Time synchronization is an enabling service that allows devices to share a consistent notion of time and thus makes it easier to build efficient and robust collaborative services. However, existing synchronization protocols based on wireless packet transmissions are not energy efficient because powering the radio often consumes a significant fraction of the energy budget. In this paper, we propose PSync, a visible light-based time synchronization protocol that relies on an LED light source and is highly energy efficient for the receivers. The key novelty in our protocol is the use of a De Bruijn sequence to provide a rough estimate of time using a minimum amount of information. Experiments show that our scheme achieves an average synchronization error of 1.3 timer ticks (32μs per clock tick). In addition, the additional energy consumed for one round of synchronization based on PSync can be as low as 19% of the energy needed to receive a small packet (1 byte) using IEEE 802.15.4 radio.
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