1. Project website: https://sites.google.com/site/nsfvlc/
A Multi-Element VLC Architecture for High Spatial Reuse
Prabath Palathingal1, Murat Yuksel1, Ismail Guvenc2, and Nezih Pala2
1 University of Nevada, Reno
2 Florida International University
Project website:
VLCS 2015

2. Why Multi-Element/Stream VLC?
LED Array
Unused space
Visible light download
Photo-detector
Multiple data streams
Narrow divergence – for higher spatial reuse
Spherical structures – to retain smooth lighting
Single data stream
PHY solution
Large divergence – for smooth lighting
VLCS 2015

3. Problem Statement Develop an efficient spatial reuse mechanism that
takes full advantage of the directionality of LEDs
provides simultaneous uniform lighting and mobile communication across a room
Challenges
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
VLCS 2015

4. The Architecture . . . The Internet RF upload A transmitter: LED board
Visible light download
Data upload
Superbowl video stream
Youtube video stream
The Internet
Photo-detector
Router with software-defined LOS management
A transmitter: LED board
. . .
RF upload
VLCS 2015

5. The Architecture Main features Main components
Allows multi-user communication in a room.
Seamless handling of mobility of receivers for seamless communication.
Hybrid RF/VLC communication mechanism. VLC is used for download and RF for upload.
Main components
The Bulb
RF/FSO LOS management protocol
VLCS 2015

6. The Bulb (as an AP)
Provides uniform lighting and simultaneous multiple data downloads
Hemisphere with multiple circular layers of LED transmitters
The transmitters are arranged so as to increase the spatial reuse
Each transmitter is connected to the router to achieve seamless steering of data across the bulb
VLCS 2015

7. The Bulb (as an AP) Transmitter placement on the bulb The bulb
θ, Angle of placement of the transmitter from the normal of the bulb
α, Angle between the transmitters in the same layer.
Φ, Divergence angle of the transmitter.
Ln , Range of the transmitter where communication is possible.
The bulb α ϑ Ø
Slanted Normal ϑ Ln
Perpendicular Normal Z
O(x,y)
N(x,y)
Normal Distance (DN)
Coverage Area
VLCS 2015

8. RF/VLC Hybrid LOS Management
Association Mechanisms
Join with LED-RAT
Maintain
Leave
VLCS 2015

9. Join with LED-RAT . . . LED-RAT Tx A Rx A Tx B Rx B Connected
Router with software-defined LOS management
Connected
SEARCH Frames
Connected
SEARCH Frames
ACK|Rx A|Tx A
ACK|Rx B|Tx B
Rx B
Rx A
VLCS 2015

10. Join with LED-RAT Every bulb sends SEARCH frames
Receivers filter the frame with the maximum intensity
ACK verification
Updating LED-RAT
VLCS 2015

11. Maintaining the Link . . . Connected SEARCH Frames Connected
LED-RAT
Tx A
Rx A
Tx B
Rx B B A
. . .
Tx A
Tx B
A transmitter: LED board
Router with software-defined LOS management
Connected
SEARCH Frames
Connected
SEARCH Frames
ACK|Rx B|Tx A
ACK|Rx A|Tx B
Rx B
Rx A
Trade off exists on the time interval between the SEARCH frame transmissions
VLCS 2015

12. Partitioning Algorithm
Divide the transmitters into sections with respect to receiver positions
Each “section” serves the same data stream to the respective receiver
Facilitates mobility
VLCS 2015

13. An Initial Evaluation 6m x 6m x 3m
The bulb in the middle of the ceiling
25 transmitters on 3 layers: 30⁰, 45⁰, 70⁰
8 transmitters per layer
Two receivers at random positions on the floor – 80K runs
Any signal received from the transmitters assigned to the other receiver is considered as noise
Transmitter radius: 4cm PD radius: 3.75cm Bulb radius: ~11cm
12W transmitter, e.g., 600 LEDs with 20mW each
25 transmitters on the bulb
VLCS 2015

14. Divergence angle = 45⁰ 3-region behavior! High spatial reuse
High interference
High spatial reuse
Low signal strength
3-region behavior!
VLCS 2015

15. Effect of Divergence angle
450
200
Large divergence angle increases the distribution of light across the room but can create sizable interference
Spatial reuse is better as expected from narrower divergence angles
For smooth lighting: need more LEDs with narrower divergence
VLCS 2015

16. Three Regions Region 3 Region 2 Region 1 High interference
Low signal strength
VLCS 2015

17. Effect of Divergence angle
Is there an optimal divergence angle?
VLCS 2015

18. Effect of Divergence angle
seems to be the best
VLCS 2015

19. Effect of Room Size Room height is 3m. Floor’s edge is varied.
LED divergence: 200
Tx power: 20W 1x 4x
SNR in region 1 reduces much slower than the floor area 9x
SNR in region 3 reduces along with the floor area
VLCS 2015

20. Effect of Room Size & Tx Power
Increase tx power along with the floor size.
LED divergence: 200
25x
SNR in region 1 saturates but does not reduce 4x
16x 1x 9x
SNR in region 3 consistently increases but sublinearly tx power
VLCS 2015

21. Summary A multi-element VLC architecture that
supports multiple simultaneous data streams and illumination
use an RF/FSO hybrid LOS management protocol
Reasonably high SNRs observed
A heuristic to partition the LEDs on the bulb/AP
3 regions: a guide to organize room layouts
VLCS 2015

22. Future Work Test the architecture with
More LEDs
More receivers
Varying Tx power of LEDs
The Bulb: Optimize the # of LEDs and their placements
Use multiple bulbs/APs in a room
Joint optimization of illumination and communication in a room
VLCS 2015

23. Other or Upcoming VLC Work
Extended results (with wall reflections):
Y. S. Eroglu, A. Sahin, I. Guvenc, N. Pala, and M. Yuksel, Multi-Element Transmitter Design and Performance Evaluation for Visible Light Communication, to appear in Proceedings of IEEE GLOBECOM Workshop on Optical Wireless Communication (OWC), San Diego, CA, December 2015.
VLC localization:
A. Sahin, Y. S. Eroglu, I. Guvenc, N. Pala, and M. Yuksel, Hybrid 3D Localization for Visible Light Communication Systems, to appear in IEEE/OSA Journal of Lightwave Technology.
A. Sahin, Y. S. Eroglu, I. Guvenc, N. Pala, and M. Yuksel, Accuracy of AOA-Based and RSS-Based 3D Localization for Visible Light Communications, Proceedings of IEEE VTC, Boston, MA, September 2015.
Y. S. Eroglu, I. Guvenc, N. Pala, and M. Yuksel, AOA-Based Localization and Tracking in Multi-Element VLC Systems, Proceedings of IEEE Wireless and Microwave Technology Conference (WAMICON), Cocoa Beach, FL, April 2015.
VLCS 2015

24. Questions? Project website: https://sites.google.com/site/nsfvlc/
VLCS 2015