Bitalign: Bit Alignment for Bluetooth Backscatter Communication

In the past decade, backscatter communications have drawn significant attention as they are an ultra-low-power solution to transmit IoT sensor data, including video and audio. However, most of the state-of-the-art backscatter systems that are fully compatible with commodity radios suffer from poor synchronization accuracy and low throughput, being unable to support various multimedia sensors. In this paper, we propose Bitalign, a Bluetooth backscatter system that can make use of uncontrolled ambient signals as excitations and deliver high throughput for multimedia streaming applications. To do so, we identify several backscatter bottlenecks and employ a set of techniques to considerably boost backscatter throughput. In particular, we introduce an identification-based synchronization method that can efficiently distinguish various ambient signals and accurately decide where to modulate. We further propose a matching-based synchronization method with higher synchronization accuracy. In addition, we propose header reconstruction to make Bitalign truly compatible with commercial Bluetooth devices. Finally, we implement a tag prototype using FPGAs and conduct extensive experiments. Results show that the minimum bit error rate of Bitalign is 0.5%, which is 60 times better than that of FreeRider, a state-of-the-art Bluetooth system that features uncontrolled excitors. The maximal theoretical throughput of Bitalign is 1.98 Mbps.