Elsevier

Ad Hoc Networks

Volume 6, Issue 7, September 2008, Pages 1051-1077
Ad Hoc Networks

Protocols and architectures for channel assignment in wireless mesh networks

https://doi.org/10.1016/j.adhoc.2007.10.002Get rights and content

Abstract

The use of multiple channels can substantially improve the performance of wireless mesh networks. Considering that the IEEE PHY specification permits the simultaneous operation of three non-overlapping channels in the 2.4 GHz band and 12 non-overlapping channels in the 5 GHz band, a major challenge in wireless mesh networks is how to efficiently assign these available channels in order to optimize the network performance. We survey and classify the current techniques proposed to solve this problem in both single-radio and multi-radio wireless mesh networks. This paper also discusses the issues in the design of multi-channel protocols and architectures.

Introduction

IEEE 802.11-based wireless mesh networks (WMNs) consist of mesh routers and mesh clients equipped with IEEE 802.11 radio interfaces,3 where mesh routers have minimal mobility and provide wireless access to clients. Each node in a WMN can operate not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations, producing a wireless multi-hop environment [1].

Considering that the IEEE PHY specification [2] permits the simultaneous operation of three non-overlapping channels in the 2.4 gigahertz (GHz) band and 12 non-overlapping channels in the 5 GHz band, the use of multiple channels can improve the capacity of WMNs [3]. Multi-channel protocols and architectures are designed to exploit the available channels to enhance the overall throughput. To achieving this goal, there are two major challenges: (i) the channel assignment mechanism, which involves assigning channels to interfaces; and (ii) the routing mechanism, which involves routing packets. Although an ideal approach might consider both channel assignment and routing simultaneously, investigating the problem separately could reduce the complexity and prompt the conceptual understanding of issues. This paper focuses on the channel assignment problem and provides a literature survey on architectures and protocols proposed to solve the problem. It also discusses the impact of channel assignment on routing as well as other relevant issues. The survey provides an analysis of a very specific problem – channel assignment – in WMNs that was briefly discussed in the survey by Akyildiz et al. [1].

The remainder of the paper is organized as follows: Section 2 presents an overview of multi-channel wireless mesh networks. Section 3 discusses the issues found in single-radio WMNs and presents a classification for multi-channel protocols for this type of networks. Protocols for single-radio networks are grouped in Refs. [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Section 4 lists relevant concerns found in multi-radio networks. Then, a classification for multi-channel protocols and architectures for this kind of networks is proposed. Refs. [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37] refer to these channel assignment approaches. A summary of channel assignment techniques is presented in Section 5, and open research issues are discussed in Section 6. Finally, the conclusion is given in Section 7.

Section snippets

Multi-channel wireless mesh networks

In WMNs, mesh routers can have more than one interface, which can be tuned to different channels, forming a multi-channel multi-hop WMN as shown in Fig. 1. Some mesh routers also act as gateways between the mesh networks and external networks such as the Internet. A wireless link is established between two neighboring nodes when they have at least one interface tuned to the same channel. This architecture allows enhanced aggregate network throughput by segregating the collision domains into

Multi-channel single-radio networks

The channel co-ordination and selection mechanisms play main roles in protocols for multi-channel single-radio networks. The co-ordination mechanism should not only provide suitable ways to negotiate channels but also avoid new problems that result from the use of multiple channels. These problems along with channel selection mechanisms are presented in Section 3.1. Then, the taxonomy is given in Section 3.2.

Multi-channel multi-radio networks

Multi-radio approaches, unlike single-radio protocols, need not implement a co-ordination mechanism to achieve concurrent transmissions. For example, in Fig. 3b, note that the three links can operate simultaneously. In addition, nodes B and D can send and receive data at the same time. In general, channels may be statically or semi-dynamically assigned in order to avoid dynamic channel negotiations that require switch the radios between successive transmissions. However, new potential problems

Summary of channel assignment protocols and architectures

Table 2, Table 3 summarize some features of the protocols and architectures reviewed in this survey, for single-radio and multi-radio networks, respectively. The columns Deafness problem and M-Channel hidden terminal problem in Table 2 indicate whether a given protocol solves the respective problem or not. For those protocols that may suffer from such problems, the respective entry is marked as Unsolved. The column Implementation in Table 3 indicates if the proposed multi-radio scheme is

Open research issues

Many research issues regarding multi-channel protocols and architectures are still open. Below we list some important topics that need to be investigated.

  • Multi-rate capability

    To the best of our knowledge, no multi-channel protocol that exploits or explores in-depth the multi-rate capability of current 802.11 wireless cards has been proposed yet. For example, the single-radio TDMA protocol presented in [17] sets the transmission rate to a fixed value of 2 Mbps. By considering only homogeneous

Conclusion

The use of multiple channels can substantially improve the performance of wireless mesh networks. A key issue in such networks is how to efficiently utilize the available channels. This paper has surveyed, classified and reviewed the most relevant approaches for channel assignment in WMNs. We have classified them into two different categories: for single-radio and for multi-radio networks. Single-radio protocols are dynamic protocols that try to maximize the number of simultaneous data

Acknowledgements

We thank the anonymous reviewers for their valuable comments. This research was partially supported by National Science Foundation of USA under Grant CNR-0626380, Natural Science Foundation of China under Grants Nos. 60573138 and 60773091, National Basic Research Program of China (973 Program) under Grant No. 2006C B 303000, and National 863 Program of China under Grant No. 2005aa122320.

Jorge Crichigno received his B.S. in electrical engineering from the Catholic University of Asuncion, Asuncion, Paraguay, in 2004. He is currently a Ph.D. student in the Department of Electrical and Computer Engineering, the University of New Mexico. From March to July of 2007 he was visiting the School of Electronic, Information and Electrical Engineering at Shanghai Jiao Tong University. His current research interests include mobile and wireless mesh networks.

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    Jorge Crichigno received his B.S. in electrical engineering from the Catholic University of Asuncion, Asuncion, Paraguay, in 2004. He is currently a Ph.D. student in the Department of Electrical and Computer Engineering, the University of New Mexico. From March to July of 2007 he was visiting the School of Electronic, Information and Electrical Engineering at Shanghai Jiao Tong University. His current research interests include mobile and wireless mesh networks.

    Min-You Wu is an IBM Chair Professor in the Department of Computer Science and Engineering at Shanghai JiaoTong University. He serves as the Chief Scientist at Grid Center of Shanghai JiaoTong University. His research interests include grid computing, wireless networks, sensor networks, overlay networks, multimedia networking, parallel and distributed systems, and compilers for parallel computers. He has published over 110 journal and conference papers in the above areas. He is a member of ACM and a senior member of IEEE.

    Wei Wennie Shu received the Ph.D. degree from the University of Illinois at Urbana, Champaign. Since then, she worked at Yale University, the State University of New York at Buffalo, and University of Central Florida. She is currently an Associate Professor in the Department of Electrical and Computer Engineering, the University of New Mexico. Her current interests include dynamic scheduling, resource management, multimedia networking, distributed systems, and sensor networks. She is a member of ACM and a senior member of IEEE.

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