Performance Anal y sis of SAC/Optical CDMA and WDM under a H y brid Overla y Scheme Isaac A. M. Ashor l , Student Member, IEEE, Hossam M. H. Shalaby, Senior Member,IEEE and P Susthitha Menon l , Member, IEEE l Instiute of Microengineering and Nanoelectronics(IMEN), Universiti Kebangsaan Malaysia, 43600 M Bangi, Selangor, Malaysia 2 Department of Electronics and Communications Engineering, School of Elecronics, Comunications, and Computer Engineering, Eypt-Japan University of Science and Technology (E-JUST), Alexandria 21934, Egpt isaacash@eng.ukm.my Absract- This paper presents a performance analysis of both optical code-division multiple-access (OCDMA) and wavelength division multiplexing (WDM) in an overlay hybrid scheme. Modiied quadratic congruence (MQC) code pulses of spectral amplitude coding (SAC) for optical CDMA is utilized as the signature address codes. This hybrid system is described, and its performance is analyzed, taking into account interferences and some types of noises. It is shown that the performance results in terms of both the bit-error rate (BER) and signal-to-noise and interference ratio (SNIR) are accepted in optical communication networks. Keywords: Optical code division multiple access (OCDMA), spectral amplitude coding (SAC), wavelength division multiplexing (WDM). I. INTRODUCTION Recently, Optical CDMA systems have an important role in optical networks because these systems provide the users simultaneous and asynchronous access to the network with high security [1, 2]. SAC/OCDMA specrum can be in-band ransmitted with multichannels of WDM system to get some advantages of ransmission capacity and data conidentiality ehancement [3, 4]. Modiied quadratic convergence (MQc) code is used as a signature address code for SAC/OCDMA system. This scheme has features such as a signiicant reduction in the effects of multiple access interference (MAl) and attenuation in the effects of phase induced intensity noise (PIIN) [ 5]. In previous studies, The WDM and SAC/OCDMA hybrid overlay system have been studied in [6, 7], where each WDM channel can employ the same set of SAC/OCDMA systems. In [3] we have investigated the feasibility of ransmitting both OCDMA and WDM users on the same specum band. Both hybrid and non-hybrid systems have been simulated and the performance comparison is presented. Our results in [3] indicate that it is possible to achieve an acceptable performance with good data conidentiality under the hybrid scheme. The results in [3] have been only demonsrated by simulation. Theoretical analysis of the performance, however, has not been demonsrated yet for this system. In this paper, we analyze the performance of both SAC/OCDMA-WDM systems under hybrid overlay system theoretically. Hence, the overall signal-to-noise and interference ratio (SNIR) is derived and the corresponding bit-error rate (BER), taking into consideration various types 978-1-61284-264-6/11/$26.00 ©2011 IEEE of noises and interferences. In addition, we obtain the numerical results with the effects of system parameters. The remainder of this paper is organized as follows: In Section 2 we describe the proposed system. In Section 3 we analyze the performance of the hybrid system. In Section 4, numerical results are presented for both sub-systems (SAC/OCDMA and WDM). Finally the conclusion of the paper is provided in Section 5. II. SYSTEM DESCRPTION In the proposed system [3, 4], narrow-band WDM signals and optical broadband CDMA signals are in-band ransmitted over the same specral region. A block diagram of the hybrid WDM-SAC/OCDMA system is shown in Fig. 1. Fig. 2 (a) illustrates that the CDMA signals are spread over a band of l v , whereas each WDM signal covers a band of Bw . In addition, the requency spacing between WDM signals is 100 GHz as the lTV standards [10]. So that, the maximum number of WDM channels, Nw is lv /1 OlHz . At the OCDMA receiver side, the WDM interferences can be attenuated by using notch ilters. Fig. 2 (b) shows the unction of an ideal notch ilter that is utilized in the proposed system. F" . ' . DataN �- ll � x� I w- -- \ PD2 t WDM ' . . . . . . . . .. . .. x-1 �� WDM -Rx-Nw U . , N Fire 1. Block-diaram of the hybrid system. WDMlneees (a) Boadband OCDMA � '( v )