performance analysis of hybrid ocdma/wdm system

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International Journal of Electronics Communication and Computer EngineeringVolume 4, Issue 3, ISSN (Online): 2249–071X, ISSN (Print): 2278–4209

Performance Analysis of Hybrid OCDMA/WDM SystemComplementary Subtraction Detection Technique

Aymen Abdalmunam Hameed

Abstract – We proposed a hybrid optical code divisionmultiple access (OCDMA) over wavelength divisionmultiplexing (WDM) system is proposed for supporting largenumbers of subscriber for fiber to-the-home (FTTH)network. The system combines two different techniques,namely OCDMA and WDM in order to support manysubscribers simultaneously. In this study, the hybridOCDMA/WDM system for FTTH access networking usingcomplementary detection technique and To analyze theperformance of the simulated system. the modified doubleweight (MDW) code is used as signature address in designingthe system because this code can accommodate more Numberof simultaneous active users under standard acceptable bit-error-rate (e.g. ≤ 10-9). The complementary subtractiondetection technique is used to detect the signal.. The MDWcode is better than other codes for improving the systemperformance by reducing the multiuser interference in asignificant amount. We have done the result of this paper byusing a simulating of matlab. We ascertained by simulationexperiments that the proposed system provides high impactperformance and enhance the network capacity. Theproposed hybrid system would then be a prospectivecandidate for the future FTTH access network. In this studyI will make a comparison between several codes to improvethat the proposed MDW is better than others.

Keywords – Optical Code-Division Multiple-Access(OCDMA), Optical Orthogonal Code (OOC), Double-Weight(DW) Code, Modified Double-Weight (MDW) Code,Modifies Frequency Hopping (MFH) Code.

I. INTRODUCTION

OPTICAL code-division multiple-access (CDMA)systems are getting more attractive in the field of all-optical communications as multiple users can access thenetwork asynchronously and simultaneously with a highlevel of transmission security. In our proposed system, thedata is encoded into OCs by the encoder at the transmitterside and multiple users share the same transmission byusing a power splitter/combiner [1]. At the receiver side,the system decoder recognizes the OCs by performingmatch filtering. However, the OCDMA network capacityis limited and spectral efficiency is low. The networkcapacity can be increased by developing a hybrid SAC-OCDMA over WDM scheme, which can support morenumber of active users because the WDM technologyoffers an enormous bandwidth of optical fibers andprovides multiple parallel channels at reasonable datarates. Due to the complex code (e.g. frequency-hoppingcodes), the system performance is always degraded. It isthen necessary to design a hybrid system without complexcode. Accordingly, we designed a SAC-OCDMA overWDM hybrid system using Modified Double Weight(MDW) code for our study to fulfill the subscriber’sdemand of transmitting high data traffic. The main reason

to choose the MDW code is that this code can successfullysuppress the MAI effect using the complementarysubtraction technique [2] [3]. As mentioned the hybridSAC-OCDMA-WDM network can support asynchronousoperation, high speed connectivity, simplified networkcontrol, flexible bandwidth management, fairnessimproved security and service differentiation, the proposedhybrid system would then be a prospective candidate forthe future FTTH access network .OCDMA is a spread-spectrum technology where multiplexing is accomplishedby encoding each data transmission with an optical coderather than assigning a wavelength or time-slot.(OCDMA)Optical code division multiple access is a promisingmultiplexing technique that is particularly suited for futureall-optical access networks[4]. OCDMA has a number ofinherent advantages such as asynchronous transmission,quality of service control and a large degree of flexibilityand scalability. Various demonstrations of enablingtechnologies have been presented. As we mentioned thehybrid SAC-OCDMA-WDM network can supportasynchronous operation, high speed connectivity,simplified network control, flexible bandwidthmanagement, fairness improved security and servicedifferentiation. The proposed hybrid system would then bea prospective candidate for the future FTTH accessnetwork.

II. MODIFIED DOUBLE WEIGHT (MDW) CODE

PROPERTIES

The MDW code is a modified version of DW codefamily and both DW and MDW code properties are thesame except that the MDW code has a weight more thantwo or any even number. Since the code weight increasesthe signal power of the system then the signal to noiseratio ( ) for MDW code is high [5]. The MDW codecan be represented by matrix [3] [4]. The basicmatrix for MDW code with weight 4 consists of a [3 × 9]matrix. The significant properties of MDW code is that theideal cross-correlation is one ( = 1) and sometime zero( = 0). An example of basic matrix construction forMDW code with chip sequences is presented in Table 1,where k indicates the number of users and indicates thecolumn number of the codes and represents the spectralposition of the chips.

The spectral position of MDW code sequenceconstruction for four weights is shown in Table 1, whereC1, kIs the first user weight and C9, k for the last user.The MDW user is given as C4k =CN and C1k = CN - 1.The MDW code possesses numerous advantages includinghigh efficient, easy code construction, simpleencoder/decoder design, existence for every naturalnumber n and optimized code length. The MDW code is



used as SAC code of each user group in our proposedscheme and the phase cross-correlations of resulting codeswill be no more than ones from the original MDW codes.Table 1: Matrix construction for MDW code when weight

(W = 4)9 8 7 6 5 4 3 2 11 0 0 0 0 1 1 0 1 1

2 0 1 1 0 0 0 1 1 0

3 1 1 0 1 1 0 0 0 0

III. COMPLEMENTARY DETECTION TECHNIQUE

The complementary subtraction detection technique is awell-known detection technique, which is known as thebalanced detection technique. Its implementation is shownin Fig. 2, where the received signals are divided into twodifferent complimentary branches of spectral chips. Thesetwo signals are then towards to the balanced detector thatcomputes the difference of correlation. The crosscorrelations are defined as.θXY (k) = ∑ Xi Yi + k (1)

Where X and Y are two OCDMA code sequence.The

complementary of sequence (X) is given by ( X ) whose

elements are obtained from (X) by X i =1-xi. Let X =

0011 and Y = 0110 and therefore X = 1100. The periodic

cross correlation sequence between and ( X ) (Y) is similarto Eq. (1) and is expressed as:

θXY (k) = X i yi + k (2)

The code cross-correlation sequences are as follows

θXY (k) = è X Y(k) (3)The photodetectors detects two complementary inputs at

the receiver. The cross-correlation output Z can beexpressed as: = θXY (k) − θ X Y(k) = 0 (4)

There is no more cross correlation at the output of thesubtractor when = 0and the channelinterferences between two channel are fully minimized

Fig.1. Implementation of the Complementary SubtractionTechnique

In our proposed, work was done on simulation of thesystem using MATLAB considering various codes withrespect to the number of active users. The variousgraphical result obtained have been studied to look at andanalyze the performance of the systems. These areillustrated in the following figure below.

Fig.2. Comparison of BER among different codes againstnumber of simultaneous users at 622 Mb/s bit Rate.

Figure 2 represents the comparison between number ofactive user and respective bit error rate. It shows theperformance output variation between MDW (modifieddouble weight), MFH (Modified frequency hopping), DW(double weight), Hadamard and OOC (optical orthogonalcode) As number of users are increasing the bit error rateis decreasing Number of users are inversely proportionalto bit error rate. Proposed to improve that MDW is betterthan others.

III. PROPOSED SYSTEM ARCHITECTURE

In designing the proposed OCDMA over WDMschemeusing MDW code for optical networks, it isassumed that thescheme is implemented by 6×6multiplexer/demultiplexer. Asimple technique has beenapplied for hybrid system channelrepresentation. Forexample, two WDM wavelengths willtransmits signal forsix OCDMA active users within a singlesystem. Figs. 3and 4 illustrate the simple block diagram of proposedscheme and its decoder details, respectively. The bothsystem chip has a spectral width of 0.8-nm. Thetransmitted signal is sliced by multiplexer and splitter.Then the signal is modulated by a modulator andcombined using demulltiplexer. The standard single-modeoptical fiber (SMF) is used for transmitting the signal tothe receiver side. TheFiber Bragg Grating (FBG) spectralphase decoder is used todecode the data at data sub matrix.In the receiver namely decoder, the complementarysubtraction detection technique is used to detect thesignal.The detected signal is then decoded by a photo-detector (PIN) followed by a 0.75 GHz low-pass filter(LPF) and errordetector respectively. The power istransmitted between 0 to10 dBm out from the broadbandsource. The random anduncurled noise is generated in thereceiver side. The darkcurrent value is 6 nA, and thethermal noise 1.8 × 10 W/Hzfor each of the photodetectors. In the system, each user light source is assumedto be unpolarized that carries the spectrum flat bandwidthΔV Hz.

K



Fig.3. Overall system block diagram of hybrid system withsix OCDMA and one WDM user.

Fig.4. Overall hybrid system decoder architecture

IV. NETWORK SIMULATION

The simulation was carried out using simulationsoftware, OptiSystem Version 9.0, accordance with thesystem architecture as shown in Fig. 3. We run thesimulation on the system of 20-km ITU-T G.652 standardsingle-mode optical fiber (SMF) using RZ modulationformat at 622 Mb/s bit rates. All fiber parameters such asattenuation, group delay, group velocity dispersion,dispersion slop are activated during simulation. Theaverage fiber loss is about 0.2 dBm including the splicingloss. The system insertion loss includingmultiplexer/demultiplexer is taken into the account 0.25dBm and 2 dBm respectively. All fiber attenuation α (i.e.,0.25 dB/km), dispersion (i.e.,18 ps/nm km), nonlineareffects such as four wave mixing and self-phasemodulation were activated and specified according to thetypical industrial values to simulate the real environmentas close as possible. The system specifications listed inTable 3 were used throughout the simulation.

Table 2: Sumerry of system parameter.Data rate of hybrid system 622 Mb/sChannel spacing 0.8-nmInsertion loss 0.25dBmMux/Dmux Insertion loss 2dBmFiber attenuation 025dB/kmBBS Wavelength 1545-1565

V. RESULT

To analyze the performance of simulated design, thecomparison is made between the BER of the hybridsystem and the conventional OCDMA for the wholelength of fiber.

Fig.5. Comparison of BER between the proposed hybridsystem and the Conventional OCDMA system against

fiber distance.

Figure 5: represents the comparison between the variousdistance and bit error rate. It shows that the BERperformance of the hybrid system is better than theconventional OCDMA for the whole length of fiberdistance (30km). It is also found that the proposed hybridsystem can handle the error free transmission (BER ≤10^ − 9) up to 15 km of fiber distance, whereas theconventional OCDMA can cover only 5 km for the sameBER . This was made possible by using two different datarates in the proposed hybrid system.

Subsequently, we observed the variation of measuredBER against received optical power for both the hybridsystem and the conventional OCDMA system. We observethat the proposed hybrid system offers better BERperformance as compared to the conventional OCDMAsystem at various optical powers.

Fig.6. Measured BER against received optical power forOCDMA-WDM and OCDMA system.

Figure 6 represents the comparison between the variousoptimal power and bit error rate. This indicates thevariation of measured BER against received optical powerfor both the hybrid system and the conventional OCDMAsystem. We also observe that the proposed hybrid systemoffers better BER performance as compared to theconventional OCDMA system at various optical powers.The average received power for the first and last users ofthe hybrid system is about -24dBm to -30 dBm, whereasthe average received power for conventional OCDMAsystem is - 24 dBm to -32 dBm. Although the proposedhybrid system consumes a little bit more power thanOCDMA. The signal quality of the hybrid system was also



investigated using eye diagrams. It was found that theperformance of the proposed system is better than theconventional OCDMA system.

Fig.7. (a) OCDMA-WDM system channel bit error rate(1-09)

Fig.7. (b) OCDMA channel bit error rate (1-08)

Fig.7 OCDMA-WDM system channel bit error rate(10 ) (b) OCDMA channel bit error rate (10 )

Figure 7 represents the channel bit error rate forOCMDA WDM system .As the time is increasing theamplitude is gradually increasing and reaches the peak ato.5sec and then gradually decreases to reach to the lowervalue at 1sec. It is observed that the output from theAWGN (additive white Gaussian noise) channel betweentransmitter and receiver of OCDMA WDM the bettersignal quality. The figure indicates difference of amplitudeand time at OCDMA WDM. Figure b, Represents the

channel bit error rate for system at 622Mb/s As time isincreasing the amplitude is gradually increasing till thepeak at o.5sec and gradually decreases reach the lowervalue at 1sec. It is observed that the output from theAWGN (additive white Gaussian noise) channel betweentransmitter and receiver of OCDMA. These figuresindicate the difference of amplitude and time at OCDMA.

VI. CONCLUSION

We proposed a new hybrid SAC-OCDMA over WDMscheme using MDW code for optical access networks. TheBER performance of the system has been investigatedagainst various lengths of the optical fiber and differentreceived power. The signal quality of the hybrid systemwas also investigated using eye diagrams. It was foundthat the performance of the proposed system is better thanthe conventional OCDMA system. Accordingly, theproposed system can be a promising solution for fiber-to-the-home (FTTH) networks offering flexibility, highspectral efficiency, cost effective and ensured security.

ACKNOWLEDGMENT

This paper is the end of my journey in obtaining myMaster degree. I have not travelled in a vacuum in thisjourney. This paper has been kept on track and been seenthrough to completion with the support andencouragement of numerous people including my well-wishers, my friends and adviser. At the end I would like tothank all those people who made it possible and anunforgettable experience for me. At the end of my paper, itis a pleasant task to express my thanks to all those whocontributed in many ways to the success of this study andmade it an unforgettable experience for me.

REFERENCES

[1] J. Huang, Y. Chang and C. Hsu (2007.). Hybrid WDM and opticalCDM Aimplemented over waveguide-grating-based FTTHnetworks.[Online]. Available :http://ieeexplore.ieee.org

[2] S. AAljunid, M. Ismail, A. R. Ramli, B. M. Ali, and M. K.Abdullah (2004 October). A new family of optical code sequencesfor spectral-amplitude-coding optical OCDMA system.[Online].Available :http://ieeexplore.ieee.org

[3] Hilal A. Fadil, S. A. Aljunid1, R. B. Ahmad (2009 June).Performance of random diagonal code for OCDMA systems usingnew spectral direct detection technique,” [Online]. Available:http://ieeexplore.ieee.org

[4] E. D. J. Smith, R. J. Blailkie, and D. P. Taylor(1998 May)Performance enhancement of SAC optical CDMA using pulse-phase modulation.[Online]. Available :http://ieeexplore.ieee.org

[5] L. Nguyen, B. Aazhang, J. F. Young (1995 March). All opticalCDMA with bipolar Codes. [Online]. Available:http://ieeexplore. ieee.org

AUTHOR’S PROFILE

Aymen Abdalmunam HameedMaster in Electronic and communication systemFrom SHIATS – Allahabad – [email protected]: Iraq

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performance analysis of hybrid ocdma/wdm system

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