S PIDER B AT : A UGMENTING W IRELESS S ENSOR N ETWORKS WITH D ISTANCE AND A NGLE I NFORMATION Georg Oberholzer, Philipp Sommer, and Roger Wattenhofer IPSN ‘11 - Sowhat

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

M OTIVATION accurate Achieve more accurate position estimation distanceangle by augmenting WSNs with distance & angle info. ultrasound positioning while using ultrasound positioning

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

C ONTRIBUTION 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

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

E XISTING A PPROACHES ’L IMITATION GPS Accuracy Indoor environment Ultrasound Range Limited beam angle Line-of-sight

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

A RCHITECTURE SpiderBat, extension board connected and powered by existing sensor node platform

A RCHITECTURE, U LTRASOUND Separate Tx & Rx for lower complexity

A RCHITECTURE, U LTRASOUND -T X DC/DC converter, 3V  12V Amplifier needed Driven by Pulse-Width Modulation output of resonance freq. 40kHz

A RCHITECTURE, U LTRASOUND -R X 3 amplification stages 2 provide amplification of 21dB 3 rd 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

A RCHITECTURE, U LTRASOUND -M ICROCONTROLLER, C OMPASS MSP430F2274 Low-power microcontroller 1kB RAM, 32kB ROM 2 hardware timer Honeywell HMC axis digital compass Connected using a 4-pin socket Read using I 2 C bus

A RCHITECTURE, I NTERFACE Register address space on extension board 16-pin connector Serial peripheral interface(SPI) 2 interrupt lines for each direction In low-power state alternatively

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

1. U LTRASOUND R ANGING T start – start of the ranging procedure on sender T receive – start of the ultrasound measurement on receiver T ultrasound – start of transmission on sender T detection – signal detected on receiver

2. A NGLE OF A RRIVAL E STIMATION Main beam width of roughly 30° 2 side lobes at -45° and 45° Using the arrival time of an ultrasound pulse at different receivers

2. A NGLE OF A RRIVAL E STIMATION, D ISTANCE C ORRECTION Distance correction term: 2.8 ~ 4cm Expected value = 3.6cm

3. P OSITIONING A LGORITHM Initial Node Placement Assign each node the anchor node with smallest hop distance Least Mean Square(LMS) Method

4. L INE - OF -S IGHT DETECTION Learning about the environment by sending out an ultrasound pulse and analyzing the echo

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

E VALUATION, U LTRASOUND R ANGING 2 nodes placed apart at different distance Variance of the distance estimation

E VALUATION, A NGLE OF A RRIVAL E STIMATION 2 SpiderBat board placed 1m apart Rotate receiving board0°, 15°, 30°, 45°, 60°, 75°, 90°

E VALUATION, P OSITIONING 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

E VALUATION, P OSITIONING – I NDOOR Standard deviation of localization error is 15.5cm in the worst-case Applying LMS  5.7m

E VALUATION, P OSITIONING – O UTDOOR Distance between nodes are larger Air disturbance Ambient temperature

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

C ONCLUSIONS 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

O UTLINES Motivation Contribution Existing Approaches’ limitation Architecture Methodology Ultrasound ranging Angle of arrival estimation Positioning algorithm Line-of-sight detection Evaluation Conclusion Discussion

D ISCUSSION 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

T HANKS FOR L ISTENING ~