Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A joint project between the KU Leuven and Stellenbosch Universities was at the time of this thesis underway to develop a space borne electronically beam steerable antenna and the associated ground-space segments. This thesis covers the development of an aircraft based satellite emulator to facilitate convenient aircraft based testing of an antenna array, intended for low earth orbit satellite deployment and subsystems to control the antenna array. A flight strategy is developed to emulate such a satellite pass as best possible, with the strategy implemented in software on in-flight PC hardware. A full interface between the aircraft avionics and satellite bus system has been developed to enable generation of the required antenna steering commands and to create a satellite bus image to the payload. Successful test results are presented, as obtained from the actual aircraft ight simulator. The thesis describes the successful development and testing of a low altitude flight test strategy for certain satellite borne systems, as a cost-effective and realistic interim step to actual and very expensive space flight testing. / AFRIKAANSE OPSOMMING: 'n Gesamentlike projek deur KU Leuven en Stellenbosch Universiteit was tydens die verloop van hierdie tesis besig met die ontwikkeling om 'n ruimte gebaseerde elektroniese straal beheerde antenna en geassosieerde substelsels daar te stel. Hierdie tesis handel oor die ontwikkeling van 'n vliegtuig gebaseerde satelliet emulator om die toetsing van 'n elektroniese stuurbare antenna, wat bedoel is vir 'n lae aardse wentelbaan, te fasiliteer en die ontwikkeling van substelsels wat die stuurbare antenna beheer. 'n Vlug strategie is ontwikkel om so 'n satelliet wentelbaan so na as moontlik te emuleer. Die strategie word dan geïmplementeer in die sagteware van die aanboord vlug rekenaar. 'n Intervlak tussen die vliegtuig instrumente en satellietbus is ontwikkel om die generering van die nodinge instruksies te fasiliteer en om 'n virtuele satellietbus vir die res van die satelliet stelsel te skep. Suksesvolle toets resultate word getoon wat met behulp van 'n vliegtuig simulator verkry is. Die tesis beskryf die suksesvolle ontwikkeling en toetsing van 'n lae vlugtoets strategie vir satelliet stelsels, as 'n koste effektiewe en realistiese tussenstap, tot baie duur ruimte vlugtoetsing.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Assessing the quality of fruit has become vitally important for farmers and growers. With retailers placing ever stricter requirements on fresh produce, growers have to spend a greater amount of time and effort sorting and grading their harvest. Increasingly, vendors are placing requirements not only on external factors like colour, and firmness, but on internal quality factors such as sugar content and acidity, because, although consumers buy fruit based on their external appearances, the taste of the fruit is what determines whether the consumer will buy again. Different techniques exist that probe the internal quality of fruit non-destructively. The technique most widely used today is Near Infrared Spectroscopy. This technique is powerful, but has certain limitations such as poor reliability and the need for constant recalibration. This thesis suggests an alternative method for evaluating internal fruit quality based on low-field nuclear magnetic resonance detected by superconducting quantum interference devices. It introduces the theory of SQUIDs and NMR, and evaluates the use of SQUID detected NMR spectroscopy as a method for determining the internal quality of fruit. The fabrication techniques and processes are explained in detail and a design for a SQUID detected NMR spectrometer is given. Relevant simulations and simulation results are also given. No working SQUID could be fabricated and, as such, no working NMR spectrometer was demonstrated. This thesis serves as a reference work for future research. / AFRIKAANSE OPSOMMING: Bepaling van die gehalte van vrugte het vir boere uiters belangrik geword. Met kleinhandelaars wat al strenger vereistes plaas op vars produkte moet boere meer tyd en inspanning bestee met die sortering en gradering van hul oes. Handelaars plaas nie net vereistes op eksterne kwaliteitsfaktore soos kleur en fermheid nie, maar begin al hoe strenger vereistes plaas op interne kwaliteitsfaktore soos suikerinhoud en suurgehalte, want, hoewel verbruikers vrugte koop op grond van hul eksterne kwaliteitsfaktore, is dit die smaak van die vrug wat bepaal of die verbruiker weer die vrug sal koop. Verskillende tegnieke bestaan wat die interne kwaliteit van vrugte op ’n nie-destruktiewe manier kan bepaal. Die mees algemene tegniek is Naby Infrarooi Spektroskopie. Hierdie tegniek is kragtig maar het sekere beperkings soos swak betroubaarheid en die noodsaaklikheid van konstante herkalibrasie. Hierdie tesis stel ’n alternatiewe metode vir die evaluering van interne vrugkwaliteit gebaseer op lae-veld kernmagnetiese resonans waargeneem deur supergeleidende kwantum inmenging toestelle voor. Dit stel die teorie van SKWITs en KMR bekend, en evalueer die gebruik van SKWIT-bespeurde KMR spektroskopie as ’n metode vir die bepaling van die interne kwaliteit van vrugte. Die fabrikasie tegnieke en prosesse word in detail verduidelik en ’n ontwerp vir ’n SWKIT opgevangde KMR spektrometer word gegee. Toepaslike simulasies en simulasie resultate word ook gegee. Geen werkende SKWIT kon vervaardig word nie en as gevolg daarvan kon geen werkende KMR spektrometer gedemonstreer word nie. Hierdie tesis dien as ’n naslaan werk vir toekomstige navorsing.

The growth of mobile networks and the imminent deployment of third generation networks and services will require signalling networks to maintain their integrity during increased unanticipated traffic volumes. As signalling networks become larger and more complex, an analysis ofprotocol operation is necessary to determine the effectiveness of the current protocol implementation and to evaluate the applicability of the proposed enhancements. The objective of this study ,is to develop analytical models to analyse the impact of Signalling Transfer Point congestion on network performance when simple message discard schemes are used as the primary flow control mechanism, and to investigate suitable congestion and flow control mechanisms to help alleviate the congestion. Unlike previous studies, that are localised and only concentrate on the nodes around the congested entity, the models presented here examine the impact of network wide and focused overloads on the entire network. The study considers both the fixed-line and mobile network environments, and analyses the performance of the ISDN User Part and Mobile Application Part protocols. The call completion rate and location update success rate are used to measure performance, instead of message throughput, since these parameters provide a more appropriate measure of the grade-of-service and more accurately reflect the level of service provided to a customer. The steady state equilibrium models, derived here, can be used to quickly estimate the safe operating regions of a signalling network, while the transient models provide a more intuitive perspective of the traffic processes that lead to congestion . Furthermore, these models can be used to examine the network performance for different message priority schemes, routing algorithms, overload scenarios and network configurations. The performance of various congestion control mechanisms that incorporate non-linear throttling schemes is also evaluated, together with an examination of the impact of congestion on multiple user parts in a mobile network environment. Message priority schemes are found to offer little or no advantage in a fixed network environment, but in a mobile network they can be used to maintain the network's performance at an optimum level during periods of overload. Network performance is also improved if congestion controls block load-generating traffic at the initial onset of congestion and then gradually restore traffic as the performance improves . / Thesis (Ph.D.)-University of Natal, Durban, 2002.

Mobile communications are becoming integrated into society at an explosive rate. While 2nd generation (2G) systems limit the user to basic services such as voice and low-bit rate data, 3G networks are characterized by their ability to accommodate wideband multi-media traffic with Quality of Service (QoS) guarantees. In the design of a system the Medium Access Control (MAC) layer is responsible for multiplexing heterogeneous traffic onto a common transmission link and its design is critical to the overall performance of a system. A number of MAC protocols for wireless networks have been proposed in the literature - the majority having time division multiple access (TDMA) at the MAC layer. However in 3G systems there is a trend towards the use of code division multiple access (CDMA) due to its proven advantages in a wireless environment. Although several papers on CDMA based MAC protocols have been published, virtually none of them tackle the analysis aspect of the protocols. Those papers that do perform analyses of CDMA protocols don't often consider heterogeneous traffic, and even fewer support QoS. The thesis addresses these shortcomings by proposing a MAC protocol that supports QoS in the form of Bit Error Rate (BER) and packet delay guarantees. The thesis begins by giving an overview of proposed wireless ATM and 3G CDMA protocols and then details how power control may be used to support BER guarantees. Various Markov based analyses are presented along with Monte-Carlo Simulations. An Equilibrium Point Analysis is then performed and the work discusses how such analyses are generally infeasible for systems supporting heterogeneous traffic. After an overview of conventional scheduling algorithms the thesis proceeds to outline a novel approach by which delay guarantees may be offered using packet dropping rates as the QoS metric. Using a stochastic source model as opposed to the conventional leaky bucket traffic regulator the thesis diverges significantly from conventional literature. The thesis also details how to calculate the probability of QoS violation and concludes with suggestions on further research avenues. As a whole the work is unique in its approach to analyse heterogeneous traffic and the methods it uses to construct session admission zones for QoS guarantees. / Thesis (Ph.D.)-University of Natal,Durban, 2002.

Research in the field of random access protocols for narrow-band systems started as early as the 1970s with the introduction of the ALOHA protocol. From the research done in slotted narrow-band systems, it is well known that contention results in all the packets involved in the contention being unsuccessful. However, it has been shown that in the presence of unequal power levels, ore of the contending packets may be successful. Ibis is a phenomenon called capture. Packet capture has been shown to improve the performance of slotted narrow-band systems. Recently, much work has been done in the analysis of spread-spectrum ALOHA type code-division multiple access (CDMA) protocols. The issue of designing power control techniques to improve the performance of CDMA systems by reducing multiple access interference (MAl) has been a subject of much research. It has been shown that in the presence of power control schemes, the performance of spread-ALOHA CDMA systems is improved. However, it is also widely documented that the design of power control schemes capable of the ideal of compensation of radio propagation techniques is not possible for various reasons, and hence the imperfections in power control. None of the research known to the author has looked at capture in spread-ALOHA systems, and to a greater extent, looked at expressions for the performance of spreadALOHA systems in the presence of capture. In this thesis we introduce spread-ALOHA systems with capture as a manifestation of the imperfections in power control. We propose novel expressions for the computation of the perfonnance ofspread-ALOHA systems with capture. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.

The emergence of portable terminals in work and living environments is accelerating the progression of wireless networks. A wireless ad hoc network is a new network concept where users establish peer-to-peer communication among themselves independently, in their small area. Since the wireless medium is a shared resource, it becomes an important design issue to efficiently allocate bandwidth among users. MAC (Medium Access Control) layer arbitrates the channel access to the wireless medium and is also responsible for bandwidth allocation to different users, therefore a large amount of research has been conducted on various MAC protocols for ad hoc wireless networks. This dissertation begins with a survey of existing wireless MAC protocols. The survey includes protocols designed for different network generations and topologies, classifying them based on architecture and mode of operation. Next, we concentrate on the MAC protocols proposed for distributed wireless networks. We propose a new MAC protocol based on a token-passing strategy; which not only incorporates the advantages of the guaranteed access scheme into the distributed type of wireless networks, but also the data rate and delay level QoS guarantees. Data rate QoS provides fairness into sharing of the channel, while delay level QoS introduces a flexible prioritized access to channels by adjusting transmission permission to the current network traffic activities. A simulation model for the protocol is developed and delay and throughput performance results are presented. To examine the efficiency and performance of the proposed MAC scheme in an ad hoc wireless environment, it is incorporated into the Bluetooth structured network. The model is then simulated in the Bluetooth environment and performance results are presented. Furthermore, an analytical model is proposed and an approximate delay analysis conducted for the proposed MAC scheme. Analytical results are derived and compared with results obtained from computer simulations. The dissertation concludes with suggestions for improvements and future work. / Thesis (M.Sc.-Engineering)-University of Natal, 2003.

The problems of optimal as well as suboptimal detection for CDMA transmissions over an additive white Gaussian noise (AWGN) channel, have been the focus of study in the recent past. However, CDMA transmissions are frequently made over channels which exhibit fading and/or dispersion; hence receivers need to be designed which take into account this behaviour. In spite of the major research effort invested in multiuser demodulation techniques, several practical as well as theoretical open problems still exist. Some of them are considered in more detail in this thesis. The aim of the thesis is to develop multiuser demodulation algorithms for mobile communication systems in frequency-selective fading channels, and to analyze their implementation complexity. The emphasis is restricted to the uplink of an asynchronous DS-CDMA system where the users transmit in an uncoordinated manner and are received by one centralized receiver. The original work that is undertaken for the MScEng study is the evaluation of a multiuser receiver structure for a frequency-selective fading channel, where there exists a steady specular path and two fading paths. Furthermore, the effect of using selection diversity is investigated by examining the bit error rate, asymptotic multi user efficiency and near-far resistance of the proposed detector structure. These results are confirmed both analytically and by simulation in the thesis. An investigation is also conducted into the application of neural networks to the problem of multiuser detection in code division multiple access systems. The neural network will be used as a classifier in an adaptive receiver which incorporates an extended Kalman filter for joint amplitude and delay estimation. Finally, some open problems for future research will be pointed out in the thesis. Keywords: AWGN channel , DS-CDMA system, frequency-selective, multi user demodulation, asymptotic multiuser efficiency, near-far resistance, neural network, Kalman filter. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Thesis (MScIng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This dissertation's research aims at studying the viability of using both low cost consumer Commodity Off The Self (COTS) PCs and libn~software in implementing a distributed real-time system modeled on a real-world engineering problem. Debugging and developing a modular satellite system is both time consuming and complex, to this end the SUNSATteam has envisioned the Interactive Test System that would be a dual mode simulator/monitoring system. It is this system that requires a real-time back-end and is used as a real world problem model to implement. The implementation was accomplished by researching the available parallel processing software and real-time extensions to GNU/Linux and choosing the appropriate solutions based on the needs of the model. A monitoring system was also implemented, for system verification, using freely available system monitoring utilities. The model was successfully implemented and verified with a global synchronization of < 10ms. It was shown that GNU/Linux and libn~ software is both mature enough and appropriate in solving a real world distributed real-time problem. / AFRIKAANSE OPSOMMING: Die tesis se navorsing is daarop gemik om die toepaslikheid van beide lae koste verbruikers Komoduteits Van Die Rak (KVDR)persoonlike rekenaars en vemiet sagteware in die implementasie van verspreide intydse stelsels te ondersoek aan die hand van die oplossing van 'n gemodelleerde ingenieurs probleem. Die ontfouting en ontwikkeling van 'n modulere satelliet is beide tyd rowend en kompleks, om hierdie te vergemaklik het die SUNSAT span die Interaktiewe Toets Stelsel gekonseptualiseer, wat in wese'n dubbel modus simulator/moniteerings stelsel sou wees. Dit is hierdie stelsel wat 'n verspreide intydse onderstel benodig en dien as die regte wereld probleem model om op te los. Die implementasie is bereik deur die beskikbare verspreide verwerkings sagteware en intydse uitbreidings vir GNU/Linux te ondersoek en die toepaslike opsies te kies gegrond op die behoeftes van die model. 'n Moniteerings stelsel is ook geimplimenteer, met behulp van libn~sagteware, vir stelsel verifikasie. Die model was suksesvol geimplimenteer en geverifieer met 'n globale sinkronisasie van < 10ms. Daar is getoon dat GNU/Linux en libn~sagteware beide volwaardig en geskik is vir die oplossing van regte wereld verspreide intydse probleme.

Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The field of topic spotting in conversational speech deals with the problem of identifying "interesting" conversations or speech extracts contained within large volumes of speech data. Typical applications where the technology can be found include the surveillance and screening of messages before referring to human operators. Closely related methods can also be used for data-mining of multimedia databases, literature searches, language identification, call routing and message prioritisation. The first topic spotting systems used words as the most basic units. However, because of the poor performance of speech recognisers, a large amount of topic-specific hand-transcribed training data is needed. It is for this reason that researchers started concentrating on methods using phonemes instead, because the errors then occur on smaller, and therefore less important, units. Phoneme-based methods consequently make it feasible to use computer generated transcriptions as training data. Building on word-based methods, a number of phoneme-based systems have emerged. The two most promising ones are the Euclidean Nearest Wrong Neighbours (ENWN) algorithm and the newly developed Stochastic Method for the Automatic Recognition of Topics (SMART). Previous experiments on the Oregon Graduate Institute of Science and Technology's Multi-Language Telephone Speech Corpus suggested that SMART yields a large improvement over ENWN which outperformed competing phoneme-based systems in evaluations. However, the small amount of data available for these experiments meant that more rigorous testing was required. In this research, the algorithms were therefore re-implemented to run on the much larger Switchboard Corpus. Subsequently, a substantial improvement of SMART over ENWN was observed, confirming the result that was previously obtained. In addition to this, an investigation was conducted into the improvement of SMART. This resulted in a new counting strategy with a corresponding improvement in performance. / AFRIKAANSE OPSOMMING: Die veld van onderwerp-herkenning in spraak het te doen met die probleem om "interessante" gesprekke of spraaksegmente te identifiseer tussen groot hoeveelhede spraakdata. Die tegnologie word tipies gebruik om gesprekke te verwerk voor dit verwys word na menslike operateurs. Verwante metodes kan ook gebruik word vir die ontginning van data in multimedia databasisse, literatuur-soektogte, taal-herkenning, oproep-kanalisering en boodskap-prioritisering. Die eerste onderwerp-herkenners was woordgebaseerd, maar as gevolg van die swak resultate wat behaal word met spraak-herkenners, is groot hoeveelhede hand-getranskribeerde data nodig om sulke stelsels af te rig. Dit is om hierdie rede dat navorsers tans foneemgebaseerde benaderings verkies, aangesien die foute op kleiner, en dus minder belangrike, eenhede voorkom. Foneemgebaseerde metodes maak dit dus moontlik om rekenaargegenereerde transkripsies as afrigdata te gebruik. Verskeie foneemgebaseerde stelsels het verskyn deur voort te bou op woordgebaseerde metodes. Die twee belowendste stelsels is die "Euclidean Nearest Wrong Neighbours" (ENWN) algoritme en die nuwe "Stochastic Method for the Automatic Recognition of Topics" (SMART). Vorige eksperimente op die "Oregon Graduate Institute of Science and Technology's Multi-Language Telephone Speech Corpus" het daarop gedui dat die SMART algoritme beter vaar as die ENWN-stelsel wat ander foneemgebaseerde algoritmes geklop het. Die feit dat daar te min data beskikbaar was tydens die eksperimente het daarop gedui dat strenger toetse nodig was. Gedurende hierdie navorsing is die algoritmes dus herimplementeer sodat eksperimente op die "Switchboard Corpus" uitgevoer kon word. Daar is vervolgens waargeneem dat SMART aansienlik beter resultate lewer as ENWN en dit het dus die geldigheid van die vorige resultate bevestig. Ter aanvulling hiervan, is 'n ondersoek geloods om SMART te probeer verbeter. Dit het tot 'n nuwe telling-strategie gelei met 'n meegaande verbetering in resultate.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The development of an integrated avionics system containing all the required sensors and actuators for autopilot control is presented. The thesis analyzes the requirements for the system and presents detailed hardware design. The architecture of the system is based on an FPGA which is tasked with interfacing with the sensors and actuators. The FPGA abstracts a microprocessor from these interface modules, allowing it to focus only on the control and user interface algorithms. Firmware design for the FPGA, as well as a conceptualization of the microprocessor software design is presented. Simulation results showing the functionality of firmware modules are presented. / AFRIKAANSE OPSOMMING: Die ontwikkeling van ‘n geïntegreede avionika‐stelsel wat al die vereiste sensors en aktueerders vir outoloods‐beheer bevat, word voorgestel. Die tesis analiseer die vereistes van die stelsel en stel ‘n hardeware‐ontwerp voor. Die argitektuur van die stelsel bevat ‘n FPGA wat ‘n koppelvlak met sensors en aktueerders skep. Die FPGA verwyder die mikroverwerker weg van hierdie koppelvlak modules en stel dit sodoende in staat om slegs op die beheer en gebruikerskoppelvlak‐algoritmes te fokus. Sagteware‐ontwerp vir die FPGA, asook die konseptualisering van die sagtewareontwerp vir die mikroverwerker, word aangebied. Simulasie resultate wat die funksionaliteit van die FPGA‐sagteware modules aandui, word ook voorgestel.