Sunny 1, Rinku Garg 2 Department of Electronics and Communication Engg. GJUS&T Hissar, India

Transcription

1 Performance Analysis of Optical CDMA System Using W/T Codes Sunny 1, Rinku Garg 2 Department of Electronics and Communication Engg. GJUS&T Hissar, India Abstract This paper represents the performance of Optical Code Division Multiple Access system using Wavelength / Codes. The OCDMA System is designed for 36 uses at 1 Gbps. We observed that the system can support only 24 users for permissible BER of 10-9, with the 15 db received power. The performance of the system is also analyzed by eye diagram and BER under the influence of number of simultaneous users with different received power. Keywords- Bit error rate, Optical code divison access, decoder,encoder I. INTRODUCTION The establishment of Optical code division multiple access needs to overcome the code orthogonality problem. Optical CDMA combines the large bandwidth of the fiber medium with the flexibility of the CDMA technique to achieve high-speed connectivity. In the optical orthogonal code family many researches have worked on two dimensional codes by using different construction methods. K.Yu. et. al. [1] proposed a 2- code structure demonstrated on signal up to 3 GHz. The combination of metal coated reflection delay lines and arrayed wave-guide gives the proposed optical coder/decode much flexibility in accommodating different codes sets. Antonio J. Mendez et. al. [2] presented a technique for constructing 2-D codes from set of optimum Goloumb ruler. It is also shown that 2-D codes have higher cardinality and spectral efficiency. In this paper the authors have described the design and construction of W/T Codes matrices, their implementation in OCDMA system and analyze the performance of a system in terms of eye diagram under the influence of number of simultaneous users with different received power and bit error rate. The encoder/decoders are realized using optical filter delays. II. CODING ARCHITECTURE The codes have been constructed by redesiging the existing 1-D optical orthogonal codes and with help of optimum goloumb ruler. Here we have considered two sequences from the goloumb ruler with length L= 18 and weighht, W = 6 i.e code 1= {1,1,1,0,0,1,0,0,0,0,0,1,0,1,0,0,0,1} and code 2 = {1,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,1} respectively. These 1-D codes are converted to 2-D codes by using ruler to matrix transformation. The dimension of matrix has been decided for the condition ( W T) L where w is the number of wavelength and T is number of time slots. If (W T)>L then the no. of filler zeros N, where N=(W T)-L has to be added at the end of the code word to form a proper matrix set.the number of filler zeros required will be 2 with W=5 and T=4 to make a proper matrix. If we choose W=3 and T=6 a (3 6) matrix can be formed without any need of filler zeros and serves as optimum solution as it saves the cost of laser by increasing the time slot. Thus code 1 can be designed by using wavelengths (W1, W2 and W3) and whereas code 2 is designed by using (W4.W5, and W6) wavelengths. Table1: Code 1 C1 T 0 T 1 T 2 T 3 T4 T 5 W W W ISSN All Rights Reserved 2014 IJEETE Page 77

2 Fig 1: Optical CDMA System Design Table2: Code 2 C2 T 0 T 1 T 2 T 3 T4 T 5 W W W III. SYSTEM DESIGN The System can be designed by using 6 mode locked lasers of different wavelength ranging from 1550 nm to nm with spacing of 0.7 nm which generates the pulses of width equal to the data rate of the system s Output PRBS 1 Generat or Modula tor 1 Filter 1 Filter 2 Filt er 3 Delay1 Delay2 Delay3 Delay4 Comb iner MUX Delay5 Opti cal Fibe r PRBS 1 PRBS 2 PRBS 36 Modulator 1 Modulator 2 Modulator 36 Encoder 1 Encoder 2 Encoder Multiplexer Delay6 Fig 2: Encoder Design of optical CDMA system In this system 36 codes can be designed for different wavelength and time delay combinations, The bit period and chip period of 1 Gbps is 1.0e-9s and 1.67 e-10s respectively. The Machgender modulator LINbO3 modulates the data generated by PRBS with the carrier, which is then fed to encoder. In the encoder the corresponding wavelength according to the codes filtered out and time delays places the pulses in their appropriate time slots which are further combined with the help of combiner. The encoded codes the decoder section filter out the corresponding wavelength according to the encoder wavelength. ISSN All Rights Reserved 2014 IJEETE Page 78

3 from all the users are then multiplexed and passed perform very well for -15 db received power and through 60 km span of single mode fiber followed accommodate 24 simultaneous users for bit error by a loss compensating EDFA amplifier. rate of e-9. If received power is kept low -22dB then The decoder, tuned to user 1, has the same structure the system design can accommodate 16 users as the corresponding encoder, but it has inverse simultaneous users. delays, which realign the pulses. The filter used in Fig5: Eye diagram output at encoder Fig3: Wavelength spectrum Fig4: Spectrum Analyzer output at encoder Fig6: Signal daigram for 1 user IV. RESULTS AND DISCUSSIONS The graph in figures 5,6,7,8 illustrate that as the number of users increases the signal amplitude start decreasing. For 1 user the maximum amplitude is V, which decrease to V for 8 users which further decreases for 27 users. The system Fig7: Signal daigram for 8 users ISSN All Rights Reserved 2014 IJEETE Page 79

4 Fig10: Bit error rate versus No. of simultaneous users at different Received power for 1Gbps Based OCDMA System Fig8: Signal daigram for16 users Fig11 :BER Vs. Received Power It can be see from figures that BER performance degrades. As received power decreases from -15 db to -30 db the BER rate decreases from e-75 to e-40 for 8 users. Fig 9: Signal daigram for 27 users V. CONCLUSION Result shows that the system under study can accommodate 24 users for permissible BER rate of 10e-9 with -15 db received power at 1 Gbps bit rate respectively. If the received power is kept low 22dB then system can accommodate 16 users only with permissible BER. The system is designed for 60 kms. Which can be further extended to long haul communication using optical amplifier, REFERENCES [1] K. Yu, J. Shin, and N. Park, Wavelengthtime Spreading Optical CDMA Systems Using Wavelength Multiplexers and Mirrored Fibre Delay Line, IEEE Photonics. Technology Letters, Vol. 12, No. 9, pp , September [2] K. Yu, J. Shin, and N. Park, Wavelengthtime Spreading Optical CDMA Systems Using Wavelength Multiplexers and Mirrored Fibre Delay Line, IEEE ISSN All Rights Reserved 2014 IJEETE Page 80

5 Photonics. Technology Letters, Vol. 12, No. 9, pp , September [3] Dr. T. Srinivas, Archana k, Vijay. P. Sompur,Simulation and Performance analysis of OCDMA System base on 2-D W/T Codes, Annual IEEE [4] Paul R. Prucnal Optical code division multiple access: Fundamentals and applications. CRC press,2006 [5] A.Stok and E.H. Sargent. Lighting the Local Area: Optical Code-Division Multiple- Access and Quality of Service Provisioning. IEEE Network, Vol. 14, pp: 42 46, November/December [6] Prucnal, P.R., Santoro, M.A, T. R: Spread Spectrum Fibre-Optic Local Area Network Using Optical Processing. IEEE/OSA Journal of Light wave Technology, Vol.4, No.5, May 1986 [7] Jawed, A.Salehi and C.A. Brackett: Code Division Multiple Access Techniques in optical fibre networks part-2: System performance analysis, IEEE transaction on communications, Vol.37, No.8,Aug 1989, pp [8] Jawed. A.Salehi, F.R.K Chung, and V.K Wei: Optical Orthogonal Codes:Design, analysis and application. IEEE Trans. on information Theory, Vol.35, No.3, May 1989, pp [9] A.J. Mendez, R.M. Gagliardi, V.J. Hernandez, C.V. Bennett, and W. J. Lennon, Design and Performance Analysis of Wavelength/ (W/T) Matrix Codes For Optical CDMA, IEEE Journal of Light wave Technology, Vol. 21, pp: , November A.Stok and E.H. Sargent. Lighting the Local Area: Optical Code-Division Multiple- Access and Quality of Service Provisioning. IEEE Network, Vol. 14, pp: 42 46, November/December , Apr ISSN All Rights Reserved 2014 IJEETE Page 81