Browsing by Subject "Wireless Mesh Networks"
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Item Open Access Analysis and mitigation of interference in multi-radio multi-channel wireless mesh networks(Bilkent University, 2013) Uluçınar, Alper RifatWireless mesh networking, which is basically forming a backbone network of mesh routers using wireless links, is becoming increasingly popular for a broad range of applications from last-mile broadband access to disaster networking or P2P communications, because of its easy deployment, self-forming, self-configuration, and self-healing properties. The multi-hop nature of wireless mesh networks (WMNs) aggravates inter-flow interference and causes intra-flow interference and severely limits the network capacity. One technique to mitigate interference and increase network capacity is to equip the mesh routers with multiple radios and use multiple channels. The radios of a mesh router can then simultaneously send or receive packets on different wireless channels. However, careful and intelligent radio resource planning, including flow-radio and channel assignment, is necessary to efficiently make use of multiple radios and channels. This first requires analyzing and modeling the nature of co-channel and adjacent channel interference in a WMN. Through real-world experiments and observations made in an indoor multihop multi-radio 802.11b/g mesh networking testbed we established, BilMesh, we first analyze and model the nature of co-channel and adjacent channel interference. We conduct extensive experiments on this testbed to understand the effects of using multi-radio, multi-channel relay nodes in terms of network and application layer performance metrics. We also report our results on using overlapping in addition to orthogonal channels for the radios of the mesh routers. We then turn our attention to modeling and quantifying adjacent channel interference. Extending BilMesh with IEEE 802.15.4 nodes, we propose computational methods to quantify interference between channels of a wireless communication standard and between channels of two different standards (such as Wi-Fi and ZigBee). Majority of the studies in the literature on channel assignment consider only orthogonal channels for the radios of a multi-radio WMN. Having developed quantitative models of interference, next we propose two optimization models, which use overlapping channels, for the joint flow-radio and channel assignment problems in WMNs. Then we propose efficient centralized and distributed heuristic algorithms for coupling flows and assigning channels to the radios of a WMN. The proposed centralized and distributed schemes make use of overlapping channels to increase spectrum utilization. Using solid interference and capacity metrics, we evaluate the performances of the proposed schemes via extensive simulation experiments, and we observe that our schemes can achieve substantial improvement over single-channel and random flow-radio and channel assignment schemes.Item Open Access Channel assignment and routing for multi-radio wireless mesh networks(Bilkent University, 2008) Gülten, SıtkıIn this study, we analyze the channel assignment and routing problem for multi-radio wireless mesh networks. We assume that each router has more than one radio, the system operates in a time-slotted mode, and channel assignments are static. In particular, within a time slot the channel assignments for radio connections have to obey the interference constraint. The union of all the connections established throughout the time horizon should result in a strongly connected network where each node can communicate with every other node within the given maximum hop-distance or the diameter value. The objective is to minimize the number of time slots used while respecting the interference and diameter restriction. An integer linear program is proposed as an exact methodology to solve the problem for small scale networks. For larger network sizes, three type of heuristic approaches are developed. In order to evaluate the quality of the heuristic solutions, the lower bound of the model is strengthened through the use of valid inequalities and lagrangian relaxation. The subgradient algorithm is used in lagrangian relaxation models to find optimal solutions or lower bounds. The heuristics are tested on a large set of varying network topology instances. The computational experiments illustrate that improvement heuristic based on local search is the most suitable approximation technique.Item Open Access Joint gateway selection, transmission slot assignment, routing and power control for wireless mesh networks(Elsevier, 2013-07) Gokbayrak, K.; Yıldırım, E. A.Wireless mesh networks (WMNs) provide cost effective solutions for setting up a communications network over a certain geographic area. In this paper, we study strategic problems of WMNs such as selecting the gateway nodes along with several operational problems such as routing, power control, and transmission slot assignment. Under the assumptions of the physical interference model and the tree-based routing restriction for traffic flow, a mixed integer linear programming (MILP) formulation is presented, in which the objective is to maximize the minimum service level provided at the nodes. A set of valid inequalities is derived and added to the model in an attempt to improve the solution quality. Since the MILP formulation becomes computationally infeasible for larger instances, we propose a heuristic method that is aimed at solving the problem in two stages. In the first stage, we devise a simple MILP problem that is concerned only with the selection of gateway nodes. In the second stage, the MILP problem in the original formulation is solved by fixing the gateway nodes from the first stage. Computational experiments are provided to evaluate the proposed models and the heuristic method.Item Open Access Joint routing, gateway selection, scheduling and power management optimization in wireless mesh networks(Bilkent University, 2011) Uzunlar, OnurThe third generation (3G) wireless communications technology delivers user traffic in a single step to the wired network via base station; therefore it requires all base stations to be connected to the wired network. On the other hand, in the fourth generation (4G) communication systems, it is planned to have the base stations set up so that they can deliver each other’s traffic to a small number of base stations equipped with wired connections. In order to improve system resiliency against failures, a mesh structure is preferred. The most important issue in Wireless Mesh Networks (WMN) is that the signals that are simultaneously transmitted on the same frequency channel can interfere with each other to become incomprehensible at the receiver end. It is possible to operate the links at different times or at different frequencies, but this also lowers capacity usage. In this thesis, we tackle the planning problems of WMN, using 802.16 (Wi-MAX) protocol, such as deploying a given number of gateway nodes along with operational problems such as routing, management of power used by nodes and scheduling while maximizing the minimum service level provided. The WMN under consideration has identical routers with fixed locations and the demand of each router is known. In order to be able to apply our results to real systems, we work with optimization models based on realistic assumptions such as physical interference and single path routing. We propose heuristic methods to obtain optimal or near optimal solutions in reasonable time. The models are applied to some cities in Istanbul and Ankara provinces.Item Open Access Solution methods for planning problems in wireless mesh networks(Bilkent University, 2012) Özdemir, GörkemWireless Mesh Networks (WMNs) consist of a finite number of radio nodes. A subset of these nodes, called gateways, has wired connection to the Internet and the non-gateway nodes transmit their traffic to a gateway node through the wireless media in a multi-hop fashion. Wireless communication signals that propagate simultaneously within the same frequency band may interfere with one another at a receiving node and may therefore prevent successful transmission of data. In order to circumvent this problem, nodes on the network can be configured to receive and send signals in different time slots and through different frequency bands. Therefore, a transmission slot can be defined as a pair of a certain frequency band and a specific time slot. In addition, by adjusting the power level of a radio node, its transmission range can be modified. Given a wireless mesh network with fixed node locations, demand rate at each node, and maximum power level for each node, we study the problem of carrying the traffic of each node to the Internet through the network. Our goal is to allocate capacities in proportion to the demand of each node in such a way that the minimum ratio is maximized. We propose a mixed integer linear programming (MILP) formulation to select a given number of gateway locations among the nodes in the network, to determine the routing of the traffic of each node through the gateway nodes, to assign transmission slots to each node in order to ensure no interference among wireless signals, and to determine the transmission power levels. In our study, we adopt the physical interference model, instead of the protocol interference, since this is more realistic. Since MILP formulation becomes computationally inefficient for larger instances; we developed several different approaches. Then, we proposed a combinatorial optimization model which successfully solves most of the instances. We tested our models and methods in several data sets, and results are presented.