International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 01, January 2019, pp. 1095-1105, Article ID: IJMET_10_01_112
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=1
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
HERMITE-GAUSSIAN MODE IN SPATIAL
DIVISION MULTIPLEXING OVER FSO SYSTEM
UNDER DIFFERENT WEATHER CONDITION
BASED ON LINEAR GAUSSIAN FILTER
1
Sara Alshwani,
Presidency of Kirkuk, Kirkuk University, Iraq
Ahmed M. Fakhrudeen,
2Networks Department, College of Computer Science and Information Technology, Kirkuk
University, Iraq
3
Mohammed Nasih Ismael
Geography Department, College of Arts, Kirkuk University, Iraq
Aras Al-Dawoodi
4Computer Science Department, College of Computer Science and Information
Technology, Kirkuk University, Iraq
Alaan Ghazi
School of Human Development & Techno-communication, Universiti Malaysia Perlis,
Malaysia.
School of Computer and Communication Engineering, Universiti Malaysia Perlis, Malaysia
ABSTRACT
The wireless telecommunication system of hybrid free-space optics (FSO) utilizes
a transmission medium of free space to transmit data at high bit rates. However, it is
exposed to various effects of noise in different weather conditions. This paper
investigates on compensation for atmospheric turbulence in optical communication
systems of 10-channels spatial division multiplexing (SDM) over FSO link under
different weather conditions based on linear Gaussian filter (LGF). The performance
of a 10-channel transceiver system is evaluated in an SDM-FSO link under the clear
sky, haze, and rain weather conditions based on Gaussian filter at the receiver.
Furthermore, the simulated system has transmitted 100 Gbit/s up for a distance of 12
km FSO in superbly very clear weather condition. Moreover, it is also transmitted 100
Gbit/s up for a distance of 4.2 km FSO during heavy rain and up to 1.1 km distance
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Hermite-Gaussian Mode in Spatial Division Multiplexing Over Fso System Under Different
Weather Condition Based on Linear Gaussian Filter
FSO during heavy haze. The results show that system capacity is effectively increased
with the use of SDM that operate at 1550 nm wavelength. Finally, the validation is
conducted based on analyzing eye diagrams, Q-Factor and Bit Error Rates
Keywords: Hermite-Gaussian Mode, Few-mode fiber, SDM, linear Gaussian filter.
Cite this Article: Sara Alshwani, Ahmed M. Fakhrudeen, Mohammed Nasih Ismael,
Aras Al-Dawoodi and Alaan Ghazi, Hermite-Gaussian Mode in Spatial Division
Multiplexing Over Fso System Under Different Weather Condition Based on Linear
Gaussian Filter, International Journal of Mechanical Engineering and Technology,
10(01), 2019, pp. 1095-1105.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=1
1. INTRODUCTION
Free-space optical (FSO) communication system is a growing communication technology,
used as an alternate technology where internet service is not a feasible solution. In FSO light
signal is sent from the transmitter to the receiver using the air as a transmission medium. FSO
systems have several advantages such as, bandwidth scalability, low cost, easy and fast
deployment, portability, license-free operation, high transmission security, high bit rates, and
full duplex transmission [1, 2]. The wireless telecommunication system of FSO utilizes a
transmission medium of free space to transmit optical data at high bit rates. In comparison
with the conventional wireless technologies, from its basic development, the technology has
been improved remarkably in recent years. FSO system uses a similar optical transceiver, like
that of optical communication technology, and it operates through free space, in full-duplex
mode. More importantly, its installation can be very swift at a very low cost. However, it is
exposed to various effects of noise in different weather conditions [3]. Concurrently, the
amount of data that is transmitted keeps increasing. It could be possibly handled by
considering several major at the transmitter like minding the modulation techniques [4],
suitable light source, estimation of transmitting power levels and wavelength transmission [5].
The demand for bandwidth in support of numerous applications keeps increasing too, over the
years [6]. When the bandwidth is expanded, the transmission capacity of the FSO is also
accordingly enhanced, which is necessary in the current video-based information
dissemination world. In addition, FSO promises to provide unlimited integrated services at
substantially high bandwidth and also to support reliability in smart cities with high
bandwidth access networks [7, 8]. In order to facilitate medium-sharing infrastructure within
wireless networks. In the literature, a number of Multiple-Input Multiple-Output (MIMO)
systems have been suggested as options for high bandwidth access networks for the smart
city. The exponential increase of data traffic has inspired researchers across the world to
explore various multiplexing techniques within access networks to increase its capacity and
transmission distance.
Most of the multiplexing schemes for access networks are based on time division multiplexer
(TDM) [9], wavelength division multiplexer (WDM) [10] have been used besides frequency
division multiplexer (OFDM) [11] and optical code division multiple (OCDM) [7].
Amongst many of the multiplexing schemes, spatial division multiplexing (SDM) is a swiftly
emerging as a potential candidate for increasing the aggregate bandwidth of current optical
fiber systems. Moreover, in order to overcome the limitation in FSO, the researchers have
motivated to use SDM. SDM was introduced in FSO which provides higher capacity and a
wide coverage area to facilitate a more number of users [12, 13]. Additionally, it is a new
scheme that has attracted remarkable attention as an innovative technology which increases
the data rate [8, 14, 15]. Besides, SDM multiplexing can support several modes propagate
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Ghazi,
through optical fibers transmission. An SDM is an optical communication method where
spatial modes are utilized as information channels carrying independent data streams. Though
FSO based on SDM has plenty of advantages, its performance is unpropitiously affected by
the atmospheric turbulence. The main causes of interference are haze and rain which changes
the characteristics of the transmitted light and as a result decreases the power density of the
signal transmitted and the effective distance of the FSO link [16]. Equalizers efficiently
mitigate the distortion resulting from noise and atmospheric turbulence [17, 18]. This postprocessing [19] mechanism ensures that the received signal is sufficiently eliminated
unwanted noise at the receiver side. Electronic and photonic equalization schemes [12, 18, 20,
21] could possibly be explored and integrated into the system. The electrical equalizer) linear
Gaussian filter( in this paper is used to affect mode filtering in order to clean the signal at the
receiver.
The rest of the paper is organized as follows. Section 2 describes the research
methodology employed to test or model. Section 3 presents data and description of our
experiments. In Section 4, this article then concludes with a summary.
2. RESEARCH METHODOLOGY
In this section, simulation of SDM over the FSO link under different weather conditions are
provided. The simulation aims to achieve the maximum possible medium range of 10channels. The simulations are carried out on optisystem software [21-27] (as shown in Figure
1). The physical layer components for the FSO based on SDM system consists of three parts:
i) a central office which operates as a transmitter; 2) FSO channel; and 3) a receiver with an
electrical filter which is the customer premises.
Figure 1 Simulation setup of spatial division multiplexing over free-space optics
In the transmitter side, the special optical transmitters are used to generate data (binary
source) at 10-Gbit/s. Additionally, the data is encoded using modulation is based on nonreturn to zero (NRZ) sequence. The transmitter has a subcarrier over a wavelength (1550 nm)
and sends 10-channel goes to ten Hermite-Gaussian (HG) modes. HG modes are HG 01, HG
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02, HG 03, HG 04, HG 11, HG 12, HG 13, HG 14, HG 21 and HG 22. These modes are
transmitted 100 Gibt/s along FSO under a number of weather conditions. Figure 2 shows the
HG modes phase in SDM over FSO. Furthermore, each particular optical transmitter carries
an array which emits one HG mode. Given 10 Gbit/s is transmitted based on one wavelength.
Thus, with 10-channel based, the total data rate is 10 x 10 Gbit/s = 100 Gbit/s over FSO
channel is 14 km long under very clear weather condition. After FSO, the de-multiplexer is
made to retrieve the signals from the FSO. Moreover, the presumed the ten Photodetector
were used to retrieve the signals with Gaussian filter. Finally, Table 1 lists the rest factors in
our simulations.
Figure 2 Modes phase of Hermite-Gaussian (HG 0 1, HG 0 2, HG 0 3, 0 4, HG 1 1, HG 1 2, HG 1 3,
HG 1 4, HG 2 1, and HG 2 2) modes in SDM over FSO.
Table 1 Factors assigned in the simulation.
Factor
value
Parameters of the receive
20 cm
transmitter apertures
20 cm
Laser power
1 dBm
beam divergence
1 µrad [14]
3. RESULTS AND ANALYSIS
To verify system performance, three performance components will be examined; the
parameters are: i) Eye diagram; 2) Bit Error Rate (BER); and 3) Q-Factor. Specifically, the
eye diagram is an oscilloscope block used to display the optical signal noise as electrical
signal noise. Additionally, BER is usually used to compute the transmitted bit errors due to
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Sara Alshwani, Ahmed M. Fakhrudeen, Mohammed Nasih Ismael, Aras Al-Dawoodi and Alaan
Ghazi,
signal loss, dispersion, scattering, or noise by matching the transmitted binary data from the
transmitter to the receiver in the optical medium. Lastly, The Q-Factor is a dimensionless
parameter that describes how under-damped an oscillator.
Therefore, the performance of a 10-channel transceiver system is evaluated in an SDM
over the maximum distance range FSO under different weather condition. The evaluation is
carried out under different weather conditions based on electrical equalization at the receiver
for high bandwidth access networks. As listed in Table 2, the examined weather conditions
are: i) very clear, ii) clear sky, iii) light rain, iv) heavy rain, v) light haze, and vi) heavy haze.
Furthermore, the simulated system has transmitted 100 Gbit/s up for a distance of 12000
meters FSO in superbly very clear weather condition with performance results 5.30377 × 10-14
for BER and 7.43223 for the Q-factor. We then transmitted 100 Gbit/s up for a distance of
11000 meters FSO during clear sky with performance results in 6.00680 × 10-11 for BER and
6.43839 for the Q-factor. Additionally, transmission is carried up to 8200 meters distance
FSO during a light rain with performance results 3.45702 × 10-14 for BER and 7.48861 for the
Q-factor. After that, we performed a transmission up to 4200 meters distance FSO during
heavy rain with performance results 1.74752 × 10-12 for BER and 6.95544 for the Q-factor.
On the other hand, for light haze weather condition, the system transmitted 100 Gbit/s up for a
distance of 2300 meters FSO with performance results 1.13274 × 10-14 for BER and 7.33126
for the Q-factor. Additionally, we transmitted up to 1100 meters distance of FSO during
heavy haze with performance results 7.18356 × 10-12 for BER and 6.75341 for the Q-factor.
Obviously, the performance improves along with the improvement of the bandwidth of the
optical wireless communication system.
Table 2. BER and Q-Factor values of SDM over maximum distance range FSO under different
weather condition.
Weather
Condition
Attenuation
(dB/km)
Very clear
0.15
Clear sky
Max-LinkRange
BER
Q-Factor
12000 m
5.30377e-14
7.43223
0.299
11000 m
6.00680e-11
6.43839
Light rain
0.61
8200 m
3.45702e-14
7.48861
Heavy rain
2.62
4200 m
1.74752e-12
6.95544
Light haze
6.80
2300 m
1.13274e-14
7.33126
Heavy haze
19.77
1100 m
7.18356e-12
6.75341
FSO
Figure 3 and 4 illustrate the comparison among the adopted weather conditions for the
different distance of FSO based on BER and Q-Factor through different distance starting from
1000 meters to 13000 meters. For instant, in distance 1000 meters the results of BER are
(0.00E+00, 0.00E+00, 0.00E+00, 0.00E+00, 0.00E+00, and 4.05E-29) and for Q-factor are
(147.63, 145.78, 141.95, 118.03, 75.31, and 11.137) for very clear, clear sky, light rain, heavy
rain, light haze, heavy haze weather conditions, respectively. Additionally, in distance 2000
meters the results of BER are (0.00E+00, 0.00E+00, 0.00E+00, 0.00E+00, 1.76E-39, and
1.00E+00) and for Q-factor are (86.7518, 83.8955, 78.1301, 47.3344, 13.0934, 0) for very
clear, clear sky, light rain, heavy rain, light haze, heavy haze weather conditions, in distance
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3000 meters for weather very clear, clear sky, light rain, heavy rain, light haze, heavy haze
conditions the results of BER are (0.00E+00, 0.00E+00, 0.00E+00, 6.90E-89, 1.00E+00, and
1.00E+00) and for Q-factor are (57.7825, 54.5719, 48.3173, 19.9523, 0, and 0), in distance
4000 meters the results of BER are (0.00E+00, 1.41703e-319, 1.72E-224, 5.21E-17,
1.00E+00, and 1.00E+00) and for Q-factor are (41.4906, 38.1977, 31.962, 8.29905, 0, and 0)
for very clear, clear sky, light rain, heavy rain, light haze, heavy haze weather conditions
Furthermore, in the distance 5000 meters for weather very clear, clear sky, light rain,
heavy rain, light haze, heavy haze conditions the results of BER are (5.49E-214, 6.60E-172,
4.26E-107, 2.86E-04, 1.00E+00, and 1.00E+00) and for Q-factor are (31.1996, 27.9232,
21.9489, 3.44435, 0, and 0), and in the distance 6000 meters the results of BER are (8.81E130, 2.29E-98, 6.21E-54, 1.00E+00, 1.00E+00, and 1.00E+00) and for Q-factor are (24.2077,
21.0153, 15.4164, 0, 0, and 0) for very clear, clear sky, light rain, heavy rain, light haze,
heavy haze weather conditions.
Figure 3 Q-factor values of HG modes in SDM over FSO different weather conditions.
Moreover, the results of Q-Factor and BER shown in Figure.3 and Figure.4 in distance
7000 meters for weather very clear, clear sky, light rain, heavy rain, light haze, heavy haze
conditions the results of BER are (1.60E-82, 6.71E-59, 1.67E-28, 1.00E+00, 1.00E+00, and
1.00E+00) and for Q-factor are (19.2058, 16.1382, 11.0112, 0, 0, and 0), in distance 8000
meters the results of BER are (1.70E-54, 1.12E-36, 7.57E-16, 1.00E+00, 1.00E+00, and
1.00E+00) and for Q-factor are (15.4999, 12.5943, 7.97477, 0, 0, and 0) for very clear, clear
sky, light rain, heavy rain, light haze, heavy haze weather conditions, in the distance 9000
meters for weather very clear, clear sky, light rain, heavy rain, light haze, heavy haze
conditions the results of BER are (3.32E-37, 1.15E-23, 2.45E-09, 1.00E+00, 1.00E+00, and
1.00E+00) and for Q-factor are (12.6896, 9.95832, 5.85012, 0, 0, and 0), and in the distance
10000 meters the results of BER are (3.82E-26, 8.12E-16, 7.05E-06, 1.00E+00, 1.00E+00,
and 1.00E+00) and for Q-factor are (10.5104, 7.96614, 4.3418, 0, 0, and 0) for very clear,
clear sky, light rain, heavy rain, light haze, heavy haze weather conditions.
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Additionally, in the distance 11000 meters for weather very clear, clear sky, light rain,
heavy rain, light haze, heavy haze conditions the results of BER are (6.88 × 10-19, 6.01 × 1011
, 5.61× 10-4, 1.00, 1.00 and 1.00) and for Q-factor are (8.79831, 6.43839, 3.25764, 0, 0 and
0), in distance 12000 meters the results of BER are (5.30× 10-14, 7.52× 10-08, 6.77× 10-03,
1.00, 1.00 and 1.00) and for Q-factor are (7.43223, 5.2516, 2.46932, 0, 0 and 0) for very clear,
clear sky, light rain, heavy rain, light haze, heavy haze weather conditions and in the
maximum distance is 13000 meters for weather very clear, clear sky, light rain, heavy rain,
light haze, heavy haze conditions the results of BER are (1.22× 10-10, 7.83× 10-06, 1.00, 1.00,
1.00, and 1.00) and for Q-factor are (6.32944, 4.31887, 0, 0, 0 and 0).
Figure 5 and 6 illustrate the eye diagram where the eye wide for all channels on the ten
HG modes have been widened under very clear weather condition. Figure.5 shows the result
of the Q-Factor and BER of (HG 0 1, HG 0 2, HG 0 3, HG 0 4, HG 1 1, and HG 1 2) modes
under clear weather case which are (7.43223, 8.73479, 7.44987, 7.07312, 6.54349, and
8.53545 for the quality factor) and (5.3037 × 10-14, 1.2073 × 10-18, 4.6261 × 10-14, 7.5361 ×
10-13, 2.9971 × 10-13, and 6.9177 × 10-13 for BER), Fig.5 show the result of Q-Factor and BER
of which are (7.53232, 6.82766, 7.39794, and 6.7143 for the quality factor) and (2.4703 × 1010
, 4.3009 × 10-11, 6.8958 × 10-12 and 9.2112 × 10-12 for BER) for HG 1 3, HG 1 4, HG 2 1,
and HG 2 2 under clear weather case
Figure 4 BER values of HG modes in SDM over FSO different weather conditions.
As shown in Figure.5, and Figure.6 illustrates the eye diagram where the eye wide for all
channels on the ten HG modes have been widened under very clear weather condition.
Figure.5 shows the result of the Q-Factor and BER of (HG 0 1, HG 0 2, HG 0 3, HG 0 4, HG
1 1, and HG 1 2) modes under clear weather case which are (7.43223, 8.73479, 7.44987,
7.07312, 6.54349, and 8.53545 for the quality factor) and (5.3037 × 10-14, 1.2073 × 10-18,
4.6261 × 10-14, 7.5361 × 10-13, 2.9971 × 10-13, and 6.9177 × 10-13 for BER), Fig.5 show the
result of Q-Factor and BER of which are (7.53232, 6.82766, 7.39794, and 6.7143 for the
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quality factor) and (2.4703 × 10-10, 4.3009 × 10-11, 6.8958 × 10-12 and 9.2112 × 10-12 for
BER) for HG 1 3, HG 1 4, HG 2 1, and HG 2 2 under clear weather case.
Figure 5 Eye diagram, Q-Factor and BER of the (HG 0 1, HG 0 2, HG 0 3, HG 0 4, HG 1 1, and HG 1
2) modes in SDM over FSO.
Figure 6 Eye diagram, Q-Factor and BER of the (HG 1 3, HG 1 4, HG 2 1, and HG 2 2) modes in
SDM over FSO.
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4. CONCLUSION
This paper investigated the performance of BER and Q-Factor over different distances of over
FSO in different weather conditions based on the linear equalizer. The evaluation aimed to
compensate atmospheric turbulence in optical communication systems of 10 modes SDM.
The findings showed that the performance improves along with the improvement of the
system capacity which can be effectively increased with the use of SDM over FSO that
operate at 1550 nm wavelength based on LGF. Furthermore, the results demonstrated that 10
x 10 Gbit/s SDM-FSO system (in different weather conditions) is effective in improving the
quality of data in an optical wireless communication system. Finally, the performance has
been validated by measuring and analyzing eye diagrams, Q-Factor and BER.
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