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Visible light communications: Challenges and possibilities

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Solid-state lighting is a rapidly developing field. White-light and other visible LEDs are becoming more efficient, have high reliability and can be incorporated into many lighting applications. Recent examples include car head-lights based on white LEDs, and LED illumination as an architectural feature. The prediction that general illumination will use white LEDs in the future has been made, due to the increased energy efficiency that such an approach may have. Such sources can also be modulated at high-speed, offering the possibility of using sources for simultaneous illumination and data communications. Such visible light communications (VLC) was pioneered in Japan, and there is now growing interest worldwide, including within bodies such as the Visible Light Communications Consortium (VLCC) and the Wireless World Research Forum (WWRF). In this paper we outline the basic components in these systems, review the state of the art and discuss some of the challenges and possibilities for this new wireless transmission technique.
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Abstract Solid-state lighting is a rapidly developing field.
White-light and other visible LEDs are becoming more efficient,
have high reliability and can be incorporated into many lighting
applications. Recent examples include car head-lights based on
white LEDs, and LED illumination as an architectural feature.
The prediction that general illumination will use white LEDs in
the future has been made, due to the increased energy efficiency
that such an approach may have. Such sources can also be
modulated at high-speed, offering the possibility of using
sources for simultaneous illumination and data communications .
Such Visible Light Communications (VLC) was pioneered in
Japan, and there is now growing interest worldwide, including
within bodies such as the Visible Light Communications
Consortium (VLCC) and the Wireless World Research Forum
(WWRF).
In this paper we outline the basic components in these
systems, review the state of the art and discuss some of the
challenges and possibilities for this new wireless transmission
technique.
Index Terms—visible light communications, optical
communications, wireless communications
I. INTROD UCTION
urrently there is rapid development in the field of
lighting and illumination. Concerns about energy
consumption are leading to the phasing out of incandescent
sources, and there is rapid growth in the use, and
development of, solid-state sources. As the efficiency of these
devices increases and their cost decreases there are
predictions that they will become the dominant source for
general illumination. At present they are widely used in
automotive applications for indicator and tail lights, and the
first LED based headlights are now becoming available. They
are also commonly used in ‘feature’ and architectural lighting
where the ability to change colour, or incorporate lights into
building structure, without reliability concerns, makes them
preferable to alternatives.
The use of solid-state sources offers the possibility of high
data-rate communication, in addition to provision of
illumination. Sources can be modulated at high-speed,
providing a data channel in addition to the illumination,
which is provided by the average signal level. Research on
such Visible Light Communications (VLC) originated in
Japan, where the Visible Light Communications Consortium
(VLCC) [1] has been in existence for several years. Interest is
now growing rapidly, both in Asia and Europe, where the
Wireless World Research Forum [2] has worked in this area.
This paper introduces the principles of VLC, and outlines
some of its major challenges. Some potential solutions and
future applications are also described.
In the next section an overview of VLC and its applications is
presented.
II. OVERVIEW
VLC has potential applications in a number of areas. Each
of these is briefly described in the following sections, together
with the motivation for using this means of communication.
A. Visual Signalling and communication
Coloured signal lights are widely used in marine,
automotive and other applications. In this case the colour
provides a signal to the observer, such as ‘red for danger’,
and augmenting this with data communications might
improve safety and other aspects of traffic management. Due
to their reliability, LEDs are widely used in these
applications, and there have been several demonstrations of
data transmission by modulation of these sources. In [3] data
is transmitted from a traffic signal to a car, and in [4] a
scheme for parallel communication is pr esen ted. An EU
research project [5] examined car-to-car communication
using white-light headlights.
B. Information display and communications
Displays, such as signboards and indicator boards, are
often fabricated from arrays of LEDs, and these can be
modulated to broadcast the signboard information to a PDA
or handheld terminal. In [6] an example of a signboard used
to transmit data is described. This might find application in
air ports, m useums an d other en vironments where location-
dependent broadcast of data is requir ed. Such location
Visible Light Communications: challenges and
possibilities
Dominic C. O'Brien1, Lubin Zeng1, Hoa Le-Minh1, Grahame Faulkner1, Joachim W. Walewski,2
Seba stian Randel,2
1University of Oxford (UK); 2 Siemens AG, Corporate Technology, Information and Communications,
Munich (Germany)
C
978-1-4244-2644-7/08/$25.00 © 2008 IEEE
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dependence and indoor positioning is an area of interest,
particularly within the VLCC. In this case a locally generated
signal can be transmitted to a terminal, thus determining its
location by its proximity to a particular lighting fixture.
C. Communications
Point-to-point links between handheld terminals rely on
there being ‘sufficient’ alignment between the two ends of th e
link. Using visible light allows the user to be involved in this,
allowing smaller beam divergence, and therefore lower path-
loss. Communication between two peripherals is described in
[7], and it may be possible to create very high bandwidth
links for secure media downloading using similar techniques.
D. Illumination and communications
White LEDs can be used for both illumination and
communications, so that information can be broadcast within
a room [8, 9], or transmitted via a car headlight [5], with the
necessary illumination provided at the same time. Several
exampl es of music broadcast demonstrators [7] have also
been reported. This may be a wide area of application, and
there is considerable interest in building systems that do this
[10].
E. Positioning and communications
Obtaining the position of a mobile user indoors is
challenging, and VLC allows the transmission of positioning
information from a lighting fixture, so that a user knows their
location in a building. There have been a number of schemes
proposed [11-13] that use eith er triangulation or proximity to
a beacon, or a combination to provide position estimation.
It can be seen that ther e ar e a number of different types of
VLC link, but in most cases the communications is a
secondary function. This makes it distinct from most other
wireless standards, as VLC must be compatible with any
standards for the primary function. This introduces a number
of constraints, and also the necessity for co-development of
standards with the primary body.
In the next section applications using white LEDs for
illumination and communication are described in more detail
III. VLC LINKS
A VLC link consists of a transmitter, the propagation channel
and a receiver . Each of these is descr ibed in the following
sections.
1) Sources
White-light LEDs either use red, green and blue LEDs that
mix to provide the desired colour, or a single LED (usually
blue) that excites a yellow phosphor to create an overall white
emission. The ‘triplet’ approach allows the colour to be
altered by varying the colour to the LEDs, and also allows
different dat a to be sent on each device. However,
maintaining colour balance can be challenging and the
devices are complex. Th e sin gle LED approach is simpl er,
and is therefore more attractive for ‘general’ applications, so
will be considered in the work described here.
Figure 1 shows the emission spectrum of a high-brightness
LED (LUXEON STAR[14]), showing the peak from the LED
(at 440nm) and the broad phosphor spectrum at wavelengths
beyond this. The small-signal frequency response is shown in
Figure 2, both for the blue component from the LED and for
the overall white emission. It can be seen that the bandwidth
is ~2MHz for the white, and ~10MHz for the blue component
only. This is due to the long decay time of the phosphor, and
provides a limitation on the overall bandwidth available. In
addition the Blue LED die is not designed for high speed
operation and is very large in area (and thus has high
equivalen t capacitance) compared with devices used for high
speed communications. Although these measuremen ts are for
one specific device they are typica l of th ose obtained for
white-LEDs from different manufacturers. The limited
bandwidth of the LEDs is therefore one of the major
challen ges for high-speed communications using these
devices. Overcoming this is discussed in later sections.
Figure 1. Emission spectrum from white-light LED
(LUXEON STAR)
Figure 2. Small-signal modulation bandwidth of LUXEON
STAR device
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2) The VLC channel
Figure 3 shows a typical office space with four LED
lighting units on the ceiling. A communication terminal
might be placed on a desk anywhere within the room, and a
channel exists between the lights and the terminal. The
channel consists of a number of line of sight paths from the
units to the terminal, together with a diffuse channel formed
by the light from the source reflecting off multiple surfaces
within the room. These two channels can be modelled
separately and combined to obtain the overall power received
at the terminal (and hence the Signal to Noise Ratio (SNR))
and the bandwidth of the channel.
Figure 3. Typical VLC indoor lighting configuration
Parameter Value Parameter Value
LED
power(optical) 20mW
Total power used
for optical
communications
115.2W
Lambertian
order 1 Receiver Area 1cm2
No. of LEDs
in 1 lighting unit
60x60
at 1-cm
pitch
Input-referred
noise current of
receiver
100pA/
Hz
No. of
lighting units
2x2,
2.5m apart
(centre to
centre)
Detector
responsivity
(averaged over
typical spectrum of
Luxeon star LED)
0.4A/W
Room
dimension
5x5x3m
Receiver
plane
0.85 m
above
ground
Position of
receiver
2.5 m,
2.5 m from
centre
Reflectivities 0.54 All
sur faces
Table 1. Simulation parameters
Several models of the optical wireless channel have been
developed [9, 15]; in [15] the LOS and diffuse channels are
combined to obtain the overall channel. Figure 4 shows the
calculated signal to noise ratio at the receiver, using the
parameters shown in Table 1.
Figure 4. Signal to noise ratio as a function of receiver
position
This, and other work [9, 16], shows that very high SNR
channels are available. The requirement for levels of
illumination suitable for reading and occupancy ensures that
sufficient communication power will be available.
The bandwidth of the channel can be determined by the
summation of the LOS and diffuse components, and there are
various meth ods of simulating this [15]. Work in [9] suggests
that bandwidths of at least 88MHz were available in ‘typical’
room environments. The bandwidth of the channel is
therefore significantly higher than the sources, and does thus
not currently constrain system performance.
3) Receiver
The receiver consists of an optical element to collect and
concentr ate the ra dia tion ont o the receiver photodetector.
This converts the radiation into photocurrent, which is then
pre- and post-amplified before data recovery.
The optical element, usually either a lens or nonimaging
concentrator has a maximum ‘gain’ limited by constant-
radiance considerations, so the photodetector area should be
as large as possible, given the required receiver bandwidth.
As discussed above, if the LED modulation bandwidth is
less than approximately 90MHz then the LED bandwidth
constrains the system data rate. Achieving sufficient
photodetector area at the LED constrained system bandwidth
is relatively straightforward, so the receiver does not provide
a significant constraint.
IV. CHALLENGES
A. Increasing data rate
Perhaps the simplest way of mitigating the low bandwidth
of the transmitter is to block the phosphor component at the
receiver by using a blue filter. In [16] it is shown that this can
increase the bandwidth substantially, albeit at the penalty of a
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small reduction in received power due to filter losses.
It is also possible to improve the response by tr ansmitter
and/or receiver equalization, or the use of bandwidth-efficient
modulation schemes that take advantage of the high available
signal to noise ratio. In addition, for higher data rates it may
be possible to use parallel data transmission from a number of
LEDs. Each of these techniques is discussed in more detail
below.
1) Transmitter equalization
Analogue equalization techniques can be used to
compensate for the rapid fall-off in response of the white
LEDs at high frequencies. It is possible to use an array of
LEDs, each driven using a resonant technique with a
particular peak output frequency to achieve this. Careful
choice of a number of different frequencies allows the overall
response to be ‘tuned’ to that desired. In [17] a 16 LED array
is modified to have a bandwidth of 25MHz (without blue
filtering) offering a data-rate of 40Mb/s for Non-Return to
Zero (NRZ) On-Off Keying (OOK). More complex
equalization can also be used for single devices, and data
rates of 80Mb/s (NRZ OOK) [18] have been demonstrated.
2) Receiver equalization
Transmitter equalization has the disadvantage that the
drive circuits for the LED (which often involve currents of
several hundred milliamps) need modification, and in a
typical coverage area ther e may be a number of sour ces,
makin g the modifications potentially costly. In addition some
of the signal energy used is not converted into light, thus
reducing the energy efficiency of the emitter.
Equalisation at the receiver allows complexity to be at the
receiver only. A simple first-order analogue equalizer is
modeled in [15], and this shows there is substantial
improvement in data-rates. More complex approaches are
likely to yield higher data rates.
3) Complex modulation
A high-SNR, low-bandwidth channel is typically suited to
high bandwidth efficiency multilevel modulation schemes.
Work in [16] shows that 100Mbit/s is possible using Discrete
Multi-Tone Modulation (DMT). At present there is little work
in this area, and further studies are required in order to assess
the relative benefits of analogue equalization with relatively
simple modulation, or complex modulation and limited
channel bandwidth.
4) Parallel communication (Optical MIMO)
In most illumination applications many LEDs are used to
provide the necessary lighting intensity. This offers the
opportunity of transmitting different data on each device or
on different groups of emitters. For this to be successful a
detector array is required at the receiver, and this creates a
Multi-Input Multi-Output (MIMO) system. Radio-frequency
MIMO techniques can be applied to such optical transmission
systems to relax the necessary alignment between the array of
detectors and array of sources. Work in [19] shows that such
a system can allow multi-channel data communication,
without the need to align a particular detector with a
corresponding source.
It can be seen that there are many different methods of
increasing data rates, and that a combination of these should
allow data rates well in excess of 100Mb/s to be successfully
transmitted.
B. Provision of an uplink
VLC using illumination sources is naturally suited to
broadcast applications, and providing an uplink to the
distributed transmitter structures can be problematic. Several
approaches have been investigated. In [20] an infra-red
uplink is used to a transmitter co-located with the VLC
source, and in [21] a retro-reflecting transceiver is proposed.
In this case the retro-reflector returns a proportion of the
incident light to the transmitter, and this returned beam is
modulated to provide a data path from the terminal to the
infrastructure. This is potentially very attractive, although the
data-rates that can be achieved using available modulators are
low. Co-operation between VLC and RF wireless standards
would also allow full connectivity for a termin al [22]. A VLC
downlink can be combined with an RF uplink, and this can
also reduce the load on shared RF channel, including overall
network performance.
C. Regulatory challenges
In most cases VLC is subject to regulation by a non-
communications standar d. This can be an eye-safety standard,
illumination regulation, or an automotive standard in the case
of traffic signals or signal lights. A VLC standard must
therefore encompass both communications and associated
illumination practices. This is distinct from most other
communication standards, an d presents the challenge of
coordination across regulatory bodies and frameworks.
Currently there are activities in several areas. Within Japan
VLCC has developed several national standards [23, 24], and
the IEEE 802.15c Study Group on VLC [20] is currently
working on producing the necessary documents to become a
working group. Interest in these activities continues to grow,
but perhaps the major challenge for the VLC community is to
develop links with other relevant regulatory bodies to ensure
compatibility of any techniques.
V. CONCLUSIONS
VLC offer s the advantage of a communications channel in
an unregulated, unlicensed part of the electromagnetic
spectrum. In applications where a visible beam is desirable
for security it can provide high data rates. There are a number
of technical and regulatory challenges to be overcome; rapid
technical progress is being made, but the challenges of
standardization will require cooperation and agreement from
a number of different bodies. However, success should bring a
low-cost high data-rate infrastructure that can increase
wireless capacity substantially.
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ACKNOWLEDGEMENT
The authors thank colleagues involved in the preparation of
the whitepaper on Visible Light Communications within the
Worldwide Wireless Research Forum(WWRF); Olivier
Bouchet, France Telecom, Jose A. Rabadan Borges, ETSIT
Universidad de Las Palmas de Gran Canaria, Klaus-Dieter
Langer and Jelena Grubor, Heinrich-Hertz-Institute,
Kyungwoo Lee and Eun Tae Won, Samsung Electronics.
REFERENCES
[1] Visibl e Light Communi cation s Consort ium,www.vlcc.net, 200 8
[2] Wireless World World Research Forum,
http://www.wireless-world-research.org
[3] Wada-M, Yendo-T, Fujii-T , and Tanimoto-M: ‘Road-to-vehicle
communication using LED traffic light’. Proc. 2005 IEEE Intelligent Vehicles
Symposiu m Proceedings. Las Vegas, NV, USA. IEEE Intelligent Transportation
Syst. Soc. 6 8 June 2005., pp.
[4] Iwasaki, S., Wada, M., Endo, T., Fujii, T., and Tanimoto, M.: ‘Basic
Experiments on Paralle Wireless Optical Communication for ITS’. Proc.
Intelligent Vehicles Symposium, 2007 IEEE, pp. 321-326
[5]
ISLE:http://www.pb.izm.fraunhofer.de/p2sa/030_Projects/Optik/Pr_isle.html
, 2006
[6] S.-B. Park, D.K. Jung, H.S. Shin, D.J. Shin, Y.-J. Hyun, K. Lee, and Oh,
Y.J.: ‘Information Broadcasting System based on Visible Light Signboard’. Proc.
Wireless and Optical Communications 2007, Montreal, Canada, 5/30/2007 -
6/1/2007 2007
[7] Le-Minh, H., Zeng, L., O'Brien, D.C., Bouchet, O. , Randel, S., Wa lewski, J.,
Borges, J.A.R., Langer, K.-D., grubor, J.G., Lee, K., and Won, E.T.: ‘Short-
range Visible Light Communic ations’, Wireless Worl d Resear ch Foru m, 2007
[8] Komine-T , and Nakagawa-M: ‘Fundamental analysis for visible-light
communication system using LED lights’, IEEE Transactions on Consumer
Electronics, 200 4, 50, (1), pp. 100-107
[9] Gru bor, J., Gaete, J.-O., Waleski-Js, Randel-S, and Langer-Kd: ‘High-speed
wireless indoor communication via visible light’, IT G Fachbericht, 200 7, pp.
203-208
[10] Bouchet, O., El Tabach, M., Wolf, M., O'Brien-Dc, Faulkner, G.E.,
Walewski, J., Randel, S., Franke, M., Langer, K.-D., Grubor, J., and Kamalakis,
T.: ‘Hybrid Wireless Optics (HWO):Building the Next-Generation Home
Network’. submitted to CSNDSP08, Graz Austria, August 2008
[11] Hugh-Sing-Liu, and Pang-G: ‘Positioning beacon system using digital
camera and LEDs’, IEEE Transactions on Vehicular Technology, 2003, 52, (2),
pp. 406-419
[12] Liu, X., Makino, H., Kobayashi, S., and Maeda, Y.: ‘Design of an Indoor
Self-Positioning System for the Visually Impaired-Simulation with RFID and
Bluetooth in a Visible Light Communication System’, Engineering in Medicine
and Biology Society, 2 007. EMBS 2007. 29th Annual International Conference
of the IEEE, 2007, pp. 1655-1658
[13] Yoshino, M., Haruyama, S., and Nakagawa, M.: ‘High-accuracy
positioning system using visible LED lights and image sensor’, Radio and
Wireless Symposium, 200 8 IEEE, 2008, pp. 439-442
[14] Lumileds:Luxeon design guides,www.lumileds.com, 2006
[15] Zeng, L., Le-Minh, H., O'Brien, D.C., Lee, K., Jung, D., and Oh, Y.:
‘Improvement of Date Rate by using Equalization in an Indoor Visible Light
Communication System’. accepted for presentation at IEEE International
Conference on Circu its and Systems for Communications 2008
[16] Grubor, J., Lee, S.C.J., Langer, K.-D., Koonen, T ., and Walewski, J.W.:
‘Wireless High-Speed Data Transmission with Phosphorescent White-Light
LEDs’. Post deadline session at European Conference on Optical
Communications.
[17] Le-Minh, H., O'Brien-Dc, Faulkner, G., Zeng, L., and Lee, K.: ‘High-
Speed Visible Light Communications Using Multiple-Resonant Equalization’,
accepted for publication in IEEE photonics technology letters, 2008
[18] Le-Minh, H., O'Brien-Dc, Faulkner, G., Zeng, L., Lee, K., Jung, D.J., and
Oh, Y.: ‘80 Mbit/s Visible Light Communications Using Pre-Equalized White
LEDs’. Submitted to ECOC 2008.
[19] O'Brien-Dc, Zeng, L., Le-Minh, H., and Fau lkner, G.: ‘VLC with white-
light LEDs: strategies to increase data-rate’, Presented at IEEE 802.15c meeting
Jacksonville, Fl, USA, May, 2008, https://mentor.ieee.org/802.15/documents.
[20] IEEE: IEEE 802.15 WPAN Visual Light Communication Study Group
(IGvlc) http://www.ieee802.org/15/pub/IGvlc.html, 2008
[21 ] Komine-T, H aru yama-S, and Na kaga wa-M: ‘Bidirectiona l visible-light
communication using corner cube modulator’. Proc. Wireless and Optical
Communication (WOC). Banff, Canada. IASTED. 2 4 July 200 3.
[22] O'Brien, D.C.: ‘Cooperation and cognition in optical wireless
communications, in Fitzek, M.K.a .F. (Ed.): ‘Cognitive Wireless Networks:
Concepts, Methodologies and Visions
- Inspiring the Age of Enlightenment of Wireless Communications -’ (Springer,
2007)
[23] JEITA: ‘CP-1221 Visible Light Communications System’, 2007
[24] JEITA: ‘CP-1222 Visible Light ID System’, 2007
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... But the data transmission rate of visible light communication (VLC) system using LEDs can reach 1-10Gbit/s, and it can simultaneously achieve illumination and date transmission. Compared with traditional RF communication, it offers several advantages, such as high data transmission rate, users access security, large bandwidth and immunity to electromagnetic interference [1,2]. Therefore, VLC has become an important supplementary technology for 5th generation (5G) wireless communication application. ...
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... The desire for advanced network provisioning has waxed stronger; VLC techniques can solve these demands. Several issues surround VLC systems, including uplink connectivity, optimum multiple access approaches, optimum modulation technique, mobility, mitigating ISI standardization, dimming control and illumination [56,57]. Multicarrier modulation, multicolour, and baseband modulation can be applied in OWC [11]. ...
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