STYROFOAM Robert LiKamWa, David Ramirez, Jason Holloway Advisors: Lin Zhong, Behnaam Aazhang, Ashok Veeraraghavan Rice University STYROFOAM – VLCS @ Mobicom

STYROFOAM – VLCS @ Mobicom 2014

STYROFOAM

Robert LiKamWa, David Ramirez, Jason Holloway

Advisors: Lin Zhong, Behnaam Aazhang, Ashok VeeraraghavanRice University


STYROFOAM

Robert LiKamWa, David Ramirez, Jason Holloway

Advisors: Lin Zhong, Behnaam Aazhang, Ashok VeeraraghavanRice University

A Tightly-Packed Coding Scheme

for Camera-based Visible Light Communication


4

Screen Camera Communication


5

Screen Camera Communication


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Benefits

Pairlessinfrastructure

Multi-cast transmission

Targeted interaction

Use Cases

Device-Specific Broadcast

Wearable Transmissions

Easy Access Media


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Camera-based VLC Research Challenges

• Efficient Marker Tracking (COBRA)

• Blur-aware Ordering (COBRA)

• Unsync’ed Camera/Screen rates (LightSync)

• Increasing block bit-depth (Styrofoam)


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OFF

ON

• Increasing block bit-depth (Styrofoam)

STYROFOAM

Screen -> Camera Communication

Understanding the channel

Styrofoam Coding Scheme

Implementation


10

sD sC

sBsA


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sA sB sC sDTX:


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sAsB sC

TX:

RX:

sA sB sC sD


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sA sB

Inter-symbol interference

sA sB sC sD

t

TX:

RX:


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TX:

RX:

sD

sA sB

rj = α0,jsA + α1,jsB

sA sB sC

TX_α0:TX_α1:

RX_α0:RX_α1:

α0,j

α1,j

t


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STYROFOAM




Implementation


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TX:

t

RX:

sD

sA sBrj = α0,jsA + α1,jsB

sA sB sC


Guaranteeing resolvability


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Constraint #1Symbol Visibility

TX:

RX:

sDsA sB sC

Capture Period


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TX:

RX:

sDsA sB sC

Capture Period

Capture Period < Symbol Period


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Capture Period < Symbol Period

This guarantees each symbol is RXed with α > 0.5

TX:

RX:

sDsA sB sC

Capture Period


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Constraint #2Symbol Color Fidelity

Adjacent symbols must match color channels.

TX:

RX:

sD

sA sB

sA sB sC

Color-cross-talk


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Constraint #2Symbol Color Fidelity

Adjacent symbols must match color channels.

TX:

RX:

sD

sA sB

sA sB sC

Color-cross-talk


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Constraint #3Symbol Resolvability

TX:

RX:

sD

sA sB

rj = α0,jsB + α1,jsC

sA sB sC

s1B sC

ri = α0,isA + α1,isB

sC sD

rk = α0,ks1 + α1,ks2

Mixed Capture: 1 eqn, 2 var


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sA sB sBsC

sC


TX:

RX:

sDsA sB sC

Mixed Capture: 1 eqn, 2 varPure Capture: 1 eqn, 1 var

rj = α0,jsB + α1,jsCri = α0,isA + α1,isB rk = α1,ksC

Ensure pure captures with Styrofoam Blocks


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sA sB sC~ ~

αCαBαA

A mixed capture target is always followed by the mixed symbol’s capture.Spacing => αA < αB < αC

Ensure pure captures with Styrofoam Blocks

Constraint #1: Visibility SpacingSpacing => Every symbol appears with α>0.5


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Styrofoam Block Size

Styrofoam blocks are only useful when symbol α>0.5Remainder of block is < 0.5.

Styrofoam blocks need only be half as wide as symbol blocks

sA sB sC~ ~~~


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Display each symbol for two frames,Styrofoam Block for one frame

Display Frame Rate < 2 x Camera Frame Ratee.g. (Display : 30 FPS, Camera : 15 FPS)`

Styrofoam Frame Timing

sD sE sF~ ~

sD sE sF~ sD sE sF ~sD sE sF~ sD sE sF sG sH sI~ sG sH sIsA sB sC~ sA sB sC


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Styrofoam CodingsA … sN~

Data Rate

sA … sN

Bit depth/Block/Display Frame

~

1 2 3 4 5 6 7 8 9 101.7

1.75

1.8

1 2 3 4 5 6 7 8 9 1005

10152025

Decode Latency

Frame Latency


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Per-block, Per-Display Frame Rate

Datarate Comparisons• Traditional (1-bit, blank alternate frames): 0.5 bits• COBRA (5-values, half-frame rate): 1.16 bit• LightSync (“Synchronization” interference blocks): 1 bit• Styrofoam: 1.7 bits• 1.7 bits * 720 blocks * 60 fps = 73.4

kbps


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STYROFOAM




Implementation


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Implementation• In paper:

– Transmitter: Blackberry Z30, 60 FPS– Receiver: Nokia Lumia, 30 FPS

• Hardware ISO & Exposure control

– Decoded offline w/ MATLAB

• Demo:– Nexus 5 + Nexus 5

• Android L hardware controls


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Styrofoam Barcode (Nexus 5)


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Styrofoam Barcode (Simplified Version)

αmax

α1

α0


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Sample TXEven Odd


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s1 s2~ ~


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Decoded Pairs


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Additional Styrofoam Research Challenges

• Steganography– Can we hide the Styrofoam blocks?

• Power Efficiency– Of the display? Of the receiver?

• Leveraging YUV color channels– Mixing colors safely?

• Geometric problems– Screen -> Camera angles?


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David RamirezRobert LiKamWa Jason Holloway

STYROFOAMCharacterize and constrain inter-symbol interference with Styrofoam spacing blocks

Behnaam AazhangLin ZhongAshok Veeraraghavan

Advisors: Authors:

s A

…

s Z

~s A

…

s Z~


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Constraints• Display Frame > Symbol Frame

– Symbol Visibility for at least half capture

• Styrofoam block spacing– To guarantee pure captures– Block at least half width of symbol

• Color Matching– To deter color filter issues

Documents

STYROFOAM Robert LiKamWa, David Ramirez, Jason Holloway Advisors: Lin Zhong, Behnaam Aazhang, Ashok Veeraraghavan Rice University STYROFOAM – VLCS @ Mobicom