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Visible light communications: Challenges and possibilities


Abstract and Figures

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
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
Index Terms—visible light communications, optical
communications, wireless communications
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
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
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)
978-1-4244-2644-7/08/$25.00 © 2008 IEEE
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
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
A VLC link consists of a transmitter, the propagation channel
and a receiver . Each of these is descr ibed in the following
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
Figure 2. Small-signal modulation bandwidth of LUXEON
STAR device
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
power(optical) 20mW
Total power used
for optical
order 1 Receiver Area 1cm2
No. of LEDs
in 1 lighting unit
at 1-cm
noise current of
No. of
lighting units
2.5m apart
(centre to
(averaged over
typical spectrum of
Luxeon star LED)
0.85 m
Position of
2.5 m,
2.5 m from
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
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.
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
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
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
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.
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.
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.
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light LEDs: strategies to increase data-rate’, Presented at IEEE 802.15c meeting
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[24] JEITA: ‘CP-1222 Visible Light ID System’, 2007
... Komunikasi cahaya tampak menjadi pilihan alternatif bagi generasi lanjut teknologi nirkabel yang menawarkan berbagai keunggulan seperti murah dalam hal biaya, masa pakai yang panjang, konsumsi daya rendah, dan dukungan infrastruktur yang sudah memadai [1]. Selain itu teknologi ini lebih aman jika dibandingkan dengan frekuensi radio dan inframerah. ...
Visible light communication can be used to display information of goods on a shelf in supermarket, so customers can find goods easily. The transmitter transmits LED’s light to receivers when the receiver is located under the transmitter. Photodiode is used in the receiver circuit to receive the signal emitted by the LED. The signal received by the photodiode is processed by the Arduino Nano board to distinguish the code from each transmitter circuit. Each code represents content information on a particular shelf. The output of Arduino Nano board is connected to an LCD that display information of goods, brands and certain product discounts. The information of goods, brands and discounts entered manually by a keypad in the receiver circuit by an operator. From the test results, it can be shown that this system can display goods type information and discount of a product with maximum distance between the transmitter circuit and receiver circuit as far as 2.7 meters and the incidence angle of 1.3° at a distance of 2.2 meters.Keywords: visible light communication, Arduino Nano, LED, photodiode Komunikasi cahaya tampak dapat digunakan untuk menampilkan informasi jenis barang di toko swalayan sehingga pelanggan dapat menemukan barang dengan mudah. Rangkaian pemancar memancarkan cahaya dari LED ke penerima bila rangkaian penerima berada di bawah rangkaian pemancar. Fotodiode digunakan pada rangkaian penerima untuk menerima sinyal yang dipancarkan oleh LED. Sinyal yang telah diterima oleh fotodiode diproses oleh board Arduino Nano untuk membedakan kode dari tiap rangkaian pemancar. Tiap kode mewakili informasi isi barang pada rak tertentu. Output dari board Arduino Nano berupa informasi jenis barang, merek, dan diskon produk tertentu ditampilkan pada LCD. Adapun informasi jenis barang, merek dagang, dan diskon dimasukkan secara manual dengan menggunakan keypad yang terdapat pada rangkaian penerima oleh operator. Melalui pengujian yang telah dilakukan dapat ditunjukkan bahwa sistem ini dapat menampilkan informasi jenis barang dan diskon suatu produk pada jarak maksimum antara rangkaian pemancar dengan rangkaian penerima sejauh 2,7 meter dan sudut datang sebesar 1,3° pada jarak 2,2 meter.Kata kunci: komunikasi cahaya tampak, Arduino Nano, LED, fotodiode.
... As a result of this limitation, the transmission bandwidth of the VLC systems is restricted to several MHz as compared to the available optical bandwidth of 400THz. As high data rates are required for highspeed communication, this restraint in bandwidth presents a challenge for researchers to design an effective VLC system [4]. ...
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In an indoor multiple-input multiple-output (MIMO) visible light communication (VLC) system, line of sight (LoS) channel links are present between a light-emitting diode (LED) based transmitter and a photodetector (PD) based receiver. The PDs in the receiver are closely packed resulting in a high channel correlation. To overcome channel correlation and improve the performance of the MIMO-VLC system, angle diversity receivers (ADRs) are commonly employed. The channel matrix entries depend on the normal vectors of the PDs, which in turn depend on the elevation angle (EA) of the PDs. Thus, by having normal vectors pointing in different directions, the channel correlation can be considerably reduced. In a fixed EA system, the EA for all the PDs is considered to be the same whereas, in a variable EA system, the EA of the PDs is chosen irrespective of other PDs. This paper considers a special type of ADR called pyramid receiver (PR) and employs a 4x4 MIMO-VLC system. In this paper, different MIMO algorithms such as repetition coding (RC) and spatial multiplexing (SMP) are considered to exhibit and compare the bit-error-rate (BER) performance of the fixed and variable EA MIMO-VLC systems. The results show that an SMP employed MIMO-VLC system outperforms the RC employed MIMO-VLC system. SMP results in a spatial multiplexing gain that varies linearly with the number of LEDs whereas RC does not yield any spatial multiplexing gain. To attain the same spectral efficiency i.e. 4 bit/s/Hz, a larger signal constellation size is required for RC employed MIMO-VLC system to achieve the same BER as of an SMP employed MIMO-VLC system. Similarly, the BER performance of variable EA MIMO-VLC systems is better as compared to fixed EA MIMO-VLC system.
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Visible light communication(VLC) has been gaining a good deal of attraction because of its ability to use the transmitter -LED’s for both communication and illumination. VLC can be used in an environment where wireless communication is not preferred such as hospitals and other chemical plants. Although Global positioning system (GPS) is generally acknowledged, within an indoor environment, VLC has the ability to provide results with better accuracy as it avoids attenuation and blocking. VLC positioning techniques such as Received signal strength (RSS) based trilateration and proximity method are currently being implemented, however the new proposed model which is the weighted k nearest neighbour(Wk-NN) models provides us with a better accuracy than some of the existing methods.
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In this paper, in order to improve the reliability of Multi-User Multiple-Input Multiple-Output Visible Light Communication (MU-MIMO-VLC) system, we propose a precoding scheme that based on Singular Value Decomposition (SVD) and Geometric Mean Decomposition (GMD) assisted Orthogonal Transformation (OT). In this design, we use SVD to conduct the decomposition of the user’s complementary channel matrix. Then, the equivalent channel matrix is obtained by multiplying the user’s channel matrix and the decomposed component. After that, the GMD is carried out to decompose the equivalent channel matrix. Finally, the precoding matrix of the proposed scheme is obtained. We then derive the theoretical Symbol Error Rate (SER) of the proposed scheme. The simulation results are provided to validate the effectiveness of the proposed scheme, and to demonstrate that the reliability of the proposed design is superior to benchmark schemes.
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In order to improve the transmission performance of visible light communication (VLC) system and user’s demand for large-capacity and high-speed, one multi-color VLC scheme is proposed. This scheme uses red-green-blue light-emitting diode (RGB-LED) as the sender to transmit 4-ary pulse amplitude modulation (4PAM) signals with 67% return-to-zero (RZ). At the receiver, one optical bandpass filter is used for channel separation. By system simulation, we have measured the time-domain waveforms before and after transmission, eye diagrams of the three colors signals, and the bit error rate (BER) performance has been analyzed. The results show that at receiver power of -11dBm, the BER at back-to-back case is slightly lower than that of the signals transmitted in the 8m channel. Since 4PAM signals have higher spectral efficiency compared with the traditional binary signals, this scheme has potential application value in indoor broadband access system.
... 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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It is crucial to design new communication technologies to surmount the setbacks in RF communication systems. A suitable energy-efficiency scheme helps evade needless energy consumption in wireless communication. Appropriate choice of the most suitable energy-efficiency scheme aids in selecting the most energy-efficient equipment to minimize the expense of energy towards decreasing individual network element energy consumption without affecting their unique features. This review presents the energy efficiency challenges in wireless communication by employing different technologies. The emergence of visible light communication (VLC) provides an energy-efficient wireless communication system despite the various challenges inherent in its adoption that limit its physical realization. This work seeks to harness the potential of the transmission capabilities of VLC while providing an insight into novel practical implementation techniques. The work also addresses the energy consumption problem of low-active components and idle period of active components of base stations by using sleep modes for their systematic turning off and on. The high cost of power supply and the environmental emission of gases from base stations are also addressed by integrating a renewable energy resource into the conventional standalone diesel generators. Overall, the work provides an overview of information necessary for foundational research in energy-efficient resources applied to emerging wireless communication systems.
Aggregation of some chromophores generates very strong fluorescence signals due to the tight molecular packing and highly restricted vibrational motions in the electronically excited states. Such an aggregation-induced emission enhancement enables great strides in biomedical imaging, security screening, sensing, and light communication applications. Here, we realized efficient utilization of a series of aggregation-induced emission luminogens (AIEgens) in X-ray imaging scintillators and optical wireless communication (OWC) technology. Ultrafast time-resolved laser spectroscopic experiments and high-level density functional theory (DFT) calculations clearly demonstrate that a significant increase in the rotational energy barrier in the aggregated state of AIEgens is observed, leading to highly restricted molecular vibrations and suppressed nonradiative processes. AIEgen-based scintillators exhibit a high X-ray imaging resolution of 16.3 lp mm-1, making them excellent candidates for X-ray radiography and security inspections. In addition, these AIEgens show a broad -3-dB modulation bandwidth of ∼110 MHz and high net data rates of ∼600 Mb/s, demonstrating their high potential for application in the field of high-speed OWC.
The research on optical wireless communication (OWC) has been going on for more than two decades. Particularly, visible light communication (VLC), as a means of OWC combining communication with illumination, has been regarded as a promising indoor high-speed wireless approach for short-distance access. Recently, lightwave, millimeter-wave (mmWave), terahertz (THz) and other spectrum mediums are considered as potential candidates for beyond fifth-generation/sixth-generation (B5G/6G) mobile communication networks. On the basis of previous studies, this review focuses on revealing how the research of next-generation OWC technology should be carried out to meet the requirements of B5G/6G for practical deployment. The research, development and engineering transformation of the OWC systems are a paragon of interdisciplinary. It involves a wide discussion on how to build a high-speed, multi-user, full-duplex, white-light OWC system based on existing technologies by showing the innovations and trade-offs at various levels with material, device, air-interface technology, system and network architecture. The compatibility of OWC is emphasized and some advanced heterogeneous OWC systems are presented, which involves the combination or integration of various functions such as sensing, near-infrared (NIR) beam-steering, positioning and coexistence with radio frequency (RF) communication. Finally, several potential directions are pointed out for the actual engineering deployment in the B5G/6G era.
Conference Paper
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Zusammenfassung: Durch doppelte Nutzung ermöglichen Weißlicht-LEDs Synergie von Raumbeleuchtung und drahtloser optischer Kommunikation/ Nachrichtenverteilung. Für einen mit LEDs gut ausgeleuchteten mittelgroßen Büroraum wird die erreichbare Datenrate bei Basisband-und DMT-Übertragung ermittelt, wobei der Einsatz handelsüblicher LEDs und Photodioden angenommen wird. Die Resultate zeigen, dass trotz relativ geringer Systembandbreite Bitraten von mehr als 100 Mbit/s zu erwarten sind. Summary: Emergence of white-light LEDs allows synergy of lighting and broadcast/communication function in one optical source. We investigate possible data transmission rates in a moderate-size office room where we assume illumination conforming to standards and the use of commercially available LEDs and photodiodes. The performances of systems relying on base-band and DMT transmission show that data rates of more than 100 Mbit/s can be expected despite the rather low bandwidth of the system.
Conference Paper
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Wireless transmission exceeding 100 Mbit/s is demonstrated using a phosphorescent white-light LED in a lighting-like scenario. The data rate was achieved by detecting the blue part of the optical spectrum and applying discrete multi-tone modulation.
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After a public experiment of the indoor guidance system using FLC (fluorescent light communication), we found that FLC provides a promising medium for the installation of a guidance system for the visually impaired. However, precise self-positioning was not satisfactorily achieved. In this article, we propose a new self-positioning method, one that uses a combination of RFID (Radio-frequency identification), Bluetooth and FLC. We analyzed the situation and developed a model that combined the three communication modes. Then we performed a series of experiments and get some results in the first step.
Conference Paper
Full-text available
Gigabit home access networks (HANs) are a pivotal technology to be developed if the European Union (EU) Vision of the Future Internet is to be realised. Consumers will require such HANs to be simple to install, without any new wires, and easy enough to use so that information services running on the HAN will be ldquojust another utility,rdquo as, for instance, electricity, water and gas are today. The hOME Gigabit Access (OMEGA) HAN project [1] aims at bridging the gap between home and access network, providing Gbit/s connectivity to users. The project considers a combination of various technologies such as radio frequency (RF) and free-space or wireless optical links (FSO - operating at infrared and visible wavelengths) in order to meet user demands and provide wireless connectivity within and the home and its surroundings. When combined with power-line communications this enables a home backbone that meets the ldquowithout new wiresrdquo vision. A technology-independent MAC layer will control this network and provide services as well as connectivity to any number of devices the user wishes to connect to it in any room in a house/apartment, and further, this MAC layer will allow the service to follow the user from device to device. In order to make this vision come true, substantial progress is required in the fields of optical-wireless physical layers, in protocol design, and in system architecture.
Conference Paper
This paper reports an 80 Mbit/s OOK-NRZ visible light communications experimental link using a single pre-equalized 45-MHz bandwidth white LED.
Conference Paper
In this paper, an optical wireless communication system that uses white LEDs is described. Equalization is employed at the receiver to improve the data rate. Simulation shows a highly reliable communication channel with an SNR of up to 81 dB. Moreover, the data rate can be improved from 16 Mb/s to 32 Mb/s NRZ-OOK at a BER of 10<sup>-6</sup>.
Conference Paper
We propose a new positioning system using visible LED lights and image sensor. GPS is widely used, but its measurement error gets dozens meters worse at indoor or urban canyon where radio wave is hard to reach. On the other hand, visible light can reach users easily since visible light devices are established at indoor and urban canyon. Our proposed system can determine the receiver's position where each LED in a lighting sends differential three dimensional space coordinate and image sensor can receive the signal. We show the availability of our proposed method by numerical analysis.
Conference Paper
In this paper, we propose parallel wireless optical communication with an LED traffic light as a transmitter and a high-speed camera as a receiver. Today, it is proposed to use visible light communication for road-to-vehicle communication, which assists drivers by providing various information. It is also proposed to use LED traffic light as its transmitter. Thus in this paper, we propose a road-to-vehicle communication system using a high-speed camera. In our proposing system, we receive data by capturing the transmitter with the high-speed camera, making it possible to recognize each LED separately. We have examined communication speed and conducted experiment of parallel data transmission under laboratory condition.
Conference Paper
We propose a parallel wireless optical communication system for road-to-vehicle communication, which uses a LED traffic light as a transmitter and a high-speed camera as a receiver. The newly proposed system which enables multichanneling in LED two dimension arrangement and spatially dividing them. LED transmitters arranged in the shape of a plane are modulated individually, and a camera is used as a receiver for demodulating the signals by using image processing techniques. We performed examination of the transmission speed according to the proposed system in this paper. The actual proof experiment of the proposed system was conducted under the laboratory conditions. We checked that it communicates with a speed of 2.78kbps while 192 LED are spatially divided into eight groups and the high-speed camera set to 500fps.
White light-emitting diodes (LEDs) are becoming widespread in commercial lighting applications, and there are predictions that they will be in common use in domestic applications in the future. There is also growing interest in using these devices for both illumination and communications. One of the major challenges in visible light communications is the low modulation bandwidth (BW) available from devices, which is typically several megahertz. In this letter, we describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall BW of 25 MHz. This is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.