Channel diversity techniques are effective ways to combat channel fading and noise in communication systems. In this thesis, I compare the performance of source and channel diversity techniques on fading and symmetric continuous channels. My experiments suggest that when SNR is low, channel diversity performs better, and when SNR is high, source diversity shows better performance than channel diversity.

Layered structures are commonly used in communication systems, but their roles in decentralized control are not understood well. In the first part of this thesis, a theoretical study of consensus (a typical decentralized control task) in layered structures is conducted. The unique graph topology approach permits explicit characterization of consensus performance based on simple graphical characteristics of MLMG structures. In the second part of this thesis, a generic LEGO test-bed to mimic multi-domain communication with layered structures is described. A search-and-rescue scenario is implemented to demonstrate the use of the test-bed.

A single user deconcentrator is designed for a circuit switched digital switching system which emphasizes mass conferencing. The switching system consists of distributed concentrators which include a first level of conferencing and a broadcast bus which includes a second level of conferencing. The deconcentrator features volume adjustment of individual conferences as well as a third and last level of conferencing- a conference of the individual conferences obtained from the broadcast bus. The design identifies the MSI and SSI components of the deconcentrator and provides an estimate of timing and board size. An alternative volume adjustment algorithm and the extension of a single user deconcentrator to a multi-user deconcentrator is discussed.

While the application of antenna diversity in a narrow band communication system is well understood, little research has been done on antenna effects in wide-band channels. Research has shown that circular polarization (CP) is more robust in combating multipath than linear polarization in line-of-sight channels. One objective of this thesis is to study the effects of antenna polarization and antenna pattern on multipath delay spread and path loss in indoor obstructed (OBS) wireless channels. A wide-band experiment was performed in a two-floored modern office building at 2.4SGHz in August 1991. Some preliminary results are as follows. Circular polarization cannot reduce delay spread in OBS channels and CP signals are more vulnerable to depolarization in OBS channels. Our results show that vertically polarized (VP) directional antennas at both the transmitter and the receiver can give better delay spread and path loss results than other antenna combinations. The performance of VP directional antennas are found to be sensitive to the alignment of the antennas, and the performance gain over omnidirectional antennas degrades as shadowing effects increase. In the second half of the thesis, a deterministic wide-band propagation model that can predict channel impulse responses inside buildings is proposed and implemented. The three dimensional image-based propagation model includes effects of antenna pattern, antenna polarization, geometry of the building, and building materials. Comparisons between measured and predicted power delay profiles are given in Chapter Seven. Preliminary results show that the worst case path loss error is IOdB, and the standard deviation of path loss error is 4.6dB. For most cases, predicted rms delay spread values are 20ns within the measured values. Possible prediction errors are due to unmodeled furniture inside the offices and limitations of Geometrical Optics (GO) assumptions. The algorithm is shown to be more efficient than brute force ray tracing algorithm if the number of objects are on the order of a few hundred. Acceleration techniques for the algorithm are also discussed in the thesis. / Master of Science

Tunneling through a potential barrier is a well-known concept in quantum mechanics. It is shown that tunneling is not an inherently quantum-mechanical phenomenon but that it occurs in classical optics as well. Single-layer and double-layer dielectrics in which optical tunneling occurs are shown to serve as the basis of optical filters, the double-layer tunnel filter having a much higher resolution capability than the single-layer tunnel filter. Optical amplifiers used as a receiver preamplifier and as linear intermediate repeaters are evaluated. Performance parameters of particular interest are the receiver sensitivity and the total system gain. The effects of optical amplifier gain and bandwidth on those parameters are studied. Finally, the effects of gain variations are considered. It is shown that gain control gives very poor results, whereas power control does not severely limit the system performance, particularly when a small number of amplifiers are used. / Master of Science

A thirty-kilohertz thirty-kilowatt full-bridge inverter design is presented. The inverter module forms an integral part of a very-low-frequency transmitter for a submarine communications application. Device selection and drive selection as well as testing data for inverter clamped mode of operation are presented. / M.S.

This dissertation describes a geometrical optics model to predict propagation in buildings for personal communication system (PCS) design. Background on the growth of wireless communications is given, and the importance of accurate propagation models is discussed. The peculiarities of propagation in mobile and portable radio environments, particularly multipath propagation and its effects on transmitted signals, are described. Current in-building propagation models are presented and the progression from statistical in the presence of scattering bodies are merged with a site-specific description of the propagation environment to improve upon the accuracy of existing propagation models. A geometrical optics ray tracing model for predicting propagation based on a building blueprint representation is developed for a transmitter and receiver located on the same floor inside a building. The measured and predicted propagation data are presented as power delay profiles that contain the amplitude and arrival time of individual multipath components. Measured and predicted power delay profiles are compared on a location-by-location basis to provide both a qualitative and a quantitative measure of the model accuracy. The concept of effective building material properties is developed.and the effective building material properties are derived for two dissimilar buildings based upon comparing measured and predicted power delay profiles. Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model. Path loss between a transmitter and receiver is predicted-with a standard deviation of less than 5 dB. Ideas for improving the accuracy and expanding the applicability of the models applied here to wireless in-building propagation prediction are suggested. / Ph. D.

Thesis (MBA) -- Stellenbosch University, 2007. / Today we face a reality where existing power relations concerning economical, political and cultural institutions and forces are changing. It is about more than just the right to use a technology in itself; it is a matter of having, or not having, access to infonnation and knowledge. The use of information and communications technology (lCT) is an important and powerful tool when it comes to distributing and sharing these resources (Bridges.arg, 2006). The unequal distribution of and the differences in the possibility to use rer effectively are often referred to by the term digital divide (DDN, 2006). Does this sound quite pessimistic? However, a change is taking place since all countries on earth from the richest to the poorest are actually increasing their Ier usage. The problem is that the developed countries are using convergence (three separate communication sectors: information technology, telecommunications and broadcasting merging to become a single communication service sector) to escalate their access to and use of ICf at a much higher speed, which in fact widens the digi tal divide instead of shrinking it (Bridges.org, 2006). Today no country can afford to neglect investments in ICf if it wishes to raise its living standards or to prevent it from being left behind as other countries exploits the possibilities of ICf. Why is ICf considered to be an effective tool for bridging the international digita1 divide? On the United Nations Development Programme's website one can read: " .. .ICf is an increasi ngly powerful tool for participating in global markets; promoting political accountability; improving the delivery of basic services; and enhancing local development opportunities" (UNOP, 2003). These aspects can be of great importance for developing countries in their effort to gain economic development and improvements. Furthermore, it is also a question about every human's right to have access to infonnation (Sida, 2004). According to Steve Case (AOL Time Warner, Chainnan of the Board) every decade has some word associated with it. In the 'SOs, it was the PC. In the '90s, it was the Internet. For the rest of this decade, the key word is going to be convergence (Thompson, 2003). In Namibia a digital divide exists between income groups as well as between the country's rural and urban population. Namibia is sti ll far from providing equal access to information, but Namibia is well positioned to deploy ICf to its advantage. Namibia has a functional telecommunication infrastructure, political stability and an attractive economic environment for investors. However. the geographic and social challenges of Namibia require innovative approaches and considerable effort. Competition and convergence will improve the situation. recommended to expand the set of potential drivers and specifically focus on the relation between convergence and economic growth.

Dissertation (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Though not so prominent as the wide band, high speed, mainstream development of data communication networks, cost and particular bandwidth limitations, still ensure extensive and continuing use of low-speed, half-duplex data link equipment. Most of these applications are radio based and aimed towards telemetry systems serving a wide range of utilities. Experience has shown that systems engineering for this type of installation, is seldom undertaken to a satisfactory analytical level. Investigation of published analyses of CSMA protocols in general, has indicated scope of extension of theoretical work to include system parameters for the type of protocol investigated in this dissertation. This dissertation describes the mathematical modeling of such a strategy by utilising a significantly modified, finite source, transition state-matrix approach derived from queueing theory. The contribution of the dissertation is to include system overhead parameters, such as backoff strategy, channel noise, equipment rise times, propagation- and retry delays, into the abovementioned model. The latter provides a relatively straightforward and readily applicable method for system analysis and performance prediction. A further contribution is the presentation of a software emulation with which different strategies could be simulated, allowing for adjustment of all design parameters. The simulation is intended for parallel and confimatory use with the theoretical model. A dual set of tools, theoretical and emulation based, is thus contributed to assist with the system design, performance prediction and protocol selection process. / AFRIKAANSE OPSOMMING: Alhoewel nie so prominent soos die wyeband, hoëspoed, hoofstroom ontwikkeling van datakommunikasie netwerke nie, verseker koste en spesifieke bandwydte beperkings nog die uitgebreide en voortdurende gebruik van laespoed half-dupleks data verbindingstoerusting. Meeste van die toepassings is radio gebaseer en gerig op telemetriestelsels wat deur 'n wye verskeidenheid diensverskaffers benut word. Stelselontwerp vir hierdie tipe installasies word selde op analitiese vlak benader. Ondersoek van gepubliseerde analises van kontensieprotokolle in die algemeen, het ruimte aangetoon vir die uitbreiding van bestaande teoretiese werk om stelselveranderlikes soos van toepassing op die tipe protokol in hierdie proefskrif ondersoek, in te sluit. Hierdie proefskrif beskryf die wiskundige modelering van sodanige strategie, deur gebruik te maak van 'n beduidend veranderde eindige bron, oorgangs-toestandmatriks benadering, afgelei van touteorie. Die bydrae van hierdie proefskrif is die insluiting van oorhoofse stelselveranderlikes, soos herhaal strategie, kanaalruis, toerusting stygtye, herhaal- en voortplantingsvertragings, in bogenoemde model. Laasgenoemde verskaf 'n relatief eenvoudige en maklik toepasbare metode vir stelselanalise en werkverrigtingvoorspelling. 'n Verder bydrae is die daarstelling van 'n sagteware simulasie waarmee verskillende strategieë nageboots kan word. Verstelling van alle ontwerpparameters word ondersteun. Die simulasie is bedoel vir parallelle en bevestigende gebruik tesame met die teoretiese model. 'n Dubbele, teoreties- en simulasie gebaseerde benadering, word dus aangebied vir gebruik by stelselontwerp, gedragsvoorspelling en optimale protokolseleksie.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / The use of older and slower protocols has become increasingly difficult to justify due to the rapid pace at which telecommunications are advancing. To keep up to date with the latest technologies, the communications system must be designed to accommodate the transparent insertion of new communications standards in all the stages of a system. The system should, however, also remain compatible with the older standards so as not to demand an upgrade of the older systems. The concept of a software defined radio was introduced to overcome these problems. In a software defined radio system, the functionality of the communications system is defined in software, which removes the the need for alterations to the hardware during technology upgrade. To maintain interoperatibilty, the system must be based on a standardised architecture. This would further allow for enhanced scalability and provide a plug-andplay feature for the components of the system. In this thesis, generic signal processing software components are developed to illustrate the creation of a basic software modem that can be parameterised to comply fully, or partially, to various standards.