Mote: Enabling Passive Chirp De-spreading and W-level Long-Range Downlink for backscatter Devices

The downlink range of backscatter devices is commonly considered to be very limited, compared to tremendous long-range and low-power backscatter uplink designs that leverage the chirp spread spectrum (CSS) principle. Recently, some efforts are devoted to enhancing the downlink, but they are unable to achieve long-range receiving and low power consumption simultaneously. In this paper, we propose mu Mote, a mu W-level long-range receiver for backscatter devices. mu Mote achieves the first passive chirp de-spreading scheme for negative SINR in long-range receiving scenarios. Further, without consuming external energy, mu Mote magnifies the demodulated signal by accumulating temporal energy of the signal itself in a resonator container, and meanwhile it preserves signal information during this signal accumulation. mu Mote then leverages a mu W-level sampling-less decoding scheme to discriminate symbols, avoiding the high-power ADC-sampling. We prototype mu Mote with COTS components, and conduct extensive experiments. The result shows that mu Mote spends an overall power consumption of 62.07 mu W to achieve a 400m receiving range at a 2kbps data rate with 1% BER, under -2dB SINR.