TPC and Non-TPC Based Topology Control Approaches for QoS Improvement in MR-WMN

Introduction

A wireless mesh network (WMN) is a networking paradigm, which enables inexpensive peer wireless network nodes to relay frames from one node to another by leveraging the broadcast nature of wireless medium. Essentially, WMN facilitates to cost-effectively and quickly extend a wired network by creating multiple topologically diversified wireless connections between peer nodes. This feature coupled with the dynamic reconfiguration of links, increases robustness. Mesh networks are very reliable and self-healing (Hossain & Leung, 2007), i.e., the network can still operate even when a node breaks down or a specific link is not usable any more. A mesh network whose nodes are all connected to each other is known as a fully connected WMN.

The drawback of a single radio mesh network is that the throughput of the link between each hop progressively decreases due to the co-channel interference (BelAir networks, 2006). As such, the core network considered in this chapter and shown in Figure 1 is a multi-radio wireless mesh network (MR-WMN) in which multi-radio nodes, which are also known as wireless routers, are used to result in a decrease of the interference between the channels of two adjacent routers (Mobileman, 2005). In Figure 1 the multi-radio routers with an exclusive wireless connectivity are termed as client nodes. The root node in the mesh networking terminology is known as the mesh portal node. MR-WMN is used to facilitate broadband wireless connectivity to the heterogeneous access networks such as 2G/3G, PSTN, Cdma etc. In the MR-WMN node, we are considering multiple 802.11 based interfaces corresponding to the 802.11 radios in a node. The 802.11 radios are: 802.11a, 802.11b, 802.11g. Each of the radio interfaces can communicate with an interface of the same radio type by using a channel within the frequency range of the radio type. The mesh nodes i.e. mesh routers which also have an access point functionality are termed as the mesh access point (MAP). The MAPs in Figure 1 essentially multi-hop the traffic to and from the access networks and the wired Internet.

Figure 1.

Multi-Radio wireless mesh network (MR-WMN) infrastructure

A self-organization (defined later in section on multi-agent systems) process that methodically allocates the channels to the MR-WMN nodes in the system facilitates to make the throughput of the links, as much as possible, less susceptible to the channel interference.

Transmit power control (TPC) has a bearing on the transmission range of the node’s radio. As such, it influences the physical distance of the link between the radios of two nodes. This leads to a topology control (TC) of the wireless mesh networks. The topology of a MR-WMN has a bearing on the overall system capacity and other Quality of Service (QoS) metrics viz. end-to-end packet transfer latency, jitter and throughput. TC is an extensively studied topic in the area of wireless telecommunication networks, particularly in the mobile ad hoc and sensor networks wherein energy is considered as a critical resource. Reference (Mobileman, 2005) informally defines TC as: “The art of coordinating nodes decision regarding their transmitting ranges, in order to generate a network with the desired properties (e.g. connectivity) while reducing node energy consumption and/or increasing network capacity.”

There are two key reasons that motivate to have a proper TC in a MR-WMN. These are enumerated below: