**1. Introduction**

46 Wireless Mesh Networks – Efficient Link Scheduling, Channel Assignment and Network Planning Strategies

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> In this section, an overview of Wireless Mesh Networks (WMNs) is presented, and some unique features which distinguish WMNs from Mobile Ad hoc Networks (MANETs) and Wireless Sensor Networks (WSNs) are listed. The main purpose of this chapter is discussed, and the contribution is presented along with the main features of this work.

### **1.1. Overview**

The use of Wireless Local Area Networks (WLANs) has grown tremendously in the past few years due to their ease of deployment and maintenance. However, the access points in these WLANs have to be connected to the backbone network through wired media. Wireless Mesh Networks offer an attractive alternative for providing broadband wireless Internet connectivity by using a wireless backhaul network and eliminating the need for extensive cabling.

In traditional WLANs, each Access Point (AP) is connected to the wired network while only a subset of APs is connected to the wired network in WMNs. An AP that is connected to the wired network is called Gateway (GW); APs without wired connections are called Mesh Routers (MRs), and they connect to the GW through multiple hops. Like routers in a wired network, MRs in a WMN forward each other's traffic to establish and maintain their connectivity. MRs and GWs are similar in design, with the only difference that a GW is directly connected to the wired network, while a MR is not. Figure 1 shows a sample mesh network in a typical enterprise such as a university [1]. The following are some unique features that distinguish WMNs from MANETs and WSNs [1].

© 2012 Chaudhry and Hafez, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Channel Assignment Using Topology Control Based on Power Control in Wireless Mesh Networks 49

To the best of our knowledge, the proposed channel assignment algorithm is the first of its kind to use topology control based on power control for channel assignment in multi-radio

The main purpose of network topology control using power control is to minimize the interference between a MR and other MRs in the network by adjusting its transmission range using transmission power control. This leads to a better frequency reuse during channel assignment, which results in achieving the objective of significant improvement in

Specifically, the contribution of this work is as follows: "*A new Topology-controlled Interference-aware Channel-assignment Algorithm (TICA) which intelligently assigns the available non-overlapping 802.11a frequency channels to the mesh routers with the objective of minimizing interference and, thereby, improving network throughput*." The main features of this work are as

 A Topology Control Algorithm (TCA) named *Select x for less than x*; that builds the network topology by selecting the nearest neighbors for each node in the network, with the objective of minimizing interference among MRs and enhancing frequency reuse. A scheme that uses the minimum power as the link weight when building the Shortest Path Tree (SPT) with the required node degree with the objective of minimizing inter-

 A Channel Assignment Algorithm (CAA), TICA, which assigns the available nonoverlapping 802.11a frequency channels to the mesh nodes with the objective of improving the overall network throughput by minimizing interference between mesh nodes as well as ensuring connectivity between them. This work was first presented in

 A centralized Failure Recovery Mechanism (FRM) for TICA which provides automatic and fast failure recovery by reorganizing the network in order to bypass the failed node

The rest of the chapter is organized as follows. The related work on topology control and CAAs is presented in Section 2. Section 3 discusses the medium access issues encountered by IEEE 802.11 [4] single-radio single-channel nodes. The channel assignment problem is presented in this section with respect to multi-radio multi-channel wireless mesh network. Section 4 presents the network architecture for the proposed model and the proposed topology control algorithm and CAA, along with the details of their respective phases. The FRM of the proposed CAA is also presented in this section. Section 5 provides a performance evaluation of the proposed CAA. The network topologies used for performance evaluation are discussed.

and to restore connectivity. This work was first presented in [3].

**1.2. Motivation** 

multi-channel wireless mesh networks.

ference and enhancing frequency reuse.

the overall network throughput.

**1.3. Contribution** 

follows.

[2].

**1.4. Organization** 

**Figure 1.** A sample enterprise WMN [1]

#### **Mesh routers are static**

Mesh routers in a WMN are stationary; therefore, the route selection should focus on discovering links that interfere with as few nodes as possible to provide high end-to-end throughput.

#### **Mesh routers have no power constraint**

In contrast to traditional wireless networks, such as MANETs and WSNs, where nodes are typically power-constrained, MRs have abundant power at their disposal.

#### **Mesh routers have multiple radios**

With the reduced cost of radios, MRs can be equipped with multiple radios. Hence, simultaneous transmission and reception can be achieved using intelligent channel assignment to these radios.

#### **The traffic model is different**

In MANETs, traffic can be from any peer Mobile Node (MN) to any other MN, while in WMNs, traffic is between MRs and the GW.

#### **Traffic is concentrated along certain paths**

In MANETs, traffic distribution is generally assumed to be uniform, while in WMN, traffic is concentrated along the paths directed towards the GW.

#### **Traffic volume is high**

MANETs have been designed essentially for enabling communication within a small group of people, while WMNs aim to provide high-bandwidth broadband connections to a large community, and thus should be able to accommodate a large number of users accessing the Internet. Due to high estimated traffic volume in WMNs, scalability and fault tolerance become important considerations in algorithm design.
