ABSTRACT
Wireless mesh network (WMN) is a radical network form of the everevolving wireless networks that marks the divergence from the traditional centralized wireless systems such as cellular networks and wireless local area networks (LANs). Similar to the paradigm shift, experienced in wired networks during the late 1960s and early 1970s that led to a hugely successful and distributed wired network formthe Internet-WMNs are promising directions in the future of wireless networks. The primary advantages of a WMN lie in its inherent fault tolerance against network failures, simplicity of setting up a network, and the broadband capability. Unlike cellular networks
where the failure of a single base station (BS) leading to unavailability of communication services over a large geographical area, WMNs provide high fault tolerance even when a number of nodes fail. Although by definition a WMN is any wireless network having a network topology of either a partial or full mesh topology, practical WMNs are characterized by static wireless relay nodes providing a distributed infrastructure for mobile client nodes over a partial mesh topology. Due to the presence of partial mesh topology, a WMN utilize multihop relaying similar to an ad hoc wireless network. Although ad hoc wireless networks are similar to WMNs, the protocols and architectures designed for the ad hoc wireless networks perform very poorly when applied in the WMNs. In addition, the optimal design criteria are different for both these networks. These design differences are primarily originated from the application or deployment objectives and the resource constraints in these networks. For example, an ad hoc wireless network is generally designed for high mobility multihop environment; on the other hand, a WMN is designed for a static or limited mobility environment. Therefore, a protocol designed for ad hoc wireless networks may perform very poorly in WMNs. In addition, WMNs are much more resource-rich compared with ad hoc wireless networks. For example, in some WMN applications, the network may have a specific topology and hence protocols and algorithms need to be designed to benefit from such special topologies. In addition, factors such as the inefficiency of protocols, interference from external sources sharing the spectrum, and the scarcity of electromagnetic spectrum further reduce the capacity of a single-radio WMN. In order to improve the capacity of WMNs and for supporting the traffic demands raised by emerging applications for WMNs, multiradio WMNs (MR-WMNs) are under intense research. Therefore, recent advances in WMNs are mainly based on a multiradio approach. While MR-WMNs promise higher capacity compared with single-radio WMNs, they also face several challenges. This chapter focuses on the issues and challenges for both single-radio WMNs and MR-WMNs, and discusses a set of existing solutions for MR-WMNs. It begins with a comparison of WMNs with ad hoc wireless networks and proceeds to discuss the issues and challenges in MR-WMNs. The main contribution of this chapter is the detailed discussion on the issues and challenges faced by MR-WMNs, presentation with illustrations of a range of recent solutions for architectures, link layer protocols, medium access control (MAC) layer protocols, network layer protocols, and topology control solutions for MR-WMNs.
