1. Project website: https://sites.google.com/site/nsfvlc/
October 27, 2005
Optimal Multi-Element VLC Bulb Design with Power and Lighting Quality Constraints
Sifat Ibne Mushfique and Murat Yuksel
Project website:

2. Why Multi-Element/Stream VLC?
LED Array
Unused space
Visible light download
Photo-detector
Single data stream
PHY solution
Large divergence – for smooth lighting
Multiple data streams
Narrow divergence – for higher spatial reuse
Spherical structures – to retain smooth lighting
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3. Problem Statement
October 27, 2005
Introduce an framework of a Multi-element Bulb Design that –
Optimizes the placement of LED boards/transmitters
- Maximizing the signal-to-interference ratio (SIR)
- Maintain a minimum evenness of the lighting on the room floor
Also, explores the optimization characteristics
- Under various constraints
Challenges of a Multi-element Bulb Design
Handle the line-of-sight (LOS) alignment management
Implement seamless communication across the room
Resolve inter-LED interference
Balance the tradeoff: uniform lighting and high spatial reuse
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4. Multi-element Bulb Configuration
October 27, 2005
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5. System Model
October 27, 2005
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6. Optimization Objective
October 27, 2005
Maximize SIR For a particular number of layers
Add divergence angle to the optimization problem
Make the problem constrained with Power
Update the problem with the constraint on the illumination quality
Two results are compared to analyze the effect of the illumination requirement on the overall optimization problem
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7. Maximum SIR Problem (MAX_SIR)
October 27, 2005
Variable Parameters
ki , Number of Transmitters in Layer i
- LED boards can be placed in layers in many different ways
- ki depends on the size of the LED boards (rt) and the Bulb radius (R)
θd, Divergence Angle of LEDs
- Large divergence angles  better lighting
- Narrow divergence angles  increased spatial reuse & higher SIR
- Different divergence angles are tried to find the configurations yielding maximum SIR
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8. Placement of the Transmitters
October 27, 2005 R
Layers
R = 40 cm, rt = 5.5 cm
No. of Layers = 4
R = 40 cm, rt = 3.5 cm
No. of Layers = 7
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9. Maximum SIR Problem (Contd.)
October 27, 2005
Fixed Parameters
Room size - 6m x 6m x 3m
R, Radius of the Hemispherical Bulb – 40 cm
rt, Radius of the LED Board/Transmitter - 3.5cm
l, Number of Layers - Depending on R and rt
- Minimum number of layers  2
- Maximum number of layers  calculated from R and rt
- The number of Layers and LED boards is varied between this minimum and maximum value
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10. Non-Linearity of the Objective Function
October 27, 2005
Local Maxima
Local Minima
SIR doesn’t increase linearly
Multiple Local Maxima and Minima
Saturation of the SIR Value
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11. Updating the Maximum SIR Problem (MAX_SIR_LQ)
October 27, 2005
Illumination Constraint (Is) is added to obtain smooth lighting
Is is calculated by continuously taking average luminous intensity of 100 random points until the value converges
Maximum allowed illumination variance, Ismax = 5
The new objective function output is then (SIR / Is) instead of SIR
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12. Results MAX_SIR has much fewer LEDs in the higher layer
October 27, 2005
Objective
l (number of layers) k1 k2 k3
θd (in degrees)
MAX_SIR 2 19 --
39.5 3 16 26
47.2
MAX_SIR_LQ 6 28
MAX_SIR has much fewer LEDs in the higher layer
MAX_SIR_LQ puts more LEDs in the higher layer to achieve more even lighting across the room
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13. Results (Contd.) VLCS 2016 13 SIR value saturates
October 27, 2005
SIR value saturates
Lighting Quality starts to deteriorate as Is increases
Optimum SIR is significantly lower in MAX_SIR_LQ
(SIR / Is) starts to fall from the same time
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14. Summary and Future Work
October 27, 2005
A framework is introduced to optimize a multi-element bulb design for both illumination and communication quality of VLC in a room
In the future, this can be done for different room size and bulb parameters
Trying with bulbs of some other shapes (Triangular, Square etc.) can be interesting
Multiple number of bulbs can be considered as well
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15. October 27, 2005
QUESTIONS?