4-evaluate the effect of dispersion of fiber on the performance of ocdma system and to find the...

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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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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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3

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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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



= 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





= 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




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5



= 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.

REFERENCES

[1] S.P. Majumder and Md. Forkan Uddin, The effect of four wave

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[3] S.P.Majumder, Member, IEEE, Afreen Azhari, and F.M. Abbou,

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[6] Michael J. OMahony, Christina Politi, Dimitrios Klonidis, Reza

Nejabati and Dimitra Simeonidou, Future Optical Networks

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2005.pdf

[8] Fiber Optic Chromatic Dispersion Effects on High Speed Optica

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[9] S. Song, High-order four-wave mixing and its effect in WDM

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[11]Kohsuke NISHIMURA, Ryo INOHARA, Masashi USAMI, and

Shigeyuki AKIBA, All-Optical Regeneration by Electro

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[12]Ng Wai Ling, F.M. Abbou, A. Abid, and H. T. Chuah

Performance evaluation of FH-OCDMA in the presence of GVD

and SPM, IEICE Electronics Express, Vol.2, No 23, pp. 583-588.

[13]C. H. Chua, F.M. Abbou, H.T. Chuah and S.P. Majumder

"Performance analysis on phase-encoded OCDMA communication

system in dispersive fiber medium", IEEE Photon. Techno/. Letts

vol. 16, pp. 668-670, Feb. 2002.

[14]T. O. Farrell and S. I. Lochmann, "Switched Correlator receiver

architecture for optical CDMA networks with bipolar capacity

Electron. Lett. vol. 31, pp. 905-906, May 1995.

[15]Xu Wang and Naoya Wada, Taro Hamanaka and Ken-ichKitayama, Akihiko Nishiki, 10-user, truly-asynchronous OCDMA

experiment with 511-chip SSFBG en/decoder and SC-based optica

thresholder

http://www.ofcnfoec.org/materials/PDP33.pdf

[16]Muhammad Haris, Advanced modulation formats for high bit rate

optical networks, School of Electrical and computer engineering

Georgia Institute of Technology, August, 2008.

[17]Abdul Gafur, Md. Humayun Kabir, and Waqas Ahmad, Optica

CDMA Network Based on Star Coupler Aspects of BER, Received
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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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.

[20]T. O'Farrell and S. I. Lochmann, Switched correlator receiver

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

Technology, Vol.15, No.8, August 1997.

[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

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