M.Ing. / Over the past few years, fibre Bragg gratings have emerged as very important components in the photonics environment. Their discovery has greatly revolutionised the design of many complex devices, introducing simplicity and cost effectiveness. Extensive research has been invested into identifying possible areas of application for fibre Bragg gratings. This has resulted in fibre Bragg gratings finding a comfortable niche in the fields of sensors and optical communication systems. This study focuses on the possible application of fibre Bragg gratings in wireless local area networks. Wireless local area networks are rapidly becoming a market of great potential for the investor. To sustain the impressive image of this market, research initiatives should strive to secure cost-effective solutions for the implementation of wireless local area networks. With reduced costs on wireless local area network products, the demand for these products is expected to escalate. Research conducted at the COBRA Institute, has produced a novel concept of optically distributing data signals across a network, and later transmitting them at radio frequencies between antenna sites. This concept, earmarked for wireless local area networks, uses a fast tuneable laser source, graded index polymer optical fibre and a periodic optical filter to generate the radio frequency microwave signals. The periodic filter in this network system serves to up-convert the frequency of the signal to radio-frequency levels. The filter is an important component of the network and it is situated at the antenna site. For wireless local area networks that require broad coverage, the number of periodic optical filters deployed for the system can be high. This can have a negative impact on the cost of the network. This research proposes a low-cost Fabry-Perot filter designed from fibre Bragg gratings, to replace the optical periodic filter discussed in the network mentioned above. The work presented in this study consolidates the design theories of Fabry-Perot filters and fibre Bragg gratings. The grating-based Fabry-Perot filter is modelled using coupled-mode theory, simulated using the transfer matrix method and fabricated via the strain controlled phase mask technique. The figures of merit that describe the spectral performance of the Fabry-Perot filter (i.e. free spectral range, minimum resolvable bandwidth, finesse and contrast factor) are compared to calculations associated with classical designs. The final part of this study presents experimental measurements of the generated radio frequency microwave signal. The purpose of these measurements is firstly to demonstrate the feasibility of the entire concept of generating radio frequency microwave signals using optical frequency multiplication. The second goal for the measurements is to benchmark the performance of the new grating-based Fabry-Perot filter against expected results approximated through calculations. Both goals were achieved with encouraging observations.

There is little literature available that is specific to the use of wireless local area network [WLAN) security among small, medium and micro enterprises (SMMEs) in South Africa. This research study developed a framework which may be used by SMMEs for the purposes of securing their WLANs. In view of the fact that the aim of the study was to develop a system for improving information technology security, the study followed a design science approach. A literature review was conducted on security control framework standards and WLAN technologies. The needs of SMMEs regarding WLANs were also established. The result of this process was an artefact in the form of a WLAN Security Control Framework for securing WLANs for SMMEs in South Africa. The suitability of the framework was validated by means of a focus group.

M.Com. (Computer Auditing) / With all the technology available in today’s world, people have become more connected to each other as well as to the world around them. This has been echoed by Rutledge (2009:1), who stated: “Emerging technologies are linking the world, but we no longer need wires and cables to connect people. People are no longer trapped by geography. We are, however, facing a digital tsunami as communications technology becomes cheaper, simpler, and more culturally-acceptable.” The new wireless technology has become an aid to most organizations, making networking simpler, cheaper and more effective, and has not only changed the way businesses operates but has changed the entire world of communications. It has not only caused a change in technology, but a change in the way of life. This is emphasized by Lawlor (2007:3), who stated: “Information technology has been a major driving force behind globalization and that information technology has now become a key component of a corporation’s global business strategy.” It is evident that the use of wireless technologies has changed the mode in which work is carried out and the manner in which communication takes place today. It has made it easier, more effective and efficient than before with wired technology. Wireless networks provide computing suppleness. It aids employees and individuals to take advantage of mobile networking for e-mail, Internet access, and sharing files regardless of where they are in the office or in a local area network (hereafter LAN). The advantage of the wireless setting is that it can be moved around at will, with no need for cables, leaving employees free to work from anywhere...

Relays in communication networks is a well-researched topic. Historically, relays were used in analog radio and television to extend the coverage. Using relays in wireless data networking applications is a more recent problem. In the early 2000s, relays were introduced for Micro-cellular and Wi-Fi deployments. Recently it has been considered for sensor networks and Vehicular Ad-hoc Networks (VANETs) applications. In this dissertation we present a novel approach to determine the optimal bounds for the Medium Access Control (MAC) throughput at the target receiver in a multi-hop multirate wireless data network. For a given relationship between the throughput and the distance, and a given distance between the access point and the target receiver, there is a minimum number of nodes that provides the maximum throughput to the target receiver. It is always desirable to optimize the deployment from various aspects. These aspects are application dependent and they range from energy conservation in sensor networks to throughput and coverage maximization in data networks. We apply this novel approach to vehicular ad-hoc network (VANET) scenarios. Using multi-hop relays, we show how to determine the optimum throughput for communciation between two vehicles. The optimal number of relays is chosen to maximize the throughput for point-to-point communication between a source and a destination as well as broadcast among all vehicles in the coverage area of the source. Additionally, in the physical layer, performance issues arise from the effects of interference and fading. The physical layer performance will in turn impact medium access control performance, effectively reducing the network throughput. We evaluate the ii performance of dense small cells for wireless local area networks (WLAN) and femto cells for data applications under the effects of interference and fading. We assume the network is fully saturated. We use the throughput-distance relationship to take into consideration the effects of interference, fading as well as the medium access control overheads. Using this model, we show that under certain conditions, the medium access control throughput for WLANs can outperform that of femto cells.

This thesis describes a performance measurement tool that allows a user to measure network performance using a handheld device. The measurement tool consists of a client program that runs on a Microsoft Pocket PC device and a server program that runs on a regular Microsoft Windows computer. Both programs are Windows applications implemented in C/C++ using the Microsoft Embedded Visual Tool and Microsoft Visual Studio. The use of a Pocket PC device provides mobility to users, which can save time and energy when performing experiments. The thesis describes the design of the performance measurement application, implementation issues, and tests conducted using the tool. / Master of Science

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Approved for public release; distribution is unlimited / The need for broadband network access is experiencing rapid growth, but what is currently available is not sufficient. Copper-based technologies cannot address the requirements of today's bandwidth-intensive Internet applications. End-users in the "last mile" demand access speeds equivalent to those supported by fiber optics backbone networks, although, the cost and time associated with its installation are prohibitive factors for bringing fiber to every home and business. This results in the well-known "last mile access problem," which prevents the Internet from reaching its full potential, and has paved the way for the development of many innovative technologies. Driven by demands for more bandwidth, wireless broadband technologies have been proposed. This thesis provides an investigation of two candidates to address the lack of adequate bandwidth in the "last mile," Free Space Optics (FSO), and the IEEE 802.11 Wireless Local Area Networking (WLAN) standard. FSO uses optical signals to deliver information at extremely high data rates, more quickly and cost-effectively than fiber systems. The IEEE 802.11 standard uses radio technology to transfer data. They both use license-free frequency bands for transmission through the atmosphere. They both are quickly deployable, easily scalable, and cheaper than wired solutions, characteristics able to support applications requiring high bandwidth and a high degree of mobility. / Lieutenant Commander, Hellenic Navy

Approved for public release, distribution is unlimited / As the need to send larger amounts of information increases, the military is looking into viable solutions to push this information throughout the battle space. IEEE 802.11a wireless LAN network presents an attractive high-speed solution by providing data rates up to 54 Mbps. At the same time, wireless LAN introduces increased security risk due to its vulnerability to exploitation of the wireless LAN physical layer. This research will develop a prototype system using low cost hardware and software solution to detect and process wireless IEEE 802.11a signals. Using the prototype, performance data will be collected to determine whether IEEE 802.11a is a feasible option as a high-speed information network for military use. Additionally, the performance data collected will provide a good basis for predicting the expected performance in an operational scenario and provide valuable information for proper deployment planning. / Major, Republic of Singapore Air Force

Approved for public release; distribution in unlimited. / With the introduction of wireless Local Area Networks (WLANs) in many organizations, it became much easier to intercept confidential files and personal health records. The present study focused on radio frequency propagation in a high-rise building, specifically, the attenuation between floors, and the possibility of intercepting signals through the floors. The current work is based on simulations using the Urbana software tool. It is used to predict the contour of the power levels of signals for a given physical model of the environment using high-frequency ray-tracing methods. The simulation results indicated that the signal levels for a 1 W transmitter could only be detected at the -70 dBm level within two floors (above or below). Even within the two floor range the signal distribution was very nonuniform due to the effects of multipath. The results indicated that closing doors reduced the signal levels, but only slightly for wood doors. Signals escaped the building through the window and were able to travel between floors via this path. The ray tracing accounted for only single diffraction, and therefore rays diffracted two or more times were not included. / Captain, Tunisian Air Force

Nowadays the widespread availability of wireless networks has created an interest in using them for other purposes, such as localization of mobile devices in indoor environments because of the lack of GPS signal reception indoors. Indoor localization has received great interest recently for the many context-aware applications it could make possible. We designed and implemented an indoor localization platform for Wi-Fi nodes (such as smartphones and laptops) that identifies the building name, floor number, and room number where the user is located based on a Wi-Fi access point signal fingerprint pattern matching. We designed and evaluated a new machine learning algorithm, KRedpin, and developed a new web-services architecture for indoor localization based on J2EE technology with the Apache Tomcat web server for managing Wi-Fi signal data from the FAU WLAN. The prototype localization client application runs on Android cellphones and operates in the East Engineering building at FAU. More sophisticated classifiers have also been used to improve the localization accuracy using the Weka data mining tool. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.