Performance Analysis of DS-OCDMA Using Novel Multi-level Periodic Codes Besma Hammami, Habib Fathallah, Member, IEEE, and Houria Rezig, Member, IEEE Abstract: In this paper we present a theoretical simulation that evaluate the performance of direct- sequence optical code-division multiple-access (DS- OCDMA) system, using a novel periodic optical encoder applied to fiber-to-the-X (FTTX) passive optical network (PONs). We investigate the performances in terms of signal to noise ratio (SNR) and bit error rate (BER) in the presence of multiple access interference (MAI) and an additive white Gaussian noise (AWGN). Three groups of parameters were considered in this work: the number of users, the parameters related to the encoder and the parameters of the receiver. Keywords: direct-sequence optical code-division multiple-access (DS-OCDMA), fiber-to-the-X (FTTX), passive optical network (PONs), periodic optical encoder. I. INTRODUCTION Among all the different means of high capacity networks, optical code division multiple access (OCDMA) has received significant attention in recent years because of its several attractions such as asynchronous multiple users access, privacy and security in transmission [1]. OCDMA techniques allow numerous signals from different users to occupy the same single mode optical fiber transmission channel, optimizing the use of the wide available bandwidth. The key components of OCDMA systems consist of the encoder and the decoder that perform all-optical code generation and data recognition, respectively. A code or sequence of pulses referred to as “chips” is attributed to each user to encode its data bits. The encoded data are then broadcasted into the network and are only recognized by the matched decoder. Depending on the coding approach, various OCDMA technique implementations have been proposed. These are temporal encoding, which is also known as direct-sequence encoding (DS- CDMA) [2], spectral phase and/or amplitude encoding [3], [4], two-dimensional (2-D) encoding [5], and hybrid encoding [6]. Most encoders/decoders of the OCDMA systems are implemented with fiber Bragg gratings (FBGs) because of their ready integrability, compactness, and low fabrication cost. In the direct detection DS-OCDMA system considered here, the encoder is achieved with a new periodic coding scheme [7], that has been previously proposed for FTTX monitoring, and to the best of our knowledge never explored for data coding/decoding. Our study is done when the direction of data transmission is the uplink direction, from Optical Network Unit (ONU), to Optical Line Termination (OLT). Using the DS-OCDMA technique for the upstream, would provide necessary bit rate, dispensing of synchronization for this track. In the work reported here, we focus our attention on the signal to noise ratio (SNR) and bit error rate (BER) performances of the DS-OCDMA system, whereas we studied the effect of the parameters of the receiver used and the size of the network, on the system performance when applied to FTTX-PON architecture. Figure 1: Direct Sequence OCDMA system The 2nd International Conference on Communications and Information Technology (ICCIT): Communication Networks and Systems, Hammamet 978-1-4673-1950-8/12/$31.00 ©2012 IEEE 171