The capacity problem in wireless mesh networks can be alleviated by equipping the mesh routers with multiple radios tuned to non-overlapping channels. However, channel assignment presents a challenge because co-located wireless networks are likely to be tuned to the same channels. The resulting increase in interference can adversely affect performance. This paper presents an interference-aware channel assignment algorithm and protocol for multi-radio wireless mesh networks that address this interference problem. The proposed solution intelligently assigns channels to radios to minimize interference within the mesh network and between the mesh network and co-located wireless networks. It utilizes a novel interference estimation technique implemented at each mesh router. An extension to the conflict graph model, the multi-radio conflict graph, is used to model the interference between the routers. We demonstrate our solution’s practicality through the evaluation of a prototype implementation in a IEEE 802.11 testbed. We also report on an extensive evaluation via simulations. In a sample multi-radio scenario, our solution yields performance gains in excess of 40% compared to a static assignment of channels.

Flash crowds and high concentrations of users in wireless LANs (WLANs) cause significant interference problems and unsustainable load at access points. This leads to poor connectivity for users, severe performance degradation, and possible WLAN collapse. To validate this claim, we present two case studies of large, heavily loaded operational WLANs. These studies provide significant insight into the degraded performance and collapse of a WLAN during heavy use. To address these problems, we propose IQU, a practical queue-based user association management system for heavily loaded WLANs. IQU grants users fair opportunities to access the WLAN while maintaining high overall throughput, even when the WLAN is heavily loaded. The basic premise of IQU is to control user associations with the WLAN through request queues and work period allocations. We implement a prototype of IQU and evaluate it on a wireless testbed. Our evaluation demonstrates that IQU significantly improves network throughput under heavy load; the tradeoff is that users have to wait for network access. We explore the impact of IQU parameters on system performance, and validate the robustness of IQU under heavy load conditions. Through IQU, WLANs can be utilized efficiently and network collapse prevented.

With the advent of small form-factor devices, protocol standardization, and robust protocol implementations, multi-hop mobile networks are witnessing widespread deployment. The monitoring of such networks is crucial for their robust operation. To this end, this paper presents DAMON, a distributed system for monitoring multi-hop mobile networks. DAMON uses agents within the network to monitor network behavior and send collected measurements to data repositories. DAMON's generic architecture supports the monitoring of a wide range of protocol, device, and network parameters. Other key features of DAMON include seamless support for multiple repositories, auto-discovery of sinks by the agents, and resiliency of agents to repository failures. We have implemented DAMON agents that collect statistics on data traffic and the ad hoc on-demand distance vector (AODV) routing protocol. We have used our implementation to monitor an ad hoc network at the 58th Internet Engineering Task Force (IETF) meeting held November 2003 in Minneapolis, MN. In this paper, we describe the architecture of DAMON and report on the performance of the IETF network using monitoring information collected by DAMON. Our network monitoring system is available online for use by other researchers.