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)

ECE 1161/2161 Embedded Computer System Design 2 3

Time of Arrival (ToA)

ECE 1161/2161 Embedded Computer System Design 2 4

• 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

ECE 1161/2161 Embedded Computer System Design 2 5

Available device Wireless Cricket http://cricket.csail.mit.edu/

Indoor range ~10-20m

Ranging precision: 1cm – 3cm

Modes: active beaconing & passive listening

ECE 1161/2161 Embedded Computer System Design 2 6

Angle of Arrival (AoA)

ECE 1161/2161 Embedded Computer System Design 2 7

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

ECE 1161/2161 Embedded Computer System Design 2 8

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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

ECE 1161/2161 Embedded Computer System Design 2 9

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

ECE 1161/2161 Embedded Computer System Design 2 10

Centroid

ECE 1161/2161 Embedded Computer System Design 2 11

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

ECE 1161/2161 Embedded Computer System Design 2 12

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.

ECE 1161/2161 Embedded Computer System Design 2 13

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);

ECE 1161/2161 Embedded Computer System Design 2 14

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

ECE 1161/2161 Embedded Computer System Design 2 15

M

A

CB

MA

CB

Inside Case Outside Case

Departure testing Recognize directions of departure via neighbor

exchange RSSI

ECE 1161/2161 Embedded Computer System Design 2 16

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.

ECE 1161/2161 Embedded Computer System Design 2 17

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:

ECE 1161/2161 Embedded Computer System Design 2 18

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

ECE 1161/2161 Embedded Computer System Design 2 19

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

ECE 1161/2161 Embedded Computer System Design 2 20

Applications Augmented and Virtual Reality

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