Towards Low-cost Sensing with Mobile Backscatter

Analog backscatter enables sensing and communication at lower power consumption than digital backscatter. In analog tags, a sensor typically changes the resistance or capacitance value that then translates into a frequency change that is backscattered on top of a carrier. However, to read the sensor data with high resolution, a powerful receiver is required. The resolution of sensor data is limited by the FFT size and computation at the receiver. This limits the use of low-cost radio receivers, like RTL-SDR, that are gaining popularity in the RF community. We propose to use higher order harmonic frequencies, that are inherently generated by square wave backscattering at no extra cost, to derive sensor data using such low-cost radio receivers. We present experimental results that demonstrate the viability of our approach.