Optical Division Multiple Access Research Articles

A Study of Bipolar Walsh-Hadamard Coding Method in Optical CDMA Networks

This study analyzes and calculates unipolar and bipolar coded configurations of spectral-amplitude-coding optical division multiple access (SAC-OCDMA) systems by using analytic and simulated methods. The important feature of the SAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed in-phase cross-correlation value. This property can be effectively canceled by 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. The eye diagram also shows that the bipolar encoding structure exhibits a wider opening than the unipolar encoding structure.

Time-spreading wavelength-hopping 2D-OCDMA system with optical hard limiter

The performance of time-spreading wavelength-hopping two-dimensional optical division multiple access (2D-OCDMA) system with optical hard limiter was analyzed firstly. Prime/OOC codes are employed as address codes. By dividing other codes into three groups according to the sum of shift cross-correlations and analyzing the probability distribution of the interference patterns, the bit error rate (BER) of the system was obtained.