This work addresses Channel Assignment in a multi-radio multi-channel (MRMC) Wireless Mesh Network (WMN) using both Wi-Fi and Dynamic Spectrum Access (DSA) spectrum bands and standards. This scenario poses new challenges because nodes are spread out geographically so may have differing allowed channels and experience different levels of external interference in different channels. A solution must meet two conflicting requirements simultaneously: 1) avoid or minimise interference within the network and from external interference sources, and 2) maintain connectivity within the network. These two requirements must be met while staying within the link constraints and the radio interface constraints, such as only assigning as many channels to a node as it has radios. This work's original contribution to the field is a unified framework for channel optimisation and assignment in a WMN that uses both DSA and traditional Wi-Fi channels for interconnectivity. This contribution is realised by providing and analysing the performance of near-optimal Channel Assignment (CA) solutions using metaheuristic algorithms for the MRMC WMNs using DSA bands. We have created a simulation framework for evaluating the algorithms. The performance of Simulated Annealing, Genetic Algorithm, Differential Evolution, and Particle Swarm Optimisation algorithms have been analysed and compared for the CA optimisation problem. We introduce a novel algorithm, used alongside the metaheuristic optimisation algorithms, to generate feasible candidate CA solutions. Unlike previous studies, this sensing and CA work takes into account the requirement to use a Geolocation Spectrum Database (GLSD) to get the allowed channels, in addition to using spectrum sensing to identify and estimate the cumulative severity of both internal and external interference sources. External interference may be caused by other secondary users (SUs) in the vicinity or by primary transmitters of the DSA band whose emissions leak into adjacent channels, next-toadjacent, or even into further channels. We use signal-to-interference-plus-noise ratio (SINR) as the optimisation objective. This incorporates any possible source or type of interference and makes our method agnostic to the protocol or technology of the interfering devices while ensuring that the received signal level is high enough for connectivity to be maintained on as many links as possible. To support our assertion that SINR is a reasonable criterion on which to base the optimisation, we have carried out extensive outdoor measurements in both line-of-sight and wooded conditions in the television white space (TVWS) DSA band and the 5 GHz Wi-Fi band. These measurements show that SINR is useful as a performance measure, especially when the interference experienced on a link is high. Our statistical analysis shows that SINR effectively differentiates the performance of different channels and that SINR is well correlated with throughput and is thus a good predictor of end-user experience, despite varying conditions. We also identify and analyse the idle times created by Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) contention-based Medium Access Control (MAC) operations and propose the use of these idle times for spectrum sensing to measure the SINR on possible channels. This means we can perform spectrum sensing with zero spectrum sensing delay experienced by the end user. Unlike previous work, this spectrum sensing is transparent and can be performed without causing any disruption to the normal data transmission of the network. We conduct Markov chain analysis to find the expected length of time of a sensing window. We also derive an efficient minimum variance unbiased estimator of the interference plus noise and show how the SINR can be found using this estimate. Our estimation is more granular, accurate, and appropriate to the problem of Secondary User (SU)-SU coexistence than the binary hypothesis testing methods that are most common in the literature. Furthermore, we construct confidence intervals based on the probability density function derived for the observations. This leads to finding and showing the relationships between the number of sampling windows and sampling time, the interference power, and the achievable confidence interval width. While our results coincide with (and thus are confirmed by) some key previous recommendations, ours are more precise, granular, and accurate and allow for application to a wider range of operating conditions. Finally, we present alterations to the IEEE 802.11k protocol to enable the reporting of spectrum sensing results to the fusion or gateway node and algorithms for distributing the Channel Assignment once computed. We analyse the convergence rate of the proposed procedures and find that high network availability can be maintained despite the temporary loss of connectivity caused by the channel switching procedure. This dissertation consolidates the different activities required to improve the channel parameter settings of a multi-radio multi-channel DSA-WMN. The work facilitates the extension of Internet connectivity to the unconnected or unreliably connected in rural or peri-urban areas in a more cost-effective way, enabling more meaningful and affordable access technologies. It also empowers smaller players to construct better community networks for sharing local content. This technology can have knock-on effects of improved socio-economic conditions for the communities that use it.

Multi-hop wireless mesh networks (WMNs) provide a cost-effective means to enable broadband wireless access (BWA) services to end users. Such WMNs are required to support different classes of traffic where each class requires certain quality of service (QoS) levels. The research direction undertaken in this thesis considers the development of enhanced routing and scheduling algorithms that enable WMNs to support various QoS metrics for the served traffic. A fundamental class of routing problems in WMNs asks whether a given end-to-end flow that requires certain bandwidth, and benefits from routing over a single path (also called non-bifurcated routing), can be routed given that some ongoing flows are being served in the network. In the thesis, we focus on the development of combinatorial algorithms for solving such incremental non-bifurcated problems for two types of WMNs: 1. WMNs where mesh routers use contention-based protocol for medium access control (MAC), and 2. WMNs where mesh routers use time division multiple access (TDMA) for MAC. For WMNs employing contention-based MAC protocols, we present a novel non-bifurcated routing algorithm that employs techniques from the theory of network flows. The main ingredient in our algorithm is a method for computing interference-constrained flow augmenting paths for routing subscriber demands in the network. For WMNs employing TDMA, we develop a number of joint routing and scheduling algorithms, and investigate the use of such algorithms to maximize the number of served flows. In chapter 4, we consider a throughput maximization problem in the well-known class of grid WMNs. We present an iterative algorithm that strives to achieve high throughput by considering routing and scheduling a pair of distinct flows simultaneously to the gateway in each iteration. In chapter 5, we explore joint routing and scheduling in TDMA-based WMNs with arbitrary topologies, and devise an algorithm that can deal with arbitrary interference relations among pairs of transmission links. In particular, our devised algorithm solves a generalized problem where a cost value is associated with using any possible time-slot on any transmission link, and a minimum cost route is sought along which a new flow can be scheduled without perturbing existing slot assignments.

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In recent years, wireless mesh networking has attracted a growing interest due to its inherent flexibility, scalability, and reliability. The IEEE 802.16 standard, commonly known as worldwide interoperability for microwave access (WiMAX), is the latest technology that enables broadband wireless access over long distances. WiMAX, which emerges as a wireless alternative to cable and digital subscriber line (DSL), is an ideal candidate to serve as the infrastructure for large scale wireless mesh networks. This thesis focuses on the quality of service (QoS) provisioning techniques in WiMAX-based metropolitan area mesh networks. We study the connection admission control (CAC) and routing issues in the design and operation of wireless multihop mesh networks. We propose a joint CAC and routing scheme for multiple service classes with the objective to maximize the overall revenue from all carried connections. Connection-level QoS constraints such as handoff connection dropping probability can be guaranteed within a threshold. Multiple service classes can be prioritized by imposing different reward rates. We apply optimization techniques to obtain the optimal CAC policies. The optimality criterion is the long-run average reward. We demonstrate that the proposed scheme can the maximum revenue obtainable by the system under QoS constraints. We show that the optimal joint policy is a randomized policy, i.e., connections are admitted to the system with some probabilities when the system is in certain states. Simulation results illustrate that the proposed scheme meets our design goals and outperforms the existing scheme.

In recent years, wireless mesh networking has attracted a growing interest due to its inherent flexibility, scalability, and reliability. The IEEE 802.16 standard, commonly known as worldwide interoperability for microwave access (WiMAX), is the latest technology that enables broadband wireless access over long distances. WiMAX, which emerges as a wireless alternative to cable and digital subscriber line (DSL), is an ideal candidate to serve as the infrastructure for large scale wireless mesh networks. This thesis focuses on the quality of service (QoS) provisioning techniques in WiMAX-based metropolitan area mesh networks. We study the connection admission control (CAC) and routing issues in the design and operation of wireless multihop mesh networks. We propose a joint CAC and routing scheme for multiple service classes with the objective to maximize the overall revenue from all carried connections. Connection-level QoS constraints such as handoff connection dropping probability can be guaranteed within a threshold. Multiple service classes can be prioritized by imposing different reward rates. We apply optimization techniques to obtain the optimal CAC policies. The optimality criterion is the long-run average reward. We demonstrate that the proposed scheme can the maximum revenue obtainable by the system under QoS constraints. We show that the optimal joint policy is a randomized policy, i.e., connections are admitted to the system with some probabilities when the system is in certain states. Simulation results illustrate that the proposed scheme meets our design goals and outperforms the existing scheme.

>Magister Scientiae - MSc / This thesis deals with the design of a business model for rural telephony based on a wireless mesh network for a rural community, the Mankosi community, located in the Eastern Cape Province of South Africa. Its aim is to understand the social, economic and technical issues that are involved in the adoption of information and communication technologies for development and how they relates to trust in e-services. Externally funded projects tend to be expensive and are often unsustainable once the external funding ceases. The cost of a mesh network (once implemented) is almost negligible, apart from its maintenance. The pillars of the project are sustainability and community ownership, and the aim was to design the wireless mesh network, provide telephony service to the community and use solar power to charge mobile phones. The community leaders of Mankosi indicated that they do not want the service to be completely free, but would charge a small fee for each call in order to generate the funds needed for the maintenance of the system. In order to do so, a prototype billing system was configured and adapted to the needs and expectations of the community. The principles and steps of soft systems methodology were used to manage the research process of this case study. This methodology was a powerful tool to carry out the research and address the research problem in a participative way with the stakeholders. The participatory design process used in the design phase of the project had the added advantage that the community understood the purpose of the network, and since they contributed to its design, they felt that they owned it and could trust its billing system. A further benefit was that a core group of participants were committed to the project and felt that the overall quality of community members' lives would be improved by it and similar projects. The process contributed to the personal development of the participants by giving the community a voice and sense of power – the ability to change things – and it vastly expanded community members’ vision of what they are capable of. It was found that the current means of communication, i.e. using mobile phones, is expensive for local users in relation to their average income. The proposed billing system – designed with the help of the community – will be trusted by the community and provide Mankosi with a low-cost communication system by making use of the existing experimental mesh network. The community will be able to sustain their network with the income generated. The network will in future provide access to the Internet and will be able to handle breakout calls to external networks.

In recent years, wireless mesh networking has attracted a growing interest due to its inherent flexibility, scalability, and reliability. The IEEE 802.16 standard, commonly known as worldwide interoperability for microwave access (WiMAX), is the latest technology that enables broadband wireless access over long distances. WiMAX, which emerges as a wireless alternative to cable and digital subscriber line (DSL), is an ideal candidate to serve as the infrastructure for large scale wireless mesh networks. This thesis focuses on the quality of service (QoS) provisioning techniques in WiMAX-based metropolitan area mesh networks. We study the connection admission control (CAC) and routing issues in the design and operation of wireless multihop mesh networks. We propose a joint CAC and routing scheme for multiple service classes with the objective to maximize the overall revenue from all carried connections. Connection-level QoS constraints such as handoff connection dropping probability can be guaranteed within a threshold. Multiple service classes can be prioritized by imposing different reward rates. We apply optimization techniques to obtain the optimal CAC policies. The optimality criterion is the long-run average reward. We demonstrate that the proposed scheme can the maximum revenue obtainable by the system under QoS constraints. We show that the optimal joint policy is a randomized policy, i.e., connections are admitted to the system with some probabilities when the system is in certain states. Simulation results illustrate that the proposed scheme meets our design goals and outperforms the existing scheme. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Dynamic channel assignment algorithms allow wireless nodes to switch channels when their traffic loads exceed certain thresholds. These thresholds represent estimations of their throughput capacities. Unfortunately, the threshold estimation may not be accurate due to co-channel interference (CCI) and adjacent-channel interference (ACI), especially with high traffic loads in dense networks. When the link capacity is over-estimated, these channel assignment algorithms are not effective. This is because channel switch is not triggered even with overloaded data traffic and the link quality decreases significantly as the channel is overloaded. When the link capacity is under-estimated, the link is under utilized. Moreover, when link traffic load increases from time to time, channel switch occurs frequently. Such frequent channel switches increase latency and degrade throughput, and can even cause network wide channel oscillations. In this paper, we propose a novel threshold-based control system, called \emph{balanced control system} (BCS). The proposed threshold-based control policy consist of deciding, according to the real time traffic load and interference, whether to switch to another channel,{which channel should be switched to and how to perform the switch. Our control model is based on a fuzzy logic control. The threshold which assists to make the channel switch decisions, could be deduced dynamically according to the real-time traffic of each node. We also design a novel dynamic channel assignment scheme, which is used for the selection of the new channel. The channel switch scheduler is provided to perform channel-switch processing for sender and receiver over enhanced routing protocols. We implement our system in NS2, and the simulation results show that with our proposed system, the performance improves by 12.3\%-72.8\% in throughput and reduces 23.2\%-52.3\% in latency. / Computer and Information Science

<p>Increasing capacity in wireless mesh networks can be achieved by using multiple channels and radios. By using different channels, two nodes can send packets at the same time without interfering with each other. To utilize diversity of available frequency, typically cards use channel-switching, which implies significant overhead in terms of delay. Assignment of which channels to use needs to be coupled with routing decisions as routing influences topology and traffic demands, which in turn impacts the channel assignment.</p><p>Routing algorithms for wireless mesh networks differ from routing algorithms that are used in wired networks. In wired networks, the number of hops is usually the only metric that matters. Wireless networks, on the other hand, must consider the quality of different links, as it is possible for a path with a larger amount of hops to be better than a path with fewer hops.</p><p>Typical routing protocols for wireless mesh networks such as Optimized Link State Routing (OLSR) use a single path to send packets from source to destination. This path is precomputed based on link state information received through control packets. The consideration of more information than hop-count in the routing process has shown to be beneficial as for example link quality and physical layer data rate determines the quality of the end-to-end path. In multi-channel mesh networks, also channel switching overhead and channel diversity need to be considered as a routing metric. However, a major drawback of current approaches is that a path is precomputed and used as long as the path is available and shows a good enough metric. As a result, short term variations on link quality or channel switching are not considered.</p><p>In this thesis, a new routing protocol is designed that provides a set of alternative forwarding candidates for each destination. To minimize delay (from both transmission and channel switching), a forwarding mechanism is developed to select one of the available forwarding candidates for each packet. The implementation was tested on an ARM based multi-radio platform, of which the results show that in a simple evaluation scenario the average delay was reduced by 22 % when compared to single path routing.</p>

Heterogeneous wireless networks will be dominant in the next-generation wireless networks with the integration of various wireless access networks. Wireless mesh networks will become to a key technology as an economically viable solution for wide deployment of high speed, scalable and ubiquitous wireless Internet services. In this thesis, we consider an interworking architecture of wireless mesh backbone and propose an effective vertical handoff scheme between 802.11 and 802.16 wireless access networks. The proposed vertical handoff scheme aims at reducing handoff signaling overhead on the wireless backbone and providing a low handoff delay to mobile nodes. The handoff signaling procedure in different scenarios is discussed. Together with call admission control, the vertical handoff scheme directs a new call request in the 802.11 network to the 802.16 network, if the admission of the new call in the 802.11 network can degrade quality-of-service (QoS) of the existing real-time traffic flows. Simulation results demonstrate the performance of the handoff scheme with respect to signaling cost, handoff delay, and QoS support.