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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Visible Light Wireless Communications
A. Chockalingam
Department of ECEIndian Institute of Science, Bangalore
Tutorial in SPCOM 2016IISc, Bangalore
12 June 2016
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Outline
1 Introduction
2 LEDs and photo diodes
3 VLC characteristics
4 MIMO, OFDM, QCM, DCM in VLC
5 VLC with lighting constraints
6 Outdoor VLC, VLC attocells
7 Concluding remarks
![Page 3: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/3.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Wireless spectrum
Source: Internet
![Page 4: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/4.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical wireless
� Optical wireless communication (OWC)
� promising complementary technology for RFcommunication (RFC) technology
� information conveyed via optical radiation in free space
� wavelengths of interest
� infrared to ultraviolet
� includes visible light wavelengths (380 to 780 nm)
Source: www.ieee802.org/15
� Visible light communication (VLC)
� communications using visible light spectrum
� abundant VLC spectrum (� 300 THz bandwidth)
� multi-gigabit rates over short distances
� LEDs as transmitters and photo diodes (PD) as receivers
![Page 5: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/5.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC: Pros and Cons
� Pros� low power, low cost devices (LEDs, PDs)� no spectrum cost� no RF radiation issues� inherent security in closed-room applications� simultaneous data transmission and lighting
� VLC technology rides along with e�cient white LEDlighting technology
� MIMO and OFDM techniques
� improve spectral e�ciency and performance
� Cons� channel itself!
� ambient light/interference from other light sources� alignment between Tx and Rx� scattering and multipath dispersion (ISI)
� no/low mobility
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC is not that new!
� 1879: `photophone' by Alexander G. Bell(Patented Dec. 14, 1880. Filing date: Sep. 25, 1880.Patent No. US235496 A. Title: Photophone-Transmitter)
� Analog voice transceiver
� Transmitter: a mirror controls the amount of lightre ected from a source
� Receiver: a photocell connected to a speaker
Source: Wikipedia
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
OWC and VLC in recent days
� 1980� infrared remote controls (analog)
� 1993� infrared data transfer in mobiles, laptops, etc.� standards body: IrDA (9.6-128 Kbps).
� IEEE 802.15c� low power, high data rate systems in satellites, portabledevices, etc.
� VLCC: Visible Light Communication Consortium
� VLC for home networks� hOME Gigabit Access (OMEGA) project
� IEEE 802.15.7� VLC PHY, up to 96 Mbps
� LiFi and attocells
![Page 8: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/8.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC implementations/applications
Source: www.ieee802.org/15
![Page 9: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/9.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC implementations/applications
G. P. Nava, H. D. Nguyen, Y. Kamamoto, T. G. Sato, Y. Shiraki, N. Harada, and T. Moriya, \A high-speedcamera-based approach to massive sound sensing with optical wireless acoustic sensors," IEEE Trans. on
Computational Imaging, vol. 1, no. 2, pp. 126-136, Jun. 2015.
![Page 10: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/10.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC implementations/applications
G. P. Nava, H. D. Nguyen, Y. Kamamoto, T. G. Sato, Y. Shiraki, N. Harada, and T. Moriya, \A high-speedcamera-based approach to massive sound sensing with optical wireless acoustic sensors," IEEE Trans. on
Computational Imaging, vol. 1, no. 2, pp. 126-136, Jun. 2015.
![Page 11: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/11.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC implementations/applications
G. P. Nava, H. D. Nguyen, Y. Kamamoto, T. G. Sato, Y. Shiraki, N. Harada, and T. Moriya, \A high-speedcamera-based approach to massive sound sensing with optical wireless acoustic sensors," IEEE Trans. on
Computational Imaging, vol. 1, no. 2, pp. 126-136, Jun. 2015.
![Page 12: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/12.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs and photo diodes
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 14: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/14.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs
� Lumen: SI unit of luminous ux (luminous power)� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 15: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/15.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 16: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/16.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy
� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 17: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/17.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt
(6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 18: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/18.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 19: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/19.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 20: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/20.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 21: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/21.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 22: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/22.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 23: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/23.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 24: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/24.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 25: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/25.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 26: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/26.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 27: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/27.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 28: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/28.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W
� claimed to have been breached! 208 lm/W LED (prototype)
![Page 29: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/29.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� E�cient lighting using white LEDs� Lumen: SI unit of luminous ux (luminous power)
� measure of the quantity of visible light emitted by a source
� example LED specs: 5 lumens, 90 lumens, 160 lumens
� Lumens/Watt: unit of luminous e�cacy� Tungsten incandescent lamp: 15 lumens/watt (6 W for 90 lm)
� Halogen lamp: 20 lumens/watt (4.5 W for 90 lm)
� Mercury vapour lamp: 50 lumens/watt (1.8 W for 90 lm)
� Fluorescent lamp: 60 lumens/watt (1.5 W for 90 lm)
� LED lamp: 90 lumens/watt (1 W for 90 lm)
� High pressure sodium vapour lamp: 117 lumens/watt (0.77W for 90 lm)
� Low pressure sodium vapour lamp: 150 lumens/watt (0.6 W for 90 lm)
� Energy saving lamps have high luminous e�cacy
� Theoretical max. for white LED (with phosphorescence mixing): 250 lm/W
� Recent claims on white LEDs: 100 to 160 lm/W� examples commercial white LED spec: 90 lm/W, 120 lm/W
� Target for 2020: 200 lm/W� claimed to have been breached! 208 lm/W LED (prototype)
![Page 30: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/30.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Why LEDs?
� Lighting arrangement in Golden Jubilee Seminar Hall, ECE
50
340
34060
60
20
20
40
40
100
100
50STAGE
� O�-stage
� 32 bulbs (20 W bulbs previously; now replaced with 5 W LED bulbs)
� On-stage
� 6 bulbs (60 W bulbs previously; now replaced with 18 W LED bulbs)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Luminous intensity (LI):� Luminous power radiated by a point light source in a particular
direction per unit solid angle
� SI unit of LI: Candela (Lumens/Steradian); cd (lm/sr)
Image source: Wikipedia
� Solid angle (in steradians) of a cone with apex angle � (in
degrees) = 2�(1� cos ��
2), i.e., cd = lm/(2�(1� cos ��
2))
� Examples of white LED spec:� Luminous ux = 90 lm; luminous intensity = 59 cd
) � = 81:5� (viewing angle at 50% power; half-power angle)
� Luminous intensity = 59 cd; � = 55�
) Luminous ux = 41.8 lm� luminous intensity = 11200 mcd (11.2 cd); � = 45�
) Luminous ux = 5.35 lm
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Luminous intensity (LI):
� Two LEDs with same luminous ux of 0.2 lumens� Left LED's solid angle is 15�. =) LI = 3.7 cd� Right LED's solid angle is 30�. =) LI = 0.9 cd
� Left LED produces a smaller, brighter spot
(a) (b)Image source: Internet
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Illuminance:� measure of how much luminous power is incident on agiven area
� brightness: subjective impression of illuminance
� SI unit of illuminance: Lux (lx)
� Lux: Lumens per square meter (lm/m2)
� illuminance varies inversely with square of the distancefrom the source in free-space line of sight� Luminous ux (lumens) = Illuminance (lx) � 4�r 2
(r : distance from source in meters)
243 lumens (fc: foot-candles)light source
Image source: Internet
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Color temperature:� di�erent shades of white
� `yellowish white' (warm white): 2700� K
� `bluish white' (cool white): 6000� K
Image source: Internet
![Page 35: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/35.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Color rendering index (CRI):� a measure of a light source's ability to show object colors
`realistically' (or `naturally') compared to a familiar referencesource, either incandescent light or daylight
� Max. value is 100� Lower CRI values
) some colors may appear unnatural when illuminated by the
light source (LED) in question
� Example CRI values:
� 70-80 (cool LED); 80-90 (warm/neutral LED)
� Switching speed (rise/fall times):� typ. tens of nsec� switch LED for the following reasons:
� to meet illumination constraints (dimming)
- consider human eye's response characteristics
� to achieve data communication
- consider photo detector's response characteristics
� to achieve both dimming control and communication
simultaneously
![Page 36: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/36.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� White LED spectrum:
� Emitted wavelengths of a white LED include peaks in blue
(450-470 nm) and yellow (570-590 nm) regions (solid curve)
� Interpreted as white light by the human eye� Relative light sensitivity of human eye is shown (dotted curve)
Image source: Internet
� Half-power semi-angle, � 12:
Image source: Internet
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
Generalized Lambertian radiation pattern of LED
R(�) = n+12�
PS cosn(�) for � 2 [��
2; �2]
� n is the mode number of the radiating lobe given by
n =� ln(2)
ln cos� 12
; � 12is half-power semi-angle
� Mode number speci�es the directionality of the source� larger the mode number, higher is the directionality� n = 1 corresponds to a traditional Lambertian source
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Generalized Lambertian radiation pattern
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
30
210
60
240
90
270
120
300
150
330
180 0
Generalized Lambertian radiation pattern of LED
R(φ)=cosn(φ)
φ1/2
=10, n=45.28
φ1/2
=22.5, n=8.75
φ1/2
=45, n=2
φ1/2
=60, n=1
φ1/2
=85, n=0.28
![Page 39: Visible Light Wireless Communicationsachockal/pdf_files/SPCOM2016_AC...VLCC:Visible Light Communication Consortium VLC for home networks hOME Gigabit Access (OMEGA) project IEEE 802.15.7](https://reader033.vdocuments.mx/reader033/viewer/2022052010/6020d80602882e04bb16e9fd/html5/thumbnails/39.jpg)
Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
LEDs
� Flicker
� Fluctuation of the brightness of light (as perceived byhuman eye)
� LEDs are switched for the purposes of
1 communication (using intensity modulation, e.g., OOK/PAM)2 dimming control (e.g., PWM)
� Human eye won't perceive icker frequency > 200 Hz
� No perceived icker as long as the signaling rate is > 200Hz (i.e., one signaling interval < 5 ms)
� Communication signaling rates are often much higher than200 Hz
� So VLC using intensity modulation is not a major source of icker
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Photo diodes
� Photo diode� Semiconductor (e.g., Si, Ge) device that converts light into
current (may contain optical �lters, built-in lenses)
� Key speci�cations� Responsivity: Amperes/Watt
� ratio of the generated photo current to incident light power
� Response/rise time (tr ):
� determined by resistance and capacitance of the photo diode
and external circuitry (typ. tens of nsec)
� determines the bandwidth available for signal modulation (fbw )
and thus data transmission
� Modulation signal bandwidth:
� fbw = 0:35tr; e.g., tr = 50 ns ) fbw = 7 MHz
� Field of view (FOV): angle (e.g., 85�)
� only the rays coming within FOVcreate response
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC characteristics
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
RFC vs VLC
� RF communication
� Transmitter
� Tx RF chain (up converter, power ampli�er), Tx antenna
� Receiver
� Rx antenna, Rx RF chain (low noise ampli�er, downconverter)
� VLC
� Transmitter
� LED
� Tx data by intensity modulating (IM) the LED
� Receiver
� Photo detector� Rx data by direct detection (DD)
� LEDs/PDs with fast switching times
� rise and fall times typ. tens of nsec
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
IM/DD channel
� VLC Tx-Rx
Source
bits
Sink
bitsmodulationPD
Intensity DirectDetection
LED
IM/DDchannel
� IM/DD channel
� Modeled using Poisson processes to account for the quantumnature of light� channel output (i.e., the detected number of photons) is a
r. v. which has a Poisson distribution with parameter �
� � corresponds to the expected received intensity level
� Signal independent noise
� originates from background radiation from other light sources
(day/ambient light, uorescent lamps, etc.) and
� electronics in the receiver (thermal noise)
� Signal dependent noise
� high-brightness LEDs where the randomness in the signal itself
can not be neglected
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
IM/DD channel
� VLC Tx-Rx
Source
bits
Sink
bitsmodulationPD
Intensity DirectDetection
LED
IM/DDchannel
� IM/DD channel
� Modeled using Poisson processes to account for the quantumnature of light� channel output (i.e., the detected number of photons) is a
r. v. which has a Poisson distribution with parameter �
� � corresponds to the expected received intensity level
� Signal independent noise
� originates from background radiation from other light sources
(day/ambient light, uorescent lamps, etc.) and
� electronics in the receiver (thermal noise)
� Signal dependent noise
� high-brightness LEDs where the randomness in the signal itself
can not be neglected
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
IM/DD channel model
� Poisson channel (memoryless, discrete-time)� Derived from photon-counting (hence the Poisson nature)
� Input: r.v � � 0
� Output: discrete r.v X drawn from Poisson distribution with
parameter � + �0, i.e., X � P(� + �0)
� Non-negative term �0:
� a constant related to ambient light or thermal noise
� Conditional output probability of this channel is
p(x j�) = e�(�+�0)(�+ �0)
x
x!; x 2 N; � � 0
� Distribution of r.v. X � P(�) for large � approaches a
Gaussian distribution N (�; �)
A. Tsiatmas, F. M. J. Willems, and C. P. M. J. Baggen, \Square root approximation to the Poisson
channel," IEEE ISIT'2013.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC Tx-Rx
� VLC Tx-Rx
Source
bits
Sink
bitsmodulationPD
Intensity DirectDetection
LED
IM/DDchannel
� Baseband communication (no passband involved)
� Signaling: positive, real-valued tx. signals
D.C.O'Brien et al, \Visible light communications: challenges and possibilities", IEEE PIMRC'2008.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC channel
� CIR between source S and receiver R at time t is given by
h(t;S;R) =1Xk=0
h(k)(t;S;R)
h(k)(t): response of light undergoing exactly k re ections
LOS
Walls
Floor, ceiling
Others
J. Barry et al, \Simulation of multipath impulse response for indoor wireless optical channels," IEEE J. Sel.Areas in Commun., vol. 11, no. 3, pp. 367-379, Apr. 1993.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC channel
� hij : LOS channel gain between jth LED and ith PD is
hij =n + 1
2�cosn � cos �
A
R2rect
� �
FOV
�
Geometry of LED source and photo detector
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO in VLC
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO RFC and MIMO VLC
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO in VLC
� Multiple LEDs and PDs
� Nt : no. of LEDs at Tx; Nr : no. of PDs at Rx
Sourcebits
Sinkbits
Detection
+
AWGN
Encoding /modulation
Demodulation
H(t)
4� 4 MIMO VLC
� Advantages� high data rates (Nt symbols per channel use)� gives MIMO gains even under LOS conditions� induced power imbalance at Tx LEDs helps
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
A typical indoor VLC con�guration
(g) Typical indoor VLC con�guration (h) SNR as a function of receiver position
D.C.O'Brien et al, \Visible light communications: challenges and possibilities", IEEE PIMRC'2008.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO LED arrays
� 8� 8 MIMO VLC system
Source: Internet (Boston Univ.)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO LED arrays
� 48-LED array
Source: Internet
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC channel
� Nt LEDs (transmitter)
� Nr photo detectors (receiver)
� H denotes the Nr � Nt VLC MIMO channel matrix
H =
26664h11 h12 h13 � � � h1Nt
h21 h22 h23 � � � h2Nt
......
. . ....
...hNr1 hNr2 hNr3 � � � hNrNt
37775
MIMO channel between LEDs and PDs
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Example VLC channel matrices
� Channel matrix for dtx = 1m� Channel gain: High� Channel correlation: High
Hdtx=1m =
240:5600 0:5393 0:5196 0:53930:5393 0:5600 0:5393 0:51960:5196 0:5393 0:5600 0:53930:5393 0:5196 0:5393 0:5600
35�10�5
� Channel matrix for dtx = 4m� Channel gain: Low� Channel correlation: Low
Hdtx=4m =
240:9947 0:9337 0:8782 0:93370:9337 0:9947 0:9337 0:87820:8782 0:9337 0:9947 0:93370:9337 0:8782 0:9337 0:9947
35�10�6
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Modulation schemes for VLC
� Transmit signals in VLC must be
� positive real-valued for intensity modulation of LEDs
� Approaches
� OOK
� M-PAM with positive signal points
� M-QAM/M-PSK with Hermitian symmetry
� SSK and spatial modulation using multiple LEDs
� QCM, DCM (Quad-/Dual-LED complex modulation)
T. Fath and H. Haas, \Performance comparison of MIMO techniques for optical wireless communications in
indoor environments," IEEE Trans. Commun., vol. 61, no. 2, pp. 733-742, Feb. 2013.
S. P. Alaka, T. Lakshmi Narasimhan, and A. Chockalingam, \Generalized spatial modulation in indoor
wireless visible light communication," IEEE GLOBECOM'2015, San Diego, USA, Dec. 2015.
R. Tejaswi, T. Lakshmi Narasimhan, A. Chockalingam, \Quad-LED complex modulation (QCM) for
visible light wireless communications" IEEE WCNC'16 Workshop on Opt. Wireless Commun., Apr. 2016.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO VLC schemes
� Spatial multiplexing (SMP)
� Nt LEDs and Nr PDs
� At any given time, all LEDs are ON
� �smp = Nt log2M bpcu
� Spatial modulation (SM)
� At any given time, any one LED is ON
� Other Nt � 1 LEDs are OFF
� �sm = blog2 Ntc+ log2M bpcu
� Space shift keying (SSK)
� Special case of SM
� Only index of active LED conveys information
� �ssk = blog2 Ntc bpcu
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO VLC schemes
� Generalized space shift keying (GSSK)
� Generalization of SSK
� Na � Nt active LEDs
� �gssk = blog2�Nt
Na
�c bpcu
� Generalized spatial modulation (GSM)
� Generalization of SM
� Na � Nt active LEDs
� �gsm = blog2�Nt
Na
�c+ Nablog2Mc bpcu
T. Fath and H. Haas, \Performance comparison of MIMO techniques for optical wireless communications in
indoor environments," IEEE Trans. Commun., vol. 61, no. 2, pp. 733-742, Feb. 2013.
S. P. Alaka, T. Lakshmi Narasimhan, and A. Chockalingam, \Generalized spatial modulation in indoor
wireless visible light communication," IEEE GLOBECOM'2015, San Diego, USA, Dec. 2015.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
MIMO VLC system model
� Each active LED emits an M-ary intensity modulationsymbol Im 2M� M: set of all possible intensity levels given by
Im =2Ipm
M + 1; m = 1; 2; � � � ;M; M = jMj
� x: Nt � 1 transmit signal vector; xi 2 fM [ 0g
� n: Nr � 1 noise vector at the receiver; ni � N (0; �2)
� n: Nr � 1 received signal vector at the receiver
y = aHx+ n
a: responsivity of the PD (amp/Watt)
� Average received SNR
=a2P2
r
�2; P2
r =1
Nr
NrXi=1
E[jhixj2]
hi : ith row of H
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM-MIMO in VLC
GSM
Encoder
1
2
3
4
. . . 0 0 1 0 1 1 1 0 1 0 1 1 0 1 1 0
1st LEDpair of activationbits pattern00 (1,2)01 (1,3)10 (2,4)11 (3,4)
2st Intensitypair of Levelsbits00 (I1, I1)01 (I1, I2)10 (I2, I1)11 (I2, I2)
GSM-MIMO transmitter for VLC system with Nt = 4;Na = 2;M = 2
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM for VLC system
� Intensity levels are I1 =23 and I2 =
43
� We need only 4 activation patterns out of�Nt
Na
�=�42
�= 6 possible activation patterns
� So the GSM signal set for this example can be chosen asfollows:
SNaNt ;M
= S24;2 =
8>>><>>>:
26664
23
23
00
37775 ;26664
23
43
00
37775 ;26664
43
23
00
37775 ;26664
43
43
00
37775 ;26664
23
023
0
37775 ;26664
23
043
0
37775 ;26664
43
023
0
37775 ;26664
43
043
0
37775 ;
26664
0
23
023
37775 ;26664
0
23
043
37775 ;26664
0
43
023
37775 ;26664
0
43
043
37775 ;26664
00
23
23
37775 ;26664
00
23
43
37775 ;26664
00
43
23
37775 ;26664
00
43
43
37775
9>>>=>>>;
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Upper bound on BER
Maximum likelihood (ML) detection rule is
x = argmin
x2SNaNt ;M
� a�kHxk2 � 2yTHx
�
Pairwise error probability (PEP) is
PEPgsm = Q
�a
2�kH(x2 � x1)k
�
De�ne L , jSNa
Nt ;Mj. An upper bound on the BER for ML
detection can be obtained using union bound as
BERgsm �1
L
LXi=1
L�1Xj=1;i 6=j
PEP(xi ! xj jH)dH(xi ; xj)
�gsm
=1
L
LXi=1
L�1Xj=1;i 6=j
Q
�r
2�kH(xj � xi )k
�dH(xi ; xj)
�gsm
where dH(xi ; xj) is the Hamming distance between the bitmappings corresponding to the signal vectors xi and xj
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Indoor VLC - A typical geometric set-up
Figure : Geometric set-up of a typical indoor VLC system
(� denotes an LED and denotes a PD)
dtx
(a) Tx, Nt = 4
drx
(b) Rx, Nr = 4
dtx
(c) Tx, Nt = 16
Placement of LEDs and PDs
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
System parameters
Length (X ) 5mRoom Width (Y ) 5m
Height (Z ) 3.5m
Height from the oor 3mElevation �90�
Transmitter Azimuth 0�
�1=2 60�
Mode number, n 1dtx 0.6m
Height from the oor 0.8mElevation 90�
Receiver Azimuth 0�
Responsivity, a 0.75 Ampere/WattFOV 85�
drx 0.1m
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance
� LED placements in a 4� 4 square grid
� Di�erent GSM con�gurations for � = 8 bpcu, 5 bpcu
(d) GSM, 8 bpcu
Nt =4;Na=2;M=8
(e) GSM, 5 bpcu
Nt =6;Na=2;M=2
(f) GSM, 8 bpcu
Nt =7;Na=2;M=4
(g) GSM, 8 bpcu
Nt =7;Na=3;M=2
(h) GSM, 8 bpcu
Nt=12;Na=2;M=2
� indicates the presence of an LED. � indicates the absence of LED.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance
� Comparison of analytical upper bound and simulated BERs
15 20 25 30 35 40 45 5010
−6
10−5
10−4
10−3
10−2
10−1
100
Average SNR, dB
Bit
E
rro
r R
ate
Nt=7, M=4, η = 8 bpcu (sim.)
Nt=7, M=4, η = 8 bpcu (ana.)
Nt=6, M=2, η = 5 bpcu (sim.)
Nt=6, M=2, η = 5 bpcu (ana.)
GSM, η=5,8 bpcu, Na=2
Figure : GSM with Nt = 6; 7, Na = 2, M = 2; 4, �gsm = 5; 8 bpcu.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance
� Performance of di�erent GSM con�gurations for �xed� = 8 bpcu
20 25 30 35 40 45 50 55 60 65 70 75
10−4
10−3
10−2
10−1
100
Average SNR, dB
Bit
E
rro
r R
ate
Nt=7, N
a=2, M=4 (sim.)
Nt=7, N
a=2, M=4 (ana.)
Nt=7, N
a=3, M=2 (sim.)
Nt=7, N
a=3, M=2 (ana.)
Nt=12, N
a=2, M=2 (sim.)
Nt=12, N
a=2, M=2 (ana.)
Nt=4, N
a=2, M=8 (sim.)
Nt=4, N
a=2, M=8 (ana.)
GSM, 8 bpcu
Figure : Comparison of the BER performance of di�erent con�gurations of
GSM with �gsm = 8 bpcu, Nr = 4.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance
� Optimum placement of LEDs
� The minimum Euclidean distance between any two GSMsignal vectors x1 and x2 transmitted through H is given by
dH;min , minx1;x22S
NaNt ;M
kH(x2 � x1)k2
� Similarly, the average Euclidean distance between any twoGSM signal vectors x1 and x2 transmitted through H is
dH;avg =1
�jSNaNt ;M
j
2
�X
x1;x22SNaNt ;M
H(x2 � x1) 2
� Choose the placement of the LEDs at the transmitter suchthat dH;min and dH;avg are maximized over all possibleplacements
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance
System GSM con�guration dH;min dH;avg
1 Nt = 4;Na = 2;M = 8 4:623� 10�17 4:520� 10�11
2 Nt = 7;Na = 2;M = 4 1:977� 10�14 6:601� 10�11
3 Nt = 7;Na = 3;M = 2 1:541� 10�14 6:003� 10�11
4 Nt = 12;Na = 2;M = 2 1:346� 10�16 4:842� 10�11
Table : Values of dH;min and dH;avg for di�erent GSM con�gurations with
�gsm = 8 bpcu.
� Con�guration 2 has the largest dH;min, dH;avg and hencethe best BER performance
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM performance for varying dtx
� GSM performance as a function of dtx for di�erent SNRs
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 510
−7
10−6
10−5
10−4
10−3
10−2
10−1
100
101
dtx
in meter
Bit
E
rro
r R
ate
SNR = 40 dB (ana.)
SNR = 40 dB (sim.)
SNR = 60 dB (ana.)
SNR = 60 dB (sim.)
SNR = 75 dB (ana.)
SNR = 75 dB (sim.)
Nt=4, GSM, N
a=2, M=8, 8 bpcu
Figure : GSM with Nt = 4, Na = 2, M = 8, �gsm = 8 bpcu.
� Opposing e�ects of channel correlation and channel chainsfor increasing dtx results in optimum dtx
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM vs other MIMO techniques
� SMP, GSSK, SM, and GSM with � = 8 bpcu
� SMP:� Nt = 4, Na = 4, M = 4
� GSSK:� Nt = 13, Na = 3, M = 1
� SM:� Nt = 16, Na = 1, M = 16
� GSM:� Nt = 7, Na = 2, M = 4
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
GSM vs other MIMO techniques
� Comparison of the BER performance of SMP, GSSK, SM,and GSM for the same � = 8 bpcu, Nr = 4
10 20 30 40 50 60 70
10−4
10−3
10−2
10−1
100
Average SNR, dB
Bit
Err
or
Rat
e
Nt=13, GSSK, N
a=3, M=1 (sim.)
Nt=13, GSSK, N
a=3, M=1 (ana.)
Nt=7, GSM, N
a=2, M=4 (sim.)
Nt=7, GSM, N
a=2, M=4 (ana.)
Nt=16, SM, M=16 (ana.)
Nt=16, SM, M=16 (sim.)
Nt=4, SMP, M=4 (sim.)
Nt=4, SMP, M=4 (ana.)
8 bpcu
� For the same � = 8 bpcu, GSM performs better (by about 9 dB at
10�5 BER) compared to SMP, SSK, GSSK, SM
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
OFDM in VLC
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
OFDM in VLC
� OFDM� Popular in wired and wireless RF communications� Attractive in VLC as well
� OFDM in RF communications� OFDM signals are in the complex domain� Signals can be bipolar
� OFDM in VLC� VLC transmit signal must be real and positive� Use Hermitian symmetry on information symbols beforeIFFT to obtain real signals
� Perform bipolar or unipolar conversion� Achieves good performance (3 Gbps single-LED OFDMlink has been reported)
J. Armstrong, \OFDM for optical communications," J. Lightwave Tech., vol. 27, no. 3, pp. 89-204,
Feb. 2009.
H. Elgala, R. Mesleh, H. Haas, and B. Pricope, \OFDM visible light wireless communication based on
white LEDs," Proc. IEEE VTC 2007-Spring, pp. 2185-2189, Apr. 2007.
D. Tsonev et al, \A 3-Gb/s single-LED OFDM-based wireless VLC link using a gallium nitride �LED,"
IEEE Photonics Tech. Lett., vol. 26, no. 7, pp. 637-640, Jan. 2014.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
OFDM in VLC
data in
dataout
& S/P
modulation
P/S,
D/A
S/P
A/D,
N -point
IFFTBipolar to
unipolar
Unipolar
to
bipolar
N -point
FFT
P/S
VLC channel
[X0, X1, · · · , XN−1]T [x0, x1, · · · , xN−1]
T
x(t)
y(t)
[y0, y1, · · · , yN−1]T[Y0, Y1, · · · , YN−1]
T
Transmitter
Receiver
mapping
Hermitian
Demapping
symmetry
demodulation
& QAM
QAM
converter
converter
Figure : A general single-LED OFDM system model in VLC.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
OFDM in VLC
� Techniques to generate VLC compatible OFDM signals inthe positive real domain:
� DCO OFDM (DC-biased optical OFDM)
� ACO OFDM (Asymmetrically clipped optical OFDM)
� Flip OFDM
� NDC OFDM (Non-DC-biased OFDM)
� CI-NDC OFDM (Coded Index NDC OFDM)
O. Gonzlez et al, \OFDM over indoor wireless optical channel," Proc. IEE Optoelectronics, vol. 152,
no. 4, pp. 199-204, Aug. 2005.
J. Armstrong and B. J. Schmidt, \Comparison of asymmetrically clipped optical OFDM and DC-biased
optical OFDM in AWGN," IEEE Commun. Letters, vol. 12, no. 5, pp. 343-345, May 2008.
N. Fernando, Y. Hong, and E. Viterbo, \Flip-OFDM for unipolar communication systems,"
IEEE Trans. Commun., vol. 60, no. 12, pp. 3726-3733, Aug. 2012.
Y. Li, D. Tsonev, and H. Haas, \Non-DC-biased OFDM with optical spatial modulation," IEEE PIMRC
2013, pp. 486-490, Sep. 2013.
S. P. Alaka, T. Lakshmi Narasimhan, and A. Chockalingam, \Coded index modulation for non-DC-biased
OFDM in multiple LED visible light communication," IEEE VTC'2016-Spring, May 2016.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
DCO OFDM
data in QAM
modulation
N
2-1
symbols
mappingsymmetryHermitian
N -point
AddingDC biasandclippingat zero
QAM
demodulation FFTRemoveDC bias
Demappingdata out
D/AP/S,
A/D,
S/P
VLC channel
Transmitter
Receiver
LED
PD
[X1, X2, · · · , XN
2−1
]
0X1
X2
XN
2−1
0X∗
N
2−1
X∗
2
X∗
1
[Y0, Y1, Y2, · · · , YN−1]T
[Y1, Y2, · · · , YN
2−1
]
x(n)xdc(t)
y(t)
y(n)
QAM
IFFT
N -point
& P/S
& S/P
O. Gonzlez et al, \OFDM over indoor wireless optical channel," Proc. IEE Optoelectronics, vol. 152,
no. 4, pp. 199-204, Aug. 2005.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
DCO OFDM
� N2 � 1 QAM symbols are modulated per OFDM symbol
� The unipolar OFDM signal xdc(t) is given by
xdc(t) = x(t) + Bdc
where x(t) is the bipolar OFDM signal
� Bdc = kpEfx2(t)g; de�ne this as a bias of
10 log10(k2 + 1) dB
� The achieved rate in DCO OFDM is given by
�dco =N2 � 1
Nlog2M
�1
2log2M bpcu, for largeN
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
ACO OFDM
data in
N
4
symbols
mapping
symmetry
Hermitian
IFFTand
Clipat zero
FFTDemapping
data out
D/AP/S,
A/D,
S/P
VLC channel
Transmitter
Receiver
LED
PD
[X1, X2, · · · , XN
4]
[Y0, Y1, Y2, · · · , YN−1]T
[Y1, Y3, Y5, · · · , YN
2−1
]
transmitpositivepart
s(n)x(n)
s(t)
y(t)
y(n)
0X1
0
XN
4
0
X∗
N
4
X∗
2
X∗
1
X2
0
0
QAM
N -point
N -point
QAM
modulation
& S/P
QAM
demodulation
& P/S
J. Armstrong and B. J. Schmidt, \Comparison of asymmetrically clipped optical OFDM and DC-biased
optical OFDM in AWGN," IEEE Commun. Letters, vol. 12, no. 5, pp. 343-345, May 2008.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
ACO OFDM
� N4 QAM symbols are modulated per OFDM symbol
� Only odd subcarriers are used to send information
� All even subcarriers are set to zero
� The unipolar OFDM signal is obtained by clipping thenegative signals at zero
� The achieved data rate in ACO OFDM is given by
�aco =1
4log2M bpcu
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Flip OFDM
data in
N
2-1
symbols
mappingsymmetryHermitian
IFFT
QAM
demodulation
FFTDemapping
data out
VLC channel
Transmitter
Receiver
PD
[X1, X2, · · · , XN
2−1
]
[Y0, Y1, Y2, · · · , YN−1]T
[Y1, Y2, · · · , YN
2−1
]
x(n)
y(t)
Polarity
separator
P/S&
x+(n)
−x−(n)
One OFDM
symbol delay
OFDMsymbol
multiplexer
D/A
LED
0X1
X2
XN
2 −1
0X∗
N
2 −1
X∗
2
X∗
1
QAM
N -point
N -point
x(t)
QAM
modulation
& S/P
& P/SA/D
Delayy+(n)
y−(n
S/Py(n)
OFDM symbol
demultiplexer
N. Fernando, Y. Hong, and E. Viterbo, \Flip-OFDM for unipolar communication systems,"
IEEE Trans. Commun., vol. 60, no. 12, pp. 3726-3733, Aug. 2012.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
� N2 � 1 QAM symbols are modulated per OFDM symbol
� The unipolar OFDM signal is obtained by ipping thenegative signals
� Two OFDM time slots are used to send one OFDMsymbol
� Positive parts are sent on the �rst slot
� Flipped negative parts are sent on the second slot
� The achieved data rate in ip OFDM is given by
� ip =N2 � 1
2Nlog2M
�1
4log2M bpcu, for large N
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
DCO, ACO, ip OFDM performance
0 5 10 15 20 25 30
10−4
10−3
10−2
10−1
100
Eb/No, dB
Bit
Err
or R
ate
ACO OFDM, M=256
Flip OFDM, M=256
DCO OFDM, M=16
η=2 bpcu, Nt=1, N
r=1
Figure : Comparison of the BER performance of ACO OFDM, ip OFDM,
and DCO OFDM with 7dB bias for � = 2 bpcu, Nt = Nr = 1.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
DCO OFDM performance for varying DC bias
� Optimum DC bias
4 6 8 10 12 1410
−5
10−4
10−3
10−2
10−1
100
DC bias, dB
Bit
Err
or
Rate
SNR=10 dB
SNR=15 dB
SNR=20 dB
SNR=25 dB Nt=N
r=1, DCO, M=16, η=2 bpcu
Figure : BER performance of DCO OFDM as a function of DC bias with
� = 2 bpcu, M = 16, and Nt = Nr = 1, for SNR = 10, 15, 20, 25 dB.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
NDC OFDM
Databits
IFFT
x+(n)
−x−(n)
D/A
D/A
A/D
A/D
LED 1
LED 2
PD1
PD2
SM detectorFFT
H
[X0, X1, ·, XN−1]T
Data out
+ AWGN
y2(n)
y1(n)
x(n)
[Y0, Y1, ·, YN−1]T
x0 x1 x3
x2 xN−1
0 0
0 0 0
x+(n)
−x−(n)
1 OFDM symbol
N -point
N -point
Polarity
& S/P
QAM
mod. &S/P
QAM
demod. &P/S
Demapping
mapping
Hermitian
N
2− 1
QAM symbols
[Y1, Y2, ·, YN
2−1]
T
separator& P/S
y(n)
symmetry
� �ndc =N2�1
Nlog2M � 1
2 log2M bpcu, for large N
Y. Li, D. Tsonev, and H. Haas, \Non-DC-biased OFDM with optical spatial modulation," IEEE PIMRC
2013, pp. 486-490, Sep. 2013.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
NDC detector
� The detector output y(n); n = 0; 1; 2; � � � ;N � 1, is
jy(n)j = maxi=1;2
jzi (n)j
signfy(n)g =
8<:+ve; if arg max
i=1;2jzi (n)j = 1
�ve; if arg maxi=1;2
jzi (n)j = 2;
where "z1(n)
z2(n)
#=
"�hT1 h1
��1hT1 y�
hT2 h2��1hT2 y
#;
and hi is the ith column of channel matrix H; i = 1; 2.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Indexed-NDC OFDM
� I-NDC OFDM transmitterD/A
D/A
LED 1
LED 2
D/A
D/A
LED 3
LED 4
data in
x+(n)
−x−(n)
01011... 10101110001..
N ⌊log2Np⌋
(
N
2− 1
)
log2M
QAMmodulation,
S/P &Hermitian
mapping
N -point
IFFTP/S
[X0, X1, X2, · · · , XN−1]T
BLOCK 1
BLOCK 2
If b(n) = 0
If b(n) = 1
Polarity
separator
Polarity
separator
x(n)
index bits modulation bits
symmetry
−x−(n)
x+(n)
Uncoded Uncoded
Switch
Np : No. of pairs of LEDs, Np = 2
� I-NDC OFDM receiver
A/D
A/D
SM detector
FFT
Demapping,
demodulation & P/S
[Y0, Y1, Y2, ·, YN−1]T
Data out y3(n)
y4(n)
y(n)
PD3
PD4
A/D
A/D
y1(n)
y2(n)
PD1
PD2
& S/PN -point
b(n)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
INDC detector
� The detector output y(n); n = 0; 1; 2; � � � ;N � 1, is
jy(n)j = maxi=1;2;3;4
jzi (n)j
signfy(n)g =
8>>>>>><>>>>>>:
+ve; if arg maxi=1;2;3;4
jzi (n)j = 1
�ve; if arg maxi=1;2;3;4
jzi (n)j = 2
+ve; if arg maxi=1;2;3;4
jzi (n)j = 3
�ve; if arg maxi=1;2;3;4
jzi (n)j = 4;
where
2664
z1(n)
z2(n)z3(n)z4(n)
3775 =
266664
�hT1 h1
��1hT1 y
�hT2 h2
��1hT2 y�
hT3 h3��1
hT3 y�hT4 h4
��1hT4 y
377775;
and hi is the ith column of channel matrix H; i = 1; 2; 3; 4.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Performance of NDC OFDM, I-NDC OFDM
� Placement of LEDs
LED1 LED4
LED2LED3
dtx = 1m
� BLOCK 1: (LED1, LED2)
� BLOCK 2: (LED3, LED4)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
NDC OFDM and I-NDC OFDM performance
15 20 25 30 35 40 45 50 55 6010
−4
10−3
10−2
10−1
100
Eb/No, dB
Bit
Err
or
Rat
e
Nt=2, NDC, M=256, η=4 bpcu
Nt=4, I−NDC, M=64, η=4 bpcu
Nt=2, NDC, M=1024, η=5 bpcu
Nt=4, I−NDC, M=256, η=5 bpcu
Nr=4
Figure : BER performance of I-NDC OFDM and NDC OFDM for
� = 4; 5 bpcu, Nr = 4
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
NDC OFDM and I-NDC OFDM performance
15 20 25 30 35 40 45 50 55 6010
−4
10−3
10−2
10−1
100
Eb/No, dB
Bit
Err
or
Rat
e
N
t=4, I−NDC, M=64
Nt=4, I−NDC (modulation bits alone), M=64
Nt=4, I−NDC (index bits alone), M=64
Nt=4, I−NDC (error−free index bits), M=64
Nt=2, NDC, M=256
Nr=4, η=4 bpcu
Figure : Reliability of modulation bits and index bits in I-NDC OFDM for
� = 4 bpcu, Nr = 4
� Reliability of index bits is poor!
� Use coding for index bits
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Coded I-NDC OFDM
� CI-NDC OFDM transmitterD/A
D/A
LED 1
LED 2
D/A
D/A
LED 3
LED 4
data in
x+(n)
−x−(n)
01011... 10101110001..
rN ⌊log2Np⌋
(
N
2− 1
)
log2M
QAMmodulation,
S/P &Hermitian
mapping
N -point
IFFTP/S
[X0, X1, X2, · · · , XN−1]T
BLOCK 1
BLOCK 2
If b(n) = 0
If b(n) = 1
Polarity
separator
Polarity
separator
x(n)
Index bits Modulation bits
symmetry
−x−(n)
x+(n)
Rate-r LDPC/Walsh encoder
N⌊log2 Np⌋
Coded index bits
� CI-NDC OFDM receiver
A/D
A/D
SM detector
FFT
Demapping,
demodulation & P/S
[Y0, Y1, Y2, ·, YN−1]T
Data out
y3(n)
y4(n)
y(n)
PD3
PD4
A/D
A/D
y1(n)
y2(n)
PD1
PD2
& S/PN -point
Rate-r LDPC/Walsh decoderb(n)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
CI-NDC OFDM performance
34 36 38 40 42 44 4610
−5
10−4
10−3
10−2
10−1
100
Eb/No in dB
Cod
ed B
ER
N=64, Nr=4
LDPC in CI−NDC: kc=504, n
c=1008
Walsh in CI−NDC: kc=5, n
c=32
NDC, M=256, Nt=2,
η=3.88 bpcu
CI−NDC, M=64, Nt=4,
LDPC, η=3.89 bpcu
CI−NDC, M=128, Nt=4,
Walsh, η=3.55 bpcu
Figure : BER performance of CI-NDC OFDM and NDC OFDM at � = 3:8
bpcu, Nr = 4
� CI-NDC OFDM performs better than NDC OFDM
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Quad-LED & dual-LED complex modulation
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Quad-LED complex modulation (QCM)
� A complex modulation scheme for VLC
� Uses 4 LEDs (hence the name `quad')
� Does not need Hermitian symmetry
� QCM signaling
� LEDs are simultaneously intensity modulated by themagnitudes of the real and imaginary parts of a complexsymbol
� Sign information is conveyed through spatial indexing ofadditional LEDs
� QCM module can serve as a basic building block to bringin the bene�ts of complex modulation to VLC
R. Tejaswi, T. Lakshmi Narasimhan, A. Chockalingam, \Quad-LED complex modulation (QCM) for
visible light wireless communications" IEEE WCNC'16 Workshop on Optical Wireless Commun., Apr. 2016.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM for VLC
� Mapping of complex symbol s = sI + jsQ to LEDs activityin QCM
Real part Status of LEDs Imag. part Status of LEDssI sQ
� 0 LED1 emits jsI j � 0 LED3 emits jsQ jLED2 is OFF LED4 is OFF
< 0 LED1 is OFF < 0 LED3 is OFFLED2 emits jsI j LED4 emits jsQ j
� Example:� If s = �3 + j1, thenLED1: OFF; LED2: emits 3;LED3: emits 1; LED4: OFFCorresponding QCM tx. vector is x = [0 3 1 0]T
� Note:� Two LEDs (one among LED1 and LED2, and another oneamong LED3 and LED4) will be ON simultaneously.Other two LEDs will be OFF
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM for VLC
� QCM transmitter
Data in
log2|A| bits
QAM/PSK s = sI + jsQ
|sI |
|sQ|
Real part
Imaginary part
DACsI ≥ 0
sI < 0
mapper
sI
sQ
DAC
DACsQ ≥ 0
sQ < 0DAC
LED 1
LED 2
LED 3
LED 4
� QCM receiver
PD 1 ADC
QCM
detectors
QAM/PSK Data bits
PD 2 ADC
PD 3 ADC
PD 4 ADC
demapper
y1
y2
y3
y4
demapperand
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM performance
20 25 30 35 40 45 50
10−4
10−3
10−2
10−1
100
Eb/No in dB
Bit e
rro
r ra
te
Nr=N
t=4
QCM, BPSK
QCM, 4−QAM
QCM, 16−QAM
QCM, 64−QAM
� Crossover between performance of 4-QAM and 16-QAM� due to multiuser detection e�ect - strong interferer helps
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM performance
� E�ect of varying LED spacing (dtx)
0 1 2 3 4 510
−4
10−3
10−2
10−1
100
dtx
in meters
Bit e
rror
rate
4−QAM
16−QAM
QCM, Nt = N
r = 4, Eb/No = 35dB
� optimum LED spacing� due to opposing e�ects of weak channel gain and weakchannel correlation for increasing dtx
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM with phase rotation
� Rotation of complex modulation symbols� known to improve performance in RF wireless
� E�ect of phase rotation in QCM (QCM-PR) in VLC?
0 10 20 30 40 50 60 70 80 90
10−4
10−3
10−2
10−1
Rotation angle (θ) in degrees
Bit e
rror
rate
QCM−PR, 4−QAM, Eb/No=37dB
QCM−PR, 16−QAM, Eb/No=40dB
Nr=N
t=4, d
tx=1m
� Phase rotation helps. There is optimum rotation.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM vs QCM-PR
� Performance of QCM and QCM-PR (with optimumrotation) as a function of dtx
0 1 2 3 4 510
−7
10−6
10−5
10−4
10−3
10−2
10−1
100
dtx
in meters
Bit e
rro
r ra
te
QCM, 4−QAM
QCM, 16−QAM
QCM−PR, 4−QAM, θ = 45
QCM−PR, 16−QAM, θ = 43
Nt = N
r = 4, E
b/N
o = 35dB
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM-OFDM
� OFDM signaling along with QCM (QCM-OFDM)
� N complex symbols drive N-point IFFT
� IFFT output vector (OFDM symbol) drives QCMtransmitter block in N channel uses
� QCM-OFDM signal detection
� Zero-forcing (ZF), minimum distance (MD) detectors
� Performance of QCM-OFDM
20 25 30 35 40 45
10−4
10−3
10−2
10−1
100
Eb/No in dB
Bit
err
or
rate
4−QAM, dtx
=1m, Nt=4, Nr=4
QCM−OFDM, MD detector, N=8
QCM−OFDM, ZF detector, N=8
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
QCM, QCM-PR, QCM-OFDM
� Performance comparison between QCM, QCM-PR,QCM-OFDM
20 25 30 35 40 45
10−4
10−3
10−2
10−1
100
Eb/No in dB
Bit e
rro
r ra
te
4−QAM, dtx
=1m, Nt=4, Nr=4
QCM−OFDM, MD detector, N=8
QCM−PR, =45, ML detector
QCM, ML detector
θ
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Achievable rate contours in QCM� Spatial distribution of received SNR
� Achievable rate (in bpcu) for a given target BER (e.g., 10�5 BER)
� Percentage area of the room covered vs achieved rate
0 1 2 3 4 5
02
4
40
45
50
Length of room (m)
QCM, dtx
=2m, half power semiangle Φ1/2
=60
Width of room (m)
Aver
age
SNR
(dB)
Length of room (m)
Wid
th o
f roo
m (m
)
0 1 2 3 4 50
1
2
3
4
5
Achi
evab
le b
pcu
for a
BER
of 1
0−−5
0
1
2
3
4
5
1 2 3 4 5 60
20
40
60
80
100
bpcu
Perc
enta
ge (%
)
Percentage of the areaof room supporting the rate
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Dual-LED complex modulation (DCM)
� Exploit representation of complex symbols in polarcoordinates
� Adequate to convey only the magnitude and phase of acomplex symbol s = re j�, r 2 R+, � 2 [0; 2�)� only two LEDs su�ce� no sign information to convey
� The 2� 1 DCM tx. vector is x = [r �]T
� DCM transmitter:
Data in
log2|A| bits
QAM/PSK s = rejφ
r = |s|
φ=arg(s)
Magnitude
Angle
DAC
mapper
DAC
LED 1
LED 2
T. Lakshmi Narasimhan, R. Tejaswi, and A. Chockalingam, \Quad-LED and Dual-LED complex modulation
for visible light communications" arXiv:1510.08805v2 [cs.IT] 2 May 2016.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
DCM
� DCM signal detection
� The Nr � 1 received signal vector is
y = rHx+ n
� ML estimate of the transmit vector x is
xML = argminx2SD
ky � rHxk2
SD : DCM signal set (all possible tx. vectors x)
� xML is demapped to corresponding complex symbol sML
� sML is demapped to get corresponding information bits
� Remark on DCM with M-PSK:� Only phase carries information in M-PSK (constant r)
� `magnitude-LED' becomes redundant
� Can be viewed a single-LED scheme with M-PAM� Both LEDs matter when M-symbols undergo somepre-processing (e.g., IFFT in DCM-OFDM)
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Performance of QCM and DCM
20 25 30 35 40 45 50 55
10−4
10−3
10−2
10−1
100
Eb/No in dB
Bit e
rro
r ra
te
DCM, 8−QAM
DCM, 16−QAM
DCM, 64−QAM
QCM, 8−QAM
QCM, 16−QAM
QCM, 64−QAM
� For small sized QAM (8-QAM), DCM performs better than QCM
� For larger sized QAM (16-QAM, 64-QAM), QCM performs better
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Performance of QCM and DCM
Modulation alphabet DCM QCM QCM-PR
8-QAM 29.2 dB 39.8 dB 39.2 dB
16-QAM 41.8 dB 40.6 dB 38.6 dB
32-QAM 45.5 dB 41.8 dB 40 dB
64-QAM 48.2 dB 43.7 dB 40.2 dB
Table : Comparison of Eb=N0 required by DCM, QCM, and QCM-PRto achieve a BER of 10�3 for di�erent M-QAM alphabets.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Performance of QCM-OFDM and DCM-OFDM
5 10 15 20 25 30 35 40 45 50 55
10−4
10−3
10−2
10−1
100
Eb/No in dB
Bit e
rro
r ra
te
N=8, 4−QAM
DCM−OFDM, MD detector
DCM−OFDM, ZF detector
QCM−OFDM, MD detector
QCM−OFDM, ZF detector
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Achievable rate contours in DCM
0 1 2 3 4 5
02
4
35
40
45
50
Length of room (m)
DCM, dtx
=2m, half power semiangle Φ1/2
=60
Width of room (m)
Aver
age
SNR
(dB)
Length of room (m)
Wid
th o
f roo
m (m
)
0 1 2 3 4 50
1
2
3
4
5
Achi
evab
le b
pcu
for a
BER
of 1
0−−5
0
1
2
3
4
1 2 3 4 5 60
20
40
60
80
100
bpcu
Perc
enta
ge (%
)
Percentage of the areaof room supporting the rate
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC with lighting constraints
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC with dimming support
� Human eye perceives the average intensity (when intensitychanges faster than 200 Hz)
� Need dimming support in lighting applications
� dimming target (e.g., 75%, 50%, 25%)
� Two approaches
� time-domain (TD) approach
� adds compensation symbols of two levels (ON/OFF)within a max. ickering time period (MFTP) to matchdimming target
� Adv: easy to implement; Disadv: rate loss
� intensity-domain (ID) approach
� changes the intensity levels; also includes bias scaling(alters DC bias level), intensity distribution adaptation
� Adv: high rate; suited for multi-level modulation like PAM� an optimization problem formulation
- maximize rate w.r.t intensity level distribution
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC with dimming support
� Data modulation (e.g., using OFDM) with dimmingcontrol (e.g., using PWM)
Direct
current
PWM
Signal
Modulating
Signal
LED Photo-
Detector
(a)
0 0:5 1 1:5 2 2:5 3 3:5 4
0:2
0:4
0:6
0:8
1
1:2
1:4
On On On On
Off Off Off Off
Duty cycle = 0.6
Time
Amplitu
de
(b)
Z. Wang. W-D. Zhong, C. Yu, J. Chen, C. P. S. Francois, and W. Chen, Performance of dimming control
scheme in visible light communication system, Optics Express, vol. 20, no. 17, pp. 18861-18868 (2012).
T. D. C. Little and H. Elgala, Adaptation of OFDM under visible light communications and illumination
constraints, Asilomar Conf. Signals, Systems, and Computers, pp. 1739-1744, 2014.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC with dimming support
� Examples of dimming support� TD approach: (b) intra-pulse insertion; (c) inter-pulse padding (IEEE
802.15.7 OOK mode uses this)
� ID approach: (d) bias-scaling; (e) distribution adaptation
S. H. Lee, S-Y. Jung, and J. K. Kwon, Modulation and coding for dimmable visible light communication,
IEEE Commun. Mag., pp. 136-142, Feb. 2015.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
VLC with dimming support
� PPM to support dimming control
� other PPM variants (MPPM, OPPM, VPPM)
S. Arnon, Ed., Visible light communication, Cambridge Univ. Press, 2015.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Outdoor VLC, VLC attocells
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Outdoor VLC
� Vehicular communication (intelligent transportation systems)
� a challenging and challenging outdoor VLC application
� vehicle-to-vehicle (V2V), infrastructure-to-vehicle (I2V),vehicle-to-infrastructure (V2I)
� Outdoor VLC elements: tra�c lights, street lights,head/tail lights, etc.
� Motivation: road-safety; reduce road accidents
� Typical requirements� Indoor applications:
� High data rates (Mbps-Gbps)� Short range (1-2 m)
� Vehicle (outdoor) applications:� Relatively low data rates (Kbps)� Longer range (80-100 m)� Robustness to numerous sources of parasitic light
(vehicular VLC channel is extremely noisy)
A-M. Cailean, B. Cagneau, L. Chassagne, V. Popa, and M. Dimian, \A survey on the usage of DSRCand VLC in communication-based vehicle safety applications," Proc. IEEE Symp. on Commun. and
Veh. Tech. (SCVT), pp. 69-74, Nov. 2014.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Outdoor VLC
� IEEE 802.11p (DSRC: Dedicated Short Range Communication)
� standard for RF wireless access in vehicular environments� based on IEEE 802.11a� 75 MHz allotted in 5.9 GHz� rates: 3-27 Mbps; MAC: CSMA/CA; range: up to 1 Km
� Issues in DSRC� high tra�c densities (numerous packet collisions, delay)
� Vehicular VLC can play a complementary role to DSRC
� IEEE 802.15.7 VLC standard - PHY I� intended for outdoor, long-range, low data rateapplications such as I2V and V2V communication
� VLC is still an early stage technology for usage in ITS
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical attocells
� Spatial reuse� an e�cient approach to improve spectral e�ciency
� Multiple light �xtures (luminaires) installed in largeindoor environments (e.g., o�ces, airports, hospitals)� provide an opportunity to set up VLC systems withdense spatial reuse
� Optical attocell network� use each luminaire as a small base station (BS) oraccess point (AP)
� smaller cell sizes compared to RF femtocells
� uplink connection to achieve full-duplexing
� handovers to allow users to roam within the roomor an entire building
� co-channel interference (CCI) is a key issue
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical attocells
� An example optical attocell network� Room size: 24m� 23m� 3m� No. of cells: 27; Cell radius: 3.3 m
Source: Ref. [1]
[1] C. Chen, S. Videv, D. Tsonev, and H. Hass, Fractional frequency reuse in DCO-OFDM-based optical
attocell networks, Jl. of Lightwave Tech., vol. 33, no. 19, pp. 3989-4000, Oct. 2015.
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical attocells
� Channel response at di�erent receiver locations
(c) (d) Source: Ref. [1]
� Receivers near walls have more variation (3 dB) than receivers far o�from walls (1.5 dB)
� This is because of the strong 1st order re ections by walls
� Adaptive bit loading in OFDM can compensate for this variation
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical attocells
� CCI mitigation in optical attocell networks� resource partitioning� use of di�erent wavelengths in adjacent cells� interference coordination based on busy-burst signaling� fractional frequency reuse
� o�ers good balance between average spectral e�ciency,cell edge performance, system complexity
� Fractional frequency reuse (FFR)� strict FFR
� one common sub-band (for cell center users)� multiple protected sub-bands (for cell edge users)
� soft frequency reuse (SFR)
� di�erent sub-band for cell edge users in each adjacent cell� allows center users to take edge users' sub-bands in
adjacent cells
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Optical attocells
� FR pattern in two-layer optical attocell network model� pattern in edge regions: reuse factor 3
Source: Ref. [1]
� Shown to be a good model to use to estimate interference
statistics and user performance in attocells
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Concluding remarks
� Visible light wireless communication� an emerging and promising complementary technologyto RF communication technology
� Several hard-to-resist advantages� with matching challenges
� A fast growing area with great potential
� MIMO and OFDM techniques for VLC are promising
� QCM and DCM: simple and novel signaling for VLC
� Open areas for research and innovation� New VLC signaling schemes
� Outdoor VLC issues (robustness, range, rate)
� VLC networking issues (MAC, coverage, mobility,handovers in attocells)
� Bright future for VLC!
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Introduction
LEDs andphoto diodes
VLCcharacteristics
MIMO,OFDM, QCM,DCM in VLC
VLC withlightingconstraints
Outdoor VLC,VLC attocells
Concludingremarks
Thank you