection with the proportion of target to non-target scores. Calibration and fusion using the information metric Cllr was showed to perform impressively with synthetic data, but minor increases in accuracy was found for our phoneme recognition system. The best results for this technique was achieved by calibrating each classifier individually, fusing these calibrated classifiers and then finally calibrating the fused system. Boosting and Bagging classifiers were also briefly investigated as possible phoneme recognisers. Our attempt did not achieve the target accuracy of the classifier trained on all the accent groups. The inherent difficulties typical of phoneme recognition were highlighted. Low per-class accuracies, a large number of classes and an unbalanced speech corpus all had a negative influence on the effectivity of the tested calibration and fusion techniques. / AFRIKAANSE OPSOMMING: Foneemherkenningstelsels het tipies lae klassifikasie akkuraatheid. As gevolg van die verskeidenheid verskillende aksent groepe is herkenning vir Suid-Afrikaanse Engels veral moeilik. Hierdie tesis ondersoek of ’n fusie van klassifiseerders, elk afgerig op ’n spesifieke aksent groep, beter kan doen as ’n enkele klassifiseerder wat op alle groepe afgerig is. Ons het basiese stem- en tellingfusie tegnieke ge¨ımplementeer, wat tot ’n klein verbetering in klassifiseerder akkuraatheid gelei het. Om te verseker dat soortgelyke uittreetellings van verskillende klassifiseerders dieselfde opinie impliseer, moet hierdie klassifiseerders gekalibreer word voor fusie. Die hoof fokuspunt van hierdie tesis is kalibrasie met die Pool Adja- cent Violators algoritme. Indrukwekkende toenames in akkuraatheid is behaal met hierdie metode en ’n in-diepte ondersoek is ingestel oor die rol van die aanneemlikheidswaarskynlikhede en die verwantskap met die verhouding van teiken tot nie-teiken tellings. Kalibrasie en fusie met behulp van die informasie maatstaf Cllr lewer indrukwekkende resultate met sintetiese data, maar slegs klein verbeterings in akkuraatheid is gevind vir ons foneemherkenningstelsel. Die beste resultate vir hierdie tegniek is verkry deur elke klassifiseerder afsonderlik te kalibreer, hierdie gekalibreerde klassifiseerders dan te kombineer en dan die finale gekombineerde stelsel weer te kalibreer. Boosting en Bagging klassifiseerders is ook kortliks ondersoek as moontlike foneem herkenners. Ons poging het nie die akkuraatheid van ons basislyn klassifiseerder (wat op alle data afgerig is) bereik nie. Die inherente probleme wat tipies is tot foneemherkenning is uitgewys. Lae per-klas akkuraatheid, ’n groot hoeveelheid klasse en ’n ongebalanseerde spraak korpus het almal ’n negatiewe invloed op die effektiwiteit van die getoetsde kalibrasie en fusie tegnieke gehad.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In recent years, the use of airships has become popular for observation purposes since they provide a cost effective alternative to other aircraft. For this project a lateral and longitudinal flight control system are required for waypoint navigation flight of an 8m long, non-rigid airship. The airship’s actuators include a rudder, elevator and a propulsion system which can be vectored longitudinally. Two airship models are evaluated for this project. A chosen model is linearised and a modal analysis is done. The modal analysis is compared to a previous modal study done on the YEZ-2A airship and is found to compare well. Each airship mode is discussed and the linear behaviour is compared to the behaviour of the non-linear model. A fuzzy logic controller design approach was undertaken for the design of speed, heading and height controllers. These non-linear controllers were designed for the non-linear model, due to the following reasons: Fuzzy logic controllers show tolerance to model inaccuracies. Complexity of design is simple. Controllers can be adjusted intuitively. Fuzzy logic controllers can be combined with conventional control techniques. Simulation results showed adequate lateral and longitudinal performance, even when subjected to light wind conditions and disturbances. The inertial measuring unit implemented in a previous project is used and additional hardware is designed and implemented for the control of the airship’s actuators. Several improvements are made to the groundstation software to allow for activation of different controllers as well as for setting up the desired flight plan. The controller performance is tested through flight tests and shows adequate performance as well as controller potential. Although further work is still required for improving the controllers’ performance, this thesis acts as a platform for future research. / AFRIKAANSE OPSOMMING: In die afgelope paar jaar het die gebruik van die lugskepe gewild geword vir waarnemings doeleindes aangesien dit ’n koste effektiewe alternatief vir ander lugvaartuie bied. In hierdie projek word ’n laterale en longitudinale beheerstelsel benodig vir merker navigasie vlugte met ’n 8m lang, nierigiede lugskip. Die lugskip se aktueerders sluit in ’n rigtingroer, hoogteroer asook ’n aandrywing stelsel wat oorlangs gestuur kan word. Vir hierdie projek is twee lugskip modelle geïmplementeer. Die gekose model is gelineariseer en ’n modale analise is gedoen. Die modale analise is met ’n vorige modale studie vir die YEZ-2A lugskip vergelyk en wys soortegelyke linieêre gedrag. Die lugskip modusse is bespreek en die linieêre gedrag word met die gedrag van die nie-linieêre model vergelyk. Daar is op ’n fuzzy logiese beheerder ontwerp besluit vir die ontwerp van spoed, rigting en hoogte beheerders. Hierdie nie-linieêre beheerders is ontwerp vir die nie-linieêre model a.g.v. die volgende redes: Fuzzy logiese beheerders toon toleransie vir modellering of meetfoute. Kompleksiteit van die ontwerp is eenvoudig. Beheerders kan intuïtief aangepas word. Fuzzy logiese beheerders kan met konvensionele beheertegnieke gekombineer word. Simulasie resultate toon voldoende werkverrigtinge, selfs in die teenwoordigheid van ligte wind sowel as ander versteurings. Die inersiële metings eenheid, wat geïmplementeer is in ’n vorige projek, is gebruik en addisionele hardeware vir die beheer van die lugskip is aktueerders is ontwerp en geïmplementeer. Talle verbeterings is aangebring aan die grondstasie sagteware vir die aktiveer van die beheerders sowel as die uitleg van die gekose vlugplan. Die beheerders se werksverrigtinge is getoets gedurende vlugtoetse en toon voldoende beheer vermoë sowel as beheerder potensiaal. Alhoewel verdere werk steeds nodig is vir die verbetering van die beheerders, dien hierdie tesis as ’n platform vir toekomstige navorsing.