On Analyzing Quasi-Cyclic LDPC Codes Over Modified Welch–Costas-Coded Optical CDMA System

A modified Welch-Costas (MWC) code family for the spectral-amplitude-coding (SAC) optical code-division multiple-access (OCDMA) system is proposed. On utilizing the property of the MWC codes, more compact coder/decoders can be realized via waveguide and fiber gratings. This system has a superior performance as compared to the previous Walsh-Hadamard-coded OCDMA system. In addition, we propose a new class of quasi-cyclic low-density parity-check (QC-LDPC) codes to improve the transmission performance over the MWC-coded OCDMA system when the data rate is high. Simulation results show that the coding gain of the proposed QC-LDPC codes is larger than that of the Reed-Solomon codes, and the performance of the MWC-coded OCDMA system can be greatly improved by these QC-LDPC codes when data rate is 2.5 Gb/s.