One interesting embedded system - sites.pitt.edu
Transcript of One interesting embedded system - sites.pitt.edu
One interesting embedded system Intel Vaunt small glass Key: AR over devices that “look normal”
https://www.youtube.com/watch?v=bnfwClgheF0
More details at: https://www.theverge.com/2018/2/5/16966530/intel-vaunt-smart-glasses-announced-ar-video
ECE 1161/2161 Embedded Computer System Design 2 1
ECE 1161/2161Embedded Computer System Design 2
Sensing - 2
Wei Gao
Spring 2019 2
Indoor Localization GPS-free methods Primary approach: range-based localization Multiple anchors Distances between nodes to anchors measured wirelessly Metrics:
• TOA (Time of Arrival )• TDOA (Time Difference of Arrival)• AOA (Angle of Arrival )• RSSI (Receive Signal Strength Indicator)
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Time of Arrival (ToA)
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• Example: GPS• Satellites broadcast
precise time• Estimate distance to
satellite using signal TOA
• Trilateration
Acoustic measurement Slower propagation speed -> easier measurement Limitations: Require line of sight Short detection rage
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Available device Wireless Cricket http://cricket.csail.mit.edu/
Indoor range ~10-20m
Ranging precision: 1cm – 3cm
Modes: active beaconing & passive listening
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Angle of Arrival (AoA)
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Use antenna array to measure direction of neighbors Flood beacons, update
bearing along the way Once bearing of three
landmarks is known,calculate position
RF Signal Strength Distance measurement using RF signals Problematic Susceptible to different signal propagation characteristics
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More on RSSI Path loss characteristics depend on environment (1/rn)
Shadowing depends on environment
Short-scale fading due to multipath adds random high frequency component with huge amplitude (30-60dB) – very bad indoors
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DistanceR
SSI
Path lossShadowingFading
Range-free Approaches Limitations of range-based localization Expensive hardware deployment Limited detection range
Range-free localization Simple hardware But less accuracy
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Centroid
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Idea: Do not use any ranging at all, simply deploy enough beacons
Anchors periodically broadcast their location
Localization:1. Listen for beacons2. Average locations of all anchors
in range3. Result is location estimate
Good anchor placement is crucial!
Anchors
Hop-Count Techniques
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Works well with a few, well-located seeds and regular, static node distribution. Works poorly if nodes move or are unevenly distributed.
r
11
2
2 3
3
33
4
4
4
445
5
6
7
8
Approximate Point In Triangle Area-based approach Anchors divide terrain into triangular regions
A node’s presence inside oroutside of these triangular regions allows a node to narrow the area in which it can potentially reside.
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AlgorithmPseudo Code:Receive beacons (Xi,Yi)
from N anchors
N anchors form triangles.
For ( each triangle Ti Є ){
InsideSet Point-In-Triangle-Test (Ti)
}Position = COG ( ∩Ti ∈InsideSet);
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3N
3N
Perfect Point in Triangle (PIT) If there exists a direction in which M is departure from points
A, B, and C simultaneously, then M is outside of ∆ABC. Otherwise, M is inside ∆ABC.
Require approximation for practical use Nodes can’t move, how to recognize direction of departure Exhaustive test on all directions is impractical
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M
A
CB
MA
CB
Inside Case Outside Case
Departure testing Recognize directions of departure via neighbor
exchange RSSI
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M
NAAnchor Receiving nodes
300
350
400
450
500
550
600
1 5 9 13 17 21 25 29 33 37Beacon Sequence Number
Sig
nal
Str
en
gth
(m
v)
1 Foot
5 Feet
10 Feet
15 Feet
Approximate PIT Test only directions towards neighbors Error in individual test exists, may be masked by APIT
aggregation.
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A
C
1
23
4
M
B
A
CB
A. Inside Case B. OutSide Case
1
23
4
M
Sources of Possible Errors Exhaustive testing on all possible directions is
impossible False positive: M is near the edge of triangle False negative:
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1
2
4
M
A
C
1
2
4
B
A
CB
A. InToOut Error B. OutToIn Error
3
M
PIT = IN while APIT = OUT PIT = OUT while APIT = IN
APIT aggregation
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Grid-Based Aggregation
-1-1-10011100
-1-1-10122200
0-1-10112211
00-10112210
0001111100
0001110100
0001000000
-1-1-10000
-1-10100
0-1011
00-1010
00011100
00011000
0001100000High Possibility area
Low possibility area
Applications Location-based services
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Applications Augmented and Virtual Reality
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