LocAP: Autonomous Millimeter Accurate Mapping of WiFi Infrastructure · 2020. 3. 24. ·...

LocAP: Autonomous Millimeter Accurate Mapping of WiFi Infrastructure

Roshan Ayyalasomayajula, Aditya Arun, Chenfeng Wu, Shrivatsan Rajagopalan, Shreya Ganesaraman, Aravind Seetharaman, Ish Kumar Jain, Dinesh Bharadia

http://wcsng.ucsd.edu/locap/


Indoor Navigation: Applications

2

Indoor Navigation: Mapping

3

Mapping

Indoor Navigation: Mapping

4

Mapping

Indoor Navigation: Localization

5

Localization


6

DLoc [Mobicom'20]

MonoLoco [MobiSys'18]

Chronos [NSDI'16]

ToneTrack [Mobicom'15]

SpotFi [Sigcomm'15]

ArrayTrack [NSDI'13]

EZ [Mobicom'10]

Horus [MobiSys'05]

RADAR [Infocomm'00] Localization


7

DLoc [Mobicom'20]


Chronos [NSDI'16]


SpotFi [Sigcomm'15]


EZ [Mobicom'10]

Horus [MobiSys'05]

RADAR [Infocomm'00]

RSSI

~10 meter accuracyLocalization


8

DLoc [Mobicom'20]


Chronos [NSDI'16]


SpotFi [Sigcomm'15]


EZ [Mobicom'10]

Horus [MobiSys'05]

RADAR [Infocomm'00]

RSSI

~10 meter accuracy

CSI

<1 meter accuracy

Localization

Indoor Navigation: What is missing?

9

Mapping Localization


10

Mapping Localization

?


11


12

Anchor Locations are not accurately known in physical space

Contributions of LocAP: Reverse Localization

13


❖ First to establish requirements for Reverse Localizing the anchor points

◦ Needs millimetre accurate reverse localization

❖ Developed a novel algorithm that accurately reverse localizes the anchor points

❖ Deployed it on an autonomous system

❖ Demonstrated it in a real world that performs 50x times better than state-of-the-art

14


❖ First to establish requirements for Reverse Localizing the anchor points

◦ Needs millimetre accurate reverse localization

❖ Developed a novel algorithm that accurately reverse localizes the anchor points

❖ Deployed it on an autonomous system

❖ Demonstrated it in a real world that performs 50x times better than state-of-the-art

15

Primer: WiFi-based User Localization

16


17


18


19


20


21

𝑑sin(𝜃)𝜃

𝑑


22

𝑑sin(𝜃)𝜃

𝑑

What happens when there are errors in Anchor Attributes

Errors in Anchor Attributes mis-locates the User

23


24

Location Error


25

Location Error Orientation Error


26

Location Error Orientation Error Antenna Spacing Error

Quantifying Reverse Localization Requirements

27

0 8

10

Y (

m)

X (m)

Requirement for Deployment Orientation

28

0 5 10 15 20

Anchor Orientation Error (degree)

0

0.5

1

1.5

2

2.5

3

Use

r Localiz

ation E

rror

(m)


29

0 5 10 15 20


0

0.5

1

1.5

2

2.5

3

Use

r Localiz

ation E

rror

(m)


30

0 5 10 15 20


0

0.5

1

1.5

2

2.5

3

Requirement: 7o

Target: 50cm

Use

r Localiz

ation E

rror

(m)

Stringent Requirements for Reverse Localization

31

❖ Requirement of median error →

Location Error Orientation Error Antenna Spacing Error

Stringent Requirements for Reverse Localization

32

❖ Requirement of median error →

< 25 cm < 7° < 5 mm

Location Error Orientation Error Antenna Spacing ErrorMillimeter requirements make manual mapping impossible

LocAP Deploys an Autonomous System

33

X

Y


34

X

Y


35

X

Y

Anchor Localization

36

X

Y

Anchor Localization

❖ Locating Anchor is equivalent to Locating any one of the Antenna – First Antenna

❖ Existing User Localization algorithms applied in reverse

❖ 100s of bot locations to triangulate the First Antenna

37

X

Y

Anchor Localization




38

X

Y

Anchor Localization




39

X

Y

𝛽1

Anchor Localization




40

X

Y

𝛽1

Anchor Localization: Handling Bot Errors

❖ A few bot locations can be erroneous

❖ We propose a novel Visual Sensors based Confidence Metric

❖ We neglect Locations with less Confidence

41

XX

Y

𝛽1𝛽2 𝛽3

Anchor Localization: Handling Bot Errors

❖ A few bot locations can be erroneous

❖ We propose a novel Visual Sensors based Confidence Metric

❖ We neglect Locations with less Confidence

42

XX

Y

𝛽1𝛽2 𝛽3

Achieved cm-accurate anchor locations

Can we locate each antenna in a similar way?

43

0

0.04

0.08

0.12

0.16

0.2

4 8 16 32 64

Med

ian

Lo

caliz

atio

n E

rro

r (m

)

Number of bot locations


44

0

0.04

0.08

0.12

0.16

0.2

4 8 16 32 64

Med

ian

Lo

caliz

atio

n E

rro

r (m

)

Number of bot locations


45

Localization error saturates to 3cm

Does not meet mm-accurate requirement for antenna separation

How to bridge this gap?

46


❖ Maximum Bandwidth of WiFi is 160MHz = ~2 meter resolution

❖ First key insight of LocAP is that the carrier frequency fc of these signals is 5GHz ~mm accurate resolution

47




48




49

360° ≡ 6cm

6° ≡ 1mm

Am

plit

ud

e

Phase ≡ Distance

Phase Difference at fc

50


51


52


53

𝜃

𝑑

𝑑sin(𝜃)

Relative antenna localization can achieve millimeter accuracy

Relative Antenna Localization: LocAP

❖ LocAP locates the rest of anchor’s antenna relative to First Antenna

❖ Estimate

54

𝑑

x

y

𝑑 = Antenna SeparationΨ = Deployment Orientation


55

Ψ

𝑑

x

y


❖ Leverage phase difference across two antennas

❖ Recall, we measured direction of First Antenna from the bot (𝛽1)

56

Ψ

𝑑

x

y




57

Ψ

𝑑

x

y

𝛽1

∆∅ =2𝜋

𝜆𝑑sin(𝜃1)

𝜃1




58

Ψ

𝑑

x

y

𝛽1

∆∅ =2𝜋

𝜆𝑑sin(𝜃1)

𝜃1




59

Ψ

𝑑

x

y

𝛽1

∆∅ =2𝜋

𝜆𝑑sin(𝜃1)

𝜃1

𝜃1 = Ψ− 𝛽1 + 90°

𝛽1

𝜃1→ Ψ

known




60

Ψ

𝑑

x

y

𝛽1

∆∅ =2𝜋

𝜆𝑑sin(𝜃1)

𝜃1

𝜃1 = Ψ− 𝛽1 + 90°

𝛽1

𝜃1→ Ψ

knownOnly one equation, but two unknowns (𝑑, 𝜃1)

Leverage from 100s of bot locations

61

Ψ

𝑑

x

y

𝛽1𝜃1

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅

Direction of bot 𝜃1 (radians)


62

Ψ

𝑑

x

y

𝛽1𝜃1

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅



63

Ψ

𝑑

x

y

𝛽1𝜃1

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅


=0.5𝑑/𝜆


64

Ψ

𝑑

x

y

𝛽1𝜃1

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅


=0.5𝑑/𝜆=1𝑑/𝜆

Differential Phase Difference

65

Ψ

𝑑

x

y

𝜃1

❖ Differential Phase Difference from two nearby bot locations

∆∅1∆∅2

𝜃2

Differential Phase Difference

66

Ψ

𝑑

x

y

𝜃1

❖ Differential Phase Difference from two nearby bot locations

∆∅1∆∅2

𝑑∆∅

𝑑𝜃=∆∅2 − ∆∅1𝜃2 −𝜃1

𝜃2

LocAP uses Differential Phase Difference

67

Dif

fere

nti

al P

has

e D

iffe

ren

ce d∆∅/d𝜃


0 /4 /2 3 /4-10

-5

0

5

10

Achieves mm-accurate Antenna separation and < 7° Orientation

=1𝑑/𝜆

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅


=1𝑑/𝜆


68

Dif

fere

nti

al P

has

e D

iffe

ren

ce d∆∅/d𝜃


0 /4 /2 3 /4-10

-5

0

5

10


=1𝑑/𝜆

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅


=1𝑑/𝜆


69

Dif

fere

nti

al P

has

e D

iffe

ren

ce d∆∅/d𝜃


0 /4 /2 3 /4-10

-5

0

5

10


=1𝑑/𝜆

- /2 - /4 0 /4 /2

-

- /2

0

/2

Ph

ase

dif

fere

nce

∆∅


=1𝑑/𝜆

Evaluation Setup

❖ COTS Quantenna chipsets

❖ 8 different anchors in 2000 sq. ft.

❖ 5 different antenna separations

❖ 7 different orientations

❖ Most popular anchor spacing of both linear and rectangular arrays

70

Antenna Separation Prediction Results

71

10 -3 10 -2 10 -1 10 0

Error in Relative Antenna Separation (m)

00.10.20.30.40.50.60.70.80.9

1

CD

F


72

10 -3 10 -2 10 -1 10 0


00.10.20.30.40.50.60.70.80.9

1

CD

F

LocAPSpotFi

Requirement


73

10 -3 10 -2 10 -1 10 0


00.10.20.30.40.50.60.70.80.9

1

CD

F

LocAPSpotFi

Requirement


74

10 -3 10 -2 10 -1 10 0


00.10.20.30.40.50.60.70.80.9

1

CD

F

LocAPSpotFi

Requirement

50x improvement

Deployment Orientation Prediction Results

75

0 10 20 30 40 50 60Orientation Error( °)

0

0.10.20.3

0.4

0.50.60.70.8

0.91

CD

F


76


0

0.10.20.3

0.4

0.50.60.70.8

0.91

CD

F

SpotFi

LocAP

Requirement


77


0

0.10.20.3

0.4

0.50.60.70.8

0.91

CD

F

SpotFi

LocAP

Requirement

8x improvement

Conclusion and Future Work

❖ First Work to define the requirements for Reverse Localization

❖ Demonstrated millimeter accurate Reverse Localization

78



LocAP: Autonomous Millimeter Accurate Mapping of WiFi Infrastructure · 2020. 3. 24. ·...

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