PD1

PD2

MicrocontrollerQuad OpAmp

Vision-Precision Ubiquitous Indoor LocalizationUsing Conventional Lights Chi Zhang (UW-Madison), Xinyu Zhang (UC San Diego)

Indoor Localizaton

Discovery Navigaton Analytcs Interacton

Current Practce: Wi-FiInaccurate Meters of errorFragile Easily afected by dynamics

Future Promise: Visible Light PositoningAccurate Robust Ubiquitous

Approach ①: Camera + PhotogrammetryNarrow View Low SensitiityEnergy-Hungry Long Latency

Approach ②: Photodiode + Intensity ModelModel is UnrealistcObstructon Breaks model

Above All: Require Extra Beacon Hardware

= Huge Retrofing Cost!

Departure from the Regime

Angle of Arrival (AoA)

Database

Reusing Existng Lights

0

25

50

75

86 88 90 92 94

Inte

nsity

(dB)

Frequency (kHz)

Localizaton

ResourcesChi Zhang, Xinyu Zhang, “Pulsar: Towards Ubiquitous Visible Light Localizaton”, ACM MobiCom’17

Chi Zhang, Xinyu Zhang, “LiTell: Robust Indoor Localizaton Using Unmodifed Light Fixtures”, ACM MobiCom’16

http://dword1511.info

AoA from Photodiodes

Light Irradiate angle

Incident angle (AoA)θ

φ

r

12

RSS1 = Pt At(θ) α(r) Ar1(φ)

RSS2 = Pt At(θ) α(r) Ar2(φ)

RSS = Pt At(θ) α(r) Ar(φ)

RSS1 Ar1(φ1)RSS2 Ar2(φ2)

Ac(φ)= =RSS1

RSS2φ = Ac

-1 ( )

Prototype

Light CFLight CFLight CF

Light CFLight CFLight AoA

3D Location Orientation

Gravity &Compass

SpectrumPhotodiode

Database

PhotodiodeProfile

Light CFLight CFLandmarkLocation

Light CFLight CFVectorEquation

3 Lights→ 3D Locaton

4 Lights→ 3D Locaton + Orientaton

÷

f -1

Retrofing is costly?Reuse existng lights!

Intensity is unreliable?Enable photodiode-based AoA sensing!

Visible Light: No Phase!Photodiodes: No Spatal Resoluton!Need New Tricks

Accuracy: 10cm / 5°

Oscillaton in Driver → High Frequency FlickerUbiquitous Stable

Manufacturing Error → Diversity in OscillatorsUnique

“Characteristc Frequency (CF)”

Turn Existng Lights into Locaton Landmarks 4X 5X 2X

How to Identfy Lights without Beacons?

(Phone not to Scale)

Obtain AoA from 2Diferent Photodiodes