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Lighting and Full-Duplex
Communication using Optical
LED technology
Dr. Fernando
EE8114
Charles Lim
Nov. 24, 2003
The LED Advantage
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Consumes only one fourth or less power than
incandescent bulbs.
25,000 to 50,000 continuous hours of life
No RF EMI
Very secure compared to RF
Robust compared to other lighting devices
High data rate capability
Design Proposal
How to modulate the LED w/ Data?
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PLC (Power Line Communications)
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Use existing power outlets that act similarly to data ports and networks
throughout the house to transfer data from the computer to the LED
system
Picks up the
Currently only support low data rates (i.e. a few hundred kbps)
data
Easy to install and cheaper for already installed houses
Power outlet
BPF
Tx LEDs & IR Rx
AC/DC
CPU
Mobile
Terminal
PLC Modem
Power outlet
Demodulator
Rx LEDs & IR Tx
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Optical Fiber Communications
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Expensive to install for already built houses.
Capable of carrying tremendously high data rates
Almost unlimited bandwidth for the home user for both optical wireless
(LED) and optically connected (fiber) wired applications
Better option for pre-built houses where installation of fiber will be
easier.
Data used to
modulate the
power
Fiber connector
O-E converter
BPF
Tx LEDs & IR Rx
AC/DC
Power outlet
CPU
Mobile
Terminal
E-O converter
Fiber connector
Demodulator
Rx LEDs & IR Tx
Factors affecting LED systems
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Thermal Temperature
Packaging Type and System Integration
Multi-path Dispersion
Reflectivity of the Room
Downlink/Uplink Data rate
LED Power
Need for Channel Equalizer
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Thermal Management
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Packaging Type
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For LEDs to achieve long lifetimes in the range of 25,000 to 50,000 hours,
the temperature of the junction must be under 75°C.
Also, once the junction temperature reaches over 125°C, problems with
LEDs become a lot more common.
Current packages have 300°C.
If assume room temperature 25°C, then minimum package thermal
resistance is 50°C.
System Integration
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Unlike incandescent bulbs, LEDs do not radiate wasted heat away from
the part. It requires the device be properly cooled.
Design and installation of not only LEDs but the cooling system is critical
as well for LED systems.
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Multi-Path Dispersion
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Reflectivity of the room
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Main issue in optical wireless technology
Due to the large amount of lighting LEDs
Minimal interference from the white LEDs and IR LED due to spectral
separation
Photodiodes also has spectral separation to minimize interference
IR and LED Tx linewidth chosen such that minimal interference with
photodiodes.
Higher reflectivity means more dispersion
Depends on color and reflectivity of materials inside room
Downlink/Uplink data rate
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Receiver and LED system circuitry determined by the downlink bandwidth
Downlink easier to design, larger power from lighting LEDs
Uplink data rate cannot be very high due to limited IR power
Uplink bandwidth restriction determined by IR transmitter and receiver
design.
Higher data rates = Higher Cost
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LED Power
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Higher Power allows for faster data rates
Limitations in power output design due to government restrictions
Channel Equalizer
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To achieve better data rates and reliability a dynamic channel equalizer is
required.
Use LMS digital signal processing algorithm
LMS block is right after modulator and demodulator for both IR and light
LEDs
Dynamically adjust downlink/uplink bit rates depending on current room
BER
Increases reliability of system
Mobility is increased
Higher Efficiency
Signal Interferences
Simple RS232 LED Downlink System
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Part of the project is to demonstrate a simple LED
system and to prove it is feasible
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TX Circuit
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Consists of 10 super bright white LEDs driven by a 5V DC power supply
and modulated by a RS232 Line Driver IC connected to a computer serial
port.
RX Circuit
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Consists of 3 visible light photodiodes and a comparator which detects
optical signals and converts it to rs232 voltage levels
TX
White
LEDs
FREE
SPACE
Detecto
r
Circuit
RX
Conclusion
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This project achieves Lighting and communication
using Optical wireless communication.
Through more research and design, optical wireless
communications will eventually achieve:
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Reliable high data rate transfers
No RF interference
Mobility and security
Minimal multi-path distortion
Higher power efficiency, lower transmit and receive power
Integrating Lighting and communication for home
Conclusion……
Future of Wireless communication ……….
References
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[1] Bala Balasingam, Charles Lim, Gajendran Wignarajah, Jeyacanthan Nesarajah,
Sarmila Selvaratnam, “Lighting and Communication from the same source”, 2003
ICUE (International Conference for Upcoming Engineers)
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[2] Toshihiko Komine, Masao Nakagawa, “Integrated system of white LED visiblelight communication and power-line communication”, 2002 IEEE
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[3] Yuichi Tanaka, Shinichirou Haruyama, Masao Nakagawa, “Wireless Optical
Transmissions with white colored LED for Wireless Home Links” , 2000 IEEE
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[4] Tsunemasa Taguchi, Yamaguchi University, “Light Gets Solid”, OE Magazine, The
Monthly Publication of SPIE October 2003
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[5] Srinath Aanegola, Jim Petroski, Emil Radkov, GELcore LLC, “Let There Be
Light”, OE Magazine, The Monthly Publication of SPIE October 2003