Low-Complexity Visible Light Networking withLED-to-LED Communication
Domenico Giustiniano, Nils Ole Tippenhauer, Stefan Mangold
Wireless Days IFIP Conference, Dublin, November 2012.
Introduction
Visible Light Communication (VLC)
VLC is an emerging technology,I it uses the visible light spectrumI light emitters (LEDs) transport information wirelessly
VLC is a low-power, low-cost alternative to traditional short-rangewireless RF communications
Image: Bytelight
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 2 / 23
Motivation
LED-to-LED communication
Most of the research on VLC has focused on wideband white LEDsused in ambient illumination.
I Wideband: 400 nm
Narrowband and visible LEDs have received little attention.I Narrowband: 15− 150 nm
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 3 / 23
Motivation
Application: Toy-to-Toy Communication
(a) Police car approach-ing....
(b) Car detecting themessage and reacting!
1) Light is safe. 2) We can control the communication through thedirectivity and the visual field of light propagation → this makes itinteractive (in contrast to infrared or RF).
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 4 / 23
Summary
Summary of the Rest of the Talk
We investigate the limit of communication using a single LED andmicrocontroller (Arduino) for applications that require low PHY rate.
We introduce an efficient MAC protocol to access the channelI CSMA/CA is here inefficient.
We study and resolve the problem of light flicker.I Previous work does not consider that the light flicker when
1 LEDs operates in ad-hoc network and2 the LED is also a receiver
We implement and evaluate the solution in a network of up to fourtransceivers communicating on the same visible color.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 5 / 23
Transceiver
Principles
The brightness of LEDs can be adapted rapidly,I at speeds orders of magnitude higher than for conventional light
emitting devices.
By varying the intensity of the LED light source,I data messages can be communicated through visible light to a receiver
sensitive to light.F In our approach, the receiver is the same LED used for transmission.F Only one microcontroller and one LED.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 6 / 23
Transceiver
Transmission
Station transmits the bits using the binary OOK modulation:
bit = 0→ symbol = ZERO
bit = 1→ symbol = ONE
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 7 / 23
Transceiver
Reception
ZERO ONE
Vth
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 8 / 23
Transceiver
Reception
Vca(T ) > Vth → symbol = ZERO
Vca(T ) < Vth → symbol = ONE.
ZERO ONE
Vth
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 8 / 23
Flicker Elimination
Flicker transmitting data
11 00001 1 0 11 100 110
No Data sent → Inter-data �i ker
Data sent → Intra-data �i ker
Single light channel to transmit and receive data → flicker effects.
Intra- and inter-data flickers
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 9 / 23
Flicker Elimination
Frequency of Intensity Modulation
Visualemotion/feedback
Flickeringregion VLC Data
FrequencyLig
ht I
nten
sity
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 10 / 23
Flicker Elimination
Data and Energy symbols
Data symbolsI Transmitter:
F carry information (bit) from the transmitter to the intended receiver.
I Receiver:F either receive any data from stations in rangeF or listen the channel before transmitting any data.
I Only one station is allowed to output energy in each Data Symbol.
Energy symbolsI No data is transmitted.I Any station is free to output energy to the optical medium.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 11 / 23
Flicker Elimination
Flicker Elimination Scheme
D EE D
Time
symbol time T
(c) Data and Energy symbols.
Time
ZERO ONEZEROONE
(d) Reception.
Time
ONE ONEZERO ZERO
(e) Transmitter, bit ’10’.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 12 / 23
Flicker Elimination
Frequency analysis
0 200 400 600−60
−50
−40
−30
−20
−10
0
Frequency [Hz]
Out
putV
olta
ge[V
(dB
)]
0 200 400 600−60
−50
−40
−30
−20
−10
0
Frequency [Hz]
Out
putV
olta
ge[V
(dB
)]
Flickerregion
Observed average
Flickerregion
Observed average
CFF=Critical flicker frequency=166 Hz
T < 14CFF = 1.5 ms
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 13 / 23
Flicker Elimination
LED noise
B5 Y5 G5 R5 B3 Y3 G3 R30
10
20
T ZERO[m
s]
B5 Y5 G5 R5 B3 Y3 G3 R30
2.5
5
T ZERO[m
s] With Ambient Noise
DarknessFlicker Region
Flicker Region
No Flicker Region
No Flicker Region1/(4CFF)
1/(4CFF)
Using blue and red LEDs, we can transmit with symbol durationbelow T = 1.5 ms, without being affected by flicker and LED noise.
We use T = 512µs unless otherwise stated.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 14 / 23
Collision Detection Protocol
Transmission and Reception with One LED
Charging: Reception:
Symbol ZEROSymbol ONE
Long time wasted in collisions due to low PHY rate →Key idea: sense the channel transmitting a ZERO symbol
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 15 / 23
Collision Detection Protocol
CSMA/CD MAC access protocol
RBT new RBT
Sta
tion
AS
tatio
n B
new RBTRBT
Message a1 Message a1
Message b1 Message b1
RBTcont'd
ACK
t
Detection is possible at the transmitter using Data Symbols ZERO, wherelight can be sensed.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 16 / 23
Collision Detection Protocol
Data packet
12 bit 8 bit 8 bit 24 bit 0−1280 bit 16 bit
Sync SFD Length MHR Data CRC
Software-based synchronization protocol.
State machine for MAC protocol.
All implemented in Arduino.I hex file of about 11 kB over the 30 kB available.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 17 / 23
Collision Detection Protocol
Two Contending LEDs
ACK Data
Data
Data
ACK ACK
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 18 / 23
Collision Detection Protocol
Three Contending LEDs
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 19 / 23
Collision Detection Protocol
Full flickering elimination
Data
Data
DataACK
ACK ACK
Data
ACK
Rx Rx
RxRx
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 20 / 23
Collision Detection Protocol
MAC Throughput
1 2 3 4
600
700
800
900
Throughput[b/s]
Number of Stations
CSMA/CA,40 byteCSMA/CD,40 byteCSMA/CA,160 byteCSMA/CD,160 byte
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 21 / 23
Collision Detection Protocol
CSMA/CD MAC Throughput
From renewal theory, the maximum system throughput Smax is:
Smax =E [P]
E [Tm]=
160
352 · T = 0.45/T (1)
For T = 512µs, Smax = 878 b/s, very close to our experiments.
We obtain a Jain’s fairness index of 0.98− 1, that indicates that bothour protocol and prototype implementation are fair.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 22 / 23
Conclusion
Conclusion
Short-range free-space LED-to-LED communication enables a widevariety of entertainment applications.
These applications benefits from:I the explicit visual feedback to the user when pointing a device,I the system simplicity and the low-cost nature of the LED-based
systems.
We proposed and evaluated an LED-to-LED communication system,I including physical layer transmission and networking protocols.
Our evaluation addressed technical challenges,I such as the elimination of flicker and detection of collisions.
D. Giustiniano, N. Tippenhauer, S. Mangold (Wireless Days IFIP Conference, Dublin, November 2012.)Visible Light Networking with LED-to-LED 23 / 23
Top Related