La radio cognitive (CR) est une radio entièrement reconfigurable qui permet de changer intelligemment ses paramètres de communication en réponse à l’activité des autres réseaux radios et demandes d’utilisateur. L’objectif ultime de la CR est de permettre à l’utilisateur secondaire (SU) d’utiliser la ressource de spectre disponible sans interférer sur l’utilisateur primaire (PU) en utilisant des trous de spectre. Par conséquent, la détection du PU est l’un des défis principaux dans le développement de la CR. Par rapport aux systèmes conventionnels de communication sans fil, le système CR introduit de nouveaux problèmes d’allocation de ressource (RA) en raison de l’interférence des canaux adjacents utilisés par le SU et le PU. Dans le contexte de la CR, la plupart des efforts ont été menés sur les systèmes de CR basés sur le multiplexage par division de fréquences orthogonales (OFDM). Toutefois, la technique de l’OFDM montre quelques points faibles dans l’application à cause des remontées significatives du spectre. Les modulations multiporteuses à base de bancs de filtre (FBMC) ont été récemment proposées pour des applications de CR. Dans cette thèse, trois points importants pour le développement d’un système de CR basé sur le FBMC sont discutés.Les trois points principaux peuvent être résumés ainsi: nous examinons premièrement les problèmes de détection de spectre des signaux OFDM et FBMC en employant le détecteur de signature de cyclostationnarité (CS). En outre, nous proposons une architecture de détection multi-bande basée sur le banc de filtre polyphasé (PFB), et montrons son avantage; deuxièmement, la comparaison entre l’OFDM et le FBMC du point de vue de l’efficacité spectrale est discutée; et enfin, nous proposons un algorithme stratégique d’allocation de ressource pour les systèmes cognitifs multi-cellulaires et multi-utilisateurs.Les algorithmes proposés dans cette thèse ont été testés par simulation. Les résultats numériques prouvent que le FBMC, par opposition à l’OFDM, pourrait réaliser une efficacité spectrale plus élevée et offre un avantage attrayant dans la détection de spectre. Les contributions de cette thèse ont accru l’intérêt d’appliquer FBMC dans les systèmes de CR à l’avenir. / Cognitive Radio (CR) is a fully reconfigurable radio that can intelligently change its communicationvariables in response to network and user demands. The ultimate goal of CR is to allowthe Secondary User (SU) to utilize the available spectrum resource on a non-interfering basis to thePrimary User (PU) by sensing the existence of spectrum holes. Therefore, the detection of PU isone of the main challenges in the development of the CR technology. Moreover, compared to conventionalwireless communication systems, CR system poses new challenges to Resource Allocation(RA) problems because of the Cross-Channel Interference (CCI) from the adjacent channels used bySU to PU. In the CR context, most past efforts have been spent on Orthogonal Frequency DivisionMultiplexing (OFDM) based CR systems. However, OFDM technique exhibits some shortcomingsin application due to its significant spectrum leakage. Filter Bank based Multi-Carrier (FBMC), asanother promising Multi-Carrier Modulation (MCM) candidate, has been recently proposed for CRapplications. In this dissertation, three important issues in developing a FBMC based CR system arediscussed.The three prime issues can be summarized: we firstly survey the spectrum sensing problemsof OFDM and FBMC signals by using Cyclostationary Signature (CS) detector. Furthermore, wepropose a Polyphase Filter Bank (PFB) based multi-band sensing architecture, and argue for its advantage;secondly, the comparison of OFDM and FBMC from the spectral efficiency point of viewis discussed; and lastly, our emphasis is placed on the strategic resource allocation algorithms fornon-cooperative multi-cell CR systems.The overall proposed algorithms have been verified by simulation. Numerical results show thatFBMC, as opposed to OFDM, could achieve higher spectrum efficiency and attractive benefit inspectrum sensing. The contributions of this dissertation have heighten the interest in applying FBMCin the future CR systems.

Multinational enterprises are continuously in search of investment opportunities to grow their businesses. For over two decades South Africa, being one of the economic powerhouses of Africa, has been one such target for global investors. A company planning to invest in South Africa will attempt to identify the most appropriate way to do so, for tax and non-tax reasons. However, tax consequences are one of the main factors influencing the decision of an investor. While certain companies choose to invest directly into the target country, the majority choose to set up a holding company outside of the investor country. Such a company is known as an intermediary holding company and is defined as a company which is interposed between a shareholder and its foreign subsidiary. The main purpose of this study is to investigate the best manner, for tax purposes, in which a foreign company would invest into South Africa, either directly or indirectly through an intermediary holding company. Should the intermediary holding company option be selected, the company will then need to select the country in which to base its intermediary holding company. Tax havens are commonly used as a base for intermediary holding companies, however, these may not be the most advantageous option in all cases. Literature on intermediary holding companies and tax havens is reviewed and thereafter the study analyses and compares the tax efficiency of a hypothetical UK company investing into South Africa using different options. The options available to the UK Company which are compared, include investing directly into South Africa or investing indirectly through an intermediary holding company based in either Cyprus, Mauritius or the Netherlands, all of which are commonly used as bases for intermediary holding companies. The comparative study on the different intermediary holding company options is performed based on the domestic tax laws of each country as well as the effects of the double tax agreements in force between these countries and other tax jurisdictions. Thereafter, the most tax efficient intermediary holding company option is compared to the tax efficiency of direct investment by the UK Company and a conclusion is reached on which is the best manner for such a company to invest into South Africa, for tax purposes. AFRIKAANS : Multi-nasionale ondernemings is voortdurend op soek na nuwe beleggingsgeleenthede ten einde besigheidsgroei te bewerkstelling. Internasionale beleggers sien Suid-Afrika nou al vir meer as twee dekades as ʼn toetreepunt tot geleenthede in Afrika, vanweë Suid-Afrika se status as een van die ekonomiese reuse in Afrika. Maatskappye wat beplan om in Suid-Afrika te belê sal ondersoek doen om die beste moontlike beleggings manier te vind. Talle besigheidsredes, waarvan belastingimplikasies een van die hoofoorwegings is, sal die faktore wees wat ʼn potensiële belegger se besluitneming beïnvloed. Terwyl sommige maatskappye verkies om direk in die beleggingsland te belê sal die meeste maatskappye eerder in ʼn houermaatskappy buite die beleggingsland belê. So ʼn maatskappy staan bekend as ʼn intermediêre houer maatskappy en word gedefinieer as ʼn “tussenganger” maatskappy wat as geleibuis optree tussen die aandeelhouer en die buitelandse filiaal. Die hoofdoel van hierdie studie is om ondersoek in te stel na die beste metode, vanuit ʼn belastingoogpunt, vir ʼn buitelandse maatskappy om in Suid-Afrika te belê. Dit kan óf direk óf indirek deur middel van ʼn intermediêre houer maatskappy gedoen word. Indien die intermediêre houer maatskappy opsie gekies word, moet die maatskappy ook die land kies waarin die intermediêre houer maatskappy opgerig gaan word. Lande wat bekend is as belastingtoevlugsoorde word dikwels gekies om intermediêre houer maatskappye op te rig. Dit is egter nie in alle gevalle die mees voordeligste metode nie. Literatuur oor intermediêre houer maatskappye en belastingtoevlugsoorde word nagevors, waarna hierdie studie die belastingeffektiwiteit van ʼn hipotetiese Britse maatskappy, wat in Suid-Afrika belê, ondersoek deur gebruik te maak van verskillende opsies. Die opsies wat beskikbaar is en ondersoek sal word sluit in, direkte belegging in Suid-Afrika en belegging deur van ʼn intermediêre houer maatskappy gebruik te maak in Cyprus, Mauritius of Nederland. Al die vooraf genoemde lande is algemeen bekend daarvoor dat dit gebruik word om intermediêre houer maatskappye op te rig. Die verskillende intermediêre houer maatskappy opsies word met mekaar vergelyk, deur die belastingimplikasies van plaaslike belastingwetgewing van elke land, asook enige dubbele belastingooreenkomste van krag tussen hierdie lande en ander regsgebiede, te oorweeg. Die mees effektiewe intermediêre houer maatskappy opsie word dan vergelyk met die belastingeffektiwiteit van direkte belegging deur die Britse maatskappy. ʼn Gevolgtrekking word gemaak oor die metode wat die mees effektiefste belastinggevolge inhou vir ‘n Britse maatskappy wat in Suid-Afrika belê. / Dissertation (MCom)--University of Pretoria, 2012. / Taxation / unrestricted

The falling cost of batteries, along with an increasing need to cut emissions, has spurred significant interest in the electrification of vehicles. In addition, as semiconductor devices have evolved, the research for electric vehicles with higher battery voltage has increased. The traction inverter is an important part of the electric power train and can account for a substantial portion of the drive train’s losses. This thesis therefore models, simulates, and studies the losses for a convectional Two-Level (2L) inverter and a Three-Level T-Type (3LT) inverter utilizing Silicon Carbide (SiC) MOSFETs and compares the two inverter topologies in terms of efficiency. The rated power of the inverters is 120 kW at a DC voltage of 800 V. The theoretical basis of SiC MOSFET and its reverse conduction, operation of 2L and 3LT inverter topologies, and Space Vector Pulse Width Modulation (SVPWM) technique are introduced in the initial part of the thesis. To estimate switching and conduction losses, Simulink is used to model and simulate an electric drive system. These estimated losses are then utilized to develop efficiency maps for both topologies over the complete speed-torque range. Based on the efficiency comparison, the 3LT topology outperforms the 2L topology for any requested torque in the medium to the high-speed range, which is typical of highway driving. In the low-speed, high-torque region, which is typical of city driving, the 2L topology is superior. The efficiency of each topology is affected by switching frequency, device junction temperature, and DC-link voltage. However, the comparison reveals that the maximum average difference in efficiency is 0.35%, with the 3LT topology being superior. Finally, the efficiency differences between the two inverter topologies are minimal. As a result, it may be concluded that the two topologies perform similarly. Thus, it can be inferred that comparing the efficiency of the two topologies should not be the sole criterion for selecting which topology should be used for the electric drive. / Den sjunkande kostnaden för batterier, tillsammans med ett ökande behov av att minska utsläppen, har lett till ett stort intresse för elektrifiering av fordon. Dessutom, har utvecklingen av halvledare lett till en ökning inom forskningen av elfordon med högre batterispänning. Traktionsomriktaren är en viktig del av den elektriska drivlinan och kan stå för en stor del av de totala förlusterna i drivlinan. I denna rapport modelleras, simuleras och studeras därför förlusterna i en konventionell omriktare med två nivåer (2L) och en T-typ omriktare med tre nivåer (3LT). Båda topologierna använder kiselkarbid (SiC) MOSFETs i jämförelsen av resultaten med avseende på verkningsgrad. Inverterarnas nominella effekt är 120 kW vid en likspänning på 800 V. Den teoretiska grunden för SiC MOSFET och hur de fungerar, hur 2L- och 3LT-inverterstopologierna fungerar samt tekniken för Space Vector Pulse Width Modulation (SVPWM) presenteras i rapporten. För att uppskatta switch- och ledningsförluster används Simulink för att modellera och simulera det elektriska drivsystemet. De uppskattade förlusterna används sedan för att utveckla verkningsgradskartor för de båda topologierna över hela det operativa området. Baserat på verkningsgradsjämförelsen mellan topologierna så presterar 3LT-topologin bättre än 2L-topologin i driftspunkter i medelhöga till höga hastigheter, vilket är typiskt för motorvägskörning. Vid låga hastigheter med högt vridmoment, vilket är typiskt för stadskörning, är 2L-topologin bättre. Verkningsgraden för de båda topologierna påverkas av switchfrekvensen, halvledarens temperatur samt DC-länkspänning. Jämförelsen visar dock att den största genomsnittliga skillnaden i verkningsgrad mellan de två topologierna är 0,35%, där 3LT-topologin är bättre. Sammanfattningsvis så är skillnaderna i verkningsgrad mellan de två topologierna minimala, vilket innebär att de båda topologierna har liknande prestanda med avseende på verkningsgrad. Man bör därför inte bara ha verkningsgrad som det enda kriteriet vid val av topologi för elektriska drivlinor.