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IEEE Communications Magazine • December 2013
60 0163-6804/13/$25.00 © 2013 IEEE
INTRODUCTION
OPTICAL WIRELESS COMMUNICATION
When using the term optical wireless communi-
cation (OWC), we consider a free-space optical
link, where the transmitter and receiver are not
necessarily aligned to each other. OWC in gen-
eral addresses quite different applications, start-
ing from chip-to-chip interconnects and ending
in intra-satellite data links.
OWC links can be realized with quite differ-
ent optical sources and detectors. For low data
rates, such as “optical telegraph,” traditional
light bulbs, liquid crystal displays (LCDs), or
plasma display panels (PDPs) can be used. As a
receiver, we can use low-cost digital cameras, as
currently they feature in practically every mobile
device. However, not only the serial read-in and
read-out of images, but their processing as well
limit achievable transmission speed. High-speed
displays and digital cameras provide frame rates
of hundreds and thousands of frames per sec-
ond, respectively; thus, only data rates of a few
kilobits per second can be achieved [1].
The new LED-based luminaires will be
omnipresent a few years from now. Besides their
original lighting function, their light can be mod-
ulated at high speed. In this way, we can realize
significantly higher data rates over moderate dis-
tances, which is the focus of this article. For
higher speed (>10 Gb/s) or longer distances,
laser diodes, as typically applied in outdoor free
space optical (FSO) communications, appear to
be the better choice. In both cases, PIN or more
sensitive avalanche photodiodes (APDs) are
used as receivers.
VISIBLE LIGHT COMMUNICATION
Visible light communication (VLC) comprises
OWC links in which visible light sources are
applied. Hereby, the main task and challenge is
the development of luminaires with an add-on
function (i.e., data transmission), which has no
negative influence on their illumination func-
tionality. This dual role can best be fulfilled by
LEDs, and over the past few years research
groups have been able to demonstrate that high
data rates up to the gigabit per second range are
possible with such devices [2, 3].
The main driver behind high-speed VLC is
the rapidly growing presence of LEDs in practi-
cally every signaling or illumination entity. By as
early as 2018, the majority of new energy-effi-
cient lighting installations are expected to be
LED-based [4]. As current-driven semiconductor
diodes, LEDs provide a respectable modulation
potential. This aspect increases the attractiveness
of VLC and offers benefits such as:
• Huge bandwidth in the visible part of the
“optical” electro-magnetic spectrum
• Absence of electro-magnetic interference
(EMI) with existing radio systems
• The intuitive option to create and isolate
communication cells with very high privacy
by either directing the light to the working
area or using any opaque material
A further important driver for VLC systems
comes from the flood of wireless applications.
According to the Federal Communications Com-
mission (FCC), a “spectrum deficit” (i.e., lack of
usable radio frequencies for new wireless applica-
tions) was already expected for this year (2013)
due to exponential growth in demand for wireless
transmission capacity [5]. While the response of
radio technology is a further increase in spatial
reuse (e.g., by using more antennas and smaller
cells), optical frequencies remain unregulated
ABSTRACT
This article presents recent achievements and
trends in high-speed indoor visible light communi-
cation (VLC) research. We address potential appli-
cations and future visions for the VLC technology,
where transport of information is “piggybacked”
on the original lighting function of LED-based
lamps. To mature this technology and transfer it
into practice, our recent research is focused on
real-time implementation and trials. For the first
time, a bidirectional real-time VLC prototype
achieving data rates of up to 500 Mb/s is present-
ed. This system paves the way for future real world
applications. Finally, we discuss the remaining
technical challenges as well as the research outlook
in the field of high-speed VLC systems.
VISIBLE LIGHT COMMUNICATIONS: THE ROAD TO
STANDARDIZATION AND COMMERCIALIZATION
Liane Grobe, Anagnostis Paraskevopoulos, Jonas Hilt, Dominic Schulz, Friedrich Lassak, Florian Hartlieb,
Christoph Kottke, Volker Jungnickel, and Klaus-Dieter Langer, Heinrich Hertz Institute
High-Speed Visible Light
Communication Systems
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IEEE Communications Magazine • December 2013 61
worldwide. Creating a small personal optical cell
is a fairly intuitive and easy task; even rice paper
is enough to isolate the light beams!
This article is organized as follows. First, we
address future visions and the main VLC applica-
tions. Then we describe high-speed VLC system
aspects and review the main laboratory achieve-
ments. Our newly developed real-time high-
speed bidirectional VLC system is presented
afterward. A short system evaluation is made in
the following, where future technical aspects are
also touched on. Before the conclusions, aspects
of rollout and standardization are discussed.
FUTURE VISIONS AND
MAIN APPLICATIONS
A few years ago, the following dense wireless
communications scenario was foreseen far into
the future: Several people sit comfortably in an
indoor environment and watch different HD
video content on their portable devices by sharing
a high-speed Internet connection. This scenario
applies, for instance, to private homes and offices
as well as in-flight and in-railway environments.
One viable solution for this scenario is individ-
ual data transmission via illumination using VLC
(Fig. 1). Such a dense high-speed access solution
is often referred to as optical WiFi. The first step
toward this vision was a real-life demonstration of
the European FP7 project OMEGA in 2011,
where the user was able to download several HD-
video streams in parallel (http://youtu.be/AqdAR-
FZd_78; more details later).
One advantage of the VLC concept is that
illumination-devised LEDs can be extended for
data transfer with only minor effort. Through the
use of visible light, the user gains very intuitive
control over sharing data with others. As soon as
an object (like a hand) gets between the light
source and the receiver, data transfer is impaired.
This can equally be seen as a positive feature as
far as communication security is concerned. VLC
is not intended to replace WLAN, PowerLAN,
or mobile networks. Rather, it is suited as an
additional high-speed data layer in a heteroge-
neous network environment, providing an alter-
native wireless data link where radio transmission
is not desired, not possible, or not sufficient.
Evidently, VLC applications based on LED
lighting are more attractive in environments
where the lights are always switched on, for
instance, in industrial settings, public transport
or medical areas. On the other hand, simple
integration of an infrared LED chip into future
LED luminaires will allow for continuous data
flows even if the lights are switched off. Deploy-
ment is rather easy as data can be provided from
a local aggregation point to the luminaires via
existing infrastructure like power cables. VLC
applications will also be related to IT-security
(e.g., in the financial sector with its high security
and confidentiality requirements) to protect pri-
vate information against jamming and tapping.
Furthermore, VLC is predestined for use in
EMI-sensitive environments like operating the-
atres or aircraft cabins, and also in places where
radio transmission is problematic such as indus-
trial production sites or exhibition halls.
Although one mostly thinks here about bidirec-
tional data links, there are a multitude of broad-
casting applications for VLC, starting with simple
messaging using street or traffic lights or advertis-
ing displays, continuing with augmented reality
applications in museum exhibitions, and ending
with HD video streaming to a display monitor.
Moreover, VLC presents a unique feature in
short-range underwater transmission where light
sources in the blue-green spectral window are
convenient. The reach is, of course, limited by
the clarity and attenuation of the water, but the
lack of alternatives for high-speed wireless under-
water communication underscores the potential
of VLC for resource exploration and yield as well
as for data exchange between divers or between
robots and submarine docking stations.
Last but not least, a further interesting
research and development topic is the applica-
tion of VLC for indoor navigation and localiza-
tion, in particular in large labyrinthine buildings
like hospitals, railway stations, or shopping malls.
While GPS signals are often not available indoors
and radio fails due to rich multipath propagation,
artificial lighting is omnipresent in such areas.
Obtaining indoor location information by means
of light sources may be an attractive solution. A
spatial resolution of a few centimeters can poten-
tially be achieved by using multiple lamps trans-
mitting individual beacon signals in combination
with imaging optics (e.g., a smartphone camera).
HIGH-SPEED VLC LINKS
CHANNEL CHARACTERISTICS
VLC can be applied in various scenarios. One
important parameter for high data rates is the
availability of a line-of-sight (LOS) optical link,
where the transmitter is directed to the receiver
(Fig. 2a), while non-directed LOS transmission
or diffused lighting is likely to limit the achiev-
able data rates (Figs. 2b and 2c). Thus, the
capacity of the VLC channel depends strongly
on the availability of the LOS path. As the light-
ing scenario may vary, a dynamic rate adaption
appears necessary, as already proposed in [6–8],
in order to achieve a robust VLC link.
LED CHARACTERISTICS
Over the past few years, growing insights have
been gained into the efficient implementation of
VLC data transmission using LEDs initially
Figure 1. An artist’s vision of a future “optical wi-
fi” real-life application.
Obtaining indoor
location information
by means of light
sources may be an
attractive solution. A
spatial resolution of
a few centimeters
can potentially be
achieved by using
multiple lamps trans-
mitting individual
beacon signals in
combination with
imaging optics (e.g.,
a smartphone cam-
era).
GROBE_LAYOUT_Layout 12/3/13 1:48 PM Page 61
IEEE Communications Magazine • December 2013
62
developed for illumination purposes. In general,
there are two main types of white-light LEDs
commonly used for lighting: phosphorescent and
multi-color (RGB). The phosphorescent type
consists of a blue LED chip plus a yellow phos-
phor layer. The multi-color type, in contrast,
consists of three (or in some cases four) individ-
ual chips, mostly red, green and blue (hence
RGB). While the phosphorescent type allows for
cost-efficient installations, mainly because of its
simpler driver design, it provides only narrow
modulation bandwidth, given the slow response
time of the phosphorescent material. However,
we were able to demonstrate that the bandwidth
can be enhanced by an order of magnitude of
about 20 MHz by suppressing the phosphores-
cent portion of the optical spectrum with the aid
of a blue filter at the receiver end [6]. In con-
trast, white-light RGB-type LEDs enable three
individual color channels, each providing approx-
imately 15 MHz bandwidth. By using three
drivers in parallel, wavelength-division multiplex-
ing (WDM) can be realized. However, the
advantage of an increased aggregate data rate is
achieved at the expense of higher costs.
VLC ACHIEVEMENTS
A couple of research groups have demonstrated
that although illumination LEDs are not intend-
ed for data transmission, they do offer signifi-
cant potential for high-speed communications.
Starting with phosphorescent LEDs and simple
on-off keying (OOK) modulation, which enable
100–230 Mb/s data rates [9], transmission speeds
have been increased continuously by applying
more spectrally efficient modulation formats. In
particular, orthogonal frequency-division multi-
plexing (OFDM) alias discrete multitone trans-
mission (DMT1) in several variants have been
studied and evaluated over the years. Using a
phosphorescent LED in an LOS configuration,
data rates up to 1 Gb/s have been achieved in
the laboratory by means of offline-processed
experiments [2], and even rates of up to 1.5 Gb/s
when using RGB-LEDs in a single-color trans-
mission mode [3, 10]. Work on optimization of
LED modulation is still in progress, for example,
on parameters such as power efficiency.
In contrast to LOS scenarios, non-directed
LOS or diffuse configurations call for adaptive
transmission schemes due to their specific channel
properties, for instance, the common appearance
of spectral notches [11]. The idea of dynamic data
rate adaptive OFDM was proposed and developed
almost at the same time by another research group
and by us independently in [7, 8]. We have contin-
ued working on implementation of such sophisti-
cated adaptive systems and have shown that data
rates up to the gigabit per second range, based on
DMT modulation with bit and power loading for
throughput maximization beyond conventional 3
dB bandwidth limitations, are feasible.
A real boost of the throughput can be
achieved with RGB-LEDs using WDM. The
principle is shown in Fig. 3. DMT via WDM
channels and VLC was studied in detail in [3]
using a commercially available high-power white-
light RGB-LED as the optical source and WDM
pass-band filters combined with an APD as the
receiver element. Compared to single-color
transmission, the aggregate data rate was extend-
ed to 1.25 Gb/s at an illuminance level of 1000 lx
at the receiver, a value within the range recom-
mended by the European lighting standard (EN
12464-1 from 2003) for working environments.
Based on a similar offline-processed WDM-VLC
setup and a low-power RGB-LED, the authors in
[10] reported an aggregate data rate of 3.4 Gb/s.
Of course, WDM is also applicable for setting
up bidirectional VLC links operating in a full
duplex mode. Corresponding experiments for
proof of principle by means of offline processing
are described, for example, in [12]. There it was
shown recently that bidirectional VLC links can
provide capacities of more than just a few hun-
dred megabits per second.
REAL-TIME 500 MB/S
BIDIRECTIONAL VLC LINK
SYSTEM DESIGN
Besides the high-speed offline-processed laborato-
ry achievements, the maturity of VLC technology
for all potential applications has to be proven with
real-time systems. This is an aspect on which we
have recently focused. The very first high-speed
VLC real-time demonstration was presented in
February 2011 at ORANGE laboratory facilities
by the consortium of the EU project OMEGA
(www.ict-omega.eu). This system provided a 100
Mb/s net data rate. OFDM-based modulation and
demodulation, forward error correction, synchro-
nization, and a specifically developed medium
1The DMT technique is
known from digital sub-
scriber line (DSL); in
radio systems it is known
as OFDM. DMT can be
realized using OFDM
where a real-valued wave-
form is obtained using a
so-called mirror function
[6, 8].
Figure 2. a) Directed LOS configuration; b) non-directed LOS configuration; c) diffused light configuration.
(a) (b) (c)
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IEEE Communications Magazine • December 2013 63
access control (MAC) were implemented on field
programmable gate arrays (FPGAs). In an area of
about 10 m2, equipped with 16 LED lamps dis-
tributed on the ceiling, four HD video streams
were broadcast simultaneously to different laptops
located in the service area [9].
In order to advance VLC technology toward
future commercial applications, more recently
we developed the first bidirectional real-time
high-speed rate-adaptive VLC system. It oper-
ates in half-duplex mode based on time-division
duplex (TDD). The idea is presented schemati-
cally in Fig. 4. Data transmission is based on a
rate-adaptive OFDM modulation and demodula-
tion scheme. The transceivers are equipped with
tailored VLC transmitter and receiver modules.
As the VLC channel is based on intensity modu-
lation and direct detection, a real-valued positive
waveform is needed. Here, DC-biased DMT is
applied to obtain a unipolar (positive valued)
time domain signal at the transmitter, while any
potentially remaining negative signal amplitudes
are clipped at the expense of an increased error
rate. Possible bit errors are handled by integrat-
ed forward error correction (FEC). The VLC
transmitter is primarily composed of a newly
developed LED current driver and an off-the-
shelf high-power visible-light LED. The VLC
receiver comprises a transimpedance amplifier
(TIA) and a commercially available high-speed
Si-PIN-photodiode. These new modules have
significantly increased the modulation bandwidth
of our optical link up to 180 MHz.
These transceiver modules can operate with-
out active cooling and are easily usable. Mean-
while, a second generation of such modules with
a reduced form factor (Fig. 5) has emerged.
Each transceiver is equipped with an external
power supply and 1000BASE-T Ethernet inter-
faces using standard RJ45 connectors (further
details will be published elsewhere).
EXPERIMENTAL RESULTS AND DISCUSSION
One particular advantage of our real-time VLC
system is the use of bidirectional rate-adaptive
OFDM transmission enabling a variable through-
put with controlled error rate, depending on the
quality of the optical communication channel. At
a typical working distance of 2 m between the
ceiling and the tabletop, and in a circular spot
covering a typical working area of roughly 60 cm
in diameter, the system enables a data rate of
200 Mb/s per user. By using the same transceiver
combined with narrow-beam optics, we improved
the system performance, achieving a data rate of
100 Mb/s over 20 m distances. As shown on the
left of Fig. 6, the most important parameter is
the light intensity at the receiver, leading to
nearly proportional adaptation of the data rate.
Thanks to the dynamic rate control, by reducing
the distance or using a more directional beam,
the data rate can steadily be increased until the
500 Mb/s peak data rate is reached (Fig. 6, right).
Our bidirectional VLC experiments demon-
strate for the first time that the dense optical
WiFi communication scenario, still considered
visionary earlier, can now be realized in a rea-
sonable indoor setup using commercially avail-
able hardware. We exemplarily used red LED
sources, as shown on the right of Fig. 5, for bet-
ter visualization of the bidirectional data trans-
mission. In fact, any other high-power LED
could be used as the light source regardless of its
color. In the near future, we expect that more
powerful OFDM chips will be available. As our
VLC components already provide the necessary
analog bandwidth, there is a significant potential
for further increased data rates.
TECHNICAL OUTLOOK
VLC has high potential if the “piggyback” effect
on the lighting function of white-light LEDs is
used. Similar to LED lamps, low-cost mass fabri-
cation is an essential prerequisite for ubiquitous
acceptance of VLC, as are minimal power con-
sumption, improved robustness, and higher data
Figure 3. The WDM principle for VLC showing in-parallel transmission of
three (RGB) channels and reception of one channel via color filtering.
R
LED-luminaire
Data 1
R/G/B
WDM
filter
Lens
VLC-channel
1000 lx
Receiver 1
G
Data 2
B
Data 3
Figure 4. The overall scheme of a bidirectional real-time LOS VLC link.
TIA
Visible
light
LED
Visible
light
LED
LED-luminaire
Tabletop
LED
current
driver
OFDM
transceiver
1000BASE-T
Ethernet
TIA
LED
current
driver
OFDM
transceiver
1000BASE-T
Ethernet
Optical
channel
Photodiode
Photodiode
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IEEE Communications Magazine • December 2013
64
rates. Our experiments have conclusively demon-
strated that there are no real technical show-
stoppers.
Deployment costs will be dominated by three
contributions. First, the LED needs a bias-T for
high-speed modulation. Second, we need a pow-
erful analog LED driver and a low-noise amplifi-
er after the photodiode. Both require careful
impedance matching. Third, a baseband chip is
needed based on adaptive OFDM providing an
interface to the network infrastructure (e.g., via
the power line). All these aspects are already
realizable today with commercial components, so
mass production appears feasible. Moreover,
low-cost mass production calls for monolithic sys-
tem integration as the form factor can be further
reduced in this way. Despite the add-on of com-
munication to lighting, the developed system is
quite energy efficient. Power consumption is only
moderately increased by 30 percent compared to
the original lighting function in our real-time
VLC system due to the optimized LED driver
design. As the choice of color temperature is rel-
atively unimportant for communication, the sys-
tem can also operate with tunable light color.
As discussed in the previous section, there is
some potential for higher link capacity in both
the optical subsystem and the baseband. In the
latter case, development depends strongly on the
availability of adaptive OFDM chips with an
extended baseband bandwidth. Depending on
the optical link setup, the choice of suitable opti-
cal lenses can significantly increase the attain-
able link margin. Until now, adaptive
transmission has been realized using DMT with
bit and power loading on individual subcarriers.
For enhanced robustness, advanced waveforms
with reduced clipping probability, such as block-
wise pulse amplitude modulation (PAM) with
frequency domain equalization [13] may be
promising because the non-directed LOS chan-
nel is essentially flat, apart from the low-pass
character of the optical transmitters and
receivers. Single-carrier transmission combined
with frequency domain equalization and modifi-
cations thereof [14], and extended to support
multiple users, as in Long Term Evolution (LTE)
mobile radio, also has high potential for VLC.
Higher point-to-point user data rates are cer-
tainly feasible utilizing higher bandwidth and
WDM, as described earlier. Moreover, there is
significant potential for spatial multiplexing
using pixelated transmitters and receivers, possi-
bly reaching 10 Gb/s and beyond. On the other
hand, hundreds of megabits per second may be
enough for a single user nowadays. Thus, it
might be wiser to exploit the spatial multiplexing
potential to achieve higher aggregate data rates
for multiple users in a homogeneously lit large
coverage area. Note that optical bandwidth is
more easily shared than radio. Using, for exam-
ple, selective light beams, data can be directed
to one user without complex signal processing.
Optical space-division multiplexing can also
enable high-speed access for each individual user
by spatially reusing the modulation bandwidth.
While optical beam-forming has often been
demonstrated in the scientific literature [15, ref-
erences therein], further research is needed to
integrate this new technology autonomously into
optical access points and terminals.
ROLLOUT AND STANDARDIZATION
From our point of view, optical wireless will
increasingly complement radio in the future.
Hybrid technologies, involving the use of unified
wireless data protocols and link management,
will accordingly play a significant role.
An important aspect of rollout in the poten-
Figure 5. Left: First generation real-time point-to-point 500 Mb/s VLC system as shown at a commercial exhibition. Middle: Zoom-in of
the desk part. Note that this setup includes an infrared uplink, while visible light could be used as well. Right: Second generation of the
bidirectional transceivers with a reduced footprint of 87 mm ×114 mm ×42 mm without lenses.
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IEEE Communications Magazine • December 2013 65
tial application scenarios is a low-cost network
behind VLC. For existing indoor environments,
it is intuitive to use the power lines to the room
lighting as a network infrastructure, in order to
accelerate deployment and reduce costs. For
extending the already existing power line com-
munications (PLC) technology with VLC, ampli-
fy-and-forward or decode-and-forward strategies
are of interest. On the other hand, for new
installations, plastic optical fibers (POF) are
considered promising, as they provide improved
data security. VLC could be combined with an
optical backhaul, paving the way for future all-
optical wireless solutions.
A dedicated standardization roadmap is
essential for the future availability of VLC in a
large number of portable devices. Standardiza-
tion activities so far emanate from the Infrared
Data Association (IrDA) interest group and
from the IEEE. Whereas IrDA provides mainly
specifications for wireless infrared protocols, the
IEEE published a first OWC standard, IEEE
802.15.7-2011, using VLC in September 2011.
The recent extension of the International
Telecommunication Union (ITU) g.hn standard
(ITU-T Recommendation G.9960, 2011) fore-
seeing an optical channel is equally of impor-
tance. Research and development is already
coordinated on several platforms: the Visible
Light Communications Consortium (since 2003,
http://www.vlcc.net), the Li-Fi (Light-Fidelity)
Consortium (launched 2011, www.lificonsor-
tium.org) and the COST action OPTICWISE
(since 2011, http://opticwise.uop.gr).
After short-range IrDA links were replaced
by Bluetooth, optical wireless became a niche
market, and substantial acceptance has not yet
been reached in the industry. We believe that
the mass market opportunities for VLC will be
drastically increased when the lighting industry
agrees on the incorporation of data transmission
features into common lighting. Standardization
needs equally to move forward from point-to-
point link design issues to address multipoint-to-
multipoint functionality. Finally, energy efficien-
cy aspects will certainly play a major role, in par-
ticular for the implementation of VLC in mobile
devices.
CONCLUSIONS
In this article we have recapitulated recent devel-
opments in the area of high-speed visible-light
communication. These systems exploit the natu-
ral opportunity of piggybacking data transmission
over new LED-based luminaires. Our focus was
on demonstrating the maturity of this technology
for a number of dense high-speed wireless com-
munication scenarios envisioned mainly in indoor
settings such as aircraft cabins, operating the-
atres, trade fair halls, or private homes.
We have summarized recent experimental
work demonstrating that VLC has high potential
for high-speed communications in these scenar-
ios. Even today, the simplest on-off keying mod-
ulation enables more than 100 Mb/s, while
transmission speed can be further increased
beyond 1 Gb/s by using more spectrally efficient
adaptive wideband modulation techniques and
wavelength-division multiplexing.
A bidirectional real-time visible light commu-
nications prototype, supporting data rate adaption
according to the lighting conditions and operating
at speeds of up to 500 Mb/s, has been presented
for the first time. It combines both lighting and
fast wireless data communications under very
realistic conditions and is entirely based on com-
mercially available low-cost hardware.
Future research and development will be
directed toward further system optimization,
hybrid integration with other wired and wireless
technologies, and the use of space-division mul-
tiple access for operating multiple optical wire-
less links in parallel. An increasingly important
aspect is an internationally harmonized view on
standardization in order to create the ecosystem
needed for the rollout of this technology in the
future.
Figure 6. Measurement results for the real-time VLC system. Left: Achieved data rates for the red LED-based transmitter depending on
the light intensity measured using a standard photometer at the receiver entity. Right: Measured data rates over varying transmission
distances demonstrating the practically color-independent bidirectional data transmission.
Light intensity (lx)
Red LED: Data rate vs. light intensity
102
101
100
0
Data rate (Mbit/s)
200
300
400
500
Distance (m)
Red and blue LED: Data rate vs. distance
50
100
0
Data rate (Mbit/s)
200
300
400
500
10 15 20 25
Blue LED
Red LED
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IEEE Communications Magazine • December 2013
66
ACKNOWLEDGMENTS
This work was supported by the FP7 funded
European Union projects OMEGA and
SODALES and by the Fraunhofer Women’s Doc-
toral Scholarship, Doktorandinnen-Programm.
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BIOGRAPHIES
LIANE GROBE (liane.grobe@hhi.fraunhofer.de) received her
Dipl.-Ing. degree on media technology from Technische
Universitaet Ilmenau, Germany, in 2008. From 2009 to
March 2011, she was with the communication research
laboratory at the same university, where she was involved
in the European project OMEGA on indoor wireless infrared
communication. From April to September 2011, she joined
the University of Applied Sciences Nordhausen, Germany,
working on the topic of signal processing for fiber optical
communication. In October 2011, she changed to the Pho-
tonic Network and Systems Department at Fraunhofer
Heinrich Hertz Institute (HHI), Berlin, Germany. Her current
activity toward her PhD is in the area of information tech-
nology and digital signal processing for wireless as well as
wire-based optical communication.
ANAGNOSTIS PARASKEVOPOULOS (anagnostis.paraskevopoulos@
hhi.fraunhofer.de) studied electrical engineering at the Technical
University in Athens and earned his Ph.D. degree from Université
Paris-Orsay with a study on RF modulation of semiconductor
lasers performed in CNET (Research Centre-France Telecom) in
Paris. He joined HHI in 1988 and has since been involved in vari-
ous technology research projects, including the ESPRIT263 pro-
ject on HBTs, a national project on VCSEL devices at 980 nm in
the early 1990s, and custom designed laser diodes for non-tele-
com applications. Over the years he has successfully coordinated
R&D projects concerning both research subjects and industrial
applications. He is an author and co-author of more than 50 sci-
entific papers.
JONAS HILT (jonas.hilt@hhi.fraunhofer.de) received his Diplo-
ma in electrical engineering from TFH — Berlin University
of Applied Sciences in 2009. Subsequently he joined the
Fraunhofer Institute for Telecommunications, HHI, where
he acts as an electrical engineer in the Department of Pho-
tonic Networks and Systems. His current activities are in
the area of high-speed FPGA implementation of algorithms
and design of signal processing systems.
DOMINIC SCHULZ (dominic.schulz@hhi.fraunhofer.de) studied
communications engineering and received his Master’s
degree in engineering from Berlin University of Applied Sci-
ences in 2012. In 2013 he joined the Photonic Networks
and Systems Department of the Fraunhofer Institute for
Telecommunications, HHI. There, he works in the field of
VLC. His current activities include the development of high
data rate VLC systems and research in long-range VLC links.
FRIEDRICH LASSAK (friedrich.lassak@hhi.fraunhofer.de) got his
Bachelor’s degree in communications and electronic engi-
neering from the University of Applied Sciences Berlin
(BHT) in 2012. Afterward he joined HHI, where he acts as a
scientific assistant in the Department of Photonic Networks
and Systems dealing with unidirectional visible light com-
munication (VLC) and the prototype development of VLC
systems. Currently, he is writing his Master’s thesis in the
field of coherent combining for free space optics (FSO).
FLORIAN HARTLIEB got his Master of Engineering degree in
communications engineering from the University of Applied
Sciences Berlin in 2013. From 2011 through fall 2013, he
was a scientific assistant at the Photonic Networks and Sys-
tems Department of the Fraunhofer Institute for Telecom-
munications, HHI. There he worked in the field of VLC,
especially in research on multi-application VLC links and
the prototype development of high-speed VLC systems.
CHRISTOPH KOTTKE (christop.kottke@hhi.fraunhofer.de)
received his Diploma in electrical engineering with empha-
sis on telecommunications from Technische Universitaet
Berlin, Germany, in 2010. In 2011, he joined the Fraun-
hofer Institute for Telecommunications, HHI, Berlin, Ger-
many, where he acts as a research associate in the
Department of Photonic Networks and Systems. His current
research interests include optical access and indoor net-
works and optical wireless systems.
VOLKER JUNGNICKEL [M‘99] (volker.jungnickel@hhi.fraun-
hofer.de) received a Dr. rer. nat. (Ph.D.) degree in physics
from Humboldt University in Berlin in 1995. He worked on
semiconductor quantum dots and laser medicine and
joined the Fraunhofer HHI in 1997. Since 2003, he has
been an adjunct lecturer at TU Berlin and project leader at
HHI. In his research, he has contributed to high-speed
indoor optical wireless links, first 1 Gb/s MIMO-OFDM
mobile radio transmission experiments, a first real-time
implementation and field trials for the LTE standard and
using joint transmission coordinated multipoint (JT CoMP).
He has authored and co-authored more than 160 confer-
ence and journal papers as well as book chapters on com-
munications engineering and holds several patents.
KLAUS-DIETER LANGER (klaus-dieter.langer@hhi.fraunhofer.de)
received his Ph.D. in electrical engineering from the Univer-
sity of Stuttgart, Germany. He is head of the R&D group
on optical metro, access, and in-house networks at Fraun-
hofer HHI, which he joined in 1981. In the 1990s, he
changed to the German Federal Ministry of Research and
Technology, where he served as an adviser on national
telecommunications, digital audio broadcasting, and pho-
tonics/ optoelectronics R&D. Subsequently, at HHI, he
addressed in particular the topics of cost-efficient fiber-
based subscriber lines and the use of wavelength-division
multiplexing in optical access networks. Moreover, his field
of work includes broadband home area networks and opti-
cal wireless indoor communications. He has been involved
in numerous national and international research projects,
and he has authored or co-authored more than 100 scien-
tific publications.
Future research and
development will be
directed toward
further system
optimization, hybrid
integration with
other wired and
wireless technologies
and the use of
space-division
multiple access for
operating multiple
optical wireless links
in parallel.
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