Channel assignment in wireless mesh network (WMN) aims at improving the network throughput by utilizing multiple orthogonal frequency channels to minimize the interference. Interference can be categorized as coordinated and non-coordinated, depending upon the relative location of the interfering links. Compared to coordinated interference, non-coordinated interference has a severe adverse impact on throughput. This thesis is based on the hypothesis that the network throughput can be improved significantly, if channel assignment minimizes non-coordinated interference with priority. We propose a static and centralized channel assignment scheme CCAS to show the effectiveness of the hypothesis. The cluster-based approach of CCAS minimizes non-coordinated interference with reduced complexity. CCAS improves the network throughput by upto 80%, compared to the existing schemes. We propose topology control scheme MATS that constructs low interference multipath network topology using a subset of links from physical topology. We report an additional improvement of upto 10% in the network throughput, when CCAS assigns channels to the links selected by MATS. In the final part of the thesis, we formulate generalized channel assignment as an optimization problem, accounting for real network traffic. The objective of the problem is to select the channels for links such that maximum incident traffic can be transmitted over the links, while ensuring a fair distribution of throughput amongst links and elimination of non-coordinated interference. For a given network and incident traffic, the solution to this problem generates the channel assignment resulting in optimal network throughput. We propose dynamic and distributed scheme LYCAS as an approximate solution to the problem. LYCAS employs MATS to construct network topology and cluster-based approach of CCAS to minimize non-coordinated interference. In addition, it periodically updates the assignment of channels to adapt to the changing traffic load. LYCAS achieves upto 68% of the optimal network throughput and upto 72% of optimal aggregate end-to-end throughput of multi-hop flows. It outperforms the existing schemes by a factor of 2.

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This work proposes a distributed dynamic channel assignment of multi-channel MAC protocol in Ad-Hoc networks. Major characteristics of the proposed protocol are: (a) each mobile node is equipped with two network interfaces, (b) no time synchronization is needed, (c) distribution channel assignment. The proposed protocol reduces the cost of channel negotiation by considering the property that a connection generates multiple frames for transmitting and can assign channel information faster. Compared with other multi-channel MAC protocols, the proposed algorithm allows the whole network channel allotment be stable quickly. The performance evaluation is conducted on NS-2. Simulation results show that the proposed protocol can reduce the cost of channel negotiation significantly, increase the network throughput.

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

One of the most popular and useful areas of graph theory is graph colorings. A graph coloring is an assignment of integers to the vertices of a graph so that no two adjacent vertices are assigned the same integer. This problem frequently arises in scheduling and channel assignment applications. A list coloring of a graph is an assignment of integers to the vertices of a graph as before with the restriction that the integers must come from specific lists of available colors at each vertex. For a physical application of this problem, consider a wireless network. Due to hardware restrictions, each radio has a limited set of frequencies through which it can communicate, and radios within a certain distance of each other cannot operate on the same frequency without interfering. We model this problem as a graph by representing the wireless radios by vertices and assigning a list to each vertex according to its available frequencies. We then seek a coloring of the graph from these lists. In this thesis, we give an overview of the last thirty years of research in list colorings. We begin with an introduction of the list coloring problem, as defined by Erdös, Rubin, and Taylor in [6]. We continue with a study of variations of the problem, including cases when all the lists have the same length and cases when we allow different lengths. We will briefly mention edge colorings and overview some restricted list colors such as game colorings and L(p, q)-labelings before concluding with a list of open questions. / Master of Science

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Automatic spectrum management and monitoring systems are very useful to manage frequencies at test ranges and assure interference-free transmission of telemetry signals. Spectrum management systems assign telemetry frequencies using database information on available and occupied channels and analysis tools which can determine whether a data link will support telemetry. Modern, DSP-based spectrum monitoring systems, in fixed or mobile configurations, automate the process of performing spectrum occupancy to verify clear channels and identify and locate sources of interference; they are integrated with and utilize the management system database. Such systems are important to assure reliable communications channels for telemetry.

This thesis proposes a potential solution for future ubiquitous broadband wireless access networks, called a cellular wireless mesh network (CMESH), and investigates a number of its performance issues. A CMESH is organized in multi-radio, multi-channel, multi-rate and multi-hop radio cells. It can operate on abundant high radio frequencies, such as 5-50 GHz, and thus may satisfy the bandwidth requirements of future ubiquitous wireless applications.<p> Each CMESH cell has a single Internet-connected gateway and serves up to hundreds of mesh nodes within its coverage area. This thesis studies performance issues in a CMESH, focusing on cell capacity, expressed in terms of the max-min throughput. In addition to introducing the concept of a CMESH, this thesis makes the following contributions.<p> The first contribution is a new method for analyzing theoretical cell capacity. This new method is based on a new concept called Channel Transport Capacity (CTC), and derives new analytic expressions for capacity bounds for carrier-sense-based CMESH cells.<p> The second contribution is a new algorithm called the Maximum Channel Collision Time (MCCT) algorithm and an expression for the nominal capacity of CMESH cells. This thesis proves that the nominal cell capacity is achievable and is the exact cell capacity for small cells within the abstract models.<p> Finally, based on the MCCT algorithm, this thesis proposes a series of greedy algorithms for channel assignment and routing in CMESH cells. Simulation results show that these greedy algorithms can significantly improve the capacity of CMESH cells, compared with algorithms proposed by other researchers.

This thesis proposes a potential solution for future ubiquitous broadband wireless access networks, called a cellular wireless mesh network (CMESH), and investigates a number of its performance issues. A CMESH is organized in multi-radio, multi-channel, multi-rate and multi-hop radio cells. It can operate on abundant high radio frequencies, such as 5-50 GHz, and thus may satisfy the bandwidth requirements of future ubiquitous wireless applications.<p> Each CMESH cell has a single Internet-connected gateway and serves up to hundreds of mesh nodes within its coverage area. This thesis studies performance issues in a CMESH, focusing on cell capacity, expressed in terms of the max-min throughput. In addition to introducing the concept of a CMESH, this thesis makes the following contributions.<p> The first contribution is a new method for analyzing theoretical cell capacity. This new method is based on a new concept called Channel Transport Capacity (CTC), and derives new analytic expressions for capacity bounds for carrier-sense-based CMESH cells.<p> The second contribution is a new algorithm called the Maximum Channel Collision Time (MCCT) algorithm and an expression for the nominal capacity of CMESH cells. This thesis proves that the nominal cell capacity is achievable and is the exact cell capacity for small cells within the abstract models.<p> Finally, based on the MCCT algorithm, this thesis proposes a series of greedy algorithms for channel assignment and routing in CMESH cells. Simulation results show that these greedy algorithms can significantly improve the capacity of CMESH cells, compared with algorithms proposed by other researchers.

Wireless communication is a rapidly growing segment of the communication industry, with the potential to provide low-cost, high-quality, and high-speed information exchange between portable devices. To harvest the available bandwidth efficientlyin a wireless network, they employ multiple orthogonal channels over multiple ra-dios at the nodes. In addition, nodes in these networks employ directional antennasas radios to improve spatial throughput. This dissertation develops algorithms forrouting and broadcasting with channel assignment in such networks. First, we com-pute the minimum cost path between a given source-destination pair with channelassignment on each link in the path such that no two transmissions interfere witheach other. Such a path must satisfy the constraint that no two consecutive links onthe path are assigned the same channel, referred to as "channel discontinuity con-straint." To compute such a path, we develop two graph expansion techniques basedon minimum cost perfect matching and dijkstra's algorithm. Through extensive sim-ulations, we study the effectiveness of the routing algorithms developed based onthe two expansion techniques and the benefits of employing the minimum cost per-fect matching based solution. Secondly, we study the benefits of sharing channelbandwidth across multiple flows. We model the routing and channel assignmentproblem in two different ways to account for the presence and absence of inter-flowbandwidth sharing. Benefits of multiple paths between a source-destination pairmotivates the problem of computing multiple paths between a source-destinationpair with channel assignment such that all the paths can be active simultaneouslyto achieve maximal flow between the pair in the considered network. Since finding even two such paths is NP-hard, we formulate the problem as an integer linearprogram and develop efficient heuristic to find these paths iteratively. Thirdly, wecompute a broadcast tree from a given root with channel assignment such that all the links in the broadcast tree can be active simultaneously without interferingwith each other. Since finding such a tree is an NP-hard problem, we formulatethe problem as an integer linear program (ILP) and develop heuristics to find thebroadcast tree with channel assignment. We evaluate and compare the performanceof the developed heuristics with respect to their success rate, average depth of theobtained tree, and average path length from root to a node in the network. Thisdissertation also analyzes the blocking performance of a channel assignment schemein a multi-channel wireless line network. We assume that the existing calls in thenetwork may be rearranged on different channels to accommodate an incoming call.The analysis is limited to single-hop calls with different transmission ranges.Finally, this dissertation evaluates the performance of disjoint multipath routingapproaches for all-to-all routing in packet-switched networks with respect to packetoverhead, path lengths, and routing table size. We develop a novel approach basedon cycle-embedding to obtain two node-disjoint paths between all source-destinationpairs with reduced number of routing table entries maintained at a node (hence thereduced look up time), small average path lengths, and less packet overhead. Westudy the trade-off between the number of routing table entries maintained at anode and the average length of the two disjoint paths by: (a) formulating the cycle-embedding problem as an integer linear program; and (b) developing a heuristic.We show that the number of routing table entries at a node may be reduced toat most two per destination using cycle-embedding approach, if the length of thedisjoint paths are allowed to exceed the minimum by 25%.