A One-Way Time Synchronization Scheme for Practical Energy-Efficient LoRa Network Based on Reverse Asymmetric Framework

Long Range (LoRa) network has been thriving in the IoT era due to its long-range coverage and energy efficiency. Prevalent LoRa applications rely on time synchronization to achieve accurate data ordering and coordination among the LoRa network. The energy-efficient nature of the LoRa network where end nodes in sleep scheduling always initiate communications, however, contradicts most conventional time synchronization methods based on message exchanges. In this paper, we propose a one-way time synchronization scheme tailored for the energy-efficient LoRa network based on the reverse asymmetric framework. We first discuss the delay minimization and compensation for the reverse one-way time synchronization in the LoRa network. We then propose a time synchronization scheme consisting of two time translation methods with different computational complexities and error bounds, respectively for resource-abundant and -constrained LoRa gateway and end nodes. Experiment results on a real LoRa testbed consisting of LoRa gateway and end nodes demonstrate that the proposed scheme could achieve microsecond-level synchronization accuracy in both scenarios between the end node and gateway and between the end node and end node; the latter scenario is advocated in the recent multi-hop LoRa network research.