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SPIDERBAT: AUGMENTING WIRELESS SENSOR NETWORKS WITH DISTANCE AND ANGLE INFORMATION
Georg Oberholzer, Philipp Sommer, and Roger Wattenhofer
IPSN ‘11
- Sowhat 2011.5.2
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
MOTIVATION
Achieve more accurate position estimationby augmenting WSNs with distance & angle
info.while using ultrasound positioning
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
CONTRIBUTION
Measure absolute angles between sensor nodes
Use distance & angle information error distance in the order of “cm” with few anchor nodes only
Line-of-sight detection
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
EXISTING APPROACHES’LIMITATION
GPS Accuracy Indoor environment
Ultrasound Range Limited beam angle Line-of-sight
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
ARCHITECTURE
SpiderBat, extension board connected and powered by existing sensor node platform
ARCHITECTURE,ULTRASOUND
Separate Tx & Rx for lower complexity
ARCHITECTURE,ULTRASOUND-TX
DC/DC converter, 3V12V
Amplifier needed
Driven by Pulse-Width Modulation output of microcontroller @ resonance freq. 40kHz
ARCHITECTURE,ULTRASOUND-RX
3 amplification stages 2 provide amplification of 21dB 3rd equips potentiometer to
1. adjust detection threshold 2. Prevent saturation
58dB ~ 75dB Low-pass filter Analog-digital-converter (ADC) Comparator circuit for detecting the presence
of ultrasound signal
ARCHITECTURE, ULTRASOUND-MICROCONTROLLER, COMPASS
MSP430F2274 Low-power microcontroller 1kB RAM, 32kB ROM 2 hardware timer
Honeywell HMC6352 2-axis digital compass Connected using a 4-pin socket Read using I2C bus
ARCHITECTURE, INTERFACE
Register address space onextension board
16-pin connectorSerial peripheral interface(SPI)2 interrupt lines for each direction
In low-power state alternatively
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
1. ULTRASOUND RANGING
Tstart – start of the ranging procedure on sender
Treceive – start of the ultrasound measurement on receiver
Tultrasound – start of transmission on sender
Tdetection – signal detected on receiver
2. ANGLE OF ARRIVAL ESTIMATION
Main beam width of roughly 30°2 side lobes at -45° and 45°
Using the arrival time of an ultrasound pulse at different receivers
4
2. ANGLE OF ARRIVAL ESTIMATION,DISTANCE CORRECTION
Distance correction term: 2.8 ~ 4cmExpected value = 3.6cm
3. POSITIONING ALGORITHM
Initial Node Placement Assign each node the anchor node with smallest
hop distance
Least Mean Square(LMS) Method
4. LINE-OF-SIGHT DETECTION
Learning about the environment by sending out an ultrasound pulse and analyzing the echo
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
EVALUATION, ULTRASOUND RANGING
2 nodes placed apart at different distance Variance of the distance estimation
EVALUATION, ANGLE OF ARRIVAL ESTIMATION
2 SpiderBat board placed 1m apart Rotate receiving board 0°, 15°, 30°, 45°, 60°,
75°, 90°
EVALUATION, POSITIONING
Indoor In a gym 10 x 6 m 1.5m above ground
Outdoor Sports ground 16 x 10m 20 cm above ground
Centralized computation Node 1 is an anchor node
EVALUATION, POSITIONING – INDOOR
Standard deviation of localization error is 15.5cm in the worst-case
Applying LMS 5.7m
EVALUATION, POSITIONING – OUTDOOR
Distance between nodes are larger Air disturbance Ambient temperature
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
CONCLUSIONS
SpiderBat, an extension board for wireless sensor nodes with a focus on low computation and energy efficiency
Multiple ultrasound receivers and transmitters accuracy distance & angle estimation Distance - mm ~ cm Angle – few degrees, depending on distance
Compass absolute angle line-of-sight detection
OUTLINES
Motivation Contribution Existing Approaches’ limitation Architecture Methodology
Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection
Evaluation Conclusion Discussion
DISCUSSION
Strength Achieve error distance in order of cm with few
anchor nodes only
Weakness The evaluations of distance & angle are not
convincing No discussion about comparator’s threshold Line-of-sight “detection” only No support on that SpiderBat may be used to learn
about the environment Environment limitation
THANKS FOR LISTENING ~