Synchronization of Packet Coupled Low-Accuracy RC Oscillator Clocks for Wireless Networks

Time-sensitive wireless applications have strict requirements on real-time data transmission and control operation. Even though time synchronization has been extensively studied for providing a common timing among distributed wireless nodes, there still exists a lack of research for low-accuracy and large-drifting clocks, such as internal Resistor-Capacitor (RC) oscillator clocks with around $4\times 10^{5}$ parts per million (ppm) frequency drift, which are widely used in wearable sensor systems. This paper proposes a Proportional Packet-Coupled Oscillators (P-PkCOs) protocol for synchronizing poor-performing internal RC oscillator clocks with high disturbances in the single-cluster wireless network. The behaviour of such a drifting clock is described by a non-identical and time-varying model. To achieve time synchronization on low-accuracy internal RC oscillator clocks, a packet-coupled synchronization scheme is proposed for adjusting drifting clocks via the proportional control-based correction scheme. The RC oscillator frequency in an embedded system cannot be corrected, and this work utilizes the clock threshold adjustment as a substitute for frequency correction. The stability region of controller parameters is given to guarantee that the clock threshold approaches a value, which is jointly determined by the nominal threshold and the corresponding clock frequency. We also propose a linear matrix inequality condition to prove that the P-PkCOs performance is robust against the large clock disturbances. We demonstrate the implementation of P-PkCOs. The experimental results show that P-PkCOs can achieve and maintain robust time synchronization on the internal RC oscillator clocks.