backscatter communication for wearables/iot · backscatter communication for wearables/iot deepak...
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Backscatter communication for wearables/IoT
Deepak GanesanAssociate ProfessorComputer ScienceUMass Amherst
Computer Science@UMASS Amherst
Emerging ecosystem of on-body sensors
activity monitoring wristband
GPS, Accelerometer, Gyroscope, Camera, Microphone
blood pressure glucose monitors
implantable “nanosensors”
sleepshirt sleep monitor
Computer Science@UMASS Amherst
Why is communication a problem?
Communica)on is a major bo/leneck for low-‐power opera)on
Pow
er C
onsu
mpt
ion
(uW
)
1
1000
1000000
Communication Sensing
802.15.4 (Zigbee)
Bluetooth Low Energy
Ultra-Wide Band Camera (Stonyman)
ECG
MicrophoneAccelerometer
WiFi
Computer Science@UMASS Amherst
Backscatter communication
Backscatter reader
Sensor
Backscatter is extremely efficient because the device is reflecting the signal rather than generating a signal.
TransistorCarrier Wave
Reflected 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
…
available energy is miniscule
distance from reader
Computer Science@UMASS Amherst
Why is backscatter a challenging domain?
Carrier Wave
Reflected Signal
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12
Am
plitu
de
Time (seconds)
I ChannelQ Channel
Antenna coupling
-1-0.8-0.6-0.4-0.2
0 0.2 0.4 0.6
0 2 4 6 8 10 12
Am
plitu
de
Time (seconds)
I ChannelQ Channel
Antenna rotation
Computer Science@UMASS Amherst
Why is backscatter a challenging domain?
Carrier Wave
Reflected Signal
Human activity
-0.4
-0.2
0
0.2
0.4
0 2 4 6 8 10
Sign
al S
tren
gth
Transmission Time (ms)
transmitted signal decoding
fails
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 2 4 6 8 10 12
Am
plitu
de
Time (seconds)
I ChannelQ Channel
Capacitor charge decay
Computer Science@UMASS Amherst
Why is backscatter a challenging domain?
Carrier Wave
Reflected SignalReader
TX
0° 90°
DAC Base Band
PLL VCO
DAC
Antenna
Power Amplifier
Mixer
Mixer Low-pass Filter
RX
0° 90°
ADC
PLL VCO
ADC
Antenna
Low Noise Amplifier
Mixer
Mixer
Low-pass Filter
Low-pass Filter
Base Band
Base Band
Base Band
Tag TX
RX
Sensor
Antenna
Packet Switch
Z0 Z1
Antenna
Comparator D1
C1 C2
R1 R2
+-
Reader Message Processing
Low-pass Filter
Reader TX
0° 90°
DAC Base Band
PLL VCO
DAC
Antenna
Power Amplifier
Mixer
Mixer Low-pass Filter
RX
0° 90°
ADC
PLL VCO
ADC
Antenna
Low Noise Amplifier
Mixer
Mixer
Low-pass Filter
Low-pass Filter
Base Band
Base Band
Base Band
Tag TX
RX
Sensor
Antenna
Packet Switch
Z0 Z1
Antenna
Comparator D1
C1 C2
R1 R2
+-
Reader Message Processing
Low-pass Filter
Reader TX
0° 90°
DAC Base Band
PLL VCO
DAC
Antenna
Power Amplifier
Mixer
Mixer Low-pass Filter
RX
0° 90°
ADC
PLL VCO
ADC
Antenna
Low Noise Amplifier
Mixer
Mixer
Low-pass Filter
Low-pass Filter
Base Band
Base Band
Base Band
Tag TX
RX
Sensor
Antenna
Switch
Z0 Z1
Antenna
Comparator D1
C1 C2
R1 R2
+-
Reader Message Processing
Low-pass Filter
Asymmetry
Computer Science@UMASS Amherst
Why is backscatter a challenging domain?
Carrier Wave
Reflected Signal
Range ThroughputPower
bit-by-bit backscatter
[NSDI 2014]
Re-thinking tag architecture [Mobicom 2014]
Hybrid harvesting [MobiSys 2012]
Concurrent backscatter
[HotWireless 2014]
Asymmetry
Computer Science@UMASS Amherst
Taking stock…
Major step is to measure/evaluate/iterate under uncontrolled environments
Many promising techniques for solving hard problems in backscatter: range (50 ft), throughput (Mbps),
harvesting (Reader/Ambient/WiFi)
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