| With the development of the wireless communication technology, many wireless communication standards have emerged to provide the convenient services and easy accessing to Internet. Technologies such as Wifi, WiMax, UWB, Bluetooth, 3G and 4G, greatly improve the user experience and make the dream of communicate at any time any where come true. However, most of these wireless networks work in infrastructure mode, in which all clients get to the Internet through Base Stations or Access Points by one hop wireless connection. Therefore, the coverage of the wireless network is relatively small due to the limitation of the transmitting distance of wireless signals. In addition, since the deployment of the wireless network depends on the availability of wired infrastructure greatly, it increases the cost of building up wireless network to cover large area. Thus, in order to expand the coverage of wireless network, reduce the deployment cost, and provide flexible network configuration, a new concept"Wireless Mesh Network"(WMN) is proposed.?WMN is a kind of multiple hop wireless network, in which the mesh routers build multiple hop forwarding paths for the Internet access of the clients. Different from traditional one hop wireless network, WMN is a distributed and multi-hop network which has a mesh topology. In WMN, the position of a mesh router is relative stable and the power supply is very steady, which makes the life of the network is long and the link state is more stable compared with Ad Hoc networks. In addition, WMN is designed for the Internet access and the flow in network is apparently directional. Due to such differences, conventional wireless Media Access Control (MAC) protocols and wireless routing protocols are not suitable for WMN and lead to low efficiency.Aiming at improving the whole performance of WMN, we study the key issues on MAC layer and routing layer from bottom to top. These issues include network accessing, packet queue scheduling, cooperative routing and load balancing by multi-path routing. We investigate the reasons why existing MAC protocols and routing protocols are inefficient and unfair in WMN scenarios, and then a series of fantastic solutions which suitable for WMN are presented. By re-designing and implementing new protocols which take the characteristic of WMN into consideration, efficiency and fairness are achieved. The network performance and the use experience are also improved.First of all, in order to provide the QoS support for access network in WMN, we present a QoS-aware time slot requesting and assigning algorithm which works in infrastructure mode. In our solution, clients evaluate the time that needed to transmit data packet in each scheduling period by calculating the transmitting time of the buffered packets. After collecting all time slot requests, the base station arranges the channel time allocation according to the QoS priority of each flow. In addition, the base station dynamically adjusts the assigned time slot according to each client's utility of the channel time allocation and the transmitting time of the buffered packet. Though this solution, the bandwidth for flows with high QoS can be satisfied and the utility of the wireless channel can be improved at the same time.Secondly, we investigate the unfairness between flows in the traditional single MAC single queue scheme when network is congested. After analyzing the reasons of the unfairness, we propose a link level load-aware queue scheduling algorithm which is a single MAC multi-queue scheme. By scheduling the transmission on non-congested or light-congested links while suppress the transmission on real-congested links, the proposed scheduling scheme reduces the unfairness between flows and in addition improves the network performance in terms of the throughput, end to end delay and packet drop ratio.Thirdly, in order to explore the advantage of wireless broadcast property, we theoretically analyze the profit that cooperative transmission can bring to WMN based on the probability of successful transmission. After that we propose an ETX-based cooperative routing metric which takes account of the potential transmitting opportunities by node cooperation. Furthermore, we expand the HWMP routing protocol and the standard CSMA/CA MAC protocol to support the node cooperation. Through the cross-layer design, the proposed solution explores the wireless broadcast advantage very well and improves the network performance by reducing the packet drop ratio.Finally, we design and implement a cross-layer load balance solution to solve the hot path problem induced by the greedy strategy in route selection. We first analyze the working principle of the standard CSMA/CA, and then investigate the relationship between the RTS resend probability and the node congestion. Then a node congestion evaluating metric is proposed based on the RTS resend probability. We expand the HWMP routing protocol to support multipath routing protocol. By computing the congestion evaluating metric in real time and distributing the traffic load properly on multiple routing paths, the proposed solution can balance the load in WMN very well and thus improve the network performance in terms of the packet drop ratio, end to end delay and the user experience, which are proven by the simulation results.On the whole, the proposed MAC protocols and routing protocols which characterized by the efficiency and fairness can provide high performance services for medium accessing and routing in WMN and further improve the user experience. The study of this dissertation provides a strong foundation for other related research in WMNs in the future.
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