Performance Analysis of Optical Wireless Communication

Yogendra Singh et al. / International Journal of Computer Science & Engineering Technology (IJCSET)
Performance Analysis of Optical Wireless
Communication Channel Link at Various
Bit Rates
Yogendra Singh
M.Tech. Scholar, ECE Department, AIACT&R,
Delhi, India
[email protected]
Manisha Bharti
Assistant Professor, ECE Department, AIACT&R,
Delhi, India
[email protected]
Jitender Kumar
M.Tech. Scholar, ECE Department, AIACT&R,
Delhi, India
[email protected]
Abstract— Optical wireless communication systems have got more popularity in last few years due to its
advantage over conventional radio frequency communication systems. This paper reports the effect of
using NRZ and RZ modulation formats on the performance of optical Wireless communication (OWC)
channel in terms of Q factor and BER at bit rate of 2.5 Gbps and 3 Gbps. It has been observed that RZ
format gives better performance for optical wireless link in comparison to NRZ format at different bit
rates.
Keywords— Non-Return to zero (NRZ), Return to zero (NRZ), optical wireless communication (OWC).
I.
INTRODUCTION
In recent years, there has been a migration of computing power from the desktop to portable, mobile formats.
Devices such as digital still and video cameras, portable digital assistants and laptop computers offer users the
ability to process and capture vast quantities of data. Although convenient, the interchange of data between such
devices remains a challenge due to their small size, portability and low cost. High performance links are
necessary to allow data exchange from these portable devices to established computing infrastructure such as
backbone networks, data storage devices and user interface peripherals [1]. One possible solution to the data
interchange link is the use of a direct electrical connection between portable devices and a host. This electrical
connection is made via a cable and connectors on both ends or by some other direct connection method. The
connectors can be expensive due to the small size of the portable device. In addition, these connectors are prone
to wear and break with repeated use. Some popular “low cost” RF links over distances of approximately 10m
provide data rates of up to 1 Mbps in the 2.4 GHz band for a cost near US$5 per module. Another solution to the
short-range interchange and longer-range networking links is wireless optical, this links can transmit at 4 Mbps
over short distances using optoelectronic devices which cost approximately US$1[1]. However, much high rates
approaching 1 Gpbs have been investigated in some experimental links. Wireless optical links transmit
information by employing an optoelectronic light modulator, typically a light-emitting diode (LED). The task of
up- and down-conversion from baseband frequencies to transmission frequencies is accomplished without the
use of high-frequency RF Circuit design techniques, but is accomplished with inexpensive LEDs and
photodiodes. Since the electro-magnetic spectrum is not licensed in the optical band, spectrum licensing fees are
avoided, further reducing system cost [1].
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Yogendra Singh et al. / International Journal of Computer Science & Engineering Technology (IJCSET)
Fig 1: An indoor wireless optical communication system [1]
This component allows for simulation of free space optical links [4] [2] [3]. The component is a subsystem
of transmitter telescope, optical wireless communication channel and receiver telescope. The optical signal
received at the receiver is given by
The term in parentheses is the free-space loss. Parameter Geometrical gain defines whether the user will
enter the transmitter and receiver gain directly or estimate the gain for a diffraction-limited beam. The Gain that
can be expressed by:
GT
GR
This paper is divided into three parts first part introduction in this section we explain the basic introduction
to the optical wireless communication channel and its advantage over other methods of data transmission,
second one is system and description this give basic components in this system and in last section Result and
Description we discuss the performance of our system in terms of Q faction and BER.
II.
SYSTEM DESCRIPTION
To analyze the performance of the optical wireless communication (OWC) system for NRZ and RZ formats
we first setup system as shown in fig2 and same setup is repeated for different bit rate different range of wireless
channel .this optical communication system contains three main parts optical Transmitter, optical wireless
channel and optical receiver. At transmitter a PRBS generator is used to generate data at high speed of 2.5 Gbps
and this feed to input of NRZ/RZ to Generate modulating formats this electrical signal further feed into
electrical input of MZM optical modulator to with CW laser to modulated signal and transmitted using wireless
communication channel and detected at receiver side using Photo detector this signal feed into low pass filter to
remove high frequency signal which is mainly noise after this Q factor and min BER analyzed using BER
Analyzer.
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Yogendra Singh et al. / International Journal of Computer Science & Engineering Technology (IJCSET)
Fig 2: Block diagram of OWC Channel link
TABLE I
LIST OF PARAMETERS USED IN SIMULATION
S. No.
Parameter
Values
1.
Modulator
Mach-Zehnder
2.
Tx. Power
6 dBm
3.
Wavelength
1550 nm
4.
Attenuation
25 dB/Km
5.
Tx. Aperture
Diameter
10 cm
6.
Rx. Aperture
Diameter
10cm
III. RESULT AND DISCUSSION
A. Performance of OWC with NRZ and RZ at 2.5 Gbps:
When we use NRZ as modulation format this gives these values for Max Q factor and Min BER are 22.17,
2.05e-109 respectively. Same system also used for RZ modulation format and gives 27.36, 2.48*e-165 values
for Max Q factor and Min BER respectively.
B. Performance of OWC with NRZ and RZ at 3 Gbps:
When we use NRZ as modulation format this gives values for Max Q factor and Min BER are 18.74 and
5.64e-95 respectively. This system also used for RZ modulation format and gives 23.20 and 1.36e-119 value for
Max Q factor and Min BER respectively.
Figure 3(a)-3(h) shows result and output graphs of system according to data bit rate
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Yogendra Singh et al. / International Journal of Computer Science & Engineering Technology (IJCSET)
Fig3 (a): Q Factor vs. Range (NRZ) at 2.5 Gbps
Fig3 (c): Eye Diagram of NRZ at 2.5 Gbps
Fig3 (b): Min BER vs. Range (NRZ) at 2.5 Gbps
Fig 3 (d): Q Factor Vs. Range (RZ) at 3 Gbps
Fig 3(e): Min BER Vs. Range (NRZ) at 3 Gbps
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Fig 3 (f): Eye Diagram of RZ at 2.5 Gbps
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Yogendra Singh et al. / International Journal of Computer Science & Engineering Technology (IJCSET)
Fig 3 (g) Eye Diagram of NRZ at 3 Gbps
Fig 3 (h) Eye Diagram of NRZ at 3 Gbps
TABLE: II
Bit
Rate
format
Q
Factor
Min
BER
2.5 Gbps
3 Gbps
NRZ
22.17
RZ
27.36
NRZ
18.74
RZ
23.20
2.05e103
2.48e165
5.64e95
1.36e119
Table II shows output values of system at two data rate.
IV. CONCLUSION
In this paper, the robustness of NRZ and RZ modulation formats at 2.5 Gbps and 3 Gbps for optical wireless
communication link has been investigated. The investigations reveals that RZ modulation format is best suited
for optical wireless communication link at different bit rates. Values of Max Q factor, Min BER at 2.5 Gbps are
22.17, 2.05e-103(NRZ) and 27.36, 2.48*e-165(RZ), Similarly Values of Max Q factor, Min BER at 3 Gbps are
18.74 and 5.64*e-95 (NRZ) and 23.20 and 1.36*e-119 (RZ). Moreover the robustness of RZ modulation format
has been justified by wide eye opening in comparison with the NRZ modulation format.
REFERENCES
[1]
[2]
[3]
[4]
Steve Hranilovic “Wireless Optical Communication Systems” ©2005 Springer Science and Business Media, Inc.
A. Polishuk, S. Arnon, 'Optimization of a laser satellite communication system with an optical Preamplifier', J. Optical Society of
America. Vol. 21, No. 7, pp 1307-1315, July 2004
S. Arnon, 'Performance of a laser satellite network with an optical preamplifier', J. Optical Societyof America. Vol. 22, No. 4, pp 708715, April 2005.
Optiwave’s Optisystem tutorials on “Optical Wireless Communication channel”
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