Sharing a Medium Between Concurrent Protocols Without Overhead Using the Capture Effect

Most wireless systems suffer from the lack of a dedicated control plane. High-priority control messages have to contend for medium access the same as any other message. Existing methods providing QoS guarantees in this setting rely upon opportunistic sending or on scheduling mechanisms, and as a result incur undesirable tradeoffs in either latency or impact on regular non-priority traffic. We present a technique to simultaneously execute multiple protocols of different priorities, without compromising bandwidth or latency of regular traffic not affected by priority traffic. Using power control and moderately tight synchronization we exploit the capture effect to give each protocol almost complete access to the network’s resources as long as no protocol of higher priority wishes to use them. We examine which impact the properties of the network graph and the capabilities of the wireless hardware have on the effectiveness of our technique. We suggest an example scenario of a wireless sensor network of fire detectors, with a low-priority protocol collecting statistical data and confirming aliveness, while a highpriority protocol wishes to report fire alarms to a base station as quickly as possible. For this example application we deploy an implementation based on Contiki on a wireless testbed of TelosB motes and achieve near optimal latency and bandwidth for priority traffic while not disturbing lowpriority traffic where it is separated sufficiently in space or time.