Magnesium Diboride (MgB₂) bulk superconductor has been manufactured for use in superconducting fault current limiters (SFCLs) via in situ reaction. SFCLs have proven to be a viable means for limiting surge currents on power lines by dissipating fault energy as the superconductor quenches. As the current limiting behaviour is determined by the normal resistance (Rn), research has been conducted to evaluate an effective means to increase Rn for bulk superconducting MgB₂. Other researchers have previously looked into the improvement and optimisation of the critical current, Jc, by carbon doping and other flux pinning techniques. Carbon doping has been confirmed as a means to increase Rn, and was implemented by chemical vapour deposition (CVD) at 600 ºC in a tubular furnace apparatus. Intragranular doping was achieved by CVD on the boron precursor powder. In situ manufacturing of MgB₂ bulk was performed using the reactive liquid magnesium infiltration technique. Carbon doping provided an adequate increase in Rn, for a small decrease in the critical temperature, Tc. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Turbo codes are a class of forward error correction (FEC) codes that offer energy efficiencies close to the limits predicted by information theory. The features of turbo codes include parallel code concatenation, recursive convolutional encoding, nonuniform interleaving, and an associated iterative decoding algorithm. The excellent performance of turbo codes explains why much of the current research is focused on applying turbo codes to different systems. This dissertation first outlines a new simple criterion for stopping the iterative process of the turbo decoder for each individual frame immediately after the bits are correctly estimated and thus prevents unnecessary computations and decoding delay. The dissertation then considers the performance of turbo coded DS-CDMA systems. The performance analysis begins with simulation results for turbo coded DS-CDMA over a multi-path Rayleigh fading channel. The channel is then modeled using the Gilbert-Elliott channel model and analytical expressions for the performance of the system are derived. The influence of various parameters such as the Doppler frequency, the signal-to-noise ratio threshold on the system performance are analyzed and investigated. / Thesis (M.Sc.Eng)-University of Natal, Durban, 2001.

Small mobile devices which have an ability to access the world wide web (WWW) wirelessly are in demand of late. This demand is attributed to the fact that video and audio streaming are cost effectively accessible via the WWW through wireless fidelity (Wi-Fi). This high demand for cheap real-time multimedia access via Wi-Fi makes it imperative for researchers to develop a wireless local area network (WLAN) standard, such as IEEE (802.11n), that has high data throughput and/or link reliability. The current drawback with the IEEE (802.11n) standard is that it is not power efficient for battery powered small mobile devices because of the high complexity multiple-input-multiple-output (MIMO) scheme implemented within the standard. Spatial modulation (SM) is a recently proposed low complexity MIMO scheme that can achieve high data throughput with good link reliability whilst being power efficient for small mobile devices. This study is aimed at further improving data throughputs of SM and also determining the bit error rate (BER) performance of SM in a city centre environment. Conventional spatial modulation has been investigated in literature with most research efforts geared towards improving the BER performance and minimizing receiver complexity of the scheme over non-cascaded fading channels. We propose adaptive M-ary quadrature amplitude spatial modulation (A-QASM) as a scheme that will improve the average throughput in comparison to conventional spatial modulation given a target BER constraint. The analytical BER lower bound is derived for this proposed scheme and validated by the Monte Carlo simulation results. The simulation results also prove that the average throughput of the proposed scheme (A-QASM) outperforms that of conventional spatial modulation. The definition for the received SNR of the A-QASM scheme is also proposed. In research literature, conventional spatial modulation has been discussed in depth in non-cascaded wireless fading channels. The performance analysis derived in literature in non-cascaded wireless fading channels; does not apply in predicting the BER performance of a mobile device, using conventional spatial modulation, in an environment where there is signal diffraction (i.e city centre or a forest) which makes the signal susceptible to independent cascaded fading. This study contributes by developing an analytical framework for the BER lower bound of conventional spatial modulation over cascaded fading channels. Simulation results closely agree with the derived theoretical framework. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Land Mobile Satellite Systems (LMSS) generally differ from other terrestrial wireless systems. The LMSS exhibit unique characteristics with regard to the physical layer, interference scenarios, channel impairements, propagation delay, link characteristics, service coverage, user and satellite mobility etc. Terrestrial wireless systems have employed the spatial diversity or MIMO (Multiple Input Multiple Output) technique in addressing the problem of providing uninterrupted service delivery to all mobile users especially in places where non-Line-of-Sight (NLoS) condition is prevalent (e.g. urban and suburban environments). For the LMSS, cooperative diversity has been proposed as a valuable alternative to the spatial diversity technique since it does not require the deployment of additional antennas in order to mitigate the fading effects. The basis of cooperative diversity is to have a group of mobile terminals sharing their antennas in order to generate a “virtual” multiple antenna, thus obtaining the same effects as the conventional MIMO system. However, the available cooperative diversity schemes as employed are based on outdated channel quality information (CQI) which is impracticable for LMSS due to its peculiar characteristics and its particularly long propagation delay. The key objective of this work is therefore to develop a cooperative diversity technology model which is most appropriate for LMSS and also adequately mitigates the outdated CQI challenge. To achieve the objective, the feasibility of cooperative diversity for LMSS was first analyzed by employing an appropriate LMSS channel model. Then, a novel Predictive Relay Selection (PRS) cooperative diversity scheme for LMSS was developed which adequately captured the LMSS architecture. The PRS cooperative scheme developed employed prediction algorithms, namely linear prediction and pattern-matching prediction algorithms in determining the future CQI of the available relay terminals before choosing the most appropriate relay for cooperation. The performance of the PRS cooperative diversity scheme in terms of average output SNR, outage probability, average channel capacity and bit error probability were simulated, then numerically analyzed. The results of the PRS cooperative diversity model for LMSS developed not only showed the gains resulting from introducing cooperative techniques in satellite communications but also showed improvement over other cooperative techniques that based their relay selection cooperation on channels with outdated quality information (CQI). Finally, a comparison between the results obtained from the various predictive models considered was carried out and the best prediction model was recommended for the PRS cooperation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

The transmission media, that is, the atmosphere, through which terrestrial and satellite signals traverse, is irregular. Thus, one requires proper knowledge on how variations in atmospheric refractive conditions will affect the optimal performance of terrestrial and satellite links. Under clear-air conditions, atmospheric changes will mainly involve variations in atmospheric pressure, relative humidity and temperature, which are the key to defining the way signals are refracted as they travel from the transmitter to the receiver. Accurate knowledge of these variations can be acquired through proper modeling, characterization and mapping of these three atmospheric quantities, in terms of the refractive index, refractivity gradient or the effective earth radius factor (k-factor). In this dissertation, both parametric and non-parametric modeling and characterizing, interpolation and mapping of the k-factor for South Africa is done. Median (k50%) and effective (k99.9%) k-factor values are the ones that determine antenna heights in line of sight (LOS) terrestrial microwave links. Thus, the accurate determination of the two k-factor values is critical for the proper design of LOS links by ensuring that adequate path clearance is achieved, hence steering clear of all obstacles along the radio path. Thus, this study is critical for the proper design of LOS links in South Africa. One parametric method (curve fitting) and one non-parametric method (kernel density estimation) are used to develop three-year annual and seasonal models of the k-factor for seven locations in South Africa. The integral of square error (ISE) is used to optimize the model formulations obtained in both cases. The models are developed using k-factor statistics processed from radiosonde measurements obtained from the South African Weather Service (SAWS) for a three year period (2007-2009). Since the data obtained at the seven locations is scattered, three different interpolation techniques are then explored to extend the three-year annual and seasonal discrete measured k-factor values for the seven locations studied to cover the rest of the country, and the results of the interpolation are then presented in the form of contour maps. The techniques used for the interpolation are kriging, inverse distance weighting (IDW) and radial basis functions (RBFs). The mean absolute error (MAE) and the root mean square error (RMSE) are the metrics used to compare the performance of the different interpolation techniques used. The method that produces the least error is deemed to be the best, and its interpolation results are the ones used for developing the contour maps of the k-factor. / M. Sc. Eng. University of KwaZulu-Natal, Durban 2013.

Thesis (MScIng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Primary health care telemedicine services require the acquisition and transmission of patient data including high quality still and video images via telecommunication networks. The objective of this thesis is to investigate the implementation of a generalpurpose medical camera as an alternative to the complex and costly CCD based cameras generally in use at present. The design is based on FillFactory’s SXGA (1280 ×1024) CMOS image sensor. A low-cost Altera Cyclone FPGA is used for signal interfacing, filtering and colour processing to enhance image quality. A Cypress USB 2.0 interface chip is employed to isochronously transfer video data up to a maximum rate of 23.04 MBytes per second to the PC. A detailed design and video image results are presented and discussed; however the camera will need repackaging and an approval for medical application by medical specialists and concerned bodies before releasing it as full-fledged product. / AFRIKAANSE OPSOMMING: Primêre gesondheidssorg telemedisyne dienste moet hoëkwaliteit televisiebeelde van hul pasiënte verkry deur van telekommunikasienetwerke gebruik te maak. Die doel van hierdie tesis is om die toepassing van n meerdoelige mediese kamera te ondersoek as n alternatief tot duur, komplekse CCD-gebaseerde kameras wat huidiglik gebruik word. Die ontwerp is gebaseer op n hoëkwaliteit CMOS beeldsensor. n Goedkoop Altera Cyclone FPGA word gebruik vir seinkoppelvlak, filtering en kleurprosessering om die kwaliteit van die beeld te verhoog. n Hoëspoed USB 2.0 poort word gebruik om die data teen die nodige spoed te versend. n Gedetailleerde ontwerp, en die beeldresultate word voorgelê en bespreek. Die kamera moet egter eers deur mediese spesialiste en relevante beheerliggame goedgekeur word voordat dit as n volledige produk vrygestel kan word.

Thesis (MScIng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Both coaxial probe and waveguide (WG) measurement systems for electric and magnetic material property extraction were investigated. These measurement techniques were used to determine electrical properties of an inhomogeneous rock sample in its solid and crushed states. A lumped element model of the probe was used and permittivity was determined by the inversion algorithm developed by Stuchly and Stuchly. To support this technique it was compared to a full wave inversion algorithm and referenced to properties of the same samples but determined by a resonant cavity technique. The Nicholson, Ross and Weir inversion algorithm was used to determine material properties from WG measurements. As a reference, the same techniques were applied to a well defined material. It was found that neither of the measurement techniques could measure low loss factors or conductive materials and literature values were used in these cases. Various simulation models of the multiphase ore in both its solid and crushed states are presented. These models were utilised in finite-difference time-domain (FDTD) simulations of different microwave (MW) cavities. Simulation and experimental S-parameter comparisons are presented. The level of accuracy achieved varies as a function of the geometrical representation and material properties. After an S-parameter comparison with simulation results it was concluded that the electrical properties of both the solid and crushed rocks have been well determined for MW cavity design. Predicted and measured field distributions in cavities were also compared and it is shown that accurate models of multiphase materials become especially important in the determination of field distributions in and around different rock phases. Recommendations for the suggested material property determination and verification processes are presented. A specific application of this work is in the field of microwave assisted comminution. / AFRIKAANSE OPSOMMING: ’n Koaksiale probe en golfgeleier (WG) stelsels vir die bepaling van materiaal eienskappe (elektries en magneties) word gebruik met die doel om ’n nie-homogene rotsmonster te karakteriseer. Die ekstraksie algoritme van Stuchly en Stuchly word gebruik om die materiaal eienskappe te bepaal vanaf die gemete S11-parameter. Hierdie ekstraksie metode word vergelyk met ’n vol golf ekstraksie van permitiwiteit vanaf dieselfde gemete data. Beide die ekstraksie metodes word dan vergelyk met resonante holte meetings van dieselfde materiale. Die Nicholson, Ross en Weir ekstraksie algoritme word toegepas op meetings wat gedoen is deur die golfgeleier stelsel. As ’n verwysing word dieselfde tegnieke toegepas op ’n bekende materiaal en daar is gevind dit stem goed ooreen behalwe dat nie een van die twee meet tegnieke lae verlies faktore kan meet nie. Verder kan nie een van die twee sisteme geleidende materiale meet nie. Vir sulke gevalle is waardes nageslaan. Verskeie simulasiemodelle van die rots word voorgestel vir beide soliede en vergruisde monsters. Hierdie modelle word gebruik in FDTD simulasies van verskeie mikrogolftoevoegers met die oog om ’n vergelyking te tref tussen gesimuleerde en gemete S-parameters. Verskillende vlakke van akkuraatheid is bereik en is ’n funksie van die geometrie en die materiaaleienskappe van die model. Nadat gemete en gesimuleerde S-parameters vergelyk is, is gevind dat die materiaal eienskappe van beide die soliede en vergruisde rots monsters goed bepaal is vir mikrogo lf toevoeger ontwerp. Voorspelde en gemete veldverspreidings word ook vergelyk en dit is veral hierso van belang om ’n realistiese model van die nie-homogene monster te gebruik. Sekere voorstelle word gemaak om die verskillende aspekte van die meet van ma teriaaleienskappe en simulasiemodelle te kan verfyn. ’n Spesifieke toepassing van hierdie werk is in mikrogolf ondersteunde skeiding van minerale en erts.

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: This project investigates the improvement of an existing radar system by means of currently available technologies and signal processing techniques. Upgrades are aimed to improve the system's speci cations with focus on range resolution. Pulse compression and Doppler processing techniques are used to accomplish the improvement in range resolution. The use of pulse compression however resulted in numerous modi cations to the RF sub-system required by the introduction of Direct Digital Synthesizer modules. A full replacement of the existing signal processor with a Doppler processing based signal processor implemented on a single programmable rmware device was designed. Certain sections of this signal processor were implemented and tested. Pulse compression was successfully implemented and tested in both the transceiver and signals processor sections. / AFRIKAANSE OPSOMMING: Hierdie projek ondersoek die verbetering van 'n bestaande radar stelsel deur gebruik te maak van huidige tegnologie en seinverwerking tegnieke. Aanpasings is gemik om die radarstelselspesi kasies te verbeter met die fokus op afstandsresolusie. Pulskompressie en Doppler- lter tegnieke is gebruik om 'n verbetering te maak aan die afstandsresolusie van die stelsel. Die gebruik van pulskompressie het 'n groot aantal veranderings aan die RF-stelsel genoodsaak a.g.v. die gebruik van Direkte Digitale Sintetiseerder modules. Die huidige radarseinverwerker is volledig vervang met 'n Doppler gebaseerde verwerker. Hierdie verwerker is volledig ontwerp op 'n enkele programmeerbare fermatuureenheid maar slegs sekere gedeeltes is getoets. Pulskompressie is suksesvol toegepas en getoets in beide die RF-stelsel en in die gedeeltes van die radarseinverwerker wat getoets is.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Very Large Scale Integration (VLSI) of the Rapid Single Flux Quantum (RSFQ) superconducting logic family is researched. Insight into the design methodologies used for large-scale digital systems and related logistics are reviewed. A brief overview of basic RSFQ logic gates with in mind their application in a cell based layout scheme suited for RSFQ is given. A standard cell model is then proposed, incorporating these cells, on which, a library of low temperature superconducting (L TS) cells are laid out. Research is made into computer techniques for storing and manipulating large-scale circuit netlists. On this base, a method of technology mapping Boolean circuits to an RSFQ equivalent is achieved. Placements on-chip are made, optimized for minimum net length, routed and exported to a popular electronic mask format. Finally, the convergent technology fields of solid state cooling and high-temperature superconducting electronics (HTS) are investigated. This leads to a proposal for a low profile, low cost, HTS cryopackaging concept. / AFRIKAANSE OPSOMMING: Grootskaalse integrasie (VLSI) van die "Rapid Single Flux Quantum" (RSFQ) supergeleidende familie van logiese hekke word uiteengesit. Insig in die ontwerpmetodes vir grootskaaIse digitale stelsels en verwante aspekte word ondersoek. 'n Kort oorsig van basiese RSFQ logiese hekke word gegee, met hulle toepassing in 'n uitlegskema wat geskik is vir RSFQ. 'n Standaard sel model, wat bogenoemde selle insluit, word voorgestel en 'n selbiblioteek word uitgele vir lae temperatuur supergeleidende bane. Ondersoek word ingestel na die manipulasie van die beskrywing van elektroniese bane en 'n manier om logiese Boolese baanbeskrywings om te skakel na fisiese RSFQ bane. Die fisiese plasing van selle word bespreek ten einde die verbindingslengte tussen selle te minimeer. Die finale uitleg word omgeskakel na 'n staandaard elektroniese formaat vir baanuitlegte. Die konvergerende tegnologievelde van "soliede toestand" verkoeling en hoe-temperatuur supergeleidende elektroniese bane word bespreek. Ten slotte word 'n nuwe tipe, lae profiel en lae koste kriogeniese verpakking voorgestel.

Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The aim of this thesis is the analysis and design of a broadband PIN diode switch. Pin diode switches are gaining popularity in RF and microwave applications today. This is due to their excellent switching and power handling capabilities, reliability, low cost and small size. An analysis and design procedure for broadband PIN diode switch design, using the series, shunt and compound topologies respectively, is presented. In order to do a proper switch design, accurate practical models for the components are required. Parameter extraction therefore formed an important consideration for this study. A parameter extraction procedure is presented, which enables the designer to very accurately extract the required models for the components in the environment they operate in. The designer can then do a proper design to ensure that the switch response when measured, closely corresponds to that simulated. A compound configuration switch was designed, built and measured to confirm the validity of the design procedure. The results illustrate that if the extracted models of the components are integrated into the design, the measured and simulated response compare remarkably well. / AFRIKAANSE OPSOMMING: Die doel van die tesis is die analise en ontwerp van 'n wyeband PIN diode skakelaar. PIN diode skakelaars is besig om meer populariteit te verwerf in hedendaagse RF en mikrogolf toepassings. Dit is as gevolg van die diode se goeie skakel- en drywing hantering vermoëns, betroubaarheid, lae koste en klein fisiese dimensies. 'n Analise en ontwerpsprosedure vir wye band PIN diode skakelaars in die serie, parallel en saamgestelde topologieë word getoon. Om 'n deeglike skakelaar ontwerp te doen, word akkurate en praktiese modele van die komponente benodig. Parameter ekstraksie was daarom 'n groot oorweging vir hierdie studie. 'n Metode om parameters te onttrek word getoon wat die ontwerper in staat stelom akkurate modelle van komponente te onttrek, in die omgewing waarin hulle gebruik word. Die ontwerper kan dan 'n deeglike ontwerp doen wat as dit gemeet word.. die gemete en gesimuleerde resultate goed salooreenstem. 'n Saamgestelde topologie skakelaar is ontwerp, gebou en gemeet om die ontwerpsprosedure te verifieer. Die resultate toon dat as die modelle wat onttrek is, gebruik word in die ontwerp, dan stem die gemete en gesimuleerde resultate baie goed ooreen.