Low-Overhead Time Synchronization for Energy-Constraint Industrial Internet of Things

Time synchronization is of significance in the Industrial Internet of Things (IIoT). For the impact of energy-constrained batteries for power in IIoT, a novel low-overhead time synchronization algorithm via one-way single packet exchange, i.e., improved packet-coupled oscillators (I-PkCOs), is proposed in this paper, which mainly consists of time-information packet exchange protocol according to a time-division multiple access scheme and an adaptive proportional-integral feedback clock adjustment algorithm. For clock adjustment, a proportional-integral controller is used to generate the clock adjustment amount and an adaptive algorithm is introduced to adjust the clock offset first and the clock skew later. This algorithm schedules Sync packets to be transmitted in different time slots, which can avoid packet collision and channel sniffing. Moreover, a node only needs to send one Sync packet per synchronization cycle, which effectively reduces the communication overhead and energy consumption. Hardware experiments on the SAM R21 board of processing the 32.768 MHz oscillator show that the proposed method reduces packet transmission by 50% compared to the Time synchronization Protocol for Sensor Networks (TPSN). Moreover, it has better synchronization accuracy and stability than the Packet-Coupled Oscillators (PkCOs) protocol and PISync algorithm and can achieve 1.61μs synchronization accuracy in a single-cluster network.