Practical Downlink Communication for Backscatter Tags with Commodity Radios

Backscatter is promising to deliver near-zero-power communications for billions of IoT devices. While significant progress has been made in uplink transmission, existing systems suffer from impractical downlink design, failing to interpret packets from ambient wireless networks. This prevents tags from applications that necessitate two-way communication, such as resource allocation or reliable backscatter services. We propose InterfereX, a novel system that enables practical downlink communication for backscatter tags with commodity radios. The key behind InterfereX is an interference-driven demodulation scheme that transforms phase shifts of ambient RF signals into amplitude-modulated waveforms. By leveraging differential phase modulation inherent in protocols like ZigBee, Bluetooth, and 802.11b WiFi, InterfereX enables energy-efficient decoding through envelope detection. We prototype InterfereX and evaluate its performance through extensive experiments. Results show that InterfereX achieves downlink throughputs of 249.3 kbps for ZigBee, 994.8 kbps for Bluetooth, and 1626.3 kbps for WiFi, with BERs as low as 0.39‰, 5.98‰, and 4.90‰. The sensitivity of ZigBee/Bluetooth/802.11b WiFi demodulation reaches -35.5 dBm, -32.5 dBm, and -30.5 dBm. These results confirm that InterfereX provides a practical downlink, enabling seamless integration of backscatter tags into wireless infrastructure.