Interference avoidance in wireless multi-hop networks

1 Motivation Wireless networks share the same unlicensed parts of the radio spectrum with devices of various types. For examples, cordless phones, wireless sensor networks, Bluetooth and microwave ovens can all access frequencies around 2.4 GHz. As a result, wireless networks operating near these devices are very likely to encounter interference from them. Since most of these devices do not know how to share frequencies with others, the only alternative left for wireless networks is to switch to another frequency (channel) if the current one is found to be occupied already. Currently in most cases, the channel assignment is done manually before deployment and often requires extensive site surveys. Another source of interference comes from within a wireless network itself. When multiple nodes within range of one another attempt to transmit simultaneously, collisions are bound to result. What’s worse, an intermediate node usually attempts to forward a received packet immediately, resulting in collision with further incoming traffic. It is known that the interference from within a multi-hop wireless network can degrade the overall performance of the network significantly [1]. To cope with the interference from both external devices and inside wireless nodes, we propose a new multi-channel MAC protocol called Blackbird. Blackbird is designed to allocate channels on a per-hop and per-burst basis and to locally blacklist channels that are found to be of poor quality. Blackbird uses blacklisting to avoid interference with external devices, while the per-hop and per-burst allocation is designed to reduce interference from within wireless networks.