Time synchronization is a prerequisite for some applications in sensor networks. In this paper, two methodologies facilitating this task will be introduced. One approach relies on the creation of a hierarchical structure to carry out synchronization. Many existing protocols, e.g., State-based synchronization protocol (SBSP) timing-sync protocol for sensor networks (TPSN), and lightweight tree-based synchronization (LTS), belong to this category. Another approach advocates pulse coupling among sensor nodes. Its basic idea is to achieve global synchronization through local pulse coupling. In this paper, we further explore self coupling by examine the impact to its performance under various network parameters such as node degree and network diameter. We will also introduce a method to reduce its message complexity by randomly turns on and off the sensor nodes for synchronization. It is shown that the self coupling can be superior to the hierarchy approach in many network environments.
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