Low latency scheduling for convergecast in ZigBee tree-based wireless sensor networks

Convergecast is a fundamental operation in many wireless sensor network (WSN) applications. When gathering data, power saving and convergecast latency are two main concerns. This work adopts the ZigBee tree networks to address these two concerns. In a ZigBee tree network, to support energy efficient operations, each node is assigned to an active portion (or say slot). A node wakes up at its slot and its parent's slot to collect data from its children and to report data to its parent, respectively. Then, it can go to sleep to save energy. To support low latency convergecast, in this work, we propose a centralized and a distributed slot assignment schemes for ZigBee tree networks. We observe that when assigning slots, the latency can be further reduced by reconnecting some tree links. More specifically, by the designed rules, a node is allowed to locally modify some of its neighbors' parents, and then the node can be assigned to a better slot that can have the benefit of reducing the node's report latency. Simulation and implementation results show that the proposed schemes can effectively reduce the convergecast latency in ZigBee tree-based WSNs.