LevelSync: A hierarchical time synchronization mechanism for wireless sensor networks

Time synchronization in wireless sensor networks is a critical requirement for distributed and collaborative processing among the nodes. This paper presents a coarse grained hierarchical time synchronization scheme `LevelSync´ which synchronizes nodes in a sensor network with regards to their distance from the sink or master node. A hierarchical tree is dynamically constructed during the synchronization with master node acting as the root. The master node initiates and controls the synchronization phase and is responsible for normalizing the virtual time with the corresponding UTC. Each node is assigned a level and maintains a virtual clock which runs at a frequency different than that of its physical clock. Virtual clocks run at a fixed frequency calculated by the root or reference nodes hence are free from the drifts. LevelSync decreases the number of messages required for the synchronization and the resynchronization periods. We evaluate the performance and energy efficiency of the LevelSync through simulation and compare with existing time synchronization protocols. LevelSync is computationally light, energy efficient and achieves long lasting synchronizations.