Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 50-51).

The presence of multipath propagation in indoor environments limits the performance of wideband radio communication systems and also the maximum data rate that can be feasible. This thesis addresses the dynamics of propagation mechanisms needed to design and exploit future broadband wireless local area networks in the 60GHz millimetre-wave band. The frequency band between 62-63GHz with data rates up to 155Mb/s, has been provisionally assigned for Mobile Broadband Systems. The main emphasis of this study was to provide an original contribution to the development, design and planning of future broadband communication systems using new high-resolution wideband channel measurement data. Based on this data, spatial and temporal statistics of several line-of-sight radio paths in a University campus are presented and analysed. In order to enable measurement of the wideband propagation characteristics a high-resolution (Ins) wideband Frequency-swept channel sounder was designed and implemented at 62.4GHz. The channel sounder has been built around a Vector Network Analyser to measure the complex transfer function of the channel. The instantaneous coherence bandwidth is found to be highly variable with the location of the receiver with respect to the base station. With delay spread values ranging from 20 to 70ns the coherence bandwidth remains most of the times below 10MHz. Based on the maximum delay spread of 68ns obtained in a 41m long narrow corridor, a BER of 10" 3 and normalised delay spread of 0.1, the minimum data transmission rate is estimated at 1.47 Mb/s. For a 12.80m room environment with maximum delay spread of 20ns the minimum data transmission rate is 5Mb/s. To achieve higher data transmission rates channel protection countermeasures appears to be necessary. However limiting the extent of a picocell size and utilising the potential capability of frequency re-use at 62.4GHz can result in radio network implementation without the complexity of countermeasures. Results relating to coherence bandwidth variability in multipath conditions confirm that higher user mobility envisaged for MBS would present a real challenge to the achievement of data transmission rates of the order of 155Mb/s. The research work reported in the thesis has been able to identify and extract from extensive high resolution wideband propagation the necessary design characteristics for the development of realistic radio planning models. Using measured results obtained in a number of radio paths geometries, the objectives of the project have been largely achieved and further work is recommended.

Thesis (MTech (Information Technology))--Cape Peninsula University of Technology, 2015. / Recently, the deployment and availability of wireless technology have led to the development of location and positioning services. These Location Based Services (LBSs) are attracting the attention of researchers and mobile service providers. With the importance of ubiquitous computing, the main challenge seen in the LBS is in the mobile positioning or localization within reasonable and certain accuracy. The Global Positioning System (GPS), as a widely known and used navigation system, is only appropriate for use in outdoor environments, due to the lack of line-of-sight (LOS) in satellite signals that they cannot be used accurately inside buildings and premises. Apart from GPS, Wi-Fi is among others, a widely used technology as it is an already existing infrastructure in most places. This work proposes and presents an indoor positioning system. As opposed to an Ad-hoc Positioning System (APS), it uses a Wireless Mesh Network (WMN). The system makes use of an already existing Wi-Fi infrastructure. Moreover, the approach tests the positioning of a node with its neighbours in a mesh network using multi-hopping functionality. The positioning measurements used were the ICMP echo requests, RSSI and RTS/CTS requests and responses. The positioning method used was the trilateral technique, in combination with the idea of the fingerprinting method. Through research and experimentation, this study developed a system which shows potential as a positioning system with an error of about 2 m – 3 m. The hybridization of the methods proves an enhancement in the system though improvements are still required

M.Sc. / Wireless networking is a fairly new technology that is important in information technology (IT). Hotels, Airports, Coffee shops, and homes are all installing wireless networks at a record pace, making wireless networks the best choice for consumers. This popularity of wireless networks is because of the affordability of wireless networks devices, and the easy installation [11]. In spite of the popularity of the wireless networks, one factor that has prevented them from being even more widespread can be summed up in a single word: security. It comes as no surprise that these two – wireless and security – converge to create one of the most important topics in the IT industry today [11]. Wireless networks by nature bring about new challenges unique to its environment. One example of these new challenges is: “Signal overflow beyond physical walls”, and with these kinds of new challenges unique to wireless networks, we have new security risks. Hence wireless networks lend themselves to a host of attack possibilities and risks. That is because wireless networks provide a convenient network access point for an attacker, potentially beyond the physical security controls of the organization [7]. Therefore it is challenging for managers to introduce wireless networks and properly manage the security of wireless networks, Security problems of wireless networks are the main reason for wireless networks not being rolled out optimally [1]. In this dissertation, we aim to present to both specialist and non–specialists in the IT industry the information needed to protect a wireless network. We will first identify and discuss the different security requirements of wireless networks. After that we shall examine the technology that helps make wireless networks secure, and describe the type of attacks against wireless networks and defense techniques to secure wireless networks. The research will concentrate on wireless LANs (Local Area Networks), and leading wireless LAN protocols and standards. The result of the research will be used to create WISP (A Wireless Information Security Portal). WISP will be a tool to support the management of a secure wireless network, and help assure the confidentiality, integrity, and availability of the information systems in a wireless network environment.

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M.Ing. / Mobile adhoc networks (MANETs) are multihop wireless topologies that have rapidly changing node structure and limited connectivity. Since MANETs are not deployed on a wide scale, the research community still depends on the simulators such as the network simulator (Ns2) to evaluate MANET protocols. The topic of how to accurately model an indoor environment in the MANET research community is explored in this dissertation. We take an empirical and simulative approach to model our mobility pattern. Our mobility model is based on activity patterns drawn from the transport science. A comparison with the random way point is made in order to understand the weighty discrepancy between the two models. Our contribution in this research is three fold: 1. We argue that mobility modelling should be based on activities other than stochastic process that have got no realistic backing; 2. We model our network using by putting up an algorithm and take an empirical approach to model the radio frequency propagation. To show the difference of the two mobility models, the behaviour of the signal strength on the two mobility models is drawn; and 3. Finally an implementation of our mobility pattern and RF measurements in ns2 is done.

Designing 802.11 wireless networks includes two major components: selection of access points (APs) in the demand areas and assignment of radio frequencies to each AP. Coverage and capacity are some key issues when placing APs in a demand area. APs need to cover all users. A user is considered covered if the power received from its corresponding AP is greater than a given threshold. Moreover, from a capacity standpoint, APs need to provide certain minimum bandwidth to users located in the coverage area. A major challenge in designing wireless networks is the frequency assignment problem. The 802.11 wireless LANs operate in the unlicensed ISM frequency, and all APs share the same frequency. As a result, as 802.11 APs become widely deployed, they start to interfere with each other and degrade network throughput. In consequence, efficient assignment of channels becomes necessary to avoid and minimize interference. In this work, an optimal AP selection was developed by balancing traffic load. An optimization problem was formulated that minimizes heavy congestion. As a result, APs in wireless LANs will have well distributed traffic loads, which maximize the throughput of the network. The channel assignment algorithm was designed by minimizing channel interference between APs. The optimization algorithm assigns channels in such a way that minimizes co-channel and adjacent channel interference resulting in higher throughput.

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