Sub-Symbol Backscatter Using CCK Signal in WiFi

Throughput is a critical performance metric in backscatter communication systems. Existing approaches either suffer from limited throughput or necessitate modifications to transmitters or receivers, leading to incompatibility with commodity radios. In this paper, we introduce SubScatter, a system that achieves both high throughput and excellent compatibility. It employs a single Complementary Code Keying (CCK)-modulated 802.11b WiFi symbol to transmit eight tag bits by manipulating the phase of the backscattered signal across eight discrete time slots within the symbol, thereby enhancing throughput. To ensure compatibility with commercial-off-the-shelf (COTS) radios, SubScatter exclusively utilizes the physical service data unit (PSDU) for recovering the backscatter modulation that conveys the tag bits. Additionally, SubScatter employs real-time Hamming distance calculations to synchronize the binary envelope from the synchronization circuit with a reference sequence, facilitating the sub-symbol backscatter modulation. In addition, we emphasize SubScatter’s versatility in adapting its modulation scheme to optimize performance across various channel conditions. Extensive experiments conducted with our prototype validate its effectiveness, achieving a throughput approximately 11 times higher than that of leading backscatter systems compatible with COTS radios. Our Hamming-distance-based synchronization method outperforms conventional designs that rely solely on signal power detection, successfully reducing the bit error rate (BER) from over 10% to below 1%. Moreover, SubScatter’s throughput can be flexibly adjusted from 11 Mbps to 1.57 Mbps, while the BER improves from 0.29% to 0.04%.