Synchronization of Pulse-Coupled Oscillators for IEEE 802.15.4 Multi-Hop Wireless Sensor Networks

As a key enabling technology in mission-critical Wireless Sensor Networks (WSNs), time synchronization provides a common timescale for distributed sensor nodes in many wireless applications, such as coordinated control and underwater navigation and tactical surveillance. Inspired by the behaviour of fireflies, along with mathematical model, Pulse-Coupled Oscillators (PCO), has been proposed to enable synchronization in complex networks, where all the PCO's firing signal Pulses are broadcasted simultaneously when synchronization is achieved. The requirement of zero-drift clock oscillators, fully-connected network and concurrent transmission of Pulses are, in reality, impossible to achieve. To avoid transmission collision and enable the PCO extension in the multi-hop WSNs, the desynchronization mechanism is adopted to enable the Pulse packets to be transmitted to the wireless channel in a uniformly distributed fashion. Due to the contention-free period's feature of low-latency, thereby avoiding the need to wait for a random and potentially long period until the channel is available, the PCO's Pulse packets are transmitted in the contention-free period of IEEE 802.15.4-2015 superframe. Thus, a novel state-space model for desynchronization-based pulse-coupled nonidentical oscillators is proposed to model a realistic drifting clock oscillator. Moreover, the timestamped Pulse packets are transmitted to determine the offset of connected sensor nodes, and an attenuated clock correction scheme is adopted to correct the local drifting clocks by using measured offset and skew. The intensive simulations of the three-hop three-cluster wireless network and the seven-hop linear network have been carried out to evaluate performance of timestamped PCO with desyn-chronization method.