Backscatter Communication Meets Practical Battery-Free Internet of Things: A Survey and Outlook

Battery-free Internet-of-Things (BF-IoT), which is realized by harvesting ambient energy to power the IoT devices, has emerged to reduce the energy consumption, and alleviate environmental concerns caused by extensive battery usage. However, current wireless technologies for IoT, such as Bluetooth, ZigBee, and long range radio (LoRa), cannot be efficiently supported by ambient energy due to high power requirement, making them unfit for BF-IoT applications. Backscatter communication (BackCom) is a promising enabling technology for BF-IoT as it achieves microwatt power consumption by eliminating the need of power-hungry radio components such as analog to digital converters. The integration of BF-IoT and BackCom is expected to revolutionize IoT applications and has attracted significant attention recently. However, several fundamental issues need to be addressed to fully harvest the potential of such integration. In this article, we conduct a comprehensive and in-depth survey of BackCom enabled BF-IoT (BackCom-BF-IoT), aiming to provide useful guidance for future research and application from a practical perspective. Specifically, we first introduce the basics of BackCom-BF-IoT by presenting its hardware architecture and key components. Then, we review the existing BackCom-BF-IoT prototypes, from which four fundamental issues related to BackCom are discussed, including link performance enhancement, multi-device concurrent transmission, security guarantee, and interplay between BackCom-BF-IoT system and ambient RF communication systems. For each fundamental issue, we thoroughly review state-of-the-art advances and discuss their prospects for practical BF-IoT applications. Finally, we provide an outlook of future research directions and several case studies.