Revisiting Sensor MAC for Periodic Monitoring: Why Should Transmitters Be Early Birds?

We propose a new sensor MAC protocol, called Bird- MAC, which is highly energy efficient in the applications where sensors periodically report monitoring status with a very low rate, as in structural health monitoring and static environmental monitoring. Two key design ideas of Bird-MAC are: (a) no need of early-wake-up of transmitters and (b) taking the right balance between synchronization and coordination costs. The idea (a) is possible by allowing a node (whether it is a transmitter or receiver) to wake up just with its given wake-up schedule, and letting a late bird (which wakes up later) notify its wake-up status to its corresponding early bird (which wakes up earlier), where the early bird just infrequently waits (i.e., nods) for the late bird's wake-up signal. The idea (b) is realized by designing Bird-MAC to be placed in a scheme between purely synchronous and asynchronous schemes. We provide rigorous mathematical analysis that is used to choose the right protocol parameters of Bird-MAC. We demonstrate the performance of Bird-MAC through extensive simulations, and real experiments using a 26 node testbed at an underground parking lot of our office building to monitor its structural health, where we confirm that energy consumption is reduced by about up to 45% over existing sensor MAC protocols.