MCU-Free Backscatter Communication with Light-Enabled Frequency Control for Ambient IoT

Ambient Internet of Things (A-IoT) adopts energy-neutral devices to conduct communication and sensing tasks, leveraging energy harvesting (EH) from ambient energy resources, such as solar, radio frequency (RF) signals, and vibrations. Using ambient backscatter communication (AmBC), a backscatter device (BD) can modulate and reflect existing RF carrier waves to transmit its local sensing data obtained from the embedded sensors. In this paper, we propose a novel A-IoT scheme, where the BD uses modulated visible light as both energy source and communication frequency controller. Specifically, the alternating current (AC) component of photovoltaic-converted light controls the frequency of communication subcarriers, eliminating the use of a microcontroller unit (MCU) for such purpose. We model the link budget of the proposed system, including the optical link and RF backscatter link. To demonstrate the implementation feasibility of the proposed scheme, we present a proof-of-concept experimental setup using the commercial off-the-shelf (COTS) electronic components. The experimental results show that the intermediate or subcarrier frequency of the backscattered signal can be shifted up to 10 MHz from the carrier, by configuring the modulation frequency of the visible light. The investigation demonstrates the feasibility of using visible light to control the subcarrier frequency of AmBC without MCUs, thereby providing extra flexibility for spectral arrangement and reducing the device cost in A-IoT systems.