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 ~