Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The purpose of this study was to investigate multi-spectral tracking. Various algorithms were investigated and developed to enhance the contrast between target and non-target classes. Different tracking algorithms were implemented on the resulting grayscale input. A physical tracking system consisting of a video input processor and DSP was designed and built to implement algorithms and investigate the viability of realtime multi-spectral tracking. It is illustrated that conventional intensity tracking clouds the available information and that by studying various spectral inputs information is extracted more efficiently from the available data.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / In this thesis, the maneuvering and orientation of an inspection/service satellite is investigated. This thesis will demonstrate a simplified satellite maneuver around another satellite (for docking purposes). This is illustrated with a cart on an air bearing table (frictionless environment) which simplifies the problem to two dimensions. A mathematical model of the system was designed and simulated (Matlab) for this maneuver. With the simulation, different strategies were considered to maneuver the cart in a circle around another object. The conclusion was made that approximating the circle with segments would conserve propellant. This strategy was implemented on the air bearing table.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / This project started a new research area in rotary-wing °ight control in the Computer and Control group at the University of Stellenbosch. Initial attempts to build a quad-rotor vehicle exposed di±culties which motivated changing to a standard model helicopter as a test vehicle. A JR Voyager E electrically powered model helicopter was instrumented with low-cost, low-weight sensors and a data communication RF link. The total cost of the sensor, communication and microcontroller hardware used is approximately US$ 1000 and the added onboard hardware weighs less than 0:4 kg. The sensors used to control the helicopter include a non-di®erential u-Blox GPS receiver, Analog Devices ADXRS150 rate gyroscopes, Analog Devices ADXL202 accelerometers, a Polaroid ultrasonic range sensor and a Honeywell HMC2003 magnetometer. Successful yaw, height and longitudinal position control was demonstrated. Signi¯cant further work is proposed, based on the literature study performed and the insights and achievements of the ¯rst rotary-wing unmanned aerial vehicle project in the group.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A complete mixed-potential integral equation formulation for the analysis of arbitrarily shaped scatterers in a planarly layered medium is presented. The integral equation is able to solve for simultaneous electric and magnetic surface currents using a Method of Moments (MoM) procedure. The MoM formulation which was developed uses vector-valued basis functions defined over a triangular mesh and are used to model electric currents on conducting scatterers and magnetic currents on slotline structures. The Green’s functions employed in the analysis were developed for a stratified medium using a Sommerfeld plane wave formulation. The scheme used for filling the method of moments matrix was designed to simultaneously solve multiple problems that are stacked and separated by an infinite conducting ground plane. The filling algorithm also efficiently packs partially symmetric matrices, which are present when solving problems that support a combination of electric and magnetic currents. Several examples are presented to illustrate and validate the analysis method. Numerical predictions of the scattering parameters (both magnitude and phase) show good correspondence with results from literature and measured data. / AFRIKAANSE OPSOMMING: ’n Volledige gemengde potensiaal integraalvergelyking formulering vir die analise van stralers van arbitrˆere vorm binne gelaagde strukture word aangebied. Die integraalvergelyking kan gelyktydige elektriese en magnetiese oppervlakstrome oplos deur die Metode van Momente (MoM) te gebruik. Die MoM formulering gebruik vektor basis funksies wat oor ’n driehoekige diskretisering gedefinieer word om elektriese strome op geleidende stralers en magnetiese strome op gleuflyn strukture te modelleer. Die Green’s funksies wat in die analise gebruik word, is ontwikkel vir gelaagde media deur gebruik te maak van Sommerfeld se platvlakgolf formulering. Die metode wat gebruik word om the moment matriks te vul, is ontwerp om meervoudige gestapelde probleme wat deur oneindig geleidende grondvlakke geskei word, gelyktydig op te los. Gedeeltelik simmetriese matrikse word ook effektief gevul. Hierdie matrikse kom voor wanneer probleme ’n kombinasie van elektriese en magnetiese strome ondersteun. Verskeie voorbeelde word gebruik om die analise metode te verifieer. Numeriese voorspellings van strooiparameters (beide grootte en hoek) vergelyk baie goed met resultate en gemete data wat in die literatuur gevind is. iv

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / 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.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / Horizon sensing is an effective way to determine the pitch and roll of a LEO satellite and Earth horizon sensors that operate in the visible range of the electromagnetic spectrum are commonly used. These sensors have the disadvantage that they cannot operate when the satellite is in eclipse. Earth horizon sensors that operate in the infrared spectral range are a solution to take attitude measurements when the satellite is in eclipse. Until recently infrared detectors could only operate at very low temperatures and needed to be cryogenically cooled. The result was that their power consumption and physical characteristics (like dimensions and mass) were such that they were not suitable for use in small and medium LEO satellites. As a result of technology expansion in the field of infrared imagers the past few years, infrared imagers were developed which do not require cooling. The scope of this project was to develop and implement an Earth horizon sensor by using a low-cost, uncooled infrared imager. The performance and physical characteristics of various imager were evaluated and it was decided to select a low resolution thermopile imager mainly as a result of the cost limitations of the project. Software algorithms were then evaluated and selected for horizon detection and attitude determination. The Earth horizon sensor that was developed did not comply with the accuracy requirement (3s < 0.1o) that was set for the project because of the low resolution of the sensor. Methods to improve the accuracy were investigated and finally a sub-pixel edge estimation algorithm was developed and implemented which resulted in an improvement of 69% in the pitch accuracy and 49% in roll accuracy. With the sub-pixel edge estimation algorithm implemented the horizon sensor almost met the accuracy requirements (s < 0.0811o for pitch and s < 0.2944o for roll). This project confirms that, with further improvement to the design and test facilities, developing a low-cost, uncooled infrared Earth horizon sensor that meets the accuracy requirements is feasible.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis presents the development of a state estimation system for use in an Autonomous Airborne Refueling (AAR) operation through the simulated implementation of GPS, monocular and stereoscopic vision, inertial measurement sensors and boom parameter measurement in combination with the Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF). A set of functional criteria for the estimation system was developed through an analysis of the control system input requirements and associated constraints. The estimation system is further developed by integrating the sensor configurations into the estimation algorithm structures through the derivation of the applicable mathematical models. Final sensor configurations are set based on a sensitivity analysis in which the effect of parameters such as sensor noise, placement and quantity are related to the accuracy with which the states are estimated. Uncertainty in the process noise, which is typically approximated, is overcome by adding an adaptive element to the estimation algorithms in which the current process noise is estimated allowing compensation for unmodeled process noise uncertainty. Finally twelve practical sensor configurations are established utilising unique combinations of the five sensors. Each configuration is simulated using both estimation algorithms after which all results are evaluated with respect to one another as well as to the minimum state accuracy criteria. Conclusions are presented based on the evaluation of the results followed by recommendation for future development. / AFRIKAANSE OPSOMMINGS: Die ontwikkeling van ’n toestandafskattingstelsel, spesifiek toegepas op outonome brandstofhervulling, word voorgelê in hierdie tesis. Hierdie ontwikkeling behels die implementering van GPS, monukulêre- en stereo-visie sensors, inersiële sensor eenhede en verbindingsarmsensors wat gebruik word in ’n Uitgebruide Kalman Filter (Extended Kalman Filter) en Geurlose Kalman Filter (Unscented Kalman Filter). ’n Volledige ontleding van die beheerstelsel se toevoervereistes en geassosieerde beperkings is gebruik om ’n stel beoordelingsmaatstawwe vir die toestandafskatting-stelsel te bepaal. Die stelsel is verder ontwikkel deur verskillende sensorkonfigurasies met die afskattingsalgoritmes te kombineer deur die afleiding van toepaslike wiskundinge modelle. Hierdie konfigurasies is verfyn deur ’n sensitiwiteitsanalise, waar die verwantskap tussen die effekte van sensorruis, sensorligging, hoeveelheid sensors ondersoek is met betrekking tot afskattingsakkuraatheid. Onsekerheid in die stelsel se prosesruis is deur ’n aanpassings substelsel hanteer, wat kompensasie vir ongemodeleerde onsekerheid moontlik maak. Twaalf praktiese sensorkonfigurasies is opgestel vanuit unieke kombinasies van die vyf sensore behartig in die projek. Hierdie konfigurasies is deur beide afskattingsalgoritmes gebruik om sodoende die akkuraatheid van die konfigurasies asook die afskattingsalgoritmes te evalueer met betrekking tot mekaar en aan die hand van die beoordelingsmaatstawwe vir die beheerstelsel. Die tesis is afgesluit deur gevolgtrekkings asook aanbevelings vir toekomstige navorsing.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In this research the possible utilization of carbon nanomaterials in gas sensing applications are investigated. These materials include the 2-dimensional honeycomb-lattice carbon structure called graphene, and the 1-dimensional structures referred to as carbon nanotubes (CNTs). The extraordinary properties and unique morphology of these nanomaterials, make them excellent candidates for sensory applications. This research thus entails the investigation and development of gas sensors with these carbon nanomaterials. This includes the synthesis of CNTs via a chemical vapour deposition (CVD) technique and the fabrication of resistive thin film sensors with the various materials. The functionalization of carbon nanomaterials is also explored, which delivers promising results for sensing gases at room temperature, especially acetylene (C2H2). Furthermore, a unique method is developed to fabricate ultra thin aluminium microstructures. These metallic electrodes are found to be ideal for nanomaterial integration. An experiment is performed to manufacture an integrated sensor with MWCNTs and following the results, a refinement of the procedure and the investigation of FET-based devices are recommended. The results obtained during this work, indicate that engineered carbon nanostructures, such as CNTs and graphene, can potentially be applied in future sensing technologies. / AFRIKAANSE OPSOMMING: Hierdie navorsing ondersoek die moontlike toepassing van koolstof nano-materiale as gas-sensor tegnologie. Hierdie materiale sluit die 2-dimensionele koolstof struktuur, grafeen, asook die sogenaamde 1-dimensionele koolstof nano-buise in. Die buitengewone eienskappe en unieke morfologie van hierdie nano-materiale, maak hul uitstekende kandidate vir sensor toepassings. Hierdie navorsing ondersoek dus die ontwikkeling van gas-sensors met koolstof nano-materiale, insluitend die sintese van koolstof nano-buise deur middel van ’n chemiese damp-neerslag proses, asook die fabrikasie van resistiewe dun film sensors. Die funksionalisering van koolstof nano-materiale is ook ondersoek en belowende resultate is opgelewer met betrekking tot die deteksie van gasse by kamertemperatuur, veral vir asetileen (C2H2) gas. Verder is ’n unieke metode ontwikkel om ultra dun aluminium mikrostrukture te vervaardig en hierdie metaal elektrodes word as ideaal beskou vir die integrasie van nano-materiale. ’n Eksperiment is uitgevoer om ’n geïntegreerde sensor te vervaardig met multi-wand koolstof nano-buise, waarvan die resultate aandui dat die proses verfyn moet word en dat die moontlike toepassing van veld-effek-transistor toestelle ondersoek moet word. Die resultate wat opgelewer is gedurende hierdie navorsing dui daarop dat ontwikkelde nanostrukture, soos koolstof nano-buise en grafeen, as toekomstige sensor tegnologie geïmplementeer kan word.

Thesis (MScEng)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The perceived quality of Voice over Internet Protocol (IP) (VoIP) communication relies on the network which is used to transport voice packets between the end points. Variable network characteristics such as bandwidth, delay and loss are critical for real-time voice traffic and are not always guaranteed by networks. It is important for network service providers to determine the Quality of Service (QoS) it provides to its customers. The solution proposed here is to predict the perceived quality of a VoIP call, in real-time by using network statistics. The main objective of this thesis is to develop a network analysis tool, which gathers meaningful statistics from network traffic. These statistics will then be used for predicting the perceived quality of a VoIP call. This study includes the investigation and deployment of two main components. Firstly, to determine call quality, it is necessary to extract the voice streams from captured network traffic. The extracted sound files can then be analysed by various VoIP quality models to determine the perceived quality of a VoIP call. The second component is the analysis of network characteristics. Loss, delay and jitter are all known to influence perceived call quality. These characteristics are, therefore, determined from the captured network traffic and compared with the call quality. Using the statistics obtained by the repeated comparison of the call quality and network characteristics, a network specific algorithm is generated. This Non-Intrusive Quality Prediction Algorithm (NIQPA) uses basic characteristics such as time of day, delay, loss and jitter to predict the quality of a real-time VoIP call quickly in a non-intrusive way. The realised algorithm for each network will differ, because every network is different. Prediction results can then be used to adapt either the network (more bandwidth, packet prioritising) or the voice stream (error correction, change VoIP codecs) to assure QoS. / AFRIKAANSE OPSOMMING: Die kwaliteit van spraak oor die internet (VoIP) kommunikasie is afhanklik van die netwerk wat gebruik word om spraakpakkies te vervoer tussen die eindpunte. Netwerk eienskappe soos bandwydte, vertraging en verlies is krities vir intydse spraakverkeer en kan nie altyd gewaarborg word deur netwerkverskaffers nie. Dit is belangrik vir die netwerk diensverskaffers om die vereiste gehalte van diens (QoS) te verskaf aan hul kliënte. Die oplossing wat hier voorgestel word is om die kwaliteit van ’n VoIP oproep intyds te voorspel, deur middel van die netwerkstatistieke. Die belangrikste doel van hierdie projek is om ’n netwerk analise-instrument te ontwikkel. Die instrument versamel betekenisvolle statistiek deur van netwerkverkeer gebruik te maak. Hierdie statistiek sal dan gebruik word om te voorspel wat die gehalte van ’n VoIP oproep sal wees vir sekere netwerk toestande. Hierdie studie berus op die ondersoek en implementering van twee belangrike komponente. In die eerste plek, moet oproep kwaliteit bepaal word. Spraakstrome word uit die netwerkverkeer onttrek. Die onttrekte klanklêers kan dan geanaliseer word deur verskeie spraak kwaliteitmodelle om die kwaliteitdegradasie van ’n spesifieke VoIP oproep vas te stel. Die tweede komponent is die analise van netwerkeienskappe. Pakkieverlies, pakkievertraging en bibbereffek is bekend vir hul invloed op VoIP kwaliteit en is waargeneem. Hierdie netwerk eienskappe word dus bepaal uit die netwerkverkeer en daarna vergelyk met die gemete gesprekskwaliteit. Statistiek word verkry deur die herhaalde vergelyking van gesprekkwaliteit en netwerk eienskappe. Uit die statistiek kan ’n algoritme (vir die spesifieke network) gegenereer word om spraakkwaliteit te voorspel. Hierdie Nie-Indringende Kwaliteit Voorspellings-algoritme (NIKVA), gebruik basiese kenmerke, soos die tyd van die dag, pakkie vertraging, pakkie verlies en bibbereffek om die kwaliteit van ’n huidige VoIP oproep te voorspel. Hierdie metode is vinnig, in ’n nie-indringende manier. Die gerealiseerde algoritme vir die verskillende netwerke sal verskil, want elke netwerk is anders. Die voorspelling van spraakgehalte kan dan gebruik word om òf die netwerk aan te pas (meer bandwydte, pakkie prioriteit) òf die spraakstroom aan te pas (foutkorreksie, verander VoIP kodering) om die goeie kwaliteit van ’n VoIP oproep te verseker.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis presents the development of an adaptive longitudinal control system for an unmanned aerial vehicle (UAV). The project forms part of a research effort at Stellenbosch University into different fault-tolerant control techniques for UAVs. In order to demonstrate the usefulness of fault-tolerant adaptive control, the control system was designed to handle damage-induced longitudinal shifts in the centre of gravity (CG) of the aircraft, which are known to have a dramatic effect on the stability of a fixed-wing aircraft. Using a simplified force and moment model, equations were derived which model the effect of longitudinal CG shifts on the behaviour of the aircraft. A linear analysis of the longitudinal dynamics using these equations showed that the short period mode can become unstable for backward CG shifts. An adaptive pitch rate controller with the model reference adaptive control structure was designed to re-stabilise the short period mode when the CG shifts backwards. The adaptive law was designed using Lyapunov stability theory. Airspeed, climb rate and altitude controllers were designed around the pitch rate controller to allow full autonomous control of the longitudinal dynamics of the UAV. These outer loops were designed with constant parameters, since they would be unaffected by CG shifts if the adaptive pitch rate controller performed as desired. Pure software simulations as well as hardware-in-the-loop simulations showed that the adaptive control system is able to handle instantaneous shifts in the centre of gravity which would destabilise a fixed-gain control system. These simulation results were validated in flight tests, where the aircraft was destabilised using positive feedback and re-stabilised by the adaptive control system. Thus the simulation and flight test results showed that an adaptive control can re-stabilise an unstable aircraft without explicit knowledge of the change in the aircraft dynamics, and therefore could be effective as part of an integrated fault-tolerant control system. / AFRIKAANSE OPSOMMING: Hierdie tesis bied die ontwikkeling aan van ’n aanpassende longitudinale beheerstelsel vir ’n onbemande vliegtuig. Die projek is deel van navorsing by die Universiteit van Stellenbosch oor verskillende fout-tolerante beheertegnieke vir onbemande vliegtuie. Om die doeltreffendheid van aanpassende beheer te demonstreer, is die beheerstelsel ontwerp om situasies te kan hanteer waar die vliegtuig só beskadig word dat sy massamiddelpunt agtertoe skuif, wat ’n groot invloed op die stabiliteit van ’n vastevlerk-vliegtuig kan hê. ’n Vereenvoudigde model van die kragte en momente wat op die vliegtuig inwerk is gebruik om vergelykings af te lei wat beskryf hoe die gedrag van die vliegtuig verander as die massamiddelpunt agtertoe verskuif. Hierdie vergelykings is gebruik in ’n lineêre analise van die longitudinale dinamika van die vliegtuig, wat getoon het dat die kortperiode-modus onstabiel kan raak as die massamiddelpunt agtertoe verskuif. ’n Aanpassende heitempobeheerder met die modelverwysings-aanpassende beheerstruktuur is ontwerp om die kortperiode-modus weer te stabiliseer wanneer die massamiddelpunt agtertoe verskuif. Die aanpassingswet is ontwerp deur die gebruik van Lyapunov se stabiliteitsteorie. Lugspoed-, klimtempo- en hoogtebeheerders is rondom die aanpassende heitempobeheerder ontwerp sodat die longitudinale dinamika van die vliegtuig heeltemal outonoom beheer kan word. Hierdie buitelusse is ontwerp met vaste parameters, aangesien hulle nie geraak sal word deur verskuiwings in die massamiddelpunt as die aanpassende heitempobeheerder na wense werk nie. Suiwer sagteware-simulasies, sowel as hardeware-in-die-lus-simulasies, het getoon dat die aanpassende beheerstelsel oombliklike verskuiwings in die massamiddelpunt goed kan hanteer, waar sulke verskuiwings ’n beheerstelsel met vaste parameters onstabiel sou maak. Hierdie simulasie-resultate is bevestig deur vlugtoetse te doen, waar die vliegtuig onstabiel gemaak is deur positiewe terugvoer, en weer deur die aanpassende beheerstelsel stabiel gemaak is. Die simulasie- en vlugtoetsresultate wys dus dat aanpassende beheer ’n onstabiele vliegtuig weer kan stabiliseer sonder eksplisiete kennis van die veranderinge in die dinamika van die vliegtuig. Aanpassende beheer kan dus doeltreffend wees as deel van ’n geïntegreerde fout-tolerante beheerstelsel.