Hybrid time synchronization protocol for large-scale wireless sensor networks

There are two common approaches to design a time synchronization protocol as reference-based and consensus-based. The first approach is mainly employed in protocols operating in large-scale wireless sensor networks (WSNs) because of its fast convergence. However, reference-based time synchronization protocols are vulnerable to node-failure in real-world applications. Although consensus-based time synchronization protocols do not experience the aforementioned problem, they are not suitable for operation in large-scale WSNs owing to their slow convergence. In this study, we propose a hybrid time synchronization protocol (HTSP) to utilize the advantages of both approaches. In particular, HTSP exploits a temporary reference node to significantly reduce the convergence time and employs average-based consensus during normal operation to cope with node failures. It is notable that each node in HTSP can seamlessly switch between the reference and consensus modes during its operation. Moreover, HTSP is a fully distributed protocol as it does not rely on any leader-election mechanism. Our simulation results demonstrated that HTSP outperforms flooding, gradient, and virtual link-based time synchronization protocols considering various types of network topologies and scales.