Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / A Synchronous Digital Hierarchy (SDH) point-to-point bi-directional link was implemented at a base Synchronous Transfer Mode level 1 (STM 1) signal rate. The full STM-1 multiplexer was implemented and the functional code developed to Virtual Container level 4 (VC4) level. The implementation was realized using a Software Defined Radio (SDR) architecture that managed and linked the SDH atomic units into a STM-1 SDH multiplexing structure. These atomic units have been well defined in recommendation G.707 [1]. The functional description of each unit was based on the G.783 [8] recommendation which specifies a library of basic building blocks and set of rules by which these atomic functions should be combined into various functional layers. These layers interconnect to ultimately form a bi-directional path in the SDH network. A SDH Management Sub network (SMS) was implemented using a graphical user interface to perform a monitoring function for the bi-directional link.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / Conventional immunity tests are both time consuming and costly. There is thus a reasonable interest in relatively quick, but accurate and cost effective, in-house pre-compliance test techniques within an engineering design-house. This thesis provides information on the equivalence between in-house and conventional immunity test techniques. Three techniques were evaluated, namely: 1. E-field radiation with a log periodic antenna (conventional test technique); 2 E-field radiation with an inhouse designed and constructed modified TEM cell (in-house test technique); 3. Current injection using a complete off the shelf EMCO current probe device (in-house test technique). After the transfer data of the EMCO probe was verified, the modified TEM cell design, construction and equivalent measurement tests were performed. These tests revealed that within the respective bandwidth of interest, the devices produced results that are equivalent to each other within 0.9dB. Hence equivalence between in-house and conventional test techniques is possible.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Structure from Motion suggests that an object or scene’s three-dimensional structure can be determined from its observed two-dimensional motion. Human efforts, manifested in computer algorithms, try to mimic the enormous power of the visual processing capabilities of the human brain. We present an algorithm to estimate structure, using the Unscented Kalman Filter, from the motion of point-wise features, produced by the Kanade-Lucas-Tomasi feature tracker. The algorithm is evaluated critically against an extensive set of motion sequences, with special attention paid to facial feature reconstruction.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / High-temperature superconductive (HTS) logic has become a large research field worldwide. The HTS advantages compared to the low-temperature circuits are the reduced cooling requirements, increased or comparable operation speeds and the "ease" of manufacturing. The potential of HTS logic circuits is vast and surpassed by very few other technologies. However, before these circuits can reach the market, suitable simulation packages and fabrication processes have to be designed. The simulation of HTS Rapid Single Flux Quantum (RSFQ) circuits are performed at temperatures between 30 and 77 Kelvin. The noise sources in Josephson junctions (JJ’s) are investigated and incorporated into these simulations. The results show that it is possible to operate these circuits in this temperature range. An objective of this thesis is the fabrication of HTS step-edge JJ’s. A process to fabricate these junctions was investigated and improved. This includes the etching of substrate steps with the use of the argon ion mill, deposition of the YBCO thin films with the Pulsed Laser Deposition (PLD) system and the etching of the final circuit by the use of dry or wet etching.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Visually estimating three-dimensional position, orientation and motion, between an observer and a target, is an important problem in computer vision. Solutions which compute threedimensional movement from two-dimensional intensity images, usually rely on stereoscopic vision. Some research has also been done in systems utilising a single (monocular) camera. This thesis investigates methods for estimating position and pose from monocular image sequences. The intended future application is of visual tracking between satellites flying in close formation. The ideas explored in this thesis build on methods developed for use in camera calibration, and structure from motion (SfM). All these methods rely heavily on the use of different variations of the Kalman Filter. After describing the problem from a mathematical perspective we develop different approaches to solving the estimation problem. The different approaches are successfully tested on simulated as well as real-world image sequences, and their performance analysed.

Type I diabetics need regular injections of insulin to survive. Insulin allows the cells of the body to extract glucose from the blood supply to use as fuel. Without insulin the cells turn to other backup fuel sources,this can cause side effects that are quickly fatal or gradual wasting of the bodies tissues. The use of insulin, however, is not danger free, as an incorrect dosage can quickly lead to the reduction of glucose circulating in the blood to drop to a dangerously low level. Without glucose circulating in the blood supply the brain quickly runs out of fuel causing coma and death. Because of this, a means to constantly monitor blood glucose levels has been sought for the last two decades. With such a device, diabetics could judge the correct amount of insulin to inject and be warned of low blood glucose levels. However, to date no reliable portable system has been produced. Recent developments in fibre optic biosensor technology, suggested a possible route to achieves this goal. The work in this thesis presents the development and testing of such a sensor. The sensor presented in this thesis is based around a commercial fibre optic blood gas sensor, the Paratrend 7. The oxygen-sensing element of this device was modified into a glucose sensor using polymer membranes incorporating the enzymes glucose oxidase and catalase. The research was aimed at building a glucose sensor that could be developed into a working blood glucose sensor in the minimum amount of time if the research proved successful. For this reason the Paratrend 7 sensor system was chosen to provide a clinically tested sensor core around which the glucose sensor could be built. The initial experiment, which used a Paratrend7 sensor coated in polyHEMA and glucose oxidase, produced a sensor of diameter of 700µm with a range of 0 to 4mM/1 of glucose and a 90% response time of <100 seconds in a solution with a 15% oxygen tension. The sensor design was then developed to incorporate the enzyme catalase to protect the glucose oxidase and an outer diffusion limiting polyHEMA membrane. This produced a sensor with a range of 0 to 6 mM/l and a response time of <100 seconds. The method of coating the sensors was'then improved, through a series of stages, until an optomised dip coating technique was developed. This technique produced sensors with ranges (in 7.5KPa oxygen tension solutions) between 0 to 3mM/l and 0 to lOmM/1, responsetimes of <100 seconds in some cases and with diameters of 300µm. By using a partial polyurethane outer coat the range of the sensors was increased form 0 to 4mM/l up to 0 to 24mM/1, in one case, with 90% response times in the 100to 500 second range. The sensors were then sterilised using gamma radiation and their performance before and after sterilisation examined. The gamma sterilisation was found to cause a reduction in the range of the sensors,for example 0 to 24 m /I down to 0 to 14mM/l in one case. The affect of 24 hour operation in a 5mM/1 solution of glucose and storage, for up to three months, was then investigated. Both processes were found to reduce the operational range of the sensors,0 to 20 reduced to 0 to 15 mM/i, in one case,for 24 hour operation and form 0 to 15mM/1 reduced to 0 to 11mM/1in one case for a storage time of three months. The use of the enzymes glucose oxidase and catalase together in a fibre optic as can sensor has not been previously reported in the literature as far be ascertained. The comparison of sensor performance before and after gamma sterilisation also appears to be unique as does the gamma sterilisation of a fibre optic glucose sensor.

This thesis describes research into communication protocols required by a wireless mesh network (WMN) that would be deployed to support emergency rescue teams in a disaster recovery scenario. WMN applications in emergency and disaster recovery require the network to facilitate multimedia group communications to enable rescue team members to share information with each other and provide access to broadband services via www and email. The work presented in the thesis proposes a scheme to improve the performance of WMN to satisfy such application requirements. Several protocols have been designed and implemented to support the exchange of information between these protocols in order to meet the QoS requirements of real-time multimedia traffic and to avoid congestion whilst routing Internet traffic in a multiple gateway environment. A novel implementation of the MAODV routing protocol is developed and modifications are proposed to enhance the protocol's performance and reliability to support the multimedia multicast operation ofWMNs. A novel Load-Balanced Gateway Discovery routing protocol called LBGD-AODV is designed and implemented which provides a multiple gateway environment and balanced Internet traffic loading to more effectively utilize the available gateway resources and minimise network congestion. The proposed QoS scheme enables both protocols to exchange information on network congestion in order to calculate the network bandwidth consumption using a novel scheme at the network layer. This information is used to provide rate-adaptive admission control for multimedia traffic at the application layer. Furthermore, the scheme also provides strategies to support efficient priorities for multimedia traffic to ensure that all the critical priority flows are facilitated even when the network is congested. LBGD-AODV uses the bandwidth information to avoid congested routes to gateway nodes for Internet traffic. A WMN testbed is designed and developed using cross-platform hardware to evaluate the performance of the proposed protocols. The test results show that the objectives set in this study have been successfully achieved by improving the WMN performance for both UDP real-time multimedia traffic and TCP internet traffic.

The increase in the scale of VLSI circuits over the last two decades has been of great importance to the development process. To cope with this ever­growing design complexity. new development techniques and methodologies have been researched and applied. The early 90's have witnessed the uptake of a new kind of design methodology based on Hardware Description Languages (HDL). This methodology has helped to master the possibilities inherent in our ability to manufacture ever-larger designs. However. while HDL based design methodology is sufficient to address today's standard ASIC sizes, it reaches its limits when considering tomorrow's design scales. Already. RISC processor chip descriptions can contain tens of thousands of HDLlines. Object-Oriented design methodology has recently had a considerable Impact in the software design community as it is tightly coupled with the handling of complex systems. Object-Orientation concentrates on data rather than functions since. throughout the design process. data are more stable than functions. Methodologies for both hardware and software have been introduced through the application of HDLs to hardware design. Common design constructs and principles that have proved successful in software language development should therefore be considered in order to assess their suitability for HDLs based designs. A new methodology was created to emphasise on encapsulation. abstraction and classification of designs. using standard VHDL constructs. This achieves higher levels of modelling along with an Improved reusability through design inheritance. The development of extended semantics for integrating Object-Orientation in the VHDL language is described. Comparisons are made between the modelling abilities of the proposed extension and other competing proposals. A UNIX based Object-Oriented to standard VHDL pre-processor is described along with translation techniques and their issues related to synthesis and simulation. This tool permitted validation of the new design methodology by application to existing design problems.

The Infrared (IR) optical medium provides an alternative to radio frequencies (RF) for low cost, low power and short-range indoor wireless data communications. Low-cost optoelectronic components with an unregulated IR spectrum provide the potential for very high-speed wireless communication with good security. However IR links have a limited range and are susceptible to high noise levels from ambient light sources. The Infrared Data Association (IrDA) has produced a set of communication protocol standards (IrDA I. x) for directed point-to-point IR wireless links using a HDLC (High-level Data Link Control) based data link layer which have been widely adopted. To address the requirement for multi-point ad-hoc wireless connectivity, IrDA have produced a new standard (Advanced Infrared -AIr) to support multiple-device non-directed IR Wireless Local Area Networks (WLANs). AIr employs an enhanced physical layer and a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) based MAC (Media Access Control) layer employing RTS/CTS (Request To Send / Clear To Send) media reservation. This thesis is concerned with the design of IrDA based IR wireless links at the datalink layer, media access sub-layer, and physical layer and presents protocol performance models with the aim of highlighting the critical factors affecting performance and providing recommendations to system designers for parameter settings and protocol enhancements to optimise performance. An analytical model of the IrDA 1.x data link layer (IrLAP Infrared Link Access -Protocol) using Markov analysis of the transmission window width providing saturation condition throughput in relation to the link bit-error-rate (BER), datarate andprotocol parameter settings is presented. Results are presented for simultaneous optimisation of the data packetsize and transmission window size. A simulation model of the IrDA l. x protocol, developed with OPNETTM Modeler, is used for validation of analytical results and to produce non-saturation throughput and delay performance results. An analytical model of the AIr MAC protocol providing saturation condition utilisation and delay results in relation to the number of contending devices and MAC protocol parametersis presented.Results indicate contention window size values for optimum utilisation. The effectiveness of the AIr contention window linear back-off process is examined through Markov analysis. An OPNET simulation model of the Alf protocol is used for validation of the analytical model results and provides non-reservation throughput and delay results. An analytical model of the IR link physical layer is presented and derives expressions for signal-to-noise ratio (SNR) and BER in relation to link transmitter and receiver characteristics, link geometry, noise levels and line encoding schemes. The effect of third user interference on BER and resulting link asymmetry is also examined, indicating the minimum separation distance for adjacent links. Expressions for BER are linked to the data link layer analysis to provide optimum throughput results in relation to physical layer propertiesandlink distance.

In recent years, Wireless Local Area Networks(WLANs) play a key role in the data communications and networking areas, having witnessed significant research and development. WLANs are extremely popular being almost everywhere including business,office and home deployments.In order to deal with the modem Wireless connectivity needs,the Institute of Electrical and Electronics Engineers(IEEE) has developed the 802.11 standard family utilizing mainly radio transmission techniques, whereas the Infrared Data Association (IrDA) addressed the requirement for multipoint connectivity with the development of the Advanced Infrared(Alr) protocol stack. This work studies the collision avoidance procedures of the IEEE 802.11 Distributed Coordination Function (DCF) protocol and suggests certain protocol enhancements aiming at maximising performance. A new, elegant and accurate analysis based on Markov chain modelling is developed for the idealistic assumption of unlimited packet retransmissions as well as for the case of finite packet retry limits. Simple equations are derived for the through put efficiency, the average packet delay, the probability of a packet being discarded when it reaches the maximum retransmission limit, the average time to drop such a packet and the packet inter-arrival time for both basic access and RTS/CTS medium access schemes.The accuracy of the mathematical model is validated by comparing analytical with OPNET simulation results. An extensive and detailed study is carried out on the influence of performance of physical layer, data rate, packet payload size and several backoff parameters for both medium access mechanisms. The previous mathematical model is extended to take into account transmission errors that can occur either independently with fixed Bit Error Rate(BER) or in bursts. The dependency of the protocol performance on BER and other factors related to independent and burst transmission errors is explored. Furthermore, a simple-implement appropriate tuning of the back off algorithm for maximizing IEEE 802-11 protocol performance is proposed depending on the specific communication requirements. The effectiveness of the RTS/CTS scheme in reducing collision duration at high data rates is studied and an all-purpose expression for the optimal use of the RTS/CTS reservation scheme is derived. Moreover, an easy-to-implement backoff algorithm that significantly enhances performance is introduced and an alternative derivation is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Finally, an additional performance improvement scheme is proposed by employing packet bursting in order to reduce overhead costs such as contention time and RTS/CTSex changes. Fairness is explored in short-time and long-time scales for both the legacy DCF and packet bursting cases. AIr protocol employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium access. A 1-dimensional Markov chain model is constructed instead of the bi-dimensional model in order to obtain simple mathematical equations of the average packet delay.This new approach greatly simplifies previous analyses and can be applied to any CSMA/CA protocol.The derived mathematical model is validated by comparing analytical with simulation results and an extensive Alr packet delay evaluation is carried out by taking into account all the factors and parameters that affect protocol performance. Finally, suitable values for both backoff and protocol parameters are proposed that reduce average packet delay and, thus, maximize performance.