Every smart phone is a backscatter reader: Modulated backscatter compatibility with Bluetooth 4.0 Low Energy (BLE) devices

In this work, we show how modulated backscatter signals can be crafted to yield channelized band-pass signals akin to those transmitted by many conventional wireless devices. As a result, conventional wireless devices can receive these backscattered signals without any modification (neither hardware nor software) to the conventional wireless device. We present a proof of concept using the Bluetooth 4.0 Low Energy, or BLE, standard widely available on smart phones and mobile devices. Our prototype backscatter tag produces three-channel bandpass frequency shift keying (FSK) packets at 1 Mbps that are indistinguishable from conventional BLE advertising packets. An unmodified Apple iPad is shown to correctly receive and display these packets at a range of over 9.4 m using its existing iOS Bluetooth stack with no changes whatsoever. We create all three BLE channels by backscattering a single incident CW carrier using a novel combination of fundamentalmode and harmonic-mode backscatter subcarrier modulation, with two of the band-pass channels generated by the fundamental mode and one of the band-pass channels generated by the second harmonic mode. The backscatter modulator consumes only 28.4 pJ/bit, compared with over 10 nJ/bit for conventional BLE transmitters. The backscatter approach yields over 100X lower energy per bit than a conventional BLE transmitter, while retaining compatibility with billions of existing Bluetooth enabled smartphones and mobile devices.