Performance of Optical CDMA Systems with Low Density Parity Check Codes

Incoherent optical code division multiple access (OCDMA) is a potential issue for future high speed optical networks. To reduce the number of errors at the detection due in particular to Multiple Access Interference (MAI), we add to the OCDMA link a block of efficient error correction codes named Low Density Parity Check codes (LDPC). The LDPC decoding algorithm, Belief Propagation (BP), usually employed to correct errors due to Gaussian noise, is reconsidered in order to take into account the MAI binomial distribution. The performance of an OCDMA link using 1 Dimensional and 2 Dimensional code sequences along with several LDPC codes is investigated. The performance is enhanced not only in an ideal case with only MAI, but also in a noisy case with MAI and thermal noise. With such error correction coding scheme, the constraints over OCDMA parameters and the signal to noise ratio are greatly relaxed.