Backscatter communication for wearables/IoT Deepak Ganesan Associate Professor Computer Science UMass Amherst
Emerging ecosystem of on-body sensors GPS, Accelerometer, Gyroscope, activity monitoring Camera, Microphone wristband blood pressure glucose monitors implantable “nanosensors” sleepshirt sleep monitor Computer Science@UMASS Amherst
Why is communication a problem? 1000000 WiFi Power Consumption (uW) 802.15.4 (Zigbee) Bluetooth Low Energy 1000 Ultra-Wide Band Camera (Stonyman) ECG Microphone Accelerometer 1 Communication Sensing Communica)on ¡is ¡a ¡major ¡bo/leneck ¡for ¡low-‑power ¡opera)on Computer Science@UMASS Amherst
Backscatter communication Backscatter Sensor reader Carrier Wave Transistor Reflected Signal Backscatter is extremely efficient because the device is reflecting the signal rather than generating a signal. Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal Energy … distance from reader available ¡energy ¡is ¡miniscule Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal Antenna coupling Antenna rotation 0.4 0.6 I Channel I Channel Q Channel 0.3 0.4 Q Channel 0.2 0.2 Amplitude Amplitude 0 0.1 -0.2 0 -0.4 -0.1 -0.6 -0.2 -0.8 -0.3 -1 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Time (seconds) Time (seconds) Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal Human activity Capacitor charge decay 0.6 I Channel transmitted 0.4 Q Channel 0.4 signal decoding Signal Strength 0.2 fails 0.2 Amplitude 0 0 -0.2 -0.2 -0.4 -0.4 -0.6 0 2 4 6 8 10 12 0 2 4 6 8 10 Time (seconds) Transmission Time (ms) Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal TX TX Low-pass Filter Mixer Antenna Antenna Base DAC Band Switch 0° Sensor PLL VCO 90° Power Base Z 0 Z 1 Amplifier DAC Band Mixer Low-pass Asymmetry Filter RX RX Low-pass Mixer Filter Antenna Antenna Base ADC Band 0° D1 Comparator PLL VCO 90° Reader + Message - Low Noise Base C1 Processing R1 Amplifier ADC Band R2 C2 Mixer Low-pass Filter Computer Science@UMASS Amherst
Why is backscatter a challenging domain? Carrier Wave Reflected Signal Power Range Throughput Asymmetry bit-by-bit Re-thinking tag Concurrent Hybrid backscatter architecture backscatter harvesting [NSDI 2014] [Mobicom 2014] [HotWireless 2014] [MobiSys 2012] Computer Science@UMASS Amherst
Taking stock… Many promising techniques for solving hard problems in backscatter: range (50 ft), throughput (Mbps), harvesting (Reader/Ambient/WiFi) Major step is to measure/evaluate/iterate under uncontrolled environments Computer Science@UMASS Amherst
Case for a backscatter testbed • Testbed #1: Backscatter-instrumented house • Reader/WiFi/Ambient Backscatter for IoT/wearables • Testbed #2: Backscatter-instrumented human • Mobile backscatter reader +“bandaid” sensors • Why? design complete solutions • Robustness in indoor environments • Perpetual link while user is mobile Computer Science@UMASS Amherst
Thank you Computer Science@UMASS Amherst
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