Performance Analysis of Dual Unipolar/Bipolar Spectral Code in Optical CDMA Systems

摘要

This study analyzes and calculates dual unipolar and bipolar coded configurations of spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) systems by using simulation methods. The important feature of the SAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed inphase cross-correlation value. This property can be effectively canceled multiple access interference by using balance detection schemes. This study uses Walsh-Hadamard codes as signature codes for the unipolar and bipolar schemes. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). The simulation results of unipolar/bipolar coding structures are first presented by commercial simulation obtained using OptiSystem software. The simulation results show that the bit error rate (BER) through use of the bipolar coding method is superior to the unipolar scheme, especially when the received effect power is large. When the system needs good performance to transmit multimedia data, we can use bipolar scheme in the network. If the users only transmit voice data, the unipolar method can be employed. The eye diagram also shows that the bipolar encoding structure exhibits a wider opening than the unipolar encoding structure. The flexible implementation of codewords assigns and integratable hardware designs for the scheme with FBGs to realize dual coding OCDMA system is proposed.