μMote: Enabling Passive Chirp De-spreading and μW-level Long-Range Downlink for Backscatter Devices

The downlink range of backscatter devices is commonly considered to be very limited, compared to tremendous longrange 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 µMote, a µW -level long-range receiver for backscatter devices. µMote achieves the first passive chirp de-spreading scheme for negative SINR in long-range receiving scenarios. Further, without consuming external energy, µMote 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. µMote then leverages a µW -level sampling-less decoding scheme to discriminate symbols, avoiding the high-power ADC-sampling. We prototype µMote with COTS components, and conduct extensive experiments. The result shows that µMote spends an overall power consumption of 62.07µW to achieve a 400m receiving range at a 2kbps data rate with 1% BER, under -2dB SINR.