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Can we get Wi-Fi connectivity for 15 µW ?

Can we get Wi-Fi connectivity for 15 µW ?. Bryce Kellogg. Prototy p e consumes 14 µW of power. Why is this hard?. Wi-Fi consumes 100 mW of power 10,000x too much. Wi-Fi Backscatter. Key Idea: Piggyback on Wi-Fi Packets. Changing reflections consumes 0.65 µW of power. RSSI.

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Can we get Wi-Fi connectivity for 15 µW ?

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  1. Can we get Wi-Fi connectivity for 15 µW? Bryce Kellogg

  2. Prototype consumes 14 µWof power

  3. Why is this hard? Wi-Fi consumes 100 mW of power 10,000x too much

  4. Wi-Fi Backscatter Key Idea: Piggyback on Wi-Fi Packets Changing reflections consumes 0.65 µW of power RSSI Wi-Fi AP 7 5 6 2 8 4 1 3 9 0 1 Wi-Fi Backscatter Tag Wi-Fi Device

  5. How to work in a network of Wi-Fi devices? How does the Wi-Fi device send data to the tag? • How do we design a network with multiple tags?

  6. How to work in a network of Wi-Fi devices? How does the Wi-Fi device send data to the tag? • How do we design a network with multiple tags?

  7. Challenge: Cannot Decode Packet Headers ??? Wi-Fi Backscatter Tag Wi-Fi Device

  8. Solution: Be Agnostic to Wi-Fi Traffic Bin backscatter bits into time slots Time Slot 1 0 0 1 0 Adjust timeslots based on network traffic t 10:34:12.12748 10:34:12.12757 10:34:12.12770 10:34:12.12773 10:34:12.12775 10:34:12.12777 10:34:12.12779 10:34:12.12786 10:34:12.12789 10:34:12.12657 10:34:12.12663 10:34:12.12678 10:34:12.12698 10:34:12.12719 10:34:12.12734 Use Wi-Fi timestamp to reconstruct bits

  9. How to work in a network of Wi-Fi devices? How does the Wi-Fi device send data to the tag? • How do we design a network with multiple tags?

  10. Encode data as presence/absence of Wi-Fi Packet CTS-to-Self 0 0 0 0 0 1 1 1 1 Wi-Fi Backscatter Tag Wi-Fi Device

  11. Low Power Wi-Fi Packet Detection Leverage structure of Wi-Fi signal OFDM: High peak-to-avg power ratio

  12. Low Power Wi-Fi Packet Detection Antenna EnvelopeDetector Comparator Set threshold Peak finder Can detect packets as short as 50 µs Consumes µWs of power

  13. How to work in a network of Wi-Fi devices? How does the Wi-Fi device send data to the tag? • How do we design a network with multiple tags?

  14. Design Request/Response Protocol Wi-Fi device act as a central coordinator None of the tags transmit concurrently 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 CTS CTS CTS 0 0 0 0 0 0 0 0 0 Wi-Fi Device

  15. Our Prototype Intel 5300 Wi-Fi Cards Wi-Fi Backscatter Prototype • 2.4 GHz Wi-Fi channels • Use both RSSI and CSI values

  16. Power Consumption MSP430: 5.0 µW RF Switch: 0.65 µW Peak Finder: 9.0 µW Total: 14.65 µW

  17. What is the maximum rate and range? 2.2 meters, 1 kbps 3.0 meters, 20 kbps Wi-Fi Backscatter Tag Wi-Fi Device

  18. Does AP Location Affect Backscatter Decoding? 12.2 m Probability of receiving a backscatter packet correctly 98% 3 AP can be far away or even in a different room 99% 3 8.5 m 94% 99% 3 3 3

  19. Does Backscatter Affect Wi-Fi Decoding? 12.2 m 3 3 8.5 m 3 3 3

  20. Does it affect Wi-Fi Performance? Wi-Fi is robust to multipath environment

  21. How does it work in a busy network? Setup in UW Networks Lab: 8 – 15 People Used University Wi-Fi as AP Observed maximumachievable bit rate over period of 8 hours

  22. How does it work in a busy network? More network traffic →faster Backscatter rates

  23. Related Work • RFID • Requires dedicated reader and new hardware installation • Wi-Fi Backscatter transforms Wi-Fi devices into RFID readers • Ambient Backscatter • Device to device communication • Wi-Fi Backscatter connects devices to existing Wi-Fi networks

  24. Conclusion Feasibility of Wi-Fi connectivity at < 15 µW Can enable RF-Powered Internet of Things, connecting next billion devices iotWiFi.cs.washington.edu

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