20.1 A 28µW IoT Tag That Can Communicate with Commodity WiFi Transceivers via a Single-Side-Band QPSK Backscatter Communication Technique

Nearly all IoT devices require wireless connectivity, and to keep costs down and deployment opportunities up, communication should ideally occur with widely deployed commodity hardware such as WiFi. However, conventional WiFi transceivers (TRXs) require 10s to 100s of mW of active power. As a result, nearly all current WiFi-compatible IoT devices require either wall power, or large/frequently re-charged batteries (Fig. 20.1.1, left). While other standards such as BLE may require less power, very low power (<<1mW) is only achievable at very low throughputs via duty-cycling; and yet, despite low average power, very small coin cell batteries or energy harvesters cannot be used due to still relatively high peak-power requirements (e.g., a few mW for BLE), thereby limiting new products to certain minimum device sizes. More importantly, standards such as BLE do not have widely distributed infrastructure in most homes, offices, or other environments, making rapid low-cost deployment difficult. To enable a new class of miniaturized, battery-powered or energy-harvested IoT devices, backscatter communication, where an incident RF source is reflected via a low-power impedance modulating tag, has been proposed [1]. However, most current solutions rely on custom tone generators [1], [2], and thus cannot be rapidly deployed at scale with low cost. To enable operation with existing infrastructure, recent work has shown that already-pervasive WiFi signals can be used as incident RF sources for backscattering, and through techniques such as codeword translation, commodity WiFi RXs can be used to receive backscattered data [3]. However, this prior art required a WiFi RF source (like a smartphone) within 6m of the tag, and two separate WiFi readers within 8m (Fig. 20.1.1, middle). More importantly, to date, there has not been any practical backscatter systems developed with low-power electronics to demonstrate the low-power potential of WiFi-based backscattering.