COCOON: A Conductive Substrate-based Coupled Oscillator Network for Wireless Communication

Advances in flexible conductive substrates such as conductive wallpaper and paint present new opportunities for optimizing the performance of IoT nodes in smart homes and buildings. In this paper, we explore an unconventional use of such substrates for pulling frequencies of oscillators across IoT devices and wireless front-ends connected to the substrate. We show that by using this technique, we can replace precise crystal oscillators by lower precision and lower cost ceramic oscillators without compromising their ability to be used for tasks that require precise frequencies such as frequency-synchronized multi-static backscatter and synchronized sampling. We present an end-to-end design including a) analysis of conditions under which frequency pulling of oscillators across conductive substrates can work, b) a new technique to detect frequency locking across oscillators without requiring explicit communication, and c) an adaptive method that can be used to synchronize oscillators at minimum power consumption. We then show that these elements can be composed to design a high-performance multi-static backscatter system that performs as well as one that uses a shared high-precision clock but at an order of magnitude less monetary cost. We show that our system can scale and operate at very low power, while having low complexity since it requires no explicit interaction among devices attached to the substrate.