Long-range ambient LoRa backscatter with parallel decoding

LoRa backscatter is a promising technology to achieve low-power and long-distance communication for connecting millions of devices in the Internet of Things. We present P 2 LoRa, the first ambient LoRa backscatter system with parallel decoding and long-range communication. The high level idea of P 2 LoRa is to modulate data by shifting ambient LoRa packets with a small frequency. To achieve long distance communication, we enhance the SNR of the backscatter signal by concentrating leaked energy in both the frequency domain and time domain. We propose a method to accurately reconstruct and cancel the in-band excitation signal, which is orders of magnitude higher than the backscatter signal. For parallel decoding, we propose a method to cancel inter-tag interference with very low overhead and address the signal misalignment problem due to different time of flight. We prototype the P 2 LoRa tag with customized low-cost hardware and implement the P 2 LoRa gateway on USRP. Through extensive evaluations, we show that P 2 LoRa achieves a long communication distance of 2.2 km with ambient LoRa, and supports 101 parallel tag transmissions.