Thesis (MScEng)--Stellenbosch University, 2004. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The increase in the complexity and functionality of new satellites leads to a growing demand for a digital communication system operating at a much higher bit rate than before. The main purpose of this thesis is to address precisely this problem. The theory as well as a practical high speed system are custom-developed. The goal of this thesis is not to reinvent the wheel, but to use off-the-shelf products as far as possible. This system demonstrates that a very high data rate is not out of reach for a developer with limited funds. The secondary goal is to understand the operation of this communication system. The emphasis is on the inaccuracies in the system. A design tool is created to act as a vehicle for understanding the influence of a single variable on the performance of the entire system. / AFRIKAANSE OPSOMMING: Die toename in die kompleksiteit en funksionaliteit van nuwe satelliete lei tot die groeiende behoefte aan 'n digitale kommunikasiestelsel wat teen "n heelwat hoër bis spoed funksioneer. Die hoofdoel van hierdie tesis is om juis hierdie probleem aan te spreek. Die teorie en 'n praktiese hoëspoed stelsel is ontwikkel. Die doel van die tesis is nie om die wiel te herontdek nie maar om sover moontlik bestaande produkte in die ontwerp van die stelsel te gebruik. Die stelsel demonstreer dat 'n hoëspoed datatempo nie buite die bereik van 'n ontwikkelaar met beperkte fondse is nie. 'n Verdere doelwit is om die funksionering van die kommunikasie stelsel te begryp. Klem is gelê op die onakkuraathede in die kommunikasiestelsel. Ontwikkeling sagteware is geskep as "n metode om die invloed van "n enkele veranderlike op die werkverrigting van die stelsel as geheel te begryp.

Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Improvements in the area of satellite orientation control in the presence of large actuator gain changes are investigated. Gain changes primarily originate from actuator failures, but may also result from intermittent sensor availability and geomagnetic field effects. The stability and performance of a classic LQR control solution under these conditions is analyzed through simulation, and two adaptive schemes are developed to improve the response. The adaptive schemes mix elements from bang-bang control to increase performance, and banded control to increase robustness. These control schemes are thoroughly tested through simulation and the results are compared with those obtained for the classic solution. Extensive modelling of the system in the MATLAB™ environment is done to support the analysis of the controllers, and hardware sensors are built to provide realistic orientation measurements to the controllers. / AFRIKAANSE OPSOMMING: Verbeterings in die veld van satelliet oriëntasie beheer in die gevalle waar die aktueerders groot veranderinge in aanwins toon, word ondersoek. Aanwins veranderinge word primêr veroorsaak deur aktueerder falings, maar kan ook deur diskontinue sensor metings en magneetveld effekte van die aarde veroorsaak word. Die stabiliteit en gehalte van 'n klassieke LQR beheer strategie onder hierdie omstandighede word ondersoek deur simulasie, en twee aanpasbare beheer strategieë word ontwikkelom die oordrag te verbeter. Die aanpasbare beheer strategieë meng elemente van "bang-bang" beheer om die gehalte te verbeter, en gebande beheer tegnieke om die robuustheid van die stelsel te verbeter. Hierdie beheer strategieë is deeglik in simulasies getoets en die resultate is vergelyk met dié van die klassieke beheerder. Ekstensiewe modelleering van die stelsel is in die MATLAB™ omgewing gedoen om die beheerders te analiseer, en hardeware sensore is gebou om realistiese orientasie metings aan die beheerders te verskaf.

Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The high pace of technological advancement enables the realisation of ever more advanced mobile communications standards with more functionality than simple voice communications. The hardware that is used to implement the radio sections of these systems generally require long design cycles, much longer than the design cycles of the other components of a communications system. Another problem is that, once new communications standards are introduced, the current hardware platforms used in the terminal equipment becomes obsolete because they can generally not be used with the new standards. This has serious cost implications for both the service provider and the consumer, because both parties have to acquire new equipment to be able to use the new standards. An elegant solution to the above issues is to use software-defined radio sections to replace the hardware radio components. New communications standards can then be supported by simply loading new software onto the equipment, provided the maximum processing capacity of the processor(s) that the software runs on can accommodate the bandwidth requirements of that specific standard. This thesis investigates the ideas behind software defined radio and also describes the design and implementation of a software architecture that can be used to implement software defined radios on general-purpose platforms such as personal computers. / AFRIKAANSE OPSOMMING: Die hoë tempo van tegnologiese vordering maak dit moontlik om baie gevorderde mobiele kommunikasie standaarde te implementeer wat meer funksionaliteit bied as blote spraakkommunikasie. Die hardeware wat gebruik word om die radios van sulke stelsels te implementeer neem gewoonlik langer om te ontwikkel as die ander komponente van die stelsels. Die ander probleem is dat hierdie hardeware gewoonlik nie hergebruik kan word wanneer nuwe kommunikasie standaarde in gebruik geneem word nie omdat die standaarde nie versoenbaar is nie. Dit het tot gevolg dat beide die verbruiker en die diensverskaffer groot bedrae geld moet spandeer om die nuwe tegnologie te kan gebruik. 'n Elegante oplossing vir hierdie probleme is om gebruik te maak van radios waarvan die funksionaliteit in sagteware gedefiniëer word. Nuwe kommunikasie standaarde kan dan gebruik word deur slegs die nodige sagteware op die toerusting te laai, solank die verwerkingskapasiteit van die mikroverwerkers in die stelsel die benodigde bandwydte kan akkommodeer. Hierdie tesis ondersoek die konsepte van sagteware-gedefiniëerde radio en beskryf die ontwerp en implementering van 'n sagteware argitektuur vir die implementering van sagteware-gedefiniëerde radios op veeldoelige platforms soos persoonlike rekenaars.

Thesis (MScEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The aim of this thesis was to investigate the use of behavioral level models in receiver simulations using the capabilities of Agilent's Advanced Design System. Behavioral level modeling has become increasingly attractive because it offers faster and easier results for system level simulations. The work in this thesis focused strongly on nonlinear measurements to characterize the various nonlinear phenomena that are present in amplifiers and mixers. Measurement automation software was developed to automate the process. An error correction technique was also developed to increase the accuracy of spectrum analyzer measurements. The measured data was used to implement the behavioral level amplifier and mixer models in ADS. The accuracy of the models was compared to measured data and the different available models were compared. Finally the models were combined to realize different receivers and were used to do typical receiver tests. These test include gain and gain compression, two-tone intermodulation and spurious responses. The results are compared to measured data to test the accuracy and usefulness of the models and simulation techniques. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om stelsel-vlak gedrags-modelle te ondersoek soos hulle in Agilent se Advanced Design System (ADS) aangebied word. Die modellering van die stelselvlak-gedrag van komponente en stelsels is aantreklik aangesien dit 'n hoë vlak beskrywing van komplekse kommunikasie stelsels moontlik maak. Akkurate stelsel-vlak simulasies sal lei tot vinnige ontwikkeling en evaluasie van nuwe sisteme. Die resultate wat verkry word is egter afhanklik van die beskikbaarheid van akkurate stelsel-vlak gedragsmodelle Die tesis het baie sterk op metings staat gemaak om die nie-liniêre gedrag van versterkers en mengers te karakteriseer. Meet sagteware is ontwikkel om die verskillende metings te automatiseer. Fout korreksie vir spetrum-analiseerder-metings is ook ontwikkel. Die gemete data is gebruik om die nie-liniêre gedrags-modelle in ADS te implementer. Die modelle is in simulasies gebruik en die akuraatheid van die simulasies is teen gemete data getoets. Die finale deel van die tesis gebruik die modelle om tipiese ontvanger karakteristieke te voorspel. Die volgende toetse is gedoen: aanwins en kompressie, twee-toon intermodulasie en hoer orde meng produkte. Die resultate van die toetse is met gemete data vergelyk om die akuraatehied en bruikbaarheid van die verskillende modelle te vergelyk.

Thesis (MScEng) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: The development of a small, cost effective short range FM-CW radar as well as the design and optimization of a double helix antenna is discussed. The FM-CW radar operates at Sband (2450 - 2550 MHz) and is limited at a maximum transmitted power of 5 dBm. The system is required to detect reflections from objects up to a 30 m range. This was made possible largely by the effective high gain antenna design and improved system isolation between the transmitted and received signals. The complete design process from fundamental requirements, through various simulations and system analysis to the final electronic circuit is discussed. The design was also built and measured in the laboratory and initial field measurements were taken. The following aspects were considered: Relation between the beat frequency and various FM-CW radar system parameters based on the theory, preliminary measurements and simulations. Radar component assessment and design. Design of a low cost Lange coupler that isolates the system's transmit and receive signals, which operates as a 90° hybrid and is used to feed a dual-fed circularly polarized patch antenna. A circularly polarized patch antenna and double helix antenna were designed, built and measured in an anechoic chamber. The antennas were implemented in the final radar system and compared on the basis of their contribution to the system's performance. Integrating the final radar system on a circular 60 mm diameter PCB with a double helix antenna mounted on top. The final radar system is able to measure range up to 40 m and meets all the design requirements. The signal processing of the measured beat frequency, however, can be taken further. / AFRIKAANSE OPSOMMING: Die ontwikkeling van 'n klein, koste effektiewe kort-afstand FM-CW radar, sowel as die onwerp en optimalisering van 'n dubbele heliks-antenna word bespreek. Die FM-CW radar werk by S-band (2450 - 2550 MHz) en is beperk tot 'n maksimum uitsaaidrywing van 5 dBm. Van die stelsel word vereis om weerkaatsings van voorwerpe tot op 'n afstand van 30 m waar te neem. Dit is grootliks moontlik gemaak deur die hoë aanwins antenna-ontwerp en verbeterde isolasie tussen die stelsel se uitsaai- en ontvangseine. Die volledige ontwerpsproses van die fundamentele vereistes af tot die finale elektroniese stroombaan word bespreek. Verskeie simulasies andstelselanalises is gebruik om die finale FM-CW radar te realiseer. Die ontwerp is vervolgens in die laboratorium gebou en gemeet en aanvangsveldmetings is geneem. Die volgende aspekte is in nagevors: Verband tussen die puls-frekwensie en verskeie FM-CW radar stelselparameters gebaseer op die teorie, inleidende metings en simulasies. Ontleding van verskeie radarkomponente en -stelselontwerp. Ontwerp van 'n lae koste Lange-koppelaar met die doelom die stelsel se uitsaai- en ontvangseine te isoleer. Die Lange-koppelaar dien as 'n 90° hibriede wat gebruik word om 'n dubbele-voer sirkulêr gepolariseerde mikrostrookantenna aan te dryf. Verder is 'n sirkulêr gepolariseerde mikrostrook-antenna en 'n dubbele heliksantenna ontwerp en opgemeet in 'n anarqoïese kamer. Beide antennas is geïmplimenteer in die finale radarstelsel en is vergelyk op grond van hulle rol in die stelsel se funksionering. Die finale stelsel is geïntegreer en gebou op 'n ronde 60 mm deursnit PCB met 'n dubbele helix-antenna bo-op gemonteer. Die finale radarstelsel kan afstand tot op 40 meter bepaal en voldoen aan al die gestelde vereistes. Seinverwerking van die gemete puls-frekwensie kan nog verder ontwikkel word.

Thesis (MScEng)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: The syllable has been proposed as a unit of automatic speech recognition due to its strong links with human speech production and perception. Recently, it has been proved that incorporating information from syllable-length time-scales into automatic speech recognition improves results in large vocabulary recognition tasks. It was also shown to aid in various language recognition tasks and in foreign accent identification. Therefore, the ability to automatically segment speech into syllables is an important research tool. Where most previous studies employed knowledge-based methods, this study presents a purely statistical method for the automatic syllabification of speech. We introduce the concept of hierarchical hidden Markov model structures and show how these can be used to implement a purely acoustical syllable segmenter based, on general sonority theory, combined with some of the phonotactic constraints found in the English language. The accurate reporting of syllabification results is a problem in the existing literature. We present a well-defined dynamic time warping (DTW) distance measure used for reporting syllabification results. We achieve a token error rate of 20.3% with a 42ms average boundary error on a relatively large set of data. This compares well with previous knowledge-based and statistically- based methods. / AFRIKAANSE OPSOMMING: Die syllabe is voorheen voorgestel as 'n basiese eenheid vir automatiese spraakherkenning weens die sterk verwantwskap wat dit het met spraak produksie en persepsie. Onlangs is dit bewys dat die gebruik van informasie van syllabe-lengte tydskale die resultate verbeter in groot woordeskat herkennings take. Dit is ook bewys dat die gebruik van syllabes automatiese taalherkenning en vreemdetaal aksent herkenning vergemaklik. Dit is daarom belangrik om vir navorsingsdoeleindes syllabes automaties te kan segmenteer. Vorige studies het kennisgebaseerde metodes gebruik om hierdie segmentasie te bewerkstellig. Hierdie studie gebruik 'n suiwer statistiese metode vir die automatiese syllabifikasie van spraak. Ons gebruik die konsep van hierargiese verskuilde Markov model strukture en wys hoe dit gebruik kan word om 'n suiwer akoestiese syllabe segmenteerder te implementeer. Die model word gebou deur dit te baseer op die teorie van sonoriteit asook die fonotaktiese beperkinge teenwoordig in die Engelse taal. Die akkurate voorstelling van syllabifikasie resultate is problematies in die bestaande literatuur. Ons definieer volledig 'n DTW (Dynamic Time Warping) afstands funksie waarmee ons ons syllabifikasie resultate weergee. Ons behaal 'n TER (Token Error Rate) van 20.3% met 'n 42ms gemiddelde grens fout op 'n relatiewe groot stel data. Dit vergelyk goed met vorige kennis-gebaseerde en statisties-gebaseerde metodes.

Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Common mode currents are a major source of interference in electrical and electronic systems. A universal solution to counteract common mode interference is to introduce an electromagnetic shield with known characteristics. Cable trays are often used to shield cables from unwanted electromagnetic interference (EM!) and its shielding characteristics are defined in terms of its transfer impedance. This thesis pursues the modelling and measurement of the transfer impedance and mutual inductance of non-magnetic cable trays. Theoretical analysis is firstly employed by means of Maxwell's equations after which method of moments (MoM) simulations are performed in order to determine the transfer impedance and mutual inductance within the interior region of a cable tray. The results obtained through simulation are then validated with measurements conducted with an automatic network analyser (ANA). The computational and measured data are in good agreement and the developed model can be used to predict the transfer impedance in the cross-section of non-magnetic cable trays. / AFRIKAANSE OPSOMMING: Gemenernodus strome is 'n bron van interferensie in elektriese en elektroniese stelsels. 'n Universele oplossing om hierdie gemenernodus interferensie teen werk is om 'n elektromagnetiese skerm met bekende eienskappe te implementeer. Geleier leikanale word dikwels gebruik om kabels teen elektromagnetiese interferensie te beskerm en die afskermings eienskappe word in terme van die kanaal se oordragsimpedansie gedefinieer. Hierdie tesis ondersoek die modelering en meting van die wedersydse induktansie en oordragsimpedansie van nie-magnetiese geleier leikanale. 'n Teoretiese analise word eers uitgevoer deur middel van Maxwell se vergelykings waarna metode van momente (MvM) simulasies uitgevoer word om die oordragsimpedansie en wedersydse induktansie in die interne gebied van 'n leikanaal te bepaal. Die resultate verkry deur simulasie word dan bevestig deur meting wat uitgevoer word met behulp van 'n automatiese netwerk analiseerder (ANA). Die numeriese en gemete data stem goed ooreen en die ontwikkelde model kan deurgaans gebruik word om die oordragsimpedansie in die deursnit area van nie-magnetiese geleier leikanale te voorspel.

Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The development of a radar system is a complex process, requiring a substantial amount of testing. In general, these tests are performed using field trials. Such trials are expensive, and their exact conditions can never be repeated. A radar environment simulator allows for repeatable testing of the majority of a radar's functionality; however, most commercial products are not cost effective. In this thesis we investigate the various approaches to modelling targets and the littoral environment, and then develop a low-cost, largely software defined simulator. This simulator is capable of generating real-time video signals for a monopulse doppler tracking radar. The core simulation routines reside in an extensible software framework which is populated with simple target and clutter models for a prototype simulator. Closed loop tracking tests verify the operation of the prototype simulator. / AFRIKAANSE OPSOMMING: Die ontwikkeling van 'n radarstelsel is a ingewikkelde proses wat verskeie stelseltoetse benodig. Veldtoetse, wat gewoonlik gebruik word, is 'n duur proses, en die toestande is nooit presies dieselfde nie. 'n Radar-omgewingsimulator kan 'n groot deel van 'n radar se funksionaliteit herhaaldelik toets. Daar is egter weinig koste-effektiewe kommersile produkte vir hierdie doel beskikbaar. Hierdie tesis ondersoek verskeie teiken- en omgewingsmodelle, waarna 'n lae-koste, meestal sagteware-gedefinieerde simulator ontwikkel word. Hierdie simulator genereer intydse videoseine vir 'n enkelpuls-dopplervolgingsradar. Die kernfunksionaliteit van die simulator is in sagteware gesetel, en basiese teiken- en omgewingsmodelle is geïmplementeer. Die prototipe-simulator word getoets deur dit aan die radar self te koppel, en dan die teiken-opsporing en -volging te verifieer.

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The SUNSAT RAMDISK was studied, and tests performed to assess its flight readiness. Errors were detected, and modifications had to be made to ensure proper operation. SUNSAT was subsequently launched, and to date the RAMDISK is still functioning correctly. The flight readiness testing of the RAMDISK was considered a pre-study to designing a second generation RAMDISK. A conceptual mass memory storage device support structure was designed. This second generation RAMDISK, or memory drive is intended to be used on a second generation SUNSAT, or SUNSAT 2. The design is targeted for implementation in fields programmable gate arrays (FPGA's) and was realised using VHDL. This hardware description language is an accepted standard, and can be implemented in a number of different programmable logic devices; both SRAM and fuse-link based. Simulations were performed to verity the functionality of the design, and to determine whether the data transfer specifications could be met using programmable logic devices. A modular design methodology was followed. The memory drive was designed so that any type and amount of memory can be added to the drive without a major design change. The simulations indicated that a data capturing speed of 130 Mbits/s could be maintained. / AFRIKAANSE OPSOMMING: Die SUNSAT massa geheue module is bestudeer, en toetse is daarop uigevoer om die vlug gereedheid te bepaal. Foute is gevind, en veranderinge moes aangebring word om korrekte werking te verseker. SUNSAT is gelanseer en die geheue module werk tot op datum nog korrek. Die geheue module se vlug gereedheid toetse is beskou as In voor studie vir die ontwerp van In tweede generasie geheue module. In Konseptueie massa stoor toestel struktuur is ontwerp. Hierdie tweede generasie geheue module, of geheue skyf is bedoel om op In tweede generasie SUNSAT, of SUNSAT 2 gebruik te word. FPGA's is die teiken tegnologie vir hierdie ontwerp en VHDL is gebruik om die ontwerp te realiseer. Hierdie hardeware beskrywingstaal word as In standaard aanvaar en kan in verskillende herprogrammeerbare tegnologieë gebruik word. Sirnulasies is gedoen om die funksionaliteit van die ontwerp te verifieer, en om te bepaal of die nodige data oordragstempo gehandhaaf kan word met herprogrammeerbare tegnologie. In Modulêre ontwerpsfilosofie is gevolg. Die geheue skyf is ontwerp sodat dit enige tipe en hoeveelheid geheue kan ondersteun sonder om groot veranderinge aan die ontwerp te doen. Die sirnulasies toon dat In data oordragstempo van 130 Mbits/s gehandhaafkan word.

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A unified method is proposed to treat saturation in both Multi-Input-Multi-Output MIMO and Single-Input-Single-Output controllers. This method offers superior performance over existing MIM 0 anti-saturation schemes. The anti-saturation problem is posed as a linear programming problem. A practical and efficient implementation of the algorithm is developed by transforming the problem into its dual linear programming form. The problem, in dual form, is then solved using the dual simplex method rather than the primal simplex method. The nature of the problem when expressed in dual form and the properties of the dual simplex method are harmonised to guarantee an initial basic feasible solution and an optimal bounded final solution in a finite, predictable and minimal number of iterations. The resultant controller never saturates, hence cannot windup. Furthermore the resultant controller always applies the optimal control effort to the plant to minimise the error signal input as follows: • The controller is governed such that while the future free response combined with the present forced response of the controller results in no saturation limits being exceeded, now or at some time in the future, the normal linear response of the controller prevails. • When the future free response combined with the present forced response of the controller will result in a saturation limit being reached, now or at some time in the future, the present time input signal into the controller is optimally governed to prevent the saturation limit from being exceeded at any future time. / AFRIKAANSE OPSOMMING: 'n Metode word voorgestel waarmee versadiging in enkel-inset enkel-uitset en meer-inset meeruitset (MIMU) stelsels beheer kan word. Die metode presteer beter as ander huidige teenversadiging- maatreels vir (MIMU) beheerders. Die teen-versadigings-probleem word as 'n lineere programmeringsprobleem herformuleer. 'n Praktiese en effektiewe implementering van die algoritme word verkry deur die probleem na die duale vorm te transformeer. Die probleem, in duale vorm, word opgelos met die duale simplex metode, in plaas van die direkte metode. Die eienskappe van hierdie formulering is 'n gewaarborgde, aanvanklike, bereikbare oplossing en 'n optimale, begrensde, finale oplossing in 'n eindige, voorspelbare en minimum aantal stappe. Die uiteindelike beheerder versadig nooit nie, en wen gevolglik nie op nie. Die beheerder wend altyd die optimale aanleg-inset aan om die foutsein te minimeer soos volg: • Wanneer die nul-inset gedrag saam met die huidige inset-gedrag geen beperkings nou of in die toekoms saloorskry nie, word geen beperkende aksie geneem nie, en tree die beheerder dus lineer op. • Sodra die toekomstige nul-inset gedrag saam met die huidige inset-gedrag, nou of later versadiging sou veroorsaak, word die huidige inset tot die beheerder optimaal begrens om latere versadiging te voorkom.