Im Bereich der Zugangsnetze werden zukünftig drahtlose Multihop-Erweiterungen des Internets durch mobile Ad-hoc-Netze sowie durch drahtlose vermaschte Netze (sog. Wireless Mesh Networks) Verbreitung finden, da diese Netztechnologien den Datentransfer einfacher und schneller, womöglich auch deutlich kostengünstiger, durchführen können als zellulare Mobilfunknetze.

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.

Although most work on Wireless Mesh Networks (WMNs) has focused on traffic flowing in and out of the network via gateways, traffic within the WMN may also be significant in many environments. This point-to-point (P2P) traffic between the nodes within WMN can be handled in different ways, particularly in WMNs containing multiple gateways. The approach used affects the performance of both the P2P flows and other traffic in the network. This work studies the impact of handling P2P traffic in the presence of gateways and gateway traffic. Through mathematical analysis of the resulting traffic patterns, along with extensive simulations, the need to route P2P traffic appropriately is demonstrated. While direct routing yields considerable performance improvements in small networks, it can actually decrease capacity in larger networks. Consequently, we extend the Hybrid Wireless Mesh Protocol (HWMP) proposed in IEEE 802.11s by adding two new message types to obtain more information useful for choosing the best route. Through simulations on different networks, HWMP shows better average delivery ratio and end-to-end delay than the original gateway-based and the P2P routing mechanisms in the simulation settings.

Although most work on Wireless Mesh Networks (WMNs) has focused on traffic flowing in and out of the network via gateways, traffic within the WMN may also be significant in many environments. This point-to-point (P2P) traffic between the nodes within WMN can be handled in different ways, particularly in WMNs containing multiple gateways. The approach used affects the performance of both the P2P flows and other traffic in the network. This work studies the impact of handling P2P traffic in the presence of gateways and gateway traffic. Through mathematical analysis of the resulting traffic patterns, along with extensive simulations, the need to route P2P traffic appropriately is demonstrated. While direct routing yields considerable performance improvements in small networks, it can actually decrease capacity in larger networks. Consequently, we extend the Hybrid Wireless Mesh Protocol (HWMP) proposed in IEEE 802.11s by adding two new message types to obtain more information useful for choosing the best route. Through simulations on different networks, HWMP shows better average delivery ratio and end-to-end delay than the original gateway-based and the P2P routing mechanisms in the simulation settings.

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Wireless Mesh Networks (WMNs) are bringing revolutionary change in the field of wireless networking. It is a trustworthy technology in applications like broadband home networking, network management and latest transportation systems. WMNs consist of mesh routers, mesh clients and gateways. It is a special kind of wireless Ad-hoc networks. One of the issues in WMNs is resource management which includes routing and for routing there are particular routing protocols that gives better performance when checked with certain parameters. Parameters in WMNs include delay, throughput, network load etc. There are two types of routing protocols i.e. reactive protocols and proactive protocols. Three routing protocols AODV, DSR and OLSR have been tested in WMNs under certain parameters which are delay, throughput and network load. The testing of these protocols will be performed in the Optimized Network Evaluation Tool (OPNET) Modeler 14.5. The obtained results from OPNET will be displayed in this thesis in the form of graphs. This thesis will help in validating which routing protocol will give the best performance under the assumed conditions. Moreover this thesis report will help in doing more research in future in this area and help in generating new ideas in this research area that will enhance and bring new features in WMNs. / Wireless Mesh Networks (WMNs) bringar revolutionerande förändring inom området för trådlösa nätverk. Det är en pålitlig teknik i tillämpningar såsom bredband hemma nätverk, nätverkshantering och senaste transportsystem. WMNs består av mesh routrar, kunder mesh och gateways. Det är en speciell typ av trådlöst ad-hoc-nätverk. En av frågorna i WMNs är resurshushållning som inkluderar routing och routing det finns särskilda routingprotokoll som ger bättre prestanda vid kontroll med vissa parametrar. Parametrar i WMNs omfatta dröjsmål, genomströmning, belastningen på nätet etc. Det finns två typer av routingprotokoll dvs reaktiva protokoll och proaktiva protokoll. Tre routingprotokoll AODV, DSR och OLSR har testats i WMNs under vissa parametrar som är försenade, genomströmning och belastningen på nätet. Testning av dessa protokoll kommer att utföras i den optimerade Network Evaluation Tool (OPNET) Modeler 14.5. De erhållna resultaten från OPNET kommer att visas i denna avhandling i form av grafer. Denna uppsats kommer att bidra till att godkänna vilka routingprotokoll kommer att ge bäst resultat enligt den antagna förhållanden. Dessutom kommer denna uppsats rapport kommer att bidra till att göra mer forskning i framtiden på detta område och bidra till att generera nya idéer inom detta forskningsområde som kommer att öka och att nya funktioner i WMNs. / +46762749245

Recent advances in Wireless Mesh Networks (WMNs) have overcome the drawbacks of traditional wired networks and wireless ad hoc networks. WMNs will play a leading role in the next generation of networks, and the question of how to provide smooth mobility for WMNs is the driving force behind the research. The inherent characteristics of WMNs, such as relatively static backbones and highly mobile clients, require new handoff management solutions to be designed and implemented. This thesis first presents our research work on handoff management schemes in traditional WMNs. In general, a handoff process includes two parts, the MAC layer handoff and the network layer handoff. For the MAC layer handoff, a self-configured handoff scheme with dynamic adaptation is presented. Before the mobile node starts the probe process, it configures parameters for each channel to optimize the scan process. Moreover, a fast authentication scheme to reduce authentication latency for WiFi-based mesh networks is introduced. A tunnel is introduced to forward data packets between the new access router and the original reliable access router to recover data communication before the complete authentication process is finished. To minimize the network layer handoff latency, a hybrid routing protocol for forwarding packets is proposed: this involves both the link layer routing and the network layer routing. Based on the hybrid routing protocol, both intra-domain and inter-domain handoff management have been designed to support smooth roaming in WMNs. In addition, we extend our work to Vehicular Mesh Networks (VMNs). Considering the characteristics of VMNs, a fast handoff scheme is introduced to reduce handoff latency by using a multi-hop clustering algorithm. Using this scheme, vehicle nodes are divided into different multi-hop clusters according to the relative mobility. Some vehicle nodes are selected as assistant nodes; and these assistant nodes will help the cluster head node to determine the next access router for minimizing handoff latency. Extensive simulation results demonstrate that the proposed scheme can reduce handoff latency significantly.

<p>The Master’s thesis report describes the wireless mesh networks functions,</p><p>characteristics, network management and finally different protocols with security issues and applications. Wireless Networks (WMNs) are replacing wireless Infrastructure networks in many areas because of their lower and higher flexibility. The wireless mesh networks (WMNs) provides network access for both mesh and conventional clients through mesh routers and mesh clients. Communication across the network is formed via the bridge functions. Mesh router also provides the minimal mobility and form the backbone of WMNs.</p><p>Wireless mesh network has resolved the limitation of ad hoc networks which is ultimately improves the performance of Ad hoc networks. Security is a very important issue which can be resolve through proper management of network. The improvment of 802.11i security has greatly improved the network perfomance and increase the encryption and integrity security capabilities. The key points which are being addressed in this report are security issues and threats and their counter measures. Attacks which can come on diffent layers are being discussed in this survey. Security of wireless mesh network is still under consideration. Wireless mesh network are attracting more attention due to its enhanced features.</p><p>Wireless mesh network topology technology is being discussed in this report. Then network management of WMNs is explained and in the concluding chapters security issues are discussed. Threats, attacks and challenges of WMNs are discussed in this survey.</p>