Spectrally Efficient 4-PAM Ambient FM Backscattering for Wireless Sensing and RFID Applications

This work presents a novel wireless tag operating solely with ambient backscatter signals while featuring high-order modulation capabilities. Specifically, the proposed tag communicates with a low-cost software defined radio reader using backscatter radio principles on ambient commercial FM station signals, while sensing information from sensors can be modulated on the analog signals using 4-pulse amplitude modulation (4-PAM). The tag transceiver implementation is based on an ultra-low-power microcontroller for data processing and an RF frontend for wireless communication. A proof-of-concept prototype was demonstrated indoors over a 2 m tag-reader distance for a low bit rate of 328 bps with a Power consumotion under 20 μA.