Completely Distributed Low Duty Cycle Communication for Long-Living Sensor Networks

A lifetime of several years for wireless sensor nodes can be achieved if their activity period is minimized. This can be done by using low duty cycle protocols. One of the challenges of these low duty cycle protocols is the synchronization of wake-up times. This becomes even more demanding if a wired central sink, which takes care of the schedule, is missing and communication links are unreliable. In this paper, we present our own distributed low duty cycle MAC (DLDC-MAC) protocol, which achieves a lifetime of two years using off-the-shelf sensor nodes. Our protocol synchronizes wake-up times of nodes in a fully decentralized way, even when plenty of transmitted packets get lost. We evaluated this in a real world scenario with 10 sensor nodes working for 14 days in our office space. Interestingly, the experiment showed that direct communication over long distances led to very high packet error rate, sometimes higher than 30%. In that case, multi-hop transmission delivered data with much higher reliability, with packet error rate close to 0%.