Optics and Photonics Journal, 2013, 3, 153-157
doi:10.4236/opj.2013.32B037 Published Online June 2013 (http://www.scirp.org/journal/opj)
Real-time Audio & Video Transmission System Based on
Visible Light Communication
Yingjie He, Liwei Ding, Yuxian Gong, Yongjin Wang*
Institute of Communication Technology, Nanjing University of Posts and Telecommunications, Nanjing, China
Email: *wangyj@njupt.edu.com
Received 2013
With the increasing popularity of solid sate lighting devices, Visible Light Communication (VLC) is globally recog-
nized as an advanced and promising technology to realize short-range, high speed as well as large capacity wireless data
transmission. In this paper, we propose a prototype of real-time audio and video broadcast system using inexpensive
commercially available light emitting diode (LED) lamps. Experimental results show that real-time high quality audio
and video with the maximum distance of 3 m can be achieved through proper layout of LED sources and improvement
of concentration effects. Lighting model within room environment is designed and simulated which indicates close rela-
tionship between layou t of light sources and distributio n of illuminance.
Keywords: Visible Light Communications; LED; Real-Time Video and Audio Broadcast System; Light Source
Arrangement; Illuminance Distribution
1. Introduction
Visible Light Communication (VLC) was first proposed
in 2004 by Toshihiki Komine and has progressed rapidly
ever since with the development of solid state light
sources, especially light emitting diodes (LEDs) [1]. The
great popularity of VLC owes largely to the advantages
of LED such as high brightness, low cost, small size, low
power consumption, long lifetime and low heat radiation.
VLC explores the unregulated visible light portion of the
electromagnetic spectrum and acts as a supplement rather
than substitute of established RF systems. With comple-
mentary strengths of both technologies, excess capacity
demands of RF channels can be off-loaded to VLC net-
works, which enable users to seamlessly access to the
Internet while keeping high Qos levels and avoiding net-
work congestions and delays. The con cept of a fulldu plex
multi-access system for LED-based wireless communi-
cations is proposed by Nakagawa laboratories [1]. Sim-
plex and duplex transceiver prototypes have been dem-
onstrated in [2] which also prove the effectiveness of
replacing existing illumination systems with LED light-
ing devices. With 300 THz of bandwidth available for
VLC, multi- gigabit-per-second data rates could be pro-
vided over short distances, for example, using array of
LEDs in a multiple-input multiple-output (MIMO) sys-
tem [3,4]. Besides wireless connectivity in home envi-
ronment, combining the function of illumination and
transmission is also attractive in specific scenarios where
healthy, secured and non-interfered communication is
necessary, such as hospital, underground mine, under-
water, airplane, etc.
In this paper, we develop a VLC prototype with large
increase in transmission distance and improvement in
channel capacity. The optical link which performs as the
substitute of connector wire can be widely applied in
video conference, real-time video frequency monitoring,
smart traffic system and various practical scenarios
where illumination and data transmission is in joint de-
mand to serve modern daily life. MATLAB program is
used to simulate the illuminance distribution for two
practical light source deploy ments.
The rest of the paper is organized as follows: In sec-
tion 2, a prototype of the VLC real-time video/audio
transmission system is presented. The experimental result
is shown and analyzed in section 3. Section 4 illustrates
the correlation between light source layout and illumi-
nance distribution based on MATLAB simulation within
a model room. Finally, Section 5 concludes the article.
2. VLC System Description
Figure 1 shows the block diagram of the real-time video
and audio broadcast system, which consists of a VLC
wireless LOS link with two optical channels.
VLC is free space optical communication, and line of
sight (LOS) is the common link between two points in
optical wireless communication system, where the trans-
*Corresponding author.
Copyright © 2013 SciRes. OPJ
mitter directs the visible light beam in a straight and un-
obstructed path to the receiver [5]. Intensity modulation
and direct detection are adopted by the prototype for data
transmission. The system is constructed as Figure 2. The
light emitter is a simple, off-the shelf LED obtained from
Cree (XLamp MX-6) which provides a luminous flux of
107 lm at the current of 350 mA. A Reflection cup is
mounted on each LED for the purpose of gaining light
that is more parallel and concentrated. Video and audio
signal captured by video camera are amplified by a
self-designed amplifier and then superimposed onto two
LED lamps respectively by the aid of a bias-T circuit.
Thus, the output light rays changes in intensity corre-
sponding to the variation in signal, which however is
insensitive to human eyes due to the rapid frequency re-
sponse of LED devices. The distance between two LEDs
was about 10 cm in order to avoid mutual interference
caused by light sources. The transmitter circuit is given
in Figure 3. At the receiver, two highly sensitive Si PIN
photodiodes (Hamamtsu S6968) are used to detect light
transmitted over two separate optical channels. And the
directionality of the PDs is required to be aligned with
the most intense portion of the emitted light beams. After
detection, optical signals are converted into photo elec-
tric current proportional to the variation of incident light
which then is amplified and filtered by a low pass filter
(LPF). The receiver circuit is shown in Figure 4. An
audio and video capture module with USB interface is
designed to convert the received analog signal into digi-
tal signal [6]. Finally, the video and audio are played real
time on the screen of a video editor for further processing
such as simple cutting, filtering or storing. In the proto-
type, transmission distance of nearly 2 m can be achieved
without an y ligh t fo cu s ing mea s u res an d c an be in cr ea s ed
to 3 m with a focusing lens inserted between the trans-
mitter and receiver.
3. Results and Analysis
To test the system performance, we have transmitted a
video signal captured by a video camera. Video and au-
dio signals were extracted from the AV output port of the
camera. Through optical transmission , high quality video
and audio were recovered and played on the laptop
screen by the aid of self-designed ADC module with USB
2.0 interface. High-speed rendering, wireless transmis-
sion and real time performance mean less time waiting
and more time creating. Figure 5 shows the waveforms
of video signal before and after transmission over the
optical channel. And the picture shown in Figure 6
Figure 1. Block diagram of real-time video/audio VLC transmission system.
Figure 2. Picture of the real-time video/audio transmission
prototype using LEDs.
Figure 3. Transmitter circuit.
Copyright © 2013 SciRes. OPJ
Y. J. HE ET AL. 155
Figure 4. Receiver circuit.
Figure 5. Experimental test of VLC prototype, received signal
at the distance of 2 m, emitted (up) and received signal
Figure 6. Comparison between original image and received
clearly indicates that signal transmitted by optical channel
can be recovered real time at 2 m without lens through
the air in the laboratory. Some distortions still exist com-
paring the original to the received image which maybe
results from the process of photoelectric conversion, sig-
nal amplification or the introduction of background noise.
To improve the system performance, analog signal from
web camera should be converted into digital signal be-
fore optical wireless transmission.
4. Modeling and Designing of an Indoor
VLC System
The final objective of VLC development is the applica-
tion of off-the-shelf LEDs in home environment wireless
network to satisfy the need s of both illuminatio n and data
transmission. The prototype presented above with single
LED replaced by LED arrays, is capable of supporting
lighting, data broadcast as well as monitoring. In the pa-
per, we modeled a room with the size of 5*5*3 (m). To
study the illuminance distribution of LED system in
practical scenarios, two types of light source arrange-
ments located on the ceiling were simulated and dis-
cussed as shown in Figure 7. The coordinate positions of
LED arrays for square and round deployments are
(1.05:0.1:1.55, 1.05:0.1:1.55, 3) and (2.5+r*cos((0:1:17+
0.5)*pi/36), 2.5-r*sin((i+0.5)*pi/36), 3respectively.
Here, 1.05:0.1:1.55 indicates that the value on coordi-
nates increases with the step size of 0.1 m, and 0:1:17
means that the step size is assumed to be 1 m. The value
of i is 1:1:18 and the radius are set to be R1=2.15 m and
R2=2.35 m. Assuming that radiation of LEDs conforms
to the Lambertian pattern and light reflection s on the wall
are not considered. The horizontal light illuminance at
the point (x, y, z) is given by
(0)cos( )
(,,) cos( )
Exyz D
where, (0)
is the center luminous intensity of LEDs,
is the angle of irradiance,
is angle of incidence,
D is the distance between the LED transmitter and the
receiver, and m is the order of Lambertian emission
given by
ln 2 / ln(cos)m
where, 1/2
is the semi-angle at half power [7,8]. MAT-
LAB simulation specifications are depicted in Table 1 .
The simulation of illuminance distribution for two dif-
ferent light source arrangements is shown in Figure 8.
Th e mi n i mu m a n d ma x i mum v a l u es fo r th e s q u ar e la y ou t
are 310.59 lx and 823.42 lx respectively. Figure 8(b)
Figure 7. Square array (Left) & Round array (right).
Copyright © 2013 SciRes. OPJ
Table 1. Parameters for MATLAB simulation.
Parameters Values(square) Values(round)
Room size 5*5*3(m) 5*5*3(m)
Number of LED arrays 4*36 4*36
Semi-angle at half power 45º 45º
Luminous intensity 10(cd) 10(cd)
Distance between LEDs 10(cm) 20(cm)
Distribution of illuminance
Distri bu t i o n of il l um i nan c e
Figure 8. Illuminance distribut ion with the LED semi-angle
of 45 degree (a) Illuminance distribution for 4x4 square
deployment (b) Illuminance distribution for round deploy-
gives the simulation results for round deployment with
the maximum value of 321.79 lx and minimum value of
592.92 lx. Considering that the lighting illumination re-
quirements of the International Organization for Stan-
dardization is from 300lx to 1500 lx [7], the two ar-
rangements of light sources proposed here can meet the
joint demands of illumination and communication based
on the simulation results. Furthermore, illuminance for
round LED arrangement is more evenly distributed than
that of the square arrangement judging from the simula-
tion diagram, so that lighting effects for round deploy-
ment should be better in this case.
5. Conclusions
In this paper, we proposed a real-time video and audio
broadcast prototype using commercial LED lamps. Sys-
tem design is illustrated in detail and experimental results
are presented. It is shown that transmission of high qual-
ity video/audio images with the distance of 3 m can be
achieved and improvements can be made by adding fo-
cusing lens between the transmitter and the receiver. Al-
though distortions still exist comparing images before
and after transmission, it demonstrates that high quality
wireless optical transmission using LED is successful.
Illuminance distribution is simulated and compared for
two light sources arrangements in a model room. Future
work will concentrate on real-time digital video/audio
transmission and communication link that can be con-
nected to a TCP/IP network [9].
6. Acknowledgements
This work is jointly supported by NSFC (11104147),
Jiangsu 973 project (Bk2011027), and research project
(NY211001, BJ211026) .
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