Performance evaluation of optical code division multiple access system

Abstract

This thesis deals with Performance evaluation of Optical Code Division Multiple Access System. The major noise source in Optical CDMA is co-channel interference from other users known as Multiple Access Interference (MAI). The system performance in terms of bit error rate (BER) degrades as a result of increased MAI. It is perceived that number of users and type of code used for optical system directly decides the performance of system. MAI can be restricted by efficient designing of optical codes and implementing it with unique architecture to accommodate more number of users. Hence it is a necessity to design 2-D wavelength-time and 3-D spectral-phase-time codes, which can provide better cardinality and good correlation property. The designing and investigation of efficient 2-D and 3-D coding techniques for different number of users in terms of Bit Error Rate (BER) performance aiming to counter the ill effects of MAI has been presented. Firstly, a WDM compatible optical CDMA system incorporating 3-D spectral-phase-time encoding/decoding is demonstrated. Coding and decoding using binary [0, and#960;] phase chips is demonstrated for six users at 10 Gb/s, and a single coded signal is separated with acceptable bit-error rate and#8804; 10-9. The coding and decoding method is based on 3-D coding of tightly spaced phase-locked laser lines that is compatible with conventional WDM networking. In our proposed optical CDMA system, encoding and decoding is done by converting Hadamard codes (used for conventional CDMA system) to phase codes. Duo-binary modulation format is reported to be the best with adequate bandwidth compression. Simulation results too confirm better results in terms of BER and MAI. The obtained simulation results have been further verified that achieved bit error rate (BER) by the use of the bipolar coding method is much improved as compared to the unipolar scheme, especially when the received power is large. Hence it is summarized that whenever the system needs good performance to transmit multimedia data.