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Global clock synchronization is important to mobile wireless multihop networks that require precise timing information for data collection and energy conservation in MAC layer protocols. In this paper, we propose a global clock synchronization protocol for Delay Tolerant Network (DTN). The protocol achieves global clock synchronization under asynchronous, long delayed, and intermittent network dynamics of DTN by compensating clock errors with contacted nodes using propagated relative clock information and updating stored information according the compensated logical clock information. Simulation results are given to demonstrate the convergence speed and robustness of the proposed protocol.

Clock synchronization is a fundamental issue in communication networks and distributed systems, and clock skew is the inherent cause for clock desynchronization. Clock skew estimation is essential to improve the efficiency and reduce the overhead of clock synchronization schemes, and it is especially beneficial for resource-constrained devices such as sensor nodes in dynamic environments. According to the measurement, clock skew is environment sensitive, and no existing clock skew estimation schemes can accurately capture such dynamic behaviors. In this paper, we investigate a general clock synchronization problem with variable clock skews and propose a new skew estimation model based on a hybrid approach to characterizing the dynamic of clock skews. To estimate the time-varying clock state vector, we employ the Interactive Multi-Model (IMM) Kalman filter, which can make soft decisions by combining results from different models. Extensive simulations have been conducted to demonstrate the effectiveness of the proposed adaptive clock skew estimation algorithm, which achieves a better performance with moderate computational complexity.