Optical CDMA: Performance of Spectral-Amplitude Coding with new Direct Recovery Scheme using Vector Combinatorial (VC) Code
Hassan Yousif Ahmed1, Mohammed Elmaleeh2, Hilal Adnan Fadhil3, and Syed Aljunid3
1Department of Electrical Engineering, Salam Bin Abdulaziz University, Kingdom of Saudi Arabia
2Faculty of Engineering, University of Gezira, Sudan
3School of Computer and Communication Engineering, Universiti Malaysia Perlies, Malaysia
1Department of Electrical Engineering, Salam Bin Abdulaziz University, Kingdom of Saudi Arabia
2Faculty of Engineering, University of Gezira, Sudan
3School of Computer and Communication Engineering, Universiti Malaysia Perlies, Malaysia
Abstract: In this paper, a new code structure with ideal in-phase cross-correlation for the Spectral-Amplitude-Coding Optical Code-Division Multiple-Access (SAC-CDMA) system called Vectors Combinatorial (VC) code is proposed. VC code is constructed using Euclidian vectors and a simple algebraic way for any positive integer number based on the relationship between the number of users N and the weight W. We have also studied the performance of OCDMA systems using a newly proposed Direct Recovery Scheme (DRS) under various link parameters. The impact of the detection techniques and data rate effects on the Multi-User Interference (MUI) is reported using a commercial optical systems simulator, Virtual Instrument Photonic (VPITM). The VC code is compared mathematically with other codes which use similar techniques. We analyzed and optimized the data rate, fiber length, and channel spacing in order to reduce the BER effect. A comparison between Complementary and DRS techniques for theoretical and simulation results taken from VPITM is demonstrated. It is verified that, for a high data rate (higher than 2.5 Gb/s), even if dispersion compensated devices are not deployed, the BER can be significantly improved when the VC code with desired parameters are selected using DRS technique. Also it is found that as the channel spacing width goes from very narrow to wide, the BER decreases and best performance occurs at a spacing bandwidth between 0.8 and 1 nm. In addition, we have shown that the proposed new DRS technique utilizing VC code significantly improves the performance compared with the conventional SAC Complementary subtraction technique.
Keywords: VC, MUI, SAC-OCDMA, BER, DRS.
Received February 1, 2011; accepted July 28, 2011