Two schemes of linear combinatorial code (LCC) coding scheme with different and multiple wavelength bandwidth were proposed using fiber grating cascades in series and parallel, respectively. The system model and probability density function are investigated. Numerical simulation confirmed that bit error ratio (BER) performance largely improved due to that of sub-codeword system. Moreover, the preference of LCC with different wavelength bandwidth is better than that of multiple wavelength bandwidth.
OCDMA allows multiple users to share a common optical channel simultaneously and asynchronously, and thus has many advantages, such as great system capacity, efficient bandwidth utilization, asynchronous access, secure communication, and so on. Many studies on OCDMA techniques have been made in recent years. In direct-sequence (DS) incoherent OCDMA systems, each user is assigned a unique signature sequence (1’s and 0’s) for spreading and identification purposes. Through the use of encoding process, the user signal is spread in the frequency domain so that each user occupies the entire bandwidth available at all times. This results in a total bandwidth utilization. The optical medium is superbly suited to spread spectrum multiple access communications due to its extremely large bandwidth, however the spectral efficiency of OCDMA system is an important factor. This paper analyses the spectrum efficiency of incoherent OCDMA systems, emphatically discusses several kinds of codes, compares and evaluates their performances.
A novel wavelength-time differential code division multiple access system is proposed for multirate transmission. The system model is given and analyzed. Differential detection can be adopted by assigning two orthogonal codes for one user and using these two codes to encode “1” and “0” with different period, respectively. When one-branch and zero-branch are balanced perfectly, the system can reduce the noise of background, thermal, dark current, and multiple access inference. Moreover, by varying the ratio of number of bit ”1” and bit “0” in data steaming, the multirate data stream transmission is achieved.