Data On the Go: Seamless Data Routing for Intermittently-Powered Battery-Free Sensing

The rising demand for sustainable IoT has promoted the adoption of battery-free devices intermittently powered by ambient energy for sensing. However, the intermittency poses significant challenges in sensing data collection. Despite recent efforts to enable one-to-one communication, routing data across multiple intermittently-powered battery-free devices, a crucial requirement for a sensing system, remains a formidable challenge. This paper fills this gap by introducing Swift, which enables seamless data routing in intermittently-powered battery-free sensing systems. Swift overcomes the challenges posed by device intermittency and heterogeneous energy conditions through three major innovative designs. First, Swift incorporates a reliable node synchronization protocol backed by number theory, ensuring successful synchronization regardless of energy conditions. Second, Swift adopts a low-latency message forwarding protocol, allowing continuous message forwarding without repeated synchronization. Finally, Swift features a simple yet effective mechanism for routing path construction, enabling nodes to obtain the optimal path to the sink node with minimum hops. We implement Swift and perform large-scale experiments representing diverse realworld scenarios. The results demonstrate that Swift achieves an order of magnitude reduction in end-to-end message delivery time compared with the state-of-the-art approaches for intermittentlypowered battery-free sensing systems.