Analysis and mitigation of interference in multi-radio multi-channel wireless mesh networks

Abstract

Wireless mesh networking, which is basically forming a backbone network of mesh routers using wireless links, is becoming increasingly popular for a broad range of applications from last-mile broadband access to disaster networking or P2P communications, because of its easy deployment, self-forming, self-configuration, and self-healing properties. The multi-hop nature of wireless mesh networks (WMNs) aggravates inter-flow interference and causes intra-flow interference and severely limits the network capacity. One technique to mitigate interference and increase network capacity is to equip the mesh routers with multiple radios and use multiple channels. The radios of a mesh router can then simultaneously send or receive packets on different wireless channels. However, careful and intelligent radio resource planning, including flow-radio and channel assignment, is necessary to efficiently make use of multiple radios and channels. This first requires analyzing and modeling the nature of co-channel and adjacent channel interference in a WMN. Through real-world experiments and observations made in an indoor multihop multi-radio 802.11b/g mesh networking testbed we established, BilMesh, we first analyze and model the nature of co-channel and adjacent channel interference. We conduct extensive experiments on this testbed to understand the effects of using multi-radio, multi-channel relay nodes in terms of network and application layer performance metrics. We also report our results on using overlapping in addition to orthogonal channels for the radios of the mesh routers. We then turn our attention to modeling and quantifying adjacent channel interference. Extending BilMesh with IEEE 802.15.4 nodes, we propose computational methods to quantify interference between channels of a wireless communication standard and between channels of two different standards (such as Wi-Fi and ZigBee). Majority of the studies in the literature on channel assignment consider only orthogonal channels for the radios of a multi-radio WMN. Having developed quantitative models of interference, next we propose two optimization models, which use overlapping channels, for the joint flow-radio and channel assignment problems in WMNs. Then we propose efficient centralized and distributed heuristic algorithms for coupling flows and assigning channels to the radios of a WMN. The proposed centralized and distributed schemes make use of overlapping channels to increase spectrum utilization. Using solid interference and capacity metrics, we evaluate the performances of the proposed schemes via extensive simulation experiments, and we observe that our schemes can achieve substantial improvement over single-channel and random flow-radio and channel assignment schemes.