Multi-Channel Multi-Hop Network Design in Unlicensed Bands

Recent success of wireless networks has increased the competition for wireless resources in unlicensed bands by a plethora of wireless devices, ranging from cordless phones to remotely controlled toys. As the overpopulation of unlicensed bands has become an imminent problem to solve, researchers in the wireless community have begun to actively seek more economic methods of utilizing the wireless spectrum. Among the proposals is the secondary use of a licensed band, where unlicensed devices use cognitive radios to identify and opportunistically access idle portions of a licensed band.;This thesis explores the idea of bringing this cognitive radio paradigm to the unlicensed wireless networking domain by devising a wireless system architecture called Cog-Fi for multi-channel multi-hop wireless networks that operate in the unlicensed band. The two major components of Cog-Fi are 1) a cognitive channel access solution in which every node measures the quality of each channel and constantly hops over channels that are sensed to be less occupied than others, and 2) a routing solution that takes channel load and link rates into account, which further improves the network performance. The thesis also suggests a channel scanning strategy that each node should employ to minimize the channel load estimation error when sensing the channels. The key idea of the schemes presented in this thesis is to equip network nodes with the ability to selectively use channels based on the level of interference that is sensed in each channel, while still maintaining the connectivity of a multi-channel multi-hop network, and this approach is shown to improve the network performance considerably.