Innovative Full-Duplex Backscatter Technology for Efficient Wireless Communication
Explore the cutting-edge full-duplex backscatter technology enabling efficient wireless communication with reduced energy consumption and enhanced network performance. Learn how instant feedback and collision detection mechanisms revolutionize the way battery-free devices operate.
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Presentation Transcript
Full-duplex Backscatter for <1 W Vincent Liu Vamsi Talla, Shyam Gollakota
Why Is This Hard? Existing solutions require O(1W) 1,000,000x too much!
Full-duplex Backscatter First full-duplex design for battery-free devices Same frequency, single antenna
Full-duplex Backscatter RF source Data (1 kbps) Feedback (100 bps) Alice Bob Brings self-interference down to the noise floor using < .75 uW
Why Do We Care? Energy Is The Bottleneck! Threshold to transmit a packet Capacitor Charge Recovery from collisions and errors takes a long time Time Capacitor charging is exponential in time
Why Do We Care? Energy Is The Bottleneck! Full-duplex can help fix this problem Instantaneous feedback enables a better network Collision detection (100x recharge time reduction) Error correction (10x overhead reduction for every packet)
How do we get full-duplex on battery-free devices? How do we use instantaneous feedback to design a power-efficient network stack?
How do we get full-duplex on battery-free devices? How do we use instantaneous feedback to design a power-efficient network stack?
Backscatter Overview RF Source Alice absorbs: Existing signal Alice reflects: Existing signal & Reflection TV Tower (RF source) Bob Alice Ambient Backscatter Additional Multipath Signal at Bob TV (Legacy receiver) Bob (Receiver) Alice (Sender) Time
Challenge: Bobs Reflections Lose Information RF Source Alice absorbs: Existing signal Alice reflects: Existing signal & Reflection TV Tower (RF source) Bob Alice Ambient Backscatter Additional Multipath Bob absorbs Bob reflects Signal at Bob TV (Legacy receiver) Bob (Receiver) Alice (Sender) Time
Solution: Change Phase Instead Bob sends 0 : Existing signal & shift (RF source) RF Source TV Tower Bob sends 1 : Existing signal & - shift Bob Alice Bob can decode Alice s signal Alice can decode Bob s signal Ambient Backscatter Additional Multipath Bob absorbs Bob reflects Signal at Bob TV (Legacy receiver) Bob (Receiver) Alice (Sender) Time
Practically, phase modulation is imperfect Residual interference
Solution: Leverage Difference in Rates to Eliminate Residual Interference Data (1 kbps) Feedback (100 bps) Alice Bob Remove interference with high-pass filter Remove interference with low-pass filter Can be done with cheap, passive circuits at NO additional power
Is Our Cancellation Effective? 10 -10 -30 Noise floor Magnitude (dB) -50 Original -70 With phase modulation Total cancellation -90 -110 -130 -150 0 200 400 Frequency (Hz) 600 800 1000 Reduces self-interference to noise floor
How do we get full-duplex on battery-free devices? How do we use instantaneous feedback to design a power-efficient network stack?
Challenge: Energy Is the Bottleneck Recovery from collisions/errors takes a long time We use Full-duplex Backscatter to achieve instantaneous feedback
Protocol: Acknowledge Data at a Bit Level 40 bits Forward data channel 1 2 3 4 5 Feedback channel 1 2 3 4 5 4 bits Time 1. Split packet into 40-bit chunks 2. Receiver returns a checksum of each chunk 3. Sender verifies checksum
Does Full-duplex Help With Collisions? Detect collisions and stop transmissions 1000 Full-duplex Backscatter Conventional 100 Recharge Time (ms) 10 1 0.1 0.01 -6 -4 -2 0 2 4 100x improvement in recharge time Input Power (dBm) 64-byte packet size
Does Full-duplex Help With Error Correction? Recover from errors by retransmitting only the failed bits 10000 Full-duplex Backscatter Conventional 1000 Average Overhead (%) 100 10 1 0.1 0 0.001 >90% decrease in overhead 64-byte packet size 0.002 0.003 0.004 0.005 Bit Error Rate
Conclusion We show The first full-duplex design for battery-free devices A power-efficient network stack that has significant gains across the board Re-design networking primitives with power as a first-class citizen MIMO (SIGCOMM 14), coding (SIGCOMM 14), UWB (?), TCP/IP (?),
