of Batteryless InternetofThings Teng Wei and Xinyu Zhang Department of Electrical and Computer Engineering University of Wisconsin Madison Batteryless Orientation Tracking Orientation is an essential input ID: 741813
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Slide1
Gyro in the Air: Tracking 3D Orientation
of Batteryless Internet-of-Things
Teng Wei and Xinyu Zhang
Department of Electrical and Computer EngineeringUniversity of Wisconsin - MadisonSlide2
Batteryless Orientation Tracking
Orientation is an essential input
Mobile gaming
Virtual reality
Indoor navigation
Battery-powered
Many
applications require
passive orientation sensing
Ad-hoc setup
Least maintenance
Low cost
Gaming
Smart Home
Supply Chain
Production LineSlide3
Technique Review
Sensitive to background variation
Image-based orientation detection
Privacy concern
Require good ambient light condition
Fail during the occlusionSlide4
Tagyro
: RFID-based Orientation Tracking
RFID Reader
Tag Array
Object
Standard phase-distance model in the RFID
0
2
π
Basic ideaSlide5
Tagyro
: RFID-based Orientation Tracking
Tracking algorithm
Input: Array layout
and phase
Process:
Compute intensity map that gauges the similarity between
measured
and
theoretical
PDoA
Output:
Orientation
estimated orientation
Phase Difference of Arrival (
PDoA
) of a Tag Array
RFID Antenna
Tag Array
Tag1
Tag2
θ
= 0
θ
> 0
θ
< 0
θ
PDoA
(Tag 1 and Tag 2)
= 0
= 0
> 0
> 0
< 0
< 0
θ
PDoA
(Tag 1 and Tag 2)
= 0
> 0
< 0
Tag1
Tag2
Tag1
Tag2Slide6
Conditions Underlying the Phase-based Tracking
Layout of the tag array is known
Tag backscatters like an isotropic point source
RFID Antenna
Phase changes linearly with tag-to-reader distanceSlide7
Imperfect Tag Radiation Pattern
RSS
Phase
signal
+X
+Y
+Z
RFID Antenna
Rotation of a single tag
Experiment Setup
blind direction
antenna polaritySlide8
Imperfect Tag Radiation Pattern
Rotation of a tag array
signal
Tag2
r
Tag1
RFID Antenna
Experiment Setup
Measured and Theoretical
PDoA
of A Two-Tag Array
Electromagnetic coupling
deviates the measured
PDoASlide9
A Summary of Problems and Solutions
Antenna polarity
Electromagnetic coupling between tags
Solution:
Array Layout Sensing
Blind direction
Cannot track orientation in 3D
Solution:
Multi-array Tracking
Solution:
Polarity Alignment
Not
Aligined
Aligned
PolaritySlide10
Dealing With the Coupling
Geometry distance
Tag1
Tag2
6 cm
Effective distance
Tag2’
9 cm
Effective distance
Key observation
Tag coupling scales
PDoA
by a constant factor
Geometry distance
Effective distance
Scaling factor depends on effective tag-to-tag distance
scalingSlide11
Array Layout Sensing
Sense the
effective layout of a tag array
Tag 1
…
Tag
i
…
Tag 1
(ref.)
d
11
…
d
1i
…
…
…
…
…
…
Tag j (ref.)
d
j1
…
d
ji
…
…
…
…
…
…
X
Y
Z
Compute the effective layout from distance matrix
t
PDoA
PDoA
scaling
Track
PDoA
scaling, and map it to the effective distance
Randomly rotate tag array and measure the phase
Construct a matrix of effective distance for each tag pairSlide12
Toward 3-DoF Orientation Tracking
Array 2
Reader antenna 2
Dual-array and dual-antenna setup
Algorithmic extension
Array 1
Array 2
Antenna 1
Y-axis,
Z-
axis
Blind
direction
Antenna 2
Blind
direction
X-axis, Z-axis
Reader
antenna 1
Array 1
X
Y
Z
Combo
Validator
OrientationTracking
Orientation
Spectrum
Synthesis
Phase
RSS
Orientation
Determine which array is
out of the blind direction
Combine the
redundant
DoFsSlide13
Calibrating Reader Frequency-Hopping
Random frequency hopping in RFID reader
902~928 MHz; 50 channels; stay at each channel for 200
ms
Frequency-hopping calibration algorithm
Key: cancel the
initial phase-offset
and calibrate
phase shift of different frequencies
Objective: Calibrate the phase so that it looks like output from a single frequency
Observation: Different frequencies induce different initial
phase-offsets
at the readerSlide14
Implementation and Evaluation Setup
Hardware
Impinj
RFID Reader
RFID
Antenna
Tag Array
RFID Tag
s
Object
Impinj
R420 RFID reader
Circular-polarized antenna
Three types of tags
Evaluation setup
Tagyro
GUI
Real-time implementationSlide15
Orientation Tracking Accuracy
Accuracy vs.
DoFAccuracy vs. Size of Tag Array
Accuracy over Distance
Average tracking error ~
5-degreeSlide16
Case Study
12-side dice
Smart home
91.7%
detection accuracy
Fine-grained
recordSlide17
Conclusion
https://www.youtube.com/watch?v=sxTKrBZXP7k
Tagyro: 3D passive
orientation sensing
by using RFID tags, based on phase-distance model
Extensive evaluation using
COTS
RFID reader, antenna and tag
Demonstrate accurate passive orientation tracking
Solve
key
challenges
that
break the
ideal phase-distance model
Blind direction
Antenna polarity
Electromagnetic couplingSlide18
Questions?
Thank you