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

TL;DR

Swift addresses data routing for intermittently-powered battery-free sensing by delivering three tightly integrated components: Swift-sync, a guaranteed synchronization protocol based on an LCG mapping with coprime cycle lengths; Swift-forward, a low-latency forwarding mechanism that preserves synchronization across hops; and Swift-route, a hop-count optimal route construction via a layered flooding approach. The combined system is implemented in OMNeT++ and validated with hardware prototypes and large-scale simulations, showing an order-of-magnitude reduction in end-to-end delivery time compared with existing methods. The approach explicitly handles energy heterogeneity and the millisecond-scale intermittency of BF devices, enabling scalable, maintenance-free IoT sensing in challenging environments. These results highlight a practical path to reliable, energy-efficient routing in battery-free networks, expanding the feasibility of sustainable IoT deployments.

Abstract

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.

Figures (8)

• Figure 1: Illustration of the node synchronization procedure: (a) charging cycles of the sender and the receiver over time (boxes represent time slots), (b) the offsets of the sender's working periods in relation to the receiver's charging cycle hypothetically, and (c) successful discovery when the working period offsets of the sender and receiver match.
• Figure 2: Illustration of the state changes with the Swift-forward mechanism, where we show how the charging cycles of the sender should be adapted to synchronize with its next hop (e.g., the receiver) directly and reverse back when the message forwarding is completed. The receiver is passive and the sender uses the receiver's charging cycle as its reference.
• Figure 3: Illustration for a contradiction where we show that hop D-F cannot exist on any constructed route.
• Figure 4: Node synchronization time (in slots) with Swift-sync and Find 2021-nsdi-find under varying energy condition ranges. The markers denote the 99th percentile.
• Figure 5: Node synchronization time on the hardware prototype.

Theorems & Definitions (4)

• Theorem 1
• proof
• Theorem 2
• proof