EFFECT OF FIBER DISTANCE ON VARIOUS SAC-OCDMA DETECTION TECHNIQUES

Vandana Nath, Nakul Jain, Sandeep Dogra

Abstract: Optical code division multiple access system (OCDMA) has been gaining importance with increasing demands of high speed and large capacity for communication in optical networks. OCDMA system is totally asynchronous, that does not require any clock signals for synchronization in the network. Therefore, OCDMA provide a network that is simpler and offers the potential for scalability to higher levels of connectivity. OCDMA encoding /decoding process also provides a level of security directly implemented in the physical layer. Using OCDMA technique high spectral efficiency is achieved, hence fiber bandwidth is used very efficiently with throughput in excess of Tbit/s. Among several kinds of OCDMA systems, spectra amplitude coding (SAC) scheme attracts increasing interest because multiple access interference (MAI) can be eliminated and preserve the orthogonality between users in the system. This paper presents comparison of three important SAC-OCDMA detection techniques, namely - Direct detection, Complementary subtraction and AND subtraction. The design of encoder and decoder modules for SAC-OCDMA system used in this paper is based on Fiber Bragg Gratings (FBGs). Here conventional single mode fiber (SMF) is used as the transmission link and the performance metric studied is Quality factor (Q) in multiple access environments of various user systems for these three detection techniques. Finally Effect of increasing number of fiber distance on the direct detection technique using NRZ and RZ data formats have been studied. Simulated results show that AND subtraction technique gives better Quality-factor (Q) than the complementary subtraction and direct detection techniques for the signal with same power

Keywords: OCDMA (optical CDMA), BER (bit error rate), MAI (multiple access interference), DW (double weight code), SAC (spectral amplitude coding) and Q (quality factor)

DOI: https://doi.org/10.15623/ijret.2013.0203011