Challenges and issues in designing architectures and protocols for wireless mesh networks

Abstract

Wireless Mesh Network (WMN) is a promising wireless technology for several emerging and commercially interesting applications, e.g., broadband home networking, community and neighborhood networks, coordinated network management, intelligent transportation systems. It is gaining significant attention as a possible way for Internet service providers (ISPs) and other end-users to establish robust and reliable wireless broadband service access at a reasonable cost. WMNs consist of mesh routers and mesh clients as shown in Fig. 1.1. In this architecture, while static mesh routers form the wireless backbone, mesh clients access the network through mesh routers as well as directly meshing with each other. Different from traditional wireless networks,WMNis dynamically self-organized and self-configured. In other words, the nodes in the mesh network automatically establish and maintain network connectivity. This feature brings many advantages for the end-users, such as low up-front cost, easy network maintenance, robustness, and reliable service coverage. In addition, with the use of advanced radio technologies, e.g., multiple radio interfaces and smart antennas, network capacity in WMNs is increased significantly. Moreover, the gateway and bridge functionalities in mesh routers enable the integration of wireless mesh networks with various existing wireless networks, such as wireless sensor networks, wireless-fidelity (Wi-Fi), and WiMAX [3]. Consequently, through an integrated wireless mesh network, the end-users can take the advantage of multiple wireless networks. Some of the benefits and characteristics of wireless mesh networks are highlighted as follows: Increased Reliability: In WMNs, the wireless mesh routers provide redundant paths between the sender and the receiver of the wireless connection. This eliminates single point failures and potential bottleneck links, resulting in significantly increased communications reliability [3]. Network robustness against potential problems, e.g., node failures, and path failures due to RF interferences or obstacles, can also be ensured by the existence of multiple possible alternative routes. Therefore, by utilizing WMN technology, the network can operate reliably over an extended period of time, even in the presence of a network element failure or network congestion. Low Installation Costs: Recently, the main effort to provide wireless connection to the end-users is through the deployment of 802.11 based Wi-Fi Access Points (APs). To assure almost full coverage in a metro scale area, it is required to deploy a large number of access points because of the limited transmission range of the APs. The drawback of this solution is highly expensive infrastructure costs, since an expensive cabled connection to the wired Internet backbone is necessary for each AP. On the other hand, constructing a wireless mesh network decreases the infrastructure costs, since the mesh network requires only a few points of connection to the wired network. Hence, WMNs can enable rapid implementation and possible modifications of the network at a reasonable cost, which is extremely important in today' s competitive market place. Large Coverage Area: Currently, the data rates of wireless local area networks (WLANs) have been increased, e.g., 54 Mbps for 802.11a and 802.11g, by utilizing spectrally efficient modulation schemes. Although the data rates of WLANs are increasing, for a specific transmission power, the coverage and connectivity of WLANs decreases as the end-user becomes further from the access point. On the other hand, multi-hop and multi-channel communications among mesh routers and long transmission range of WiMAX towers deployed in WMNs can enable long distance communication without any significant performance degradation. Automatic Network Connectivity: Wireless mesh networks are dynamically self-organized and self-configured. In other words, the mesh clients and routers automatically establish and maintain network connectivity, which enables seamless multi-hop interconnection service. For example, when new nodes are added into the network, these nodes utilize their meshing functionalities to automatically discover all possible routers and determine the optimal paths to the wired Internet [3]. Furthermore, the existing mesh routers reorganize the network considering the newly available routes and hence, the network can be easily expanded. In this chapter, we present a survey of recent developments in the protocols and architectures for WMNs and discuss the opportunities and challenges of WMNs. The motivation of this chapter is to provide a better understanding of wireless mesh network technology that can ensure heterogeneous application requirements. Consequently, our aim is to present a structured framework for the end-users who plan to utilize WMNs for their applications and hence, to make the decision-making process more effective and direct. The rest of the chapter is organized as follows. In Section 1.2 the network architecture of WMNs is presented, while in Section 1.3 the design challenges of WMNs are described. The recent advances and open research issues in protocol design for WMNs are investigated in Section 1.4. Physical testbeds and standardization activities in WMNs are explored in Section 1.5 and 1.6, respectively. Finally, the conclusions are stated. © 2007 Springer Science+Business Media, LLC. 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