Universal Timestamping with Ambient Sensing

Universal time is critical for coordinating function-alities among co-located as well as geographically distributed IoT devices. Current time alignment approaches for IoT devices rely on radio-based communication that puts an extra burden on the already resource-constrained devices. Other timing approaches depend either on customized hardware frontends or on fixed networking capabilities. Intermittent network connectivity fur-ther deteriorates timing performance for these devices. These constraints motivate us to create a new design that actively embeds time information into the surroundings of IoT devices that can harvest timing signals with off-the-shelf sensing capabil-ities. Our design decouples clock performance from the network uncertainties, introduce resource efficiency and extensibility, and requires no modification in existing devices. A unique property of our design is that it leverages the ubiquitous Electric Network Frequency (ENF) fluctuations as global time reference for the sensing devices, and takes on a variety of challenges at the in-tersection of sensing and signal processing to provide a universal sense of time without custom hardware frontends and network dependability. We evaluate the extensibility of our design in remote setups and show its robustness in real world settings.