Quality-of-service (QoS) guarantees have become critically important for the transmission of real-time multimedia traffic in next generation mobile wireless networks. The aim of this dissertation is to investigate the cross-layer design for support of delay bound QoS guarantees over fading channels. Providing diverse QoS guarantees presents a challenge due to the time-varying fading nature of wireless channels. Existing physical layer modelling is inadequate in supporting real time QoS metrics such as delay, hence adaptive techniques need to be extended to the upper-protocol layers. The first objective of this dissertation is to introduce a cross-layer design framework which investigates the impact of the physical layer on the data link delay bound QoS performance. At the physical layer, adaptive modulation and coding (AMC) is utilized for transmission over block fading channels. At the data link layer, the effective capacity approach is used to model the delay bound QoS performance subject to physical layer variations. The effects of varying physical layer parameters, such as average signal-to-noise ratio (SNR), the fading parameter for the kagami- model, and target packet-error rate (PER), on the analytical delay bound performance are investigated and then validated by the simulation of a queuing system. Due to the cross-layer design framework, the system’s throughput has a significant impact on bounded delay at the data link layer. The switching levels of the conventional AMC scheme used in the first objective were fixed, subject to a target PER. However, fixed switching levels results in the system’s throughput limiting the delay bound performance. The second objective of this dissertation is to optimize the switching levels of the AMC scheme employed at the physical layer, by maximizing the average throughput, while maintaining the target PER constraint. The analytical and simulated results show that by optimizing the switching levels, a superior delay bound performance is achieved, when compared to the deterministic switching levels of the conventional AMC scheme used in the first objective. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Two non-destructive methods of extracting audio from Edison phonographic cylinders were investigated. A recording device with high accuracy positioning was designed and manufactured. A microscopic image method was investigated first. Surface images of the cylinder were obtained using a webcamera. An audio signal was then extracted from the width modulation. Results were not pleasing as echoes caused by intergroove modulation were perceptable. The audio also lacked resolution. The true modulation of the audio is not embedded in the width, but in the depth of the groove. The second audio extraction method involved using a laser pick-up from a compact disc player to measure the depth of the groove. Three laser recording methods were investigated. The first was forward recording, that measured the depth modulation in the recording direction of the groove. The second method, backward recording, was identical to forward recording with the mechanical system moving in reverse. Four recordings from different positions in the groove were combined to create an audio signal. This combination of recordings showed a substantial improvement in the signal-to-noise ratio. A third recording method, transverse recording, that measured the whole depth profile of the groove was also investigated. The groove profile was then processed to an audio signal. A manual audio restoration program was written to replace visible sections of distorted data with better interpolations. Two speech enhancement methods were investigated, the first being the most commonly used speech enhancement method for digital audio restoration, Short-Time Spectral Attenuation (STSA). The second method is based on linear predictive coefficient (LPC) estimation of short-time frames. The two methods were evaluated by means of listening tests. The LPC enhancement method was preferred because it enhanced the intelligibility of the speech. / AFRIKAANSE OPSOMMING: Twee nie-destruktiewe metodes om klank van Edison-fonograafsilinders te onttrek, is ondersoek. 'n Opneemtoestel, wat die silinders met baie hoë akkuraatheid posisioneer, IS ontwerp en vervaardig. 'n Mikroskopiese beeldrnetode IS as eerste klankonttrekkingsmetode ondersoek. Mikroskopiese beelde is met 'n webkamera van die silinderoppervlak geneem. Klank is vanuit die wydtemodulasie sigbaar in die beelde onttrek. Resultate was nie bevredigend nie weens groefintermodulasie-eggo's en 'n tekort aan resolusie. Die ware modulasie van die klank is nie in die wydte van die groefie gegraveer nie, maar in die diepte. Die tweede klankonttrekkingsmetode gebruik 'n aangepaste lasersensor van 'n CD-speler om die dieptemodulasie van die groefie te meet. Drie laseropneemmetodes is ondersoek. Die eerste is voorwaartse opname, wat die dieptemodulasie in die opneemrigting van die groefie meet. 'n Tweede opneemmetode, truwaartse opname, is identies aan voorwaartse opname, behalwe dat die meganiese stelsel in trurat beweeg. Vier opnames vanuit verskillende posisies in die groefbreedte is gekombineer om 'n klanksein te vorm. Die kombinasie van vier opnames toon 'n beduidende verbetering op die sein-tot-ruis-verhouding. Dit het aanleiding gegee tot die derde opneemmetode, dwarsskandering, wat die hele profiel van die groef meet. Die groefprofiel word dan verwerk tot 'n klanksein. 'n Handoudiorestourasieprogram is geskryf om sigbare verwringing in die klanksein met beter interpolasies te vervang. Twee spraakverheffingsmetodes is ondersoek. Short- Time Spectral Attenuation (STSA) is die mees gebruikte metode vir oudiorestourasie. 'n Tweede spraakverheffingsmetode wat van 'n lineêre voorspellingskoëffisiëntafskatting (LPC-afskatting) van korttydraampies gebruik maak, is ook toegepas. Die twee metodes is deur luistertoetse teen mekaar opgeweeg. Die LPCmetode is verkies aangesien dit die verstaanbaarheid van die spraak beter behoue laat bly.

Thesis (MScEng)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: This thesis investigates the possible use of NAND flash memory for a mass memory unit on a micro-satellite. The investigation begins with an analysis of NAND flash memory devices including the complexity of the internal circuitry and the occurrence of bad memory sections (bad blocks). Design specifications are produced and various design architectures are discussed and evaluated. Subsequently, a four bus serial access architecture using 16- bit NAND flash devices was chosen to be developed further. A VHDL design was created in order to realise the intended system functionality. The main functions of the design include a sustained write data rate of 24 MB/s, bad block management, multiple image storing, error checking and correction, defective device handling and reading while writing. The design was simulated extensively using NAND flash simulation models. Finally, a demonstration test board was designed and produced. This board includes an FPGA and an array of 16 8-bit NAND flash devices. The board was tested sucessfully and a write data rate of 12 MB/s was achieved along with all the other main functions. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die moontlike gebruik van NAND flash tegnologie as die geheue eenheid van ’n mikrosatelliet. As ’n beginpunt word NAND flash tegnologie ondersoek in terme van die kompleksiteit van interne stroombane en die voorkoms van defektiewe geheuesegmente. Daarna word ontwerpspesifikasies voortgebring en verskillende ontwerpsmoontlikhede met mekaar vergelyk. Vanuit hierdie oorwegings is daar besluit om die oplossing te implementeer met ’n vier-bus seri¨ele struktuur bestaande uit 16-bis NAND flash toestelle. Om die ontwerpspesifikasies te realiseer, is ’n VHDL stelsel geskep. Die belangrikste funksies van hierdie stelsel is ’n konstante skryftempo van 24 MB/s, die bestuur van defektiewe geheuesegmente, die stoor van meer as een beeld, foutopsporing en -herstel, optimale werking in die geval van defektiewe geheuetoestelle en laastens, die gelyktydige lees en skryf van data. Die stelsel is breedvoerig getoets met NAND flash simulasiemodelle. Ten slotte is ’n fisiese demonstrasiebord, bestaande uit ’n FPGA en 16 8-bis NAND flash toestelle, ontwerp en gebou. Fisiese metings was ’n sukses. ’n Skryftempo van 12 MB/s is gehaal, tesame met die korrekte werking van die ander hooffunksies.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Recent advances in semiconductor device development pushed a large number of network devices onto the market. These devices can solve network problems more effectively and economically than ever before. Network planners need tools to analyse and implement such devices to help solve the largest network problem in South Africa: voltage regulation. Rural networks experience the majority of voltage-regulation problems in South Africa. The networks are long sub-transmission and reticulation networks and are modelled by two generic networks, namely a radial network and a two-source ring network. The equations describing voltage regulation for the generic networks are developed and implemented in PSAT, a software analysis tool. The voltage regulation for two case studies that represent the two generic networks are analysed. Four generic network devices are defined and various control methods for these devices are developed to solve the network problem. The aim of PSAT is to help the network planner to quickly evaluate a number of possible solutions and to choose the best solution for further studies. This is demonstrated with the aid of the case studies. PSAT provides a sturdy platform on which future developments, such as stability analyses, can be built. However, PSAT can already function as a stand-alone analysis tool to solve voltage regulation as a network problem. / AFRIKAANSE OPSOMMING: Onlangse vooruitgang in halfgeleier ontwikkeling het 'n groot aantal netwerktoestelle op die mark geplaas. Hierdie toestelle kan netwerk probleme doeltreffender en meer ekonomies oplos as ooit vantevore. 'n Behoefte aan 'n pakket wat netwerkbeplanners in staat stelom die netwerktoestelle te analiseer, is geïdentifiseer. So 'n pakket sal hulle help om die vernaamste netwerkprobleem in Suid-Afrika, nl. spanningsregulasie, op te los. Die oorgrote meerderheid spanningsregulasie probleme word op die platteland ondervind. Plattelandse netwerke word gekenmerk deur lang sub-transmissie en retikulasie netwerke. Hierdie netwerke word met behulp van twee generiese netwerke gemodelleer. 'n Radiale netwerk en 'n dubbelbron ringnetwerk word aangewend om enige plattelandse netwerk te analiseer. Vergelykings is vir spanningsanalise ontwikkel en in PSAT, 'n analitiese sagteware pakket, geïmplementeer. Twee gevallestudies is gedoen om die twee netwerke afsonderlik voor te stel en die vergelykings van PSAT te evalueer. Alle netwerktoestelle is in een van vier generiese kategorieë geklassifiseer. Modelle is vir elk van die kategorieë ontwikkel vtr spanningsregulasie analise. Die doel van PSAT is om die netwerk beplanner te help om vinnig en effektief soveel moontlik opsies te ondersoek as oplossings vir 'n spesifieke netwerk probleem. PSAT is reeds 'n alleenstaande pakket wat in die toekoms uitgebrei sal word om na die analise van stabilitietsprobleme te kyk.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Satellites are not all made equal. The large number of possible orbits, desired functionality and budget constraints are but a few of the factors that influence the design of a satellite. Given a particular set of design requirements, a number of designs may meet these requirements. Each of these designs will typically entail a trade-off between a number of (conflicting) parameters, whilst still satisfying the system requirements. The On-Board Computer (OBC) of a satellite, the satellite subsystem primarily responsible for the operational control of a satellite, can consequently be designed in any of a number of different ways. As the factors that influence the flight performance of an OBC differs to those of a terrestrial computer, the OBC design will therefore be significantly different. A high-level overview of the factors that impact OBC design and operation is presented. Improvements to the existing designs are proposed. In conclusion, a number of guidelines for a future OBC design also are given. / AFRIKAANSE OPSOMMING: Elke satelliet het unieke eienskappe wat bepaal word deur onderandere, die teiken wentelbaan, verwagte funksionaliteit en koste oorweegings. Vir 'n spesefieke stelselontwerp bestaan daar 'n aantal moontlike ontwerpe wat aan die stelsel vereistes voldoen. Elk van hierdie ontwerpe sal tipies behels dat verskillende parameters teen mekaar afgespeel word, terwyl die stelsel vereistes steeds aan voldoen word. Die Aanboord Rekenaar (AR) van 'n satelliet, die satelliet substelsel hoofsaaklik verantwoordelik vir die beheer van die satelliet, kan vervolgens uit een van veele moontlike ontwerpe bestaan. Aangesien die faktore wat die werkverrigting van 'n AR beinvloed verskil van die van 'n rekenaar wat op die aard oppervlak gebruik word, sal die AR ontwerp dienooreenkomstig verskil. 'n Hoevlak oorsig van die faktore wat AR ontwerp beinvloed sal gegee word. Verbeteringe wat aan die huidige AR ontwerpe gedoen kan word sal bespreek word. Ter afsluiting sal 'n aantal riglyne vir toekomstige AR ontwerpe gegee word.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Rapid Single Flux Quantum (RSFQ) logic cells are discussed, and new cells developed. The expected yield of every cell is computed through a Monte Carlo analysis, and where necessary these cells are optimized for use in a complex system. A mathematical study of the Josephson junction and SQUIDs (Superconducting Quantum Interference devices) as switching elements precede a discussion on the operation of RSFQ and COSL (Complementary Output Switching Logic.) These logic families are implemented in low temperature niobium technology, and require liquid helium cooling. A 10 GHz oversampling delta modulating analogue-to-digital converter is then designed and constructed using RSFQ and COSL building blocks in a hybrid configuration. The design emphasis is on devising ways to test the operation of RSFQ with limited equipment. Yield analysis procedures on the complex system are discussed, followed by a detailed discussion on the circuit layout and layout problems. Software routines are developed to calculate the required dimensions of layout structures. / AFRIKAANSE OPSOMMING: Rapid Single Flux Quantum (RSFQ) logiese selle word bespreek, en enkele nuwe selle word ontwikkel. Die verwagte opbrengs, of kans dat 'n sel sal werk, word bereken deur 'n Monte Carlo analise. Waar nodig word selle met behulp van die analise verbeter vir gebruik in 'n komplekse stelsel. 'n Wiskundige studie van die Josephson-vlak en SQUIDs (Superconducting Quantum Interference devices) word gevolg deur 'n bespreking oor die werking van RSFQ en COSL (Complementary Output Switching Logic.) Hierdie logiese families word geïmplementeer in laetemperatuur niobiumtegnologie, en vereis vloeibare helium-verkoeling. 'n Deltamodulerende analoog-na-digitale omsetter met 'n intree-monstertempo van 10 GHz word ontwerp en vervaardig met 'n hibriede samestelling van RSFQ en COSL boublokke. Die ontwerp fokus op maniere om die werking van RSFQ teen 10 GHz te kan toets met die beperkte toerusting wat beskikbaar is. Opbrengsanalise op die komplekse stelsel word bespreek, gevolg deur 'n volledige bespreking van die stroombaanuitlegprosedure en uitlegprobleme. Roetines word in sagteware ontwikkel om die nodige dimensies van uitlegstrukture te bereken.

Thesis (MEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: SRMA currently used on the SUNSAT field station is an effective MAC layer protocol but lacks several features. Sufficient support for flexible communication, acknowledgement of individual data packets, simultaneous communication of multiple instances from a higher layer over a single underlying layer, and a robust FTP procedure to transfer large amounts of data are some of the features that the SUNSA T field station should cater for. ORBCOMM, GSM and WAP implementations are discussed. Some features from these implementations that are useful in the LEO communication environment are designed into an additional layer of software. This additional layer, called middleware, is proposed and uses SRMA services to deliver store-and-forward services. It supports high volumes of short transactions and session suspend and resume facilities between the SUNSA T satellite and field station. Keywords: SUNSAT, Communication, Field station, WAP, GSM, ORBCOMM / AFRIKAANSE OPSOMMING: Die SRMA pakketkommunikasie-protokol op SUNSA T se prototipe grondterminaal is voldoende om die oordrag van boodskappe oor die kommunikasieverbinding te reguleer. Dit is onvoldoende om fasiliteite soos kommunikasie van 'n aantal instansies in 'n hoër kommunikasie laag oor 'n enkele laer laag en om 'n robuuste data oordrag protokol vir groot hoeveelhede data van 'n grondterminaal te ondersteun. ORBCOMM, GSM en WAP stelsel toepassings word bespreek. Resultate wat spruit uit die drie toepassings word gebruik om kommunikasie in 'n lae wentelbaan kommunikasie omgewing te bevorder. 'n Bykomende sagteware laag, bekend as middle-ware, word aanbeveel om voorafgenoemde funksionaliteit mee te implimenteer. Die middle-ware gebruik die beskikbare dienste van die SRMA pakketkommunikasie-protokol om toegang te verkry na die kommunikasie kanaal. Sodoende kan hoë volumes kort transaksies, en sessie-stop en hervat fasiliteite 'n werklikheid gemaak word. Sleutelwoord: SUNS AT, Kommunikasie, grondterminaal, WAP, GSM, ORBCOMM

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The use of commercial-off-the-shelf (COTS) components and emerging technologies in satellite systems has become increasingly popular over the past few years. This is mainly due to advances in radiation shielding and system-level reliability improving techniques. The use of a new generation commercial processor in the design of a satellite's on-board computer (OBC) is now considered a feasible option. The aim of this thesis was to evaluate the use of a commercial grade ARM processor in a low earth orbit (LEO) microsatellite on-board computer. The process began with the selection of the most suitable ARM processor for an aBC design. A typical aBC system was developed for the chosen processor, in order to test its functionality and performance in anOBC design. / AFRIKAANSE OPSOMMING: Die afgelope paar jaar het die gebruik van gewone kommersiële komponente en die nuutste tegnologie in satelliet stelsels heelwat toegeneem. Dit kan grootliks toeskryf word aan die vordering in bestralings afskerming en stelselvlak betroubaarheid tegnieke. Die gebruik van 'n nuwe generasie kommersiële verwerker in die ontwerp van 'n satellite aanboord rekenaar (AR) is nou prakties uitvoerbaar. Die doel van hierdie tesis was om die gebruik van 'n ARM verwerker in 'n lae aardwentelbaan mikrosatelliet aanboord rekenaar te evalueer. Eerstens moes die mees geskikte kommersiële ARM verwerker vir 'n AR ontwerp gevind word. Daarna is 'n tipiese AR stelselontwikkel om die verwerker se funksionaliteit en werkverrigting te toets.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The aim of this thesis is to investigate the implementation of a high-speed serial bus based on the IEEE Std 1394-1995 specification for use in a microsatellite. Earth observation microsatellites carry imagers (or cameras) that take photographs of the earth. Each photograph generates a large volume of digital data that has to be transferred to either a storage device, a RF transmission unit or a video processing device. Traditionally, the connection between such systems were dedicated serial bus systems that were custom designed for just that purpose. This thesis will investigate the the implementation of a generic alternative to such a custom serial bus. The IEEE 1394 serial bus will allow many devices and subsystems to be connected to the serial bus and will allow these different subsystems to exchange data between each other. As an example implementation, a real-time video link between two points using the IEEE 1394 serial bus will be developed. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om ondersoek in te stel na die bou van 'n hoëspoed seriebus vir gebruik in 'n mikrosatelliet gebaseer is op die IEEE Std 1394-1995 spesifikasie. Aardobservasie-mikrosatelliete bevat kameras wat fotos van die aarde neem. Elke foto genereer groot volumes digitale data wat na óf 'n massastoor, óf 'n RF-sender, óf 'n video-verwerkingseenheid gestuur word. Tradisioneel is elkeen van hierdie verbindings met 'n toegewyde seriebus gedoen wat spesiaal vir daardie doel gemaak is. Hierdie tesis het dit ten doelom ondersoek in te stel na 'n generiese alternatief vir hierdie toegewyde seriële busse. Die IEEE 1394 seriebus sal toelaat dat verskeie eenhede en substelsels aan mekaar gekoppel kan word en dat hulle data tussen mekaar kan uitruil. Ter demonstrasie sal 'n intydse videoskakel ontwerp word wat die IEEE 1394 seriebus gebruik om data tussen twee punte oor te dra.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This thesis investigates the viability of implementing the AX.25 protocol in Java, for satellite applications. The AX.25 protocol forms part of the Communications subsystem of a micro-satellite. It describes the implementation of a standard packet-radio link-layer communication protocol in Java, for future use on satellite on-board computers, allowing amongst other things, a reliable communications platform. An investigation into factors that make AX.25 preferable over other communication protocols, as well as advantages of Java as a language used in the implementation, is made. The design of the implementation is described. Finally, efficiency of the Java implementation is evaluated and optimizations identified and recommended. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die lewensvatbaarheid van 'n Java implementering van die AX.25 protokol vir satelliet toepassings. AX.25 is deel van die kommunikasie stelsel van 'n mikro-satelliet. Dit beskryf die implementering van 'n standaard radio data kommunikasie intervlak in Java vir die toekomstige gebruik op die aanboord-rekenaarstelsels van satelliete. Hierdie intervlak bied, insluitende ander eienskappe, 'n betroubare kommunikasie platform. In Deeglike ondersoek na die faktore wat AX.25 meer aanloklik maak vir satellite toepassings is gemaak, asook hoe 'n Java implementering vergelyk met ander beskikbare tegnologie. Die geskiktheid van Java vir die implementering word ook bespeek in die lig van evaluerings wat gedoen is op die finale protokol.