Bootstrapping Battery-free Wireless Networks: Efficient Neighbor Discovery and Synchronization in the Face of Intermittency

Due to their favorable size, cost, and sustainability, batteryfree devices are preferable in various applications. However, battery-free devices operate only intermittently since ambient energy sources, such as light and radio-frequency signals, are often too weak to continuously power the devices. This paper addresses the unsolved problem of efficient device-to-device communication in the face of intermittency. We present Find, the first neighbor discovery protocol for battery-free wireless networks that uses randomized waiting to minimize discovery latency. We also introduce Flync, a new hardware/software solution that synchronizes indoor light harvesting nodes to powerline-induced brightness variations of widely used lamps, which we exploit to further speed up neighbor discovery. Experiments with an open-source prototype built from off-theshelf hardware components show that our techniques reduce the discovery latency by 4.3× (median) and 34.4× (99th percentile) compared with a baseline approach without waiting.