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7/30/2019 4-Evaluate the effect of dispersion of fiber on the performance of OCDMA system and to find the limitations impo
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
AM Publishers Corporation
1
Evaluate the effect of dispersion of fiber on theperformance of OCDMA system and to find the
limitations imposed by dispersion on the
number of user and length of transmission
Abdul Gafur,Doru Constantinescu, and Md Dulal Haque
Abstract This article represents the effect of dispersion of fiber
considering m-Sequence Optical Code Division Multiple Access
(OCDMA) network based on star coupler and optical receiver. Matlab
simulations can be performed to find the limitations imposed by
dispersion on the number of user and length of transmission of fiber.
As a result we investigated the performance curve for bit error rate
(BER), signal to noise ratio (SNR) and eye diagram. In the curve of bit
error rate, it is found that the error is decreased when the number of
simultaneously users increased. In the performance curve of SNR, it is
also observed that the system performance is increased with the
raising SNR. We simulate the various scenarios of eye diagram
considering the effect of dispersion .The eye diagrams can be
performed to reduce the dispersion index ().
Index Terms Signal to Noise Ratio (SNR), Optical Correlator
Receiver (OCR), Optical CDMA (OCDMA).
I. INTRODUCTION
n the decade 1985-1995, four significant events heralded the
possibility of optical net-working namely that both
transmission and switching could be based on fiber optic
communication. This was realized due to four main factors:
Realization of optical amplifiers, Economic deployment of
Wavelength Division Multiplexing (WDM), Introduction of an
Optical Cross Connect (OXC) enabling rapid reconfiguration of
light paths based on the wavelength channels, Convergence of
services and transport transmission rates [6].
Nowadays wavelength division multiplexing (WDM)
transmission technologies realize optical link capacities
exceeding 10 Tbit/s per fiber based on 40 Gbit/s per wavelength
channel [11].In the optical technology, light propagates
considering the total internal reflection technology. For this
reason the carrier of optical fiber is the light. The bandwidth
depends on the frequency .The frequency of light is abundant. Inthis paper we use the star coupler. The loss of optical coupler is
minimum which is around 0.5dB.Without star coupler we can
transmit and receive optical signal. In this situation, the loss is
maximum than the star coupler. In this paper we tested the
performance curve by computer simulation for Bit error rate
versus optical received signal considering multiple subscribers. I
is also simulated the Signal to noise ratio versus optical received
signal which is measured in dBm. The simulations of Eye
diagram are performed to reduce the dispersion effect in theOptical Code Division Multiple Access Network with differen
lengths of fiber.Development of the optical fiber communications
technology has evolved rapidly in order to achieve larger
transmission capacity and longer transmission distances [12]
Nowadays, OCDMA systems are highly interesting as they offer
several sought-after features such as asynchronous access
privacy, secure transmissions, and ability to support variable bi
rates and busy traffic and provide high scalability of the optical
network [3].
Manuscript received December 15, 2009.
II. SYSTEM DESCRIPTION
The typical diagram of an OCDMA system is described in
Figure 1 and 2, for an OCDMA transmitter and for an Optical
Correlator Receiver (OCR) with switched sequence inversion
keying, respectively [1] [22].
I
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
AM Publishers Corporation
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Figure 1: Transmitter of Optical CDMA
Figure 2: Receiver of Optical CDMA
In the OCDMA transmitter, a modulation is occurred which is
intensity modulation .In this section users use a signature
sequence .in this paper we use the 7chip m sequence. This
electrical signal is converted to optical signal through the optical
driver .Than it is sent to the star coupler. Star coupler put this
signal to optical channel. Due to the signature sequence the
multiple access interference is low here.
In the receiver section a PIN diode and a switched optical
correlator used In order to recover the original data, a bipolar
reference sequence is correlated directly with the channels
unipolar signature sequence [1].
In addition, the optical correlator follows unipolar switching
functions for de-spreading the optical channel signal [5].The
photodiode of PIN is called the p-i-n photodetectorr. Here, i is
undoped intrinsic region between the doped regions of n and p.
Finally, the PIN photodiode cancels the de-spreaded signal
integrated with the periodic data. This happens before the
detection of the zero threshold voltage [22].
III. SYSTEM ANALYSIS
In the Optical code division multiple access (OCDMA)
transmitter, the Sequence Inversion Keying (SIK) modulated
signal is passed through the optical drive to a laser diode.
Mathematically , the expression forthK users can be written as
[3]
)1()()()(1
0
c
N
l
kkTk lTtAtBPtS =
=
In (1), provides information about the transmitted outpu
pulse shape for different users in single mode fiber while l is the
period of the chip and is the optical power of the chip
Furthermore, and are the users binary signal and
signature codes, respectively. The operator
)(tSk
TP
kB
kA
describes the
sequence inversion key modulation, where is transmitted for
a 1,
kA
kA is transmitted for a 0, respectively. Furthermore
is the pulse interval. In the OCR with switched sequence
inversion keying, due to chromatic dispersion of the optical fiber
the output can be expressed mathematically as [3]
cT
)(sin*
1)(
)4
()(
)1
(1
0
2
c
c
signT
lTtjn
l
outputT
lTtcetS
c
c
=
=
Here, indicates the index of chromatic dispersion of the
optical fiber which can be expressed mathematically as [5]
)3())((
)( 22
LDbc
c
=
In (3),, c ,L and describes wavelength of the optica
carrier, velocity of light, length of fiber and coefficient o
chromatic dispersion respectively of optical fiber . is the
duration of chip. The signal is sent to the photo detector and is
integrated in the output of the correlator for the i
D
cb
th user which is
mathematically expressed as [3]
)(*})()({*)()()(2
)(0 1
1
0 0
0 =
=
+=T K
K
N
l
T
cicicKoutKR
i dtndtlTtAlTtAlTtAtStBRP
tZ
Here, R, K and 0n shows the responsivity of the photodiode
multiple subscriber of the system and noise in the channe
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
AM Publishers Corporation
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respectively. Represents the optical received power given by
[5]
RP
)5(fTR PPP =
The mean of is given by [3])(tZi
)6()(40
1
0
= =
T N
l
coutR
dtlTtST
RP
U
The interference variance due to multiple accesses is given by
[20]
)7(3
)1(222
N
KU
=
The thermal noise and the shot noise of the photo detector
are given by [5]
THN
)8(*)4(
L
rrB
THR
BTKN =
)9(4
2
T
qRKPN RSH =
In (9) and (10), ,
.and define Boltzmann constant,
receivers bandwidth and temperature respectively. q. and
.denote the electrons charge and the load resistor of the
receiver section.
BK rB rT
LR
The signal to noise ratio (SNR) and bit error rate (BER ) of theOCDMA system are given by [1]
)10(0
2
2
N
USNR
+=
)11()2
()2
1(
SNRerfcBER =
IV. SYSTEM PERFORMANCE
In this simulations work we use the matlab 7.5. The system is
evaluated by means of 10x109 chips/s. We tested the performance
curve for bit error rate and signal to noise ratio considering m
signature code, wave length of 1550nm, and single mode of
optical fiber. It is also performed the eye diagram by means of 17
ps/km-nm dispersion coefficient. In the receiver, Electron charge
(1.6e-19 c), Boltzmann constant (1.38e-23 W/K. Hz), Received
optical power gain (-20), Dark current(10 nA), Thermal current(1
pA2Hz-1) are used to simulate system performance.
-20 -18 -16 -14 -12 -10 -810
-30
10-25
10-20
10-15
10-10
10-5
100
Received Optical Power(DBm)
BitErrorRate
No of Users(k) 4
No of Users(k) 8
No of Users(k) 13
No of Users(k) 21
Figure 3: Simulation for bit error rate versus received optica
power
The figure (3) describes the performance of OCDMA network
for bit error rate versus received optical power considering
multiple users. It is observed that the bit error rate is decreased
with increased the number of users. For 10-15 BER, the received
optical power is -13 dBm and -11dBm for users 4 and 8
respectively.
-20 -18 -16 -14 -12 -10 -80
10
20
30
40
50
60
70
80
90
100
SignaltoNoiseRatio
Received Optical Power(DBm)
No of users 4
No of users 8
No of users 13
No of users 21
Figure 4: Simulation for SNR versus received optical power
The signal to noise ratio effects the receiver section of OCDMA
network. It is found that the performance is improved when the
signal to noise ratio is increased. In the above graph , for SNR 50
the received optical power is -13dBm and -12 dBm for users 4
and 13 respectively.
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
AM Publishers Corporation
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20 40 60 80 100 120 140 160 180 2000
0.2
0.4
0.6
0.8
1
1.2
1.4
OutputCurre
nt
Samples in a Chip
Figure 5: Eye-diagram with chromatic dispersion index
= 0.3 & length of fiber 50Km
The above graph (5) is for eye diagram to measure the dispersion
effect on the OCDMA system with chromatic dispersion index
= 0.3, the fiber length 50 Km and dispersion coefficient
17ps/km-nm
20 40 60 80 100 120 140 160 180 2000
0.2
0.4
0.6
0.8
1
1.2
1.4
OutputCurrent
Samples in a Chip
Figure 6: Eye-diagram with chromatic dispersion index =
0.4 & length of fiber 50Km
The above graph (6) is for eye diagram to measure the dispersion
effect on the OCDMA system with chromatic dispersion index
= 0.4 , the fiber length 50 Km and dispersion coefficient
17ps/km-nm. The performance of the system depends on the
opening and closing the Eye in the Eye diagram. Here it is found that
the eye is more closed for chromatic dispersion index = 0.4
than chromatic dispersion index = 0.3 when the fiber length is
50 KM.
20 40 60 80 100 120 140 160 180 20
0.2
0.4
0.6
0.8
1
1.2
1.4
OutputCurrent
Samples in a Chip
Figure 7: Eye-diagram with chromatic dispersion index =
0.3 & length of fiber 60Km
The above graph (7) is for eye diagram to measure the dispersion
effect on the OCDMA system with chromatic dispersion index
= 0.3 ,the fiber length 60 Km and dispersion coefficient
17ps/km-nm
20 40 60 80 100 120 140 160 180 2000
0.2
0.4
0.6
0.8
1
1.2
1.4
Outp
utCurrent
Samples in a Chip
Figure 8: Eye-diagram with chromatic dispersion index =
0.3 & length of fiber 70Km
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
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The above graph (8) is for eye diagram to measure the dispersion
effect on the OCDMA system with chromatic dispersion index
= 0.3, the fiber length 70 Km and dispersion coefficient
17ps/km-nm. The performance of the system depends on the
opening and closing the Eye in the Eye diagram. Here it is found that
the eye is more closed for fiber length of 70 Km than fiber length of
60Km when chromatic dispersion index = 0.3
V. CONCLUSION
The bit error rate , signal to noise ratio and eye diagram is
simulated according to system analysis .In the bit error rate
performance curve the error is decreased when the number of
subscriber is increased side by side the optical power is reduced
when the users is added. Here for the user sequence is the m
sequence .In the case of SNR it is found that the system
performance is improved with raising the level of signal to noise
ratio. To reduce the effect of dispersion we simulate the different
scenario of Eye diagram with dispersion index, dispersion
coefficient and fiber length. It is found that the size of eye is
reduced when the chromatic dispersion index gamma and the
fiber length is increased. These scenarios play a role to reduce
the dispersion for the OCDMA system for manufacture ring.
ACKNOWLEDGMENT
The execution of this article is the consequence of great attempt
of group members.
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http://www.ds.eng.monash.edu.au/techrep/reports/2005/MECSE-4-2005.pdfhttp://www.ds.eng.monash.edu.au/techrep/reports/2005/MECSE-4-2005.pdfhttp://www.ee.kent.ac.uk/research/theme_project.aspx?pid=94http://smartech.gatech.edu/handle/1853/14130http://www.ofcnfoec.org/materials/PDP33.pdfhttp://www.ofcnfoec.org/materials/PDP33.pdfhttp://smartech.gatech.edu/handle/1853/14130http://www.ee.kent.ac.uk/research/theme_project.aspx?pid=94http://www.ds.eng.monash.edu.au/techrep/reports/2005/MECSE-4-2005.pdfhttp://www.ds.eng.monash.edu.au/techrep/reports/2005/MECSE-4-2005.pdf -
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Canadian Journal on Signal Processing Vol. 1, No. 1, February 2010
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Optical Power and Number of Users, BTH transaction on
Engineering Research Methodology , Karlskrona, Sweden,
November 2008.
[18]Dr.Yuliya Semenova, Optical Communications Systems, Dublin
Institute of Technology, School of Electronics and Communication
engineering
http://www.electronics.dit.ie/staff/ysemenova/OCS/Optical%20Rec
eivers.pdf
[19]S. P. Majumder, Afreen Azhari, Performance Analysis of an
Optical CDMA in the Presence of Fiber Chromatic Dispersion,
Bangladesh University of Engineering and Technology.
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architecture for optical CDMA networks with Bipolar capacity,
Electron. Lett,vol. 31, pp. 905-906, May. 1995.
[21]Kenneth O. Hill and Gerald Meltz, Fiber Bragg Grating
Technology Fundamentals and Overview, Journal of Lightwave
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[22]Abdul Gafur, Dr. Doru Constantinescu, Dispersion Effects on
OCDMA system performance Blekinge Institute of Technology,
School of Computing , September 2009,Sweden
http://www.bth.se/fou/cuppsats.nsf/1d345136c12b9a52c125660800
4f0519/30ad855f8cbc8679c125763a0078360f!OpenDocument
[23]Abdul Gafur, Dr. Doru Constantinescu and Md. Dulal Haque,
Dispersion Effects on OCDMA system performance Journal of
Scientific Research ,Rajshahi University, Bangladesh, (Submitted
for publication),
http://www.banglajol.info/index.php/JSR/index
Abdul Gafur was born in Coxsbazar, Bangladesh in 1981. He
received his B. Sc (CCE) Bachelors of Science in Computer &
Communication Engineering from International Islamic
University Chittagong (IIUC), Bangladesh; in 2005.He is a
Lecturer at University of International Islamic University
Chittagong (IIUC), the department of Computer &
Communications Engineering (CCE) since 2005. He received
the degree of M.Sc. in Electrical Engineering at Blekinge
Institute of Technology (BTH), Sweden. His research interests
are in the fields of Optical Fiber Communications.
Doru Constantinescu is the Faculty member of School of
Computing, Blekinge Institute of Technology, 371 79
Karlskrona, Sweden. (E-mail: [email protected]).He
received the PhD in Telecommunication Systems (December
2007).His research interests focus on traffic modeling and
analysis, wireless communications and protocols, mobility
prediction, overlay multicast networks and services, IMS-enabled
networking, seamless communications, network graph theory
with focus on social network analysis.
Dulal Haque (e-mail:[email protected]) is serving
as a lecturer in the dept. of Computer and Communication
Engineering, International Islamic University Chittagong
Bangladesh. He received the B.Sc. and M.Sc. in Applied Physics
and Electronics from the Rajshahi University,Bangladesh. His
research interests focus on electronics, wireless communications
and information theory and error coding.
http://www.electronics.dit.ie/staff/ysemenova/OCS/Optical%20Receivers.pdfhttp://www.electronics.dit.ie/staff/ysemenova/OCS/Optical%20Receivers.pdfhttp://www.bth.se/fou/cuppsats.nsf/1d345136c12b9a52c1256608004f0519/30ad855f8cbc8679c125763a0078360f!OpenDocumenthttp://www.bth.se/fou/cuppsats.nsf/1d345136c12b9a52c1256608004f0519/30ad855f8cbc8679c125763a0078360f!OpenDocumenthttp://www.banglajol.info/index.php/JSR/indexmailto:[email protected]:[email protected]:[email protected]:[email protected]://www.banglajol.info/index.php/JSR/indexhttp://www.bth.se/fou/cuppsats.nsf/1d345136c12b9a52c1256608004f0519/30ad855f8cbc8679c125763a0078360f!OpenDocumenthttp://www.bth.se/fou/cuppsats.nsf/1d345136c12b9a52c1256608004f0519/30ad855f8cbc8679c125763a0078360f!OpenDocumenthttp://www.electronics.dit.ie/staff/ysemenova/OCS/Optical%20Receivers.pdfhttp://www.electronics.dit.ie/staff/ysemenova/OCS/Optical%20Receivers.pdf