Implementation of Timestamped Pulse-Coupled Oscillators in IEEE 802.15.4 Networks

Time Synchronization (TS) is a key enabling technology of mission-critical Wireless Sensor Networks (WSNs) to provide a common timescale for distributed sensor nodes. Inspired by synchronous flashing of fireflies, a bio-inspired model, Pulse-Coupled Oscillators (PCO), has been intensively studied. The most studies on PCOs are theoretical work, and the assumption is given that oscillators broadcast and receive the Pulses simultaneously when synchronization of a network is achieved. This is not true when it comes to any real-world environments. From the viewpoint of WSNs, the clock of a sensor node driven by crystal oscillators can be modelled as an oscillator, and Pulse firing can be implemented by transmitting a packet. However, the concurrent transmission of Pulse packets is impossible due to the packet collision in the single wireless channel. To avoid this issue in WSNs, this paper adopts a desynchronization mechanism, in which the Pulse packets are transmitted to the wireless channel in a uniformly distributed fashion and in accordance with standard IEEE 802.15.4. A hardware testbed is developed to implement the desynchronized pulse-coupled oscillators, and it can also be extended to the large-scale wireless sensor networks.