Comparative Performance of SAC-OCDMA ZCC code system using modulators and filters

IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 08, 2015 | ISSN (online): 2321-0613

Comparative Performance of SAC-OCDMA ZCC Code System using Modulators and Filters Meet Kumari1 Himali Sarangal2 M.Tech. Student 2Assistant Professor 1,2 Department of Electronics & Communication Engineering 1,2 GNDU Regional Campus, Jalandhar, Punjab, India 1

Abstract— In continuing growing optical communication Spectral Amplitude Coding- Optical Code Division Multiple Access (SAC-OCDMA) system plays a vital role. The presence of Zero Cross- Correlation (ZCC) code in SACOCDMA system; enhance its performance as compared to other codes due to its properties. This innovative SACOCDMA ZCC code system can be used for long haul distance communication by using an effective modulator and filter. Hence, in this paper the performance of SACOCDMA ZCC code system compared in terms of using different modulators and filters. The results shows that SAC-OCDMA ZCC code system using both electro absorption modulator and low pass raised cosine filter can be used for large distance of 70 km and high data bit rate of 10 Mbps for 5 no. of users. The simulation is done in Optisystem 7.0.

Key words: SAC-OCDMA ZCC Code System, Modulators I. INTRODUCTION The optical communication technique is the most incoming future demand because of its bandwidth utilization capacity with high speed. This communication can use for different systems applications [1]. SAC-OCDMA system is such a future’s advance and attractive technology. It provides the high security, asynchronous data access, simple design and satisfies users’ demands [2]. In this technique the information is send threw spectral encoding, where each user has a unique orthogonal code pattern in the form of ‘on’ and ‘off’ [3], [4]. As SAC-OCDMA technique uses different types of codes. But a high performance can be obtained by choosing an effective code, which should have the property of minimum cross-correlation and maximum auto correlation [5], [6]. Hence, ZCC code shows high performance than other codes in SAC-OCDMA. This code has the property of zero cross-correlation and maximum auto correlation. This code is simple in design, eliminate MAI and PIIN noises can handle large number of users (>100 users) [7].

As the performance SAC-OCDMA ZCC code system highly depends on components used at transmitter and receiver side. Hence, at transmitter side modulator is such an effective component. As the future communication services are based on millimeter based optical communication, hence to transmit the signal over optical fiber modulator is used. Optical modulator helps in transmission of incoming data in light signals. So, there are many modulators can be used. But Mach-Zehnder optical modulator (MZM) is mostly and demanding used modulator in optical systems, because this modulator has the ability to improve the modulation efficiency. Similarly, filter is another one important component used at receiver side as it reduces the noises and provides the desired output. This again depends upon the choice of filter. In optical communication mostly used filter is low pass filters. These electrical Low-pass filters have the advantages of better quality, small size, reliable, sensitive to signals and cost effective as compared to others filters, hence mostly used in optical communication. The mostly used filter in optical communication is Low pass Bessel filter because of its advantages [8]-[11].

In this paper, the performance of SAC-OCDMA system using ZCC code is compared using different modulators at transmitter side and different filters at receiver side. This performance is compared at different distances.

The aim of this paper is to use effective modulator and filter in SAC-OCDMA ZCC code system as compare to earlier.

Thus using Electroabsorption Modulator and low pass raised cosine filter improves the system performance. For simulation of this system Optisystem 7.0 is used.

II. SYSTEM MODEL Fig. 1 shows the block diagram of SAC-OCDMA system using ZCC code for 5 numbers of users. It consists of transmitter, optical channel and receiver.

Fig. 1: Basic block diagram of SAC-OCDMA ZCC code system for 5 numbers of users At the transmitter side, LASER is used an input combined and transmitted through optical fiber cable. At the light source. Here, the encoder consists of Bit Sequence receiver side, power splitter is used for splitting power to (PRBS) generator, Non Return to Zero (NRZ), WDM dedecoders. The decoder consists of WDM de-multiplexer, multiplexer and modulator. Then each modulator’s power is PIN photodiode, filter, 3R regenerator and BER analyser.

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Comparative Performance of SAC-OCDMA ZCC Code System using Modulators and Filters (IJSRD/Vol. 3/Issue 08/2015/115)

For comparison, Amplitude Modulator, Electroabsorption Modulator and Mach-Zehnder Modulator are used. Then low pass chebyshev filter, low pass butterworth filter, low pass Gaussian filter, low pass Bessel filter and low pass raised cosine filter are used from 20 to 70 km distance. The performance is measured using BER value, Q factor and eye diagram in bER analyser. The simulation parameters used are given in TABLE I [12]-[13].

Sr. No Parameters Values 1 Laser Input power 20 dBm 2 Filter Cut off frequency 0.65 * Bit rate 3 Reference wavelength 1550 nm 4 Dark current 5 nA 5 Respostivity 1 A/W 6 Quantum efficiency 0.5 7 Data bit rate 10 Mbps Table 1: Simulation Parameters Used III. RESULTS AND DISCUSSIONS In the Fig 2, it shows the comparison graph of distance Vs BER output for 5 numbers of users for three modulators Amplitude Modulator, Electroabsorption Modulator and Mach-Zehnder Modulator in SAC-OCDMA ZCC code system.

Fig. 2: Comparative BER performance of Amplitude Modulator, Electroabsorption Modulator and Mach-Zehnder Modulator in SAC-OCDAMA ZCC code system Firstly Amplitude Modulator is used which shows high BER value as compared to others. With increase in distance its value increases. So at higher distance means greater than 70 km its value becomes greater than 10 -9, which means low performance system. Secondly, mostly used modulator i.e. Mach-Zehnder Modulator is used instead of Amplitude Modulator. This modulator shows the low BER value as compared to previous at different distances. Hence, shows better performance as compared to Amplitude Modulator. Thirdly, Electroabsorption Modulator is used in place of Mach-Zehnder Modulator. This modulator shows low BER performance as compared to others two modulators. Also it shows the a linear graph with respect to distance, which means high quality and performance system.

Thus, it is clear that using Electroabsorption Modulator shows better performance as compared to others.

Fig. 3: Comparative BER performance of low pass chebyshev filter, low pass butterworth filter, low pass Gaussian filter, low pass Bessel filter and low pass raised cosine filter in SAC-OCDAMA ZCC code system In the Fig 3, it shows the comparison graph of distance Vs BER output for 5 numbers of users using Electroabsorption Modulator at transmitter side and different five filters at receiver side in SAC-OCDMA ZCC code system. Using side low pass chebyshev filter shows highest BER value as compared to others and with increase in distances its value further increases. At higher distances means 70 km system performance decreases. The low pass butterworth filter shows better performance as compared to previous. This performance can be further enhanced by using low pass Gaussian filter. As the low pass Bessel filter is mostly used filter in this system. This filter shows the better performance as compared to three previous used filters for 70 km distance. But using the low pass Raised cosine filter shows the lowest BER value and highest performance system. Using this filter a long distance more than 70 km, system can be obtained. Thus, it is clear that using electroabsorption Modulator and low pass Raised cosine filter shows high performance.

(a) at 20km (b) at 70km Fig. 4: Eye diagrams of one of user using Electroabsorption Modulator and low pass Raised cosine filter in SACOCDAMA ZCC code system at (a) 20 km and (b) 70 km respectively.

Fig. 4 shows the Eye diagrams of one of user in SAC-OCDAMA ZCC code system using Electroabsorption Modulator at transmitter and low pass raised cosine filter at receiver side at 20 km and 70 km respectively. From this, it is clear that for lower distance eye diagram have large eye opening and high Q factor. And at 70 km, the eye opening

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Comparative Performance of SAC-OCDMA ZCC Code System using Modulators and Filters (IJSRD/Vol. 3/Issue 08/2015/115)

reduces and also Q factor. Thus this shows the better system performance at low distance as compared to higher distance.

IV. CONCLUSION In this paper, the performance of SAC-OCDMA ZCC code system is determined by comparison of different modulators and filters. As the ZCC code is most efficient and efficient code for SAC-OCDMA system. Thus SAC-OCDMA ZCC code system is a cost effective and simple in design. To make it as a more usable for long distance, its performance can be improved by using electroabsorption modulator and low pass raised cosine filter at transmitter and receiver side respectively. Using these components, a high quality, longer distance (>70km), high bit rate of 10 Mbps and a secure SAC-OCDMA ZCC system can be obtained.

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