Decimeter-Level Localization with a Single WiFi Access Point Deepak - - PowerPoint PPT Presentation

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Decimeter-Level Localization with a Single WiFi Access Point Deepak - - PowerPoint PPT Presentation

Mar 15, 2024 194 likes •721 views

Decimeter-Level Localization with a Single WiFi Access Point Deepak Vasisht Swarun Kumar, Dina Katabi Indoor Localization is Cool! SpotFi [SIGCOMM 15], ToneTrack [Mobicom 15], Phaser [Mobicom 14], Tagoram [Mobicom 14], LTEye

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SLIDE 1

Decimeter-Level Localization with a Single WiFi Access Point

Deepak Vasisht Swarun Kumar, Dina Katabi

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SLIDE 2

Indoor Localization is Cool!

  • Locate off-the-shelf devices
  • Accuracy of tens of cm

SpotFi [SIGCOMM’ 15], ToneTrack [Mobicom’ 15], Phaser [Mobicom’ 14], Tagoram [Mobicom’ 14], LTEye [SIGCOMM’ 14], ArrayTrack [NSDI’13], PinPoint [NSDI’13], PinIt [SIGCOMM’13], Zee [MobiCom’12], PinLoc [MobySys’12], EZ [MobiCom’10], ….

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But… They Need 4-5 Access Points Homes and small businesses have ON ONE access point (AP)

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SLIDE 4

Application : Control heating based on occupancy

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SLIDE 5

Application : WiFi Geo-Fencing

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Application : Device-to-device Localization Enable device-to-device localization without infrastructure support

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SLIDE 7

Chronos

  • Enables decimeter-accurate localization using a

single off-the-shelf WiFi card

  • A novel algorithm to estimate propagation time to

sub-nanosecond accuracy using a WiFi card

  • Implemented and evaluated in practical settings
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SLIDE 8

Why past work needs multiple AP’s?

θ

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SLIDE 9

Single Access Point?

θ distance

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SLIDE 10

Measuring Distance

Distance = speed of light x propagation delay

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SLIDE 11

Measuring Distance

Distance = speed of light x propagation delay

How do we measure propagation delay?

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SLIDE 12

Propagation Delay

t Phase of the signal( ) = 2𝜌𝑔𝑢

ϕ

𝑛𝑝𝑒 2𝜌

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Propagation Delay: Example

2.41 GHz 0.5 1 1.5 t (ns)

𝜚 = 2𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌

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SLIDE 14

Propagation Delay: Example

2.41 GHz 0.5 1 1.5 t (ns) 2.48 GHz 5.18 GHz 5.8 GHz

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Mathematically

𝜚- = 2𝜌𝑔

  • 𝑢 𝑛𝑝𝑒 2𝜌

𝜚. = 2𝜌𝑔

.𝑢 𝑛𝑝𝑒 2𝜌

𝜚/ = 2𝜌𝑔

/𝑢 𝑛𝑝𝑒 2𝜌

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SLIDE 16

Mathematically

𝜚- = 2𝜌𝑔

  • 𝑢 𝑛𝑝𝑒 2𝜌

𝜚. = 2𝜌𝑔

.𝑢 𝑛𝑝𝑒 2𝜌

𝜚/ = 2𝜌𝑔

/𝑢 𝑛𝑝𝑒 2𝜌

Use Chinese Remainder Theorem to get the propagation delay

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SLIDE 17

Can’t measure propagation delay without detection delay

Distance = speed of light x propagation delay Measured delay = propagation delay + detection delay

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SLIDE 18

Packet Detection Delay

Detection Decoding

  • Detection delay >> Propagation delay

§ Detection Delay ≈ 200 ns, Propagation Delay ≈ 20 ns

  • Detection delay is unpredictable

Detection Delay

How do we eliminate detection delay?

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Problem: Separate detection delay from propagation delay

Solution: Leverage that propagation delay and detection delay happen at different frequencies

f

Detection Decoding

f-fc Propagation Delay Detection Delay

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SLIDE 20

f

Detection Decoding

f-fc Propagation Delay (t) Detection Delay (t’)

𝜚 = 2𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌 𝜚 = 2𝜌𝑔𝑢 + 2𝜌 𝑔 − 𝑔

4 𝑢′ 𝑛𝑝𝑒 2𝜌

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Detection Decoding

f-fc

Idea: Use OFDM to measure phase at f=fc

f Propagation Delay (t) Detection Delay (t’)

𝜚 = 2𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌 𝜚 = 2𝜌𝑔𝑢 + 2𝜌 𝑔 − 𝑔

4 𝑢′ 𝑛𝑝𝑒 2𝜌

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But WiFi does not transmit at f=fc

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Solution: Leverage OFDM

𝑔

4

𝑔

4 + 𝜀

𝑔

4 + 2𝜀 𝑔 4 + 3𝜀

𝑔

4 − 2𝜀

𝑔

4 − 3𝜀

Phase 𝑔

4 − 𝜀

Phase at f=fc 𝜚 = 2𝜌𝑔𝑢 + 2𝜌 𝑔 − 𝑔

4 𝑢′ 𝑛𝑝𝑒 2𝜌

𝜚4 𝜚4 = 2𝜌𝑔

4𝑢 + 0 𝑛𝑝𝑒 2𝜌

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Mathematically

𝜚4,- = 2𝜌𝑔

4,-𝑢 𝑛𝑝𝑒 2𝜌

𝜚4,. = 2𝜌𝑔

4,.𝑢 𝑛𝑝𝑒 2𝜌

𝜚4,/ = 2𝜌𝑔

4,/𝑢 𝑛𝑝𝑒 2𝜌

Chronos eliminates packet detection delay by leveraging OFDM properties

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Additional System Components

  • Initial Phase Offset Compensation
  • Multipath resolution
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Additional System Components

  • Initial Phase Offset Compensation
  • Multipath resolution
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Initial Phase Offsets

t

𝜚 = 2𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌 𝜚 = 2𝜌𝑔𝑢 + Δ𝜚 𝑛𝑝𝑒 2𝜌

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Idea: Use Acknowledgements

t

𝜚- = 2𝜌𝑔𝑢 + Δ𝜚 𝑛𝑝𝑒 2𝜌 𝜚. = 2𝜌𝑔𝑢 − Δ𝜚 𝑛𝑝𝑒 2𝜌 𝜚- + 𝜚. = 4𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌

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Idea: Use Acknowledgements

t

𝜚- = 2𝜌𝑔𝑢 + Δ𝜚 𝑛𝑝𝑒 2𝜌 𝜚. = 2𝜌𝑔𝑢 − Δ𝜚 𝑛𝑝𝑒 2𝜌 𝜚- + 𝜚. = 4𝜌𝑔𝑢 𝑛𝑝𝑒 2𝜌

Chronos eliminates phase offsets by using acknowledgements

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Additional System Components

  • Initial Phase offset Compensation
  • Multipath resolution
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Problem: Multipath Effect

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Solution: Find delays for each path Distance to source corresponds to the smallest delay.

5.2 ns 10 ns 16 ns

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Experimental Evaluation

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Implementation

  • Evaluation with off-the-shelf Intel WiFi 5300 cards
  • Kernel modifications to the iwlwifi driver in the Ubuntu kernel
  • Ground truth measurements using laser distance measurement

device ( 1mm accurate)

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Evaluation Testbed: Office Environment

20 m 20 m

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Distance Measurement Accuracy

0.2 0.4 0.6 0.8 1 1 2 3 CDF Error (m)

LOS NLOS

14 cm 21 cm

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Localization Accuracy

0.2 0.4 0.6 0.8 1 2 4 CDF Error (m)

LOS NLOS

65 cm 98 cm

3 AP’s 190 cm 4 AP’s 80 cm 5 AP’s 60 cm

SpotFi (SIGCOMM’ 15)

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SLIDE 38

Localization Accuracy

0.2 0.4 0.6 0.8 1 2 4 CDF Error (m)

LOS NLOS

Chronos can achieve state-of-the-art localization accuracy with a single AP

65 cm 98 cm

3 AP’s 190 cm 4 AP’s 80 cm 5 AP’s 60 cm

SpotFi (SIGCOMM’ 15)

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Applications

Smart Homes WiFi Geo-fencing Device to Device localization

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Applications

Smart Homes WiFi Geo-fencing Device to Device localization

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Application: Smart Homes

Living room Bedroom1 Bedroom2 Kitchen Bath 13 m 9 m

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Application: Smart Homes

Living room Bedroom1 Bedroom2 Kitchen Bath 13 m 9 m

Chronos detects the correct room with accuracy 94%.

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Applications

Smart Homes WiFi Geo-fencing Device to Device localization

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Application: GeoFencing

Coffee Station 7 m 9 m

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Application: GeoFencing

Coffee Station 7 m 9 m

Chronos can accurately authenticate WiFi users with 97% accuracy.

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Applications

Smart Homes WiFi Geo-fencing Device to Device localization

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Application: TakeMyPicture Drone

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  • 2

2

  • 3
  • 2
  • 1

1 2 3

Application: TakeMyPicture Drone

Drone User x (m) y (m)

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Application: TakeMyPicture Drone

0.2 0.4 0.6 0.8 1 5 10 15 CDF Error (cm) 4.2 cm

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Application: TakeMyPicture Drone

0.2 0.4 0.6 0.8 1 5 10 15 CDF Error (cm)

Chronos enables a drone to follow the user with no infrastructure support.

4.2 cm

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Related Work

  • WiFi Localization: SpotFi [SIGCOMM’ 15], ToneTrack [Mobicom’

15], Phaser [Mobicom’ 14], Tagoram [Mobicom’ 14], ….

  • Closest Work: SAIL [MobiSys’ 14]
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Conclusion

  • Chronos is the first system to enable accurate

localization on off-the-shelf WiFi cards

  • Its key enabler is a novel algorithm that can

estimate accurate propagation delay, by eliminating the detection delay