SubScatter: Sub-symbol WiFi Backscatter for High Throughput

Throughput is one of the key performance indicators in backscatter communication systems. Existing works either have limited throughput or modify the transmitter or receiver to fit the backscatter tag, thereby causing incompatibility with commodity radios. In this paper, we present SubScatter, which realizes a high throughput and keeps compatibility at the same time. For high throughput, SubScatter uses one CCK-modulated 802.11b WiFi symbol to carry eight tag bits by manipulating the phase of the backscattered signal in eight-time slots of a symbol separately. For compatibility with commercial-off-the-shelf (COTS) radios, SubScatter leverages only the physical service data unit (PSDU) to recover the backscatter modulation in which the tag bits are conveyed. And still, to fit the sub-symbol backscatter modulation, SubScatter calculates the Hamming distance between the binary envelope provided by the synchronization circuit and a reference sequence in real-time for synchronization. Extensive experiments in our prototype have proven the effectiveness of SubScatter. SubScatter achieves a throughput of about 11× over state-of-the-art backscatter systems compatible with COTS radios. The Hamming-distance-based synchronization outperforms the design of merely detecting the change of signal power and helps reduce the bit error rate from over 10% to below 1%.