Mitigating effect of flickering and dimming in visible light communication using mimo

International Journal of Electrical and Computing Engineering
Vol. 1, Issue. 1, July – 2014 ISSN (Online): 2349-8218
Mitigating Effect of Flickering & Dimming in Visible
Light Communication Using MIMO
A. Suban
[1]
, P. Prabu
[2]
, R. Manikandan
[3]
, M. Pradeep
[4]
Assistant professor, Dept of ECE, Velammal College of Engineering and Technology, Madurai
[2]
PG student, Dept of CSE, Indian Institute of Information Technology, Trichy
[3]
Project Engineer, WIPRO Lmited, Chennai,
[4]
Lecturer, Nagasiva Polytechnique College
Abstract— Visible Light Communication (VLC) refers
to short-range optical wireless communication using
visible light spectrum from 380 to 780nm and it has
many advantages such as it can provide a maximum
speed of 10GB/S. The other advancement is that the
bandwidth available for visible light communication is
300THz whereas it is below 6GHz on RF
communication. The transmission of data in VLC is
done with the intensity modulating optical source,
such as light emitting diodes (LEDs) because of its
energy efficiency and recent advancement in LED
technology with fast nanoseconds switching time. This
paper applies OPPM (Overlapping Pulse Position
Modulation) to provide higher data rate during its
transmission of digital data when we compared to
other modulation techniques. The result shows that
the best performance can be obtained using OPPM,
making it an ideal modulation technique for future
visible light communication. MATLAB and Lab View
are the two methodologies we used for simulation
purpose. Moreover Multiple Input Multiple Output
(MIMO) techniques is potentially adopted for
achieving high data rates. MATLAB Simulations are
carried out and depicted.
Index Terms— Visible light, White LED, On Off
Keying, Variable Pulse Modulation, Overlapping
Pulse Position Modulation.
I. INTRODUCTION
In the development of wireless communication
system when the third generation mobile communication
system is employed, manufacturers and the scientific
group are increasingly turning their research interest
towards future wireless communication system because
traditional radio frequency (RF) communication below 6
GHz is rapidly running out of spectrum bandwidth for
high data-rate communication. Visible Light
Communication has recently been developed by scientists
seeking to create an ultra-high speed, high security,
biologically friendly communication networks
Suban. A, Electronics & Communication Engineering, Velammal
College of Engineering and Technology, Madurai
Prabu.P, Computer Sceince & Engineering, Indian Institute of
Information Technology
Manikandan.R, Project Enineer, WIPRO Limited, Chennai.
Pradeep.M, Electrical & Electronics Engineering, Nagasiva
Polytechnique College, Madurai
that allow the creation and expansion of continuous
computing applications using very large bandwidth high-
frequency pulsed light instead of radio waves and
microwaves. Visible Light Communication (VLC) is the
short-range optical wireless communication using the
visible light spectrum from 380 to 780nm. With ~300 THz
of bandwidth available for VLC, multi-gigabit-per second
data rates could be provided over short distances.
This wide spread of bandwidth removes one of
the major difficulties faced by new communication
schemes. Some of the noted advantages of visible light
communication over RF (Radio Frequency) and IR (Infra-
Red) based systems are:
  Higher security than RF communication system.  
 No restriction on transmission power unlike in 
 IR communication system.  
 No regulations in the use of the visible
 electromagnetic spectrum. 
 The key advantage of VLC is the duality in the
use of the visible light. The same light that is
used for the communication can also be used for
illumination applications such as domestic light
bulbs, LED TVs, and traffic lights. 
In an optical communication system, there is a
possibility of modulating the transmitted optical signal in
a variety of ways. The phase, frequency and the intensity
of the optical signal can be modulated. VLC transmits
data by the intensity modulating optical sources, such as
light emitting diodes (LEDs) and laser diodes, because it
is easy to implement and the optical output power is
simply changed in accordance with the modulating signal.
There has been renewed interest in visible light optical
communication due to widespread deployment of LEDs
for energy efficiency and recent advancements in LED
technology with fast nanosecond switching times.
Figure 1. An Alternate Technology-VLC
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Vol. 1, Issue. 1, July – 2014 ISSN (Online): XXXX-XXXX
LED VISIBLE LIGHT COMMUNICATION
In this 21st century, LEDs are extensively used
in various electronic devices, consumer products and due
to their small size they are preferred for illuminating
technologies. Recently experiments have shown that
advance in semiconductor material and manufacturing
techniques of LED is to be suitable for general indoor and
outdoor applications. In addition to that LED produces
less heat than other fluorescent and incandescent light
bulbs. In the industry side, LEDs are referred as “cool
lights” and most sustainable in light technology. Low cost
LED instead of lasers can be used as communication
transmitters connected to the electric grid, receiving high-
bit rate signals. So LED (Light Emitting Diode) Visible
Light Communication systems are recognized as creating
a possible valuable addition to future generation of
technology, which have the potential of using light for the
purpose of advanced technological communication at
ultra-high speed surpassing that of current wireless
systems. If it is developed correctly, the possibility exists
than many of the problems associated with present day
infrared, Bluetooth and radio wave could be at least
partially resolved, and industries and the general public
can gain a more biologically friendly system. The main
reasons for using LED are followed:
• High usage of bandwidth.
• Existing local power line infrastructure can
potentially be utilized.
• Very simple transmitter and receiver circuit
and it is not expensive.
• Eco-friendly.
• Long life expectancy.
A further advantage is that VLC systems can
transmit data more securely over short distances than
other communication devices whose signals can be easily
detected outside the rooms and buildings they originate in.
In the following section, the paper describes the system
design for the visible light communication, modulation
method and their benefits for flickering.
III. SYSTEM DESIGN
A typical Visible Light Communication system
contains two parts namely transmitter module and
receiver module. VLC system appears in the form of point
to multi-points which permits data transmission in one
direction only. The following figure shows the overall
VLC system block diagram. The receiver occupant may
realize information uplink with extra optical devices, and
more sophisticated the duplex system is the duplex
system.
A. TRANSMITTER MODULE
In the transmitter module, the Light Emitting Diode is
used to transmit the data and it has to be designed in such
way that power and the colour temperature both safe and
comfortable for human eyes.
when the same LED is used for illumination because it
won't make people feel uncomfortable and dizzy. It’s
important to note that the receiver occupant may block the
light beam and put the receiver in shadows, so more than
two LED lamps should be modulated simultaneously from
various directions to cover a larger recipient area. In some
case where the receiver loses connection with the
transmitter, it will be able to receive data from another
transmitter instantaneously.
Figure 2. Visible Light Communication Transmitter and Receiver Block
Diagram
B. RECEIVER MODULE
A receiver module is mostly composed of PIN
detectors and signal conditioning devices. The output
signal from the detector is weak with a lot of background
light noise and a long free space communication distance
only makes the situation worse. Therefore, the critical part
of our VLC system is the signal conditioning circuit .
The receiver’s PIN photo detector is connected to a trans-
impedance amplifier to convert the current signal into a
voltage signal. A high pass filter is applied next to bypass
the light noises and power line noises. Finally, the signal
is amplified by a main amplifier and it is reshaped by
comparator.
IV. MODULATION TECHNIQUE IN VLC
In the modulation process, the baseband signals
constitute the modulating signal and the high-frequency
carrier signal is a sinusoidal waveform or cosine
waveform. The sine wave carrier can be normally
modulated by three basic ways. For the modulation of
binary digital data, the three modulation techniques used
are binary amplitude-shift keying (BASK), binary
frequency-shift keying (BFSK) and binary phase shift
keying (BPSK).
A. AMPLITUDE SHIFT KEYING
Amplitude-shift keying (ASK) is a form of modulation
technique that represents digital data as variations in the
amplitude of a carrier wave. To transmit digital data over
optical fibre ASK technique is normally used. For
transmission using LED, binary 1 is represented by a short
pulse of light whereas absence of light represents binary 0.
This process is said to On Off Keying (OOK).
9

Figure 3. MATLAB simulation of Bit Error Rate for various
modulation methods
C. OVERLAPPING PULSE POSITION
MODULATION
Although VPM can provide data rates in terms of
few hundred megabits/s but even higher data rate than the
existing one is not possible due to its inherent throughput
limitations. Reducing the pulse width is the one and only
way to increase the throughput of the VPM. So there is a
need for some other modulation methods to provide
higher data rate but that should not have the limitations as
with that of VPM. OPPM is one of the promising
modulation scheme that allows more than one pulse per
pulse width and it has some of the useful properties such
as equal energy signals and low duty cycle.
Figure 4. Lab View simulation of Bit Error Rate for various
modulation methods
From the simulated results, the following conclusions
are made. The error rate for all the modulation techniques
decreases monotonically with increasing value of SNR.
For any given value of SNR, coherent PSK & OOK
produces same and smaller error rate than any of the other
modulation technique. So, coherent PSK and OOK are the
optimum system for transmitting binary data because it
achieves the minimum probability of symbol error for the
given value of SNR. But considering OOK and coherent
PSK, OOK is the best and most efficient modulation
technique in terms of bandwidth and power consumption.
DPSK require an SNR that is 3 dB less than that of
coherent FSK and noncoherent FSK to achieve same error
rate. For higher values of SNR, DPSK and noncoherent
FSK performs almost as well as coherent PSK and
coherent FSK. For higher values of SNR, coherent PSK
and QPSK have same error rate performance. Also it has
been inferred that MSK has exactly the same error
performance as that of QPSK.
B. Variable Pulse Position Modulation
Pulse position modulation (PPM) encodes the
data using the position of the pulse within a set time
period. The duration of the period containing the pulse
must be long enough to allow different positions to be
identified.
Figure 5. MATLAB simulation of Data rate Vs Duty cycle for OOK &
OPPM
Figure 6. Lab View simulation of Data rate Vs Duty cycle for
OOK & OPPM
From the simulated results, the following conclusions are
made. We can see that the OPPM signal has the best
flicker performance, followed by VPM and OOK.
10

The flicker severity value is 0.525 for any dimming
levels, which is far less than the limited value. We can
also notice that the 90% duty cycle VPM signal has
the same flicker performance as OPPM. But the flicker
severity of OPPM signal is invariant with changing
different dimming levels.
D. MULTI-ANTENNA CONFIGURATION
Solid-state lighting is a rapidly growing area of
research and applications, due to the reliability and
predicted high efficiency of these devices. The white LED
sources that are typically used for general illumination
can also be used for data transmission, and Visible Light
Communications (VLC) is a rapidly growing area of
research. One of the key challenges is the limited
modulation bandwidth of sources, typically several MHz
However, as a room or coverage space would typically be
illuminated by an array of LEDs there is the potential for
parallel data transmission, and using optical MIMO
techniques is potentially attractive for achieving high data
rates. In this paper we investigate non-imaging and
imaging MIMO approaches: a non-imaging optical
MIMO system does not perform properly at all receiver
positions due to symmetry, but an imaging based system
can operate under all foreseeable circumstances.
Simulations show such systems can operate at several
hundred Mbit/s and up to Gbit/s in many circumstances.
Figure 6. MATLAB simulation of Bit Error Rate (BER) Vs
Signal to Noise Ratio (SNR) for various systems such as SISO,
MISO and MIMO using OPPM Technique
From the simulated results,it can be inferred that
using SISO system model i.e. using single LED in the
transmitter side and a single photodiode or LED in the
receiver side we have very large bit error rate for increase
in SNR for given input. In the next case of MISO,i.e.
using two LED transmitter side at the transmitter side and
a single LED or photodiode at the receiver side we
achieve the bit error rate smaller than SISO system but
not smaller than MIMO system. In the next case of
MIMO system,i.e.using arrays of LED at the transmitter
side and arrays of LED or photodiode at the receiver side
we get a very smaller BER when we compared to SISO
and MISO system and it proved that VLC is adaptable for
MIMO configuration and it give best results when we
compared to all other system configurations.
Following assumptions are made for the
simulated results
Channel: AWGN
Modulation technique used: OPPM
ANTENNA SIZE: 2*2 for MIMO
1*1 for SISO
2*1 for MISO
V. DISCUSSIONS
We analysed the Performances of OOK and OPPM
signals by investigating the cutoff data rate and Bit Error
Rate analysis of various modulation techniques. We
proved that OPPM signal has the smallest and constant
flicker severity under all dimming levels spanning a
reasonably large brightness dimming range. This
modulation scheme also provided the largest and steady
cutoff data rate. OPPM appears as the desirable
modulation solution to emerging LED-based high
capacity visible light communication.
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