12.2 Improving the Range of WiFi Backscatter Via a Passive Retro-Reflective Single-Side-Band-Modulating MIMO Array and Non-Absorbing Termination
Miao Meng, Manideep Dunna, Hans C. Yu, Shih-Kai Kuo, Po-Han Wang, Dinesh Bharadia, Patrick P. Mercier
Abstract
Wi-Fi is the most ubiquitous wireless networking technology for IoT in homes, offices, and businesses. Since the power of Wi-Fi transceivers (10s-to-100s of mW) can be prohibitively high for emerging classes of IoT devices (which desire <; 100μW), recent work has suggested piggybacking baseband signals from the IoT device directly on top of incident Wi-Fi signals generated by access points (APs) via Wi-Fi-compatible backscatter modulation [1-4], where as low as 28μW of active power has been demonstrated [4]. However, the major limitation of this approach is range: signals generated by the transmitting AP experience 1/d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> path loss to the backscattering tag, which has insertion loss P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L,ins</sub> to perform single-side band (SSB) modulation, and then re-radiated modulated signals back to the receiving AP (or to another AP) experience an additional 1/d2 path loss, resulting in an overall loss ∝ 1/d4 + P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L,ins</sub> . With no active RF amplification, the tag in [4] experienced P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L,ins</sub> =15dB, limiting AP-to-tag-and-back-to-AP distance to ~10m, which is not sufficient in many single-AP homes.