Content uploaded by Wenbo Ding
Author content
All content in this area was uploaded by Wenbo Ding on Mar 11, 2015
Content may be subject to copyright.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
IEEE TRANSACTIONS ON BROADCASTING 1
An Indoor Broadband Broadcasting System
Based on PLC and VLC
Jian Song, Senior Member, IEEE, Wenbo Ding, Fang Yang, Senior Member, IEEE, Hui Yang,
Bingyan Yu, and Hongming Zhang
Abstract—Visible light communication (VLC) using the
light-emitting diode (LED) will become an appealing alter-
native to the radio frequency communication technology for
indoor wireless broadband broadcasting. However, the LED
lamps should access to the backbone information network and
this requirement is not easily satisfied. Power line communica-
tion (PLC) systems utilize the ubiquitous power line network
to power the LED lamps while serving as the backbone net-
work for the VLC systems naturally. In this paper, we propose a
novel and cost-effective indoor broadband broadcasting system
based on the deep integration of PLC and VLC. The pro-
posed scheme significantly reduces the complexity of the VLC
network protocol, and requires much less modification to the
current infrastructure, while providing better signal coverage. A
two-lamp network demo is implemented and the performance
evaluation for the proposed scheme is carried out in the labora-
tory. The proposed scheme is an appealing solution for the indoor
family broadcasting, and could be well extended to the scenarios
including the hospitals, shopping malls, stadiums, music halls,
and etc.
Index Terms—Visible light communication (VLC), power line
communication (PLC), indoor broadband broadcasting system,
single frequency network (SFN).
I. INTRODUCTION
WITH the increasing demands for the indoor
broadband multimedia wireless broadcasting
services [1], [2], the current radio frequency (RF) based
solutions, such as Wi-Fi [3], digital television terrestrial
broadcasting (DTTB) [4], etc., have to deal with the serious
spectral overcrowding issues, especially in the giant shop-
ping mall or dense residential buildings. In this context,
visible light communications (VLC) [5], which utilize the
illuminating light-emitting diode (LED) for broadband trans-
mission, offers a huge and unlicensed bandwidth to cope with
Manuscript received December 4, 2014; revised January 14, 2015; accepted
January 14, 2015. This work was supported by the National Natural Science
Foundation of China under Grant 61401248 and Grant 61471219.
J. Song and F. Yang are with the Department of Electronic Engineering
as well as Research Institute of Information Technology, Tsinghua National
Laboratory of Information Science and Technology, Tsinghua University,
Beijing 100084, China, and also with Guangdong Province as well as
Shenzhen City Key Laboratory of Digital TV System, Shenzhen 518057,
China (e-mail: jsong@tsinghua.edu.cn).
W. Ding, H. Yang, B. Yu, and H. Zhang are with the Department
of Electronic Engineering, Research Institute of Information Technology,
Tsinghua National Laboratory of Information Science and Technology,
Tsinghua University, Beijing 100084, China.
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TBC.2015.2400825
crowded radio spectrum for highly-localized communication
systems [6]–[8]. Besides, the VLC technology has many other
attractive features, such as worldwide availability, radiation-
free, high-capacity, and etc., and hence is considered as an
appealing alternative of RF technology for indoor multimedia
coverage [9], [10].
However, VLC must access the backbone network in case
of being the so-called “information isolated island” [11]to
realize the communication purpose. The conventional and
intuitive network access solution for VLC is connecting
the LED lamps to the modem via network cables, which
requires large modification of the indoor layout and is not
cost-effective [12]. The integration of VLC and power line
communications (PLC) comes from the observation that all
the LED lamps are connected to the power line and the
power line can naturally act as the backbone for VLC while
powering the LED lamp. In this way, it will save the addi-
tional cables and be easier to be installed [13]. The first PLC
and VLC integration prototype was proposed in 2003 [14],
using single carrier binary phase shift keying (SC-BPSK)
modulation to provide a low rate transmission. Then orthog-
onal frequency division multiplexing (OFDM) is applied
in the hybrid PLC and VLC system to combat the fad-
ing channel and achieve higher spectral efficiency [15], [16].
However, in the field of PLC and VLC integrated tech-
niques for indoor broadcasting, there are still some challenges,
such as 1) How to design the structure of the integration
network to reduce the layout modification as well as the
network protocol complexity; 2) All the demos still remain
in the point-to-point and off-line communication system [7]
and there are no implementation reports of a feasible indoor
broadcasting system based on PLC and VLC with OFDM
techniques; 3) Some technical details including the chan-
nel modeling, coded modulation, frequency band segment,
network protocol and so on, are needed to be chosen and
verified.
In this paper, we propose a novel and cost-effective indoor
broadband broadcasting system based on the deep integration
of PLC and VLC to mainly address those issues listed above, a
two-lamp network demo is implemented and the performance
evaluation is carried out in the laboratory. The contributions
of this paper can be specified as follows.
1) A deeply integrated PLC and VLC system is proposed in
this paper for efficient indoor broadband broadcasting, where
the signal in the power line is amplified and forwarded to
the LED without decoding and all the LED lamps in one
0018-9316 c
2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
2IEEE TRANSACTIONS ON BROADCASTING
group transmit the same signal. In this way, the broadcasting
network could be homogeneous and characterized as a single
frequency network (SFN), which avoids complicated net-
work switching for the devices roaming between different
LED lamps.
2) A prototype integrated PLC and VLC system with
two LED lamps with aggregating payload data rate over
48 Mbps data rate within 8 MHz bandwidth is implemented
in the laboratory. The length of the power line part is
200 meters and the communication distance of visible light
part is 3 meters with the power of the white LED being 1 W
(in our point-to-point system, the maximum communication
distance of visible light part is 8 meters with the same power),
of which the performance is the best ever in the reported
implementations.
3) Experiments are carried out on the demo to evaluate the
performance of the proposed system. It can be found that in
the proposed system, the channel of the whole communication
link can be modeled as multi-path and thus good perfor-
mance can be achieved through matured channel estimation
and equalization techniques.
The rest of the paper is organized as follows. The pro-
posed broadcasting system model is introduced in Section II
together with the two classical and intuitive models. Section III
details the theoretical analysis, and Section IV investigates the
demo implementation and performance evaluation. The pos-
sible features and applications of the proposed system, the
open issues together with the future work are described in
Sections V and VI, respectively. Finally, the conclusions are
drawn in Section VII.
II. SYSTEM MODEL
Fig. 1generally reviews the system models of the differ-
ent indoor broadcasting schemes based on PLC and VLC.
AsshowninFig.1(a), in the classical scheme (denoted as
Scheme A), the network cable sends the information to the
LED lamps so that they can act as access points (APs) [12],
which is quite intuitive. However, this scheme requires large
modifications to the indoor cable layout and the specific LED
drivers as well as modems must be added to couple the signal
from communication cables to the LED, which is complicated
and not cost-effective at all.
With the development of PLC technologies, researchers start
considering the integration of PLC and VLC for indoor signal
coverage, since power line can naturally act as the backbone
for VLC while powering the LED lamp. In this way, the mod-
ifications of the indoor cable layout could be avoided as much
as possible, which is more suitable to the existing buildings,
particularly, the historic buildings. As illustrated in Fig. 1(b),
one possible scheme (denoted as Scheme B) is using the PLC
modem to couple the data from the Ethernet to the power
line [13]. As shown in Fig. 2, the PLC modem integrated with
the decoding and forwarding (DAF) unit is added on each
LED lamp to obtain the needed data from the data bus, i.e.,
the power line, while the “PLC to VLC” module is equipped
to modulate the signal to the light. Hereby, the transmitted
signal from different LED lamps could be different according
Fig. 1. System models of the different indoor broadcasting schemes based
on PLC and VLC. (a) Classical VLC-based broadcasting scheme (Scheme A).
(b) Classical PLC and VLC-based broadcasting scheme (Scheme B).
(c) Proposed deeply integrated PLC and VLC system for indoor broadcasting.
to the request of the devices. Both Schemes A and B directly
adopt the framework for networking from the idea of the con-
ventional RF based wireless communications, which is quite
straightforward but may not well suit for the VLC application
scenarios. Since the visible light signal usually has much less
coverage compared to the RF signal, the LED APs should be
placed much intensively than the conventional wireless APs.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
SONG et al.: INDOOR BROADBAND BROADCASTING SYSTEM BASED ON PLC AND VLC 3
Fig. 2. Block diagram of “PLC to VLC” module.
Then such architectures will lead to the significant increase of
the number of the modems added to the LED APs, which is not
cost-effective at all. Moreover, there is another drawback for
the two schemes, that the devices roaming between different
LED lamps have to switch the APs frequently, and hence the
corresponding protocol will be very complicated which will
increase the power consumption of the devices and reduce the
quality of service during switching [17].
In this paper, we proposed one deeply integrated1PLC and
VLC system for efficient indoor broadcasting, as shown in
Fig. 1(c). In the proposed scheme, the signal is first obtained
from the Ethernet and then coupled to the power line by
the PLC modem. Only a “PLC to VLC” module excluding
the modem will be added to the LED illumination fixture to
receive the coupled signal from the power line, which is the
same as that in Scheme B. After signal amplification, this mod-
ule adds the data signal to the direct current (DC) bias of LED
in order to drive the LED lamps and acts as an optical transmit-
ter to cover the indoor area. All the LED lamps connected to
the same power adapter share one common PLC modem which
acts as the base station (BS) and hence transmit the same
data. In this way, the broadcasting network could be homoge-
neous and simplified as an SFN [18], [19], which could well
solve the problem mentioned above. For the LED lamps con-
nected to different power adapters, the transmitted signal could
be different for various services and larger network signal
transmission rates. It could be seen from Fig. 1that the pro-
posed scheme has significantly simplified the complexity of
the whole network and required much less modification to the
current infrastructure. Moreover, since the modem is saved,
the size of the “PLC to VLC” module can be minimized so
that it can be easily installed to the LED lamp and then turn
it to an AP immediately, which will be very effective in both
cost and signal coverage.
The feature comparison of the three different schemes is
also summarized and provide in Table Ifor brief illustration.
III. THEORETICAL ANALYSIS
In this section, we will investigate the channel model of
the proposed indoor broadcasting system integrated PLC and
VLC as well as the noise and interference. In addition, we
will also discuss the modulation scheme and SFN for VLC in
such scenario.
1Here “deep integration” or “deeply integrated” means that the modem
added to each LED AP is removed and only a “PLC to VLC” module is used
so that the baseband signal carried by both PLC and VLC is the same.
TAB LE I
COMPARISON AMONG THE DIFFERENT SCHEMES1
A. Channel Model
The channel model of our proposed scheme is the cascade of
the PLC and VLC parts together with the LED lamp equivalent
channel. The channel model of the PLC part can be usually
represented by [20]
HPLC(f)=
L
l=1
gle−α0+α1fkτlvp·e−j2πfτl(1)
where gldenotes the weighting factor of the l-th path which
consists the reflection and transmission factors along this path,
α0and α1are the attenuation parameters, kis the exponent
of the attenuation factor (usual values between 0.2 and 1),
vpis the group velocity and τlis the delay of l-th path, and
Lrepresents the number of the paths, respectively.
The channel model of the VLC part consists of a line-
of-sight (LOS) component and a diffuse or non-line-of-sight
(NLOS) component, which can be written as [9]
HVLC(f)=ηLOSe−j2πftLOS +ηDIFF e−j2πftDIFF
1+jf/fC(2)
where ηLOS,ηDIFF,tLOS and tDIFF are the gains and delays
of the LOS and diffuse signals, respectively. fCis the 3-dB cut-
off frequency of a purely diffuse channel. Hereby, the LOS and
NLOS gains are given by [21]
ηLOS =AR(r+1)cosrφcos ϕ/ 2πd2(3)
ηDIFF =ARρ/(AROOM(1−ρ)) (4)
where ARand AROOM are the effective receiver area and the
room area, respectively. ρis the average reflectivity from the
walls. φand ϕdenote the angles of irradiance and incidence,
while dis the distance between the LED lamp and the receiver.
The Lambert index rdepends on the half-intensity beam angle
θ1/2,as
r=−1/log2θ1/2.(5)
Moreover, for VLC systems, the white light is usually gen-
erated by a device that uses a blue LED for exciting a yellow
phosphor coating. Then, the yellow and blue lights jointly cre-
ate the white illumination. This approach has the advantage
of requiring only a single electrically driven source, which is
simple and cheap. However, the yellow phosphor has a long
decaying time, resulting in that the modulation bandwidth of
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
4IEEE TRANSACTIONS ON BROADCASTING
the LED lamp is constraint to several megahertz. An efficient
way to achieve a higher effective bandwidth and higher data
rates is to detect only the blue component of the emission
with a blue filtering before the receiver, which could expand
the bandwidth to dozens of megahertz [10]. In this way, the
low-pass impact of the LED lamp could be ignored.
Considering the network structure, the channel model for a
certain receiver is the superposed effects of all the LED lamps
and given by,
H(f)=
NLED
i=1
Hi,PLC(f)Hi,VLC(f)(6)
where Hi,PLC(f)and Hi,VLC(f)represent the PLC channel
between the PLC modulator and the i-th LED lamp, and the
VLC channel between the i-th LED lamp and the receiver,
respectively. NLED denotes the number of the LED lamps that
the receiver can detect.
B. Noise and Interference
A lot of investigations and measurements were achieved in
order to give a detailed description of the noise characteristics
in a PLC or VLC environment. In the integrated PLC and VLC
systems, the noise could be described as a superposition of
four noise types listed below, which are distinguished by their
sources, time duration, spectrum occupancy, and intensity.
1) Colored background noise [22] is the sum total of various
noise sources with low power and varying with frequency.
Its power spectral density (PSD) varies over time in terms of
minutes or even hours.
2) Narrowband noise [23], [24] is caused by induction from
radio station signals in medium and/or short wave bands. It can
be modeled by the sum of several sinusoidal signals and its
level is generally varying with daytime.
3) Impulsive noise [22], [25] is caused by transients due
to switching or lightning phenomena within the power net-
work. The impulses have durations of some microseconds up
to a few milliseconds with random occurrence. The PSD of
impulsive noise can reach values of more than 50 dB above the
background noise. The common statistical model for impulsive
noise is the Middleton’s Class A model with the parameters
of the overlapping factor Aand the background-to-impulsive-
noise power ratio [23]. Hence, the probability distribution
function of the noise amplitude p(n)is given by
p(n)=
∞
m=0
e−AAm
m!
1
2πσ2
m
e−n2
2σ2
m,(7)
σ2
m=mA+
1+.(8)
Moreover, the occurrence of the impulsive noise has approx-
imately a Poisson distribution.
4) Optical background noise [26] arises from sunlight,
skylight, incandescent and fluorescent lamps, or other light
sources. In practice, the optical background noise could be
modeled as additive white Gaussian noise (AWGN).
C. Modulation
Since the optical signal is unipolar, any bipolar scheme
requires the source to be biased with the aid of a DC offset
for the VLC. Consequently, in the previous research, simple
modulation schemes such as on-off keying (OOK) and pulse
position modulation (PPM) [27] have been extensively adopted
for VLC. However, such unipolar modulation schemes suf-
fer from lower spectral efficiency and hence the technique
of OFDM with more spectrum-efficient quadrature amplitude
modulation (QAM) has been applied in VLC to achieve higher
data rates [28].
Considering the fact that OFDM has been widely deployed
in the PLC standards and systems to achieve data rates up to
gigabits, the OFDM with QAMs are adopted as an appealing
modulation solution for the proposed integrated system.
D. Single Frequency Network
In our proposed scheme, the transmitters (LEDs) send the
same signal on the same frequency band (the light color),
which forms a natural SFN [18], [19], [29]. SFN has been
widely employed to improve the spectral efficiency and pro-
vide reliable as well as robust coverage for DTTB services.
Moreover, since the coverage area of each LED lamp is lim-
ited, the SFN-like structure could avoid the frequent network
switching for the mobile device when roaming under different
lamps. The only drawback of SFN structure is that there are
severe multipath effects as shown in (6) and thus results in the
frequency-selective fading and inter-symbol interference (ISI).
Fortunately, this problem could be well solved by the utiliza-
tion of OFDM, which divides the wideband signal into many
narrowband sub-carriers so that each sub-carrier would expe-
rience a flat fading channel individually. Furthermore, due to
the good spatial directivity of the visible light, such multipath
effects will only occur in the overlapping areas.
IV. DEMONSTRATION IMPLEMENTATION
AND EVALU AT ION
A. Demonstration Setup
In the laboratorial environment, a demonstration is built
and its feasibility is shown through experiments, as shown
in Fig. 3. The video data is encoded, modulated and coupled
to the power line in the PLC modulator. In the “PLC to VLC”
module, the signal is added to the DC offset to drive the LED
lamp, which is the key component of the integrated system.
The signal are detected in the avalanche photo diode (APD),
then demodulated and decoded at the receiver. To evaluate the
interference of the LED lamps, we use two LED lamps to
construct a simplest SFN, as described in Fig. 4.
This composition of whole system is quite simple and does
not require new installation of communication wiring. After
the basic communication modules of the system, such as
PLC modulator, “PLC to VLC” module, and the receiver,
being plugged in, the system will start to work without too
much modification of the existing infrastructures. In fact,
such modules can be small enough to be easily installed for
commercializing. From implementing the system in real-life,
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
SONG et al.: INDOOR BROADBAND BROADCASTING SYSTEM BASED ON PLC AND VLC 5
Fig. 3. Demonstration setup of the broadcasting system in the laboratorial
environment.
Fig. 4. Block diagram of the laboratorial demonstration.
Fig. 5. (a) LED lamp. (b) PLC to VLC module.
we learned that some key parameters, such as the system
operating point, the modulation depth, and the sensitivity of
the optical detector, etc., should be rationally chosen, while the
key parameters are listed in Table II for illustration. All the
hardware except the optical detector is designed by us, as
shown in Figs. 5–7.
B. Performance Evaluation
The high-definition TV program is modulated by the time
domain OFDM (TDS-OFDM), and then transmitted in the
hybrid system to evaluate its performance. We use the mode
(64QAM, Multi-carrier, PN420, FEC 0.6, TI 720) [30]forthe
first-step demo.
The system bandwidth is 8 MHz located from
2 MHz to 10 MHz. The point to point system (with one
LED lamp on) can still work well with the visible light path
Fig. 6. PLC modulator.
Fig. 7. Demodulator in the receiver.
TAB LE I I
DEMONSTRATION CONFIGURATIONS
up to 8 meters with the interference from the normal indoor
lighting devices and provide a date rate of around 48 Mbps
within 8MHz bandwidth.
For the two LED lamps, LED A is connected directly to the
PLC modulator and LED B is connected to the modulator via
a section of power line. Since 3 m is the typical height of the
ceilings in many indoor scenarios, the receiver which contains
the APD is placed with an equal distance of 3 meters away
from the two LED lamps to imitate the case that the receiver is
located in the overlapping area or roaming between different
LED lamps. In order to evaluate the system performance under
different multipath propagations, the length of power line con-
nected to the LED B and the power of the transmitted signal
from LED B are set to different values, while the power of the
transmitted signal from LED A is fixed in our demonstration
configurations. The evaluation configurations are provides in
Table III.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
6IEEE TRANSACTIONS ON BROADCASTING
TABLE III
EVALUATI ON CONFIGURATIONS
Fig. 8. Spectrum of the receive signal when LED B is switched off.
Fig. 9. Spectrum of the receive signal when the power of the transmitted
signal from LED B is equal to that from LED A (Case 1).
We also measured the spectrum of the received signal
as well as the multipath channel of the whole system, as
shown in Fig. 8–10. Due to the constraint of the paper
length, we only provide the screenshots of the measure-
ment for Case 1. It can be seen from Fig. 9and 10
in our proposed scheme, the multipath effect will cause
channel frequency selectivity. Fortunately, compared to the
complex network structure and the corresponding switch-
ing or handover protocols, such drawback can be perfectly
solved via the mature channel estimation and equalization
techniques [31]–[33].
Furthermore, the modulation error ratio (MER), a com-
monly used parameter to quantify the communication link
Fig. 10. Measurement of the multipath channel of the whole system in
Case 1.
TAB LE I V
MEASURED MERS
Fig. 11. Measured constellation diagram of the received signals for the
64QAM mode in Case 1.
quality is used to evaluate the demo, which is defined as [34]
MER =10log10 Ij−ˆ
Ij2+Qj−ˆ
Qj2
ˆ
I2
j+ˆ
Q2
j(9)
where Ijand Qjare the real and imaginary components of
the ideal j-th symbol, respectively, and ˆ
Ijand ˆ
Qjare the com-
ponents of the received j-th symbol, respectively. The MER
represents the signal-to-ratio quality per symbol and higher
MER ensure the probability of successful demodulation for
the system. As shown in Table IV, we could find that the MER
is proportional to the power line length and inversely propor-
tional to the power of the transmitted signal from LED B.
It can be explained by that the interference will be less as the
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
SONG et al.: INDOOR BROADBAND BROADCASTING SYSTEM BASED ON PLC AND VLC 7
delay of the secondary path becomes larger or the power of
it reduces. The constellation diagrams of the received signals
are measured for the 64QAM mode, and we only provide the
diagram for case 1 for brief illustration, as shown in Fig. 11.
V. FEATURES OF THE PROPOSED SYSTEM
The integrated system for indoor broadcasting inherits the
advantages of both the PLC and VLC systems, and meanwhile
overcomes some of their shortcomings, such as the difficulty
for mobile coverage in PLC and the “information isolated
island” for VLC. The features of the integrated system can
be summarized as follows.
1) Locatable: The system can be used for indoor positioning
due to the excellent directionality of the light and the ubiq-
uity of the LEDs with PLC backbone. Based on the lately
VLC techniques, this system can also provide many useful
indoor location-based services, including indoor navigation
and device tracking [35]–[37]. Moreover, due to the radiation-
free features, the proposed system is particularly suitable for
the indoor hospital applications where the electro-magnetic
radiation of the communication systems should be as less as
possible.
2) High-Capacity: The integrated system inherits the high-
capacity feature or the ability to support many users simul-
taneously from VLC system, which is mainly guaranteed
by the following three aspects: Broader available bandwidth
which is much more than that of the traditional RF band
(Wi-Fi or 3G/4G); Wavelength division multiplexing (WDM)
which could support different users with different colors of
red, green and blue; Space division multiple access (SDMA)
which could create parallel spatial pipes by differing spatial
locations of the users and hence improve the capacity [38].
Meanwhile, the recent PLC techniques with the data rate up
to 1Gbps [39] make it possible to increase the data rate of
the whole integrated system to a considerable level. Hence,
the proposed system is very suitable for the indoor shopping
malls, stadiums, and music halls, where the users are very
crowded.
3) Easy to Install and Low Cost: For VLC, the integration
with PLC is much easier and more natural than with other
communication and power supply systems. It can utilize the
ubiquitous power line to back up the VLC by adding a small
module, which couples the signal from PLC and adds it to the
bias current of LED. In this way, the costs on the additional
communication lines can be saved and meanwhile the instal-
lation can be very easy by adding such module to the LED
adapter without any changes to the facilities.
4) Data Security: The light waves cannot pass through
walls, preventing others from snooping and ensuring the user
privacy. Meanwhile, the encryption methods adopted in the tra-
ditional communication systems can also be directly applied
to the integrated system for enhanced security.
VI. OPEN ISSUES AND FUTURE WORK
In this section, we detail some of the promising research
areas. These are by no means exhaustive, but outline some
important areas where some future work is required.
A. MU-MIMO System
In our previous work [8], LED arrays have been utilized
to support higher data rates and more reliable signal cov-
erage. In fact, multiple LEDs can be exploited to support
multiple users with the aid of multiple input multiple output
(MIMO) architectures [6], [40]. This design philosophy is par-
ticularly promising, since large arrays of sources/transmitters
are relatively straightforward to fabricate and install. Similarly,
receiver arrays constituted by hundreds of detectors become
feasible in the interest of constructing massive multiple user
MIMO (MU-MIMO) systems. By utilizing the lately proposed
bit division multiplexing (BDM) [41], the capacity region
for the down-link communication of multiple users can be
approached. In this way, the system throughput will signifi-
cantly increase to fulfill the explosive demands for real-time
broadband communications.
B. Cooperative Optical Communications
Since the predominantly LOS VLC systems exhibit a poor
performance in the presence of obstructing objects, it is of
great importance to develop cooperative techniques, which
are capable of circumventing the problems imposed by LOS
propagation. The widespread use of Wi-Fi and mobile broad-
band services means that future VLC systems will coexist
with established RF communications. How best to use these
systems cooperatively is still a relatively open research ques-
tion. The use of VLC hotspots providing very high data-rate
connections, combined with RF coverage for reliability, is
attractive. In the case of VLC, the ability to visually see the
hotspots and move toward them is a further advantage. The
analysis disseminated in [42] shows that there is advantage
even if only an optical “downlink” is available, which indicates
the potential promise of the technique.
C. Access Strategy for the Optical Terminals
In the integrated broadcasting network, the optical terminals
are usually uncertain about the network state when making
decisions. For example, when choosing a VLC hotspot, the
optical terminals may not know exactly the reliability and
effectiveness of each LED lamp. Besides, the optical termi-
nals have to consider subsequent others decisions to avoid
increasing the waiting time and the blocking rate. Recently, the
Game theory has been introduced into the field to optimize the
network protocol and provide the access strategy from the per-
spective of the users [43]. More research work including the
modeling, strategy designing, and so on, is needed to be done.
D. Channel Coding for the Integrated PLC and VLC
Channel
For indoor VLC and the integrated system, there has been
relatively little work on channel coding, since their design has
usually followed optical fiber practices, where the informa-
tion typically remained uncoded [44]. Nonetheless, recently,
forward error correction (FEC) coding has been introduced
in VLC and the integrated system, combined with OFDM
modulation schemes [45]. The channel of the hybrid sys-
tem is intuitively time-variant due to the volatility of the
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
8IEEE TRANSACTIONS ON BROADCASTING
Fig. 12. Frequency allocation plan for PLC and VLC integration system.
PLC part and the presence of obstructing objects in the VLC
part. Hence, a punctured LDPC and a raptor code adaptively
controlled by the transmission rate which accommodates the
near-instantaneously fluctuating channel conditions with the
aid of a feedback channel need to be investigated.
E. Regulations of the Frequency Band
Although VLC offers wider bandwidth compared to the RF
solutions, it is still of great necessity to set up some regula-
tions for the segments of the visible light band when integrated
with PLC to avoid the communication conflicts and interfer-
ence, just like the RF band regulations [46]. The regulations
should consider the reservation for up-link communications,
narrowband services, broadband services, the localization ser-
vices, the emergency communications for security or alerting
notification, and so on. One possible frequency allocation plan
is given in Fig. 12, whereby the frequencies below 500 kHz are
reserved for the automatic message recording (AMR) based on
PLC [47], the frequencies from 500 kHz to 2 MHz are used
for narrowband communication, localization, and emergency
communication services, while the frequencies above 2 MHz
are used for broadband services and up-link communications.
F. F uture Work
Our next step for the demonstration is to try higher
order constellation mapping and wider band occupation to
fully utilize the system potential. We have implemented
the off-line VLC system with a data rate of 481Mbps in
a 100 MHz bandwidth [7] and are working on the real-
time integrated system with a date rate of 192 Mbps in a
24 MHz bandwidth. At the same time, some efficient tech-
niques, such as the Gray amplitude phase shift keying (APSK)
constellation [48], the appropriate channel coding, MIMO and
the relays [13], [49], [50], will be adopted as the system
options to enhance the robustness and throughputs of the sys-
tem and satisfy different quality of services. Moreover, we
will investigate the handover or switching protocols discussed
in Section II. The prototypes integrated with the simplified
network and access protocol will be implemented as well.
Meanwhile, as shown in Fig. 13, we have implemented a
laboratory demo with an Android APP for indoor localiza-
tion and communication based on VLC and also started the
implementation of a lower data rate (up to several kbps) com-
munication system by utilizing the commercial camera of the
mobile phones with the interface permissions from the mobile
phone manufacturers. Considering the needs that the inte-
grated system can still work during day-time, some techniques
to ensure the communication performance under illuminance
constraints and various dimming constraints should be inves-
tigated. Such work could speed the commercialization of our
proposed systems and prototypes.
Fig. 13. Demo and Android APP for indoor localization based on VLC.
(a) Demo. (b) Receiver (back). (c) Receiver (front). (d) Signal detection in
the Android APP. (e) Map localization in the Android APP.
VII. CONCLUSION
In this paper, we propose a novel, feasible, and cost-effective
indoor broadband broadcasting system based on the deep
integration of PLC and VLC. The proposed scheme could
significantly simplify the complexity of the VLC network
protocol and require much less modification to the current
infrastructure, which is very efficient in both cost and signal
coverage. We have implemented a two-lamp network demo
and carry out the performance evaluation for the proposed
scheme based on this demo. The proposed scheme inherits
the advantages of both VLC and PLC systems and make them
complementary to each other, which is an appealing solution
for the indoor broadcasting and “data-push”. Moreover, by
exploiting the lately techniques, such as MIMO, BDM, Game
theory, channel coding and so on, high capacity region can be
approached in this scheme, and hence it could be well extended
to the user-crowded scenarios, for examples, the hospitals,
shopping malls, stadiums, music halls, and etc.
REFERENCES
[1] Y. Wu, S. Hirakawa, U. H. Reimers, and J. Whitaker, “Overview of
digital television development worldwide,” Proc. IEEE, vol. 94, no. 1,
pp. 8–21, Jan. 2006.
[2] Cisco Visual Networking Index: Forecast and Methodology, 2010–2015,
Cisco Syst., San Jose, CA, USA, Jun. 2011.
[3] F. Adachi and E. Kudoh, “New direction of broadband wireless
technology,” Wireless Commun. Mobile Commun., vol. 7, no. 8,
pp. 969–983, Oct. 2007.
[4] C. Ong, J. Song, C. Pan, and Y. Li, “Technology and standards of digital
television terrestrial multimedia broadcasting,” IEEE Commun. Mag.,
vol. 48, no. 5, pp. 119–127, May 2010.
[5] IEEE Standard for Local and Metropolitan Area Networks-Part 15.7:
Short-Range Wireless Optical Communication Using Visible Light,
IEEE Standard 802.15.7, Dec. 2011.
[6] D. O’Brien, “Visible light communications: Challenges and potential,”
in Proc. IEEE Photon. Conf., Arlington, VA, USA, 2011, pp. 365–366.
[7] B. Yu, H. Zhang, and H. Dong, “Optimized 481 Mb/s visible light com-
munication system using phosphorescent white LED,” Chin. Opt. Lett.,
vol. 12, no. 11, p. 110606, Nov. 2014.
[8] H. Dong, H. Zhang, K. Lang, B. Yu, and M. Yao, “OFDM visible
light communication transmitter based on LED array,” Chin. Opt. Lett.,
vol. 12, no. 5, p. 052301, May 2014.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
SONG et al.: INDOOR BROADBAND BROADCASTING SYSTEM BASED ON PLC AND VLC 9
[9] J. Grubor, O. C. G. Jamett, J. W. Walewski, S. Randel, and K.-D. Langer,
“High-speed wireless indoor communication via visible light,”
in Proc. ITG Fachbericht, Mar. 2007.
[10] D. O’Brien et al., “Indoor visible light communications: Challenges and
prospects,” in Proc. SPIE Free Space Laser Commun. VIII, San Diego,
CA, USA, 2008.
[11] T. Komine and M. Nakagawa, “Fundamental analysis for visible-
light communication system using LED lights,” IEEE Trans. Consum.
Electron., vol. 50, no. 1, pp. 100–107, Feb. 2004.
[12] J. Rufo, J. Rabadan, F. Delgado, C. Quintana, and R. Perez-Jimenez,
“Experimental evaluation of video transmission through LED illu-
mination devices,” IEEE Trans. Consum. Electron., vol. 56, no. 3,
pp. 1411–1416, Aug. 2010.
[13] H. Ma, L. Lampe, and S. Hranilovic, “Integration of indoor visible
light and power line communication systems,” in Proc. IEEE Int. Symp.
Power Line Commun. Appl. (ISPLC), Johannesburg, South Africa, 2013,
pp. 291–296.
[14] T. Komine and M. Nakagawa, “Integrated system of white LED visible-
light communication and power-line communication,” IEEE Trans.
Consum. Electron., vol. 49, no. 1, pp. 71–79, Feb. 2003.
[15] T. Komine, S. Haruyama, and M. Nakagawa, “Performance evaluation of
narrowband OFDM on integrated system of power line communication
and visible light wireless communication,” in Proc. Int. Symp. Wireless
Pervasive Comput., Phuket, Thailand, 2006.
[16] P. Amirshahi and M. Kavehrad, “Broadband access over medium and
low voltage power-lines and use of white light emitting diodes for indoor
communications,” in Proc. IEEE Consum. Commun. Netw. Conf.,Las
Vegas, NV, USA, 2006, pp. 897–901.
[17] D. O’Brien, “Cooperation in optical wireless communications,” in
Cognitive Wireless Networks. Dordrecht, The Netherlands: Springer,
2007, pp. 623–634.
[18] D. Plets et al., “SFN gain in broadcast networks,” in Proc. IEEE Int.
Symp. Broadband Multimedia Syst. Broadcast. (BMSB), Nuremberg,
Germany, 2011, pp. 1–6.
[19] K. Yan, F. Yang, C. Pan, and J. Song, “Reception quality prediction
in a single frequency network for the DTMB standard,” IEEE Trans.
Broadcast., vol. 58, no. 4, pp. 629–636, Dec. 2012.
[20] M. Zimmermann and K. Dostert, “A multipath model for the powerline
channel,” IEEE Trans. Commun., vol. 50, no. 4, pp. 553–559, Apr. 2002.
[21] J. Grubor, S. Randel, K. D. Langer, and J. W. Walewski, “Broadband
information broadcasting using LED-based interior lighting,” J. Lightw.
Technol., vol. 26, no. 24, pp. 3883–3892, Dec. 2008.
[22] M. Zimmermann and K. Dostert, “An analysis of the broadband noise
scenario in powerline networks,” in Proc. IEEE Int. Symp. Power Line
Commun. Appl. (ISPLC), Limerick, Ireland, 2000, pp. 131–138.
[23] D. Middleton, “Statistical-physical models of electromagnetic interfer-
ence,” IEEE Trans. Electromagn. Compat., vol. 19, no. 3, pp. 106–127,
Aug. 1977.
[24] S. Liu, F. Yang, and J. Song, “Narrowband interference cancella-
tion based on priori aided compressive sensing for DTMB systems,”
IEEE Trans. Broadcast., to be published.
[25] S. Liu, F. Yang, and J. Song, “An optimal interleaving scheme with max-
imum time-frequency diversity for PLC systems,” IEEE Trans. Power
Del., to be published.
[26] C. W. Chow, C. H. Yeh, Y. F. Liu, and P. Y. Huang, “Mitigation of
optical background noise in light-emitting diode (LED) optical wire-
less communication systems,” IEEE Photon. J., vol. 5, no. 1, pp. 1–10,
Feb. 2013.
[27] G. Hu, C. Chen, and Z. Chen, “Free-space optical communication using
visible light,” J. Zhejiang Univ. Sci. A, vol. 8, no. 2, pp. 186–191,
Feb. 2007.
[28] D. J. F. Barros, S. K. Wilson, and J. M. Kahn, “Comparison of orthogo-
nal frequency-division multiplexing and pulse-amplitude modulation in
indoor optical wireless links,” IEEE Trans. Commun., vol. 60, no. 1,
pp. 153–163, Jan. 2012.
[29] A. Mattsson, “Single frequency networks in DTV,” IEEE Trans.
Broadcast., vol. 51, no. 4, pp. 413–422, Dec. 2005.
[30] Error-Correction, Data Framing, Modulation and Emission Methods
for Digital Terrestrial Television Broadcasting, ITU-R Recommendation
Standard BT. 1306-6, Dec. 2011.
[31] B. Yang, K. B. Letaief, R. S. Cheng, and Z. Cao, “Channel estimation for
OFDM transmission in multipath fading channels based on parametric
channel modeling,” IEEE Trans. Commun., vol. 49, no. 3, pp. 467–479,
Mar. 2001.
[32] W. Ding, F. Yang, C. Pan, L. Dai, and J. Song, “Compressive sensing
based channel estimation for OFDM systems under long delay channels,”
IEEE Trans. Broadcast., vol. 60, no. 2, pp. 313–321, Jun. 2014.
[33] X. Zhou, F. Yang, and J. Song, “Novel transmit diversity scheme
for TDS-OFDM system with frequency-shift m-sequence padding,”
IEEE Trans. Broadcast., vol. 58, no. 2, pp. 317–324, Jun. 2012.
[34] J. L. Pinto and I. Darwazeh, “Error vector magnitude relation to mag-
nitude and phase distortion in 8-PSK systems,” Electron. Lett., vol. 37,
no. 7, pp. 437–438, Mar. 2001.
[35] L. Dai, Z. Wang, C. Pan, and S. Chen, “Wireless positioning
using TDS-OFDM signals in single-frequency networks,” IEEE Trans.
Broadcast., vol. 58, no. 2, pp. 236–246, Jun. 2012.
[36] W. Zhang and M. Kavehrad, “Comparison of VLC-based indoor
positioning techniques,” in Proc. SPIE Broadband Access Commun.
Technol. VII, San Francisco, CA, USA, 2013.
[37] C. Sertthin, E. Tsuji, M. Nakagawa, S. Kuwano, and K. Watanabe,
“A switching estimated receiver position scheme for visible light based
indoor positioning system,” in Proc. IEEE Int. Symp. Wireless Pervasive
Comput., Melbourne, VIC, Australia, 2009, pp. 1–5.
[38] H. L. Minh et al., “High-speed visible light communications using
multiple-resonant equalization,” IEEE Photon. Technol. Lett., vol. 20,
no. 14, pp. 1243–1245, Jul. 2008.
[39] A. M. Tonello, P. Siohan, A. Zeddam, and X. Mongaboure, “Challenges
for 1 Gbps power line communications in home networks,” in Proc.
IEEE Int. Symp. Pers. Indoor Mobile Radio Commun. (PIMRC), Cannes,
France, 2008, pp. 1–6.
[40] T.-P. Ren, C. Yuen, Y. L. Guan, and G.-S. Tang, “High-order intensity
modulations for OSTBC in free-space optical MIMO communications,”
IEEE Wireless Commun. Lett., vol. 2, no. 6, pp. 607–610, Dec. 2013.
[41] H. Jin, K. Peng, and J. Song, “Bit division multiplexing for broadcast-
ing,” IEEE Trans. Broadcast., vol. 59, no. 3, pp. 539–547, Sep. 2013.
[42] J. Hou and D. O’Brien, “Vertical handover-decision-making algorithm
using fuzzy logic for the integrated radio-and-OW system,” IEEE Trans.
Wireless Commun., vol. 5, no. 1, pp. 176–185, Jan. 2006.
[43] C. Jiang, Y. Chen, Y. H. Yang, C. Y. Wang, and K. J. R. Liu, “Dynamic
Chinese restaurant game: Theory and application to cognitive radio net-
works,” IEEE Trans. Wireless Commun., vol. 13, no. 4, pp. 1960–1973,
Apr. 2014.
[44] J. Vuˇ
ci´
c, C. Kottke, S. Nerreter, K.-D. Langer, and J.W. Walewski,
“513 Mbits visible light communications link based on DMT-modulation
of a white LED,” J. Lightw. Technol., vol. 28, no. 24, pp. 3512–3518,
Dec. 2010.
[45] J. A. Anguita, M. A. Neifeld, B. Hildner, and B. Vasic, “Rateless cod-
ing on experimental temporally correlated FSO channels,” J. Lightw.
Technol., vol. 28, no. 7, pp. 990–1002, Apr. 2010.
[46] Radio Frequency Division Regulation of China, Ministry Ind. Inf.
Technol., Beijing, China, Dec. 2010.
[47] HomePlug AV, IEEE Standard 1901, 2010.
[48] F. Yang, K. Yan, Q. Xie, and J. Song, “Non-equiprobable APSK constel-
lation labeling design for BICM systems,” IEEE Commun. Lett., vol. 17,
no. 6, pp. 1276–1279, Jun. 2013.
[49] W. Ding, F. Yang, W. Dai, and J. Song, “Time-frequency joint sparse
channel estimation for MIMO-OFDM systems,” IEEE Commun. Lett.,
vol. 19, no. 1, pp. 58–61, Jan. 2015.
[50] W. Ding, F. Yang, J. Song, and Z. Niu, “Energy-efficient orthogo-
nal frequency division multiplexing scheme based on time-frequency
joint channel estimation,” IET Commun., vol. 8, no. 18, pp. 3406–3413,
Dec. 2014.
Jian Song (M’06–SM’10) received the B.Eng.
and Ph.D. degrees in electrical engineering from
Tsinghua University, Beijing, China, in 1990 and
1995, respectively. He has worked at the Tsinghua
University. He has also worked at the Chinese
University of Hong Kong and the University of
Waterloo, Canada, in 1996 and 1997, respectively.
He was a Professor at Tsinghua University in
2005. He has been with Hughes Network Systems
in USA for seven years. He is currently the
Director of Tsinghua’s DTV Technology Research
and Development Center. He has been working in quite different areas of
fiber-optic, satellite and wireless communications, as well as the power line
communications. His current research interest is in the areas of digital TV
broadcasting. He has published over 160 peer-reviewed journal and confer-
ence papers and holds two U.S. and over 40 Chinese patents. He is a fellow
of the Institution of Engineering and Technology.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
10 IEEE TRANSACTIONS ON BROADCASTING
Wenbo Ding received the B.S.E. degree
(highest honor) from the Department of Electronic
Engineering, Tsinghua University, Beijing, China,
in 2011. He is currently pursuing the Ph.D.
degree from the DTV Technology Research and
Development Center, Tsinghua University. His
research interests lie in the field of channel estima-
tion and equalization for multimedia communication
systems as well as the power line communication
and visible light communication.
Fang Yang (M’11–SM’13) received the B.S.E. and
Ph.D. degrees from the Department of Electronic
Engineering, Tsinghua University, Beijing, China,
in 2005 and 2009, respectively. He is currently
working as an Associate Professor with the DTV
Technology Research and Development Center,
Tsinghua University. His research interests lie in
the field of channel estimation and interference can-
celation for digital wireless communication system,
space-time coding, and diversity techniques, as well
as the training sequence design.
Hui Yang received the B.S.E. and M.S.E degrees
from the Department of Electronic Engineering,
Tsinghua University, Beijing, China, in 1993 and
1996, respectively. He is working as a Senior
Engineer with the DTV Technology Research
and Development Center, Tsinghua University. His
research interest lies in the digital television trans-
mission.
Bingyan Yu received the B.S.E. degree from the
Department of Electronic Engineering, Tsinghua
University, Beijing, China, in 2010, where he
is currently pursuing the Ph.D. degree from the
Opitcal Wireless Information Systems Laboratory.
His research interests lie in the field of high speed
visible light communication based on orthogonal
frequency division multiplexing or single carrier
frequency domain equalization.
Hongming Zhang received the B.S. and Ph.D.
degrees from the Tsinghua University, Beijing,
China, in 1998 and 2003, respectively, all in electri-
cal engineering. He is an Associate Professor with
the Department of Electronic Engineering, Research
Institute of Information Optoelectronics, Tsinghua
University. His research interests include visible
light communication and positioning, production of
ultrashort optical pulses, and high speed optical
sampling and processing.
