Distributed channel assignment for interference-aware wireless mesh networks

The rapid success of wireless radio communication has shaped several aspects of our social and work lives. This success is still far from reaching its full potential: with the advent of the Internet of Things, future trends indicate an exponential increase of wireless devices for machine-to-machine communication. Due to the broadcast nature of the shared medium, wireless transmissions are potentially received by all network stations in the communication range of the sender. With an unsynchronized medium access, multiple transmissions may be active at the same time and thus interfere with each other. In consequence, multiple transmissions may collide at the receiver side and can not be properly decoded [1]. For this reason, protocols have been developed on the MAC layer to synchronize the medium access and thus reduce interference e ects [2]. One of these approaches in wireless mesh networks (WMNs) is channel assignment. The idea of channel assignment is to minimize the network-wide interference by utilizing non-overlapping channels for otherwise interfering wireless transmissions. This is feasible, since wireless mesh routers are usually equipped with multiple radios and commonly used wireless network technologies, such as IEEE 802.11, provide multiple non-overlapping channels [3]. Since IEEE 802.11 operates in the unlicensed frequency spectrum, the dense distribution of private and commercial network deployments of WLANs in urban areas poses a new challenge. Co-located networks compete for the wireless medium, thus decreasing the achievable network performance in terms of throughput and latency. Therefore, an important issue for e cient channel assignment is to also address external interference. This task is not trivial, since the external networks and devices are not under the control of the network operator and their radio activity is therefore hard to capture. The contributions of this dissertation comprise the design, implementation, and validation of models and algorithms to enable wireless multi-hop networks to become interferenceaware. This includes a measurement-based interference model that determines e ciently and accurately the interference relationships among network nodes in large-scale network deployments. A distributed channel assignment algorithm has been developed that considers external sources of interference. The overall solution has been experimentally validated in a large-scale wireless multi-hop multi-radio testbed and has signi cantly increased the network performance with regard to the network capacity.