Design and development of a portable visible-light communication transceiver for indoor wireless multimedia broadcasting

Abstract

Recent rapid progress in information and communication technologies has spurred the exponential surge in the demand for unlimited high-speed and ubiquitous broadband wireless access (BWA), resulting in severe congestion of the radio frequency (RF) spectrum and wireless traffic bottleneck. Visible-light communications (VLC) is poised to become a promising BWA candidate to resolve the existing 'last mile' problems. In this paper, we propose and initiate the implementation of a low-cost portable VLC transceiver capable of indoor wireless communication and multimedia broadcasting, thus presenting an economical and cable-free solution to various multimedia applications. The proposed optical transceiver design is based upon the integration of the transmitter and receiver hardware and an interactive software module, and relies upon a microcontroller which forms the system hub to manage the data and process flows among the different block components. The interactive software module consists of a graphical user interface (GUI) and a data processing algorithm, in order to control file transmission and reception in various format and to enable realtime interaction and viewing of multimedia applications.

Full text

Design and Development of A Portable Visible-Light
Communication Transceiver for Indoor Wireless
Multimedia Broadcasting
It Ee Lee1,2,*, Jia Chin Law1, Kat Yee Chung1, Kean Yeong Fong1, Yi Qin Liew1, Sheue Yun
Quan1, Jia Zun Tuen1, and Chee Keong Tan1
1Faculty of Engineering, Multimedia University
Cyberjaya, Malaysia
2Faculty of Engineering and Environment, Northumbria University
Newcastle Upon Tyne, United Kingdom
*Corresponding author: ielee@mmu.edu.my, it.ee.lee@northumbria.ac.uk
Abstract—Recent rapid progress in information and
communication technologies has spurred the exponential surge in
the demand for unlimited high-speed and ubiquitous broadband
wireless access (BWA), resulting in severe congestion of the radio
frequency (RF) spectrum and wireless traffic bottleneck. Visible-
light communications (VLC) is poised to become a promising
BWA candidate to resolve the existing “last mile” problems. In
this paper, we propose and initiate the implementation of a low-
cost portable VLC transceiver capable of indoor wireless
communication and multimedia broadcasting, thus presenting an
economical and cable-free solution to various multimedia
applications. The proposed optical transceiver design is based
upon the integration of the transmitter and receiver hardware
and an interactive software module, and relies upon a
microcontroller which forms the system hub to manage the data
and process flows among the different block components. The
interactive software module consists of a graphical user interface
(GUI) and a data processing algorithm, in order to control file
transmission and reception in various format and to enable real-
time interaction and viewing of multimedia applications.
Keywords—visible-light communication (VLC); light-emitting
diode (LED); transceiver; graphical user interface (GUI);
multimedia broadcasting
I. INTRODUCTION
In the recent decade, rapid progress in information and
communication technologies has spurred the exponential surge
in the demand for unlimited high-speed and ubiquitous
broadband wireless access, in order to accommodate the ever-
increasing utilization of internet and multimedia services,
thereby resulting in severe congestion of the radio frequency
(RF) spectrum and wireless traffic bottleneck. Furthermore, the
enormous growth of portable information terminals in work
and living environments is accelerating the deployment of
wireless digital links and local area networks (LANs) [1]. The
desire for inexpensive, high-speed wireless links to cope with
these demands has motivated research interests in the
development and deployment of wireless optical
communication systems spanning the visible-light [2-3] and
infrared [1, 4] spectrum.
Visible-light communications (VLC) is a wireless
communications technology employing visible-light signals
with wavelengths between 400 nm and 700 nm to transmit
information, which is made possible through the fast switching
capabilities of the light-emitting diodes (LEDs) (i.e., in ranges
of nanoseconds) to modulate the visible-light waves to enable
wireless communication [5]. Complementing the existing
wireless RF solutions, the VLC system is poised to become a
promising broadband wireless access (BWA) candidate to
resolve the existing “last mile” problems, due to the superior
characteristics of this technology option, which include: no
licensing requirements or tariffs for its utilization, capability of
achieving a very high aggregate capacity, flexibility, cost-
effectiveness, mobility, and simplicity of system design [1, 5-
6].
In this paper, we propose a low-cost portable VLC
transceiver capable of indoor wireless communication and
multimedia broadcasting, thus presenting an economical and
cable-free solution to various multimedia applications, such as
text messaging, file transmission, and real-time audio and
video streaming. The proposed optical transceiver design is
based upon the integration of the transmitter and receiver
hardware and an interactive software module, and relies upon a
microcontroller which forms the system hub to manage the
data and process flows among the different block components.
The software implementation is motivated by the emergence of
various on-line multimedia applications, which have gained
enormous popularity in the internet nowadays due to their real-
time streaming capabilities, whereby playback is possible even
when file transfer is still in progress. Multimedia sources
encrypted in various format, such as text (e.g., .txt, .doc, .rtf),
image (e.g., .bmp, .jpg, .png), audio (e.g., .wma, .mp3) and
video (e.g., .wmv, .mp4, .avi), are first encoded into series of
binary bit streams using an algorithm within the software
module, and then relayed to the microcontroller and queued for
forwarding to the transmitter. Correspondingly, the line codes
are modulated and propagated through free-space via the fast-
switching of the LEDs using the LED driver circuit.
QG,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF'HVLJQ,&('$XJXVW3HQDQJ0DOD\VLD
,((( 

Fig. 1. The proposed portable VLC transceiver.
1010110111…
LED Driver
Circuit
4×4 LED Array
Transmitter
Buffer
Circuit
Bandpass
Filter
Cascaded
Amplifier
Receiver
Data Processing Algorithm
Graphical User Interface
RS-232
USB
System Hub
(Microcontroller)
Demodulation Baseband
Signal Recovery
Photodiodes
The remainder of this paper is organized as follows:
Section II describes the physical construction and principles of
operation of our proposed VLC transceiver. Next, an in-depth
discussion on the system implementation involving both
hardware and software modules are presented in Section III.
We conclude this paper in Section IV, in which
recommendations for future improvement to the system design
are justified accordingly here.
II. THE PROPOSED VLC TRANSCEIVER
Fig. 1 illustrates the block diagram of the proposed portable
VLC transceiver, which clearly outlines the two main modules
(i.e., hardware and software) involving the construction of the
communications device and their interconnections.
The interactive software module which comprises two main
components – (1) graphical user interface (GUI) and (2) data
processing algorithm, is installed on a mobile terminal unit (in
this case, a host computer), and establishes connection with the
transceiver hardware via the RS-232 or Universal Serial Bus
(USB) [7] port. The GUI is employed as a medium for end
users to control file transmission and reception in various
format, such as text (e.g., .txt, .doc, .rtf), image (e.g., .bmp,
.jpg, .png), audio (e.g., .wma, .mp3) and video (e.g., .wmv,
.mp4, .avi), with much convenience by just clicking a button,
and to enable real-time interaction/viewing of multimedia
applications, such as text messaging and audio and video
streaming. Upon selection of a multimedia source for file
transfer, the data processing algorithm will estimate the file
size of the selected multimedia source, which is an important
parameter required by the software to enable equal partitioning
of the corresponding file into smaller data chunks. Each
segmented data block is encoded into series of binary bit
streams, which is then relayed to the system hub (i.e.,
microcontroller) via the RS-232/USB port for queuing and
timely forwarding of the binary data to the transmitter
hardware.
The transmitter hardware relies upon the LED driver circuit
to modulate the baseband information signal with a higher
carrier frequency using the on-off keying with non-return-to-
zero (OOK-NRZ) technique, thereby resulting in rapid
switching of the high-brightness LEDs between “on” and “off”
states. Correspondingly, the visible-light pulses transmitted
from the LEDs propagate through free-space, and are then
detected by a positive-intrinsic-negative (p-i-n) silicon
photodiode of the receiving transceiver, which converts the
optical signals into electrical format according to the detector
responsivity (in unit of A/W). The relatively weak electrical
output (with amplitude in ranges of mV) from the
photodetector subsequently goes through a series of signal
amplification, bandpass filtering, demodulation and processing,
in order to recover the original baseband information (in binary
format) with minimal bit error.
Blocks of recovered binary data are then relayed to the
microcontroller via the input/output (I/O) port, which in turn
manages the queuing and data delivery to the receiving
computer by means of RS-232 or USB connection. Upon
reception of the first binary data chunk, the GUI will trigger a
pop-up menu to request the user to select the destination
location, in which the data processing algorithm will decode
and concatenate the received blocks and save the resulting
baseband information in the desired location as a single file
(even if the file transfer is incomplete). For real-time audio and
video streaming, the corresponding data blocks of the received
multimedia source will be accessed by the software module
sequentially and displayed through a media player within the
GUI, which poses some challenge in the present work to enable
multimedia playback with minimal latency.
QG,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF'HVLJQ,&('$XJXVW3HQDQJ0DOD\VLD


III. SYSTEM IMPLEMENTATION
A. Transmitter Module
Fig. 2 presents the block diagram of the VLC transmitter
module, which describes the mechanism involving the
modulation of the encoded binary signals and biasing of the
4×4 LED array, in order to enable transmission of the
modulated optical pulses via free-space.
Baseband information encoded in binary format are
forwarded from the host computer to the PIC18F2550
microcontroller [8] through the RS-232 or USB 2.0 connection,
and subsequently goes through the modulation process using
the OOK-NRZ technique, whereby the desired binary data is
imposed onto a higher frequency carrier signal to produce the
modulated signal. The PIC18F2550 microcontroller is selected
as the system hub for the transceiver hardware due to its
superior characteristics particularly in high performance, power
sensitive applications, such as (1) high computational
performance at an economical price (~USD 7 per unit), (2)
high endurance, (3) efficient power management capability, (4)
enhanced flash program memory, (5) USB 2.0 compliant (up to
12 Mbps in Full Speed mode), and (6) universal serial
asynchronous receiver transmitter (USART) functionality [8-9].
We consider the use of timer555 configured in astable mode to
generate continuous stream of rectangular pulses having a
frequency of 100 kHz as the carrier signal, in which the carrier
frequency can be adjusted within a designated range in
accordance to the resistance of the potentiometer. The OOK-
NRZ modulation is implemented using NAND logic operation,
which can be conveniently constructed from a simple diode
circuit as shown in Fig. 3.
Correspondingly, the output of the diode circuit is
connected to the LED driver circuit, which employs IRFZ44N
metal-oxide-semiconductor field-effect transistors (MOSFETs)
[10] to enable efficient and reliable biasing of the super-bright
LEDs between “on” and “off” states, thus releasing the optical
energy of the modulated pulses into the transmission medium.
The rapid switching of the LEDs in ranges of microseconds is
imperceivable to the human eye. MOSFETs are suitable for
switching LEDs at high frequency due to their distinct
advantages, which include: (1) rapid switching capability, (2)
small switching current requirement (hence, easy to drive), (3)
lower power consumption, (4) wider safe operating region
(since high voltage and current can be applied simultaneously
for a short duration), (5) ideal for use in parallel (due to equal
current flow across parallel paths), and (6) simplicity of circuit
design [11]. Fig. 4 shows the prototype for the VLC transmitter
module, which is powered by a 12 V adapter.
B. Receiver Module
The block diagram of the VLC receiver module in Fig. 5
highlights the processes required to reconstruct the desired
binary information, which include: optical-to-electrical
conversion, signal buffering and pre-amplification, bandpass
filtering, signal amplification, demodulation, and baseband
signal recovery.
Upon detection of the modulated signal, the p-i-n silicon
photodiode converts the corresponding optical intensity into
photocurrent, in which the optical-to-electrical conversion
efficiency is determined by the detector responsivity, effective
detection area, and angular response (typically at half-power)
[1]. The VTB8440B [12] photodiode is a more practical option
Fig. 2. Block diagram of the VLC transmitter module.
PIC18F2550
Microcontroller
Host
Computer
Modulation Process
(NAND Logic
Operation)
RS-232
USB 2.0
Carrier Frequency
Generator
(Timer555)
LED Driver Circuit
(MOSFETs)
To 4×4 LED
Array
Fig. 3. Schematic diagram depicting the interconnection of the diode circuit,
driver circuit and 4×4 LED array.
From
PIC18F2550
Microcontroller
From Timer555
Output
NAND Logic
Operation
LED Driver Circuit
4×4 LED Array
Fig. 4. Prototype for the VLC transmitter module.
QG,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF'HVLJQ,&('$XJXVW3HQDQJ0DOD\VLD


for a low-cost, small-size optical receiver design requiring least
circuit complexity due to the following considerations: (1)
wide availability at low price (~USD 3.65 per unit), (2)
integrated infrared rejection filter, (3) detector responsivity of
0.38 A/W at 660 nm, (4) spectral application range
encompassing the visible-light spectrum (i.e., between 330 nm
and 720 nm), (5) active detection area of 5.16 mm2, and (6)
wide angular response of 50°. Next, the photocurrent is fed into
the input of a simple buffer circuit, which performs current-to-
voltage conversion and signal pre-amplification.
Correspondingly, undesirable noise is removed from the
relatively weak input signal using a multiple-feedback (MFB)
bandpass filter, which can be implemented with only one
operational-amplifier (op-amp) configured in the inverting
mode. The MFB bandpass filter is designed using PSpice to
attain the following design specifications: (1) centre frequency,
݂
௖ൌ100 kHz; (2) 3-dB bandwidth, ܤܹ
3dB ൌ10 kHz; and (3)
quality factor, ܳൌ݂
௖ܤܹ
3dB
Τൌ10 . A two-stage inverting
cascaded amplifier is constructed to achieve higher gain and
provide better control of both the input and output impedances,
in order to amplify the electrical signal to a desirable level for
demodulation and further signal processing.
Since the OOK-NRZ technique has been considered in the
modulation process, non-coherent envelope detection using
simple RC circuit presents the most straight-forward approach
in recovering the baseband information, which is made
possible by tracing the corresponding peak of the received
modulated signal. Therefore, the time constant ߬ൌܴܥ should
be made much larger than ͳ݂
௖
Τ through proper selection of the
resistance ܴ and capacitance ܥ, in order to minimize the ripple
in the signal envelope. Subsequently, the demodulated signal
goes through a series of baseband signal recovery processes
using a Schmitt trigger and simple pulse-holding circuit, in
order to enable proper reconstruction of the binary data with
fixed amplitude (i.e., +5 V for “on” state and 0 V for “off
state”) and equal pulse duration, respectively. Binary data bit
streams are sequentially forwarded to the PIC18F2550
microcontroller, which in turn sends the corresponding data to
the receiving terminal via RS-232 or USB connection.
C. Software Module
Fig. 6 and Fig. 7 present flow diagrams which describe the
mechanism involving the data processing algorithm in handling
data transmission and reception between a host computer and
receiving terminal via serial communication, and vice versa.
Upon triggering of a file transmission by the end-user (Fig.
6), the parameters Send_Counter and Loop_Counter are
initialized to 1 and 0, respectively. While Send_Counter is less
than (Looping_Times + 2), the algorithm will perform a check
to ensure that the clear to send (CTS) flag is set to the “on”
state before executing the subsequent instructions. If the
conditions CTS = “on” and Send_Counter < Looping_Times
are true, the first data chunk of the selected file will be
transmitted across the channel and Send_Counter will be
incremented by 1, in which the transmission progress will be
reflected accordingly on the status bar of the GUI. On the other
hand, if the program encounters the condition CTS = “off”,
Loop_Counter will be incremented by 1 while Send_Counter
will cease counting, thereby putting the transmission of
subsequent data chunks on-hold until the CTS flag is triggered
back to the “on” state. If Loop_Counter > 10, a “Send Failed”
command will be displayed on the status bar, in order to notify
the user that an error has occurred and no data has been sent.
The file reception mechanism is explained in a separate
flow diagram as shown in Fig. 7. Upon triggering the reception
of the first data chunk, the data processing algorithm initializes
Loop_Counter to 0, and then checks the status of
Received_Counter. If the condition Received_Counter == 1 is
true, a “Nothing to Receive” command will be displayed on the
Fig. 6. Flow diagram describing the data transmission mechanism.
Fig. 5. Block diagram of the VLC receiver module.
MFB Bandpass
Filter
Multistage Cascaded
Amplifier
Schmitt
Trigger
VTB8440B Photodiodes
(Optical-to-Electrical
Conversion)
Buffer Circuit
(Current-to-Voltage
Converter)
Envelope Detector
(Demodulation)
Baseband Signal Recovery
Pulse-Holding
Circuit
Receiving
Te rm i n a l
RS-232 USB 2.0
QG,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF'HVLJQ,&('$XJXVW3HQDQJ0DOD\VLD


status bar to indicate that the data chunk is yet to be received.
Else, the program will ensure that the condition CTS = “on”
and the request to send (RTS) flag is set to the ‘on’ state, in
order to start receiving data. After a chunk of data has been
received, the RTS flag will be toggled back to the “off” state to
avoid transmission of the second chunk from the host
computer. Correspondingly, Received_Counter will be
incremented by 1 and the process will repeat until the complete
file is received.
The developed GUI application comprises a built-in media
player for direct playback of the received multimedia file.
Additional enhancements made to the GUI include calendar
and access to online applications, such as Facebook
(http://www.facebook.com), Google (http://www.google.com),
etc. A snapshot of the GUI is available in Fig. 1.
Subsequent efforts are required to enable integration of the
hardware and software modules, in which the transceiver
hardware will be linked to the GUI to control the data flow in a
more efficient manner, thus enabling transmission and real-
time streaming of various multimedia files. In addition, further
improvements to the data processing algorithm will be
required, in order to minimize the delay in executing the data
handling/ processing and forwarding tasks, which is
particularly critical for on-line multimedia playback.
IV. CONCLUSIONS
In this paper, we have proposed and initiated the
implementation of a low-cost portable VLC transceiver, which
is based upon the integration of the transmitter and receiver
hardware and an interactive software module, in order to
enable indoor wireless communication and multimedia
broadcasting. The RS-232/USB enabled VLC transceiver relies
upon a microcontroller which forms the system hub to manage
the queuing and timely forwarding of binary data among the
different hardware and software components. The interactive
software module consists of a GUI and a data processing
algorithm, in order to control file transmission/reception in
various format and to enable real-time interaction/viewing of
multimedia applications. In particular, the data processing
algorithm handles a series of processes, which include file size
estimation, file partition/concatenation, source
encoding/decoding and multimedia playback with minimal
latency.
Nonetheless, this project requires more extensive
improvement and development work to enhance the features
and performance of both the transceiver hardware and software
module, which include: (1) to increase the data rate (and thus
the carrier frequency) above 100 kbps; (2) to reduce the size of
the prototype while maintaining design simplicity and low
cost; (3) to consider data transmission using the ethernet
connection for establishing a link to the internet; (4) to improve
the efficiency of the data processing algorithm, in order to
minimize the delay in executing various tasks/commands; and
(5) to reduce the latency currently experienced in multimedia
playback and real-time streaming.
REFERENCES
[1] J. M. Kahn and J. R. Barry, “Wireless infrared communications”, Proc.
IEEE, vol. 85, no. 2, pp. 265-298, Feb. 1997.
[2] T. Komine, J. H. Lee, S. Haruyama and M. Nakagawa, “Adaptive
equalization system for visible light wireless communication utilizing
multiple white LED lighting equipment”, IEEE Trans. Wireless
Commun., vol. 8, no. 6, pp. 2892-2900, Jun. 2009.
[3] 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.
[4] S. T. Jivkova and M. Kavehrad, “Multispot diffusing configuration for
wireless infrared access”, IEEE Trans. Commun., vol. 48, no. 6, pp. 970-
978, Jun. 2000.
[5] I. E. Lee, M. L. Sim, and F. W. L. Kung, “Performance enhancement of
outdoor visible-light communication system using selective combining
receiver”, IET Optoelectron., vol. 3, no. 1, pp. 30-39, Feb. 2009.
[6] A. Mahdy and J. S. Deogun, “Wireless optical communications: a
survey”, in Proc. IEEE Wireless Communications and Networking
Conference (WCNC), Atlanta, USA, Mar. 2004, pp. 2399-2404.
[7] “Universal serial bus specification revision 2.0”, http://www.usb.org/
developers/docs [online], last accessed: Apr. 25, 2011.
[8] “Microchip PIC18F2455/2550/4455/4550 datasheet”, http://ww1.
microchip.com/downloads/en/devicedoc/39632c.pdf [online], last
accessed: Apr. 25, 2011.
[9] M. A. Mazidi, R. D. Mckinlay and D. Causey, PIC microcontroller and
embedded sytems using assembly and C for PIC18, Prentice Hall, 2008.
[10] “IRFZ44N HEXFET® power MOSFET datasheet”, http://www.irf.
com/product-info/datasheets/data/irfz44n.pdf [online], last accessed:
Apr. 25, 2011.
[11] K. S. Oh, AN9010, MOSFET Basics, Fairchild Semiconductor, July
2000.
[12] “VTB process photodiode datasheet”, http://www.perkinelmer.com/
PDFs/Downloads/DTS_VTB8440BH-8441BH.pdf [online], last
accessed: Apr. 25, 2011.
Fig. 7. Flow diagram describing the data reception mechanism.
QG,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF'HVLJQ,&('$XJXVW3HQDQJ0DOD\VLD
