STYROFOAM Robert LiKamWa, David Ramirez, Jason Holloway Advisors: Lin Zhong, Behnaam Aazhang, Ashok...
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Transcript of STYROFOAM Robert LiKamWa, David Ramirez, Jason Holloway Advisors: Lin Zhong, Behnaam Aazhang, Ashok...
STYROFOAM – VLCS @ Mobicom 2014
STYROFOAM
Robert LiKamWa, David Ramirez, Jason Holloway
Advisors: Lin Zhong, Behnaam Aazhang, Ashok VeeraraghavanRice University
STYROFOAM – VLCS @ Mobicom 2014
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
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Screen Camera Communication
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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
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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
Screen -> Camera Communication
Understanding the channel
Styrofoam Coding Scheme
Implementation
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TX:
t
RX:
sD
sA sBrj = α0,jsA + α1,jsB
sA sB sC
Styrofoam Coding Scheme
Guaranteeing resolvability
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Constraint #1Symbol Visibility
TX:
RX:
sDsA sB sC
Capture Period
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Constraint #1Symbol Visibility
TX:
RX:
sDsA sB sC
Capture Period
Capture Period < Symbol Period
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Constraint #1Symbol Visibility
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
Constraint #3Symbol Resolvability
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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Constraint #3Symbol Resolvability
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
Screen -> Camera Communication
Understanding the channel
Styrofoam Coding Scheme
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