The flexible cross-correlation (FCC) address code for Spectral-Amplitude Coding Optical Code-Division Multiple-Access (SACOCDMA) systems has been developed.The FCC code has advantages, such

as flexible cross-correlation property at any given number of users and weights, as well as effectively suppressed the impact of phase-induced intensity noise (PIIN) and multiple-access interference (MAI) cancellation property.The results revealed that the FCC code can accommodate 150 users, where FCC code offers 66 %, 172 %, 650 % and 900 % improvement as a contrast to 90, 55, 20 and 15 number of users for dynamic cyclic shift

(DCS), modified double weight (MDW), modified frequency hopping (MFH) and Hadamard codes, respectively, for a permissible bit error rate

(BER) of 10−9

A. K, Rahman

C. B. M., Rashidi

M. S, Anuar

S. A., Aljunid

UUM Repository

Proceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  583  CAPACITY ENRICHMENT OCDMA BASED ON ALGORITHM OF NOVEL FLEXIBLE CROSS CORRELATION (FCC) ADDRESS CODE  *Rashidi, C. B. M., Aljunid, S. A., Anuar, M. S., and Rahman, A. K. Optical Research Group, Advanced Communication Engineering, Centre of Excellence, School of Computer and Communication Engineering Universiti Malaysia Perlis (UniMAP) *Corresponding Author E-mail: rashidibeson@unimap.edu.my ABSTRACT. The flexible cross-correlation (FCC) address code for Spec-tral-Amplitude Coding Optical Code-Division Multiple-Access (SAC-OCDMA) systems has been developed. The FCC code has advantages, such as flexible cross-correlation property at any given number of users and weights, as well as effectively suppressed the impact of phase-induced in-tensity noise (PIIN) and multiple-access interference (MAI) cancellation property. The results revealed that the FCC code can accommodate 150 us-ers, where FCC code offers 66 %, 172 %, 650 % and 900 % improvement as a contrast to 90, 55, 20 and 15 number of users for dynamic cyclic shift (DCS), modified double weight (MDW), modified frequency hopping (MFH) and Hadamard codes, respectively, for a permissible bit error rate (BER) of  10−9. Keywords: FCC code, correlation properties, MAI, SAC-OCDMA systems introduction  INTRODUCTION The higher the cross-correlation between any two code words will produce stronger impact of the MAI and erroneous decisions which will degrade the system performance of BER (Karbassian, & Kueppers,  2010). Therefore, the correlation properties of the code address play a significant part in the performances of OCDMA systems. Furthermore, when it in-volves the correlation properties it also noticed issues of the code size and the code length. The code length has a limitation to the number of simultaneous users that the OCDMA sys-tems can accommodate (Weng & Wu., 2003). Since, the OCDMA system performance de-pends on the address code then the technique to adapt in OCDMA system must have big ca-pacity and good correlation (Kok, Zhang & Soh., 2009;  Mrabet, 2009; Zan, 2005; Abd, 2012 ). Most address codes have been proposed for the OCDMA to overwhelm the impact of correlation properties such as DCS, MFH, MDW and Hadamard codes, respectively (Wei, 2002; Aljunid, 2004; Abd, 2012). However, these address codes have several limitations such as the code construction is complicated (e.g. MFH code) and fixed an even natural number for MDW code. In this paper, a new coding algorithm called FCC code is proposed to improve system capacity and achieve higher performance possible through suppressing PIIN and elim-inating MAI. The proposed code also has an advantage of high cardinality and low received power with shorter code length. Proceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  584  ESSENTIAL OF OCDMA CODE DEVELOPMENT In SAC-OCDMA network to allow receivers to distinguish each of the possible users, to reduce channel interference and to accommodate large number of users, optical codes should have large values of W and the size K.  Step 1:  A set of an optical code consists of code length N, weight W, cross-correlation λmax and for users K, (N, W, λmax). This set of codes is then represented by K×N code matrix     where, it can be expressed by equation (1);   (1)    where     The K×N code matrix       is called the Tridiagonal code matrix, whose elements aij of K×N code matrix      is the binary sequence [0, 1] and can be written as;                    (2)  The rows of A1, A2 and Ak represent the K codeword and it is assumed that, the code weight of each of the K codeword is to be W. Step 2: The K codes represented by the K rows of the K×N code matrix in equation (1) is to repre-sent a valid set of K codeword with in phase cross-correlations λmax and code weight W; it must satisfy the following conditions; 1. The code weight of each codeword should be equal to W where,     (3)  2. The in phase cross-correlation λmax, between any of the K code words (K rows of the matrix,    ) should not exceed code weight W. That is, WKA11 12 13 121 22 23 24 232 33 34 35 343 44 45 460 0 000 00 00 0WKKN Ka a a Aa a a a Aa a a a AAa a a aa A                              1 11 12 13 12 21 22 23, 24 23 31 32 33, 34 31 2 3, , ..., , ..., , ..., , ...NNNK K K K KNA a a a aA a a a a cA a a a a cA a a a aWKA1,2,...1,2,...0 1i KWK ij j NA a or for , 1,2...1Na W i Kijj WKAWKAProceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  585   (4)   3. From equation (4), it is seen that the W = XiXiT is the in- phase auto-correlation function of codes. Xi YjT is the out of phase cross-correlation between the ith and the jth codes. It follows that XiXiT should be greater than Xi YjT. In other words, W >λmax                                                                                                                    4. All K rows of     should be linearly independent because each codeword must be unique-ly different from other words. That is to say the rank of the K×N code matrix      should be K. Moreover, for      to have rank K, thus, it can be written as N ≥ K                                                                     Step 3:        From the four conditions above in Step 2, one  of the matrices binary sequences as shown in equation (1) in Step 1, whose the first ith row for the first K user is given by;  (5)  The N of the codes which is the length of the rows of the K×N code matrix      is given by;                                                                                                                                                                                                                                                                                                                                                                                               N=WK- λmax (K-1)                                                              (6) It can be seen that the N is minimum under the assumed conditions.  Table 1 shows the FCC code for a given K=3, W=2 and λmax ≤1. Table 1. Codewords of FCC Code for K=3, W=2 and λmax ≤1                Wavelength        Users λ1 =1550.0 λ2 =1550.8 λ3 =1551.6 λ4 =1552.4 User 1 1 1 0 0  User 2 0 1 1 0 User 3 0 0 1 1 FCC SAC-OCDMA ENCODER-DECODER DESIGN  The FCC SAC-OCDMA encoder-decoder have been designed using simulation software called OptiSystem software from OptiwaveTM. The encoder designs utilizing one single broad-band source being sliced for three channels with code weight equal to two. An evasion inter-ference subtraction is used as the detection scheme at the receiver.  Figure 1 shows the encoder design utilizing the FCC code sequence offers simplicity and cost-effectiveness using the LED as a light source, Mach-Zehnder as an external modulator, WDM Mux-Demux acting as wavelength combiner as well as code spectrum slicing also with ( 1) ( )0...0 11..1 0...0ir i r K iWA WKAmaxTi jfor i jX XW for i j   WKAWKAWKAProceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  586  the Non-Return Zero modulation format and pseudo random bit sequences (PRBS), respec-tively.  Figure 1. FCC Code Encoder Design Figure 2 shows the FCC decoder design utilizing fiber Bragg grating (FBG) which will decode the receiving signal from an optical fiber. A single FBG will encode two wavelengths represented by λ2, λ3, and λ3, λ4 which are correlated or overlapping wavelength as shown in Table 1. Due to that, FBG bandwidth will have a spectral width of 1.6 nm for correlated wavelength and 0.8 nm for uncorrelated wavelength such as λ1 and λ4 for both wavelengths. This design will reduce much bandwidth allocated for the code that has been selected for SAC-OCDMA system transmissions.  Figure 2. FCC Code Decoder Design PERFORMANCE ANALYSIS AND RESULTS The details of numerical expression for the Signal - to - noise ratio (SNR) with the pres-ence of noises such as shot noise, intensity noise and thermal noise respectively for the FCC code was derived in (C.B.M. Rashidi, 2014). The SNR and bit error rate (BER) for the FCC code are defined by the numerical expression as follows;   (7)     2222.2 43 3srsr sr b nLP WNSNReB P P KW K T BW B WN N V R               Proceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  587  Since, there is no pulse or data send for bit ‘0’and assuming that the noise distribution is Gaussian, thus the BER can be obtained as follows (Smith, E. D. J., 1998)   (8)   Figure 3. Number of simultaneous users versus system performance BER  for various SAC-OCDMA codes  Figure 3 shows the system performance BER degrade as the number of simultaneous users increased. At system performance BER of 10-9, the FCC code can accommodate 150 numbers of simultaneous users which is the highest number of users as compared to 90, 55, 20 and 15 for DCS, MDW, MFH and Hadamard codes, respectively. The percentage of the number of simultaneous users improvements are 66 %, 172 %, 650 % and 900 % as a contrast to DCS, MDW, MFH and Hadamard codes, respectively. From this fact, the FCC code had indicated good performance due to arrangement of code algorithm and flexibility cross-correlation function.  Figure 4. Performance of effective received power versus PIIN noise  for FCC code (W=4) at different bit rates 155 Mbps, 622 Mbps and 1 Gbps  Figure 4 illustrates the curves of effective optical received power Psr versus PIIN noise at bit rates of 155 Mbps, 622 Mbps and 1 Gbps for FCC code (W=4). The values of Psr are var-ied from - 50 dBm to 20 dBm. It can be seen that, the linear curves show an increase in PIIN 0.58     SNRBER erfcProceedings of the 5th International Conference on Computing and Informatics, ICOCI 2015 11-13 August, 2015 Istanbul, Turkey. Universiti Utara Malaysia (http://www.uum.edu.my ) Paper No.  115  588  noise as the bit rate increases. The low bit rate of 155 Mbps, maximally suppressing the ef-fects of PIIN noise. The magnitude of PIIN noise is eliminated by a factor of 1.0 where 1×10-13, 1×10-13 and 1×10-14 as values of bit rates decreases from 1 Gbps to 155 Mbps at Psr = - 10 dBm. The FCC (W=4) coding system performance degradation as the bit rate increases which will introduce to higher noise effects. CONCLUSION The algorithm of the FCC address code to enhance the impact of correlation has been pre-sented. The FCC code had shown good performance indicated that FCC OCDMA coding system can accommodate a high number of simultaneous users equal to 150 at permissible BER of 10-9. We can ascertain from these results that, this will give an opportunity in OCDMA system for better quality of service in optical access networks for future genera-tion’s usage REFERENCES Abd, T. H., Aljunid, S. A., Hilal A. Fadhil, Ahmad, R. B., & Rashid M.A. (2012). New Approach for Evaluation of the Performance of Spectral Amplitude Coding-Optical Code Division Multiple Access System on High-Speed Data Rate. IET Communications Journal, 6(12), 1742-1749. Aljunid, S. A., Ismail, M., Ramli, A. R., Borhanuddin M. Ali, & Mohamad Khazani Abdullah. (2004) A New Family of Optical Code Sequences For Spectral-Amplitude-Coding Optical CDMA Sys-tems. IEEE Photonics Technology Letters, 16(10), 2383-2385. Karbassian, M. M., &  Kueppers, F. (2010). OCDMA Code Utilization Increase: Capacity and Spectral Efficiency Enrichment. Global Telecommunications Conference, 1-5. doi 10.1109 Kok, S.W., Zhang, Y., & Soh,Y.C. (2009). An optimal chip-level OCDMA detector by using photon counting. IEEE Transaction on Communication, 57, 141-149. Mrabet, H.,  Dayoub, I., Attia, R., & Haxha, S. (2009). Performance improving of OCDMA system using 2-d optical codes with optical SIC receiver. Journal of Lightwave Technology, 27, 4744-4753. Rashidi, C.B. M., Aljunid, S. A., Ghani, F., Fadhil, H. A., Anuar, M. S., & Arief. A. R. (2014). Cardi-nality enrichment of flexible cross correlation (FCC) code for SAC-OCDMA system by allevia-tion interference scheme (AIS). Optik-International Journal for Light and Electron Optics, 125(17), 4889-4894. Smith, E. D. J., Blaikie, R.J., & Taylor, D.P. (1998). Performance Enhancement of Spectral-Amplitude-Coding Optical CDMA Using Pulse-Position Modulation. IEEE Transactions on Communications, 46(9), 1176-1185. Wei, Z. & Ghafouri-Shiraz, H. (2002). Unipolar Codes with Ideal In-Phase Cross-Correlation for Spec-tral Amplitude-Coding Optical CDMA Systems. IEEE Transaction on Communication, 50(8), 1209–1212. Weng, C.S. & Wu, J. (2003). Optical Orthogonal Codes With Large Cross-Correlation and Their Per-formance Bound For Asynchronous Optical CDMA Systems. Journal of Lightwave Technology, 21(3), 735-742. Zan, Z.,  Aljunid,  S. A., Yaacob, M. H., Abdullah, M. K., & Shaari, S. (2005). Design Configuration of Encoder and Decoder Modules for Modified Double Weight (MDW) Code Spectral Ampli-tude Coding (SAC) Optical Code Division Multiple Access (OCDMA) Based on fiber Bragg gratings. International Conference on Advanced Optoelectronics and Lasers. 2, 249-252.   

Capacity enrichment OCDMA based on algorithm of novel flexible cross correlation (FCC) address code

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Capacity enrichment OCDMA based on algorithm of novel flexible cross correlation (FCC) address code

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