Quasi-Coherent Demodulation of Ambient FM Signal Backscatter

Ambient backscatter is is a relatively-recent technique being considered for communication from ultra-low power devices. Unlike typical backscatter applications where a dedicated reader-generated signal is used to power the tag, ambient backscatter uses readily available ambient signals such as FM radio, TV or WiFi signals. In this paper, we propose a simple, yet effective way to implement the receiver for a tag backscattering incident FM radio signals. The technique is based on treating the ambient FM as a carrier, which can be recovered using a phase-locked loop or another FM receiver. Coherent demodulation of the backscattered signal is then possible. Significant performance improvement can be expected over receivers that use energy-detection or other non-coherent demodulation techniques that are commonly used for ambient backscatter in the literature. We show that the FM radio signal can be recovered with a high fidelity even in the presence of the tag signal, with about 20-50 dB SINR in practical scenarios. Our results show up to 5 dB improvement in error performance over non-coherent reception.