Resource planning and packet forwarding in multi-radio, multi-mode, multi-channel, multi-rate (M 4 ) wireless mesh networks q Ting-Yu Lin a, * , Wai-Hong Tam b , Kang-Lun Fan a , Yu-Chee Tseng b a Department of Communication Engineering, National Chiao-Tung University, 1001 University Road, Hsinchu 300, Taiwan b Department of Computer Science, National Chiao-Tung University, 1001 University Road, Hsinchu 300, Taiwan Available online 8 February 2008 Abstract Most earlier works in the area of wireless mesh network assume a single interface being equipped in each node. In this paper, we consider the next-generation wireless mesh networks in which each node may be equipped with multiple radio interfaces, each capable of running in one of several modes (IEEE 802.11b/g 2.4 GHz or 802.11a 5 GHz mode), one of several channels, and each capable of supporting multiple modulations. We call such a network an M 4 (multi-radio, multi-mode, multi-channel, multi-rate) wireless mesh network. For example, from off-the-shelf components, one can easily construct a mesh node with multiple IEEE 802.11a/b/g radio interfaces. Our goal is to address the resource planning and packet forwarding issues in such an environment. The proposed methodology is based on linear programming with network flow principles and radio channel access/interference models. Given a network topology, traffic requirements, and gateway capac- ities, we show how to allocate network interface cards and their channels to fully utilize channel bandwidths. The results can be utilized by a wireless Internet service provider to plan their networks under a hardware constraint so as to maximize their profits. To the best of our knowl- edge, this is the first work addressing resource planning in a wireless mesh network. Our numerical results show significant improvement in terms of aggregate network throughput with moderate network-layer fairness. The importance of network planning is further corroborated by the simulative comparisons with other multi-radio systems assuming a known and fixed number of interfaces at each mesh router. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Resource planning; Routing; Channel assignment; Linear programming; Wireless ad hoc network; Wireless mesh network 1. Introduction The wireless mesh network (WMN) is a promising solu- tion to the last-mile wireless Internet access problem. It can effectively complement the limitation of WLAN coverage. Applications of WMN include enterprise wireless back- bones and community networks [15]. In [5], two mesh hier- archies are defined: infrastructure mesh and client mesh, where the former has much less mobility than the latter. Ref. [14] points out that a WMN may suffer from the sca- lability problem as the network grows due to the conten- tion and interference among hosts. To mitigate the scalability problem, one may explore advanced transmis- sion technologies (such as smart or MIMO antennas [11,17,22]) or layer-2 or layer-3 solutions based on com- modity radio modules [3,6,8,12,9,16,18,19,21]. Several works show how to increase WMN capacity by adaptively adjusting the data rates [4,7,13,20]. In this work, we adopt the latter approach based on commodity components. We explore the possibility of multi-interface, multi-channel model. For example, IEEE 802.11a/b/g has 12/3/3 non-overlapping channels avail- able. One can easily make a multi-interface mesh node by off-the-shelf components. 1 Several works have addressed 0140-3664/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2008.01.059 q The research of Ting-Yu Lin is sponsored by the NSC of Taiwan under Grant No. NSC96-2221-E-009-017. * Corresponding author. Tel.: +886 921 591603. E-mail address: tylin@csie.nctu.edu.tw (T.-Y. Lin). 1 With the advance of communication hardware technology, and cost- reduced networking modules, nowadays computing devices are often capable of operating/communicating on/through different radio frequen- cies (e.g., WiFi/Bluetooth/WCDMA possibly readily available at a single laptop, which may be installed with another WiFi card via the PCMCIA interface). Hence, equipping multiple wireless interfaces at a single host is getting affordable and its popularity can be expected in next-generation wireless-enabled computers. www.elsevier.com/locate/comcom Available online at www.sciencedirect.com Computer Communications 31 (2008) 1329–1342