New code structure for enhanced double weight (EDW) code for Spectral Amplitude Coding OCDMA System Ali Z. Gahzi Zahid Dr. Feras N. Hasoon Prof Dr. Sahbudin Shaari Photonics Technology Laboratory Faculty of Information Science & Technology Photonics Technology Laboratory Institute of Micro Engineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia Multimedia University,Jalan Ayer Keroh Lama Institute of Micro Engineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia UKM, Bangi, Selangor, Malaysia 75450 Bukit Beruang, Melaka, Malaysia UKM, Bangi, Selangor, Malaysia alizahid@vlsi.eng.ukm.my feras.n.hasoon@mmu.edu.my sahbudin@eng.ukm.my Abstract—This paper presents a new structure for spectral amplitude coding optical code division multiple access systems based on the enhanced double weight (EDW) code. The new structure is based on mathematical model and step sequences. The reconstruction is carried for higher weighted code to build the code matrix by rules which will make high level weight inspection automatic sequenced and mathematically formed. Some simulation results are shown with comparison on performance. Keywords-Optical CDMA; Enhanced double weight (EDW); Double weight (DW) I. INTRODUCTION Optical CDMA proposed and developed in about two decades, many codes have been developed for optical CDMA system [1], [2]. This is due to its excellent performance, such as asynchronous access to the network [3], and high security operation [4]. Optical spectrum code division multiple access (OSCDMA) is a multiplexing technique adapted from the successful implementation in wireless networks [5]. Many codes have been introduced for OCDMA system. Some popular codes are Hadamard code [6], modified frequency hopping (MFH) code, and Double Weight (DW) code [7]. This paper will discuss about the Enhanced Double Weight (EDW) [8] code reconstruction. In this paper theoretical analysis presented to reconstruct the code and new mathematical model is presented for the code instead of using the old method depending on by inspection, some simulation results for higher weighted code is shown. The main structure for the code will remain the same. The change is clear from W=5 and up, the new method uses shifting theory. II. ENHANCED DOUBLE WEIGHT (EDW) CODE CONSTRUCTION EDW is the enhancement version of DW code whereby the number of weight can be increased to more than 1. EDW codes can also be represented by using the K x N matrix. The basic matrix for EDW can be developed by using the following steps:- A. Step 1: The basic matrix for EDW code consists of a K x N matrix depending on the value of code weight. The general form for the basic matrix of EDW code with weight, W is shown in Figure 1, where the component matrices [A1], [A2]… and [Aw] all depend on W. The basic matrix consists of a minimum number of K and N for specific number of code weight. From the basic matrix, larger number of K can be achieved by using mapping technique. [HW]= ۏ ێ ێ ێ ۍ ڭ ڭ ڭ ڭ ڭ ڭ A1 ڭA2 ڭ ڮ ڭAw ڭ ڭ ڭ ڭ ڭ ڭ ے ۑ ۑ ۑ ې Fig 1: General Form of EDW Code Matrix. In Figure 1, the elements in each section are defined as:- a. The number of matrix [A] depend on W. (i.e. if W=5, so number of matrix is 5). b. The size of matrix [A] consist of Ka x Na Where: Ka = W (1) Na ൌ ∑ ୨ ౭ ౠసభ W (2) 2009 International Conference on Future Computer and Communication 978-0-7695-3591-3/09 $25.00 © 2009 IEEE DOI 10.1109/ICFCC.2009.26 658 2009 International Conference on Future Computer and Communication 978-0-7695-3591-3/09 $25.00 © 2009 IEEE DOI 10.1109/ICFCC.2009.26 658